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The demand for antimicrobial textiles is rapidly growing particularly in medical sector. In an effort to develop a simple and efficient antimicrobial treatment for cotton, layer-bylayer deposition of chitosan and magnesium lignosulfonate, followed by in situ synthesis of silver (Ag) nanoparticles, was accomplished. Lignin is exploited as a natural reducing and stabilizing agent1,2, producing Ag nanoparticles in amounts even larger than those obtained with sodium borohydride as a strong reducing agent. The influence of the number of bilayers (4 and 12) and initial concentration of AgNO3 solution (10 and 20 mM) on antimicrobial activity of cotton fabric against Gram-negative bacteria E. coli, Gram-positive bacteria S. aureus, and C. albicans, yeast was examined. The presence of evenly scattered Ag nanoparticles all over the fiber surface is confirmed by FESEM analysis (Figure 1). The number of bilayers does not affect the size of nanoparticles (~56 nm), but an increase of bilayers results in greater Ag content. The samples treated with 20 mM AgNO3 solution contain more Ag than those treated with 10 mM solution. The formation of metallic Ag nanoparticles is confirmed by XPS analysis. Synthesized Ag nanoparticles provide excellent antibacterial activity against bacteria S. aureus (99.9 %), independent of the initial concentration of AgNO3 and number of bilayers. Larger content of Ag nanoparticles i.e., higher initial concentration of AgNO3 solution leads to considerably enhanced antibacterial activity against E. coli. A similar trend is evident with the C. albicans yeast, but the desired yeast reduction of 99 % was not obtained.

Poor antimicrobial activity and lack of protection against UV irradiation are weaknesses of cottontextiles. 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 UVprotective macromolecule and natural reducing and stabilizing agent, allowing formation of Ag NPs. Fourbilayers of this coating is sufficient for fabrication of a chitosan/lignin/Ag-NP textile nanocompositetreatment 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-bilayercoating, 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 sufficientantimicrobial activity independent of an added reducing agent. This treatment exhibits no inhibition ofhuman keratinocyte cells growth on the skin, indicating low cytotoxicity.

Creating multifunctional textiles using chemicals from renewable sources is challenging. In an effort to develop a sustainable and efficient multifunctional cotton treatment, a lignin-based multilayer nanocoating comprising magnesium lignosulfonate, chitosan, and monoammonium phosphate (MAP) was deposited using layer-by-layer assembly. A five bilayer coating adds 15.5 wt % to cotton and imparts fire extinguishing behavior and excellent UV and antimicrobial protection to the fabric. Just a two bilayer coating imparts sufficient self-extinguishing behavior to pass the standard vertical flame test. The combined influence of lignin as a char-forming and UV-protective macromolecule, chitosan as a char-forming biopolymer, and MAP acting as an antimicrobial agent (and a blowing agent and an acid source in an intumescent flame retardant system) results in a very powerful multifunctional textile treatment with very few layers of deposition.