Tailoring recycled paper structure through mechanical refining to optimize polysaccharide-stabilized beeswax barrier...

The development of sustainable packaging requires improving the barrier properties of renewable materials like paper, which inherently lacks gas and moisture resistance. This work investigates how engineering paper's physical structure through mechanical refining can enhance the performance of a novel bio-based coating. Recycled fiber pulps were refined to different intensities to obtain handsheets with varied porosity, which were then coated with a beeswax-in-water Pickering emulsion stabilized by TEMPO-oxidized cellulose nanofibers. Two application rods were used to control coating thickness. Refining was identified as a critical factor governing coating-substrate interaction. Microscopic analysis showed that on less-refined, porous paper, the coating penetrated deeply into the fiber matrix, whereas on highly refined, denser paper, reduced porosity promoted coating hold-out, forming a more uniform and continuous film. This improved film formation led to major barrier enhancements. The optimal combination of high refining and thicker coating yielded up to 94% reduction in water vapor transmission rate, a > 90% decrease in air permeability, and an increase in water contact angle to 110°. Grease resistance also improved, reaching a Kit rating of 10. These findings demonstrate that co-designing paper structure and coating is crucial for developing high-performance, functional, and sustainable packaging materials.