Solid-state 1H-NMR relaxation behavior for ultra-high-molecular-weight polyethylene reactor powders with different morphologies

Abstract

The relaxation behaviors of several commercial ultra-high-molecular-weight polyethylene (UHMW-PE) reactor powders were compared. The surface and internal morphologies of these powders were characterized by scanning and transmission electron microscopy observations. On the basis of these morphological analyses, the reactor powder consisted of particles and fibrils between them, the relative amounts of which depended on the powder preparation conditions. Molecular motions were detected by solid-state proton nuclear magnetic resonance (1H-NMR) techniques. The temperature dependence of the molecular motion characterizes the structural differences between these powders. The intermediate region between crystal/amorphous phases first relaxes during gradual heating from room temperature for all reactor powders examined in this study. Such a release of constraint for boundary chains induces structural reorganization beyond the critical temperature before melting. This trend was also confirmed by an increase in crystallinity beyond the critical temperature. In contrast, the results of differential calorimetry (DSC) analysis could not distinguish these powder characteristics because of the remarkable reorganization of these reactor powders during heating scans. A relationship between the morphological and 1H-NMR relaxation characteristics was interpreted for several reactor powders. The relaxation behaviors for several commercial ultra-high molecular weight polyethylene reactor powders were compared. On the basis of the morphological analyses, the reactor powder consisted of particles and fibrils between them, the relative amounts of which depended on the powder preparation conditions. The results of differential scanning calorimetry analysis could not distinguish these powder characteristics because of the remarkable reorganization of these reactor powders during heating scans. In contrast, molecular motions detected by solid-state proton nuclear magnetic resonance techniques characterize the structural differences between these powders.