Food-grade shellac/AKD synergy creates nanoparticle-free superhydrophobic paper for sustainable food packaging

Abstract

The urgent global shift toward replacing single-use plastics in food packaging requires high-performance hydrophobic substrates that ensure both environmental sustainability and compatibility with industrial converting lines. This study presents a nanoparticle-free and fluorine-free strategy for fabricating superhydrophobic paper utilizing exclusively Generally Recognized as Safe (GRAS) additives—shellac and alkyl-ketene dimer (AKD)—in conjunction with the intrinsic micrometer-scale roughness of commercial kraft paper. By optimizing a 25 vol% shellac loading relative to the AKD emulsion, a hierarchical micro/nano-textured film was formed via spontaneous phase separation and covalently grafted to cellulose through β-ketoester linkages using a single wire-rod pass. The resulting paper attained a static water contact angle of 155.3°, a sliding angle of 4.74°, and a surface free energy of 2.50 mJ/m², comfortably exceeding the superhydrophobic threshold. Water absorption was reduced by 87.8% (to 3.2 g/m²), while the mechanical integrity remained largely on par with the base paper. The surface demonstrated exceptional self-cleaning performance, resistance to staining from diverse aqueous media, and robust durability against thermal stress (up to 120 ℃), mechanical abrasion, and 12-month environmental aging. Free from fluorinated moieties and inorganic nanofillers, this material is fully recyclable and compliant with food-contact regulations. The integration of green chemistry with high-throughput manufacturability offers a practicable platform for scalable, plastic-free food packaging within a circular economy framework.