dx.doi.org/ 10.18577 / 2307-6046-2015-0-6-9-9
UDC 541.6: 539.25
Methodological issues of analyzing phase morphology materials based on synthetic resins modified by thermoplasts (review)
An effective way to increase the viscosity of the destruction of polymer composite materials (PCM) is the modification of synthetic resins to thermoplasts. Structuring formation in such systems is accompanied by microphaded bundle with the formation of characteristic phase morphology. The current state of electron-microscopic studies of the phase morphology of the "reactoplastic thermoplastic" systems and PCM on them is considered. The following methodological issues of research of phase morphology are considered: the level of information of the research method, the effectiveness of contrasting the characteristic elements of the microstructure, the rationale for choosing the key morphological parameters and the methods of their measurement.
Introduction
Improving the service properties of react plates in their modification of thermoplasts is an important direction in polymer material science. The main purpose of such modification is to increase the viscosity of the destruction of the reactoplast and composite materials on its basis. The increase in impaired and crack resistance is particularly relevant for materials used in the aircraft industry.
Many modern scientific works emphasize the need to apply the "Composition-technology-structure-structure" approach in developing new materials. This approach is effective and in the development of polymer composite materials (PCM) with an increased viscosity of destruction. The physicochemical properties of the components and the composition of the mixture of thermoplastic with a synthetic resin allows you to create new structural and functional materials with a predetermined complex of properties. One of the key parameters by which it is possible to regulate and monitor the properties of a material based on the system "Reactoplast thermoplastic", is its phase morphology. Currently, the influence of the PCM structural and phase state on their properties is the subject of intensive research. An integral part of scientific works to increase the dissipative properties of PCM polymer matrices is the study of phase morphology and its influence on the service properties of the material.
The "reactor-thermoplast" systems differ significantly in phase morphology. Depending on the concentration and thermodynamic compatibility of components, the temperature of the chemical reaction of curing and a number of other factors, a structure with different phase morphology and interfacial adhesion is formed. If the initial reaction mixture was a homogeneous solution of thermoplastic in a synthetic resin, then as the curing reaction flows, the solubility of the thermoplast falls due to an increase in the molecular weight of the resin. Another important factor affecting the thermodynamic compatibility of components in the reaction of the curing reaction is the change in the chemical structure of the synthetic resin when the functional groups turn into the reaction products. In most systems, "reactoplast thermoplast", interesting from the point of view of practical application, a further increase in conversion leads to microphadium separation. The primary morphology is formed mainly to gelation in the α-phase (phase enriched with reactoplastic). The formation of secondary phase morphology may be observed in the β-phase (phase enriched with thermoplastic) after gelation in the α-phase. The parameters of the secondary phase morphology are sensitive to the dust temperature of the "reactoplastic thermoplastic" system. Depending on the properties of the synthetic resin-thermoplastic system and the parameters of the curing mode, the phase decay can be held according to the mechanism of nucleation and growth, according to the mechanism of spinodal bundle or by mixed type. From the phase decay mechanism, such morphological parameters depend such as the size, spatial distribution and distribution of particles of the dispersed phase.
The thermoplastic concentration in the initial reaction mixture is one of the main parameters that determine the phase morphology of the cured material. With an increase in the thermoplastic concentration, the phase morphology proceeds from dispersion morphology first to sonar, and then to morphology with phase treatment (Fig. 1). To summarize the influence of the curing temperature on the morphological parameters of the microstructure is much more difficult, because it changes the ratio of the velocity of the phase separation and chemical reactions of curing. The analysis of scientific and technical literature shows that in the development of materials on the basis of synthetic resins modified by thermoplasts, the focus of microstructural studies is paid to the effect of the concentration, chemical structure and molecular weight of the thermoplastic and the temperature of the curing on the material phase morphology. Currently, active studies are underway to regulate phase morphology and interfacial adhesion using compabilizers (substances that reduce the interfacial surface tension and increasing interfacial adhesion at the interface of the Polymer Polymer section).
Fig. 1. Type of phase morphology:
a - dispersed; b - sonpral; in - with phase treatment; G - its connection with the concentration of thermoplastic
Electron microscopy in combination with specialized methods of sample preparation is an informative method for studying the phase morphology of polymers mixtures. The main methodological issues of the electron microscopic study of phase morphology are: the level of information of the research method, the effectiveness of contrasting the characteristic elements of the microstructure, the rationale for the choice of key morphological parameters and the methods of their measurement. The decision of the designated issues in combination with a deep understanding of the physicochemical processes of formation of the structure of the test polymer material will contribute to the development of electron microscopy as one of the methods that provide information on the relationship "Composition-technology-structure-structure" in materials based on systems "Reactoplast-thermoplast" . This article discusses the current state of electron microscopic studies of phase morphology materials based on synthetic resins modified by thermoplasts, and the application of the results of these studies. All micrographs given in the work were obtained by the authors of the article with electron-microscopic studies of the "Retoplast-thermoplast" systems (as the article discusses general methodological issues, information on specific brands of materials is not given).
Information content of the structure of materials
based on systems "Reactoplast thermoplast" by electron microscopy
The main information provided by an electron-microscopic study of the "reactoplastic thermoplastic" systems is the type of phase morphology, the geometric characteristics of the phases and their spatial distribution. The primary phase morphology (decay on the α- and β-phase) is examined by raster electron microscopy (RAM). It is for this level that the organization of the structure of materials knows some correlation dependences of properties on phase morphology parameters. An interesting feature of the structural formation predicted on the basis of thermodynamic analysis of phase bundles using the model of the middle field of Flor Haggins is the formation of secondary phase morphology during the decay of the β-phase. When the β-phase is decayed, the dispersion of the domains (γ-phase) enriched in the continuous phase enriched with thermoplastic (Δ-phase) is formed. Secondary phase morphology is investigated using translucent electron microscopy (PEM) on the semicircular thicknesses prepared on the microtome. In scientific literature, there are only single work devoted to the study of this level of the structure of the structure, so information on the effect of the parameters of secondary phase morphology on the properties of materials is absent. In fig. 2 shows the micrographs of the phase morphology of epoxy reactoplast, modified by the polysulfone.
Fig. 2. Primary ( but) and secondary ( b.) Phase morphology of the system "Reactivoplast thermoplastic"
The informativeness of the electron microscopic study is currently significantly increased by using analytical electron microscopy, which is a set of methods united by the overall task - obtaining information about the elemental composition and chemical structure of the phases. The use of X-ray microanalysis allows you to identify the spatial distribution of the polymer in the mixture if it consists of air atoms. For example, if the thermoplastic component of the system "reactoplastic thermoplastic" is a polysulon (contains sulfur atoms), then the intensity of the characteristic X-ray radiation of the sulfur atoms, the researcher will be able to conclude about the distribution of the polysulfone. An example of construction by the method of analytic translucent microscopy of the concentration profile of sulfur in epoxy reactoplast, modified by the polysulfone, is shown in Fig. 3. It is shown that the characteristic phase formations correspond to the change in the concentration of sulfur in the coordinate, which allows the nature of the identified structural elements to determine the nature of the identified structural elements. The spatial resolution during the elemental microanalysis of the system "Retoplast-thermoplastic" is significantly increased when the methods of translucent analytical electron microscopy are applied. The method of raster analytical electron microscopy is more universal and provides information on elemental composition not only in microstructural, but also in fractographic studies.
Fig. 3. Concentration sulfur profile in epoxy reactoplast, modified polysulfone
The limited applicability of x-ray microanalysis for the study of polymer materials is due to the low sensitivity of this method to elements with low atomic numbers (C, O, N, etc.), low electrical conductivity and insufficient radiation-thermal stability of most polymers. Another disadvantage of this method is that it provides information only about the elemental composition. The promising method deprived of many of the above-described disadvantages is the formation of an electron microscopic image based on data spectroscopy data of characteristic energy losses by electrons (SHPEE). The use of this method provides information on the chemical structure of the phases, allows non-special contrasting samples to identify phase formations in mixtures of polymers consisting only of elements with low atomic numbers, and also significantly increases the accuracy of the quantitative elemental analysis of such systems. In the use of this method, the signs of microphadic bundle in the BIS system (vinylphinyl) ethane polyphenylene oxygen were revealed and the oxygen distribution cards were constructed (consequently, the phases enriched with polyphenylene oxide) with a spatial resolution of up to 10 nm.
Special sample sample preparation methods
for electron microscopic examination
The main task of sample preparation is the achievement of the best contrast between the heterogeneities studied by the microstructure of the material. Depending on the method of electron microscopy and the required information about the structural and phase state of the system, various contrast methods are used. Samples for the study by the PEM method are prepared using microtoming. The most effective means of contrasting the microtomic sections are Tetroxide Osmia OSO 4 and the tetroxide of RUO 4 ruthenium. Tetroxide Osmia is used for phases staining containing components with unsaturated bonds. To contrast the phase morphology of the Reactoplast-thermoplastic systems, RUO 4 is more efficient, since intensively stains components containing essential, alcohol, amine and aromatic groups.
The depth of the sharpness of the RAM allows you to apply this method to study samples with a developed surface relief. In this regard, for the study of phase morphology, the RAM method makes chips of a polymer matrix at a liquid nitrogen temperature. The resulting samples are suitable for a rough estimate of the interfacial adhesion and the distribution of the particles of the dispersed phase in size. In many works on the quantitative analysis of phase morphology, selective etching solvents are used. The etching by organic solvents leads to the full removal of the thermoplastic phase and allows you to obtain an electron microscopic image suitable for direct stereometric quantitative analysis. Another popular method of sample preparation for RAM is the manufacture of grinds. In this case, as in the microtoming, the study of phase morphology is carried out on a two-dimensional cut of the material and to determine the true spatial morphological parameters, a certain mathematical data processing is required.
Parameters defined in high-quality and quantitative analysis
phase morphology, and their connection with macroscopic material properties
The qualitative parameter of the phase morphology, to which the properties of the synthetic resin-thermoplastic system and the curing parameters of this system have the greatest impact, is the type of phase morphology. This parameter provides important information about the dissypagative properties of the material. It is shown that in the general case, the viscosity of destruction increases during the transition from dispersed morphology to morphology with phase conversion. At the same time, data on the optimal type of phase morphology, in which a significant increase in the viscosity of destruction is simultaneously achieved and the valuable properties of the reactoplasts are preserved (high module, heat resistance, resistance to organic solvents, etc.) differ. In this paper, it is indicated that the optimal combination of properties is achieved in the formation of dispersed morphology with the maximum possible volume fraction of the thermoplastic, while in the paper it is indicated that the most effective morphology is son recreational. These works indicate the need to control such a quantitative morphological parameter, as the volume fraction of the dispersed phase of thermoplastic. The definition of this parameter using the RAM method is most correctly carried out on the sluff. According to the first basic stereometric ratio, the volume fraction of the phase in the material is equal to the share of the sections of the phase on the grind area.
Other important quantitative morphological parameters are the size and distribution of phase particles. The direct measurement of these parameters is carried out according to low-temperature chips of the polymer matrix. More accurate values \u200b\u200bof these parameters can be obtained by special mathematical processing of data obtained in the study of grinds or microtomic sections. The algorithm of mathematical processing and model, on the basis of which mathematical processing is carried out, are described in operation. In this case, it is indicated that the optimal combination of the properties of the modified react floor is achieved if the size of the thermoplastic phase is in the range from 0.1 to 10 microns. The particle size of the dispersed phase of thermoplastic depends on the concentration of thermoplastic, temperature of curing, the use of compabizers and a number of other factors. When forming a dispersed morphology, the particle size of the thermoplastic phase increases with increasing the concentration of thermoplastic. Increasing the initial curing temperature can lead to opposite trends in the size of the particle size. In the scientific literature, both an increase and a decrease in the particle size of the thermoplastic phase by increasing the initial point of curing. This is due to the fact that an increase in temperature leads to an increase in the speed of the chemical reaction of curing and to the increase in the phase separation rate. These processes affect the particle size of the thermoplastic phase in the opposite way and to the fact that the process will be intensified to a greater extent when the temperature is raised and determines the phase morphology of the cured polymer matrix. In a number of work, it is indicated that the formation of morphology with the bi- or polymodal distribution of particles of thermoplastic in size leads to an additional increase in the dissipative properties of the material. Phase morphology with such a particle size distribution may be formed when co-modified synthetic resin by thermoplasts of various chemical structures or at high curing reaction rate.
The definition of phase morphology parameters provides important information when performing fractographic studies of Retoplast-thermoplast systems. Currently, high-quality mechanisms for increasing the dissipative properties of polymer matrices with dispersed particles of thermoplast are described and quantitative hardening models are proposed. The main mechanisms of hardening in reactoplasts modified by thermoplasts include the cracking of the thermoplastic particles, the drying of particles of the thermoplastic crack, the formation of the shear bands and microcracks in the matrix. The mechanism that most effectively increases the dissipative properties of the polymer matrix, is considered to overlapping the crack with particles of the dispersed phase of thermoplastic, which is accompanied by plastic stretching and gap of these particles. This mechanism is implemented with high interfacial adhesion and nanoscale phase particles of thermoplastic. In fig. 4 shows the surface of the destruction of the polymer matrix of epoxy reactable, modified by a polysulfone, with sonar phase morphology. In the area of \u200b\u200bdispersed morphology, the characteristic element of the structure is destroyed as a result of plastic deformation of the particle of thermoplastic. For the area of \u200b\u200bmorphology with phase treatment, a complex relief of the destruction surface is characterized, which is due to the envelope of the growing cracks of rigid particles of epoxy reactative and plastic deformation of the continuous phase of thermoplastic.
Due to the fact that the system "reactoplastic thermoplast" is used as polymeric matrices of modern PCM, an important issue is the change in phase morphology in the presence of a reinforcing filler. Systematic study of the influence of the chemical nature of the fibers of the reinforcing filler and the state of their surface on high-quality and quantitative parameters of phase morphology are devoted to a number of research and development. The paper shows that around the glass fibers is formed by a layer enriched with epoxy reactoplast, which negatively affects the dissipative properties of PCM. Around carbon and aramid fibers of such a layer is not found. The paper consists of an increase in the average size of the particle phase of thermoplastic near the fiber reinforcing filler. The works proposed a quantitative parameter of changing phase morphology in the presence of a reinforcing filler: the number of particles of the dispersed phase of thermoplastic per unit area at a certain distance from the fiber. It is also shown that the concentration of dispersed particles of thermoplastic near the fiber is increasing when its surface is activated and depends on the chemical structure of the thermoplastic. It should be noted that, despite the research work carried out in this direction, a single idea of \u200b\u200bthe influence of filler on the formation of phase morphology is currently not formulated.
Fig. 4. Phase morphology of epoxy react floor, modified by a polysulfone ( but), and the surface of the destruction in the dispersion morphology ( b.) and morphology with phase appeal ( in)
The submitted work reflects the role of electron microscopic studies in the development of polymer matrices based on the systems "reactoplast thermoplastic" for PCM with high impaired and crack resistance. Due to the fact that the optimal combination of properties of such materials is achieved in the formation of a microstructure resulting from microphage separation, the most important issues are the control and control of phase morphology. This paper provides examples of information on the structural and phase state of the system, which provides an electron microscopic examination. It is shown that currently electron microscopy allows not only to conduct phase morphology studies at various hierarchical levels of the system of system, but also to determine the elemental composition and the chemical structure of phase formations with a high spatial resolution. The currently available views on the management of morphological parameters in the development of materials based on synthetic resins modified by thermoplasts are described. Methodical approaches to measure such parameters as the volume fraction of the dispersed phase of the thermoplastic, the average particle size and particle size distribution is marked. Information on the effect of high-quality and quantitative parameters of phase morphology on the properties of the material is given. The global and domestic experience of applying the results of studies of phase morphology to manage the properties of the PCM proves the effectiveness of electron microscopy as one of the methods providing information on the relationship "Composition-technology-structure-structure" in materials based on the systems "Retoplast-thermoplast".
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43. Zhang J. et al. INTERPHASE STUDY OF THERMOPLASTIC Modified Epoxy Matrix Composites: Phase Behavior Around A Single Fiber Influenced by Heating Rate and Surface Treatment // Composites: Part A. 2010. V. 41. №6. P. 787-794.
5.4.2. Composites with polymer matrix
Composite materials with a polymer matrix are distinguished by low density (1200 ... 1900 kg / m 3), low sensitivity to incision, heat and electrical conductivity, high fatigue and specific strength, processing technological, radio transmission (a number of materials) and others. As a polymer Composite matrices are used both thermoactive (mainly) and thermoplastic polymers, and fillers are any of those listed above.
Materials based on thermoplastic polymerswith dispersed fillers of various nature (talc, graphite, metal oxides, layered solid lubricants, metal powders, discrete fiberglass, etc.) are used for the manufacture of weakly and medium-wide parts of machines and devices, cabinet parts, gear wheels and sprockets, bearings and seals, drive belts, tanks, etc.
Among thermoplastic composites, glass-filled materials were most widely used. The fiber is used as a fiber with a diameter of 9 ... 13 μm from brushless aluminular glass, short (0.1 ... 1 mkm long) and long (3 ... 12 mm long) with a degree of filling 10 ... 40% of Polymer masses. Glass-filled plastics based on polyamides, polycarbonate, polypropylene, etc. Thermoplasts are available. Filling the thermoplastic fiberglass increases the strength characteristics of polymers and heat resistance, reduces in 1.5 ... 2 times creep, reduces in 2 ... 7 times the temperature expansion increases the endurance limit and wear resistance. Introduction to composites of solid layered lubricants, such as graphite, Molybdenum disulfide, boron nitride, etc., reduces the friction coefficient of polymers and increases their wear resistance.
