超高分子量聚苯乙烯的流变性能

以毛细管流变仪和Hakke转矩流变仪对稀土催化合成的超高分子量聚苯乙烯 (UHMWPS)的流变与加工性能进行了研究 .结果表明 ,UHMWPS最显著的流变特征为超高的熔体粘度和低剪切速率下出现不稳定流动 .不稳定流动与超高分子量聚合物长的松弛时间有关 ,并提出了临界剪切速率与分子量和温度的定量关系式 .较低的分子量和较高的温度有利于提高临界剪切速率 ,改善挤出物外观质量和降低熔体粘度 .分子链极度缠结不仅导致超高的熔体粘度 ,也使UHMWPS链解缠加快 ,导致更高的剪切速率敏感性 .UHMWPS塑化时熔体粘度高 ,转矩大 ,加工性能劣于通用聚苯乙烯 (GPPS)

RHEOLOGY OF ULTRA HIGH MOLECULAR WEIGHT POLYSTYRENE

The rheology and processability of ultra high molecular weight polystyrene (UHMWPS) synthesized by rare earth catalyst were investigated by using capillary rheometer and Hakke torque rheometer. It was found that the rheological behavior of UHMWPS is remarkably characterized by its unstable flow at low critical shear rate and ultrahigh melt viscosity. The unstable flow is attributed to the long relaxation time of the samples resulted from their ultrahigh molecular weight, and a dependence of the critical shear rate on the molecular weight and temperature is presented. Moreover, the low molecular weight and higher temperature are favorable to reduce the melt viscosity, to increase the critical shear rate and to improve the apparent quality of extrudates. The extreme entanglement of polymer chains results in not only the ultrahigh melt viscosity, but also the faster dis\|entanglement process which leads to a stronger dependence of melt viscosity on shear rate. Furthermore, it is indicated that the processability of UHMWPS is inferior to that of conventional PS because of its higher balance torque determined by Hakke rheometer.