Aqueous PHA Solution-Based Knife Coatings: A Sustainable Approach to the Production of Coated Cotton Fabrics

Footwear is traditionally manufactured using non-biodegradable polymers and leather, raising well-documented environmental and health concerns related to their production and disposal. This study explores polyhydroxyalkanoates (PHAs) as sustainable alter-natives for bio-based footwear components. A stable aqueous suspension of PHBHHx was successfully formulated and applied to cotton fabrics via knife-coating. Various formulations, with and without additives and employing natural or synthetic thicken-ers, were evaluated in terms of surface morphology, wettability, permeability, and du-rability. The 10% PHBHHx formulation provided the best balance between material ef-ficiency, coating uniformity, and surface performance. Additives and thermal treatment both influenced wettability, reducing contact angles and enhancing water vapor per-meability. Notably, coatings with additives and hot pressing exhibited the highest permeability (68.0 ± 3.1 L/m²/s; 651.0 ± 5.4 g/m²/24 h), while additive-free, non-pressed coatings showed significantly lower values (19.5 ± 4.4 L/m²/s; 245.6 ± 66.2 g/m²/24 h), likely due to excessive compaction. Abrasion resistance remained excellent across all samples, especially with thermal treatment, withstanding 51,200 cycles. Washing re-sistance results revealed a synergistic effect between additives and heat, promoting long-term hydrophobicity and coating adhesion. Overall, PHBHHx coatings demon-strated potential to enhance water resistance while maintaining breathability, repre-senting a sustainable and effective solution for functional and technical footwear applications.