High-strain deformation of polyethylenes in plane-strain compression at elevated temperatures

The deformation and recovery behavior of several polyethylenes and ethylene-based copolymers with various molecular architectures and a broad range of molecular masses and molecular mass distributions was studied. Because of the differences in the molecular characteristic, this series exhibited a relatively broad range of crystallite sizes and crystallinity levels. The samples were subjected to high strain compression under plane-strain conditions at the elevated temperature of 80 degrees C. The unloading of the compressed samples led to substantial nonelastic recovery of the strain. The stress-strain and recovery behavior was related to the molecular parameters. The results confirmed the common deformation scheme with four crossover points related to the activation of subsequent deformation mechanisms, as proposed by Strobl. Although the critical strains, related to the activation of deformation of the crystalline component, are invariant, the critical strain of the last point, which is related to the activation of chain disentanglement in the amorphous component, depends on the temperature of deformation. That critical strain decreases from 1.0 to approximately 0.8-0.9 as the temperature of deformation increases from room temperature to 80 degrees C. This shift results from an increase in the chain mobility with increasing temperature, and this makes modification of the molecular network through chain disentanglements easier. (C) 2007 Wiley Periodicals, Inc.