Gelation of concentrated polyacrylonitrile solutions. II

Abstract

Abstract The rate of gelation of concentrated polyacrylonitrile solutions is measured by the increase of the elasticity modulus of the gels with time at constant temperature. The influence of the following factors has been determined : temperature, concentration, molecular weight of the polymer, and water content of the solutions. The rate of gelation increases when the temperature decreases and becomes rapid enough to be measured between 0 and −10°C. The rate of gelation increases further by a factor 150 when the concentration varies from 18 to 23% and by a factor of approximately 3, for a 20% solution, when the molecular weight changes from 100,000 to 150,000. The influence of the water content is such that gelation already takes place at room temperature when the solution contains more than 2% water. The gelation has been ascribed to the formation of crystalline nuclei in the supersaturated solutions and the influence of the factors mentioned above is in agreement with the prediction of the nucleation theory.