Synthesis Of Efficient And Durable Flame Retardant Containing Nitrogen-Phosphorus,preparation Of Flame-retardant Cotton Fabrics And Research Its Properties

As the most important natural fiber in textile industry,cotton fiber has the advantages of softness,high hygroscopicity,comfortable wearing and skin-friendly properties.However,the extremely flammability of cotton fibers has been greatly limited its scope of use,especially in areas where flame retardant properties is required.Therefore,it is necessary to perform flame retardant finishing and research on cotton fabrics.In recent decades,ecologically and environmentally friendly phosphorus-containing compounds have become a research hotspot of flame retardants.The first batch of organophosphorus flame retardants for cotton based on crosslinked tetramethylolphosphonium salt and N-alkyl substituted phosphonopropionamide derivatives,two representative flame retardants,tetramethylolphosphonium chloride?THPC?and N-hydroxymethyl-3-?dimethoxyphosphono?propionamide?Pyrovatex CP?have dominated the flame retardant market so far.However,cotton treated with this type of flame retardant will release formaldehyde during use.In this paper,three kinds of flame retardant containing nitrogen-phosphorus were designed and synthesized for cotton fabrics,and no formaldehyde release during use.The active reactive groups containing-P=O?NH₄⁺?of this kind of flame retardant can react with the-OH of cotton fiber.The reaction forms a P-O-C covalent bond,which not only improves the durability of the flame retardant,but also has a synergistic flame retardant effect with the phosphorus element and further improves the flame retardant efficiency.The main research work of this thesis is as follows:?1?Tetraethylenepentamine heptamethylenephosphonic acid was prepared from tetraethylenepentamine,formaldehyde and phosphorous acid,and ammoniated with urea to synthesize tetraethylenepentamine heptamethylammonium phosphate?ATEPAHP?.The structure was characterized by Fourier transform infrared spectroscopy?FT-IR?,nuclear magnetic resonance hydrogen?¹H NMR?,carbon(¹³C NMR)and phosphorus(³¹P NMR)spectra.Flame-retardant cotton fiber is prepared by traditional dip-roll-curing technique,using thermogravimetric analysis,thermogravimetric infrared,cone calorimetry,limiting oxygen,vertical combustion,tensile strength,stiffness and X-ray diffraction test to evaluated the properties and physical properties of flame-retardant cotton.The results show that the cotton fiber treated with 20 wt%flame retardant solution has good flame retardant performance,and its limiting oxygen index value reaches 40.5%before washing.After 50 washings,the limiting oxygen index can still maintain 31.8%,much higher than the limit oxygen index value of control cotton?18.5%?.In the vertical burning test,there is obvious self-extinguishing phenomenon.The cone calorimetric data revealed that the residual carbon content of the treated cotton fiber is greatly increased.This is because the flame retardant decomposes to form an acid source containing phosphoric acid,which causes the matrix to dehydrate,promotes carbon formation and belongs to condensed phase flame retardant.The flame retardant mechanism of the flame retardant also includes gas phase flame retardant which is the scanning electron microscopy indicated that many small bubbles appear on the surface of the fiber structure of the residual carbon after combustion,because the non-flammable gas is released during the combustion process,and the concentration of oxygen around the matrix can be diluted,and increases the flame retardant efficiency.In addition,high temperature curing results in a slight decrease in the mechanical properties of the treated cotton fibers,but does not affect the use in subsequent stages.The advantages of the flame retardant is that the phosphorus content is high,and the cotton fiber treated with a low-concentration flame retardant solution can achieve good flame retardant effect.?2?Ammonium salt of aminopropyl silanol diammonium phosphate?AASMP?with aminopropyltriethoxysilane,formaldehyde,phosphorous acid and urea was synthesized and characterized by Fourier transform infrared,nuclear magnetic resonance spectroscopy,carbon spectroscopy and phosphorus spectroscopy.The Fourier transform result suggested that the flame retardant was grafted on cotton fabric via P-O-C covalent bonds.This flame retardant includes three elements?nitrogen,phosphorus and silicon?,which have a synergistic flame retardant effect,imparting more efficient flame retardant properties for the cotton fiber.The limit oxygen index of the flame retardant cotton fiber treated with 30%AASMP can reach 45.0%,after 50 LCs,the limiting oxygen index value is still maintained at 31.0%.The thermogravimetric infrared spectra further confirms the release of flammable gases?ethers and carbonyls?for the treated cotton is much lower than that of raw cotton at high temperature,and the release of non-combustible gases such as water vapor and ammonia increases,diluting the concentration of air around combustibles,and achieve the effect of gas phase flame retardant.Cone calorimetry data indicated that the peak heat release rate of treated cotton decreased by96.5%compared to pure cotton.X-ray diffraction results suggested that the treatment had a little effect on the crystallinity of the cotton fabric,and the mechanical properties were also kept good.The advantage of using flame retardants for finishing the cotton fabric are good thermal stability and thermal oxidation stability at high temperatures,and the mechanical properties still retained well.?3?The environmentally friendly flame retardant ammonium salt of diethylene glycol diphosphate?ADGP?was synthesized using low-cost diethylene glycol,phosphoric acid and urea.The structure of the flame retardant was characterized by Fourier transform infrared and nuclear magnetic resonance.The flame retardancy,thermal stability,surface morphology and mechanical properties of treated cotton were investigated by limiting oxygen test,cone calorimetry,scanning electron microscopy,elemental analysis and tensile strength test.The results displayed that the limiting oxygen index value of the flame retardant cotton treated by 40%ADGP reached 43.7%.After50 LCs,the limiting oxygen index value was 32.5%.Compared with carbon content of pure cotton?7.3%?,the residual of treated cotton?42.6%?was increased at high temperature,the surface of treated cotton fiber is as smooth as pure cotton without damage.Since the flame retardant solution is nearly neutral,the damage to the fiber structure is a little and the mechanical properties of treated cotton fabric are also kept good.The synthesis process of the flame retardant is simple and easy to operate,and the halogen-free formaldehyde-free synthetic raw material is environmentally friendly,and is an efficient and durable flame retardant being suitable for industrial production.