Preparation And Application Of Durable Flame Retardants For Cotton Containing Phosphorus Based On Starch

Cellulose is the most abundant polymer in the world,and cotton fiber is one of the natural resources with the highest purity of cellulose.The cotton fiber products are widely used in people’s daily life because of their excellent taking properties.However,cotton fiber is a flammable material that can easily cause a fire.In fact,the flammability of household textiles is the major reason in causing residential fires.The addition of flame retardant in cotton fabrics can reduce the rate of flame spread or delay the appearance of flame,or even make cotton fabrics can not burn.Due to restriction and ban the use of halogen-based flame retardants in the international arena,seeking a variety of other flame retardants instead of halogen,has received great attention and development.Because of the specific flame retardancy of phosphorus-containing flame retardants on cellulose fibers,phosphorus-containing flame retardants Proban and Pyrovatex CP are commonly used for flame retardant treatment of cotton fabrics,but they will release toxic substances formaldehyde during use.In recent years,with the increasing awareness of environmental protection and the gradual depletion of oil resources,the development and application of biomass materials has become an international research hotspot.In the flame retardant field,some biomasses such as whey protein,DNA,phytic acid（PA）and tannic acid（TA）have been used as flame retardants for direct application in the study of flame retardant finishing of cotton fabrics.While other biomolecules such as amino acids,lignin,starch and casein are used as basic raw materials through chemical synthesis to introduce flame retardant elements（such as phosphorus,sulfur and nitrogen,etc.）into their molecules,the biomass is developed into flame retardants and used in the flame retardant finishing of cotton fabrics.However,except for phytic acid,these biomasses used directly as flame retardants or biobased flame retardants based on biomasses by chemical synthesis have almost no reactive groups which can be covalently grafted with cotton fibers,and therefore the finished cotton fabrics have almost no durability.Therefore,this study proposes to develop a durable active starch series of flame retardants by introducing different reactive ammonium phosphonate groups as well as phosphonate groups into the starch molecules using biomass starch as raw material.The main studies are as follows:（1）Synthesis of a novel bio-based polymeric flame retardant ammonium starch phosphonate（ASTP）and its application on cotton fabrics.Ammonium starch phosphonate（ASTP）flame retardant was synthesized using soluble starch,phosphoric acid and urea as raw materials,and it was used for flame retardant finishing of cotton fabrics.The chemical structure of ASTP was characterized by nuclear magnetic resonance(¹H,¹³C and ³¹P NMR)and Fourier transform infrared spectroscopy（FT-IR）tests,and its molecular weight（M_w=8.12×104 g/mol）was determined by multi-angle laser light scattering-gel permeation chromatography（GPC-MALLS）.The vertical flame and limiting oxygen index（LOI）test results showed that the char length of 30 wt%ASTP-treated cotton was only 22 mm and the LOI value was as high as 45.2%,which exhibited excellent flame retardancy.According to AATCC 61-2013 2A washing standard,the char length of 30 wt%ASTP treated cotton after 50 laundering cycles（LCs）was 42 mm and the LOI value was 32.1%,which indicated that the ASTP-treated cotton had excellent durability.The FT-IR,scanning electron microscopy（SEM）,energy dispersive X-ray spectroscopy（EDS）and durability results indicated that ASTP was grafted on the surface of cotton fibers through P-O-C covalent bonds.The results of cone calorimetric tests showed that the heat release rate（HRR）and total heat release（THR）of ASTP-treated cotton were significantly lower than the raw cotton,and the char residue was increased.SEM results showed that the char residue of ASTP-treated cotton after burning maintained complete fabric structure.The thermogravimetric（TG）test results showed that ASTP produced acidic products such as phosphoric acid and poly（metaphosphoric acid）by decomposition at high temperature could promote the dehydration of cotton fibers into char,which mainly exhibited a cohesive phase flame retardant mechanism.The physical properties of ASTP-treated cotton were reduced to some extent.These results suggested that soluble starch can be used to replace polyols in petroleum for the synthesis of more durable flame retardants.