Formaldehyde-free Anti-wrinkle Finishing On Cotton Fabrics By Polycarboxylic Acids

Cotton is one of the most favored textile materials because of its superior wearing comfortand excellent wearability.Unfortunately,cotton fabric wrinkles easily during home laundering and causes considerable inconvenience for users.The poor resiliency of cotton is caused by the structure of biopolymer-cellulose in fibers,as it has hydrogen bonds as the major intermolecular interactions but is lack of intermolecular chemical crosslinkages.As the demand for natural fibers increasing,anti-wrinkle finishing of cotton fabrics became an important part for textiles processing.N-hydroxymethyl formaldehyde isthe earliest wide range of industrial application agent for anti-wrinkle finishing,mainly dimethyloldihydroxy ethylene urea(DMDHEU)is introduced to overcome winkles.However,when treated cotton fabric is subjected to multiple laundering cycles,ether linkages of DMDHEU gradually hydrolyze to become N-methylol groups.Hence,free formaldehyde releases continuously during the entire life of the treated garment.In 1987,the U.S.Environmental Protection Agency classified formaldehyde as “a probable human carcinogen”.The risk of formaldehyde exposure was upgraded to “carcinogenic to humans” by the working group of WHO International Agency for Research on Cancer in 2004.Treated fabric releases formaldehyde which is extremely harmful to human health during the process of treatment and wearing.Since late 1980 s,extensive efforts have been made to develop formaldehyde-free crosslinking agents for cotton to replace the traditional formaldehyde-based reagents.Aldehyde,epoxy resin,vinyl sulfides,water-soluble polyurethane,reactive silicon,modified chitosan,polycarboxylic acid,ionic liquid are all for the non-formaldehyde anti-wrinkle finishing on cotton fabrics.Polycarboxylic acids(PCAs)were recognized as the most promising one among all formaldehyde-free alternatives since Welch found sodium hypophosphate as the most effective catalyst.In recent years,the study of PCAs for anti-wrinkle finishing was mainly focused on crosslinking mechanism,catalyst selection and process optimization.As far as the author knows,no literature has designed and synthesized the novel crosslinker from molecular structure,reactivity,affinity,flexibility,effective crosslinking size,etc.From this point,the new crosslinker was designed and synthesized.Active groups were selected for crosslinking.New crosslinkers were used for anti-wrinkle finishing and compared with normal to testify the rationality of the design.Moreover,discuss the relationship between wrinkle performance and molecular size,affinity,reactivity,active energy,effective crosslinking size of the crosslinkers,hope to offer the theory support and practice guidance to design novel crosslinking agent.In the first part,acryloyl succinate was synthesized and applied on cotton fabrics as a novel crosslinking agent.Maleic acid(MA)has been explored to replace formaldehyde-based dimethyloldihydroxy ethylene urea(DMDHEU)for anti-wrinkle finishing on cotton fabrics.However,the resilience of treated fabrics was not satisfactorily improved.In unsaturated carboxylic acids,only both the esterification(-COOH)and polymerization(double bond)can impart fabric with anti-wrinkle performance.The reactivity of double bond is affected by steric hindrance.From the view of chemical structure,MA is a di-substituted unsaturated acid and its reactivity is lower than a mono-substituted one.Therefore,a mono-substituted unsaturated acid,acryloyl succinate(AMA and ATA)was selected as a potential crosslinking agent for cotton fabrics.The synthesized route and purification of acryloyl succinate were studied and optimized.The structure was confirmed by NMR and MS spectra.The affecting factors for crosslinking,include reagent concentration,p H,curing temperature,catalyst concentration,were analyzed.The optimum condition of AMA used for anti-wrinkle finishing: AMA 0.8mol/L,SHP 0.5mol/L,p H 2.8,curing condition 180 oC for 2min.ATA has similar structure and also shows similar optimum recipe as AMA.Under the optimum condition,AMA and ATA reached wrinkle recovery angle(WRA)261°and 265°,respectively.Possible crosslinking mechanism between AMA and cellulose was investigated by means of 13 C NMR,MS,FTIR and phosphorus content analyses.Due to the steric hindrance,double bond in AMA showed higher reactivity than MA resulted to the better wrinkle recovery performance.It was found that AMA could form ester bonds with cellulose by formation of anhydride intermediate.Meanwhile,additional reaction of double bonds on AMA with another molecule or P-H of SHP residual has also contributed to the crosslinking.The three cross-linkages imparted fabrics with excellent wrinkle recovery