Effect of a dispersed filler on the modulus of elasticity of composites in the glassy state

An expression is proposed for predicting the reinforcement of composites by a dispersed filler in both the rubbery and glassy states with allowance for the internal thermal stresses in the polymer matrix. It is shown that by varying the plasticizer concentration in composites based on polyvinyl chloride it is possible to regulate the thermal stresses in the polymer matrix. The time-stress and time-concentration superposition principles are shown to be applicable to the dependence of the relative modulus of elasticity on filler concentration for glassy composites.     

Application of the reduced concentration principle to filled polymers

The filler-concentration dependence of the modulus of elasticity of composites based on polyester resin filled with various kinds of dispersed fillers has been investigated. The applicability of the reduced concentration principle to this class of materials is demonstrated. The question of the existence of a universal dependence of the modulus of elasticity of composites on the filler content, invariant with respect to the nature of the polymer and the filler, is examined.     

Effect of fillers on the viscosity and viscoelasticity of low-density polyethylene melts. Communication 1

An investigation of low-density polyethylenes filled with up to 30% by volume dispersed particles, has shown that for both the matrix and the composites the apparent viscous flow activation energy does not depend on the shear stresses and increases starting from a certain filler concentration at which the conformation range in the matrix is depleted. The dependence of the relative viscosity of the compositions on the volume filler content is satisfactorily described by an equation that contains the reduced filler concentration, defined as the ratio of the nominal filler concentration to the limiting concentration at which the adsorption layers on the particles extend throughout the matrix. The thickness of the polymer layer adsorbed on the particles must be determined from the specific exterior particle surface, with allowance for the volume of the polymer in the sorption space of the porous filler.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 478–486, May–June, 1976.     

Effect of filler on relaxation-time spectra of filled polymers

The frequency and temperature dependence of the complex shear modulus G* and tan δ of epoxide compositions with various fillers have been studied. Relaxation-time spectra of filled polymers with various fillers have been plotted by the Ninomi-Ferry method. The principles governing changes in the shape of the spectrum curves with increase in filler concentration have been observed, enabling conclusions to be drawn on the effect of the filler on the change in properties of a polymer matrix and the deformation conditions of the polymer layers between the filler particles.     

Thermal dependence of electric conductivity in thermoplastic composites

Thermal dependence of the electric conductivity of thermoplastic composites based on both amorphous (hiPS) and crystallized (PP) polymers is investigated in this study. Two types of carbon black fillers with different values of BET surface area were used as charge conductors. Composites based on crystallized polymer matrices indicate the sharp growth of electric resistivity just before the melting range. This maximum is followed by substantial decrease of resistance at T > T_melt. With the decrease of carbon black concentration both relative growth of resistance at the T T_melt and further dropping resistance at T > T_melt increase. Composites filled with particles of higher surface area are characterized by less pronounced matrix influence on thermal dependence of electric conductivity than composites filled with particles of lower surface area; this can be caused by more pronounced matrix/filler interaction in the first case. The range of temperatures at which the resistance increase occurs does not depend on the type of carbon filler and its concentration. Composites with amorphous matrices are characterized by distinct increase of resistance above glass transition. Thermal treatment of the sample significantly affects the initial values and intensity of the temperature dependence of the resistance.To be presented at the Ninth International Conference on the Mechanics of Composite Materials, Riga, October, 1995.Published in Mekhanika Kompozitnykh Materialov, Vol. 31, No. 4, pp. 526–532, July–August, 1995.     

Influence of the concentration of carbon nanotubes (CNT) on the thermophysical properties of epoxy/CNT nanocomposites at low temperatures

The influence of the content of carbon nanofillers (multi-and single-wall nanotubes) on the thermophysical properties of epoxy nanocomposites was investigated on the temperature range from −150 to 150°C. A “plateau” was found to exist in the concentration dependence of thermal conductivity on the concentration interval from 0.1 to 1.0 wt.% carbon nanotubes (CNTs). The thermal conductivity of the CNT composites exceeded that of pure epoxy resin by about 40%. A further increase in CNT content de creased the conductivity, owing to increasing interfaces between the two phases and the additional thermal resistance caused by phonon scattering on them. It is found that the temperature interval of transition of the composite from a glassy to a viscoelastic state greatly depends on the filler type and concentration. There exists a critical concentration at which a drop in the glass-transition temperature by 30% can be observed. The reason is the undercure of binder as a result of interaction between CNTs and epoxy macromolecules, which reduces the cross-linking density of structure of the polymer. Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 5, pp. 697–708, September–October, 2008.     

