Characteristic rheological features of high concentration PVA solutions in water with different degrees of polymerization



This work aims to study the impact of the degree of polymerization (Pn) on the rheological behavior of PVA solutions (15 wt %) under steady and oscillatory shear conditions. The values of Pn range from 1300 to 2400. The results show that PVA-13 solution exhibits almost Newtonian flow behavior, whereas high Pn PVA solutions exhibit shear thinning behavior, for which the complex viscosity increases with Pn. However, the shear viscosity of PVA-24 is lower than that of PVA-20 at low shear rate (<1 s−1). In addition, the storage modulus of PVA solutions increases with increasing degree of polymerization from 1300 to 2000. There is a sharp increase at degrees of polymerization higher than 1300. However, the storage modulus of PVA-24 is lower than that of PVA-17 and PVA-20 at low shear rate (<1 rad/s). The viscoelastic exponent of the PVA solutions shows a minimum value at degree of polymerization 2000. Thixotropy is detected by a hysteresis loop of the flow curves. The creep response of PVA solutions has also been investigated, with PVA-24 showing negligible compliance recovery. These facts indicate that increasing Pn produces a corresponding effect in varying the molecular structure and types of hydrogen bonding, including intra- and inter-chain, and polymer–water hydrogen bonding. Rheological parameters (G′, n, tanδ, J, and so on) can be used to evaluate the change in the molecular structure and type of hydrogen bonding. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010