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Abstract

Directional dependence of the PMR-narrow-band in oriented fibers of nylon 66, poly(vinyl alcohol), and cotton has been investigated to study the orientation of hydrogen bonds in the unit cell. Filaments of oriented fibers were conditioned to 75% relative humidity, then aligned together axially and packed in a teflon tube. The teflon tube was suspended in the NMR probe in such a manner that the fiber axis was horizontal and could be rotated to a desired angle with respect to the magnetic field. Variation of the narrow-band line width as a function of the angle between the fiber axis and the magnetic field-direction shows a minimum at 0° orientation for nylon 66 and PVA, but in the case of cotton it shows a minimum at about 80° orientation. This indicates that in the case of nylon 66 and PVA, hydrogen bonds are oriented nearly prependicular to the chain axis. This would suggest that nylon 66 and PVA have interchain hydrogen bonding, but the hydrogen bonds contributing to directional dependence, in the case of cotton fiber, are intrachain. The interchain hydrogen bonds between the lateral chains, if they exist, must be random and, therefore, do not contribute to directional dependence. The interchain H bonds between central and corner chains are probably oriented in such a way that the horizontal component of p–p vectors have nearly the same orientation in the unit cell as the p–p vectors of the intrachain hydrogen bonds.