Temperature dependence of the strength of adhesive joints based on crystalline polymer adhesives

The temperature dependence of the stripping strength of adhesive joints between steel and dural plates using crystalline polymers as adhesive (mixed polyamide-4, 5, 8 and guttapercha, both unfilled and filled with an inert filler) has been investigated. The temperature-strength curves pass through two local maxima, near the glass transition temperature of the crystalline adhesive and near its melting point. It is shown that the presence of a high-temperature maximum is determined by recrystallization of the polymer in the overstressed zone at the tip of the developing crack. The relationship between temperature and strength in adhesive joints based on crystalline polymer adhesives is very pronounced in both cohesive and adhesive failure. It is shown that the addition of filler reduces the recrystallization stress of guttapercha.Mekhanika Polimerov, Vol. 1, No. 3, pp. 63–67, 1965     

Effect of a filler on the strength properties of thermosets

The effect of a filler on the strength properties of polymers in tension is investigated. The thermostructural stresses that develop in the composite during cure are taken into account. Relations are given for the strength of the filled polymer as a function of the percentage filler content. In the process of analyzing the thermostructural stresses an analytic expression is obtained for the linear expansion coefficient of the composite with allowance for the structural distribution of the components. Calculated values of the strength and thermostructural stresses are presented for composites with different filler contents. The theoretical determination of the strength of filled polymers is compared with the results of experimental investigations of composites based on epoxy resin filled with quartz dust.Leningrad Mechanical Institute. Translated from Mekhanika Polimerov, No. 1, pp. 97–101, January–February, 1973.     

Effect of the structure of a polymer matrix and its area of contact with the surface of the filler on the rigidity of a polyethylene composite

The distribution of the orientation of the macromolecules over the wall cross section of a filled polyethylene tube is analyzed. A direct proportionality is established between the degree of orientation (estimated from the shrinkage) and the elastic modulus. The effect of various fillers on the melting and crystallization of low-density polyethylene is considered. For a specified filler concentration the elastic modulus of the composites depends very considerably on the relative area of contact between the polymer matrix and the surface of the filler.Institute of the Mechanics of Polymers, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 387–391, May–June, 1974.     

Effect of quartz sand filler on the mechanical and thermophysical properties of alkyd and epoxy coatings

The effect of a filler on the mechanical and thermophysical properties of polymer coatings has been investigated. It is shown that quartz sand particles are centers of structure formation in alkyd and epoxy coatings. It has been found that a denser, oriented, and stressed polymer structure, much exceeding the size of the individual macromolecules, is formed around the filler particles. The size of the spheres around the filler particles depends on the nature of the film-former, on the filler surface, and on the filler content. It is postulated that secondary supermolecular structures, and not individual polymer macromolecules, are adsorbed on the surface of the filler particles.Mekhanika Polimerov, Vol. 3, No. 3, pp. 507–510, 1967     

Effect of aging creep of polyestermalein resin/mineral filler composites

Long-term (More than 20 years) creep under compression of two polymer concretes, polyestermalein resin/mineral filler composites, was studied. The concretes differ with diabase filler size (d=5–10 mm and d=10–20 mm). It was shown that nonlinearity of viscoelastic properties of concrete increases as the size of filler particle decreases. Aging of the polymer concretes reduces their viscoelastic compliance and shortens the time interval necessary to reach equilibrium conditions under stable loading state.Presented at the Ninth International Conference on the Mechanics of Composite Materials, Riga, October, 1995.Institute of Theoretical and Applied Mechanics of the AS CR, Prague 9, Prosecká 74, Czech Republic. Central Laboratory of Physical-Chemical Mechanics of the BAS, Sofia 1113 Acad. Bontchev Street, IV km, Bl. 1. Published in Mekhanika Kompozitnykh Materialov, Vol. 32, No. 2, pp. 190–194, March–April, 1995.     

Effect of the composition and concentration of fibrous wastes from linen yarn production on the physicomechanical properties of polyolefin composites

An analysis is made of the feasibility of using wastes from the production of linen yarm (scutch, spinning and carding refuse) to modify low-density polyethylene. The effect of the composition and concentration of wastes on the processing properties (melt index), physicomechanical indices (tensile strength, elastic modulus in bending), and water resistance of composites based on low-density polyethylene is studied. It is found that the melt index decreases with an increase in the content of filler and that even a composite with a high filler content (40–50% by weight) maintains values of 0.2–0.3 g/10 min. The elastic modulus in bending increases with an increase in the content of waste, regardless of the nature of the latter. Tensile strength increases slightly and depends on the choice of filler. This result, combined with the reducation in the scatter of values of elastic modulus with an increase in filler concentration, is an indicator of the relatively high degree of heterogeneity of the systems that were studied. The water resistance of the composites decreases with an increase in filleer content. To reduce the heterogeneity of the systems, mixing should be intensified and modifiers such as stearic acid and polyisocyanates should be added.Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 3, pp. 408–416, May–June, 1997.     