The strength of composites based on thermoplastics reaches 150 ... 160 MPa with a sufficiently high shock viscosity (KCU \u003d 8 ... 60 J / m 2).
Composite materials based on thermosetting plasticscreated on the basis of polymers that curable during heating or under the action of hardeners to form three-dimensional polymer structures to the number of hydro-formaldehyde, urea and melamine-formaldehyde, silicone and melamine-formaldehyde, silicone and other resins include composites based on heating. The second type includes composites based on polysiloxanes, epoxy resins and unsaturated polyesters.
Thermoreactive plastics, in contrast to thermoplastics, are characterized by a complete absence of cold consumption, they have significantly greater heat resistance, differ in insoluctivity, have a minor swelling. They show the stability of properties up to heat resistance temperature, the ability to withstand long loads at temperatures from - 60 to +200 ... 300 ° C, depending on the type of polymer, have good dielectric properties. But these materials are less technological than thermoplastics.
Epoxy resins have the greatest adhesion to the filler. Cerenated epoxy resins resistant to alkalis, oxidizing agents, most organic acids. However, composites based on them have low-resistant mechanical properties, they have heat resistance up to 200 ° C, moreover, these resins are toxic.
Composites on silicon-organic and polyimide binders (up to 280 ... 350 ° C) have the greatest heat resistance.
The use of epoxy resins and unsaturated polyesters makes it possible to obtain materials capable of curing at room temperature (cold curing), which is very important in the manufacture of large-sized products.
Composite materials S. dispersed fillerswhich are used in organic powders (wood flour, cellulose) and mineral (quartz, talc, mica, metal oxides, solid layered lubricants, incl. graphite, molybdenum disulfide, boron nitride) substances possess isotropic properties, low mechanical strength and shock viscosity.
As fibrous reinforcing materialscotton products, cord threads, asbestos fiber, fiberglass are used. Accordingly, these materials are called fibrities, cordonol fiber, asboloknitis, fiberglasss.
Fibers - plastics based on cotton products impregnated with phenol-formaldehyde resin. Materials have an increased, compared to press powders, shock viscosity (up to 10 kJ / m 2), but have a significantly less fluidity, which does not allow to obtain thin-walled parts. Fibers have low dielectric properties, unstable to tropical climates, have anisotropy properties. They are used for the manufacture of products of general appointment with increased resistance to vibrations and shock loads operating on bending and twist, for example, pulleys of belt gears, flanges, handles, covers, etc.
Asbovolokniti - composites containing fibrous mineral - asbestos, splitting on thin fibers with a diameter of up to 0.5 microns. Fenolo-formaldehyde and silicone resins are used as a binder. They have a high shock viscosity and heat resistance up to 200 ° C, sustainable acid media, have good frictional properties. Used mainly as materials for brake devices (brake pads, lining, clutch discs).
Phenol-formaldehyde based asboloknitis are used to produce high-strength heat-resistant electrical installation parts (electrical panels, high and low-voltage collectors), and based on silicone polymers - for parts for a long time at temperatures up to 200 ° C (material K-41-5) And for the extinguishing chambers of the contactors of high power, terminal blocks (KMK-218). The latest materials of tropical resistant. Faitat -asbovoloknitis obtained by impregnation asbovolocone with a phenol-formaldehyde resin followed by the shading of the mixture is used for the manufacture of acid-resistant pipes, tanks.
Fiberglass present plastics containing fiberglass as a filler. Used fiberglass with a diameter of 5 ... 20 μm high strength with a time resistance q \u003d 600 ... 3800 MPa and high-modulus (VM-1, VMP, M-11), having a \u003d 3900 ... 4700 MPa and a module of elasticity at Tensile up to 110 GPa. Fibers, threads, harnesses of different lengths, are used, which largely determines the shock viscosity of fiberglass. The thinner fiber, the less its defectness and the higher strength.
The mechanical properties of fiberglass depend on the composition, the amount and length of fiberglass, the type of binder, the physicochemical processes occuring on the border of the fiberglass - binder, the processing method. For example, the replacement of glass fiber from glass E (Bigless aluminosilicate) on the fiber of glass S (heat-resistant high strength) in the epoxy binder makes it possible to increase the strength of the composite by 40%.
In order to improve the wettability of fiberglass binding, reducing the stresses arising at the interface, an increase in adhesion between the fiber and the binder is used to apply (processing) of fibers with compounds containing various reactive groups (vinyl, methacryl, phenyl, amino and intrigues, etc.). A decrease in stresses in a border border with a fiber layer of binder, a decrease in shrinkage and porosity, an increase in heat resistance contributes to the binder of powdered fillers, in particular, the powder of the cured binder.
Fiberglasss are divided into: confused-fibrous, granulated and finely dispersed molds.
Constructed fibrous fiberglassit is obtained by impregnating fiber segments with a length of 40 ... 70 mm with a subsequent flipper and drying to remove the solvent (for example, AG-4B). The disadvantage of these materials is the uneven distribution of the binder, greater variation of mechanical properties and less fluidity compared to other fiberglass.
Granulated fiberglasss(premixes)they are obtained by impregnation of non-executed glass bottles and styles, followed by drying and cutting on granules with a length of 5, 10, 20 and 30 mm. The diameter of the granules is 0.5 ... 8 mm. The material has good flowability and fluidity, greater stability of mechanical properties. This category of materials includes dseables dosable fiberglass.
Fiberglass Fiberglass Moldsit is made by mixing chopped fiberglass up to 1.5 mm with a binder with subsequent granulation (granules with a size of 3 ... 6 mm). "Groxcock" with granules up to 10 ... 50 mm from impregnated fiberglass waste are available.
Fiberglass granulated with granules up to 6 mm measured by injection molded. Small fiberglass can be recycled with injection injection molding, and in the manufacture of products with metal reinforcement - injection molding. Fiberglass with a length of 10 mm with a length of 10 mm is processed with mold and direct pressing, and with a length of the granules 20 and 30 mm long - only by direct pressing.
Case parts are made of fiberglass parts, elements of shields, insulators, plug connectors, derangers of antennas, etc. Products operated at temperatures from -60 to +200 ° C are made on the basis of anilino-phenol-formaldehyde resins and brushless alumina-rope fiberglass, and for the temperature range - 60 ... + 100 ° C based on epoxy resins.
Fiberglass based on silicone resins is operated to a temperature of 400 ° C, and using quartz or silica fiber briefly and at higher temperatures. Fiberglass based on silica fiber and phenol-formaldehyde resins are used for heat protection details.
Based on glass mats and unsaturated polyester resins get prepreg, which are used for the manufacture of large-sized parts (body, boats, enclosure details of devices, etc.). The use of oriented fibers allows to obtain fiberglass with elevated mechanical properties. For example, fiberglass-oriented fiberglass has: B \u003d 200 ... 400 MPa, KCU \u003d 100 kJ / m 2; While at AG-4B based on confused fiber: B \u003d 80 MPa, KCU \u003d 25 kJ / m 2.
Organizations they are composite materials based on polymer binders, in which fibers are organic polymers (polyamide, lavsan, nitron, vinol, etc.). For reinforcement, harnesses, fabrics and mats from these fibers are also used. The binders are used thermosetting resins (epoxy, phenol-formaldehyde, polyimide, etc.).
The use of polymer binders and fillers with close thermophysical characteristics, as well as diffusion and chemical interaction between them, provide composites stability of mechanical properties, high specific strength and shock viscosity, chemical resistance, resistance to thermal shrink, tropical atmosphere, abrasion. The permitted temperature of the operation of most organo-fiber is 100 ... 150 ° C, and based on polyimide binder and heat-resistant fibers - up to 200 ... 300 ° C. The shortcomings of these materials should include low strength in compression and creep.
To obtain high-strength composites, fibers based on aromatic polyamides (Aramid fibers of the USD, Terlon, Kevlar), which have high mechanical properties, thermal stability in a wide range of temperatures, good dielectric and fatigue properties. Under the specific strength, these fibers are inferior only by boric and carbon.
Borovolokniti - Composite materials on a polymer matrix filled with boric fibers. They have good mechanical properties, low creep, high heat and electrical conductivity, resistance to organic solvents, fuel and lubricants, radioactive radiation, cyclic alternating loads.
Boric fibers are obtained by chemical precipitation of boron from a gas mixture Bcl 3 + H 2 on a tungsten thread at a temperature of ~ 1130 ° C. To increase the heat resistance, the fibers are covered with silicon carbide, also precipitated from the vapor-gas phase in the argon and hydrogen medium. Such fibers are called a boards. A modified epoxy resins and polyimides are used as a binder for boronol fuses. Borovoloknitis KMB-3, KMB-ZK provide productivity of products at temperatures up to 100 ° C, KMB-1 and KMB-1K to 200 ° C, and KMB-2K up to 300 ° C. In order to increase the processing techniques, composites containing a mixture of boric fiber with fiberglass are used.
Borovoloknitis are used in aviation and space technology for the manufacture of various profiles, panels, components of compressors, etc.
Karbovolokniti (carbon focus) - composite materials based on polymer binder and carbon fibers. Carbon fibers are distinguished by high heat resistance; specific strength, chemical and weather resistance, low thermal linear expansion coefficient.
The fibers of two types are used: carbonized and graphitized. As a starting material, viscose or polyacrylonitrile (pan) of fibers, stone and oil peks are used, which are subject to special heat treatment. In the process of high-temperature processing in a chaotic environment, a transition from organic fibers to carbon is occurring. Carbonization is carried out at a temperature of 900 ... 2000 ° C, and graphitization - at temperatures up to 3000 ° C. Carbon fibers through mechanical properties are divided into high-strength and high strength. The binders use thermosetting polymers: epoxy, phenol-formaldehyde, epoxy phenolic resins, polyimides, etc., as well as carbon matrices.
Karbovolocrokes have good mechanical properties, static and dynamic endurance, water and chemical resistance, etc.
Karbovoloknitis on the epoxy-anilino-formaldehyde binder (KMU-3, KMU-CL) are functionable at temperatures up to 100 ° C, on epoxy-phenolic (KMU-1L, KMU-LY) to 200 ° C, on a limid (KMU 2, KMU-2L) up to 300 ° C, on a carbon matrix up to 450 ° C in air and up to 2200 ° C in an inert medium.
Karbovoloknitis are used for the manufacture of structural details of aviation and rocket equipment, antennas, ships, cars, sports equipment.
Layered composite materialssheet fillers (tissues, paper, veneer, etc.), impregnated and bonded between themselves with a polymer binder. These materials have anisotropy properties. The fibrous reinforcing elements use tissues based on high-strength fibers of various nature: cotton, glass-asbotani, organoticani, treat, organospectorate, boroorgangetic chill. The fabrics differ in each other by the ratio of fibers at the base and duck, according to the type of weave, which affects their mechanical properties. Local composites are produced in the form of sheets, pipes, blanks.
Getinax - plastic based on modified phenolic, amino-formaldehyde and carbamide resins and various paper varieties.
Organogenetinax is made on the basis of paper from synthetic fibers, most often from aromatic polyamides and polyvinyl alcohol. Polyimides, phenol-formaldehyde, epoxy resins and others are used as binders. Compared to Ghetynaksami, they have a higher resistance in aggressive media and stability of mechanical and dielectric properties at elevated temperatures.
Textolit - layered plastic based on polymer binding and cotton fabrics. Material has high mechanical properties, resistance to vibrations. Depending on the main purpose, the textolites are divided into structural, electrical, graphitized, flexible gaskets.
The design textolite of PTK brands, PT, PTM is used to make gear wheels, sliding bearings operating at temperatures in the friction zone not higher than 90 ° C, in rolling mills, turbines, pumps, etc. is available in the form of sheets thick from 0.5 to 8 MM and plates thick from 8 to 13 mm.
Electrical textolite is used as an electrical insulating material in the operating temperature environments from minus 65 to + 165 ° C and humidity up to 65%. It produces in the form of sheets with a thickness of 0.5 to 50 mm grades A, b, r, HF. Electrical strength in transformer oil to 8 square meters / mm. Brand A - with elevated electrical properties for operation in transformer oil and in air during an industrial frequency of 50 Hz. Brand B - with elevated electrical properties for air operation at a frequency of 50 Hz. Mark G - according to the properties and areas of use similar to the brand A, but with advanced tolerances for warping and thickness. Mark HF - to operate in air at high frequencies (up to 10 6 Hz).
A graphitized textolite is used for the manufacture of bearings of rolling equipment and is produced in the form of sheets with a thickness of 1 ... 50 mm, up to 1400 mm long and a width of up to 1000 mm.
Flexible gasket textolite is used to produce sealing and insulating gaskets in nodes of machines exposed to oils, kerosene, gasoline. Release in the form of sheets with a thickness of 0.2 ... 3.0 mm.
IN asbotextolites and asbogytinaksakh as fillers, respectively asbotan or asbobumaga (up to 60%), and as a binder - phenol-formaldehyde and melamine-formaldehyde resins, silicon-organic polymers, which determine the permissible operation temperature.
Materials on the melamine-formaldehyde basis allow the work of products at temperatures up to 200 ° C, on phenol-formaldehyde up to 250 ° C and on a silicone to 300 ° C with long-term operation. Brief temperature can reach 3000 ° C. Asbotextolites are used mainly for the manufacture of brake pads, brake linings, as thermal insulating and heat-shielding materials.
Fiberglass made on the basis of fiberglass and various polymer binders. On phenol-formaldehyde resins (caste, caste-c, caster, they are more heat-resistant than the textolite PTK, but worse vibration resistance. On the silicone resins (STK, SK-9F, SK-9A) have high heat and frost resistance, they have high chemical resistance, do not cause corrosion of the metal in contact with it. Gyklotelts are used mainly for large-sized radio engineering products.
High shock viscosity of KCUDO 600 kJ / m 2, time resistance up to 1000 MPa possess fiberglass anisotropic materials, steam-reinforced glassshop (Swam). According to the specific stiffness, these materials are not inferior to metals, and according to the specific strength in 2 ... 3 times exceed them.
Gas-filled plasticsit can also be attributed to the class of composites, since the structure of them is a system consisting of solid and gaseous phases. They are divided into two groups: foam and poroplasts. Foamshave a cellular structure, the pores in which are isolated from each other with a polymer layer. Popoplaststhey have an open porous system and the gaseous or liquid products present in them are communicated with each other and the environment.
Foams it is prepared on the basis of thermoplastic polymers (polystyrene, polyvinyl chloride, polyurethane) and thermosetting resins (phenol-formaldehyde, phenol-rubber, silicon-organic, epoxy, carbamide). To obtain a porous structure in most cases, gas-forming components are introduced into the polymer binder porofors.However, there are also self-confined materials, for example, polyuretheretic, polyurethe foam. Foams based on thermoplastic resins are more technologically elastic, but the temperature range of their operation from -60 to +60 ° C.
Popoplasts it is mainly obtained by mechanical foaming of compositions, such as compressed air or using special foaming agents. When solidification of the foamed mass, the solvent, removing in the process of drying and curing from the walls of the cells, destroys them. Through the pores can be obtained by filling the composition with water-soluble substances. After pressing and curing the product, it is immersed in heated water, in which soluble substances are washed.
Popolopers are used for the manufacture of shock absorbers, soft seats, sponges, filters, as vibration-absorbing and soundproofing gaskets in ventilation plants, silencers, gaskets in helmets and helmets, etc. Their density is 25 ... 500 kg / m 3.
Metal-and-dimensional frameworkscomposite materials in which the carrier base is a three-dimensional metal mesh, and the intercrotane cavity is filled with a polymer composition containing various functional components (Fig. 5.11).
Fig. 5.11. Structure of metal-polymer framework material (A) and MAT material (b):
1 - metal particles, 2 - polymer, 3 - solid lubricant, 4 - pyrolytic graphite
In mechanical engineering, metal-cell-meter self-lubricating materials based on metal-ceramic frame and polymer binders containing various dry lubricants (graphite, molybdenum disulfide, iodide cadmium, etc.) have been used in mechanical engineering. Such materials are used to make gliding bearings, rolling bearings separators, piston rings, etc.
To obtain a metal-ceramic frame, tin bronze powders, stainless steel, glass ceramics are used. Intercriver cavities are filled with fluoroplastic- 4d by impregnating with a 50% aqueous suspension of fluoroplastic or a mixture of fluoroplast-4d with lead. Metal ceramic antifriction material MPK, made on the basis of stainless steel powders, contains pyrographic and fluoroplast - 4.
The technology of obtaining it is as follows: the frame with porosity 20 ... 70% is compressed from metal powders. Then, in a special chamber, carbon-containing gas is passed through the pores at a temperature of the gas pyrolysis and the deposition of graphite on the frame walls before filling around 3/4 of the pore volume, after which it is carried out by a multiple vacuum impregnation of fluoroplastic-4 suspension with simultaneous heat treatment.
The self-sensitive materials of the above type are operational at temperatures up to 250 ° C.
Extremely promising the use of tape frame of self-lubricating materials, which are a metallic base (tape), to which a layer of porous metal-ceramic frame is accumured. Frame pores are filled with fluoroplastic-4-based compositions and solid lubricants.
Ribbon materialsextremely technologically, allow you to make the sliding bearings (rolling) and inserts of any size) allow operating without lubrication at temperatures up to 280 ° C at high pressures (up to 200 ... 300 MPa) and sliding speeds. The use of a metal ribbon base and bronze porous frame provides a good heat sink from the friction zone, and in the pores and on the surface of fluoroplastic-4 with solid lubricants - the low friction coefficient and high wear resistance of friction pairs. Abroad are widely used tape materials TUDU, DP, DQ.
