Real-Time X-ray Diffraction Study on Two-Stage Drawing of Ultra-High Molecular Weight Polyethylene Reactor Powder above the Static Melting Temperature

Abstract

The polyethylene for the study was ultra-high molecular weight polyethylene (UHMW-PE) reactor powder extrusion drawn to a low draw ratio (DR) of ∼6 (first-stage draw). The structural change during the second-stage tensile draw of the extrudate has been studied above the static melting point by real-time wide-angle X-ray diffraction (WAXD). Information on the phase structure was also obtained by WAXD as a function of sample DR, temperature (Td), and applied tensile load and by retractive stress measurements. Upon heating the extrudate with the fixed ends in an X-ray high-temperature chamber, part of the initially orthorhombic crystals transformed into the hexagonal crystalline and amorphous phases at ≥150 °C, indicating that the retractive stress was not homogeneously distributed within a drawn sample. Such a transformation temperature increased with sample DR. When draw was initiated at a constant Td of 150−155 °C, the chain orientation in both the hexagonal and the amorphous phases rapidly increased, and...