共混对HDPE熔体高速挤出压力振荡现象的影响

采用恒速型双筒毛细管流变仪研究了高密度聚乙烯(HDPE)及其共混物的高速挤出行为,对高挤出速率下发生的挤出压力振荡和熔体黏-滑破裂等不稳定流动现象进行了定量描述。结果表明,升高熔体温度和采用共混改性有助于减轻熔体流动的不稳定性;温度升高,压力振荡频率呈减小趋势,熔体沿毛细管壁的滑移速度减小,外推滑移长度缩短,开始发生压力振荡的临界挤出速率提高;HDPE与低密度聚乙烯(LDPE)或聚丙烯(PP)共混后,熔体的挤出压力振荡明显减轻,而当m(HDPE)/m(PP)=70/30的共混物挤出时,未观察到压力振荡现象。

The Effect of Blending on the Pressure Oscillation of HDPE Melts During High Speed Extrusion

Rheological behaviors of HDPE and its blends with certain contents of LDPE or PP at high speed extrusion were studied by double capillary rheometer of constant speed type.The unsteady flow phenomenon at high extrusion flow rate,such as pressure oscillations and stick-slip instability,were described quantitatively.The results suggested that the unsteady flow could be weakened by increasing the melt temperature and blending with other additives.Increasing the temperature would decrease the frequency of pressure oscillations.At the same time,the melt slip velocity along the die wall and the critical slippage extrapolation length were reduced,while the critical shear rate at which the pressure oscillations occurs was increased.After blending with LDPE or PP,the pressure oscillations of HDPE melts was reduced obviously.Especially,there was no pressure oscillations on the blends when the mass ratio of HDPE and PP was 70/30.