Thermomechanical Properties of Radiation-Modified Polyethylene/Ethylene-Propylene-Diene Copolymer/Liquid-Crystalline Copolyester Blends
Radiation-modified blends of high-density polyethylene (PE) with ethylene-propylene-diene copolymer (EPDM; 10-65 wt.%) and thermotropic liquid-crystalline polymer (LCP; 10 wt.%) were investigated. The LCP was a liquid-crystalline copolyester of 40% poly(ethylene terephthalate) with 60% 4-hydroxybenzoic acid. The constituents were blended using a circular extruder, the specimens were prepared by compression molding and irradiated by 60 Co γ-radiation up to 200 kGy. Mechanical, thermal, and morphological properties in wide temperature range were investigated for the irradiated and non-irradiated specimens. The effects of irradiation on the thermomechanical behaviour of the PE matrix are discussed. The LCP addition significantly affected the stress-strain behaviour of PE at temperatures above its melting point resulting in some anomalies in kinetics of formation of thermorelaxation stresses, which arise if the material is previously oriented. Thermosetting properties (thermorelaxation stresses and residual setting stresses under conditions of isometric heating and cooling) of the PE/EPDM/LCP blends crosslinked by irradiation and then oriented were also established. The results obtained suggest that such ternary blends improve the application properties of irradiated polyethylene and obtain useful thermosetting materials.