聚烯烃熔体两类挤出畸变现象的定量描述

Quantitative Characterization of Two Kinds of the Extrudate Distortion of Polyolefine Melts

采用恒速型双毛细管流变仪研究一批聚烯烃熔体的高速挤出行为。定义了定量描述两类挤出畸变现象———鲨鱼皮畸变和挤出压力振荡的若干物理参数。定量描述了温度、挤出速率、熔体材质及成分对挤出压力振荡和鲨鱼皮畸变的影响规律。发现:线型聚合物熔体高速挤出时易发生鲨鱼皮畸变和挤出压力振荡,而支化聚合物或主链含大侧基聚合物熔体很少出现同类畸变。挤出速率增大,压力振荡的频率加大,振荡加剧;挤出温度升高,开始发生振荡的临界剪切速率增高,熔体流动不稳定性减轻;但对同一熔体而言,不同温度下开始发生压力振荡的临界剪切应力变化不大。

The high speed extrusion behaviors of several polyolefine melts were investigated by a double capillary rheometer of constant speed type. Some physical parameters to characterize two kinds of the extrudate distortions-sharkskin fracture and extrusion pressure oscillation were defined. The influences of temperature, extrusion rate, melt structure and component on the the extrudate distortions were quantificationally characterized. It was indicated that the sharkskin and pressure oscillation occurred often when a linear polymer melt was extruded with high speed,hut not a branched polymer melt. With the increasing of extrusion rate,the pressure oscillation and sharkskin became more aggravated. And with the raising of temperature the critical shear rate, when the oscillation just started, increased and consequently the melt flow instability became lightened, But the critical shear stress for same melt changed very small at different extrusion temperatures.