Rheological investigation on the associative properties of poly(vinyl alcohol) solutions

We report intrinsic viscosity and flow curve measurements on a set of five industrial poly(vinyl alcohol) (PVOH) samples, with varying degree of hydrolysis, molecular weight, and concentration in two solvents: water and dimethyl sulfoxide (DMSO). Aqueous poly(vinyl alcohol) solutions exhibit clear features of associative polymers, and the hydroxyl-carbonyl hydrogen bonds seem to dominate polymer chain associations. We propose a "sticky-blob"model, applicable to any associating polymer solution with many stickers inside each correlation blob, which predicts the concentration dependence of the specific viscosity and the chain relaxation time in the entanglement regime. When PVOH polymers are dissolved in DMSO, a strong hydrogen bond acceptor, chain-chain associations are fully prevented for all relevant degrees of hydrolysis. The specific viscosity and the relaxation time of the chain recover the expected concentration dependences for nonassociating flexible polymers in DMSO. The same concentration dependences are exhibited by literature data on 100% hydrolyzed PVOH in water, as the acetate content, dominating interchain associations, is zero. Comparing entangled aqueous and DMSO solutions at the same concentration enables the experimental measure of the time delay due to associations as the ratio between the terminal relaxation time of solutions in water and DMSO. The concentration dependence of such a time delay was also captured by the simple sticky-blob model introduced in this work.