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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 NH2. 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.

Five chitosans with different degrees of N-acetylation (DAs), molar masses, and origins were depolymerized by nitrous acid treatment in acidic media, leading to water-soluble 2,5-anhydro-d-mannose chain end oligomers with DPn< 20. The kinetics of the reaction was studied, and the best work conditions were found to be 3 h reaction at 50 °C. It was shown that the DPnof oligomers only depends on the quantity of NaNO2involved. Molar masses or DAs do not have an impact on the depolymerization process when targeting oligomers with less than 20 units. This depolymerization process also leads to free 2,5-anhydromannofuranose (AMF) that might react with the free amines of obtained oligomers to form imines. This reaction is pH-dependent and in acidic condition leads to the formation of 5-hydromethyl-2-furfural (HMF). At the end, the oligomers were purified by dialysis to get rid of most of the free AMF (<5%) and other residual salts and appeared to have no acute toxicity.