Functionalization of Chitosan Oligomers: From Aliphatic Epoxide to Cardanol-Grafted Oligomers for Oil-in-Water Emulsions

摘要

Hydrophobically modified chitooligosaccharides (COSs) were tested for suitability as an emulsifier in cationic bituminous emulsions. COSs with polymerization degrees (DPs) of 5, 10, 15, and 20 were obtained by nitrous acid deamination. A complete study on depolymerization and precise product and side product characterization was undergone. Chemical modification of COSs was performed to achieve amphiphilic structures using three fatty epoxides with a growing chain length butyl (C4), octadecyl (C9), and hexadecyl glycidyl ether (C16)). The grafting efficiency according to reaction conditions was established. Different substitution degrees (DSs) were obtained by modulating the ratio of fatty epoxy to NH_(2). It was shown that after a certain DS, the oligomers thus formed were not water-soluble anymore. At the end, cardanol glycidyl ether was grafted on DP 5, 10, and 15 COSs, cardanol being a biobased compound extracted from cashew nut shell; this reaction led to a potentially fully biobased structure. Water-soluble candidates with a higher DS were used as surfactants to emulsify motor oil as a simulation of bitumen. Cardanol–chitosan-based surfactants led to direct oil-in-water emulsion (60/40 w/w) composed of particles of 15 μm average size that were stable at least for 24 h.