Morphology and mechanical properties of low‐molecular ‐ weight polyethylene and ultrahigh‐molecular‐weight polyethylene films drawn up to 200‐fold

Abstract

AbstractUltrahigh‐molecular‐weight polyethylene (UHMWPE) and low‐molecular‐weight polyethylene (LMWPE) blend films were prepared by gelation/crystallization from solutions. UHMWPE with the viscosity‐average molecular weight (Mv) of 6×106 and three kinds of LMWPE with (Mv) <5×104 were used. The LMWPE/ UHMWPE compositions chosen were 1/1, 2/1, 4/1 and 9/1. The resulting blend gels with the 9/1 composition (10% UHMWPE content) became films by evaporating the solvents, although LMWPE homopolymer gels have no ability to form films. The films with the above compositions could be readily elongated up to 200‐fold in a hot oven. Such high elongation is assumed to be due to the existence of a suitable level of entanglements between UHMWPE and LMWPE chains. The orientational degree of LMWPE crystallites became poorer as the LMWPE content in the blend film increased, indicating a decrease in the number of entanglements. The storage modulus of the blend films at the same draw ratio decreased as the LMWPE content increased. The storage modulus of the 1/1 blend film with λ = 200 reached about 50 GPa at 20°C but the storage modulus decreased drastically with further increase in the LMWPE content: The value of the 9/1 blend film with λ = 200 was less than 10 GPa. This means that a suitable level of entanglements between LMWPE and UHMWPE chains plays an important role in transmitting the drawing force effectively and promoting the orientational degree of the c‐axis, owing to the crystal transformation from a folded to a fibrous type.