Reinforcement of high density polyethylene with a side chain LCP by graft copolymerization—thermal, mechanical and morphological properties

Abstract

In this study, high density polyethylene (PE) has been reinforced with a side chain LCP by graft copolymerization of p-benzophenoneoxycarbonylphenyl acrylate (BPOCPA). The mechanical and thermal behavior of the graft coproducts were investigated in relation to the structural changes (in unit cell parameters) of PE matrix. The crystalline melting temperature of PE, varying consistently with the poly(BPOCPA) content in the coproducts, significantly increased (from 131 °C to 132–138 °C). The unit cell dimensions, a and b, of the orthorhombic structure, the ab basal area and particle size of PE crystals initially expanded, and then consistently contracted with the graft content. The c parameter, however, remained relatively unchanged. Remarkable improvements were achieved in the tensile properties of the material; with the maxima of 38 % increase in tensile strength and 67 % increase in Young’s modulus with the coproduct comprising 9.3 % poly(BPOCPA). These developments were found to be explained by the advances in the orientation and alignment of PE chains, conduced by greater chain mobility in the larger ab basal area and intensifying cohesive forces arising from the glassy nematic structured graft units. Furthermore, SEM analyses of the coproducts showed completely homogeneous structures without any phase separation. At low contents, the samples were mainly ductile, whereas at high contents, they displayed brittle nature that increased with poly(BPOCPA) percentage. Moreover, TG analyses demonstrated that both homo and grafted polymers commenced to degrade predominantly at about 275 °C. The decomposition of poly(BPOCPA) graft units was explicitly retarded by PE matrix in the coproducts.