Antimicrobial and UV protective chitosan/lignin multilayer nanocoating with immobilized silver nanoparticles

Poor antimicrobial activity and lack of protection against UV irradiation are weaknesses of cotton textiles. In an attempt to impart superior antimicrobial and UV-protective properties to cotton, layer-by-layer deposition of chitosan and magnesium lignosulfonate, and in situ synthesis of silver (Ag) nanoparticles (NPs), was performed. Lignin, in a chitosan/lignin multilayer, simultaneously acts as a UV protective macromolecule and natural reducing and stabilizing agent, allowing formation of Ag NPs. Four bilayers of this coating is sufficient for fabrication of a chitosan/lignin/Ag-NP textile nanocomposite treatment with 50+ UV protection. 100% reduction of Gram-negative bacteria Escherichia coli, gram-positive bacteria Staphylococcus aureus, and yeast Candida albicans can be achieved with a 12-bilayer coating, when 20 mM silver nitrate solution and sodium borohydride are applied. On the other hand, four bilayers impregnated with Ag NPs, using 10 mM silver nitrate solution, provides sufficient antimicrobial activity independent of an added reducing agent. This treatment exhibits no inhibition of human keratinocyte cells growth on the skin, indicating low cytotoxicity.