Sustainable Waterborne Polycaprolactone/Chitosan Coatings for Potentially Recyclable and Compostable Paper-Based Packaging

Abstract Sustainable and compostable coatings for paper-based packaging substrates represent a promising strategy to replace conventional petroleum-derived packaging materials while improving substrate performance. In this work, environmentally friendly waterborne coatings based on blends of the immiscible polymers polycaprolactone (PCL) and chitosan (CS) were developed for the first time through an emulsification–evaporation approach. The proposed methodology enabled the production of stable aqueous polymer dispersions with controlled concentrations by adjusting emulsion parameters, allowing the stabilization of coatings with high CS content despite polymers immiscibility. This approach yields formulations with adjustable PCL/CS ratios and complementary functional properties, while avoiding the use of organic solvents in the final coating system. The coatings were applied onto two paper substrates and a commercial poly(lactic acid) (PLA) film, and their barrier and surface properties of the resulting multilayer systems were comprehensively evaluated. The effects of thermal post-treatment and double coating application were also investigated. The developed coatings significantly enhanced oxygen barrier performance, achieving permeability reductions of up to 98% compared with uncoated paper substrates and 69% relative to uncoated PLA film. In addition, the surface properties of paper were markedly improved, increasing both water and oil repellency, with water contact angle values increasing from 56° to 99° and oil contact angle values from 17° to 67°. Overall, the combination of biodegradable PCL and bio-based chitosan in stable waterborne formulations provides a sustainable route for the development of high-performance coatings designed for paper-based packaging applications with potential compatibility with recyclable and compostable end-of-life scenarios.