Biobased amide surfactants derived from cellulose-waste hydroxy acids: mechanochemical synthesis, foam fractionation and performance

Abstract

A series of hydroxycarboxylic acids (HAs) with excellent hydrophilic properties are produced from alkali treatment of cellulose-containing materials. The great majority of these hydroxy acids are glucoisosaccharinic acids (GISAs), which are promising starting materials for surfactant synthesis. Amide surfactant mixtures were produced by combining these HAs with primary amines of various alkyl chain lengths, namely, 12, 16 and 18 carbons. The reactions were performed under liquid-assisted grinding (LAG) conditions, a type of mechanochemical synthesis employing small quantities of liquid, water in this case, to favour the homogenization. Yields up to 90% were achieved with the purchased GISAs and up to 85% in terms of GISA–amides using non-purified HA mixtures, regardless of the amine used. Products derived from other HAs were detected as well. The amount of water influenced the efficacy of the mechanical stimuli and, hence, the yield of the reactions. Foam fractionation was employed as an alternative purification method and was effective in enriching the surfactants up to 33% in the described setup. The resulting GISA–amides were able to lower the water surface tension below 27, 31, and 34 mN m⁻¹ for the 12-, 16- and 18-carbon alkyl chains, respectively. The surfactants were also able to form foams and emulsions. Preliminary considerations using data-fitting software and comparison with commercial surfactants (e.g., SPAN® 20, MEGA-12, and MEGA 14) showed excellent potential in terms of possible applications and biodegradability.