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。 A series of polyolefm melts were investigated for high-speed extrusion behavior using a constant speed, double capillary rheometer. A number of physical parameters that quantitatively describe both types of extrusion distortions - shark skin distortion and extrusion pressure oscillations are defined. The effects of temperature, extrusion rate, melt composition and composition on the extrusion pressure oscillation and shark skin distortion were quantitatively described. It is found that shark skin distortions and extrusion pressure oscillations are prone to occur when the linear polymer melt is extruded at high speed, whereas the branched polymer or main-side polymer melt containing large side groups rarely undergoes the same kind of distortion. The extrusion rate increases, the frequency of pressure oscillation increases, the oscillation aggravates; the critical temperature at which the extrusion temperature begins to oscillate increases and the melt flow instability decreases; but for the same melt, Under the pressure oscillation began to change the critical shear stress changed little.