Improvement in ductility of chitosan through blending and copolymerization with PEG: FTIR investigation of molecular interactions

Chitosan is an important biomaterial used widely in medical applications. One of the key concerns about its use is the fragile nature of chitosan films. By comparing the component molecular interactions using FTIR, this study attempts to understand how the ductility of chitosan can be improved by blending and copolymerizing with poly(ethylene glycol) (PEG). An improvement in ductility was obtained for all compositions of blend as manifested by a decrease in modulus and an increase in strain at break. For comparable PEG composition (∼30%), the properties of the solution-cast blend were better than those of the grafted copolymer. Therefore, blending may be a more efficient way to improve ductility of chitosan. FTIR characterization of the materials revealed subtle decreases in molecular interactions upon annealing the partially miscible blend. These may not be apparent in DSC or X-ray diffraction, yet they play a key role in the mechanical behavior. It appears that in the case of the graft copolymer the improvement in the properties comes from suppression of the crystallinity of each component and not from component interactions. On the other hand, in the blend, the improvement appears to come predominantly from the "well-dispersed", "kinetically trapped" phase morphology and from the intermolecular interactions. Therefore, annealing the blend leads to decreased intermolecular interactions, phase coarsening, and deterioration in properties.