Phase Interconnectivity and Environmental Stress Cracking Resistance of Polyethylene: A Crystalline Phase Investigation

Studies of the effect of inter-lamellar linkages on environmental stress cracking resistance (ESCR) of polyethylene have traditionally focused on changes in the amorphous phase. Since polyethylene is a semi-crystalline polymer, the crystalline phase also plays an important role in the mechanical behavior of the polymer. In this work, percentage crystallinity and lamella thickness of several high density polyethylene (HDPE) resins were studied to determine their effect on ESCR. It was observed that when average molecular weights of resins were widely different, these crystalline phase indicators could not adequately reflect changes in interconnectivity between crystalline and amorphous phases of polyethylene, and therefore, could not be correlated to ESCR of the resins in a straightforward fashion. Since polyethylene lamellae are three-dimensional crystals, the study of the crystalline phase effect on ESCR was extended to investigating the lateral surface characteristics of the lamella. An increase in ESCR was observed with increases in lateral lamella area of resins. It was postulated that a larger lateral lamella area results in higher probability of formation of inter-lamellar linkages. This increase in phase interconnectivity directly results in increasing ESCR of resins.