Polyolefin/PET Microplates–Reinforced Composites with Improved Barrier Properties

Abstract

In this article an attempt was undertaken to improve the barrier properties of polyolefin films against oxygen by creating internal micro-platelets of a second polymer component using the previously developed concept of micro-fibrils reinforced polymer-polymer composites (MFC). By means of melt blending of partners with mutually complementing barrier properties, and by extrusion and pressing the extrudate in order to convert the dispersed spherical particles of the minor component into platelet-like ones with thickness of about 1 µm, it is possible to improve the barrier properties of the neat major component. The described morphologic transition of the dispersed phase is proven by Scanning Electron Microscopy. Attempts to manufacture thin films from such pressed blends with improved barrier properties in industrial-scale experiments via extrusion blow molding or slit-die extrusion failed so far. This was due to the fact that void formations occurred during the processing, as already reported for blends of thermoplastics with liquid crystalline polymers. For this reason, using compression molding, films were prepared from the pressed strips, in which the platelets can be converted into thin sheets depending on the processing conditions. Compression molded plates or films of polypropylene/poly(ethylene terephthalate) (70/30 by wt) composites with an MPC structure (MPC = micro-platelets reinforced composites) showed up to four times better barrier properties against oxygen than films of the neat PP.