HDPE及其共混物的挤出压力振荡现象

采用恒速型双毛细管流变仪研究高密度聚乙烯及其共混物的压力振荡现象,测量了压力振荡的振幅及频率,计算了熔体在管壁的滑移速率和临界外推滑移长度。结果表明,发生压力振荡时,熔体与毛细管壁的界面出现“时黏时滑”转变。黏界面时,挤出物表面出现“鲨鱼皮”现象;滑界面时,挤出物表面粗糙,类似于无规破裂。随剪切速率的增加,压力振荡的振幅减小,而滑移速率、临界外推滑移长度及振荡频率均有提高。升高挤出温度和采用共混改性都可抑制压力振荡现象。

The extrusion pressure oscillation of HDPE and its blends

The extrusion pressure oscillation of high density polyethylene (HDPE) and its blends were quantitatively studied by a double capillary rheometer of constant speed type. The amplitude and frequency of the pressure oscillation were measured; the slide velocity of the melt along the tube wall and critical slide length were calculated. The results show that stick-slip transition and slip-stick transition alternatively appears on the interface between the melt and tube wall of the capillary when the pressure oscillation goes on. Where the stick interface occurs, the extrudate possesses sharkskin-like even surface; where the slip interface occurs, the extrudate has rough surface, resembling irregular rupture. As the shear rate rises, the amplitude of pressure oscillation reduces, whereas the slide velocity, critical slide length and the frequency increase. The pressure oscillation can be suppressed by either raising extrusion temperature or adopting blending modification.