Biomimetic water-mediated nanosilica-zinc hydroxide-polyvinyl alcohol hydrogels for antimicrobial coatings on polylactide and cellulose substrates.

Conventional powder of silica nanoparticles has the issue of hard agglomeration that limits nanoscale properties in waterborne paint and coating applications. To prevent the hard agglomeration, silica nanoparticles can be separated and mediated by water layers, which is biomimetic to hydration layers on biological structures. In this research, dry nanosilica powder (SP) and water-mediated nanosilica hydrogel (SH) are synthesized from potassium silicate precursor for characterizations and comparisons. While dry SP contains stacked nanoparticles with bigger particle sizes, SH showed separate and smaller silica nanoparticles, leading to better dispersibility in water and ethanol solvents for subsequent preparations of waterborne paints. The aqueous syntheses of novel nanosilica-zinc hydroxide (SH-ZH) and nanosilica-zinc hydroxide-polyvinyl alcohol (SH-ZH-PVA) hydrogels were conducted using energy-saving agitation. It is found that the SH-ZH-PVA formulation of 75% SH-ZH and 25% PVA resulted in uniform nanostructured coatings on polylactide (PLA) and cellulose (Cel) substrates. SH-ZH-PVA-coated PLA films (SH-ZH-PVA/PLA) presented potent antibacterial activity, coating stability in aqueous environments and good tensile properties. SH-ZH-PVA-coated Cel papers (SH-ZH-PVA/Cel) showed the significant increases of 398.93% in specific surface area, 141.17% in tensile strength, 19.25% in elastic modulus, 44.32% in elongation and 364.9% in tensile energy in comparison with pristine cellulose papers. Biomimetic to zinc phytochemical systems in plants, SH-ZH-PVA paints and coatings release Zn2+cations for antimicrobial function. In general, water-mediated SH hydrogel provides the advantages of separate nanoparticles and aqueous dispersibility for synthesizing antibacterial SH-ZH and SH-ZH-PVA hydrogels for multifunctional coatings on various substrates.