PARISON FORMATION AND INFLATION BEHAVIOR OF POLYAMIDE-6 DURING EXTRUSION BLOW MOLDING

Parison formation and inflation behavior of three polyamide 6 resins d uring extrusion blow molding were investigated using cinematography, a transparent mold, a pinch-off mold and a modified blow pin, which all owed the pressure inside the parison to be determined during inflation . The glass fiber filled polyamide exhibited negligible extrudate swel l and significant drawdown, whereas polyolefin modified polyamide exhi bited appreciable extrudate swell and relatively small drawdown effect s. The inflation behavior of the polyolefin modified polyamide was sim ilar to the behavior of conventional blow molding grade polyolefins, w hereas the unmodified and glass filled polyamides exhibited different inflation characteristics. Their inflation behavior at different inter nal pressures was characterized by decreasing and increasing Hencky st rain rates with inflation time at high and low internal blow pressures , respectively. The characterized parison formation and inflation beha vior of the polyamides emphasize the importance of rigorous blow molda bility experiments and the difficulties associated with Linking variou s rheological material functions to the blow moldability of modified p olyamides.