STRUCTURAL-CHANGES IN ULTRA-HIGH-MOLECULA R-MASS POLYETHYLENE DURING SOLID-PHASE EXTRUSION

Structure and mechanical properties of the extruded samples of ultra-h igh-molecular-mass polyethylene were studied. The degree of crystallin ity of polymer samples was shown to increase linearly with an increase in the draw ratio. The degree of crystallinity, as estimated by densi ty measurements, was found to be higher than that estimated from X-ray studies. With increasing draw ratio, an increase in elastic modulus w as greater than that predicted by the linear dependence. Thermal shrin kage of the extruded samples was shown to be controlled by their draw ratio. Experimental evidence was examined in terms of the model for se micrystalline polymers, according to which a semicrystalline polymer i s composed of the crystalline, amorphous, and interfacial regions.