Effect of the Polyolefin Fraction Structure on the Morphology and Properties of Polymer Compositions Based on Ultrahigh Molecular Weight Polyethylene

The influence of the polymer fraction structure on the physico-mechanical properties of bimodal reactor polymer compositions based on ultrahigh molecular weight polyethylene has been studied. The compositions included 30 wt % of the modifying polymer fractions. They represent linear high-density polyethylene with a molecular weight of 160, 110, and 48 kg/mol and branched ethylene/hexene-1 copolymers with the hexene-1 content of 6.3 and 8 mol % introduced into compositions directly in the synthesis. The thermal properties of materials have been studied by means of the DSC method. The presence of linear low molecular weight polyethylene fractions of highly crystallinity (62–83%) in compositions with ultrahigh molecular weight polyethylene of low crystallinity (52.5%) leads to a sharp increase in the content of the crystalline phase in the materials. Compositions with branched copolymer fractions have the lower degree of crystallinity (28.4 and 23%). A correlation was found between the content of the crystalline phase and the values of the elastic modulus of reactor compositions. For compositions including linear low molecular weight polyethylene, there is a sharp increase in this indicator up to 1100–1535 MPa relative to unmodified ultrahigh molecular weight polyethylene (733 MPa) with approach to the values characteristic of pure polyethylene (1230–1670 MPa). Branched copolymer fractions cause a decrease in the modulus of elasticity to 151–345 MPa. All the studied compositions demonstrate sufficiently high strength properties. The values of elongation at break exceed this characteristic of unmodified ultrahigh molecular weight polyethylene (550±36%) and vary in the range from 560±14 to 850±22%. The introduction of modifying polymer fractions led to the appearance of fluidity of compositions based on ultrahigh molecular weight polyethylene.