Antibacterial and biodegradable keratin-based quaternary ammonium salt surfactant potential as hair care additive

Abstract

Biomass-based surfactants have excellent surface activities, showing the common characteristics of natural biomass including biocompatibility, biodegradability and non-toxicity, which are environmental-friendly and accord with the green development direction. In this study, a keratin based quaternary ammonium salt surfactant (denoted as E-K) was prepared by cationic modification of keratin with epoxypropyldodecyldimethylammonium chloride (EPDDMAC). The characterization of E-K by FTIR and the conversion rate of -NH2 in keratin confirmed the successful preparation of E-K. Subsequently, surface activity such as surface tension (γcmc) and critical micelle concentration (cmc), physicochemical properties such as HLB value, isoelectric point, foaming property and emulsifying property, as well as antibacterial activity and biodegradability were investigated. The results show that E-K possesses good surface activity, acceptable emulsifying and foaming ability. The HLB of E-K is 14-15, and it has excellent compatibility with commercial surfactants commonly used in hair care products. Particularly, E-K is a betaine zwitterionic surfactant, and its isoelectric point increases from 3.8 to 9.2 due to cationization. This means that the quaternized keratin hydrolysate is easily adsorbed on the hair surface, and makes the hair surface smoother and denser, which was proved by the adsorption test and SEM observation. Furthermore, E-K has outstanding antibacterial activity against E. coli and S. aureus, and the BOD5/CODCr value indicated that it is easily biodegradable. Therefore, the prepared biomass-based surfactant (E-K) has great potential application in hair care products and other products related to antibacterial and biodegradable surfactants.