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

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 microlayer coextrusion. 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 microlayer coextrusion, PP layers and (PP + EVOH) layers were combined as an alternatingly 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.