Sustainable Hydrophobic Coatings Enabled by Aqueous Dispersions of Birch Bark Suberin Hydrolysates and Hemicellulose-derived Latex Binders with High Biomass Content

The development of high-performance barrier coatings is critical for the transition toward sustainable packaging. In this study, softwood galactoglucomannan was utilised to synthesise sustainable latex binders, with GGM content increased from 50% to 90%, thereby reducing the synthetic lauryl acrylate component to 10%. When employed as a binder for suberin dispersions, the systems demonstrated improved colloidal stability with Turbiscan Stability Index values below 2. The resulting coatings imparted a hydrophobic character to paperboard substrates, achieving water contact angles exceeding 90°. Functional barrier testing revealed improved properties, including a 95% reduction in n-heptane permeability relative to the base paper and sustained grease resistance for more than 7 days. While water vapour transmission rate values as low as 9 g/m²·day were recorded at standard conditions (23 °C, 50 % RH), performance was compromised under tropical conditions with elevated temperature and humidity. Under high relative humidity, the suberin based composite coatings showed increased vapour transport, indicating humidity dependent barrier behaviour even though suberin is intrinsically hydrophobic. Notably, the small performance gap between the 50% and 90% modified GGM formulation underscores the efficiency of hemicellulose-based binders. These findings provide a viable pathway for utilising forest-derived industrial side streams to formulate high-performance barrier coatings.