NONISOTHERMAL THERMOPHYSICAL EVALUATION OF A POLYPROPYLENE PLUS ETHYLENE-PROPYLENE DIENE (EPDM) BLEND

Recent theoretical evidence indicates that the rate effects of quenchi ng seen in the isothermal crystallization kinetics can be eliminated t hrough use of a nonisothermal method based on constant rate heating an d cooling through inclusion of an activation energy. To investigate th e potential of this method for polymers, we apply it to semicrystallin e polymers: polypropylene (PP), a binary blend PP + ethylene propylene diene rubber (EPDM) and a ternary system PP + EPDM + high-density pol yethylene (PE). As opposed to traditional rubber-modified systems such as high-impact polystyrene (HIPS) wherein an amorphous component is b lended with a rubbery one, the PP + EPDM system has a semicrystalline component. From the perspective of crystal lamellae growth or stress i nduced slip, the thermophysical properties are also a concern. Therefo re, we use differential scanning calorimetry (DSC) and thermomechanica l analysis (TMA). The results indicate that differences between isothe rmal and nonisothermal conditions must be taken into account since the latter conditions prevail in extrusion, injection molding, and in hot coating-slow cooling processes. Our nonisothermal analysis of crystal lization should assist in the optimization of cooling of semicrystalli ne polymers.