Theoretical Description of Unconstrained Thermally Induced Shape-Memory Recovery in Crosslinked Polyethylenes

摘要

A new theoretical approach based on the modified three-element Eyring-Halsey model was developed for the derivation of an equation describing the thermally induced recovery of predeformed and crystallized crosslinked polymers. The proposed approach takes into account the influence of crystallizable covalent network and of entangled slipped molecular chains. Modeling of thermally induced shape-memory (SM) recovery strain and SM recovery rate detected at constant heating rate has been successfully performed for nearly linear and two short-chain branched polyethylenes, which were crosslinked by peroxide. The values of material constants determined by fitting agree with the estimations existing in literature. Fitting results have shown that increase of degree of branching and crosslink density accompanied with reducing crystallinity results in increasing contribution of the entangled slipped chains to the total stored SM strain. The physical sense of main fitting parameters and their dependences on the material constants such as crystallinity are discussed. VC 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 815-822