Durable Flame Retardant and Antimicrobial Nano-Finishing

Abstract

Due to the costs associated with processing, materials, and the inherent difficulties in applying durable flame retardant and/or antimicrobial finishes, alternatives to conventional finishing methodologies are one of the focal points in today’s textile research and industry. We, therefore, propose a new nano-finishing, involving the use of conventional flame retardants, titanium dioxide (TiO2) nanoparticles, and multifunctional silanes, to replace conventional methodologies as this new finishing combines the functionality of flame retardant and antimicrobial performance, each feeding off of the synergistic properties of the other. In this work, 100% cotton and 80/20 polyester/cotton fabrics were treated with a combination of Degussa P25 TiO2 nanoparticles, tetrakis(hydroxymethyl)phosphonium chloride and urea flame retardants, and silane cross-linkers (such as tetraethoxysilane). These fabrics were prepared using a conventional pad-dry-cure laboratory-scale methodology. Following the coating process, fabrics were evaluated for flame retardant performance through the use of a vertical flame chamber. Fabrics were also evaluated for antimicrobial performance under varying light conditions (i.e. ultraviolet, visible, and no light) at Aerobiology Labs in Dulles, VA. Fabrics showing most flame resistant promise were further investigated for finish durability by flame retardant testing following a series of 5 washing and drying cycles. These laundered fabrics received further flame retardant evaluation in the flame chamber and also ICP elemental analysis comparing active ingredient concentrations on the fabrics pre and post-laundering. Results of this work show that without the addition of TiO2, THPC and urea were unsuccessful in imparting flame retardant properties on 80/20 polyester/cotton blended fabrics. However, flame retardant properties of both 100% cotton fabrics and 80/20 polyester/cotton fabrics are enhanced as add-on of titanium dioxide nanoparticles increase, specifically when using the silane cross-linker tetraethoxysilane (TEOS). Properties that were enhanced include char length as well as length of ignition. As on-weight-of-bath percentage of TiO2 increased to levels of 6% and above, all poly/cotton fabrics self-extinguished. Similar results were observed on 100% cotton fabrics. This, in fact, does show that TiO2 possesses synergistic effects with the phosphorus-based, condensed phase flame retardant, THPC + urea. Flame retardant performance levels following the laundering process were much more variable. In the case of the 100% cotton fabrics, some flame retardant property enhancements were noted, however poly/cotton fabrics showed no improvement over the control. Antimicrobial properties of un-treated poly/cotton fabrics were compared to fabrics treated with only THPC + Urea flame retardants and a combination of THPC + Urea + TiO2. Un-treated poly/cotton fabrics had no resistance to bacteria as each sample exhibited colony growth after 24 hours of incubation. THPC proved to be antimicrobially active against gram positive S. aureus under no light and active against gram negative K. pneumoniae under no light, visible light, and UV light. THPC + Urea + TiO2 proved to be antimicrobially active against both gram positive S. aureus and gram negative K. pneumoniae under no light, visible light, and UV light. This shows that both THPC + Urea and THPC + Urea + TiO2 have antimicrobial efficacy, however, the efficacy of THPC + Urea + TiO2 has higher overall efficacy than THPC + Urea as it is able to effectively eliminate both S. aureus and K. pneumoniae at all conditions. It is suggested that in future works, further attempts are needed to increase durability of flame retardant and antimicrobial coatings to the abrasive forces of laundering. Other cross-linkers, flame retardants, and application methodologies should be investigated.