Non-Formaldehyde Anti-Wrinkle Finishing Of Pure Cotton Fabrics By 1,2,3,4-Butanetetracarboxylic Acid

Anti-wrinkle finishing of pure cotton fabrics is a kind of critical post-finishing process in the dyeing and finishing for fabrics.Presently,the main products for anti-wrinkle finishing of cotton fabrics are formaldehyde-containing compounds,which endow the treated fabrics with good anti-wrinkle properties.However,the released formaldehyde during manufacturing and wearing process will irritate human skin or respiratory tract,and even cause cancer.Therefore,it is very necessary to develop non-formaldehyde finishing agents,which can reduce or remove the harm of formadehyde to human body and reach the requirements of ecological environmental performance of textiles.The most widely studied ones are polycarboxylic acids,especially that the fabrics treated by 1,2,3,4-butanetetracarboxylic acid(BTCA)show the optimum anti-wrinkle performance and durable washing.However,the main drawback is that BTCA will cause significant strength loss to treated fabrics,which restricts the widespread industrial application.To solve this issue,the primary thing is to clarify the catalytic actions of catalysts and the mechanism of crosslinking reactions between BTCA and cellulose.Up to now,the catalysis of sodium hypophosphite(SHP)and the anhydride formation followed by ester reactions between BTCA and cellulose hydroxyls have not been very clear,causing that the issue of the significant strength loss of treated fabrics has not been essentially resolved.Besides,they become the obstacles for seeking new effeicient catalysts and finishing agents.To solve the above problems,new experimental conditions were designed here.SHP cations and anions were clarified to separately catalyze the formation of anhydride and the esterification between anhydride and cellulose,and a new type of co-catalyst was developed based on the results.By investigating about the step-by-step anhydride formation and esterification reactions between BTCA and cellulose hydroxyls,the curing temperature was decreased and a kind of mixed efficient catalyst was prepared.Furthermore,the essential reasons for the strength loss of BTCA treated fabrics were analyzed from two new viewpoints of compound size and chemical affinity,and new insights were proposed.Finally,the p H effects of BTCA and catalyst pyrophosphoric acid(PPA)finishing bath on the anti-wrinkle properties were investigated in details,and results indicated that divalent PPA anions were more efficient than monovalent PPA anoions to catalyze the esterification between anhydrides and cellulose.In addition,divalent PPA anions showed higher efficiency when its relative concentration as well as the concentration increasing rate was higher.These studies would provide theoretical supports and directions for the development of new finishing agents and catalysts in the future.The first part investigated the catalytic mechanism of catalyst SHP.In order to develop new kinds of efficient catalysts,the catalytic mechanism of SHP should be profoundly clarified.The weak alkalinity of SHP was considered as one of the reasons for its good catalytic efficiency.Fourier transform infrared(FTIR)results showed that some carboxylate was formed after SHP was added into the BTCA solution.Based on the results of FTIR and wrinkle recovery angle(WRA),alkaline metal ions would accelerate the formation of BTCA anhydrides,and K~+was the most efficient one among Li~+,Na~+and K~+.Thermogravimetric analysis(TGA)also showed that K~+was the most efficient to decrease the temperature for anhydride formation.Besides,Gaussian calculation directly indicated that the hydrogen bonds between BTCA molecules would be weakened or eliminated by the alkaline metal ions.For studies on the catalyst anions,FTIR and WRA both showed that SHP,sodium phosphite,phosphoric acid,pyrophosphoric acid(PPA)and dichloroacetic acid(DCAA)presented their respective optimum p H value,at which ester absorbance and WRA of the treated fabrics would show the highest values.The optimum p H value was correlated to the p Ka1 of corresponding acid of the catalyst:an acid with a smaller p Ka1would show a lower optimum p H value and a higher anion relative concentration.Based on the above studies,the specific catalytic mechanism of SHP was explained that the metal cations of alkaline salt catalysts accompanied by the low p H condition would accelerate the formation of anhydride by weakening the H-bonds between molecules,and then the corresponding catalyst anions would promote the esterification between anhydrides and cellulose hydroxyls by removing