Acylated starches of varied chain lengths: Sustainable emulsification, thickening, and physical stability in face creams.

To mitigate environmental impacts and address the sustainability challenges associated with synthetic cosmetic ingredients, developing biodegradable alternatives has become a key industry priority. In this study, acetylated starch (ACS), succinylated starch (SCS), and octenyl succinylated starch (OSAS) were prepared by controlling the acyl chain length and degree of substitution. Their performance as emulsifiers and thickeners in face cream formulations was systematically evaluated to establish structure-function relationships. The results demonstrated that all acylated starches imparted significantly enhanced rheological properties to the face creams compared to native starch. Contact angle measurements revealed that, at the same anhydride addition level, OSAS-3 exhibited the highest hydrophobicity (88.67 ± 0.45°), significantly greater than that of ACS-3 (68.80 ± 0.69°) and SCS-3 (68.25 ± 1.83°). Notably, OSAS-3 achieved this at the lowest DS (0.008), indicating that acyl chain length governs interfacial efficacy beyond DS. In face cream formulations, the OSAS-based sample showed higher storage modulus (G'), hardness (39.77 ± 0.81 g), and springiness (0.89 ± 0.01), with its overall performance exceeded that of both a traditional emulsifier and other acylated starch derivatives. This study establishes that chain-length-dependent interfacial conformation is the primary determinant of starch-based emulsifier performance in cosmetic formulations, offering both novel material candidates and a theoretical framework for the green formulation of cosmetics.