Preparation of acrylic emulsion coating with melamine polyphosphate, pentaerythritol and titanium dioxide for flame retardant cotton/polyethylene terephthalate blend fabrics

•Melamine polyphosphate (MPP) was synthesized with two-step approach.•Flame-retardant coating was prepared using MPP, pentaerythritol (PER) and TiO2.•MPP-PER-TiO2 coatings were applied to cotton/polyethylene terephthalate (C/T) blends.•Good flame retardancy of coated C/T blends was verified through vertical flame test.•Three-stage degradation of MPP/PER coating and role of TiO2 were revealed. An organic phosphorus-nitrogen containing flame retardant melamine polyphosphate (MPP) was synthesized with two-step approach using melamine and phosphoric acid, and characterized through Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance analysis. The intumescent flame retardant (IFR) coatings were prepared using MPP, pentaerythritol (PER) and anatase-type TiO2 as FR additives and acrylic emulsion as a binder, and applied to cotton/polyethylene terephthalate (C/T) blends. The vertical flame and cone calorimeter tests were carried out to measure after-flame time, damaged length, limiting oxygen index and peak heat release rate, confirming the good flame retardancy being enhanced with increasing the content of TiO2 in the coatings. The scanning electron micrography images showed formation of numerous pores and voids on the C/T blend samples treated with only MPP and PER while the formation of compact and dense char layer with no void by adding TiO2. Through the thermogravimetric, FTIR, and X-ray diffraction analysis, it was revealed that the three-stage degradation of MPP/PER coatings released incombustible water vapor and ammonia gas, while TiO2 could react with polyphosphoric acid to produce titanium pyrophosphate ceramic layer covering the char layer.