A microcalorimetric study of crystallizable polymers subjected to severe plastic deformation

Differential scanning calorimetry has been used to investigate the evolution of the structural and thermophysical parameters of a number of semicrystalline polymers (high-density polyethylene, polyamide-6, polyoxymethylene) that is initiated by severe plastic deformation imposed through equal-channel multiple-angle extrusion. Thermograms of the deformed polymers have been found to exhibit an additional high-temperature melting peak. It has been shown that the onset, maximum, and end temperatures for both melting peaks increase with the strain buildup. The degrees of crystallinity and the thicknesses of crystallites increase as well. The magnitude of the effects is determined by the deformation route selected. It has been revealed that conformational transitions due to the formation of “double-triple” folds in macromolecular chains can occur during the course of equal-channel multiple-angle extrusion.     

Solid-state extrusion of polymerization-filled polymer compositions

The mechanical properties of ultra-high molecular polyethylene and filled compositions based on it produced by solid-state extrusion of powder semifabricates have been investigated. It is shown that high-level properties are obtained by extrudates with fillers possessing high disposition to adhesive interaction with the polymer matrix. A mathematical model of solid-state extrusion of the compositions is derived considering the possibility of compaction and loosening of the material in the process of deformation. Satisfactory agreement of the calculated and experimental data is obtained.Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 1, pp. 101–108, January–February, 1999.     

The Shape Memory Effect in Structurally Heterogeneous Polymer Systems

The kinematics of shape recovery for the mixtures of thermodynamically incompatible polymers and polymer composites filled with thermoexpanded graphite has been investigated. It is shown that in these systems the shape recovery is accompanied by an increase in volume. The latter is attained at the expense of formation of microdiscontinuities at the interfaces (the polymer mixtures) or of recovery of filler porosity.     

Influence of the molar ratio of tetraethoxysilane and glycidoxypropyltriethoxysilane on the properties of anhydride-cured epoxy-siloxane composites

The topological structure of epoxy-siloxane composites prepared by anhydride curing was studied in relation to the molar ratio of glycidoxypropyltriethoxysilane and tetraethoxysilane and to the total content of siloxane components of the system. The optical characteristics, glass transition point, sol fraction yield, concentration of internodal chains, and maximal rate of oxygen uptake by the hybrid materials were determined.     

Structural and morphological features of organic-inorganic hybrid materials based on ethoxysilanes and epoxy resin

The structure of epoxy-silica nanocomposites prepared by the sol-gel method via the cationic polymerization of the organic component and anhydride curing was studied by small-angle X-ray scattering. In the presence of 1.5% silica in the epoxy polymer, mass-fractal aggregates of the inorganic component are formed. In the range of low and high concentrations of SiO₂, microphase segregation with the separation of inclusions randomly distributed in the epoxy matrix occurs.