Synthesis and Properties of Amino Acid Surfactants Based on Waste Hair

ABSTRACT

Sustainable surfactants derived from renewable and low‐cost feedstocks are increasingly demanded to reduce environmental burden. Herein, waste human hair was valorized as a keratin source for the production of an oleoyl hydrolyzed keratin surfactant (OHKS). The keratin was first hydrolyzed under alkaline conditions to obtain a mixture of amino acids, which was then N‐acylated with oleoyl chloride to afford OHKS. FT‐IR and ¹ H NMR provided evidence supporting amide bond formation and oleoyl incorporation. OHKS is a hydrolysate‐derived, compositionally distributed mixture rather than a single defined compound. As a hydrolysate‐derived mixture, OHKS still delivered surface activity comparable to sodium dodecyl sulfate and sodium lauryl sulfate, with a critical micelle concentration of 0.4 g·L ⁻¹ and a surface tension at CMC of 27.6 mN·m ⁻¹ , while exhibiting markedly improved mildness, with irritation indices of 1.42, 4.43, and 4.75 for OHKS, sodium dodecyl sulfate (SDS), and sodium lauryl sulfate (SLS), respectively. This study suggests a feasible and value‐adding route to convert keratin‐rich waste into a functional surfactant, highlighting the potential of waste protein valorization in advancing sustainable surfactant development and circular bioeconomy strategies.