ISOTHERMAL CRYSTALLIZATION-INDUCED FOAMING OF POLYPROPYLENE UNDER HIGH PRESSURE CARBON DIOXIDE

摘要

Crystals can strongly influence plastic foaming behavior, final foam structure and properties. Using an improved visualization system, foaming process of polypropylene was captured and compared with differential scanning calorimetry analysis. It was observed that crystals nucleated and grew into spherulite. At low temperatures, cell nucleation occurred at crystals' boundaries due to CO_2 exclusion from crystal growth fronts and increase in tensile stresses in surrounding amorphous regions. At higher temperatures, these two mechanisms became less apparent.