Synthesis and characterization of chitosan-based 'comb-like' zwitterionic surfactants

Low-cost surfactants are of great importance for many applications. Chitosan is one of the abundant promising candidates as a raw material for low-cost surfactants. However, how to tune the molecular structure to achieve high solubility, low surface tension, and good foam stability is a great challenge. Herein, the 'comb-like' zwitterionic polymer surfactant based on chitosan by partial N-alkylation and quaternization was prepared. The experimental results demonstrate that the length and degree of substitution of the alkyl chain have a significant influence on the properties of the products. Such comb-type zwitterionic polymer surfactants have good water solubility, and the water solubility can reach up to 85 g/L. Surface tension and foam performance tests reveal that such 'comb-like' zwitterionic polymer surfactants have excellent surface activity and good foam stability, especially for the products with a degree of substitution of 20%; their surface tension can be as low as 27.1 mN/m, and the foam stability can be improved by 59.32%.