Chemical flame retardation mechanisms of viscose-polyester fabrics: Dissertation

Systematic investigation of structurally identical modalpolyester and viscosepolyester blended light-weight fabrics was carried out in order to developing a chemical basis for effective flame retardant products.Normal and two different types of flame retardant polyesters were used in the blends, which were subjected to various chemical aftertreatments.The blends of mainly 50/50 and 65/35 of cellulosic polyester were also prepared from the yarns containing a small amount of cotton type PVC-fibre.The oxygen indices and elementary contents of phosphorus, nitrogen, sulphur, chlorine and bromine were used in efficiency and synergy evaluations.NMPPA and pyrophosphate-DMDHEU showed the highest P-N synergy and efficiency for viscose and modal fabrics based on the dominance of gas phase flame retardant mechanism.PETP reacted slightly with DP and FR chemicals showing no or minor effectiveness compared with inherently flame retarded fibres.No simple mathematical correlation between the oxygen index increase (up to 26-27 %) of FR MD-PETP fabrics and the contents of elements was found.Phosphorus-nitrogen synergy was observed with NMPPA and pyrophosphate-DMDHEU flame retardants when used with phosphinic acid copolymer-PETP.Chlorine also showed a strong synergy with phosphorus and nitrogen, and self-extinguishing 65/35 MD-PETP fabrics could be manufactured with very low total amounts of flame retardants.Some evidence for phosphorusbromine synergism was also detected.In the case of THPC no synergistic action was found.Modal fabrics compared with cotton and FR polyester fabrics compared with normal showed slightly decreased TG-temperatures.In the blend with modal, the TG-temperature of PETP was lowered resulting also in lower char yields than expected.All FR fabrics decomposed at lower temperatures with regard to both component fibres. Pyrolysis gas-liquid chromatograph connected with gas phase Fourier Transform infrared spectrometer and simultaneous identification by computer showed altered decomposition products of FR fabrics with different flame retardants. The main gaseous products of the untreated component fibres were often still found.These comprise known and new small-molecular products, 5-membered oxidized and furan derivatives from modal as well as benzoic and terephthalic acid derivatives from PETP.The increase in the amount of the small-molecular fraction was closely related to increasing FR efficiency.Untreated MD-PETP 50/50 fabric produced in rapid pyrolysis at 800 °C also new volatile flammable products. which decreased the amount of water and carbon oxides, thus increasing the flammability of the blend compared with its component fibres. Solid 13C NMR (CPMAS) analysis of charred residues of FR fabrics indicated a condensed oxidized aromatic structure with some aliphatic character.Phosphorus and nitrogen escaped mainly from most of the samples during heating up to 900-1100 °C and during LOI-determination.The combination of solid-gas phase mechanism with low v decomposition temperature producing enough non-flammable gases at the beginning of the fire seems important for FR modal-viscose-PETP fabrics.A large amount of carbon and energy is then bonded to char, and production of fuel is reduced.