| As the most common natural textile,cotton fabric has the advantages of good wearability,comfort and dyeability,etc.It is widely used in clothing,furnishing,automobile,industry and other fields.However,cotton fabric is highly flammable,which poses a great threat to the safety of human life and property,and limits its application in some fields.So,the flame-retardant modification is necessary to endow cotton fabric with excellent flame retardancy.The flame retardants for cotton fabric can not meet the requirements of halogen-free,formaldehyde-free,efficient and durable.Nowadays,the most widely used flame retardants for cotton fabrics are Pyrovatex CP and Proban,which have high flame retardancy and excellent durability.But these flame retardants have the problem of formaldehyde release.As the problem of oil shortage becoming a global issue,much attention has been paid to the application of renewable resources.Using different biomass materials such as proteins and DNA as flame retardants for textiles has been considered a promising strategic approach.These biomass materials are widely existing in the nature of various plants and animals,with safe,non-toxic and environmental-friendly characteristics.They can be used to prepare halogen-free,formaldehyde-free cotton fabrics with flame retardancy,and to develop potential application of some agricultural and sideline products in the fields of flame retardants.However,the flame retardancy and durability of cotton fabrics treated with these biomass materials could not meet the commercial requirements.In this study,7 types of flame retardants containing reactive groups based on amino acids or proteins were synthesized.Treating with these flame retardants,8 types of flame-retardant cotton fabrics were prepared.The possibility of amino acids and protein as raw material to prepare flame retardants was explored.The flame retardancy,durability,thermal stability of treated cotton fabrics and the flame-reatardant mechanism of these flame retardants were systematically analyzed.The cause of poor durability of flame retardats with ammonium phosphonate groups was studied.The effects of these novel flame retardants on formaldehyde release,cell toxicity and skin irritation of cotton fabrics were also analysized.The conclusions were summarized as follows:(1)FR-G and FR-L,the new flame retardants,were synthesized by introducing ammonium phosphonate and ammonium carboxylate reactive groups to glycine and lysine,and their structures were characterized by nuclear magnetic resonance(NMR)?fourier transform infrared spectroscopy(FTIR)and thermogravimetry(TG).And the flame-retardant cotton fabrics were prepared by FR-G and FR-L.The results of limited oxygen index(LOI),vertical burning and conical calorimetry tests showed that the LOI values of treated cotton fabrics could increase to 42.1% and 42.9%,and the treated cotton fabrics were not ignited in the vertical burning and conical calorimetry tests.The LOI values of cotton fabrics treated with FR-G and FR-L remained at 26.1% and 27.0% after 50 times of gentle hand washes;but they dropped to 21.4% and 22.1% after 50 times of home machine washes.And the structure of treated cotton fabrics,grafting mechanism and flame-retardant mechanism of flame reatardants were studied by FTIR,TG,TG-FTIR,SEM and EDS.The results showed that the ammonium phosphonate and ammonium carboxylate reactive groups could react with the –OH of cellulose to form P(=O)-O-C and C(=O)-O-C bonds,so that FR-G and FR-L were garafted on the cellulose firmly.FR-G and FR-L played an important role in the condensed phase.During combustion,FR-G and FR-L decomposed to form phosphoric acids to promote the dehydration of cellulose,reduce the decomposition of cellulose,and form a dense carbon layer on the surface of the fiber.Besides,the effects of FR-G and FR-L on whiteness,breaking strength and formaldehyde content of cotton fabrics were also analyzed.The results showed that the whiteness and breaking strength of treated cotton fabrics slightly reduced,and no free formaldehyde was detected on the treated cotton fabrics.(2)The CAU was synthesized by introducing ammonium phosphonate and ammonium carboxylate reactive groups to the complex amino acides hydrolyzed from casein,and the structure of CAU was characterized by FTIR,X-ray photoelectron spectroscopy(XPS)and TG.Cotton fabrics were treated with CAU,and the cotton fabric with high flame retardancy and good durability was obtained.The results of FTIR,XPS and EDS showed that CAU was grafted on cellulose by forming P(=O)-O-C and C(=O)-O-C bonds.The results of LOI,vertical burning and conical calorimetry tests showed that the LOI values of treated cotton fabrics could increase to 41.9%,and the treated cotton fabrics were not ignited in vertical burning and conical calorimetry tests.And the LOI value of cotton fabirc treated with CAU could remain at 26.3% after 50 times of gentle hand washes,which remained at 21.1% after 50 times of home machine washes.The results of TG,TG-FTIR,SEM and EDS showed that CAU also played an important role in the condensed phase to promote the dehydration of cellulose,form a dense carbon layer on the surface of the fiber.The whiteness and breaking strength of treated cotton fabrics reduced slightly,and the content of formaldehyde on treated cotton fabric was 32 mg/kg.Besides,the treated cotton fabric was not cytotoxic and did not irritate the skin.