Melting of drawn polyethylene films

If drawn, crosslinked, high molecular weight polyethylene films are restrained during melting, two endothermic peaks may be noted on a scanning calorimeter. In x-ray diffraction experiments, the appearance of a single new peak accompanies the disappearance of the orthorhombic pattern. The new peak is thought to be due to hexagonal chain packing above the melting temperature. The results are interpreted in terms of a small amount of fibrillar crystals in the drawn films.