Effects of concentration and degree of polymerization on the rheological properties of methylcellulose aqueous solution.

Abstract

Rheological studies were carried out on aqueous solutions of five methylcellulose (MC) preparations, with degrees of polymerization (DP) between 330 and 1020. Comparison of the intrinsic viscosity of MC with that of sodium carboxymethylcellulose (CMC) of similar DP indicated that MC molecules were relatively compact coils when they were present as isolated coils in dilute solution. However, the Huggins constants (k'1) of MC samples were higher than those of CMC samples, suggesting that intermolecular interaction of MC was larger than that of CMC at low concentration. The second virial coefficients of MC samples in dilute solution, determined by ultracentrifugation analysis, were divided at about DP 500 int two groups, low and high DP samples. A similar tendency was observed in the rheological properties of concentrated MC solution. It is suggested that the increase in DP was accompanied with an increase not only in molecular size but also in intermolecular interaction of MCs in solution. Interesting rheological characteristics were observed in high DP samples, particularly at concentrations higher than a critical concentration. The dynamic viscoelastic behavior of these samples depended significantly on both DP and concentration.