Redox Optimization for Emulsion Polymer Chase: New Approach to Reduce VOCs, Cycle Time, and Cost

摘要

Reduction of residual free monomer is required in the manufacture of latexes to lower volatile organic compound (VOC) emissions. This has become even more critical as consumers are demanding coatings with reduced odor. Conventional post-polymerization chase techniques using reducing agent/oxidizer redox pairs can achieve low levels of residual monomers, but this can increase production time, add cost, and reduce production capacity. A post-polymerization redox optimization study was conducted on a production latex made with a thermal persulfate to initiate the main polymerization. The monomers used were methyl methacrylate, styrene, methacrylic acid, and butyl acrylate. Various redox combinations were tested in the post-polymerization stage at different dosage levels and feed rates to minimize redox quantity, residual monomers, and time. It was found that the right redox pair, fed simultaneously at high concentration, was capable of eliminating free monomer down to non-detectable levels in 15 minutes. This can enable up to 75% cycle time reduction for post-polymerization.