Interfacial strength of joints between fibers and dispersedly filled epoxy matrices

The concentration dependences of adhesive strength are investigated for fiber/dispersedly filled epoxy matrix systems. The measurements were carried out using an improved model of adhesiometer under normal conditions at a constant rate of loading. It is shown that the adhesive strength as a function of filler concentration has a maximum, which is more or less pronounced. The location of the maximum depends on the nature of filler and particle geometry. The increase in the adhesive strength at the maximum reaches 20–30% in comparison with that for the unfilled epoxy matrix. Since the interfacial strength between steel wire and all the mineral powders investigated is zero, the growth in the adhesive strength upon introduction of a finely divided filler in polymer binders is rather un expected. The possible reasons for the phenomenon observed are discussed. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 1, pp. 3–14, January–February, 2007.     

Anisotropy of elasticity of a composite with irregularly oriented anisometric filler particles

The effects of orientation and shape of filler particles on the elastic properties of composites have been analyzed. The elastic constants of a composite with irregularly oriented filler particles were calculated by using the method of orientational averaging of the properties of a representative structural element. The elastic constants of the structural element were found according to a known generalized Eshelby solution for a finite concentration of ellipsoidal inclusions. The diagrams of elasticity anisotropy for a transversely isotropic structural element and an orthotropic composite with irregularly oriented inclusions are presented. A quantitative estimate for the degree of anisotropy of elastic properties of composites is suggested. Data on the influence of shape anisometry of inclusions on the anisotropy coefficient of filled composites are also reported.     

Fractial parameterization of the structure of filled polymers

It is suggested to consider the structure of a filled polymer as a set of two or more multifractals. It is shown experimentally that the basic factor determining the fractal dimension of distribution of a disperse filler in the polymer is the size distribution of filler particles.Moscow State Open University, Moscow, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 3, pp 269–290, 1999.     

Dynamic mechanical spectroscopy of polyethylenes with aggregating disperse and hybrid granular-fibrous fillers

Conclusion Based on the results of dynamic experimental studies, it was shown that addition of mineral fillers to polyethylenes does not result in a significant change in the relaxation properties of the polymer matrix of CM. It was found that aggregation of the particles of the granular filler causes a significant increase in the real part of the modulus and a decrease in the mechanical loss tangent of the CM. The possibility of using a modified elastic solution for predicting the effective characteristics of the dynamic viscoelasticity of composites was demonstrated.Translated from Mekhanika Kompozitnykh Materialov, No. 4. pp. 579–586, July–August, 1989.     

Structure and Properties of Teflon Composites with Natural Diamond Powders

The results of experimental investigations of the structure and properties of composites based on polytetrafluorethylene (PTFE) containing natural diamond powders (NDP) of different dispersity are presented. To obtain diamond-containing compositions for antifrictional applications, we used a preliminary mechanical treatment of NDP (40 m) in a planetary mill. It was stated that the formation of the maximum ordered small-spherulite structure of PTFE after injection of NDP significantly increased the wear resistance and deformational and strength characteristics of the polymer composite materials. To produce abrasive materials, PTFE was filled with NDP having a larger graininess (from 40 to 125 m). It was found that the injection of NDP did not cause evident morphological changes in the binder — the bonds between diamond grains and the polymer are created by physicomechanical forces. To strengthen the adhesion interaction at the interface between the binder and diamond grains and to raise the wear resistance of the material, a complex modification of the polymer with inorganic and organic fillers was carried out. It is shown that the injection of the complex filler significantly improves the tribotechnical and operational properties of the diamond-containing composite material. The general laws of the influence of NDP on the formation of the supermolecular structure of PTFE are revealed. It is shown that, by varying the degree of dispersity and the content of NDP in PTFE, and by applying different methods of their injection into the polymer matrix, it is possible to control the operational properties of the composites and to produce materials of different functional application, from antifrictional to abrasive ones.     

Effect of aggregation of a dispersed rigid filler on the elastic characteristics of a polymer composite

Conclusions We proposed a method for describing the effective elastic characteristics of a polymer composite with a rigid aggregating filler. An important feature of such a medium is the variable coupling of the inclusion phase in relation to its volume content. A change in the degree of coupling of the filler is accounted for by introducing an additional parameter. We examined a method of determining the coupling parameter from the results of statistical modeling of the geometry of the medium. Using the example of a calcite-HDPE composite, we showed that aggregation has a significant effect on the dependence of the elastic modulus on the volume content of filler; satisfactory agreement was obtained between the theoretical and experimental data.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 14–22, January–February, 1986.