微层共挤出(PP+EVOH)/PP阻隔材料的结构与性能研究

STRUCTURE AND PROPERTIES OF(PP+EVOH)/PP BARRIER MATERIAL PREPARED BY MICROLAYER COEXTRUSION

利用微层共挤出技术制备了具有交替层状结构的(PP+EVOH)/PP复合材料,其中PP为聚丙烯,EVOH为乙烯-乙烯醇其聚物.通过扫描电子显微镜观察、气体渗透实验、差示扫描量热仪分析以及力学性能测试研究了微层共挤出复合材料的形态结构及其对复合材料气体阻隔性能、力学性能以及结晶性能的影响.研究结果表明,通过微层共挤出技术,PP层和(PP+EVOH)层沿挤出方向交替排列,EVOH在PP基体中的的分散形态由零维球形变为一维纤维状,进而演变为二维片状.这些形态导致微层共挤出材料的氮气渗透系数和断裂伸长率较普通共混物分别下降了两个数量级和提高了27倍,并且显著影响其结晶行为.当层数超过64层后,由于PP层减薄,界面增多,EVOH不仅对(PP+EVOH)层中PP相存在结晶成核作用,而且对PP层也有结晶成核作用.

A novel barrier material consisting of alternating layers of pure polypropylene （PP） and polypropylene conventionally blended with ethylene-vinyl alcohol copolymer （EVOH） was prepared by mierolayer eoextrusion .The morphology structure of（PP ＋ EVOH）/PP microlayered composites and its effect on gas-barrier properties, mechanical properties and crystallization behavior were characterized by SEM, DSC, gas-permeability and tensile tests. The results suggested that, through mierolayer eoextrusion, PP layers and （PP ＋ EVOH） layers were combined as an ahernatingly multilayered structure along the extrusion direction. The morphology of EVOH phase in PP matrix was changed from zero-dimensional sphere to one-dimensional fiber,then to two-dimensional sheet with the increase of layer number, which caused significant improving of gas-barrier properties and enlongation at break of （ PP ＋ EVOH）/PP microlayered composites compared with （PP ＋ EVOH） conventional blends. The crystallization behavior of microlayered composites was also influenced obviously by their structure and morphology. In addition to the PP phase in （PP ＋ EVOH） layer, PP layer was also affected by the heterogeneous nucleation of EVOH due to the thin PP layer and the increase of interface when the layer number exceeded 64 layers.