Reverse temperature injection molding of Biopol™ and effect on its properties

A novel reverse temperature profile for the injection molding of BiopoI(TM) was studied. It was found that both the mechanical properties and the part quality of BiopoI(TM) were improved with this new reverse temperature process. When injection molded, most conventional thermoplastic polymers are processed at 30 to 70degreesC above the Melting temperature; under these conditions, BiopoI(TM) degraded rapidly and the resulting material showed poor mechanical properties. In contrast, when using a reverse temperature molding process, where Biopol(TM) was melted in the first zone and then was conveyed through the barrel with a decreasing temperature pathway and was injection-molded at a temperature below its melting point, the resulting material showed higher mechanical properties. The processing of Biopol(TM) was also greatly improved. The reverse temperature process uses the characteristically slow crystallization rate of Biopol(TM), which can be easily injected as hot melt even below its normal melting point. DSC analysis suggested that the reverse temperature process resulted in a more homogeneous crystalline phase than the conventional process. GPC analysis also indicated that thermal degradation of Biopol(TM) was largely reduced in the reverse temperature injection-molding process compared with conventional methods. (C) 2004 Wiley Periodicals, Inc.