Study On Preparation And Application Of Novel Durable Phosphorus-containing Reactive Flame Retardant For Cotton

Cotton has long been recognized as an important industrial crop throughout the world and is widely planted for the manufacture of textile materials.Cotton fabrics have comfort,breathability,hydrophilicity,biodegradability,skin friendliness and other superior properties,thus being widely used in upholstery,clothing,medical and other fields.However,cotton fabrics are extremely flammable,with a limit oxygen index（LOI）value of only 16%-18%,which will mean that it is easy to cause a fire,thus endangering human life health and property safety.Therefore,it is very necessary to give cotton fabrics with flame retardant properties.In the current research,in order to improve flame retardant properties of cotton fabrics,various types of flame retardants are successfully applied to cotton fabrics.Among them,halogen flame retardants are the earliest and most effective.However,due to the halogen flame retardants in the combustion process will produce toxic substances,they are gradually abandoned in the textile field.Low toxicity phosphorus flame retardants are an ideal alternative to halogen flame retardants.The main phosphorus-based flame retardants on the market today are Proban and Pyrovatex CP,which have good flame retardancy and excellent durability.However,cotton fabrics treated by them will release formaldehyde in the process of use,which is harmful to human health.Therefore,the development of a durable,good flame retardant,halogen-free and formaldehyde-free flame retardant cotton has attracted a lot of attention from researchers in the field of flame retardant cotton fabrics.Many halogen-free,formaldehyde-free and environmentally friendly flame retardants have been reported,but the durability of cotton fabrics treated with these flame retardants is poor.Therefore,we urgently need to further research new efficient,durable,halogen-free and formaldehyde-free flame retardants for cotton fabrics,which can be used to prepare flame retardant cotton with good durability and flame retardancy.In this thesis,three highly efficient and durable cotton flame retardants containing active ammonium phosphonate groups were designed and synthesized,namely,ammonium of diethylenetriamine pentamethylene phosphonate glycol ester phosphonate（ADTPMPAEG）,ammonium of triethylenetetramine phosphamide phosphonate（ATPP）and ammonium of triethylenetetramine cyclophosphonamide phosphonate（ATCP）.The flame retardancy and washing resistance of cotton fabrics treated with the three flame retardants were studied and discussed.The relationship between washability of treated cotton and molecular structure of flame retardants was also analyzed.The specific research process and conclusions are as follows:（1）A new halogen-free,highly efficient,durable,flame retardant containing both phosphonate groups and ammonium phosphonate groups,ADTPMPAEG,was synthesized from diethylenetriamine pentamethyleneglycol phosphate,ethylene glycol and urea,and ADTPMPAEG treated cotton was prepared by applying it to cotton fabrics using the dip-rolling and baking method.The molecular structure of ADTPMPAEG was characterized by Fourier transform red spectroscopy（FT-IR）.FT-IR,X-ray photoelectron spectroscopy（XPS）and energy dispersive X-ray spectroscopy（EDS）analysis suggested that ADTPMPAEG was bound to cotton fabrics by forming–P（=O）–O–C covalent bonds.Forming some of the ammonium phosphonate reactive groups into phosphonate groups could reduce the effect of metal ions on their flame retardancy by combining unreacted ammonium phosphonate reactive groups with metal ions during washing to form metal phosphonates.25 wt%ADTPMPAEG treated cotton had a LOI of 45.1%after 50 laundering cycles（LCs）of AATCC 61-2013 2A standard washing,the LOI value remained at 32.7%.The results of scanning electron microscopy（SEM）and X-ray diffraction（XRD）tests indicated that ADTPMPAEG had little effect on the surface morphology and crystal structure of the cotton fibers.The cotton fabrics were subjected to thermogravimetric（TG）analysis,cone calorimetry and vertical combustion measurements,which the results showed that the ADTPMPAEG treated cotton had excellent flame retardant properties and excellent durability properties.The measurements of mechanical properties revealed that ADTPMPAEG had no significant effect on the mechanical properties of cotton fabrics.（2）A new type of flame retardant ATPP was synthesized by a two-step reaction of triethylenetetramine with phosphorus oxychloride and urea,and applied to cotton fabrics.In the ATPP molecule,except for the essential–P=O（O^-NH₄⁺）₂ group,all other P elements formed P（=O）–N covalent bonds.the molecular structure of ATPP was characterized by FT-IR.The ATPP treated cotton fabric not only had high flame retardancy but also high durability,which could pass AATCC 61-2013 3A standard 50LCs with a LOI value of 32.6%.This is due to the presence of p-πconjugation in the P（=O）–N group,resulting in the P（=O）–N chemical bond of the flame retardant and the–P（=O）–O–C of cellulose chemical bond is very stable and not easily hydrolyzed during washing.FT-IR,XPS,EDS and durability suggested that ATPP grafting forms–P（=O）–O–C covalent bonds on cellulose.SEM,XRD and mechanical properties showed that ATPP had no significant effect on the surface morphology,crystal structure and mechanical properties of cotton fibers.Compared with control cotton,the peak heat release rate（PHRR）and total heat release（THR）of ATPP treated cotton were significantly reduced by 85.43%and 43.62%,respectively,indicating that the ATPP treated cotton fabric had good flame retardant properties.In particular,the metal content of ATPP treated cotton fabric was the lowest after washing,which was consistent with the high durability of ATPP treated cotton fabrics.Therefore,ATPP flame retardant can be used as a very durable flame retardant.（3）A novel flame retardant ATCP was synthesized by a two-step reaction with triethylenetetramine,phosphorus pentoxide and urea,and applied to cotton fabrics by chemical grafting.In the ATCP molecule,except for the indispensable–P=O（O^-NH₄⁺）reaction group,other P elements existed in the form of P（=O）–N covalent bonds.The molecular structure of ATCP was characterized by FT-IR.FT-IR,XPS,EDS and durability results suggested that ATCP formed–P（=O）–O–C covalent bonds with hydroxyl groups in cotton fibers,which were grafted onto cotton fabrics.Compared to control cotton,the PHRR and THR of FRC-ATCP-30 were significantly reduced by90.3%and 72.9%,respectively,and the LOI was 41.7%after 50 LCs of AATCC61-2013 3A standard.These results indicated that the ATCP treated cotton fabrics have good flame retardancy and even superior durability.This is due to the high stability of the P（=O）–N group,which is not easily hydrolyzed during washing.SEM and mechanical properties showed that ATCP had little effect on the surface morphology and mechanical properties of cotton fibers.It is noteworthy that the ATCP treated cotton had the lowest metal content after 50 LCs washing,which was consistent with the superior durability of ATCP treated cotton.