Direct miniemulsification of Kraton rubber/styrene solution. I. Effect of Manton-Gaulin homogenizer, sonifier, and membrane filtration

A direct miniemulsification process was utilized to prepare an artificial latex from a Kraton(R) D1102 thermoplastic elastomer. The Kraton rubber was dissolved in a styrene monomer and emulsified in an aqueous surfactant solution in the presence of a costabilizer using a sonifier, a Manton-Gaulin homogenizer, and membrane filtration. Each miniemulsion droplet contained 20 wt % Kraton rubber in styrene, and, thus, the Kraton rubber particle size and size distribution can be used to estimate the droplet size and size distribution of the miniemulsion. It was found that Kraton rubber particles obtained using the Manton-Gaulin homogenizer had an extremely broad size distribution ranging from 20 nm to 2 mum. The use of a cetyl alcohol costabilizer produced Kraton rubber particles with a narrower size distribution by lowering the interfacial tension between the oil and aqueous phases, compared to the use of hexadecane as a costabilizer. The broad size distribution of the Kraton rubber particles could be narrowed by employing a membrane-filtration technique. However, small miniemulsion droplets remained undisturbed in the miniemulsion since they easily passed through the pores of the filter. These small droplets resulted from the sonification process conducted prior to the use of the membrane-filtration process. The Kraton rubber particle-size distribution became narrow with an increase in the sonifier duty cycle due to the viscoelastic behavior of the oil phase. (C) 2003 Wiley Periodicals, Inc.