One of the shortcomings of frame belt materials is a small thickness of the surface permafront layer (10 ... 20 μm), which eliminates the possibility of mechanical processing of bearings after they are installed in the housing.
Effectively use of frame self-lubricating materials whose frame is sintered from metal fibers or grids, and various polymer compositions are used as the matrix, as well as materials based on carbonithic and metallized cargophyt tissues impregnated with polymer binders with solid lubricants.
Currently, widespread use composite wood materials,presenting reinforcing wood materials (fillers), combined in the matrix (usually polymer) with the introduction of special additives. In some cases, they are called the name of anodette, or KDPM (compositional wood polymeric materials).
Choppers - large-sized products manufactured by the method of hot flat pressing of wood particles mixed with binding. According to GOST 10632-89, the plates are released in size 2440x1220; 2750x1500; 3500x1750; 3660x1830; 5500х2440 mm, thickness from 10 to 25 mm, polished and not polished. In accordance with the purpose of the slab divided into three stamps: P-1 (P-1M multi-layered and p-1t three-layer)- Cases, panels and other parts in radio and instrument making, elements of furniture and construction. Facing films based on thermosetting and thermoplastic polymers, paint materials; P-2 (P-2T and P-20 single-layer, divided into groups A and B) - Made the body of instruments, machines, containers and containers (except food), racks, elements of furniture and building structures. Apply lined with veneer, decorative paper - layered plastics and without facing; P-3 (P-ET)- Details of car body bodies, partitions of wagons, elements of construction supporting structures. The quality of the surface of the plate is divided into polished (1 and II varieties) and unlocked (I and II varieties).
Plates of tree fiber (GOST 4598-86) Depending on the density, it is divided into soft (M), semi-solid (PT), solid (T) and superhard (st) and, depending on bending strength limit - by seven brands: M-4, M- 12, M-20, PT-100, T-350, T-400 and ST-500, where numbers mean the minimum size of the stove strength when bending in kgf / cm 2. Plate thickness 2, .5; 3.2; four; five; 6; 8: 12; 16 and 25mm, width from 1220 to 1830 mm and length from 1200 to 5500 mm. Designed for use in products and structures protected from moisture.
Wood laminated plastics (chipboard) - hot laminated multi-layered, with synthetic resins, veneer sheets of various wood breeds. The chipboard is characterized by high strength and wear resistance, a small coefficient of friction and good older.
Chipboarda thickness of 1 to 15 mm is made in the form of rectangular sheets, thickness from 15 to 60 mm - in the form of plates. Sheets and slabs, glued together by the length of veneer sheets, are called solid, and from several are composite (with several reduced properties). Solid sheets are produced by a width of 950 mm and a length of 700, 1150 and 1500 mm and 1200x1500 mm; Composite 2400x950, 4800x1200, 5000x1200 mm; Solar plates: 750x750, 950x700 (1150, 1500); 1200x1200 (1500), composite plates produce the same dimensions as composite sheets. In accordance with GOST 13913-78 and GOST 20366-75, the chipboard is divided into 11 brands.
To the number promising nodes and parts from KDPMcan be attributed:
rollers of belt conveyors;
rolling bearings housing;
deaf and passing covers, hatches;
central parts of wheels and rollers (wheel centers with bands made of steel);
cable blocks for cranes, telphers, polyspers, etc.;
pulleys, asterisks, gears, fixed on shafts using cellpone compounds;
cargo, counterweight, calm, flywheels with the inside of compressed metal chips and the outer part of the CDPM;
panels of internal sheat car, buses, wagons, cabins of various machines, etc.;
pistons of pneumatic and hydraulic cylinders;
window frames;
frames for details from polyurethane foam;
gnuto-glued profiles and veneer panels;
sandwich panels with outer sheets of plywood, Feds, Dstp, DSG1, DBSP or metal (steel, aluminum) and central part of foams with wood fillers;
parts of foams with wood fillers of structural and heat-insulating purposes (for example, parts of fastening of ceilings of wagons, heat, noise and vibration insulation of wagons, diesel locomotives, refrigerators and doors of garages, thermal insulation of pipes with volatile gasket, etc.);
reservoirs (gas tanks, receivers, etc.).
slip bearings operating in selective transfer mode;
Of course, the considered promising directions of the use of KDPM do not claim completeness, do not exhaust all possible areas of use and can be significantly expanded.
"Definitions and classification of polymer composites composite called materials obtained from two or more components and ..."
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Topic 1. Definitions and classification of polymer
Composites. Mechanism of interaction of components
Modern era can be called the age of polymers and composite materials.
Definitions and classification of polymer composites
Composite call materials obtained from two or more components and
consisting of two or more phases. One component (matrix) forms continuous
phase, the other is filler. Composite materials are heterogeneous systems and can be divided into three main classes:
1. Matrix systems consisting of continuous phase (matrix) and dispersed phase (discrete particles).
2. Compositions with fibrous fillers.
3. Compositions having a mutual structure of two or more continuous phases.
Advantages of heterogeneous polymer compositions compared to homogeneous polymers:
1. Increased rigidity, strength, size stability.
2. Increased destruction and impact strength.
3. Increased heat resistance.
4. Reduced gas and vapor permeability.
5. Adjustable electrical properties.
6. REDUCED COST.
It is impossible to achieve a combination of all these properties in the same composition. In addition, achievement of advantages is often accompanied by the appearance of unwanted properties (the difficulty of the flow, therefore, molding, the deterioration of some physico-mechanical properties).
A wide variation of composition properties can only be achieved by changing the morphology and adhesion strength between phases.
For uniform transmission of external effects through the matrix and the distribution of it on all particles of the filler, a solid grip is needed on the border of the matrix - filler achieved due to adsorption or chemical interaction.
The existence of such a clutch between the uncomplicated components in heterogeneous plastics distinguishes them from mechanical mixtures.
The matrix can be metallic, ceramic, carbon. The filler is represented as particles and fibers that have significantly higher physicomechanical properties than the matrix.
Particles are usually called dispersed filler, they have an indefinite, cubic, spherical or scaly shape with dimensions from the fraction of MM to micron and nanoscale values.
The inert filler practically does not change the properties of the composition.
The active filler significantly changes the properties of the composition. For example, fibers have the extralative characteristics of which are two orders of magnitude higher than the properties of the matrix. They can be continuous and short. The diameter of thin fibers 5-15 μm, thick (boric or carbidremium) - 60-100 μm. Length of short fibers from 1-2 to 20-50 mm.
The name of the composites corresponds to the nature of the fibers: glass, coal, organo, borplastics, etc. for hybrid variants - glass biplastics, organoboroplasty, etc.
The fiber orientation determines the transition from filled plastics to reinforced plastics. This is a system of oriented fibers, bonded polymer matrix. Plastics include materials, the indispensable component of which is some polymer located during the molding period of products in a plastic or viscous state, and during operation - in glassy or crystalline. Plastics can be homogeneous or heterogeneous. Plastics are divided into thermoplastics and reactors.
Classification of composites:
1. By nature, the matrix:
thermoreactive thermoplastic.
hybrid.
Thermoreactive matrix is \u200b\u200ba matrix obtained by curing epoxy, ethereal, immediate, silicone and other oligomers in the process of manufacturing composites.
Thermoplastic matrix is \u200b\u200ba matrix that is melted for impregnating the filler and then cooled. This is PE, PP, polyarilenersulfones, sulphides, ketones.
The hybrid matrix can combine thermosetting and thermoplastic components.
2. By nature and the shape of the filler.
Organic and inorganic substances of natural or artificial origin. The modulus of the elasticity of the filler may be lower or higher than the module of the elasticity of the binder. Low-module fillers, which usually use elastomers, without lowering the heat resistance and the hardness of the polymer, give the material an increased resistance to alternating and shock loads, but increase its thermal expansion coefficient and reduce deformation stability. The higher the modulus of the elasticity of the filler and the degree of filling, the greater the deformation stability of the material.
Dispersed - filled composites, materials based on short and continuous fibers.
The chemical nature of the particles is diverse: chalk, mica, metal oxides, glassware, carbon in the form of soot or fullerenes, aerosil, flakes of glass or clay, rubber-like inclusions, etc.
Reinforcing fibers - glass, organic, carbon et al. Also known high-neur-resistant boric and carbide fibers, which are more often used for reinforcing metals.
3. According to the structure of polymer composites, matrix - for materials based on dispersed and short fibrous particles, layered (two-dimensional) and volumetric plastics based on woven and nonwoven materials.
Gradient materials with variable structure.
4. According to the degree of filling orientation, the anisotropy of the material:
Composites with a chaotic arrangement of particles and fibers, with an isotropic structure, composites with a unidirectional orientation of fibers, with sharply expressed anisotropy, 90o), composites with cross-proclaimed, orthotropic orientation (0, with a given anisotropy, composites with rolling orientation of fibers at angles that differ from 90 , Composites with a fan structure consisting of layers with different orientation of fibers.
5. According to the methods of manufacturing materials and products:
singaddia methods - extrusion and "wet" winding, Pultruzia (broach), vacuum molding, two-stage methods of pre-obtaining impregnated with binding non-oriented (premix) or oriented (prepregs) of fibrous materials (semi-finished products) with subsequent molding of material (laminate) Methods "Dry" winding , pressing, autoclave molding.
6. By the number of components:
two-component, three-component PCMs combining dispersed particles and short fibers, polyvolocon hybrid PCM, combining fibers with close (glass gamingoplasty) or substantially different (glass hydroplasty) deformability, polymatum structures, for example, based on a combination of thermosetting and thermoplastic binders.
7. In terms of filler content:
with a non-oriented structure - the content of filler content of 30-40% - with a focused structure - 50-75%, highly and extremely filled organo-bins - 75-95% -.
8. According to functionality:
single-functional (structural), multifunctional, capable of self-diagnosticity (smart), multifunctional capable of self-testing and self-adaptation (intellectual).
When constructing composite plastic, there are two stages (see Table):
1-Calculated - analytical, 2 - experimentally - technological.
1 - Includes: Analysis of the specified loading conditions and determining the method of designing plastic with the necessary properties. Presentations and formulas taken from mechanics of composite materials are used:
a) the phenomenological approach is based on the use of equations of the theory of elasticity, creep, etc. For anisotropic materials, b) - the establishment of the dependences of the mechanical characteristics of the composition from the size of the particles of the filler, the mechanical properties of the components, their volumetric content, etc. These dependences are analyzed on microscopic, macroscopic and intermediate levels. The micro level is the level of structural heterogeneity, commensurate with the transverse dimensions of the filler elements - the diameter of the particles of the filler or the thickness of the reinforcing layer.
Table Required mechanical characteristics of composite plastic Select components and their choice of reinforcement scheme ratio in the composition
- & nbsp- & nbsp-
Shape Size Ratio Mechanism of interaction of PCM components Consider the mechanism of transmission of voltages from the matrix to the filler depending on its configuration.
In the simplest embodiment, when the polymer is reinforced with unidirectional continuous fibers and is stretched in the direction of their orientation, the deformation of the components is the same and the voltages arising in them are proportional to the modulus of the elasticity of fibers and the matrix. If the fiber is discrete in the same model, the voltage distribution is inhomogeneous along the length of the fiber. The voltage at the ends of the fiber is absent, but the tangent stresses occur at the border of the fiber matrix, which gradually involves fiber into operation. The growth of tensile stresses in the fiber continues until they reach the average level of stresses observed in continuous fiber. Accordingly, the length on which this happens is called "ineffective." With an increase in the deformation "ineffective" length grows and reaches the maximum value at a voltage corresponding to the fiber strength. In this case, the "ineffective" length is called "critical". It is an important characteristic of the interaction of composites and can be calculated according to the Kelly formula LDC / DVV \u003d WH / 2MAT (1) where the DVI and the WH is the diameter and strength of the fiber; Mat - the yield strength of the matrix or the adhesive strength of the system.
Depending on the strength of the fibers and the type of polymer matrix, the ratio of the LDKR / DVV may vary from 10 to 200; When Doll 10 μm, LDC \u003d 0.15-2.0 mm.
From the above reasoning, it follows that when switching from continuous fibers to a discrete part of the length of each fiber will not perceive the full load. The shorter the reinforcing fiber, the less its effectiveness. With l LDKR matrix under no circumstances can transmit voltage fiber sufficient for its destruction. It follows from this that the reinforcing ability of short fibers (an increase in the extrachart characteristics of the polymer) is very low. Especially if you consider the orientation of the fibers, which in such materials does not happen ideal.
The structure of materials based on short fibers is rather chaotic. The advantage of short-fiber fillers is determined by the possibility of high-speed processing of materials in the product. However, in the process of casting or extrusion, additional destruction of the fibers, the length of which is usually reduced to 0.1-1 mm.
When moving to a dispersed powder filler, the ability to transmit voltage from the matrix to the filler is so decreased so that its contribution to increasing the strength of the composite begins to compete with a decrease in the strength of the matrix due to the emergence of the stress and development of defects. Because of this, the strength of such a composite is usually not increasing compared with the strength of the matrix (sometimes even decreases somewhat).
When filling viscous thermoplastics, rigid fillers in the amount of more than 20% there is a transition from plastic flow to fragile destruction. At the same time, there is a significant decrease in shock viscosity, the work of destruction. The modulus of elasticity is growing with an increase in the amount of filler, but the size and amount of cracks, the "pseudopor" arising during the loading process when making the matrix from dispersed particles at the time of the voltage corresponding to the system's adhesion strength. Theoretical and experimental studies show that by reducing the size of the filler particles and the scatter of their diameters, it is possible to significantly reduce the likelihood of the appearance of large defects.
The main cause of hardening is the change in the direction of growth of cracks when they are contaminated with solid particles of the filler. The most likely direction of the crack growth is perpendicular to the direction of the validity of the applied force. If the filler particle is located in this direction, the crack must change its direction on the tangent to the surface of the particle. Consequently, if the particles have the form of fibers and stretched in the direction of the current force. The propagation of cracks along the particles of the filler is excluded.
When using the monolithic fiber of the circular cross section, the indicators of mechanical properties reach a maximum usually at 2 \u003d 0.65 - 0.7. When using precision methods for laying profile fibers, it is possible to increase 2 to 0.85, after which the strength of the compositions begins to a greater degree depend on the adhesion strength at the border of the fiber - binding than that of the fiber strength.
With the same degree of filling (2 \u003d 0.7) and the ratio of moduli of elasticity (E2 / E1 \u003d 21), the stiffness of the plastic with the triangular fibers in the transverse direction exceeds the stiffness of the plastic with the fibers of the circular cross section of 1.5 times.
The replacement of the monolithic fiber hollows makes it possible to dramatically increase the specific values \u200b\u200bof the strength and rigidity of products during compression and bending, since with the same mass of the fibers increases the moment of inertia.
It is ineffective to use hollow fibers in stretching compositions due to the low strength of profile fibers. When shift, it is better to use profile fibers.
Another direction in the creation of dispersed-filled polymers is their modification by rubber particles to reduce the brittleness and increase the stroopiness.
Positive results were obtained for shockproof polystyrene, epoxy and other matrices. The mechanism of hardening materials seems to be very complex, but the main role is allocated to braking the development of cracks with rubber particles. Many authors indicate the feasibility of creating in order to increase the strength of the transition layer having a high adhesion to the matrix polymer and the rubber phase.
Let's return to a unidirectional composite based on continuous fibers and consider the micromechanical models of its destruction. Elementary fibers have very high strength characteristics, ten times exceeding the strength of bulk samples. For example, the strength of the bulk glass is 50-70 MPa, and in the form of fibers - 2.5-3.0 GPa; A similar picture is observed for organic and carbon fibers, the strength of which reaches 4-6 GPa. Such a difference is explained by either the influence of a large-scale factor (the magnitude of the surface of the fiber determines the size of a possible defect), or the orientation effect, very characteristic of organic fibers.
When testing elementary fibers, a large variation of experimental strength values \u200b\u200bis observed. Therefore, at least 50 samples are usually experiencing, the average and dispersion is found.
Based on the hypothesis of a weak link, Weibull received the following equation of the probability of destruction p () of the sample at the voltage and length of the sample L:
P () \u003d 1 - EXER (-L), (2)
constants of which are determined from the experimentally obtained distribution of the strength of elementary fibers. The P parameter characterizes the defects of samples.
The values \u200b\u200bof the coefficient vary from 3-5 for normal and up to 10-12 for "intact" glass fibers.
Really rarely deal with elementary fiber, usually with a beam consisting of a variety of fibers. According to the theoretical representations of Daniels, a decrease in the strength of the beam of unrelated fibers compared with the average strength of the ox is determined by the dispersion of their strength. In the process of loading, when achieving the strength limit of any fiber, it is broken and no longer participates in the work.
The effort is redistributed to whole fibers, the process continues until the avalanche-like destruction of most, and then all the fibers in the thread (beam). At \u003d 10, the strength of the thread H is approximately 80% of the average strength of the elementary fiber.
Analysis of the loading diagram of the thread - makes it possible to trace the entire process of gradual fiber break. It also makes it possible to identify some defects of the thread, in particular, differentity (multi-displays) of fibers, reinforcing the polarism of their destruction. Interaction (connectedness) of fibers due to a twist or partial clearance, manifests itself in the character of charts
- that become more linear. The Waibulla coefficient for an unbound bundle of fibers should remain the same as for elementary fibers: in the case of their connected, tends to increase.
