Influence of plasticiser type and nanoclay on the properties of chitosan-based materials

Chitosan, a biocompatible polysaccharide having antimicrobial efficacy, is highly useful for biomedical and other applications. How chitosan properties can be tailored continues to attract intense research interest. Herein, chitosan and chitosan/carboxymethyl cellulose (CMC) materials filled with montmorillonite (MMT) were thermomechanically processed resulting in excellent nanoclay dispersion. Inclusion of MMT significantly increased molecular relaxation temperatures, tensile mechanical properties, and film surface hydrophobicity. When plasticisers such as 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]) or glycerol were introduced, the effect of MMT on the biopolymer properties largely depends on whether the MMT alters plasticiser–biopolymer interactions. [C₂mim][OAc]-plasticised chitosan exhibited a relatively high contact angle (100 ± 7°) similar to the un-plasticised chitosan/MMT material, derived from the strong hydrogen-bonding capability of [C₂mim][OAc]. Polyelectrolyte complexation (PEC) allowed the glycerol-plasticised chitosan/CMC material to have a hydrophobic surface (contact angle: 90 ± 6°) similar to that of the un-plasticised chitosan/CMC/MMT material. Specifically, further inclusion of MMT interrupted biopolymer–plasticiser interactions, leading to increased surface wettability. However, while addition of [C₂mim][OAc] resulted in reduced hydrophilicity of the chitosan/CMC matrix, addition of MMT counteracted this effect by interacting with the IL. This work shows the plasticisers and MMT influence surface hydrophilicity mainly by determining the availability of free biopolymer polar groups.