Synthesis and characterization of n-alkyl chitosan for papermaking applications

Chitosan is a natural cationic polymer whose reactive amino groups and primary and secondary hydroxyl groups confer to it interesting properties for papermaking applications, such as cationic polyelectrolyte behavior and high affinity for the cellulose fiber surface. However, the main barrier to these applications of chitosan is the lack of water solubility under neutral pH of the wet-end papermaking system. This paper is aimed at obtaining and characterizing a water-soluble chitosan derivative by introducing alkyl groups along the chitosan chain, to confer to it hydrophobic nature, without affecting significantly its cationic character. The N-alkyl chitosan derivative was obtained by reductive amination, and was investigated by spectroscopic techniques (FT-IR, 1H-NMR, and MS), solubility in water and ionic charge density. The analysis demonstrated the obtaining of alkylated chitosan with a 0.03 substitution degree, completely soluble in water at room temperature, and with a cationic character in a neutral pH medium. These characteristics of N-alkyl chitosan, beside its amphiphilic nature induced by hydrophobic/hydrophilic sequences, make this polymer a very promising additive for papermaking applications.