【摘要】 针对超高分子量聚乙烯在熔融挤出过程中容易产生挤出缺陷的问题，借助毛细管流变仪挤出超高分子量聚乙烯（PE-UHMW）/高密度聚乙烯（PE-HD）共混物，通过观察纯PE-UHMW、纯PE-HD及共混挤出物的表面形貌，分析了不同挤出温度下共混物的不稳定流动行为，包括挤出过程中发生振荡畸变和熔体破裂现象的临界剪切速率，以及超过临界剪切速率后挤出物的压力振荡行为和壁面滑移现象。结果表明，共混物的挤出形貌经过了鲨鱼皮-振荡畸变-整体熔体破裂的演变过程。毛细管挤出温度为260℃时，当剪切速率达到116 s^-1后，挤出压力产生剧烈振荡，熔体与管壁界面存在动态黏-滑转变特征，引起挤出物的振荡畸变和壁面滑移现象。同时，挤出温度的升高可以延缓挤出物不稳定流动的发生，引发振荡畸变形貌发生的剪切速率区间从116～522 s^-1增加至152～686 s^-1。更多还原

【Abstract】 This study investigated the unstable flow behavior of ultra-high molecular weight polyethylene（PE-UHMW）/high-density polyethylene（PE-HD） blends during capillary extrusion. The surface morphology of extrudates, including pure PE-UHMW, pure PE-HD, and their blends, was analyzed to characterize flow instabilities at various extrusion temperatures. Key phenomena examined include the critical shear rate for the onset of oscillatory distortion and melt fracture, as well as pressure oscillations and wall slip beyond this critical rate. The results indicated that the extrusion morphology evolved through a sequence of shark skin, oscillatory distortion, and global melt fracture. At an extrusion temperature of 260 ℃, severe pressure oscillations occurred at a shear rate of 116 s^-1, accompanied by a dynamic stick–slip transition at the melt–wall interface that induces oscillatory distortion and wall slip. Furthermore, increasing the extrusion temperature delayed the onset of unstable flow, expanding the shear rate range for oscillatory distortion from 116～522 s^-1 to 152～686 s^-1.更多还原