The polymer matrix connecting the beam into a single integer - microplastic - leads to an increase in its strength. At the same time, the strength is almost independent of the length of the sample (\u003d 30-50), which indicates a change in the mechanism of destruction. The fact is that the fiber torn in any place does not cease to perceive the load, as in the thread, but continues to work at the same stress level as in adjacent fibers. This happens at the distance of LDC from the destroyer in accordance with the mechanism, which was considered above for the materials based on short fibers.
According to the statistical theory of strength developed by Goraland and the Rosen, the destruction of the unidirectional composite under tension occurs by accumulating the gaps, crushing the fibers in the polymer matrix. In this case, the theoretical strength of the fibers of the TP in the composite is equal to the strength of an unbound beam of the fiber "critical" length of the LCR.
tr \u003d (LDKE) -1 / In practice, the process of crushing the fibers cannot be finished. It is usually interrupted by the emergence and development of the trunk crack due to overvoltages in the section, where the greatest number of defects accumulates, or decreases on the border of the fiber-binding section. This mechanism allows to obtain the highest strength values, since it is associated with the energy dissipation for the formation of large free surfaces. Based on this, when considering the implementation of the strength of the fibers in the composite, it is advisable to compare the experimental values \u200b\u200bof the ox with the strength of TP, which could be when implementing the mechanism of crushing fibers:
KP \u003d WH / TR, where kr is the coefficient of strength.
Real values \u200b\u200breach 60-80% for unidirectional glass, organo and carbon fiber based on superpower.
A similar approach is also proposed to study the implementation of fiberglass strength with longitudinal compression.
Currently, two main variants of destruction mechanisms are considered:
Destruction due to the loss of stability of fibers on an elastic basis;
Delamination of material from the effects of shear stresses.
The main dependence arising from consideration of the first model of destruction binds the strength of the material when compressing the HOA with the GM matrix shift module and its volumetric content M:
hOA \u003d GM / VM Calculations carried out according to this formula give very high theoretical values \u200b\u200bof HOA. For example, when the shift module gm \u003d 1-1.5 GPa, characteristic of epoxy resins, and m \u003d 30%, the strength in compression of HOA could be 3-5 GPa, while for real materials it does not exceed 1.5 GPa .
It can be argued that in all cases there is a proportionality between the strength of fiberglass when compressing the HOA and the shift of the ADD:
hOA \u003d K ADD, which suggests that the second mechanism is prevalent. This can be explained by defects with the structure of the samples and an inhomogeneous field of stresses arising from the test. Special methods of preparation and research of unidirectional fiberglass allowed us to increase the HOA to 2-3 GPa to increase, that is, a significant extent was able to implement the mechanism of loss of fiber stability, increasing the coefficient of the strength of 30-40 to 60-70%.
In the compression of organoplastics, the destruction occurs along a shift plane oriented at an angle of 45 ° to the fiber axis, which is characteristic of plastic fibers.
A similar mechanism, apparently, takes place for carbon firing, although in this case it is combined with the element of the shift.
The diversity of composite destruction mechanisms allows you to raise the question of optimizing the properties of the binder. For example, to increase the strength of the material when stretching along the fibers, it is necessary to reduce the "critical" length, which is achieved by increasing the rigidity of the matrix. On the other hand, this leads to an increase in the concentration of stresses and the growth of the trunk crack. Competition of these mechanisms is observed in the form of an extreme dependence of the strength of the composite from the binder yield limit, which varies with a change in temperature, test speed or the introduction of plasticizing additives.
In each case, the optimum is yours:
it depends on the nature of the fibers, the presence of existing technological stresses and defects. The inconsistency of the requirements for the binder is exacerbated during the accounting of its technological, heat resistance, the ability to absorb dynamic effects (shock viscosity), etc. The weakest place of composite materials is their low strength and deformability during the shift. Therefore, technological and operational stresses often lead to cracking material.
The crack resistance of the composite is taken to characterize the specific viscosity of the destruction of GC - the energy dissipated when the new surface is formed. The greater the specific viscosity of destruction, the higher the resistance of the composite to resolveing. Interlayer viscosity increases with an increase in the deformity of the matrix, adhesion between the fiber and the matrix, as well as the thickness of the binder interleavers between the fibers (VCB).
Modification of epoxy matrices with rubber did not lead to a significant improvement in the properties of materials. It may be due to the fact that the zone of plasticity in the composite is limited by the size of the intervoloconse space. A much greater effect is observed when using thermoplastic matrices, for example, PSF polyarylene sulfone, the deformability of which reaches 80-100%. In this case, GC values \u200b\u200bincrease almost an order.
Micromechanical models of polymer composites make it possible to identify analytical dependencies showing the effect of the properties of fibers, matrices, their adhesive interaction, material structure and mechanisms of destruction on the macroscopic elastic characteristics of the unidirectional layer. They are most successful. They describe the limit modulus of the elasticity and strength of the composite compound. In the case when the deformations of the fibers and matrices are the same, the following additive relations occur, which show the contribution of each component in proportion to its volumetric content of the EC \u003d EUV + EMM
- & nbsp- & nbsp-
These equations are called "Magnify Rule."
Since the contribution of the polymer matrix usually does not exceed 2-5%, then it can be not taken into account:
EC () \u003d EUV and K () \u003d BB The lengthening of the composite of the composite when tensile in the transverse direction is composed of the deformation of the fibers and the binder. The elastic module E () can be calculated according to formula 1 / EK () \u003d B / EB + M / EX, it should be borne in mind that the modulus of the elasticity of the fibers themselves in the transverse direction coincides with the modulus of elasticity in the longitudinal direction only for isotropic glass and boric fibers. For carbon and organic fibers, the transverse module is significantly lower than the longitudinal. A similar dependence occurs for a shift module of a single-directional composite "in the plane" of fibers.
The strength of the composite-tension compression and shift depends on many factors, primarily on the properties of the matrix, adhesive interaction, the structure of the material - the presence of pores and other defects. Analytical dependencies in this case may only be correlated. It is believed that reinforcement reduces the strength of the composite in the transverse (transversal) direction by about 2 times compared with the strength of a homogeneous matrix.
The elastic conventional properties of composites strength and rigidity are the most important characteristics of any material. When the sample is loaded with a stretch or compression, normal stresses arise and the corresponding deformations that grow up to the destruction of the material.
The limit (maximum) voltage is called its strength. For linearly elastic materials, there is a direct proportionality between the voltage and deformation of the law of the throat \u003d E. The coefficient of proportionality characterizes the stiffness of the material and is indicated as a modulus of elasticity, or the Yung module E.
This law is also carried out when the sample is loaded with shear (tangent) stresses and deformations arising, for example, when taking.
The proportionality coefficient in this case is called the shift module G: \u003d .G.
When stretching the material simultaneously with the elongation, its transverse dimensions occurs, which is characterized by the Poisson coefficient, which establishes the connection between the deformations along x and across the s sample: x \u003d μ y.
The elastic properties of isotropic materials are well described by two constants E and G, the relationship between which corresponds to the equation G \u003d E / 2 (L + μ).
The reduced ratios are well described by isotropic materials whose properties in all directions are the same. Such can include dispersed-filled polymers, as well as composites based on short or continuous fibers of the chaotic structure. (For fibrous materials there is always a certain degree of orientation, determined by the influence of technological factors.) When loading any design, the stress-strain state of the material is most often becoming heterogeneous. At the same time, it is possible to identify the main (maximum) voltages that may be the cause of its destruction. For example, in the case of a pipe that is under inner or external pressure, the circle voltages are twice the axial stresses, that is, half the thickness of isotropic material from the point of view of axial stresses is ineffective. The inhomogeneity of the voltage field can be significantly higher. For open-yield shells (rifle, grenade launchers), the ratio of radial and axial stresses reaches 8-10 or more. In these cases, it is necessary to take advantage of the remarkable ability of fibrous materials that can be oriented into the matrix in accordance with the distribution of main operational stresses.
Consider an example of a unidirectional layer. The unidirectional layer isotropene in the direction perpendicular to the fiber orientation axis of the typical values \u200b\u200bof the elastic constants of unidirectional composites are shown in Table. one.
- & nbsp- & nbsp-
The tensile strength of the unidirectional layer along the fibers can be from 1.0 to 2.5 GPa, depending on the level of strength of the fibers, such as the content of the binder. At the same time, the strength in the transverse direction does not exceed 50-80 MPa, i.e. The anisotropy coefficient is 20-30.
A small deviation of the direction of the load from the direction of orientation of the fibers practically does not affect the strength of the composite when stretching. Therefore, some fiber optic (3-5 °) is allowed, created by a special layout or an increase in winding step in order to increase the transverse strength of the material. In the case of compression, this is unacceptable, since it contributes to the development of shear stresses that determine the strength of the material in compression.
Unidirectional composite is the basis of a complex structure that is created by a combination of individual layers in accordance with the operational requirements for the design element. Methods of manufacture: Vacuum or autoclave molding, pressing, winding.
Consider further theoretical models for describing the processes of deformation and destruction of layered composites of a complex structure. It is possible to distinguish two main approaches in the development of calculation methods: phenomenological and structural. In the phenomenological approach, the composite material is considered as a homogeneous anisotropic medium, the model of which is built on experimentally obtained data. The selected strength criterion belongs to the whole material as a whole. The advantage of phenomenological models is the simplicity of calculations. However, for materials with a complex reinforcement scheme, a lot of empirical coefficients are required, which requires a large number of experiments. In addition, phenomenological models do not take into account structural processes in the destruction: the formation of cracks, microwave, etc.
Determination of the optimal dimensions of the filler particles The voltage arising from different parts of the particle surface (micro-fiber or microfiber) depends on the distance R from the corresponding surface section \u003d - o (1 -) / 2R, where is the Poisson coefficient.
The strength with increasing the specific surface of the highly dispersed filler increases to a certain maximum depending on the nature of the composition components.
The optimal diameter D of continuous fibers in stretched orthotropic plastic at a predetermined distance between the fibers is determined by equation D (1/2 - 1), where 1, 2 - relative elongations during the breaking of the binder and fibers of the filler, respectively.
Selecting the shape of the filler particles The form of particles affects the mechanism of plastic destruction. The size and form of products, processing technology is taken into account.
In the case of small thickness products and complex configuration, preference is given to highly dispersed fillers (powders), as they are easily distributed in the binder, while maintaining the original distribution in the process of molding the product.
The use of highly dispersed fillers reduces the likelihood of destruction, separating products upon subsequent mechanical processing.
Solid inclusions in the stretched sample reduce the voltage in the contact zone of the binder with the filler, but in the spherical particle, the voltage exceeds in
1.5 times the voltage in the zones of the binder removed from it, i.e. The filler perceives the bulk of the load.
The effect of filler increases if the particles have an ellipsoidal shape and are oriented towards the deformation axis.
Selection of components with an optimal ratio of mechanical characteristics Conditions: adhesion interaction MORE COZEZIA OF BANGING, Both components work together until the destruction, the ideal elastic behavior of the filler material and the binder.
Determination of the optimal degree of filling even reinforcing fibers do not always have a reinforcing effect on plastics. If the ratio of the deformation characteristics of a binder and reinforcing in unidirectional plastic satisfies the condition with B, then even a linear decrease in tensile strength \u003d c (1 - c) is observed before the critical volumetric content of fibers (B, CR).
Due to the insignificant deformation of the binder with a break, equal to C, the voltage perceived by the fibers is too little in order to compensate for the reduction of the strength of the polymer matrix. Only starting with B, kr, the total strength of the reinforced fiber can compensate for the reduction of the strength of the matrix, and the strength of the plastic starts to increase.
Each plastic is characterized by its in, kr, which for the selected polymer binder, the smaller than the stronger the reinforcing fibers, and with the selected type of fibers grows with an increase in the strength of the binder with.
The maximum degree of filling in, MAX in the ideal case corresponds to such a density of the packaging of the fibers at which they touch each other by forming cylindrical surfaces. The maximum density of the packaging is achieved at different degrees of filling.
Ltd., Max \u003d 0.785, Hexagonal LLC B, Max \u003d 0.907 Tetragonal Ltd. LLC If fibers of different diameters are used, then can be achieved in, max \u003d 0.924.
The optimal degree is less than the maximum in, optimum 0.846 / (1 + min / d) 2, where min is the minimum possible distance between the fibers.
Features of the structure and properties of polymer composite materials (PCM).
PCM with high fiber content. The physico-mechanical properties of composites are significantly dependent on the relative content of components. According to the "Mixture rule", the greater the fiber content, the higher the density of their packaging, the higher (with other things being equal) there must be a module of the elasticity and strength of the composites. The calculation of the mass content of the ox fiber in the material is made on the basis of their quantity in the sample, which is determined from technological considerations (linear density, number of layers of tissue or winding parameters). For fiberglass, you can use the burning method of the binder. The ratio of WH + SV \u003d 1 takes place.
Theoretically, the maximum possible content of the fibers of one diameter with a dense hexagonal package is 90.8% by volume. Taking into account the real dispersion of the diameters of the fibers (10%), this value decreases to about 83%. In many works, the optimal fiber is considered optimal \u003d 0.65. This value apparently characterizes not the thickness of the binder films (they are different), and the fibrous frame formed by the molding of the material with a one or another method. The impact of power factors (tension when winding and pressing pressure) in this case is ineffective, as it will only lead to the destruction of the fibers.
The real way to increase the elastic conventional properties of composites by increasing the content of the fiber is to compact their laying in prepregs until the position of their position in the structure of the composite. A decrease in the viscosity of the binder and an increase in the effects of force factors was able to increase the content of glass and organic fibers in a unidirectional composite up to 78% by volume. At the same time, its elastic-strength characteristics increased accordingly. Theoretically, the content of the fibers does not depend on their diameter, but practically it is of great importance. In the case of carbon fibers having a diameter of two times smaller compared to glass or organic fibers, it was possible to increase their content in the carbon fiber to only 65%, since overcoming friction in such a system and remove excess binding more difficult.
When using organic fibers, HM, there is the possibility of obtaining highly charged organoplastics with a fiber content of up to 90-95%. This is achieved due to the irreversible thermodetorming of the fibers in the direction perpendicular to their axis, leading to a change in the cross section of the fibers from the round to the cross section of an arbitrary shape, due to contact with adjacent fibers. The interaction between the FIQs is achieved either through the thinnest layers of the binder, probably partially located inside the fibers, or by an auto-syntic bond, which is formed with the mutual diffusion of the fiber components.
The modulus of the elasticity and strength of the ring samples vary linearly in almost the entire range of increasing the volumetric content of the fibers, which indicates the implementation of the "Mixture Rules".
The effect of increasing the elasticity characteristics of the composite (20-40%) is so significant that significantly overlaps the observed decrease in the shift and transversal properties of materials, as well as an increase in their water absorption.
Highly and extremely reinforced composites should be used in elements that do not experience shear loads. To increase the weather resistance, the outer layers of the design can be made from composites with the usual or elevated content of the binder.
Hybrid and gradient reinforced plastics (HAP) with
Adjustable mechanical properties
The creation of hybrid polymer composite materials that combine two or more types of fibers - glass, organic, carbon and borogne, is a promising direction for the development of modern technology, since it determines the expansion of the possibility of creating materials with specified properties. The most significant factor influencing the nature of the mechanical behavior of the HAP, especially when tensile, is the magnitude of the limiting deformations of the fibers reinforcing the material. Gap, in which fibers having close deformative characteristics are combined include organospectorates and carbon plastics.The mechanical behavior of such materials under tension, compression, bending and shift mainly corresponds to the principle of additivity, i.e., "Mixtures".
Another nature of the patterns is observed in the study of HAP, combining fibers with different deformability. When tensile, the destruction of the fibers occurs simultaneously, the destruction of the fibers does not occur simultaneously, the destruction of the fibers and boroorganoplastics.
The limit deformation of the composite is determined in this case mainly by deformation of those fibers whose volumetric content prevails.
Denote by the index "1" high-modulus fibers, the index "2" - low-module.
With a high fiber content with a large modulus of elasticity (and the low value of the limiting deformation 1), the strength of the composite is calculated by the formula K1 \u003d 1 (ECSB + E11 + E22) with a high content of fibers with a low modulus of the elasticity of the composite strength to calculates by the formula K2 \u003d 2 (ECSB + E22) The mechanism for the destruction of three-component materials changes to achieve a certain critical ratio of different-scale fibers μKr, in which the destruction of the fibers with various discontinuous elongations is equally even, i.e. K1 \u003d.
k2. Neglecting the strength of the matrix, we obtain a ratio of 1 E11 + 1E22 \u003d 2 E22 after the transformation of which we have:
1/2 \u003d k \u003d e2 (2 - 1) / 1 E1 as 2 \u003d 1 - 1, then μkr2 \u003d k / (1 + k).
For coals, it is possible to take E1 \u003d 250 GPa, E2 \u003d 95 GPa, 1 \u003d 0.8%, 2 \u003d 3.5%, then k \u003d 0.3; μKr1 \u003d 23% or μkr2 \u003d 77%.
The concept of critical volume occurs for composites based on the same type of fibers. It characterizes the transition from the destruction of the fibers binding to the destruction.
Due to the large difference in their elastic characteristics of μK, it is very small and is 0.1-0.5% of fibers.
