Control of structural viscosity and liquid separation stability of fabric softener by using nonionic surfactants and associative thickeners

Many fabric softeners on the market are given structural viscosity to stabilize the dispersion of functional particles. One example of techniques for imparting structural viscosity is depletion flocculation. The depletion effect caused by the coexistence of cationic vesicles (large particles) and small particles such as polymers and nonionic surfactant’s micelles that do not adsorb on the vesicles in the fabric softener causes the vesicles to aggregate (depletion flocculation) and form a network structure, resulting in the development of structural viscosity. Balance of particle size and concentration is important for depletion flocculation to occur. In past studies, it was found that if the concentration of the ingredient is increased too much, the formulation separates into the vesicle network phase and the bulk phase. Thus it is difficult to achieve both dispersion stability of functional particles and liquid separation stability by adjusting the concentration of the ingredient alone. Furthermore, the fact that vesicle size varies depending on the type of fragrance present in the vesicle also contributes to the difficulty in controlling depletion flocculation.
As a result of our study to solve this problem, we succeeded in suppressing liquid separation while maintaining stable dispersion of functional particles during long-term storage of the formulation by combining nonionic surfactants and a small amount of associative thickeners (polymers). Formulations using a combination of nonionic surfactants and polymers were found to exhibit structural viscosity while maintaining a robust vesicle network due to depletion flocculation, as evidenced by rheology analysis and optical microscopy observations. It became clear that this composition also demonstrated excellent stability in samples containing different types of fragrances prepared under the same conditions.