Dispersion granulation method leveraging pH responsiveness of monoalkyl sulfosuccinate.

: Monoalkyl sulfosuccinate is an anionic surfactant having two types of hydrophilic groups in one molecule, carboxylic acid group and sulfonic acid group, resulting in three ionization states depending on its pH. In state I, both carboxylic acid and sulfonic acid groups are not ionized; in state II, only sulfonic acid group is ionized; and in state III, both carboxylic acid and sulfonic acid groups are ionized. The ionization state affects the hydrophile-lipophile balance (HLB) of the surfactant, an index of the distribution coefficient of water/oil ratio of the surfactant. The decrease in HLB promotes the adsorption of the surfactant to the oil/water interface and improves the interface activity. State II has high emulsifying property for high interface activity but low water solubility. In contrast, state III has low emulsifying property for low interface activity but high water solubility. We applied the pH responsiveness of monoalkyl sulfosuccinate to the dispersion granulation method to change the state from II to III in a mild range of pH (weak acidity and weak alkalinity). Consequently, we successfully developed a novel dispersion granulation method that decreased the amount of surfactant needed for emulsifying resin solution by employing state II for its high emulsifying property, and we also reduced the amount of surfactant remaining on resin particles after the washing process by employing state III for its high water solubility.