Effect of rubber on the environmental stress-crack resistance of polyethylene

The property of environmental stress cracking is a critical performance factor in the polyethylene product areas of rigid and flexible containers, wire and cable insulation and pipe or conduit. It has been known for quite some time that the addition of an elastomeric material to polyethylene can improve its resistance to environmental stress cracking. However, the information reported in the literature on the subject is rather limited and as far as can be determined no attempt has been made to determine the rubber variables affecting the environmental stress cracking performance of polyethylene. In studying the effect of rubber on the environmental stress crack resistance (ESCR) of low and high density polyethylene, the choice of base resin is important. With some resins the addition of rubber doubles the ESCR while with others a fiftyfold improvement can be effected. Of the elastomers investigated in this study, Enjay Butyl 007 a copolymer of isobutylene and isoprene gave the greatest stress‐crack improvement in both low and high density polyethylene. Evaluation of a series of polyisobutylenes indicate that the higher its molecular weight the more effective its performance as a stress crack additive. The effect of rubber on other properties of the polyethylenes such as melt index, stiffness, permeability, chemical resistance, brittle point temperature, and impact strength is also discussed.