EFFECT OF PRESSURE AND SHEAR-STRESS ON CRYSTALLIZATION BEHAVIORS IN INJECTION-MOLDING

We studied in detail the effects of pressure and shear stress on the c rystallization behaviors during injection molding process. Crystalliza tion of isotactic-polypropylene (iPP) was simulated for various inject ion flow rates. The crystallization started during the filling stage u nder long filling condition. Moreover, the crystallization in some lay ers showed two-step growth behavior, while in other layers the crystal lization does not progress during the packing-cooling stage. Since pre ssure becomes very high during molding process under long filling time condition, the change of pressure is the most important factor govern ing the crystallization.