Clear and Transparent Methyl Ester Sulphonate Micellar Systems for Mild Hair Shampoo Applications

"Methyl ester sulphonates (MES), which are produced from renewable vegetable oil-based materials and have an ISO 16128 natural origin index of 0.84, are promising new surfactants for conditioning hair shampoos. Previous studies have shown that MES has low skin irritation potential (i.e., mild to the skin), provides easier deposition of conditioning agents compared to sodium lauryl ether sulphate (SLES), and readily delivers desired rheology profiles. A drawback of MES is that it has poor solubility at low temperatures. The Krafft temperatures (TK) of MES-C16 and MES-C18 are 28 °C and 41 °C, respectively, which can be lowered substantially by using eutectic mixtures of MES-C16 and MES-C18; for example, MES-C16/C18 (3:1, w/w) has a TK of 15 °C. At temperatures below 15 °C, all mixtures of MES-C16 and MES-C18 are turbid due to the formation of MES crystals, and phase separation could occur during long-term storage. The solubility of MES could be further improved by incorporating the MES molecules into the micelles of other surfactants. In this study, the solubility of MES in pure water at 5 °C in the presence of alkyl polyglucosides (APG) was investigated. The results showed that the solubility of MES improved by > 28 times in the presence of APG at low total surfactant concentrations and predicts that at higher total surfactant concentrations, solutions of MES and APG will remain transparent at 5 °C when the weight fraction of MES-C16, MES-C18, MES-C16/C18 (80:20), and MES-C16/C18 (60:40) are below 28 %, 15 %, 35 %, and 38 %, respectively. Predictions for MES-C16/C18 (80:20) and MES-C16/C18 (60:40) were verified using 25 % total surfactant concentration and storage at 5 °C for 12 weeks. MES/APG-based surfactant systems have promising potential in hair shampoo applications, because both surfactants have low skin irritation potentials and are produced from renewable raw materials."