Effects of molecular weight on thermoreversible gelation and gel elasticity of methylcellulose in aqueous solution

Abstract

Aqueous solutions of two methylcellulose (MC) polymers with different molecular weights ( M w=100,000 and 400,000) have been studied. The thermoreversible gelation `properties and the gel elasticity were measured as a function of polymer concentration by means of micro differential scanning calorimetry and rheology, respectively. The experimental results prove that the aqueous solutions of MC are completely thermoreversible and the thermoreversibility of MC is independent of either polymer concentration or molecular weight. The total enthalpy required for the sol–gel transition is a linear function of polymer concentration, which is again independent of molecular weight. The quasi-equilibrium modulus G e could be scaled with concentration c as G e∼ c 2.19 ( c>1.0 wt%) and G e∼ c 3.12 ( c<1.0 wt%) for the high molecular weight MC, while G e∼ c 3.12 and (c<1.0 wt%)for the low molecular weight MC. At the same concentration of MC, with increasing molecular weight, G e increases while the heat absorbed during the sol–gel transition remains constant.