Towards flame retardant cotton fabrics by atmospheric pressure plasma-induced graft polymerization: Synthesis and application of novel phosphoramidate monomers

The synthesis of two novel phosphoramidate flame retardant monomers for application to cotton textiles using atmospheric pressure dielectric barrier discharge (DBD) plasma was achieved and the molecular structures were characterized using +ESI-MS and FT-IR. The effects of plasma exposure time, monomer concentration, crosslinker chemistry, crosslinker concentration and photoinitiator concentration on grafting yield were investigated and the process was optimized for highest grafting yield. SEM images of the treated fabrics showed a grafted polymer layer covalently bonded to the polymer structure of cotton that survived a lengthy extraction process to remove ungrafted homopolymer and/or unreacted monomer. Thermogravimetric analysis showed that fabrics treated with the monomers demonstrated an increased thermal stability relative to untreated cotton. Vertical burn testing demonstrated the effectiveness of the grafted phosphorus-containing polymer at promoting char formation even though the fabrics were not self-extinguishing. Measurement of the amount of phosphorus present on the treated samples confirmed that the add-on using this application strategy was too low for self-extinguishing properties, but the rest of the evidence suggested that these cornpounds have the potential for use in generating flame retardant cotton substrates provided that a more suitable application strategy is developed to further improve grafting yield. (C) 2012 Elsevier B.V. All rights reserved.