THERMODYNAMICAL BEHAVIOR OF DEFORMED SEMICRYSTALLINE POLYMERS IN TEMPERATURES BETWEEN T-G AND T-M .1. UNIAXIAL COMPRESSION OF CYLINDRICAL SAMPLES OF HIGH-DENSITY POLYETHYLENE, ISOTACTIC POLYPROPYLENE, POLYVINYLIDENEDIFLUORIDE AND POLYTETRAFLUOROETHYLENE

The deformation through uniaxial compression at room temperature of cy lindrical samples of high density polyethylene (HDPE), isotactic polyp ropylene (i-PP), polyvinylidenedifluoride (PVDF) and polytetrafluoroet hylene (PTFE) was studied. A comparison between undeformed and deforme d materials is based on the characterization of morphology, density an d thermodynamical data like thermal expansion coefficient and thermal capacity behavior. Morphological and density changes have been studied by using deformation dimensional analysis, densimetry, X-ray diffract ion and optical polarizing microscopy techniques. The characteristics of the nonequilibrium thermodynamical state of the deformed materials are demonstrated during consecutive thermal cycling through the irreve rsible transitions and modifications of the linear thermal expansion c oefficient and the thermal capacity studied by means of Thermomechanic al Analysis (TMA) and Differential Scanning Calorimetry (DSC) techniqu es, respectively. The expected partial shape recovery of the deformed material under study was observed during temperature elevation.