Mass Transfer in Emulsion Polymerization: High Solids Content Latex and Mixing Effects

The impact of different agitator configurations used during the emulsion polymerization of vinylidene fluoride (VDF) was studied with the goal of achieving a solids content of 55 wt % while minimizing particle coagulation and maintaining low levels of surfactant. The design and number of impellers, their spacing and the agitation speed were shown to have a strong influence on the transfer of gaseous monomer to the aqueous phase, and thus the rate of polymerization. Increasing the number of impellers on the central shaft, and decreasing the spacing of the impellers close to the latex surface had a strong influence on the ability to incorporate gaseous monomer, so the solids content and the latex level in the reactor increased. Furthermore, it was found that changes in the agitation rate during the reaction was necessary at high solids content to avoid destabilizing the particles in view of the low surfactant concentrations used.