Assessing Epoxy-Acrylate/Chitosan Films for Banknote Coatings: Thermal, Mechanical, and Gloss Performance

This study introduces a novel approach to improving the functional performance of document coatings through the development of a chitosan-modified epoxy-acrylate varnish intended for application on the specialized substrate used in banknotes. In this first phase, the work focuses exclusively on assessing the thermal, mechanical, and optical behavior of the varnish films to establish the technical feasibility of incorporating chitosan into this type of high-security coating. Chemical characterization was conducted via FTIR, while DSC and DMA were used to evaluate the thermal transitions and viscoelastic properties of the cured films at different chitosan concentrations. Gloss measurements were used to quantify the visual impact on the coating. The results reveal a systematic increase in crosslinking and stiffness with higher chitosan content, accompanied by a reduction in gloss. Formulations containing 1% and 5% chitosan emerge as the most technically viable, maintaining adequate mechanical integrity and appearance while enabling future antimicrobial enhancement. The antimicrobial properties of chitosan-based films, central to the next stage of this research, will be reported in subsequent work. This first-stage evaluation provides a solid foundation for integrating biopolymer additives into security and commercial printing technologies, advancing the development of sustainable functional coatings.