Synthesis and Surface Properties of Amino Acid Surfactants from Industrial Waste Proteins

Abstract

N-Acyl amino acid surfactants (AAS) were chemically derived from industrial waste protein hydrolysates [cottonseed (CSD), silk residue (SR), and silk chrysalis (SC)] according to two methods: (1) reacting hydrolysates with alkyl acyl chloride, followed by purification and neutralization with alcoholic sodium hydroxide; (2) reacting hydrolysate with fatty alcohols in organic solvents followed by purification. The yield of purified mixed AAS (sodium salt) was ∼60−75%; amino acid ester from glutamic acid was considerably higher (85−92%) than the sodium salt derivatives. Results indicate that as acyl chain length (i.e., C12−C18) increased, surface tension of AAS increased, critical micelle concentration (cmc) decreased, and Krafft point increased. The emulsifying power of AAS in O/W emulsion was better with n-decanol as an oil phase than liquid paraffin. The C12 derivatives of all the mixed AAS showed high foaming power. Mixed AAS from CSD exhibited the best lime soap dispersing requirement (5.7−6.5 g/100 g). The diameter of micelle increased for glutamic acid AAS (GA-AAS) and CSD-AAS as the acyl chain length increased (i.e, C12−C18). The hydrodynamic diameter of AAS followed the order SC > CSD > GA. Generally, AAS with C12 produced good surface properties. Keywords: Amino acid surfactants; synthesis; surface properties; industrial waste proteins