Consider the deformation curves of carbon plastic with different content of different modulus. At the initial section I, deformation curves are linear, carbon and glass fibers are deformed together, the elastic module is composed of two components and meets additive ideas. Samples containing the amount of carbon fibers are more critical, destroyed during deformation of 0.7-0.9%. Nonlinear section II on deformation curves - coalstoplastics, in which carbon fiber content is less critical, can be considered as a plot of "pseudoplasticity", due to the gradual fraction of carbon fibers in a fiberglass matrix, which ensures the integrity of the material. The nonlinear portion II ends with deformation equal to about 2%. Further, there is almost a linear portion III, on which the elastic module corresponds to the proportion of glass fibers in the composite, and the limit deformation
- Limit deformation of glass fibers 2 3-3.5%.
When the sample is reloaded, the diagram is completely linear and corresponds to the third portion of the initial curve. At the same time, the crushing of the fibers, apparently, occurs for another two or three load cycles - unloading, since only after that a constant correlation dependence of electrical resistance from sample deformation is established.
The dependence of the strength when tensile HAP on the ratio of different-forming fibers is characterized by a curve with a minimum corresponding to the critical ratio of fibers.
For materials tested for compression, diagrams - and strength dependencies are almost linear. Low-strength (on compression) Organic and carbon fibers, while in a glass or boropastics matrix, may not lose stability during deformation and, therefore, at voltages 2-3 times large than in conventional organo and carbon styles. These effects, as well as an increase in the deformability of carbon fibers in a fiberglass matrix when tensile, many authors call synergistic.
The fibers of various types are mixed within the same layer or alternate layers.
Below are several examples of the most rational combination of different-scale fibers in HAP:
the combination of glass and organic fibers allows to obtain materials, on the one hand, with a higher strength in compression and shift (compared to organoplastics), on the other hand, increase the specific characteristics of the hybrid system when tensile (compared to fiberglass);
Gap based on a combination of glass and carbon fibers have a higher modulus of elasticity compared to fiberglass, while the specific characteristics of the strength of materials during compression are reduced and slightly decreased during tension; the work of the destruction of the samples increases;
the addition of bore fibers in fiberglass allows you to significantly increase their elastic modulus, while maintaining (or rises) the strength of materials during compression.
One of the types of GAP is gradient PCMs, the structure and properties of which are spatially inhomogeneous. Smooth, adjustable change in the elastic conventional properties of the PCM in some cases allows you to create a uniform voltage field. For example, when loading homogeneous shells from PKM internal or external pressure with an increase in the thickness of the structure, a significant reduction in their effective elastic characteristics is observed. Only layers adjacent to the crushing medium are fully loaded. Starting with some thickness, PCM practically ceases to perceive additional load, and an increase in the shell thickness does not make sense. Theoretically, it is possible to avoid this phenomenon if you use the PCM with variables (increasing in thickness) by the elastic module.
At the same time, the mass-size characteristics of the material will be improved by 1.5-2 times.
Almost this option can be implemented, for example, winding the shell of PCM layers, gradually (in accordance with the calculation) by increasing the amount of carbon fibers relative to the glass. With similar problems (and their decision), you also have to meet when creating supermarkets or gangs of rotors rotating at high speed. Varing the position of the layers with different content of fibers makes it possible to increase the shift, vibration and fatigue strength, water and weather resistance of materials.
The gradient-structural composites significantly expand the possibilities of PCM.
Almost all "natural constructions" have such a structure (trunks and plants, protective needles of plants and animals, the beaks and feathers of birds and many other examples). Obviously, in this issue there is a strong lag of nature and there is a huge reserve to increase the performance characteristics of artificially created products.
"Intellectual" composites at the end of the XX century. A new term has appeared in the material science - "Intellectual"
materials. The adopted concept of "intellectual" material determines it as a structural material capable of self-identification and self-adaptation. These materials should be able to recognize the emerging situation (sensory function), analyze it and make a solution (processor function), as well as excite and carry out the necessary reaction (executive function).
Currently, there are no composites that would respond to all of the listed requirements. However, partially (phasate) these tasks can be solved, first of all, the tasks of creating materials informing about their state, about the approximation of operational loads to the maximum permissible, on cracking, chemical corrosion, water absorption, etc.
The main requirement for sensory elements of such composites is the sensitivity to mechanical exposure and the ability to be distributed throughout the volume. The perfect sensor is relaxing to turn deformation into electrical signals. In this sense, conductive fibers are promising, which can be embedded in composites during their molding. These include constantane or nichrome wire, conductive carbon or boric fibers, piezoelectric films from polyvinylidenefluoride and more.
The control of the viscoelastic properties of polymer composites (flaw detection) is carried out with the help of acoustic methods, fixing the relationship between sound speed and its absorption coefficient. When using the magneto-dielectric properties of polymers for diagnosis of PCM, the addition of dispersed (colloidal) particles of magnetic and electrically conductive materials, including ultrafine iron, copper, nickel, nickel nanoparticles (fullerenes and nanotubes), is recommended.
The current principle of executive (adaptation) mechanisms is the deformation, as a result of any phenomena - heating, supply of an electrical signal, etc. To activate the material, the most acceptable piezoelectric effect, electric and magnetostriction and the memory effect of the form. These mechanisms ensure the transformation of the electrical signal in the triggering deformation. The greatest effect is observed for metal memory metals. The alloy of titanium and nickel provides deformation up to 2%. Another important indicator of the actuator is its elastic module, which determines the possibility of creating a given stress-strain state. It is usually comparable to the elastic modulus of the main material.
The process of manufacturing "intellectual" composites mainly corresponds to the process of producing a product from the main material. At the same time, it is necessary to introduce information and executive elements into material, the minimum disturbing its structure. It is also necessary to draw attention to the complexity of micromechanical processes occurring during the curing of the binder.
"Intellectual" composites - of course, the material of the future, however, currently abroad (in the USA, Japan, Great Britain, Canada), there are intensive scientific and technical work on the creation of such materials for modern technology, primarily aviation, rocket and space and t . p., as well as for mass communication. As examples of structures using "intelligent" materials, the front edge of the F-15 aircraft wing, a segment reflector and executive mechanisms of the turning of spacecraft, aircraft with reduced noise and vibration can be noted. German firms that create modern windy electric generators are monitored by the state of blades having a diameter of up to 100 m or more. Optical fibers placed inside material make it possible to monitor its structural integrity and evaluate the loads acting on the blades in order to automatically support them at an optimal level. It is also controlled by the possibility of separating the material, for example, due to the lightning strike.
The dependence of the properties of composite plastics on the interaction of components The mutual influence of the components in the interfacial zone is determined by the composition of the composition and conditions of its formation. In rare cases, it is possible to establish a functional dependence between mechanical characteristics and interaction.
When an appression increases adhesion strength, a correlation is observed between adhesion strength and destructive tension voltage.
The choice of the location scheme of the fibers is made on the basis of data on the distribution of the power field and the nature of loading.
Residual stresses in products made of composite materials affect operational properties. Under residual voltage (mechanical, thermal, shrinkable, diffusion, etc.), there are voltages that are mutually balanced in the amount of the product, appeared in it as a result of the effects of external power, thermal and other fields and exist in the product after the cessation of the field and the disappearance of temporary Voltages. Temporary temperature, shrinkage, diffusion stresses disappear, as soon as the temperature, curing depth, the degree of crystallinity, or the amount of absorbed substances will be the same in terms of material. Mechanical time voltages disappear after the external field termination.
Residual stresses occur in a molded product only in the case when the maximum time voltages in some part of the product volume exceeds the yield strength of the material and it will be irreversible at normal deformation temperature (plastic and highlylastic), or due to the unequal degree of transformation (curing, crystallization ) Separate areas of the material will acquire various thermoelastic properties. The difference in the thermoelastic properties of the polymer matrix and filler also leads to the appearance of residual stresses.
The molding process is performed at elevated temperatures and pressures.
Therefore, temperature gradients arise, which are even more increasing, as curing usually flows exothermally.
When cooled in surface layers, significant thermal stresses occur, which can lead to the appearance of additional irreversible deformations and cause an increase in residual stresses in finished products.
Method for determining residual stresses. Solvent method.
The sample is treated with a solvent, which penetrates the polymer and increases the strength of the surface layer. When the surface voltage exceeds the destructive voltage of the swelling layer, the network of small cracks will appear. In this case, lg \u003d lgm + nlgost, where the OST is a residual voltage (kg / cm2), m and n are constant values.
Voltage at the boundary of the contact of the binder with the filler.
The main reason is the shrinkage of the polymer matrix during curing and cooling, which differs significantly from the temperature shrinkage of the filler associated with the matrix of the adhesive bond. The pressure of the cured resin on the filler can be calculated by equation (1 2) TE 2 P \u003d, (1 + 1) + (1 + 2) (E1 / E 2) where 1 and 2 - the thermal expansion coefficients, T - the difference between curing temperatures and cooling, 1 and 2 are the coefficients of Poisson, E1 and E2 - deformation modules (1 - binder, 2 - filler).
If the voltages arising in the material are asymmetrical, they can cause a form distortion.
Topic 2. Unsaturated polyester resins
In unsaturated oligoethers are called oligomeric esters obtained using unsaturated monomers containing a vinyl group. Such oligomers are widely used in the production of reinforced plastics and other composite materials. At the same time, unsaturated oligoeffers of two types are used: oligoeffermalainates and oligoefiracrhelates.The idea of \u200b\u200ba combination of reactive polymers and monomers was proposed by K. Ellis in the 1930s, which found that unsaturated polyester resins obtained in the interaction of glycols with maleic anhydride are curable into an insoluble solid material when adding a peroxide initiator. Ellis patented this discovery in 1936.
Oligoethermaleinates are obtained by the interaction of a maleic anhydride with dioxide alcohols (ethylene glycol, diethylene glycol, 1,2-propylene glycol), while to regulate the number of double bonds in the obtained oligomer and the preparation of a finite polymer with the required properties to the reaction system also introduces other dicarboans of acids (adipic, isophthalic, phthalic anhydride, etc.). It should be noted that in the process of synthesis of oligomers, which is carried out during heating from 50 to 230 ° C, it is partial or almost complete isomerization of Maleinathy units into fumarate: fumarate double bonds are 20-60 times more active than melting reactions in curing reactions and contribute to obtaining a cured polymer more High Quality.
Later, Ellis found that more valuable products can be obtained by interacting with an unsaturated polyester alkyd resin with monomers such as vinyl acetate or styrene. The introduction of monomers significantly reduces the viscosity of the resin, which facilitates the addition of the initiator to the system and allows the curing process is energetically and fully. In this case, the polymerization of the mixture passes faster than each component separately.
Since curing passes along a radical mechanism, initiators serve as a source of free radicals and initiating the chain reaction of polymerization are introduced into the mixture during curing. Free radicals can be formed from peroxides or other unstable compounds, for example, azosocedutenine. To increase the speed of their decomposition into the composition, activators (promoters) are additionally introduced by typical curing initiators are benzoyl hieroxide and benzoyl hydroperoxide / disintegration of benzoyls are most effectively accelerating tertiary amines (dimethyl, diethyl, diethanolanine), disintegration of IEC, cyclohksanone cobalt salts Acid. To cure the polymaleinatstroll binding at 20 - 60 ° C. Nafthenate CO is usually used. At 80 - 160 ° C - the rail of benzoyl, dicumila.
Oxygen - inhibitor. Therefore, wax substances are introduced. Possessing the low temperature of softening and being surfactant, they cover the surface of the binder and protect it from access of oxygen.
Sometimes to increase fire resistance to polymaloyal binders introduce anti-epires: SB2O3, chloro and phosphorus-containing organic compounds.
Restricted polyester compositions are obtained by replacing styrene per less volatile (styrene flying and toxic) monomers, such as divinylbenzod, vinyltoluolet, diallyloftulat.
Instead of styrene, triethy-lenglikoldimetacrylate (TGM-3) is successfully used as an active diluent:
At room temperature, liquid resins are stable for many months and even years, but when adding peroxide initiator is solidified in a few minutes. Curing occurs as a result of the "reaction of attachment and convert double bonds into simple; In this case, no by-products are not formed. Styrene is most often used as a joining monomer. It interacts with reactive double bonds of polymer chains, stitching them in a solid three-dimensional structure. The curing reaction passes with the release of heat, which in turn contributes to a more complete flow of the process. It has been established that usually about 90% of double bonds available in the reaction in the reaction are reacted.
Oligo-ethiracrylates are obtained by polycondensation of polyhydric alcohols, extreme aliphatic dicarboxylic acids and unsaturated acrylic acid aliphatic acids. For the synthesis of these oligomers, dioxide alcohols (glycols) are usually used. OligoEFi-robes are liquid or low-molecular substances with a molecular weight of 300-5000. Polymerizing in the presence of initiators of radical polymerization, they turn into default and insoluble polymers of a three-dimensional structure, which, depending on the chemical structure of the original oligomer, are solid glass-like or elastic materials. Oligo-ethirachos are capable of copolymerization with various monomers (styrene, methyl methacrylate, etc.), as well as with polyestermaleinates.
OligoEFi-Easterns have a certain advantage over oligoeffermaleinates: they are capable of homopolymerization, which allows you to prepare varnishes and other compositions based on them without the use of volatile and toxic unsaturated monomers.
In the technique of oligoephiracrhythm cure by radical polymerization or copolymerization; The bulk shrinkage during curing is 4-10%.
The initiators of the curing at 50-120 ° C (hot curing) are benzoyl peroxides, dicumila, etc. For curing at room temperature (cold cure), binary systems are used (for example, benzoyl peroxide + dimethylaniline; Cumol hydroperoxide + naphthenate or cobalt linolet).
The curing of oligoephirarilates can also be initiated by light, high energy emissions (-lchi, fast electrons) and ionic polymerization catalysts.
Epoxyacrylate oligomers can be considered as a kind of oligoefiracrilates. They are obtained by the interaction of oligomers containing end epoxy groups with methacryl or acrylic acids.
Allyl alcohol ethers prepolymers are obtained by the polymerization of allyl alcohol esters and phthalic or isophthalic acids. It is less likely to use diallylmaleinate, diethylene glycol-bis-allyalkarbonate or triallyl cyanurate.
The polymerization is carried out in the monomer medium, planting a pompolymer with methanol, or in a thin layer of the monomer with an excess of its excess at a given stage of reaction in vacuo.
The reaction is stopped before gelation, i.e. Before conversion of 25% of all double ties in the monomer. Molecular weight 6000, softening temperature ~ 60o S.
The prepolymers have a long viability at N.U. and high curing speed at 135-160 ° C in the presence of dicozyl or tertbutyl perbenzoate. The prepolymers are more often used in the production of prepregs and premixes with a reduced viscosity and filling forms at low pressure.
Polyester resins are used in the production of a large number of products, including boats, construction panels, car parts and aircraft, fishing rods and golf clubs. About 80% of polyester resins produced in the United States are used with reinforcing fillers, mainly with fiberglass.
Unnamed polyester resins are used in the production of buttons, furniture, artificial marble and body putty.
In contrast to most other plastics, which consist of one ingredient, polyester resins often contain several components (resin, initiator, filler and activator). Chemical nature and ratio of components may vary, which allows to obtain a large number of different types of polyester resins.
As a source of reactive double bonds for a large number of unsaturated polyester resins, maleic anhydride is used. When it interacts with glycols (propylene glycol is usually used), linear polyester chains with a molecular weight of 1000 ... 3000 are formed. Despite the smaller cost of ethylene glycol compared to the cost of propylene glycol, the first is used only to obtain several special resins. This is due to poor polyester compatibility based on ethylene glycol with styrene. In the process of esterification, the cis configuration of the maleic anhydride goes to the fumarone trans structure. This turns out to be useful due to the greater reactivity of the double bonds of the fumaric fragment in the reaction with the styrene. Thus, the high degree of isomerization into the trans structure is an important factor in the preparation of reactive polyester resins. Despite the high degree of isomerization of a maleic anhydride, which reaches more than 90%, to obtain polyester resins with an increased reaction capacity, more expensive fumaric acid is used.
Other two-axis acids or anhydrides, such as adipic and isophthalic acid or phthalic anhydride, are often added to the main reagent for changing the final properties of the resin and the number of double bonds.
The typical structure of the polyester resin is shown below (where R is an alkyl or aryl group of modifying two-axis acid or anhydride):
Oh about CH3 O OH 3 II II II.11 I N [O-C-R-C-O-CH-CH2-O-C-CH \u003d CH-C-O-CH-CH2] NOH due to a variety of properties and Low cost polyester resins are widely used to obtain various products.
Types of unsaturated polyester resins The wide variety of properties of polyester resins makes them suitable for use in various fields. The following are brief characteristics of the seven specific types of unsaturated polyester resins.
- & nbsp- & nbsp-
This type of polyester resins is obtained by esterification of propylene glycol with a mixture of phthalic and maleic anhydrides. The ratio of phthalic and maleic anhydrides can vary from 2: 1 to 1: 2. The resulting polyester alkyd resin is mixed with a styrene in a 2: 1 ratio. The resins of this type have a wide range of applications: they are used for the manufacture of pallets, boats, parts of shower, racks, swimming pools and water tanks.
2. Elastic polyester resins
If instead of the phthalic anhydride, the linear two-axis acids (for example, adipine or sebacing) are used, then a significantly more elastic and soft unsaturated polyester resin is formed. Used diethylene or dipropylene glycols instead of propylene glycol also give resins elasticity.
Adding such polyester resins to rigid general purpose resins reduces their fragility and simplifies processing. Elastic resins can also be obtained when replacing part of the phthalic anhydride with monosocondary acids of tall oil, which create flexible groups at the ends of the polymer chains. Such resins are often used for decorative casting in the furniture industry and in the manufacture of frames for paintings. To do this, cellulose fillers are introduced into elastic resins (for example, a walled nut shell) and cast them in the form of silicone rubber. Excellent reproduction of wood thread can be achieved when using forms of silicone rubber, cast directly on the original thread.
