UNUSUAL BEHAVIOR OF POLYETHYLENE IN ETHYLENE-PROPYLENE-DIENE MATRIX

Polyolefine blends of isotactic polypropylene (iPP), high density poly ethylene (HDPE) or low density polyethylene (LDPE) with ethylene-propy lene-diene rubber (EPDM) were studied. According to properties yielded by the blends, their plastomer components fall into two groups: iPP-p roducing better mechanical properties of the rubber, due to the better recrystallization process of the plastomer in the elastomer matrix; a nd polyethylenes-enhancing mechanical properties of EPDM to a limited extent, but in the case of LDPE somewhat better in terms of friction d ecrease. The tribological effect was not observed when HDPE was blende d with EPDM. It may be explained by considering composition of the sur face layer of the materials and the degree of surface crystallinity. B etter tribological performance is the result of low molecular weight e thylene 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.