AFM analysis of the Surface of Highly Drawn Ultra High Molecular Weight Polyethylene Fibers

摘要

Large epitaxial structures on the surface of ultra-drawn, ultra high molecular weight polyethylene (UHMWPE) fibers are observed using atomic force microscopy (AFM). These epitaxial structures are prevalent, oriented perpendicular to the fiber axis with a nominal thickness of 10-25 nm in the direction of the fiber axis and a width of 100-200 nm. The observed surface morphology is different from the traditional shish-kebab morphology in scale, bridging tens of microfibrils. A series of annealing experiments of single filaments over a temperature range of interest for the processing of ballistic laminates ( 110°C-130°C), show significant thickening of these surface features consistent with melting and recrystallization of thin lamella crystals. AFM scans performed before and after annealing reveal considerable reorganization, and in some instances, the appearance of new epitaxial features in areas where none had existed previously. These results suggest that these larger scale epitaxial structures form as a result of melting and recrystallization of less stable crystalline structures and/or surface melting of more stable crystals. A discussion of the implications of these observations with respect to both fiber and composite processing and mechanical properties will be presented.