Solving the limitations for paper packaging with coating strategy

Paper-based packaging is regarded as a sustainable alternative to plastics, yet its poor resistance to water and oil has limited its applications, particularly in food packaging. Now, researchers have presented a new coating strategy that could address the challenges that currently limit its usage.

In a study published in Journal of Bioresources and Bioproducts, researchers have presented a coating strategy that integrates biodegradable components into a lignin nanoparticle-stabilised Pickering emulsion — uniting water resistance, oil repellency, biodegradability and recyclability in paper-based materials.

The new approach uses the amphiphilic nature of lignin nanoparticles to stabilise an oil-in-water emulsion composed of polyvinyl alcohol (PVA) and stearic acid (SA), forming a multifunctional coating that can enhance the water- and oil-resistance properties of the paper while remaining fully degradable and easily recyclable.

While there are other solutions that can improve barrier properties, such as fluorinated coatings or polyethylene laminates, they have can limitations such as undermined recyclability.

In this new system, PVA serves as a hydrophilic, film-forming polymer in the aqueous phase, providing mechanical reinforcement and oil resistance through a dense hydrogen-bonded network. Stearic acid, a naturally derived fatty acid, acts as the hydrophobic oil phase, imparting water repellency. Lignin nanoparticles, prepared through a solvent-exchange self-assembly process, irreversibly adsorb at the oil–water interface, stabilising the emulsion without synthetic surfactants. This Pickering emulsion design enables the uniform dispersion of hydrophobic components within a water-based coating system.

When applied to paper substrates, the emulsion forms a continuous and compact coating layer that seals surface pores and creates a synergistic barrier against both water and oil. The coated paper exhibits a water contact angle exceeding 110°, a Cobb 60 value below 18 g/m², and a Kit oil resistance rating above 9/12 — levels comparable to those of commercially used plastic-coated papers. At the same time, tensile strength and wet strength are significantly improved, allowing the paper to maintain structural integrity even after prolonged water exposure.

Beyond barrier and mechanical performance, the study places strong emphasis on end-of-life considerations. Unlike conventional plastic-coated papers, the reported coating can be removed through a simple hot-water repulping process. During recycling, PVA dissolves, stearic acid melts and disperses, and lignin nanoparticles are released, enabling clean recovery of cellulose fibres without degrading recycled paper quality. Soil burial tests further demonstrate that the coated paper fully degrades within approximately 120 days, while polyethylene films show no observable degradation under identical conditions.

Food-based applications tested

The coated paper has also demonstrated functional advantages in food preservation. Packaging tests using fruits such as bayberries, grapes and cherry tomatoes show that the coating effectively reduces moisture loss by lowering water vapour transmission, extending freshness compared with uncoated paper. These results suggest potential applications in fresh produce and food packaging, where moisture control is critical.

By combining biomass-derived materials with Pickering emulsion technology, the reported strategy provides a scalable and environmentally benign route to high-performance paper packaging. While further optimisation is needed — particularly in simplifying lignin nanoparticle production and improving gas barrier properties — the work illustrates how renewable nanomaterials can help bridge the performance gap between paper and plastics.

Image credit: iStock.com/Yulcha