THE USE OF BIREFRINGENCE FOR PREDICTING THE STIFFNESS OF INJECTION-MOLDED POLYCARBONATE DISCS

Polycarbonate discs were infection molded with different sets of moldi ng conditions. The parameters studied were the flow rate, melt- and mo ld-temperature. The discs were subjected to three point support flexur al tests. Those tests are specially intended for injection molded disc s because of their inherent non-flatness. The through-thickness molecu lar orientation was assessed by birefringence measurements along and a cross the flow direction using the wedge method. This method is ideal to measure the birefringence of materials that are difficult to cut wi th a microtome. The through-thickness stiffness of the discs was calcu lated from the measured birefringence distributions. A composite model of the disc was used in the Algor finite element method (FEM) package to simulate the flexural tests.