the protons of the intermediates.In addition,a new kind of alkaline catalyst HD-30 was prepared based on the theoretical study.According to the acquired results,HD-30 increased the p H value of finishing bath and consequently decreased the strength losses of treated fabrics cured at high temperature without affecting the WRA value.The second part mainly clarified the crosslinking mechanism between BTCA and the cellulose hydroxyls.Though the catalysis of catalyst SHP in accelerating the formation of anhydride was explained in the first part,each BTCA molecule contains four carboxyl groups and can form two anhydrides at the same time theoretically.However,it was not clear whether one or two anhydrides would be formed before reacting with cellulose hydroxyls,which hinders the development of new kinds of catalysts.This is the study focus of this part.At different molar ratios,the mixture of BTCA and Na OH was processed by TGA and the weight loss percents were compared with the theoretical values for the formation of one anhydride.The correlation between anhydride absorbance as well as ester absorbance change and one anhydride formation by BTCA was investigated by adopting acetone washing of treated fabrics.Based on the above study,a step-by-step reaction mechanism of anhydride formation and esterification between BTCA and cellulose was illuminated:one anhydride was formed firstly and reacted with a cellulose hydroxyl,and then the second one was formed and reacted with another cellulose hydroxyl.On the basis of step-by-step anhydride formation,FTIR was employed to select 160? as an optimal curing temperature,reducing the strength loss of treated fabrics.In addition,DSC results indicated that SHP and trisodium citrate(TSC)would decrease the onset temperature of BTCA most,which was also confirmed by the TGA results that they would promote BTCA to form more anhydrides at the same temperature.Therefore,SHP and TSC were mixed at a molar ratio of 2:3 as a hybrid catalyst HD-MP,which imparted good ant-wrinkle property to the fabrics and decreased the consumption of SHP by 60%.Interestingly,TSC not only brought in cations to promote the anhydride formation,but also decreased the strength loss by increasing the p H of finishing bath,so HD-30 is no longer necessary to be added.The fabric treated under the proposed process achieved similar DP ratings to that of fabric treated under the traditional process.The third part mainly focused on the effects of BTCA molecular size and affinity on the strength losses caused by acidic degradation,hoping to illuminate the reasons for fabric strength loss on the basis of molecular physical and chemical properties and provide a direction for the development of new non-formaldehyde finishing agents.There are two major reasons for the significant strength losses of BTCA treated fabrics:strength losses due to acidic degradation of cellulose chains(TSL_A)and strength losses due to crosslinking between cellulose chains(TSL_C).It was proposed that the acid diffusibility and the affinity of the polycarboxylic acid(PCA)to cellulose,separately based on the molecular sizes and the Hansen solubility parameters(HSP),were the reasons for the TSL_A.FTIR and anti-wrinkle properties confirmed that BPTCA is more active to react with cellulose,causing less TSL_A.By Chem Bio3D software calculation,results indicated the radius of BTCA is smaller than that of BPTCA.BTCA showed better diffusibility in fibers than the latter according to the diffusion coefficient and would diffuse into the inner part of the fiber.However,due to the ineffective crosslinking,BTCA would also degrade more cellulose chains,resulting in more TSL_A.The optical microscope results of the dyeing fiber cross-section also confirmed the better diffusibility of BTCA.Besides,the model acids further proved that an acid with a smaller radius would cause more TSL_A.The Hansen distances(Ra)between acid molecule and dihydrogen oxide or cellobiose were calculated by HSPi P4.1.07 software.The Ra values of BTCA were much smaller than those of BPTCA,so BTCA showed higher chemical affinity to cellulose and therefore caused more TSL_A.Based on the studies,it was concluded that the smaller molecular size and the better affinity of BTCA to cellulose would explain the significant TSL_A of the treated fabrics.However,BPTCA is more reactive.This provided a direction for the development of new kinds of finishing agents,namely the new one should present higher reactivity than BTCA with the radius locating between BTCA radius and BPTCA radius and contain both aliphatic PCA end group and aromatic PCA end group.The