Eco-Friendly and pH-Responsive Nano-Starch-Based Superhydrophobic Coatings for Liquid-Food Residue Reduction and Freshness Monitoring

As a biodegradable and low-cost natural polymer, starch nanoparticles (SNPs) could be used as a substitute for nondegradable inorganic nanoparticles in many advanced materials. However, nano-starch-based superhydrophobic coatings have not yet been reported. Herein, an eco-friendly nano-starch-based superhydrophobic coating was achieved by combining SNPs with poly(dimethylsiloxane). The chemical composition, morphology, superhydrophobicity mechanism, durability, and water resistance of the coating were also investigated. The coating exhibited superhydrophobic properties (water contact angle > 152.0° and sliding angle < 9.0°) owing to the hierarchical micro- and nanostructures formed by SNP aggregates combined with the low surface energy of the PDMS covering. The excellent water resistance, self-cleaning, and liquid-food residue reduction abilities were confirmed. Then, an anthocyanin-rich extract was innovatively loaded into the SNPs to endow the coating with pH responsiveness. Consequently, a waterproof pH-sensing colorimetric coating was successfully developed without the involvement of a chemical reagent for food freshness monitoring. The coating shows great potential in developing advanced eco-friendly food-contact materials to promote the sustainable development of resources in industrial production and daily life.