Production of oil-containing polyterephthalamide microcapsules by interfacial polymerization. An experimental investigation of the effect of process variables on the microcapsule size distribution

Oil-containing polyterephthalamide microcapsules were prepared by the interfacial polymerization technique. The inner phase of the microcapsules consisted of a mixture of an organic solvent, toluene, and a commercial oil, santosol. Microcapsules with mean Sauter diameters in the range 0.5–20 μm were prepared by varying the rate of agitation (2000–7000 rpm) and the concentration of a poly(vinyl alcohol) stabilizer (0.1–1.0wt% w/v), in the presence of several ionic and non-ionic cosurfactants. High agitation rates resulted in a significant reduction of the mean size of the oil droplets, although a slight increase in the breadth of the droplet size distribution was observed. High concentrations of PVA also resulted in a decrease of the microcapsule size, although the effect of stabilizer concentration was generally less important than that of the agitation speed. Finally, the effect of various ionic and non-ionic cosurfactants on the microcapsule size distribution was investigated. It was found that the addition of a cosurfactant significantly reduced the mean droplet size of the initial emulsion, leading to the formation of microcapsules in the submicron range.