Solid-state ¹³C NMR characterization of the morphology of ultrahigh molecular weight, high performance polyethylene fibers

Among the many routes which have been explored for converting flexible polymers to high performance fiber structures, the gel spinning process for the manufacture of ultrahigh molecular weight polyethylene (UHMWPE) fibers with high tenacity represents the most successful to date. Stretching of an entangled molecular network of long flexible chains to a very high extent, in order to reduce defects while forming a highly aligned spatial architecture, is believed to be a basic element of the gel spinning process. Studies by various investigators have shown clearly that it is necessary to have extended fibrillar morphology with a high degree of crystallinity to achieve high strength and modulus in UHMWPE fibers. There is, however, some disagreement regarding the extent, if any, of a non-crystalline phase and the structure within, and between, the microfibrils. In this paper we report a solid-state ¹³C CP/MAS study of the morphology of these polymer fibers. We report the detection of three components in the ¹³C NMR spectra. The intensities of these components were determined quantitatively. The orientational order of these components were characterized by 2-dimensional rotor synchronized CP/MAS technique.