Reversible and irreversible crystallization in high-density polyethylene at low temperature

Reversible and irreversible crystallization and melting of high-density polyethylene at low temperature has been re-evaluated and is discussed in terms of the concept of the specific reversibility of a crystal. The concept of the specific reversibility links reversible and irreversible melting of a specific crystal such that reversible melting occurs only at slightly lower temperature than irreversible melting. In this study evidence for irreversible crystallization at low temperature in high-density polyethylene is provided, non-avoidable by primary crystallization and extended annealing at high temperature. The simultaneously observed reversible crystallization and melting at low temperature can be attributed to lateral-crystal-surface activity in addition to the well-established reversible fold-surface melting, dominant at high temperature, and evidenced by small-angle X-ray data available in the literature.