WIDE-ANGLE X-RAY-SCATTERING STUDIES ON POLYETHYLENE AT LOW-TEMPERATURES

Linear polyethylene (Lupolen 6041 D) and a polyethylene fraction (PE 2 000) were investigated by WAXS at temperatures 8 K < T < 293 K. From t he position and integral widths of the reflections the lattice constan ts (and expansion coefficients) and lattice distortions are determined . Lattice distortions are of the strain type, induced by inherent stre sses. They increase with decreasing temperature up to similar to 50 K and then to lower temperatures a decrease is observed. This is explain ed by the decrease of the thermal expansion coefficients. For PE 2000 for some reflections a minimum in the integral widths at T similar to 38 K occurs. The explanation of this effect is given by the occurence of a stress induced martensitic transformation (orthorhombic to monocl inic) of part of the material. The corresponding weak reflections are observed.