Preparation Of Phosphorus/Nitrogen Synergistic Flame Retardant Containing Reactive Groups For Cotton And Its Flame Retardant Mechanism

As a common natural fiber,cotton fiber has been applied for thousands of years.The textiles produced by cotton fiber possess many characteristics,such as soft handle,breathability,hygroscopicity,warmth retention property and wear resistance,which are widely favored by clothing,automobile decoration,indoor home and other industries.However,the limiting oxygen index(LOI)of cotton fabrics is only about 18%,and it is a common flammable material which is prone to violent combustion after contacting with the fire source in the air.Therefore,it is of practical significance to develop flame retardants with excellent effects and apply them to the modification of cotton fabrics.Also,with the progress of human ecological civilization construction,the research of flame-retardant cotton fabrics is moving towards the direction of green environmental protection.Based on the above purpose,two novel P/N synergistic flame retardants with reactive group-P=O(O^-NH₄⁺)are designed and synthesized in this article.They can react with-OH of cellulose through the conventional padding-drying-curing process to modify the surface of cotton fabrics.Meanwhile,no toxic by-products are released during the whole finishing process,as well as the processed cotton fabric has good flame retardancy and thermal stability.The synthesis and flame-retardant properties of these two novel flame retardants for cotton fabrics are as follows:The ammonium salt of N,N-dimethylene-piperazine-(methylphosphonic acid)(ASNDP)was synthesized by phosphorous acid,N-Aminoethylpiperazine,urea and other compounds as raw materials.The chemical structure of the flame retardant was characterized by Fourier transform infrared(FTIR)spectroscopy and nuclear magnetic resonance spectrum(NMR),which proved that ASNDP had been successfully synthesized.The combustion behavior and flame retardancy of flame retardant cotton fabrics were studied by cone calorimetry,oxygen index method and vertical burning test.It was found that the weight gain of cotton fabrics treated with 450 g/L ASNDP was 17.4±0.3%,the LOI value of this sample increased from 18.6%±0.2%to 29.5±0.1%,and the total heat release(THR)was reduced from 5.6 MJ/m² to 3.7 MJ/m².The surface morphology of the flame-retardant cotton fabrics before and after burning was observed in detail by scanning electron microscope(SEM).It can be seen that ASNDP had been successfully processed to the surface of cotton fabrics,and the fibrous structure of the sample was basically complete after burning.Meanwhile,thermogravimetric(TG)analysis results demonstrated that the cotton fabrics treated with ASNDP possessed better thermal stability.The synthesis process of ASNDP was concise,and it could endow good flame retardancy toward cotton fabrics.This other flame retardant,ammonium salt of N,N-dimethylene p-benzenesulfonic phosphonic acid(ADBSPA),was synthesized by phosphorous acid,sulfanilic acid,urea and other compounds as raw materials,and the P and N elements contained in the flame retardant achieve a synergistic flame-retardant effect on cotton fabrics.The chemical structure of ADBSPA was analyzed by FTIR and NMR.The crystal structure,element composition and flame retardancy of unfinished and finished cotton fabrics were measured by X-Ray diffraction(XRD),Energy dispersive X-ray spectrometer(EDX),vertical burning test,oxygen index method and cone calorimetry test.Meanwhile,the washing durability and mechanical properties of the finished cotton fabrics were evaluated through washing test and tensile strength.These results demonstrated that the finished cotton fabrics showed good flame retardancy and thermal stability.The after-glow time of all cotton fabrics treated with ADBSPA was 0 s,and the LOI value(26.4±0.1%)of optimum finishing sample after 20 washing cycles was still higher than that of unfinished cotton fabrics.In addition,the tensile strength of the finished samples in the warp and weft direction decreased,but the decrease of both was small,which did not affect the subsequent application of cotton fabrics.Therefore,the ADBSPA not only endowed the cotton fabrics with good flame retardancy,but also possessed little influence on the mechanical properties of cotton fiber.