ASA Emulsion Size Measurement The active ingredient of ASA is an oily monomer. The product is almost always delivered as a light amber oil that must be kept very dry until emulsi?cation. ASA is added to the process in the form of an aqueous emulsion, in which the stabilizer is usually cationic starch and a small amount of surfactant to aid in emulsi?cation. The key goals in using ASA are to avoid hydrolysis and distribute it well in the process. Hydrolysis is minimized by preparing the emulsion as late as possible, usually only seconds before the material is added to the thin stock. Particle size analysis can show whether one has achieved the desired narrow size distribution of droplets, usually with an average size near or below one micrometer. Because of the instability of the emulsion,

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