3. Elastic polyester resins Polyester resins of this type occupy an intermediate position between rigid general-purpose resins and elastic. They are used for the manufacture of shock load-resistant products, such as playing balls, protective helmets, fences, car parts and aircraft. To obtain such resins, instead of phthalic anhydride use isofthalic acid. First, the reaction of isophthalic acid with glycol is obtained by a polyester resin with a low acidic number. Then the maleic anhydride is added, and the esterification continues. As a result, polyester chains are obtained with the predominant location of unsaturated fragments at the ends of molecules or between blocks consisting of glycol-isophthalic polymer. In this type of esterification, phthalic anhydride is significantly less effective compared to isophthalic acid, since the phthalicic mono ester is inclined to the opposite transformation into an angidride with those high temperatures that are used in the preparation of high molecular weight polyester resins.
4. Polyester resins with a small shrinkage
When molding with fiberglass-reinforced polyester, the difference in the shrinkage between the resin and fiberglass leads to the appearance of shells on the surface of the product. The use of polyester resins with a small shrinkage weakens this effect, and thus obtained products do not require additional grinding before painting, which is an advantage in the manufacture of parts of cars and household appliances.
Polyester resins with a small shrinkage include thermoplastic components (polystyrene or polymethyl methacrylate), which are only partially dissolved in the original composition. When curing, accompanied by a change in the phase state of the system, the formation of microfucts compensating for the usual shrinkage of the polymer resin is occurring.
5. Polyester resins resistant to atmospheric influences
This type of polyester resins should not turn yellow when exposed to sunlight, for which the absorbers of ultraviolet (UV) radiation are introduced into its composition. Styrene can be replaced with methyl methacrylate, but only partially, for methyl methacrylate poorly interacts with double bonds of fumaric acid, which is part of the polyester resin. The resins of this type are used in the manufacture of coatings, outer panels and roof lights.
6. Chemically resistant polyester resins ester groups are easily hydrolyzed by alkalis, as a result of which the instability of polyester resins to alkalis is their principled disadvantage.
The increase in the carbon skeleton of the original glycol leads to a decrease in the proportion of essential bonds in the resin. Thus, the resins containing the "bisglolkol" (product of the interaction of bisphenol A with propylene oxide) or hydrogenated bisphenol A, have a significantly smaller number of essential bonds than the corresponding general purpose resin. Such resins are used in the production of components of chemical equipment: exhaust caps or cabinets, chemical reactors and containers, as well as pipelines.
7. Fire resistant polyester resins
Molded products and layered plastics made of fiberglass reinforced polyester resins are a combustible material, but have a relatively low combustion rate. An increase in resin resistance to ignition and combustion is achieved when used instead of a phthalic angidride of halogenated dioxide acids, such as tetrafluoroptale ,.tetrabromphalive and "chloride" (hexachlorcyclopentadiene attachment product to maleic anhydride, which is also known as het acid). Dibromneopentyl glycol can also be used.
Further increase in fire resistance is achieved by introducing various combustion inhibitors to the resin, such as phosphoric acid esters and antimony oxide. Fire resistant polyester resins are used in the production of exhaust caps, parts of electrical equipment, construction panels, as well as for the manufacture of cases of certain types of naval vessels.
The seven types of unsaturated polyester resins are most commonly used in industry. However, there are still resins of special purpose. For example, the use of triallylisocyanurate instead of styrene significantly improves the heat resistance of the resin. Replacing styrene on less volatile diallyloftulat or vinyltoluolet, one can reduce the monomer losses during the processing of polyester resin. Special resins can be obtained with a curing with ufacity, for which such photosensitive agents such as benzoin or its ethers are introduced into them.
The production of unsaturated polyester resins is usually for the production of unsaturated polyester resins, periodic processes are used. This is due to a variety of source products necessary for obtaining various resins, since the frequency of the process allows for a quick and easy transition to the production of other resins. Continuous processes are usually used for multi-donate general-purpose resin production.
The preferred structural material for the manufacture of equipment is corrosion-resistant steel, due to its chemical resistance to polymeric resins and other reagents used in the production of polyester resins.
Since iron and copper ions inhibit free radical polymerization of polyester resins, these materials are not used for the manufacture of reactors. When used as the initial products of halogen-containing materials, reactors with a glass lining are preferred.
Usually, glycol is loaded into the reactor, and then phthalic and maleic anhydrides are added. As a rule, 5 - 10% excess of glycol use to compensate for the losses caused by evaporation and side reactions. Before stirring and heating, the air in the reactor is displaced with inert gas. The first stage of the reaction is the formation of "semi-flee" - occurs spontaneously at a relatively low temperature, after which the reaction mass is heated to complete the formation of ether. The flow rate of the inert gas through the reactor can be increased to distil the water generated during the condensation reaction. For more complete removal of water from the glycol returned to the reactor, a heated heat exchanger is often used.
During the last stage of esterification, the temperature of the reaction mass rises to 190 - 220 ° C. Higher temperature favors the isomerization of Maleatov to fumarats, but at the same time causes adverse reactions for double bonds. There is an optimal temperature at which the fraction of fumarate reaches a maximum. For a general purpose resin, this occurs at 210 ° C.
To control the degree of esterification, the acidity and viscosity of the reaction mass is determined and the polyester is reached on the achievement of the required values \u200b\u200bpumped into the final reactor.
In this reactor, the required number of styrene is already located, and the polyester alkyd resin dissolves in it as they arrive. To eliminate any polymerization processes that can occur when a hot alkyd resin with a styrene can be added, an inhibitor can additionally be added to the reaction mass. Sometimes to maintain the required temperature, the reaction mass must be cooled. After completion of the process, the compliance of the properties of the reaction mass of the technical requirements. A full production cycle lasts 10-20 hours. The described method of producing polyester resins is often implemented as a melting process. The melt of the reagents is heated until the conversion reaches the required level. In another method, a small amount of solvent (toluene or xylene) is used to remove water released during the esotherification in the form of azeotropic mixture.
The solvent is no more than 8% of the entire reaction mass; It is separated from water decantation and returned to the reactor. After the end of the esterification process, the remaining solvent is distilled off from the reaction mixture first at atmospheric pressure, and then for its complete removal - under vacuum. In esterification, some adverse reactions may occur. For example, an attachment of the hydroxyl glycol group to a double binding of a maleic or fumarium fragment can occur with the formation of a branched polymer. It has been established that about 10 - 15% of dual bonds of an unsaturated polymer is consumed on the adverse reactions.
The simplest continuous process of producing unsaturated polyester resins is the reaction of a mixture of maleic and phthalic anhydrides with propylene oxide.
To initiate this chain reaction, it is necessary to have a small amount of glycol. Since the reaction of the interaction of anhydrides with epoxy groups occurs at relatively low temperatures, the dual communication of the maleate is not isomerized into a more active trans-configuration. To implement this isomerization required for further interaction with the styrene, the resulting polymer must be subjected to additional heating.
Continuous production of polyester resin from anhydrides and glycols can also be carried out in a series of heated reactors with stirrers, consistently pumping the resin through reactors with different temperature modes.
Unsuring unsaturated polyester resins Unsaturated polyester resins are cured by the introduction of initiators serving the source of free radicals and initiating the chain reaction of polymerization.
Free radicals can be formed from peroxide or other unstable compounds, such as azo compounds. These compounds can be cleaving for radical fragments when heated or exposed to ultraviolet or other high-energy emissions. As a rule, polyester resin contains an inhibitor, which is essentially a catlifier of free radicals. The polymerization reaction with the introduction of initiators begins only after the effect of inhibitors is overcome. This induction period makes it possible to mechanically mix the generator-containing resin initiator with the reinforcing agent and place it in the form necessary for curing before the start of the polymerization reaction. Good polymerization inhibitors are hydroquinone and its derivatives, as well as quaternary ammonium halides.
Most peroxidant initiators when entering the polymer mass decomparumes relatively slowly. To increase the speed of their decomposition, activators (promoters) are used. In fact, activators are catalysts for initiators.
Both the initiator and the activator are reactive compounds, the rapid interaction of which is accompanied by ignition or even an explosion. These compounds should be added to the resin, convinced before adding the second to the first dissolution of the first. Many resins contain a predetermined activator.
The behavior of polyester resin during curing is determined by the ratio of the effects of the inhibitor, initiator and activator.
The substituents in the ethylene carbon atom can bilo affect the reaction capacity of the double bond. The spatial effect is due to the fact that the volume groups shield double bonds and reduce the possibility of the second reacting group to take a favorable position for the attack, thereby reducing the reactivity of the entire compound. Polarity is determined by the ability of a replacement group to attract or give electrons. Electroneal groups (for example, methyl, phenyl and halogen) make a dual connection of electronegative. It is this action that is manifested in styrene, vinyltololet and chlorinated styrene.
Electric chargers (for example, vinyl or carbonyl) make a double bond with electropositive. This occurs in fragments of fumaric acid in the circuits of polyester resin. The opposite polarity of the double bond in styrene and in fumaric fragments of the alkyd resin contributes to their interaction and curing polyester resins. The monomeric styrene, more movable than long polymeric chains of an unsaturated polyester, can be homopolymerized. It is experimentally established that the molar ratio of styrene and double bonds of polyester 2: 1 is optimal.
Initiators and activators
There is a wide variety of systems initiator - an inhibitor - an activator available for use in the production of polyester resins. For example, a general-purpose resin inhibited by hydroquinone can be very quickly cured when using such an active peroxide initiator, as a peroxide of methyl ethyl ketone in combination with an activator - naphthenate or cobalt octate. In another case, a significantly more stable initiator is introduced to curing a polyester resin: tertstorebenzoate. This allows you to fill the polyester composition with calcium carbonate and crushed fiberglass. Such a containing initiator and molded compound is stable at room temperature for months, but can be cured for one minute with hot pressing at a temperature of 140 - 160 ° C.
The choice of a suitable initiator and its quantity depends on the type of resin and the temperature of its curing, from the required time of the entire process and the time of gelation. Since none of the available initiators usually does not fully meet all the necessary requirements, it is used to obtain the best results using various combinations of initiators and initiators with activators.
With thermal curing of polyester resins, the most frequently used initiator is benzoyl peroxide (BP), which is extremely effective and easy to use. It is easily soluble in styrene, it can be stored for a long time without loss of activity, stable at room temperature and easily decomposed at elevated temperatures. In addition, BP causes a high exothermic temperature peak, which contributes to the complete curing of the resin. The amount of BP administered in the resin varies from 0.5 to 2% depending on the type of resin and the monomer used. When using BP in the form of a paste (usually in a mixture with a 50% tricpsyl phosphate), the amount of the initiator introduced slightly increases (~ 1 - 3%).
Sometimes it is desirable (or even necessary) to carry out the process of curing the resin from the beginning to the end at low temperatures so that the heat released during the polymerization is dissipated. This is especially important when the wet forming the layered plastics when the use of heating is difficult. In such cases, methythyl ketone peroxide (PMEK) is usually used as an initiator. Although the use of PMEK does not lead to a complete curing of the resin at room temperature, however, adding an activator .. (for example, naphthenate cobalt) leads to gelation and almost complete rejection of the resin for a short period of time.
Topic 3. Resins based on complex dieters
Vinyl carboxylic acids
Resins based on complex diesters of vinyl carboxylic acids (DVK) are thermosetting polymers, the main chain of which is esterified by end hydroxyl groups residue, R, acrylic (I: R \u003d H) or methacryl (II: R \u003d CH3) acid: -O- C- R \u003d CH2. The main chain of the macromolecules of these resins is epoxy, polyester, polyurethane or other segments, and almost valuable materials are obtained based on epoxy resins.Although various DVK was obtained in laboratory quantities since the end of the 50s, the industrial production of these resins was established only in 1965. Shell Kemikal under the trademark "Epogonyl resins". These resins have been identified as epoxymethacrylates and have excellent chemical resistance, superior to the resistance of the best (for that time) polyester resins.
In 1966, Dow Kemikal released the resin "Derakan", which is a complicated diester of vinyl carboxylic acids, as well as a number of similar resins intended for coatings. In 1977, Interplastic and Reichhold Kemikal firms began the production of DVK called "Korecin" and "corrode"
respectively.
Characteristics of resin
Resins can be used as in pure form (i.e. without diluent), and in a mixture with other ingredients. In the latter case, the resin may contain a reactive vinyl-containing comonomer (styrene, vinyltoluolet, triacrylate of three-methylolpropane), or a non-reactive "diluent" (methyl ethyl ketone, toluene). As a rule, resin based on methacrylic acid esters contain styrene and used in the production of chemically resistant reinforced fiberglass plastics (CCMS). The resins - derivatives - acrylic acid are supplied undiluted, and the corresponding sore agents are administered directly upon receipt of coatings and typographical paints curable under the action of UV radiation.
The physical properties and fields of the use of DVK depend on the type of terminal groups (methacryl or acrylic), on the number and type of sore agents, as well as on the nature and molecular weight of the blocks that make up the main chain of the macromolecules of the resin. As a result of curing, styrene - containing DVKM-II acquire high resistance to the effects of acids, bases and solvents. Acrylic acid derivatives are more sensitive to hydrolysis compared with methacrylic acid derivatives, and therefore they are usually not used in the manufacture of chemically resistant materials. Due to the high reactivity, these resins are preferable to construct the radiation method.
Underproof DVK - solid or waxy substances. Therefore, to ensure that necessary for processing viscosity and increase their reactivity, both reactive and inert diluents are introduced into the composition.
The main part of the Macromolecules of DVK consists of epoxy oligomeric blocks of various molecular weight. The greater the molecular weight of such blocks, the higher the strength and elasticity of the resin, but below the heat resistance and its resistance to the effects of solvents.
Compared to complex polyesters, DVK is characterized by lower maintenance of ester groups and vinyl fragments. This leads to an increase in the stability of these resins to hydrolysis, as well as to a decrease in the peak temperature of the exotherma. Shrinkage resin during curing decreases. As well as complex polyesters, DVK have a limited shelf life, which is ensured by the introduction of polymerization inhibitors ("traps" of free radicals) during the production of resin.
Manufacture of resin.
DVK is obtained by the interaction of methacrylic or acrylic acids with oligomeric epoxy resin. Acid attachment reaction to epoxide (esterification) is exothermic. As a result of this reaction, free hydroxyl groups are formed on the oligomeric unit, but the formation of by-products does not occur (as, for example, during polyterification, when water is formed). After the end of the reaction or during its flowing into the reaction mixture, suitable diluents or polymerization inhibitors are added.
Epoxy resins that are used for the production of DVK can be based on bisphenole A (in the case of general purpose and heat-resistant DVK), on phenol-novolac fragments (heat-resistant DVK), as well as on the tetrabrum derivative of bisphenol A (fire-resistant DVK). When obtaining DVK with acrylic groups at the ends, oligomeric epoxy blocks based on bisphenol A. is usually used as a polymer of the main chain.
Curing
DVK, similar to unsaturated polyester resins, contain double bonds, which react with the formation of intermolecular stitching. This process occurs in the presence of free radicals, which are formed as a result of chemical, thermal or radiation transformations. The curing process flowing through a free-radical mechanism includes the initiation stages (induction period), growth and breakage of the chain. Initiation of the stage, limiting the speed of the process, during which the initiator suppresses the action of polymerization inhibitors. This leads to a reaction in the double bonds of vinyl ether, which is part of the macromolecule, and its sorent.
The molding of semi-finished products (prepregs) based on DVK for volumetric molding or for sheet plastics is used with direct pressing of fittings for pipes, household appliances, impeller, pumps and car parts. Usually these prepregs contain approximately equal mass fractions of resin, crushed fiberglass and fillers. They also include: "hidden" initiator, pigments, anti-adhesive lubricants and thickeners.
Topic 4. Polbutadiene resins
Polbutadiene resins are high molecular weight, hydrocarbon thermosetting resins. They have excellent electrical properties, significant chemical resistance, sufficiently high thermal stability, have low moisture absorption and are easily cured in the presence of peroxide initiators. They can be used for recycling by direct and injection molding, injection molding, method of wet output in the form for the form of layered plastics and for the preparation of prepregs. Due to the fact that there are many polybutadiene derivatives, the scope of application of these polymers is extensive: they are used as modifiers of other resins, for the manufacture of coatings, adhesives and electrical insulating filling compounds.Polybutadiene resins were obtained around 1955 and used in the "Bud" type compounds in the laboratories "Inji". The resin, which was applied in these compounds, consisted of a large amount of liquid 1,2-polybutadiene, a certain number of butadienestrol copolymers and adducts of these two resins. Since then, similar products produce Richardson and Lithium. In 1968, under the trademark "GISIL" began to produce polybutadiene with a high content of double bonds and a small amount of isocyanate groups at the ends of the macromolecule. It introduced a certain number of peroxidant initiator.
This resin is now produced by Diananiam and Nippon Soyuz under the trade name "Nisso-RV". This resin is a liquid astactic polybutadiene with a molecular weight of 1000 - 4000, about 90% of the double bonds of which are located in the side chains (vinyl groups).
There are three types of this resin:
type B does not contain end functional groups; Type G contains hydroxyl groups and type C - carboxyl groups at both ends of macromolecules. Other polybutadiene resins are now produced under the name "Ricon" by the company "Colorado Kemikal SPESHIALTIZ". Resins "DIMENIT" are a mixture of 1,2- and 1,4-polybuta-dnen (DN-702, PD-503 doniths) or mixtures with monomers-co-reagents, such as vinyltoluol (RM-520, RM-503 ) or Styrebutadiene oligomer (PDPD-753).
