THERMOMECHANICAL BEHAVIOR OF SEMICRYSTALLINE POLYMERS SUBMITTED TO PLANE-STRAIN COMPRESSION

High-density polyethylene (HDPE) and poly(vinylidene fluoride) (PVF2) were submitted to plane-strain compression at temperatures between the glass transition temperature (T-g) and the melting point (T-m) by usi ng a deep channel die; this device allowed compression along the Z-axi s, elongation along the X-axis and no dimensional change along the Y-a xis. The thermomechanical and morphological changes occurring during t he plastic deformation process and relaxation of the deformed material s were investigated by thermomechanical analysis, differential scannin g calorimetry and density measurements. The results show that the defo rmation process affects the thermodynamic properties of polymers, intr oducing different characteristics into the material. An increase of am orphous phase was registered in both materials. The plastically deform ed semicrystalline polymers showed non-regular linear thermal expansio n behaviour in the deformation directions (X and Z). The relaxation pr ocess, which is obtained by heating the deformed materials, is charact erized by 'shape and temperature memory'. (C) 1998 Elsevier Science Lt d. All rights reserved.