Study of hydrogen bonding in poly(vinyl alcohol) by a nuclear magnetic resonance method

Abstract

AbstractThe effect of water fixation in poly(vinyl alcohol) yarn has been studied by the NMR method. Water content in the PVA specimen was varied by exposing the specimen to different relative humidity conditions. The NMR wide line spectra have been registered for samples of PVA (a) dried at 80°C. for 24 hr., (b) conditioned to 40% relative humidity, and (c) conditioned to 80% relative humidity. Wide line spectra for the dry specimen of PVA have a broad band only, but the 40% relative humidity conditioned sample has a broad band and a narrow band, and at the same time the sample conditioned to 80% relative humidity has a broad band and two narrow bands. Variation of intensity as a function of water content has been studied. Variation of wide and narrow band intensity shows that at low relative humidity water enters the amorphous and crystalline regions and is held there by the formation of hydrogen bonds. Hydroxyl groups may replace hydrogen atoms at random on a carbon chain without destroying crystallinity. In the amorphous regions water molecules are held relatively free and are accommodated in voids. This would then account for the second peak in the narrow band of the spectrum seen at higher water contents.