fourth part dealt with the effects of molecular structure and chemical affinity of catalyst on the TSL_Cof BTCA treated fabrics.Although the third part has revealed the reasons of BTCA on the TSL_A of the treated fabrics,it did not clarify the effect factors on TSL_C.However,TSL_C is closely related to the efficiency of catalyst in accelerating the ester crosslinking between BTCA and cellulose.So it is very important to clarify this issue.The third part gave us a good understanding about the effects of molecular sizes and affinity of the acids to the cellulose on TSL_A,and based on the similar idea,these two aspects of the catalysts,which affected the crosslinking between BTCA and cellulose,should affect the TSL_C of treated fabrics.For the selected five catalysts,the treated fabrics under their separate optmal p H condition showed different TSL_C values.Based on the calculation results of Chem Bio3D14.0,the anion radius of SHP was the smallest among the selected catalysts,so it would show the best diffusibility,promoting more crosslinking between BTCA and cellulose.Besides,the Connolly accessible area(CAA)of SHP anion was also the smallest among the catalysts,which was beneficial to the collision between catalyst anions and reaction substrates,accelerating the initiation of reactions between anhydrides and cellulose.HSPi P4.1.07 results indicated the largest Ra between hypophosphorous acid(HPA)and BTCA or cellobiose.As a result,it was easier for HPA to leave from the surface of the substrates and promote the completion of esterification between anhydride with cellulose,resulting in more crosslinking and higher TSL_C.All the above results proved that the catalyst with a smaller anion radius and a weaker affinity to the substrates would cause more crosslinking and consequently higher TSL_C.Dichloroacetic acid(DCAA),as a non-phosphorous catalyst,showed similar molecular structure parameters to HPA and was employed to further confirm the hypothesis.The benefit of DCAA catalyst also lied in that the treated fabrics would show similar WRA and less strength losses due to the higher optimum p H condition.Above all,the sought of new efficient catalysts based on molecular sizes and chemical affinity is reliable.The last part investigated the anti-wrinkle properties of fabrics treated by catalyst pyrophosphoric acid(PPA).Though PPA is also a kind of phosphorus-containing catalyst,the difference from SHP is that it can ionize divalent anions at low p H condition,so it is important to study its catalytic actions for the development of new catalysts.According to studies in the fourth part,although the raidus and the CAA of PPA were both the largest among the selected catalysts,the treated fabrics still showed similar WRA and TSL_C.Interestingly,PPA was the only one that can ionize the divalent anions at lower p H condition among the selected catalysts.According to the anionic actions on removing protons in the reactions between anhydrides and cellulose hydroxyls,the anion valence should affect the crosslinking reaction and is worth of further study.At first,WRA and TSR of the fabrics processed under different p H conditions were analyzed based on the BTCA reaction efficiency.And then,the TSL_A and the TSL_C of the treated fabrics were separated by alkaline hydrolysis,and FTIR was used to measure the ester bonds.The relative concentrations of BTCA and the corresponding anions as well as PPA and the corresponding anions were calculated,and it was found that a higher relative concentration and a faster increasing rate of divalent PPA anions were beneficial to improve the anti-wrinkle properties.Besides,the hydrogen bonds between BTCA carboxyl and cellulose hydroxyls can improve WRA of fabrics,and this was further confirmed by the model chemicals of succinic acid and BTCA.Finally,the washing resistant performance of the treated fabrics was studied.Based on the above studies,the optimum p H value for catalyst PPA was about 2.8,at which WRA and TSL_C both reached the highest values,as well as ester absorbance.In addition,the divalent PPA anions were proved to be more efficient than the monovalent anions to accelerate the esterification between BTCA and cellulose.Hydrogen bonds between BTCA and cellulose hydroxyls and higher softness both improved WRA values of the treated fabrics.So PPA can be used as a kind of efficient catalyst for anti-wrinkle finishing of cotton fabrics with polycarboxylic acid.Besides,it was inspired that the compound which can ionize multiple-valent anions at low p H condition and remove protons is highly efficient catalyst for anti-wrinkle finishing with BTCA.