(3)A large number of ammonium phosphonate reactive groups were introduced into polylysine to synthesize the new flame retardant,PLU,and its structure was characterized by FTIR and TG.Before the flame-retardant modification,cotton fabric was pretreated with NaOH solution to obtain the pre-treated cotton fabric,D-cellulose.The results of X-ray diffraction(XRD)showed that the crystalline region of cellulose was transformed into amorphous region during the pretreatment.Cotton fabric and D-cellulose were treated with PLU to prepare flame-retardant cotton fabrics,PLU-cotton and PLUD-cotton.The flame retardancy and durability of treated cotton fabrics were investigated by LOI,vertical burning and micro calorimetry tests,and the results showed that the LOI values of PLU-cotton and PLUD-cotton reached 41.6% and 42.8%.The pretreatment by NaOH and improving the molecular weight of the flame retardant could further improve the durability of treated cotton fabric.The LOI values of PLU-cotton and PLUD-cotton remained at 27.0% and 27.3% after 50 times of gentle hand washes;they remained at 22.7% and 23.3% after 50 times of home machine washes.The results of FTIR,SEM and EDS showed that PLU could graft on cellulose by forming covelent bonds.And the main reason for the decrease of flame retardancy of treated cotton fabrics after washings was that there were unreacted ammonium phosphonate reactive groups on treated cotton fabric,which reacted with the metal ions in washing soap to form metal salts of phosphonic acids.However,the metal salts of phosphonic acids had low flame-retardant effect on cotton fabrics.The flame-retardant mechanism of PLU were studied by FTIR,TG,TG-FTIR,SEM and EDS,and the results showed that PLU also played an important role in the condensed phase.Besides,the whiteness and breaking strength of the treated cotton fabrics reduced,and no free formaldehyde was detected on PLU-cotton and PLUD-cotton.(4)The molecular structure of PLU was optimized with ethylene glycol,and part of the ammonium phosphonate reactive groups was replaced with phosphonate ester groups.Then the flame retardant containing both phosphonate ester and ammonium phosphonate groups,PLUEG,was synthesized,and the structure was characterized by FTIR and TG.Cotton fabrics with high flame retardancy and durability was prepared by PLUEG,the flame retardancy and durability of treated cotton fabrics were investigated by LOI,vertical burning and micro calorimetry tests.The results showed that the LOI values of treated cotton fabric could increase to 42.8%,and it remained at 28.6% after 50 times of home machine washes.The phosphonate ester groups could not react with the metal ions in washing soap,so the durability of treated cotton fabric was significantly improved.The results of FTIR,TG,TG-FTIR,SEM and EDS showed that PLUEG could graft on cellulose by forming covelent bonds,and PLUEG promoted the dehydration of cellulose during the combustion.Besides,the whiteness and breaking strength of the treated cotton fabric maintained well,and no free formaldehyde was detected on the treated cotton fabric.(5)Phosphonate ester groups were introduced into polylysine and casein by dimethyl phosphite,and the ammonium phosphonate groups were added to the molecules by phosphite,formaldehyde and ammonia.Then the novel flame retardants,PLDP and CADP,were synthesized,and their structures were characterized by FTIR and TG.Cotton fabrics were treated with PLDP and CADP,and PLDP-cotton and CADP-cotton were obtained.The results of LOI,vertical burning and micro calorimetry tests showed that the LOI values of PLDP-cotton and CADP-cotton reached 43.1% and 41.6%,which could not be ignited in air.The method of using dimethyl phosphite and phosphite to synthsize “self-sealing” flame retardants containing both phosphonate ester and ammonium phosphonate groups could reduce the displacement reaction between treated cotton fabrics and the metal ions in washing soap more effectively,and the durability of treated cotton fabrics was further improved.The LOI values of PLDP-cotton and CADP-cotton remained at 30.2% and 26.4% after 50 times of home machine washes.The results of FTIR,TG,TG-FTIR,SEM and EDS showed that PLDP and CADP could promote the dehydration of cellulose during combustion.After the modifications,the whiteness and strength of PLDP-cotton and CADP-cotton remained well.In addition,no free formaldehyde was detected on PLDP-cotton,and the content of free formaldehyde on CADP-cotton was only 42 mg/kg. |
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