The flow-induced crystallization behavior in capillary extrusion of high density polyethylene melts

The advances in studies of the melt flow-induced crystallization behavior a nd its mechanisms of polymeric materials in processing are reviewed in the present paper. The melt density and the factor affecting it for two kinds o f high-density polyethylene (HDPE) with the same solid density and melt flo w index. samples A and B, were measured by using a standard melt flow index er with various temperatures and loading. It was found that the melt densit y suddenly increased at some temperature and loading. This phenomenon can b e attributed to the onset of the melt flow-induced crystallization. Further more, a simple method for estimation of crystalline degree in flow of polym er melts was proposed. On the basis of experimental observation, the crysta llinity during capillary extrusion of the sample melts was estimated and th e flow-induced crystallization mechanisms were analyzed. The results showed that the crystalline degree for sample A is higher than that of sample B, and the crystallinity of the former was up to 83.90% at 180 degreesC and lo ad of 5 kg. (C) 2001 Elsevier Science Ltd. All rights reserved.