화학공학소재연구정보센터
Macromolecules, Vol.29, No.5, 1540-1547, 1996
Real-Time X-Ray-Diffraction Study on 2-Stage Drawing of Ultra-High-Molecular-Weight Polyethylene Reactor Powder Above the Static Melting Temperature
The polyethylene for the study was ultra-high molecular weight polyethylene (UHMW-PE) reactor powder extrusion drawn to a low draw ratio (DR) of similar to 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 (T-d), 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 greater than or equal to 150 degrees 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 T-d of 150-155 degrees C, the chain orientation in both the hexagonal and the amorphous phases rapidly increased, and these phases transformed into the orthorhombic crystals. Even when the T-d was raised to 160 degrees C during drawing, the orthorhombic phase was predominant with no significant increase in the amorphous component. These results show that the major deformation proceeded in a highly crystalline state where the orthorhombic crystalline phase was predominant, giving an efficient draw in terms of molecular DR, at least up to 155 degrees C, and reflecting the characteristics of the UHMW-PE reactor powder used in this work. Such deformation behavior in the high-temperature range is markedly different from that previously reported for single-crystal mats and gel and melt-crystallized films of UHMW-PE, which produced poor mechanical properties.