Industrial types of polybutadiene resins are usually a mixture of low molecular weight 1,2- and 1.4-polybutadiene. These isomers are distinguished by the provision of the reaction center participating in the polymerization. 1,2-polybutadiene, in which double bonds are located in side chains, more reactive than 1,4-polymers, where double bonds are in the main chain. Therefore, resins with a large content of 1,2-polybutadiene are cured faster and easier, and the resins with a significant fraction of the 1.4-polymer are usually used to obtain highly elastic materials.
In order for the 1.2-polybutadiene (PBD) resin to be more convenient to process into composite materials, it should be obtained with a high molecular weight and narrow molecular weight (mm) distribution. To increase the resin reactivity at various chemical transformations, end functional groups (for example, hydroxyl, carboxyl or isocyanate) are introduced into its macromolecules, and mixtures containing polybutadiene and reactive monomers, such as styrene and vinyltoluolet. End hydroxyl groups allow reactions with polyurethanes, and carboxyl groups with epoxy groups. PBB containing isocyanate end groups are used mainly to obtain electrical insulating fillings.
With a high content of vinyl groups (over 85%), polybutadiene resins are easily cured in the presence of peroxide initiators. Reactive end functional groups allow you to increase the molecular weight of the resin before curing. An increase in mm causes a decrease in resin flow to stitching, which causes the gelatinization and appearance of rigid polymer structures.
As a result, a more convenient technological time of recycling resin is also achieved in the reactor. The chain growth stage can be monitored (in time) so as to obtain polymers with different properties: from highly viscous liquids to solids with high mm. The ability to increase the chain is the basis for the widespread use of polybutadiene resins in the preparation of press-compositions, coatings, adhesives, electrical insulating filling compounds and thermosetting layered plastics. The following polybutadiene derivatives can be used both as modifiers for other resins and upon receipt of special layered plastics
- & nbsp- & nbsp-
Curing resin The similarity of the process of curing polybutadiene resins with curing of well-known polyester polymers when using peroxide initiators makes them extremely useful for composite materials technology.
The polymer curing passes through three stages: low-temperature gelation, high-temperature curing and thermal cycling. At low temperatures there is an increase in the molecular weight and viscosity of the resin.
This can cause gelation and the beginning of curing. High temperature curing begins at a temperature of 121 ° C, while the reactions are predomined by double bonds of vinyl groups. During this stage of the process, solid products are formed. Thermal cyclization begins at a temperature of ~ 232 ° C, and the remaining unsaturated fragments of the polymer substrate react to the formation of the density grid.
Below are the typical data of the processing mode prepreg:
Molding temperature, ° С
Pressure, MPa
Current cycle at 77 ° C for layered plastic thickness 3.2 mm, min |
The period after curing ................... no Chemical structure and properties The polybutadiene resins have excellent electrical properties and chemical resistance. The high content of hydrocarbon parts and the minimum content of aromatic links are the cause of low values \u200b\u200bof the dielectric constant and the attenuation coefficient, as well as excellent chemical resistance. A small content of aromatic fragments explains high dug resistance, as well as resistance to the formation of conductive traces.
These properties of polybutadiene resins, similar to the behavior of polyethylene, are associated with the stability of these polymers. For the formation of carbon in pyrolysis under the action of high voltage. The absence of essential bonds that make polyesters vulnerable to the effects of acids and bases explains the hydrophobicity, as well as the stability of polybutadiene resins to the action of acids and alkalis.
The use of KM based on PBD due to the unique combination of excellent electrical properties with the chemical resistance of the PBD-based CBS was successfully used in the design of the fairing of onboard radar antennas. To work in the frequency band exceeding K-range (10.9 - 36.0 GHz), reinforced epoxy fiberglass were used, which are inadequately satisfying this purpose due to the high values \u200b\u200bof the dielectric constant (4.5 - 5.0).
This becomes clear if we take into account that the thickness of the fairing wall, as follows from the equality below, is the function of the dielectric constant and the working wavelength:
n 0 d \u003d, 2 (sin 2) 0.5 where D is the wall thickness of the antenna fairing; P is an integer 0 (n \u003d 0 for a thin wall; P - 1 for the wall thickness equal to the length of the half-wave); 0 - wavelength in free space; - the dielectric constant; - angle of incidence.
Since the thickness of the fairing wall should be directly proportional to the active wavelength, but inversely proportional to the dielectric constant, then the combination at which the frequency is simultaneously increasing and the composite material with a high dielectric constant is used, it creates a problem of the wall thickness inconsistency when using longer waves.
It is obvious that if the wavelength simultaneously decreases and the dielectric permeability of the material increases, then the possibility of reducing the thickness of the fairing walls appears. However, the use of thin walls leads to a problem associated with the destruction of them from shocks, which can accelerate with serious surface erosion of thin layered structures.
Another problem arising from the use of materials with higher dielectric properties is possible deviations in the thickness of the fairing wall, which leads to the increase in the cost of production or the use of additional materials to provide accurate "electrical" thickness. When using antennas on aircraft and ships to km, from which fairings are manufactured, additional requirements are made: they must have stable properties in a wide range of temperatures and in conditions of high humidity. Strict requirements for materials associated with high values \u200b\u200bof working frequencies and complex environmental conditions are not easy to satisfy using conventional composite materials. However, these requirements can be implemented more complete when using polybutadiene materials.
Upon receipt of prepregs, the curing resin is carried out in the presence of a peroxide initiator. Despite the excellent processability of this KM and the simplicity of curing, which is completed into one stage in 2 hours at 177 ° C, low mechanical properties in the transverse direction limit it as a structural material. This disadvantage may be associated with a large density of intermolecular stitching, leading not only to fragility, but also to low adhesion of binding to carbon fibers.
When obtaining polybutadiene layered plastics of structural purposes, various reinforcing fibers are used: glass, quartz and aramid (Kevlar-49). Composites reinforced by the fiber "Kevlar-49" with a volume fraction of 60% are suitable for the manufacture of derangers of radar antennas. In order to increase some mechanical indicators of the material, especially the tensile strength in the transverse direction and during the interlayer shift, the adhesive properties and wettability of the Kevlar-49 fiber need to be improved.
An additional requirement when using these materials for the manufacture of fairing radar antennas is low moisture absorption.
Storage Polbutadiene resins do not require any special storage conditions compared to conventional, associated volatile, easily flammable organic solvents, such as heptane or toluene. When stored at temperatures 0, 20 or 35 ° C for 10 weeks, noticeable viscosity changes or solutions are notable. It should, however, avoid longer storage at temperatures above 35 ° C due to the propensity of the solution to gelation.
Epoxy resins Epoxy resins are one of the best types of binders for a large number of fibrous composites, which is explained by the following reasons:
Good adhesion to a large number of fillers, reinforcing components and substrates;
A variety of available epoxy resins and curing agents, allowing to obtain after curing materials with a wide combination of properties, satisfying various requirements of technology;
Lack of water release or any volatile substances during the chemical and small shrinking phenomena during curing;
Chemical resistance and good electrical insulation properties.
The main component of epoxy binders is a mixture of oligomeric products with epoxy groups in the terminal links (epoxy resins).
They get:
epichlorohydrine interaction with dioxide (less often polyatomic) alcohols or phenols with the formation of Diglycide oxyters CH2-CH-CH2Cl + HO-R-OH CH2-CH-CH2-OR - (- O-CH2-CH (OH) -CH2-O- RO O) -O-CH2-CH-CH2 \\ / O or CH2-CH-CH2Cl + H2N-C6H4-NH2 \\ / O or CH2-CH-CH2Cl + HO-C6H4-C (CH3) 2-C6H4-OH Bisphenol A / O is the most common resin obtained from epichlorohydrin and diphenylolpropane (bisphenol A) (ED) or epichlorohydrin and methylolfenol polycondensation products (epoxyphenol resins EF, EN). Recently, resins from epichlorohydrin and aniline (resin ea), diaminodiphenylmethane (EMDA) are used.
Application Epoxy resins are used when obtaining various composite materials and structural parts. They are also used as encapsulating and sealing compounds, press powders and for the manufacture of adhesives.
Epoxy resins are very resistant to the effects of acids, alkalis and moisture, are not deformed when heated to a high temperature, have a low shrinkage and high specific voluminous resistance. Epoxy resins can be used not only to protect materials from environmental action, but also for adhesive connection parts. In the electronics industry, for example, epoxy resins are used to encapapo welded modules, fill the windings of transformers and engines, as well as for sealing electrical cable joints.
Since World War II, epoxy resins are used to make equipment (for example, molds used for sheet stamping or models in the manufacture of parts). The reinforcing fillers in the form of particles or fibers are easily introduced into the resin, reducing its cost and increasing the stability of the size. The possibility of replacing metals by epoxy resins is due to two factors: efficiency in production and speed (without large material costs) modifications. In addition, these resins retain the form and dimensions well, have high mechanical properties and low shrinkage, which allows you to make parts with small tolerances from them.
Molding epoxy molding compounds (powdered, partially cured resin mixtures and hardeners who acquire fluidity during heating) are used for the production of all, species of structural parts. Fillers and reinforcing substances are easily introduced into epoxy resins, forming a molding mass. Epoxy resins provide low shrinkage, good adhesion with fillers and reinforcing substances, chemical stability, good rheological properties.
Bonding from all known polymeric materials Epoxy resins have the greatest adhesion strength. They are used to impregnate the set of substrates, while giving the minimum shrinkage. Therefore, these resins can be used to connect many heterogeneous materials. In addition, they can be cured at different temperatures and at different speeds, which is very important in the industrial release of adhesives.
The manufacture of km winding and in the form of layered plastics is one of the most important epoxy resin applications or binding - this is obtaining layered plastics and fiber-winding composites for the manufacture of structural parts. Such details are used in various industries, including in aircraft construction, in space and military equipment. Layered plastics are also used in the electronics industry for the manufacture of printed circuit boards. In the chemical and petrochemical industry, containers and pipes made from epoxy composites are widely used.
Epoxy resins can be used in various processes: with a wet winding of the fiber or "wet" molding of layered plastics, with a dry winding or laying layers with preliminary impregnation of strands of fibers, tissues or tapes (in the form of prepregs). In general, epoxy resins are more expensive than most other resins, but excellent performance properties often make their use in the ultimately more profitable.
Curing resin amines The overwhelming majority of epoxy oligomers are either viscous liquids, or low-melting solids, well soluble in ketones, ether, toluene.
The hardeners of epoxy oligomers by the action mechanism are divided into two large groups:
Crosslinking hardeners contain functional groups, chemically interacting with the functional groups of the epoxy oligomer;
Catalytic actions hardeners cause the formation of a spatial structure by polymerization of epoxy groups.
Crosslinking hardeners contain in molecules amino, carboxyl, anhydride, isocyanate, hydroxyl and other groups.
Aminic type hardeners are used for curing in the operating temperatures area of \u200b\u200b0-150 ° C. The aliphatic amines are widely used 1,6-hexamethylenediamine and polyethylene polyamine of the general formula H2N (CH2CH2NH), CH2CH2NH2, where n \u003d 1-4, which have high activity even at a temperature of 20 ° C.
As aromatic amines, M-phenylenediamine, 4.4 "dyaminodiphenylmethane, 4.4" -diamineodiphenylsulfone is used. Aromatic amines are less active than aliphatic, and curing them is carried out at temperatures of 150 ° C and higher.
Ditiaceamine is widely used as a hardener of the amine type.
Diciandiamine practically does not react with epoxy oligomers at room temperature, but quickly cures them at elevated temperatures (150 ° C and higher).
For a complete crosslinking of epoxy resin, the ratio between the amount of hydrogen atoms in the accumulator amino groups and the number of epoxy groups in the resin should be 1: 1. The reaction between aliphatic amines and epoxy groups occurs at room temperature. In the case of the use of hard aromatic amines, heating is needed. The chemical bond between carbon and nitrogen atoms arising from the "crosslinking" of amines resin is resistant to the action of most inorganic acids and alkalis. However, to the effects of organic acids, this relationship is less stable than intermolecular bonds formed by hardeners of other classes. In addition, the electrically insulating properties of the "amino-perched" epoxy resins are not as good as if other curing agents are used. It may be due to the polarity of hydroxyl groups formed during curing.
Isocianate hardeners are easily reacting with hydroxyl groups of epoxy oligomers even on cold (\u003d 20 ° C). At high curing temperatures (180-200 ° C), a reaction is a reaction of an isocyanate group with epoxy to form an oxazolidone cycle. Asocyanates are used as isocyanates, and hexamy-thylenediisocyanate and the prepolymers based on them with end isocyanate groups.
For curing epoxy oligomers, phenol-formaldehyde oligomers of both newmarium and resolved types are widely used. Novolaki cure epoxy oligomers by reacting phenolic hydroxyls with epoxy groups at 150-180 ° C, and in the presence of catalysts (tertiary amines) - at 80c. In the case of resolves, hydroxymethyl groups of resolves respond to secondary ON-groups of epoxy oligomers, and, in addition, aromatic cycles of epoxy oligomers can be alkyl.
Catalytic catalytic catalytic catalyzing polymerization of epoxy groups on cationic and anion mechanisms.
Cationic polymerization is initiated by Lewis acids - BF3, BF30 (C2H5) 2, SNCl4, etc.
Anionic polymerization is initiated by hydroxides and alkali metal alcoholates, as well as tertiary amines, such as triethanolamine and 2,4,6-tris (dimethylaminomethyl) phenol.
When anionic polymerization in the presence of tertiary amines, the active center is formed during the joint reaction of the amine, the epoxy center and alcohol according to the scheme of it aliphatic tertiary amines are usually hardeners of cold curing. Recently, as hardeners such as Lewis bases, imidazoles (in particular, 2-ethyl-4-methylimidazole) are successfully used, which give polymers increased heat resistance during the storage of amine hardeners usually do not arise special problems. However, they can cause skin irritation in some people, in connection with which they require careful circulation.
Curing Resin Anhydrides acids as acid hardeners The largest application was found cyclic aldehydes of carboxylic acids, such as phthalic, malein, as well as trimellite (TMA), pyromellite (PMA), benzofenontetracarboxylic acid anhydride (ABTC) curing with the help of carboxylic acid anhydrides are carried out at 120- 180 ° C.
Storage of these hardeners requires special care to prevent their decomposition under the action of air moisture. To ensure complete curing, the reaction leads when heated. Often, to accelerate the curing process, which goes extremely slowly, a small amount of accelerator is introduced. There are also anhydride hardeners who react with a resin when heated above 200 ° C. Acid anhydrides interact with epoxy resins with the formation of esters. So that this reaction occurred, the disclosure of the anhydride cycle is required. A small amount of proton-containing substances (for example, acids, alcohols, phenols and water) or Lewis bases contribute to the opening of the ring.
The resulting curing ester group is resistant to the action of organic and some inorganic acids, but is destroyed by alkalis. The materials obtained have greater thermal stability and better electrical insulating properties than using amine hardeners.
Lewis acid catalytic casing is only one of the Lewis acids - the boron is widely used as an epoxy resins hardener. When in a small amount to pure epoxy resin, this hardener acts as a cationic homopolymerium catalyst for the resin to form a simple polyester. The trifluorian boron causes a very fast, flowing in a few minutes, exothermic polymerization. Therefore, when a large amount of resin is cured to maintain in the ground temperature, it requires its blocking on a special technology. When connected to monoethylamin (MEA), to form a BF3-MEA complex, a trifluoride is converted at room temperature in a latent curing agent. At temperatures above 90 ° C, it becomes active and rapidly curing epoxy resin, accompanied by controlled heat output. When receiving prepregs, which are often stored for weeks before processing, the use of a latent hardener is absolutely necessary.
Epoxy resins containing the BF3-MEA complex are widely used for sealing, in the manufacture of snap, layered plastics and winding products.
Some restriction is the detected instability of prepregs and curable compositions containing VG3MEA, to the action of moisture.
Accelerators accelerators are added to mixtures of resin and hardener to accelerate the reaction between them. They are injected in small nonstihiometric quantities, which are selected empirically, guided by the properties of the material obtained. Some of the tertiary amines - curing catalysts - can also be accelerators for a number of systems. The most commonly used to increase the curing rates of epoxy resins of acid anhydrides. Oktanate tin is used for this purpose, which is Lewis acid. In some cases, it allows you to cure at room temperature.
Cerencing epoxy resins can be made some generalizations relating to the link between the chemical structure and properties of cured epoxy resins:
The greater the aromatic rings is part of the epoxy resin, the higher its thermal stability and chemical resistance;
When using hardeners of the aromatic series, more rigid and durable materials are formed than in the case of aliphatic agents, however, the increased rigidity of such systems reduces molecular mobility and thus makes the interaction between reaction groups, and curing in this case is carried out at elevated temperatures;
Reducing the density of intermolecular "stitching" can lead to an increase in the strength of the material, due to the increase in the discontinuous elongation;
Reducing the density of "stitching" can also lead to a decrease in the shrinkage of the resin during curing;
An increase in the density of "stitching" leads to an increase in the chemical resistance of the cured material;
The increase in the density of "stitching" leads to an increase in the temperature of thermal destruction (and the temperature of the TC), but too high the density of "crosslocks"
reduces deformation of destruction (increased fragility);
When the aromatic fragments are replaced by aliphatic or cycloaliphatic molecules, not accompanied by a change in the number of "crosslocks" in the system, elasticity and elongation of the cured resin increase;
Characteristics of epoxy resins cured acid anhydrides, better when operating in an acidic environment than in alkaline.
