Agglomeration and Reinforcement of Synthetic Latexes by Freezing

Abstract

Abstract For most applications rubber latexes must have high solids content. To achieve this, with reasonable fluidity, the latex particles must be large. Limitations in the kinetics of emulsion polymerization make it desirable to polymerize a small particle latex and postagglomerate to a larger size. This paper deals with the process of freezing and thawing a latex under controlled conditions which result in a substantial increase in particle size. The variables controlling the process such as soap coverage of the particles, pH, freeze duration, and freeze temperature are analyzed. The type of soap used is shown to affect the lower limit of usable freezing temperature. The polymer composition and hardness are shown to affect coagulum formation and the shape of the particles after freeze-agglomeration. Coagglomeration of a mixture of rubber and resin latexes by freezing is found to result in a reinforced polymer system analogous to that obtained by carbon black reinforcement of dry rubber. The effects of the particle size and the softening temperature of the reinforcing resin are demonstrated. An optical microscopic method for observing the freeze-agglomeration process is described and an attempt is made to elucidate the mechanism of the process.