The Huggins viscosity coefficient of aqueous solution of poly(vinyl alcohol)

Although water at room temperature is not a poor solvent for poly(vinyl alcohol) (PVA), the values of the Huggins viscosity coefficient k(H) are typically higher than 1/2. This is attributed to association. Based on the model put forward by Peterlin, the k(H) values reported in the literature for aqueous solutions of PVA were examined and the equilibrium constant K+ was estimated. It turned out that it increases with increasing molecular weight and depends on the content of residual acetate units. The effect of temperature seems to be weak. Based on the theory of phase equilibria in solutions of crystalline polymers, the values of the Flory-Huggins interaction parameter x, necessary for molecular dissolution in water of semicrystalline samples, were estimated and compared with the experimental data for samples of PVA with different content of vinyl acetate units. Differences in stability (aging) of PVA solutions can be explained on this basis. Existing experimental data on the viscosity of fresh dilute solutions of PVA in water are interpreted in terms of a model, where the association is due to intermolecular hydrogen bonds between the OH groups of polymer chains. On the contrary, aging phenomena may be attributed to an increase in size and amount of semicrystalline domains acting as multifunctional cross-linking agents. (C) 2000 Elsevier Science Ltd. All rights reserved.