Interplay between processing and performance in chitosan-based clay nanocomposite films

Chitosan sodium montmorillonite (NaMMT) nanocomposite films, with or without addition of glycerol, are prepared by three different processing methods, i.e., solution casting, heat pressing and casting of sonicated solutions. The effect of processing is being investigated using X-ray diffraction, tensile tests, dynamic mechanical analysis, and water sorption tests. Processing plays a significant role in the hydrated crystalline structure of chitosan; however, it is less crucial for the degree of exfoliation/intercalation of NaMMT. The addition of NaMMT fillers induces substantial reinforcing effects in the chitosan/NaMMT systems with up to 160 % increase in stiffness, strength and 200 % increase in the storage modulus in comparison to the unfilled systems. Although highest stiffness and strength are achieved at different NaMMT contents for the three processing routes, the overall enhancement is similar. The addition of glycerol reduces the reinforcing efficiency of the NaMMT filler and results in plasticization by lowering the stiffness, strength, storage modulus and the glass transition temperature of chitosan (Tg). In the absence of glycerol, sonication results in nanocomposite films with higher strain at break and higher Tg values. Heat pressing results in a tremendous reduction (more than one order of magnitude) of the absorbed water in chitosan nanocomposite films without glycerol.