Antibacterial chitosan-based blends with ethylene–vinyl alcohol copolymer

This study reports for the first time about the formulation, morphology, water barrier and the antimicrobial activity of high and low molecular weight chitosonium-acetate based solvent-cast blends with ethylene–vinyl alcohol (EVOH) copolymers. The blends based on the low molecular weight chitosan grade showed enhanced phase morphology, transparency, enhanced water barrier properties, up to 86% water permeability reduction compared to pure chitosonium-acetate films, as well as excellent antimicrobial activity. When the fraction of low molecular weight chitosan exceeded the phase inversion in the blend, phase segregation became noticeable but good interfacial adhesion was still observed. On the other hand, the blends with the high molecular weight chitosan grade were translucent, even when this component was in the dispersed phase, and exhibited clearly separated phase morphology but also presented antimicrobial performance. In both cases, and in accordance with previous works in our laboratory, the release from the blends of protonated glucosamine groups (so-called active species) correlated well with the antimicrobial phenomenology of the developed materials. The study also showed that EVOH copolymers can also be made antimicrobial by a water sorption-induced release mechanism, if acetic acid is incorporated into the polymer formulation before casting from solution. On the overall, antimicrobial chitosan-based blends with EVOH copolymers, when low molecular weight chitosan was used as the dispersed phase in the blend, exhibited optimum performance in terms of optical properties, water resistance, enhanced water barrier and, therefore, excellent application outlook in antimicrobial applications.