（2）Synthesis of a novel polysaccharide flame retardant 2,6-dimethoxy polysaccharide ammonium phosphonate（DOPSAP）and its application on cotton fabrics.After degrading soluble starch into a series of polysaccharide molecules with relatively low molecular weight by phosphite,adding formaldehyde and phosphite to the reaction synthesized 2,6-dimethoxy polysaccharide ammonium phosphonate（DOPSAP）flame retardant,and it was used for flame retardant finishing of cotton fabrics.The chemical structure and molecular weight（M_w=8570.13 g/mol）of DOPSAP were characterized by NMR,FT-IR and GPC-MALLS tests.EDS analysis showed that DOPSAP introduced more phosphorus elements compared with ASTP.FT-IR test results showed that DOPSAP was successfully grafted onto cotton fibers through P-O-C covalent bonds.The char length and LOI value of 30 wt%DOPSAP-treated cotton were 42 mm and 49.4%,respectively.Under the violent washing conditions（AATCC 61-2013 3A washing standard）,the char length of the 30 wt%DOPSAP-treated cotton was only 52 mm after50 LCs,and the LOI value was 37.5%.These results indicated that cotton fabrics treated with DOPSAP have excellent flame retardancy and durability.The TG test results showed that DOPSAP-treated cotton retained 40.8%of char residue under N₂ atmosphere.In the cone calorimetric test,the THR of DOPSAP-treated cotton was significantly reduced.The FT-IR and EDS results of char residue after burning of DOPSAP-treated cotton showed that DOPSAP produced phosphoric acid and poly（metaphosphoric acid）at high temperature.Combined with the TG-FTIR test results,it was shown that DOPSAP changed the decomposition pathway of cotton fibers,inhibited the production of combustible gases,and promoted the dehydration of cotton fibers to produce more char,which showed a cohesive phase flame retardant mechanism.The mechanical properties of DOPSAP-treated cotton were well maintained.These results indicated that more phosphorus-containing groups can be introduced into the starch molecule using formaldehyde,which effectively improved the flame retardancy of treated cotton fabrics and achieved higher durability.（3）Synthesis of a novel phosphorus-containing flame retardant 2,6-dimethoxy polysaccharide phosphonate ammonium phosphonate（DOPSPAP）and its application on cotton fabrics.The 2,6-dimethoxy phosphonate ammonium phosphonate（DOPSPAP）flame retardant was synthesized from soluble starch,formaldehyde,phosphorous acid and dimethyl phosphite,and it was used for flame retardant finishing of cotton fabrics.The chemical structure and molecular weight（M_w=3.32×10⁴ g/mol）of DOPSAP were characterized by NMR,FT-IR and GPC-MALLS tests.The DOPSPAP-treated cotton had no after-flame and after-glow in the vertical flame test,and it was observed by SEM that the char residue remained an intact fiber structure after the DOPSPAP-treated cotton burning.The LOI value of the 25 wt%DOPSPAP-treated cotton was as high as 44.5%,and the LOI value was still 34.5%after 50 LCs according to AATCC 61-2013 3A standard.The presence of DOPSPAP molecules on the treated cotton fiber surface was observed by SEM.Durability,FT-IR and EDS confirmed the grafting of DOPSPAP on cotton fibers through P-O-C covalent bonds.The cone calorimetry results showed that DOPSPAP could effectively inhibit the heat release during the cotton fabric burning.The results of TG and TG-FTIR tests showed that DOPSPAP changed the decomposition pathway of cotton fibers and promoted their dehydration into char.The mechanical properties of DOPSPAP-treated cotton were slightly reduced.Compared with DOPSAP,DOPSPAP-treated cotton have better flame retardant durability and tensile breaking strength.After50 LCs,the content of metal ions that were combined with DOPSPAP-treated cotton during the washing process was significantly lower than DOPSAP-treated cotton.These results showed that the introduction of both phosphonate and ammonium phosphonate groups to synthesize flame retardants not only improved the durability of flame retardants,but also maintained the mechanical properties of cotton fabrics better.