Phase composition of nascent and thermai-treated superhigh-molecular-weight polyethylene investigated by wide-angie X-ray diffraction at stepwise increased temperature

The phase composition of nascent and thermally pretreated superhigh-molecular-weight polyethylene are investigated at stepwise increased temperature by means of wide-angle X-ray diffraction. In addition to the usual dominating orthorhombic lattice, a monoclinic and several lattices with hexagonal symmetry are observed. The intensity of the additional reflexes changes with temperature below and above the melting point of the orthorhombic lattice. These peculiarities of the phase composition are explained through the existence of strong stresses applied on the crystallites, caused by strained tie molecules with high concentration in the nascent sample.