Structure and mechanical properties of alternatively stacked films of ultra high molecular weight isotactic polypropylene and ultra high molecular weight polyethylene

By two-staged roll-drawing of the three layer sheets where a ultra high molecular weight polyethylene (UHMW-PE) layer is sandwiched by ultra high molecular weight isotactic polypropylene (UHMW-iPP) layers, we tried to prepare a film which exhibits excellent mechanical properties. The temperature range available to roll-draw at the first stage of the stacked sheet is 125 similar to 135 degrees C and that at the second stage of the specimens drawn once is 130 similar to 145 degrees C. The highest draw ratio (DR) was performed at a drawing temperature of 135 similar to 140 degrees C at the second stage. By differential scanning calorimetry (DSC) of the thus-prepared specimens, we observed endothermic peaks originating from various crystalline states, i.e. folded-chain crystals and extended-chain crystals even at low DR of about 20. From the X-ray diffraction of the films, it was recognized that the roll-drawing easily induces the: double orientation of PE. By comparison with the specimen which was uniaxially drawn to same DR for the tensile modulus and strength, the advantage for the mechanical property of the roll-drawn specimen in two-stages was recognized.