Due to the fact that epoxy resins are viscoelastic materials, their properties depend on both temperature and test duration (speed, frequency).
Properties of epoxy resins cured by special ways.
When using specifically curable epoxy systems, some restrictions must be taken into account. For example, in the case of the manufacture of large parts, uncomfortable for warming up, and thick-walled parts, where thermal stresses must be minimal, inappropriate use of systems requiring high-temperature curing. In these cases, systems with low-temperature hardeners are used. Such compositions include epoxy resins, curable under the action of aliphatic amines. The curing of such compositions at room temperature leads to the preparation of materials with excellent properties, even more improving with weak heating. Of course, these resins cannot be used at high temperatures.
Epoxy oligomers and polymers are used in various fields of technology due to the successful combination of simple processing technology with high physical and mechanical indicators, heat resistance, adhesion to various materials, durability to various media, and the ability to cure at atmospheric pressure with a small shrinkage. So, they are widely used in the production of high-strength structural materials, in rocket and space technology, aviation, shipbuilding, mechanical engineering, electrical engineering, electronics, instrument making.
Epoxy oligomers and polymers are widely used as matrices to produce carbon firing characterized by a combination of high strength and stiffness with low density, low temperature coefficient of friction, high heat conduction, wear resistance, thermal resistance and radiation impacts. Cocated and pyro-carbon epoxy ports are resistant to thermal and thermo-acid destruction, have high strength characteristics, have good thermal protection properties.
Epoxy polymers are good matrices for creating fiberglass. In addition to fiberglass and glass fiberglass, quartz fibers and fabrics, borcelock fibers, carbidremium, etc. are used. Inorganic fibers.
In addition to inorganic fibers to obtain reinforced epoxy plastics, fibers from organic polymers are used, in particular, high-strength synthetic fibers made of poly-and-phenylene terephthamide and other arams.
Due to good adhesion to glass, ceramics, wood, plastics, metals, epoxy oligomers and polymers are widely used in the production of adhesives, hot and cold curing compounds.
Epoxy oligomers are used to seal and encapsulating various parts in order to protect against environmental action.
In electrical engineering, epoxy oligomers are used to fill the windings of transformers and engines, to seal the joints of the electrical cables, etc.
Topic 6. Heat-resistant resin
Heat-resistant resins are linear or stitched heteroaromatic polymers having a high glass transition temperature and capable to withstand long-term heating over 300 ° C without noticeable structure changes.Despite the process of heat-oxidative destruction, which inevitably proceeds under these conditions, the decomposition of such polymers is relatively slow. In addition, it is assumed that fragments for which these polymers disintegrate are relatively stable, which increases the "lifetime" material at elevated temperatures.
The key point in obtaining heat-resistant resins is the synthesis of polymers containing a large number of heteroaromatic fragments. These fragments containing the minimum number of hydrogen atoms capable of oxidizing can absorb heat energy. Unfortunately, the same elements of the chemical structure that determine the thermal-acid stability of such resins leads to serious difficulties, and often even to the impossibility of their processing into the necessary products.
In the 1960s, a number of heteroaromatic polymers were synthesized, which, according to thermogravimetric analysis (TGA), had good thermo-oxidative stability at elevated temperatures. However, attempts to use these polymers as binders for composite materials with improved properties were either unsuccessful or economically disadvantageous.
Therefore, in the early 1970s, the future of heat-resistant polymer binders looked very foggy and uncertain. It seemed that this useful class of materials would remain "laboratory curiosity". However, the development of the chemistry of polyimide polymers in 1972-74. Not only revived interest in them and caused new developments in the field of heat-resistant binders, but also made it possible to practically implement many of the potential capabilities of these binders. Currently, polyimide fibrous composite materials are used as structural materials operating at a temperature of about 300 ° C, depending on the chemical structure of organic radicals, which are part of imiderate groups, oligoimides are divided into aromatic, aliphatic and alicyclic, and on the form of chains - on linear or three-dimensional (spatial).
The main disadvantage of composite materials based on high molecular weight polyimides is a high porosity, which dramatically limits the possibility of effective practical use of these materials under conditions of simultaneous exposure to high mechanical loads, high temperatures and oxidative atmosphere.
Therefore, it is more appropriate to use the use of initial flexural oligomeric imides that can be cured by polymerization reaction, since the polymerization is not accompanied by the release of by-volatile products leading to the high porosity of the materials obtained. Polymerization-free oligomericimide and endomethylene-tetrahydrofthalimide groups are of the greatest importance to the ease of chains.
The listed requirements largely satisfy the bismarinimilas obtained by the interaction of diamines of various structures and the maleic acid anhydride. Double bid in bis-maleinimides is an electron deficient due to the neighborhood with carbonyl groups of the immediate cycle, so bis-maleinimides are easily polymerized when the melting point is heated above, forming a three-dimensional polymer.
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"The phenomenological model of a composite material based on the thermoplastic matrix and short coal fibers of Mashtakkov A.P., Melikhov K.V., Manjak ..."
Phenomenological model of composite material based on thermoplastic matrix and short coal fibers
Malikhov A.P., Melikhov K.V., Manyak I.S.
JSC NPP "Radar MMS",
st. Petersburg, Russia
The mechanical characteristics of a composite material consisting of a thermoplastic matrix reinforced with short coal fibers are experimentally investigated. The characteristics are obtained on samples that were cut from plates obtained by injection casting from a series of experiments on uniaxial stretching. The process of injection casting plate was modeled by the method of finite volumes. At the same time, a system of equations of motion of the polymer melt was solved as a viscous Newtonian fluid, supplemented by a folgera-taper equation for determining fiber orientation tensors in the matrix. To construct an analytical model of the material, a two-stage homogenization scheme was used: first, according to the Mori-Tanaka scheme, the effective characteristics were determined for the unit inclusion of a given form, then on the basis of the calculated component of the orientation tensor, the effective characteristics of the entire cell of the representative volume according to the Foyt scheme were determined. The fibers were taken with elastic isotropic, the matrix - elastic-plastic with the criterion of Mises and isotropic, power of hardening (J2-model). As a model of destruction, a model of the destruction of the "first pseudo-grain" was chosen with the criterion of the strength of Tsay-Hill. The characteristics of the matrix and fibers, as well as the parameters of the destruction criterion, were selected iteratively based on the condition of the best coincidence of the calculated and experimental deformation curves for the three types of samples using the least squares method. The results presented in the form of a comparison of deformation curves indicate a satisfactory coincidence with the experiment both in elastic and in an inelastic region. Literature
S. T. Chung and T. H. WON. Numerical Simulation of Fiber Orientation in Injection Molding of Short-Fiber-Reinforced Thermoplastics. Engineering and Science, Mid-April 1995, Vol. 35, no. 7. - p. 604-618.
B. E. Verweyst, C. L. Tucker III, P. H. Foss_, J. F. O'Gara. Fiber Orientation in 3-D INJECTION Molded Features: Prediction and Experiment / International Polymer Processing, June 18, 1999.
Mori T, Tanaka K. Average Stress In Matrix and Average Elastic Energy of Materials with Misfitting Inclusions. Acta Metall 1973; 21: 571-574.
R. Christensen. Introduction to the mechanics of composites / R. Christensen. - M.: Mir, 1982. - 334 p.
S. Kammoun, I. Doghri, L. Adam, G. Robert, L. Delannay. First Pseudo-Grain Failure Model for Inelastic Composites with Misaligned Short Fibers. COMPOSITES: Part A 42 (2011) 1892-1902.
J. M. Kaiser, M. Stommel. Strength Prediction of Short Fiber Reinforced Polymers. Journal of Plastics Technology 8 (2012) 3, 278-300.
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- Chapter 1. Unidirectional fibrous composite materials
- Analysis of the mechanical properties and models of deformation
- 1. 1. Used fibrous composite materials and their properties
- 1. 2.
Nonlinear deformation of composite materials
- 1. 2. 1. Fiber composite materials deformation diagrams
- 1. 2. 2. Description of the nonlinear diagram of deformation of layered composites
- 2. 1. Violation of the monolithic of polymer composite materials
- 2. 2. Micromechanical model of a unidirectional layer
- 3. 1. Nonlinear deformation of isotropic materials
- 3. 2. Model of nonlinear behavior of unidirectional fibrous composite material
- 3. 3.
Composite materials on thermosetting and thermoplastic binding
- 3. 3. 1. Composites on the thermosetting matrix
- 3. 3. 2. Composites on the thermoplastic matrix
- 3. 4.
Obtaining a two-charted fibrous composite material
- 3. 4. 1. Theoretical aspects of obtaining two-person composite material
- 3. 4. 2. Obtaining and properties of composite fiber
- 3. 4. 3. Dual-sized composite material. Giving technology
- 3. 5.
Results of tests of samples of two-dimensional composite material
- 3. 5. 1. Stretching of the material along the direction of reinforcement
- 3. 5. 2. Loading material in the transversal direction
- 3. 5. 3. Shear deformation of the material
- 4. 1.
Calculation of layered plates from two-chart composite material
- 4. 1. 1. Stress-deformed state of a layered composite plate
- 4. 1. 2. Stretching symmetrically reinforced panel
- 4. 2.
Cylindrical shell of two-month composite material
- 4. 2. 1. Sample structure. Test Methods
- 4. 2. 2. Test results
- 4. 2. 3. Description of the mechanical behavior of the cylindrical shell
Nonlinear deformation of dual-free composite structures (abstract, term, diploma, control)
Studies and development of materials continue continuously, which leads to the emergence of all new and new materials and to constant progress in the material science. Currently, there are a large number of diverse materials on the manufacture of structures, machines, instruments. Among them are most intensively developed by the materials that called composite, or composites.
Currently, the requirements imposed on the properties of materials became extremely diverse due to the fact that the conditions of operation of materials have become more rigid and complex. As an example, you can specify the following properties that may be required from the material: strength, rigidity, corrosion resistance, wear resistance, low weight, durability, heat resistance, thermal conductivity, soundproofiness, etc. It is quite natural that using traditional materials is very difficult to satisfy sufficiently specified above requirements. That is why there were ideas for using appropriate combinations of materials, which allow to obtain the specified properties.
Composite materials are materials formed by a combination of two or more phases (discrete phase - reinforcing fibers, particles, and continuous phase - matrix) with a clear boundary of the partition between them, and characterized by a complex of properties that each components are separately posted. The widespread use of composites in the aerospace, shipbuilding, oil and gas, agricultural, energy, automotive and other industries is due to the possibility of creating materials with advanced properties, in particular with the strength and rigidity regulated in the wide range. The use of glass, carbon, boric, organic and other high-strength fibers as reinforcing elements and polymeric binders in the role of matrices allows you to create structures with significantly higher strength and rigidity compared to metal counterparts. At the same time, it is possible to obtain a noticeable gain of mass and dimensions and increase the reliability of structures not only due to the corresponding specific characteristics of the material, but also by eliminating a number of intermediate stages of processing characteristic of traditional materials.
It should be noted that, being substantially anisotropic materials, unidirectional fibrous composites on the polymer matrix are clearly insufficient deformability in the transverse direction. Thus, the limit deformations in tension along and across the fibers, respectively, for fiberglass are 3% and 0.25%, for carbon firms 1.5% and 0.5%), for organoplastics 2% and 0.6%, for boroplastics 0.7 % and 0.35%, that is, the ratio "Limit deformation along the fibers / limit deformation across the fibers" ranges in the range 2. 12. As a result of this, in the package formed by a set of unidirectional layers, cracking and destruction of the matrix occurs noticeably earlier than the fibers achieved of its strength This phenomenon is called monolithism.
It is quite obvious that the noted lack is not always significant. In disposable products with short-term operating modes (for example, in RDTT structures), the monolith violation is considered to be permissible and design under the condition of strength of the fiber allows to obtain an extremely high degree of weight perfection.
On the other hand, when a monolithic impaired, the design loses hermeticity, there is a rapid increase in the accumulation of damage, the cyclic strength of the material is reduced, the shape and the size of the product is lost, which is in responsible long and multiple-exploited structures (for example, pressure batteries) is invalid. Designing on a safe loading level (limit of the strength of the matrix) leads to short-use fiber strength, that is, to incomplete implementation of the main characteristics of composites.
One of the most successful variants of solving this problem (increase in transverse deformability, provided that the longitudinal strength is preserved) is a model of a two-person composite material. The longitudinal strength of the material is provided by using composite fibers formed by a combination of elementary fibers (threads) and a rigid matrix, and transverse deformability - due to the elastic matrix that binds composite fibers.
This dissertation is devoted to research aimed at the development of this concept in relation to thermoplastic materials, since thermoplastic polymers have a number of benefits over thermosetting of both operational and technological nature. At the same time, the requirement of high transverse deformativity of the composite forces the material with its own deformability of at least 70% as an elastic matrix. This, in turn, is the cause of the material manifestation of a substantially nonlinear deformation mechanism, which entails the need to develop a new, capable of considering strong nonlinearity, model of describing the deformation of the material.
Thus, the scientific and practical significance of the work is determined by:
Proposed by the phenomenological model of nonlinear deformation of the composite
Developed by the modification of the two-chart composite
Experimental study of the mechanical characteristics of the source components and materials with different structure of the package
The results of the calculation of elements of structures from a two-chart composite and an assessment of its effectiveness.
The first chapter is devoted to the analysis of existing composite materials on the polymer matrix, their strength and deformation properties, as well as the existing models of the mathematical description of nonlinear behavior of composites.
The second chapter discusses the problem of violation of the monolithic KM and the way to overcome it. In particular, on the basis of the analysis of the two most obvious ways to maintain the integrity of the matrix, up to the destruction of the fibers of the fibers of the rigidity of the reinforcing elements and reducing the rigidity of the matrix, it is confirmed by the expediency of separating the rigid functions of the binder between the two matrices, that is, the main idea of \u200b\u200ba two-person composite material.
The third chapter considers the mathematical model of nonlinear behavior of the composite, the results of which are compared with experimental data on loading samples oriented at angles of 0 ° and 90 ° to the direction of loading and during the shift. There is also a technology for obtaining and theoretical substantiation of the proposed modification of a two-person km with a combination of two types of polymers: a rigid thermosactive and elastic thermoplastic.
The fourth chapter is devoted to the calculation of elements of structures based on the proposed mathematical model from a two-person composite material. Here are considered panels oriented under the angles of & plusmn-φ to the direction of loading, as well as the axisymmetric deformation of the cylindrical shell loaded with the internal pressure. The calculation results are compared with the experiment.
In conclusion, the main results and conclusions are formulated.
The main results of work are reported on:
XVIII European International Conference Sampe, Paris, 1997 (18th Sampe Europe / Jec International Conference and Exhibition "97) - 8
All-Russian Scientific and Technical Conference "New Materials and Technologies NMT-98", Moscow, 1998-
XXV International Youth Scientific Conference "Gagarin readings", Moscow, 1999- and published in:
Patent No. 2 097 197 (Sh) -
Patent No. 2 107 622 (BSH) -
Salov O. V. Development and creation of two-person fibrous km. "XXII Gagarin readings": Tez. Dokl. Youth Scientific Conference, April 1996- MGATU. M., 1996, Part 3, p. 10
Salov O. V. To the question of the nonlinear behavior of layered structures. "XXIV Gagarin's readings." Tez. Dokl. All-Russian youth scientific conference. April 1998- MGATU, M.: 1998, Part 6, p. 73.
Salov O. V. Dual-sized fibrous composite material on thermosetting and thermoplastic matrices. // in Sat. "Scientific works Mati them. K. Tsiolkovsky. " Vol. 2 (74) .- M.: LATMES Publishing House, 1999, p. 59-63
Salov O. V. Stretching a unidirectional layer with a finite number of fibers. "XXV Gagarin's readings." Abstracts of the reports of the international youth scientific conference Moscow, April 6-10, 1999. - M.: Publishing House "LATMES", 1999. Volume 2, p. 708.
In conclusion, we formulate the main results and conclusions.
1. The exact solution of the micromechanics problem of composites for a unidirectional monolayer, reinforced by an arbitrary finite number of fibers, and describes the fiber destruction process. The influence of the mechanical properties of fibers and matrix on the strength of the composite in terms of turning on the fiber to work is investigated. It was confirmed that the simultaneous increase in the rigidity of the reinforcing fibers on one side and the decrease in the rigidity of the matrix with the other as the combination of the two possible ways to solve the problem of the monolithization of the composite reduces the main characteristics of the material. It is concluded about the expediency of a two-person composite.
2. A applied phenomenological model of nonlinear deformation of composites is proposed, which allows to describe the behavior of composites and confirmed by the published experimental results in tension and compression.
3. A two-dimensional thermosetting thermoplastic composite is proposed and implemented, in which the joint operation of the fibers is provided by thermosetting binding connecting the elementary fibers and forming composite fibers, and transversal composite is ensured by a thermoplastic matrix connecting composite fibers. An experimental study of the mechanical properties of a two-chart composite based on glass and carbon fibers was carried out and it was established that the behavior of the material is characterized by significant non-linearity with transverse tension, compression and shift.
4. Theoretical and experimental study of the plates with various reinforcement and cylindrical shell schemes are carried out. It has been established that the proposed deformation model satisfactorily describes the behavior of these structural elements.
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Thesis
Publications. Total on the thesis published 8 scientific papers, including: 3 articles in leading peer-reviewed scientific journals and publications recommended by the WAK RF- 5 articles in the materials of All-Russian conferences. Structure and scope of work. The thesis consists of introduction, five chapters, conclusion, a list of sources used from 137 names. Volume of dissertation 126 pages, including 28 ...
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