DRYING BEHAVIOR OF ACRYLIC LATEXES

The drying behavior of a series of monodisperse acrylate-based emulsion polymers was studied with respect to two existing drying models. The latexes were all film forming poly(methyl methacrylate-co-butyl acrylate)-based materials, having different polymer morphologies. Crosslinks were introduced via the addition of ethylene glycol dimethacrylate comonomer to the emulsion synthesis, while the molecular weight was reduced by addition of CBr4 chain transfer agent. Weight loss experiments showed no discernible differences in the drying behavior of the various latexes, but environmental scanning electron microscopy (ESEM) indicated marked differences. It was found that a percolation model developed by Croll describes the drying process well. However, certain experimental observations were not consistent with theory. ESEM revealed that the most 'fusible' of the latexes formed a skin during drying, prior to the complete evaporation of the water. It was postulated that the skin remained sufficiently porous to allow unhindered water flux.