performance.In the second part,a 5-(carbonyloxy succinic)-benzene-1,2,4-tricarboxylic acid(BSTA)was synthesized and applied as an effective crosslinking agent.It’s known that aromatic acid can esterify with cellulose without forming anhydride and shows higher reactivity than aliphatic carboxylic acids.In this study,pyromelliticdianhydride was reacted with hydroxyl succinic acid(DL-Malic acid)to prepare a 5-(carbonyloxy succinic)-benzene-1,2,4-tricarboxylic acid(BSTA).The succinic group incorporation can improve the solubility of the aromatic carboxylic acid without affecting its reactivity.The synthesized route and purification of BSTA was studied and optimized.Take THF as solvent and 80℃ reflux for 48 h as the optimum condition.The structure was confirmed by NMR.Finishing conditions such as agent concentration,curing temperature,and bath p H were also discussed to evaluate crosslinking effect of cellulose.The optimum condition of BSTA used for anti-wrinkle finishing: BSTA 0.3mol/L,SHP 0.15mol/L,p H 2.0,curing condition 160 oC for 3min or 180 oC for 2min.BSTA,as a derivative of photo-active conjugated compound,can absorb ultraviolet lights and offer ultraviolet(UV)protective property on treated materials.The treated fabrics showed excellent UV protection performance due to the addition of aromatic conjugated system on fabrics.After 3 times wash,the WRA of BSTA treated fabrics reached 275°and DP rating 3.0.After 10 times wash,the WRA of BSTA treated fabrics reached 265°and DP rating 2.5.Possible crosslinking mechanism between BSTA and cellulose was investigated.The FTIR confirmed the new ester bond formed on cellulose.Temperature-dependent FTIR and TGA confirmed the anhydride structure.Direct esterification was confirmed by comparing DL-MA,124-BTA and BSTA and the relative intensity(RI)value for anti-wrinkle finishing without catalyst.The optimum p H for esterification was 2.0.In BSTA structure,-COOH on phenyl ring can reacted with cellulose directly,the succinate can dehydrate and form anhydride with catalyst and high temperature,thus formed the cross-linkage.In the third part,BSTA was analyzed and compared with other two extensively investigated polycarboxylic acids(BTCA,BPTCA)for anti-wrinkle finishing.The product(BSTA)was applied on cotton fabrics as a novel crosslinking agent for anti-wrinkle finishing,and the resulting fabrics showed excellent performance similar to those treated by BTCA.To understand the excellent crosslinking effect of BSTA,a series of experiments were conducted in this study.The factors of acid structures,potential reactive sites,molecular size,and affinity to cellulose,ester formation rate and Arrhenius activation energy were discussed to evaluate the differences of the PCAs on crosslinking cellulose.BSTA is an acid containing both aromatic and aliphatic carboxylic acid groups with a medium molecular size and can crosslink cellulose as efficiently as BTCA without causing significant loss of tensile strength of the products.In addition,BSTA exhibits better hydrophilicity,and higher affinity to cellulose than aromatic acids.Temperature dependent FTIR revealed that esterification of BTCA with cellulose is limited to formation rate of its anhydrides,while BPTCA is different.The kinetic data of BTCA,BPTCA and BSTA with cellulose were calculated by measuring the concentrations of the carboxylic acids on the fabric.The Arrhenius activation energy was discussed to evaluate the differences of the PCAs on crosslinking cellulose.The results indicated an order of reactivity,BPTCA(38.49 k J/mol)< BSTA(48.82 k J/mol)< BTCA(57.08 k J/mol).The reactivity was further confirmed by FTIR.In the fourth part,the extensively investigated reagents CA,BTCA,124-BTA,BPTCA,EGBTA,BSTA,DMDHEU were applied for anti-wrinkle finishing on cotton fabrics to study the differences with respective optimum conditions.Anti-wrinkle finishing with reagent was similar to dyeing process with absorption,diffusion,and reaction process.The Hansen Solubility Parameter was used to evaluate the affinity to water and cellulose of cross-linkers.The affinity of cross-linker to water reflects its solubility.Affinity to cellulose indicates the difficulty level for absorption and diffusion in part,further influenced the reactivity on cellulose.Chem Bio3 D 12.0 soft was used to calculate the Connolly solvent excluded volume(CSEV)and Rotatable bond number(RBN).CSEV value presents size of molecular and influences the diffusion into cellulose.RBN value affects the flexibility of molecular and thus the crosslinking efficient.Chem Bio3 D 12.0 soft was also applied for single crosslinking calculation.The effective crosslinking size distribution of different conformation was analyzed.The results show that the effective crosslinking size range is 5.0-10.0?.