Simulations of injections of selected multiprocessed thermoplastics

The deteriorating processability in multiprocessed (injection molding) LDPE, PP, and glass fiber-reinforced PET thermoplastics, observed in mold filling and in molded piece warpage, was studied by simulations using the I-DEAS Master Series 4 system. Melt viscosity of the multiprocessed polymers was modeled by using database-retrieved equations (1a, b) which relate the viscosity to process parameters. Temperature and pressure relations of polymer density allowed to estimate shrinkage variations in the recyclates. Simulations showed mold filling to be only slightly affected by viscosity changes. The calculated warpage was distinctly lower in glass fiber-reinforced PET molded pieces than in unreinforced polyolefins. A special holding pressure profile was found to suppress warpage in both polyolefins examined.