INJECTION-MOLDING OF POLYPROPYLENE DISCS .1. EFFECT OF HOLDING PRESSURE ON ORIENTATION DISTRIBUTION

It is well known that the injection molding process has a major impact on the properties of injection-molded polymers. In this study, the ef fect of the holding pressure on the orientation in injection-molded di scs of polypropylene has been examined. The orientation has been deter mined by IR-dichroism and the orientation factors calculated according to Herman's orientation function, the average factor as well as the c rystalline and the amorphous. The distribution of the orientation in t he length as well as in the depth direction has also been examined in order to understand how the flow has propagated in the cavity during b oth the filling and the packing phases. The results show that the hold ing pressure clearly affected the orientation, but that it was an unev enly distributed effect over the disc.