MORPHOLOGY AND ORIENTATION OF PP STRUCTURAL FOAM MOLDINGS

An experimental study was conducted to investigate the interaction bet ween the macrostructure and morphology of PP-structural foam moldings made by gas-counter pressure process by egression of foamed melt from the core of the molding. The structural foam moldings, center-gated cy lindrical plate ''disc'' (diameter 1800 mm. high Il mm) were produced on an in -line injection molding machine KuASY 800/250, varying the sh ot weight and melt temperature. The polymer used was isotactic polypro pylene ''Buplen'' 7523 with 1 wt% chemical blowing agent (azodicarbona mide) added. The morphology, orientation, and processes of non isother mal phase transition have been studied using polarized optical microsc opy, SALS, DSC and birefringence. Samples were cut from the discs at d ifferent distances from the gate. The presence of a two-layered struct ure was observed in the solid skin: an outer smectic layer and an inne r particular crystalline layer. The thickness of the smectic layer and size of spherulites from skin to the foamed core were determined. The orientation in radical and tangential direction of the flow and perpe ndicular to the disc surface were studied in mold filling and egressio n stage. The fixed orientation in final moldings is a complex picture of bubble growth, bubble orientation and shear flow. It was found that the radical orientation decreases with the distance from the gate. Ma ximum orientation is located in the solid skin, and minimum in the foa med core, and was shown by means of a birefringence profile.