Enhancement of Bagasse Paper Properties for Sustainable Packaging via Bentonite and Alginate Loading in Shellac coatings

This study addresses a key limitation in sustainable packaging; the inadequate mechanical strength and barrier properties of unmodified paper-based materials, particularly those made from agricultural residues like bagasse. Although natural biopolymers such as shellac, alginate, and bentonite have shown individual promise in improving paper properties, their combined effects and potential synergistic interactions remain underexplored. Here, we investigate how incorporating bentonite and alginate into a shellac matrix improves the mechanical, hydrophobic, and air-barrier characteristics of bagasse paper sheets. Three composite formulations were prepared; the first by mixing a 2% alginate solution with 1-5% shellac; the second by mixing a 1% bentonite solution with 0.5-3.5% shellac; and the third by combining 1% bentonite with 2% alginate and 1-5% shellac. These formulations were applied to bagasse paper via a simple dip-coat and oven-dry protocol. Scanning Electron Microscopy (SEM) confirmed the formation of a uniform, continuous macromolecular network that facilitated enhanced surface coverage and cohesion. Results revealed that the addition of alginate and bentonite significantly improved both mechanical and barrier properties. For instance, a 2% shellac formulation when combined with 2% alginate or with a 2% alginate/1% bentonite mixture, eliminated air permeability and doubled the burst strength. These enhancements are attributed to increased hydrogen bonding and ionic interactions among the components, which enhance composite density and structural integrity. The most effective formulation (2% alginate + 3% shellac) improved tensile strength by 129% and elongation by 103%, demonstrating a desirable balance of rigidity and flexibility. Consequently, the modified bagasse paper sheets exhibit superior tensile strength, reduced air permeability, improved water vapor permeability (WVP), enhanced thermal stability, and increased biological activity compared to untreated sheets, single-component (shellac-only) and binary (shellac-alginate or shellac-bentonite) systems previously reported. These findings introduce a novel ternary shellac/alginate/bentonite bio-based composite coating system that significantly enhances the functional performance of bagasse paper. This system represents a viable, eco-friendly solution for sustainable packaging applications requiring moisture resistance, mechanical durability, and biodegradability.