Dielectric investigation of the molecular mobility of silicone ladder polymers

Dielectric spectroscopy has been used to study the molecular mobility in polyphenylsilsesquioxane, polyphenylisobutylsilsesquioxane with a 1:1 ratio of phenyl to isobutyl groups, and poly-m-chlorophenylsilsequioxane on the temperature interval from –196 to 300°C at frequencies from 10² to 10⁶ Hz. The investigation was carried out in air and in a nitrogen atmosphere. The flexibility mechanism of silicone ladder polymers is considered and the development of molecular mobility is shown to be discrete.Institute of Heteroorganic Compounds, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 3–7, January–February, 1976.     

Effect of uv irradiation on the mobility of the molecular chains in polyethylene

Conclusions 1. A decrease in the mobility of molecular chains in polyethylene after UV irradiation was discovered by the spin probe method. This decrease is proportional to the time of irradiation.2. A discontinuity lacking in unirradiated polyethylene was found on the curve for the logarithm of the rotational correlation time of the spin probe in polyethylene as a function of the inverse temperature. It was shown that the nature of the discontinuity is related to a "thawing out" of the rotational motion of the chains in the crystalline phase.Institute of the Mechanics of Metal-Polymer Systems, Academy of Sciences of the Belorussian SSR, Gomel. Translated from Mekhanika Polimerov, No. 4, pp. 603–608, July–August, 1976.     

Impregnation of fibrous fillers with polymeric binders 6. Effect of parameters of ultrasound treatment on strength properties of wound fibrous composites

Conclusion Tests of annular PCM specimens — fiberglasses and organoplastics formed by the method of wet winding using low-frequency ultrasound — were conducted. Three alternate US-impregnation schemes were investigated. Optimal alternate schemes and insonification parameters were established experimentally: frequency, amplitude, intensity, and time. Optimization was carried out on the basis of investigation of the relationships between the values of the tensile, compressive, bending, and interlayer-shear strengths, and also the relative content of filler as a function of treatment parameters. It was shown that deviation of insonification parameters from the optimal leads to a reduction in strength characteristics, as well as to a different character of specimen failure in tension and interlayer shear.The effect of US modification in producing PCM is provided by an increase in structural uniformity, and improvement of the strength and production characteristics of the polymer matrix, as well as by a reduction in the composite's effectiveness as a result of a reduction in the content of air inclusions and improvement of the binder's distribution across the section of the filler.For previous communication, see [9].Translated from Mekhanika Kompozitnykh Materialov, No. 4, pp. 724–731, July–August, 1989.     

Effect of chemical nature of matrix on the strength of bonds with Armos aramide fibers

This investigation deals with adhesion between high-strength and high-modulus Armos aramide fibers (polyheteroarylene-co-p-phenyleneterephthalamide) and a series of different thermosetting matrices. The effect of the chemical nature of the matrix, time-temperature conditions of bond formation, and test temperature on the strength of the fiber-matrix interface was studied. Modified epoxy and heat-resistant matrices were used as adhesives. As a measure of adhesion, the shear adhesive strength ₀ determined by the fiber pull-out technique was used. It was found that both the adhesive strength and the fracture location in adhesive bonds depended on the nature of the matrix. At room temperature, chlorine-containing epoxy matrices provide the highest values of ₀, while the smallest strength of the interface is observed for bonds with heat-resistant (bismaleimide, oligomethacrylate) matrices. Fracture of adhesive bonds does not always occur at the fiber-matrix interface. A number of the specimens failed near the interface of the fiber. With temperature increase, the values of ₀ decrease. The adhesive strength falls especially drastically in the region of matrix softening. An advantage of heat-resistant matrices is that they retain 60–67% of ₀ value even at 250°C. The strength of unidirectional composites based on the investigated fibers and matrices was also estimated under different loading conditions such as tension, shear, compression, and bending. It was found that the strength in shear and compression did not correlate with the interface strength. The values of _c in bending and tension increased linearly with increase of ₀. The obtained dependences _c–₀ were compared with those of composites based on the SVM polyheteroarylene fibers determined by us earlier.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 3, pp. 391–406, May–June, 1998.     

Effect of chemical crosslinks on stress relaxation in polyamide fibers

The crosslinks in polyamide fibers can be determined from the stress relaxation in a medium causing swelling of the test specimen.Mekhanika Polimerov, Vol. 4, No. 1, pp. 53–58, 1968     

Determination of the modulus of elasticity of the amorphous regions of chemical fibers

A method of calculating the orientation index and modulus of elasticity of the elements of a two-phase fiber model is presented. The effect of orientational drawing on the variation of these characteristics has been investigated for nylon [capron] fibers.Mekhanika Polimerov, Vol. 3, No. 3, pp. 409–412, 1967     

Application of the finite-element method to the diffusion and reaction of chemical species in multilayered polymeric bodies

Application of the finite-element method (FEM) to chemical species diffusion and reaction in polymers by Fickian mass transport is described. The method is developed by analogy to heat conduction and is extended to include multiple, reactive chemical species dissolved in multilayered polymeric materials. Because of the analogy to conductive heat transfer, existing FEM thermal codes can be readily adapted to solve chemical diffusion problems. The method described is limited to Fickian diffusion at a constant material temperature.     

Electron-microscope study of cellulose and Capron fibers with different strenghts

Oriented polymer fibers whose strengths differ by a factor of two have been subjected to an electron-microscope study. Both cellulose (=40 and 75 kgf/mm²) and Capron (=80 and 170 kgf/mm²) fiber were investigated. Specimens were obtained by ultrasonic dispersion followed by negative contrasting of the dispersion products with FVK solution. It is shown that there is no correlation between the transverse dimensions of the microfibrils and the strength of the investigated fibers.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 364–366, March–April, 1971.     

Families of curves over P1 with 3 singular fibers

Suppose $f:S\to {\mathbb{P}}^1$ is a fibration of genus g with 3 singular fibers and two of them are semistable. We show that the Mordell–Weil group of f is finite, the surface S is rational and $2g??K_S^2?4g?4$. We construct some examples to show that such fibrations exist for infinitely many g.