Effect of polymer crystallinity on morphology in ceramic injection molding

Many ceramic injection molding vehicles include semicrystalline polymers which characteristically adopt a spherulitic growth morphology. Usually the spherulites are rendered invisible by the opacity of the ceramic powder but in this study they are clearly visible. Polyoxymethylene (POM), has been used as the vehicle. The growth of the spherulites is shown to be dependent on cooling rate and hence on position in the molding. Furthermore, migration of low molecular weight additives by syneresis is shown to occur and to influence the crack path in the as-molded state. An unusual composite fractograph is shown in which fracture faces made after molding, after binder removal, and after sintering are contiguous. Only after molding does the crack path follow the spherulite boundaries; behavior that is also widely reported for unfilled POM.