Study Of Novel Phosphorus-based Durability Flame Retardant For Cotton And Structure-activity Relationship

Cotton is the largest production of plant fiber in the world.Clothing,curtains,carpets,bedding and other materials made from cotton are favored by consumers all over the world because of its advantages such as comfortable wearing,beautiful appearance and good performance.However,common cotton products are flammable,and their limiting oxygen index is only 16%-18%,which has great safety risks.Therefore,the flame retardant finishing of cotton fabric to improve its flame retardant is an important research to ensure consumer safety and reduce national loss.Halogen flame retardants have become an important part of early flame retardants because of their strong flame retardant effect on flammable products and little effect on the properties of materials.However,halogens and their hydrides have been found to interfere with normal physiological metabolism and have the risk of causing cancer.Proban and Pyrovatex CP are currently the two most widely used flame retardants for phosphorus-containing cotton fabrics.The finished cotton fabrics have good flame retardancy and durability,but the finished fabric will release formaldehyde which is harmful to human body during use.In recent years,some novel formaldehyde-free flame retardants have been developed,such as DNA flame retardants based on biomass and hydrophobic protein flame retardants.However,the washable performance of cotton products treated with these flame retardants is not up to the standard.Cotton fabrics treated with organic ammonium phosphate flame retardant have good flame retardancy and can pass the AATCC 61-2013 1A mild washing standard,however,it is difficult to pass the more stringent washing test.Therefore,the research and development of cotton flame retardant with high durability and formaldehyde-free is in urgent need of the market.In this paper,two flame retardants containing phosphonate group and active ammonium phosphate group and one relatively high molecular weight flame retardant containing active ammonium phosphate group were designed and synthesized and used in cotton fabric finishing.In order to produce high durability flame retardant cotton fabric and explore the method to improve the durability of flame retardant.The main studies are as follows:(1)Synthesis of 3-dimethyl phosphonate-N,N-dimethyl phosphonate ammonium propanamide and flame retardant finishing of cotton fabric.In this study,a new flame retardant 3-dimethyl phosphonate-N,N-dimethyl phosphonate ammonium propanamide(FR-AM)was synthesized.The structure of FR-AM was characterized by nuclear magnetic resonance spectrum(¹H NMR,¹³C NMR,³¹P NMR),the structure of FR-AM and its finished cotton fabric was analyzed by Fourier transform infrared spectroscopy(FT-IR),analysis showed that FR-AM was successfully synthesized and grafted into cotton fibers.Scanning electron microscope(SEM)showed that the surface of the finished cotton fiber was smooth and the fiber still kept its intact structure after burning.Flame retardant elements of phosphorus and nitrogen were detected in finished cotton fibers by energy dispersive X-ray(EDS).The flame retardant properties of cotton fabrics were tested by limiting oxygen index(LOI)method.The results showed that the LOIs of cotton fabrics increased from 18.4%to33.4%,38.8%and 41.8%,respectively,after treatment with 10 wt%,20 wt%and 30wt%FR-AM flame retardant.After 50 laundering cycles(LCs),the LOIs of treated cotton fabrics were 24.4%27.2%and 28.7%,respectively.The finished cotton was not ignited in the vertical combustion test,and char was produced.The results of thermogravimetric(TG)and thermogravimetric infrared(TG-IR)tests showed that the phosphoric acid and polyvinylidene phosphoric acid produced during the combustion process of finishing cotton fibers could catalyze the dehydration of cellulose to carbon.The results of cone calorimetry showed that the heat release rate(HRR)and total heat release rate(THR)of treated cotton were significantly lower than those of untreated cotton.The mechanical properties of the treated cotton fabric are partially reduced.The introduction of phosphonate group into the flame retardant of cotton fabric can significantly increase the durability of finished cotton fabric.(2)Synthesis of 2,7-dimethyl diphosphonate-3,7-dimethyl-3-ammonium phosphonate and flame retardant finishing of cotton fabrics.In this study,a novel formaldehyde-freeactiveflameretardant2,7-dimethyl diphosphonate-3,7-dimethyl-3-ammonium phosphonate(FR-LO)with two phosphate ester and one ammonium phosphate group in a single molecule was synthesized.The ratio of phosphate ester group to ammonium phosphate group was 2:1,which was higher than that of FR-AM flame retardant 1:2.The chemical structure of the flame retardant was characterized by NMR spectrum and FT-IR spectra.The cotton fabric treated with FR-LO has high flame retardancy and good durability.The LOI value of the cotton fabric treated with 30%FR-LO flame retardant is 43.4%,and the LOI value of the finished cotton fabric treated with AATCC 61-2013 2A standard after 50 times of washing is 29.7%.The SEM,vertical combustion,EDS and XPS analysis showed that the cotton fiber still maintained a complete structure after combustion,and the fiber contained nitrogen and phosphorus.TG and TG-IR analysis showed that the treated cotton fiber produced more carbon residue and released less combustible gas during the thermal decomposition process.The results of microcalorimetry(MCC)showed that the HRR and THR of treated cotton fibers were significantly lower than that of pretreated cotton fibers during combustion.XRD test showed that FR-LO flame retardant did not cause the morphologic change of cellulose crystal.Compared with the pretreated cotton,the hardness of the fire-retardant cotton treated with FR-LO increased and the tensile strength decreased.The durability of flame retardants can be improved by increasing the ratio of phosphonate group to phosphonate ammonium group in flame retardants.(3)Synthesis of N,N-dimethylphosphonate ammonium polyacrylamide and flame retardant finishing of cotton fabric.In this study,a novel type of phosphorus and nitrogen flame retardant N,N-dimethylphosphonate ammonium polyacrylamide(FR-PA)with relatively high molecular weight was synthesized.The structure of FR-PA was characterized by NMR spectrum as well as FT-IR spectra,and its viscosity average molecular weight was 3700.Flame retardant cotton fabric was prepared by grafting FR-PA onto cotton fabric by dip-pad-cure method.The LOI value of cotton fabric treated with 30%FR-PA reached 40.1%,and the LOI value of cotton fabric treated after 50 laundering cycles still maintained 28.5%.SEM analysis showed that the surface of the treated fiber was smooth and the structure remained intact after ignition.EDS spectrum analysis showed that the flame retardant was successfully introduced into the cotton fiber.TG analysis results showed that the treated cotton fibers degraded in advance at high temperature and a large number of carbon residues were generated.TG-IR analysis results show that the treated cotton fibers release less combustible gas at high temperature.The results of cone calorimetry show that the HRR and THR of treated cotton fabrics are significantly lower than those of pretreated cotton fabrics.The stiffness and tensile strength of the treated cotton fabric were also maintained.Relatively high molecular weight flame retardants are more difficult to elute than small molecular flame retardants,so they have good durability.