Online conductivity and stability in the emulsion polymerization of n-butyl methacrylate: Batch versus semibatch systems

Abstract

A homemade resistance probe (R) and a torroidal probe (T), which work on different principles to measure conductivity, were used as online sensors to monitor conductivity during the course of emulsion polymerizations of n-butyl methacrylate (BMA). Six batch emulsion polymerizations of BMA (20% solids content) were carried out using sodium lauryl sulfate (SLS) as surfactant. To compare latex stability and conductivity profiles, the SLS concentration was varied (5, 6, 8, 10, 20, and 30 mM). Seven semibatch emulsion polymerizations of BMA (40% solids content) were also run. All semibatch polymerizations had the same seed stage, while different amounts of SLS were fed during the feed stage. During these reactions, the conductivity curves obtained from the two different probes overlapped if the SLS concentration was high enough (20 and 30 mM); on the other hand, the two curves diverged if the SLS concentration was low. Since the final conductivity values obtained from the two probes were not the same in most of the reactions, the ratio between them (R/T) was used to correlate conductivity to latex stability. A blender test and turbidity measurements were carried out to estimate the mechanical stability and the electrolyte stability of the prepared latexes, respectively. The results showed that R/T varied linearly with the latex stability. These results showed that latex stability could be predicted through online conductivity measurements. Moreover, the reason for an observed increase in conductivity during these emulsion polymerization reactions was also investigated. This increase was related to the disappearance of monomer droplets, which demonstrated that the conductivity measurements could also be used to aid in the study the kinetics of the emulsion polymerization process. Copyright © 2013 Wiley Periodicals, Inc.