(15)N CP/MAS NMR of Aramids: A Tool for Characterization of the Morphology of High Modulus Fibers for Composites

摘要

Natural abundance 15N solid state NMR was found to provide unique molecular and microscopic level information on aramids and aramid-containing copolymers. Poly(p-phenyleneterephthalamide) (PPTA) coagulated from H2SO4 into water displayed a broad envelope of overlapping peaks between 90 and 100 ppm (relative to solid glycine). Annealing significantly reduced the width of this envelope although not to the level of the commercial Kevlar fiber spectrum. Molecular level composites of PPTA grafted with nylon 3 in a nylon 3 matrix showed broad peaks for the aramid components up to 30% by weight content. Peak widths were comparable to that of the precipitated PPTA. Above 30% PPTA, phase separation (confirmed by IR, x-ray and SEM) is observed by solid state NMR as narrow peaks for the aramid nitrogens. (JES)