Unusual behaviour of polyethylene in ethylene-propylene-diene matrix

Abstract

Polyolefine blends of isotactic polypropylene (iPP), high density polyethylene (HDPE) or low density polyethylene (LDPE) with ethylene-propylene-diene rubber (EPDM) were studied. According to properties yielded by the blends, their plastomer components fall into two groups: iPP-producing better mechanical properties of the rubber, due to the better recrystallization process of the plastomer in the elastomer matrix; and polyethylenes-enhancing mechanical properties of EPDM to a limited extent, but in the case of LDPE somewhat better in terms of friction decrease. The tribological effect was not observed when HDPE was blended with EPDM. It may be explained by considering composition of the surface layer of the materials and the degree of surface crystallinity. Better tribological performance is the result of low molecular weight ethylene fraction, migrated towards the surface of the LDPE/EPDM system. It probably originates from LDPE. The segregated plastomer exhibits less regular supermolecular structure in comparison to the iPP or HDPE on the surface of their blends with EPDM. It may act as some kind of lubricant, lowering the coefficient of friction of the material.