线型与支化聚烯烃熔体高速挤出时的不稳定扰动源

采用恒速型双毛细管流变仪对比研究线型与支化聚烯烃熔体在高速流场中的流动曲线、挤出畸变、挤出压力变化及粘弹性的特征,分析讨论了引发熔体不稳定流动的扰动源位置及扰动性质.结果表明,高速流场中的扰动源有:口模入口区的扰动、口模壁处的扰动、口模出口区的扰动.支化聚合物易受入口区的扰动干扰,造成挤出物无规破裂;线型聚合物易受口模壁处的扰动干扰,造成挤出压力振荡和挤出物有规畸变;鲨鱼皮畸变主要由于口模出口区的振荡扰动造成.

The Trouble Headstream of Unstable Flow in High Speed Extrusion of Linear and Branched Polyolefine Melts

The flow curves,extrudate distortions,extrusion pressure variety and the characters of viscoelasticity of linear and branched polyolefine melts in high speed extrusion was investigated by a double capillary rheometer of constant speed type.The unstable flow behaviors and the trouble headstream of different melts were discussed.The results indicate that there are three kinds of trouble headstreams in high speed extrusion flow field,such as the destabilization on die entrance,on die wall,and on die exit.Branched polymer is easily disturbed by the destabilization on die entrance,which will cause a irregular extrudate fracture;while the linear polymer is easily disturbed by the destabilization on die wall,which will cause an extrusion pressure oscillation and a regular extrudate distortion.The sharkskin-like distortion is caused by an oscillatory destabilization on die exit.