The effect of combined atmospheric plasma/UV treatments on improving the durability of organophosphorus flame retardants applied to polyester fabrics

Following application of three commercially available, flame retardants (FR) to polyester and exposure to an atmospheric plasma in the presence or absence of simultaneous UV 308nm excimer laser radiation, the retentions to a 30 min 40°C water-soak for the mono- and dimeric cyclophosphonate (PE-CONC and PCO 900 respectively) and a 30 min methanol- soak treatment for the resorcinol bis(diphenyl phosphate) (RDP) agents were generally enhanced with respect to unexposed controls. These results suggested that the formation of PET-FR bonding had occurred as a consequence of plasma/UV exposure. The effect of plasma/UV process sequence (pre-exposure and/or post exposure with respect to FR impregnation) as well as plasma gas type, showed that maximum post-soaking FR retentions occurred when both pre- and post-exposure conditions operated. Plasma/UV exposed fabrics both before and after soaking treatments were examined for morphological changes by SEM and surface phosphorus retention by EDX, FTIR-ATR, XPS as well as TGA/DTG/DTA, each of which showed evidence on the surface of changes in surface topography, increased phosphorus levels and modified thermal behaviour. When subjected to vertical fabric strip flammability testing, these changes were insufficient to generate significant changes in the burning rate apart from in post-methanol soaked, RDP-containing fabrics where almost all plasma/UV process sequences reduced specimen burning rates. During all experiments, the presence or absence of the UV laser radiation appeared to have no obvious effect on post-soaking FR retentions, suggesting that its presence is not required since plasma activation alone appears to be the key to improving PET-FR bonding.