CELLULOSE AND CELLULOSE POLY(VINYL ALCOHOL) BLENDS .2. WATER ORGANIZATION REVEALED BY SOLID-STATE NMR-SPECTROSCOPY

Cellulose as well as two cellulose/poly(vinyl alcohol) blends with com positions 60/40 and 80/20 w/w exposed to water are investigated by H-1 -, H-2-, and C-13 solid-state NMR spectroscopy. For pure cellulose, th e lower temperature, secondary dielectric relaxation process can be at tributed to the onset of motion of adsorbed water molecules as reveale d by H-2-NMR spectroscopy. This water is not crystalline below 270 K. Three distinct kinds of water bound to the polymer matrix are detected , as far as dynamic behavior is concerned. First there is nonfreezable , strongly bound water that is rigid but amorphous at low temperatures . The second component is highly mobile and exhibits isotropic motion even below 270 K. Interestingly, there is a third component of water m olecules that undergo well-defined 180 degrees flips around their bise ctor axis with a rate greater than 10(5) s(-1) due to anisotropic cons traints. In contrast to the first two kinds, this component cannot be removed from the polymer matrix by drying even at elevated temperature s and its motional process is observed over the whole temperature rang e, investigated from 190 to 370 K. All three kinds of matrix water coe xist in a wide temperature range. In the blends, 2D H-1-C-13 heteronuc lear wide line separation (WISE) NMR spectroscopy shows that at our lo w concentrations the water is predominantly associated with the cellul ose backbone. No water can be detected in the immediate vicinity of th e poly(vinyl alcohol). Applying spin diffusion, we detected nanohetero geneities in the range of about 3 nm within these systems.