Durable Press Finishing of Cotton Fabrics with Citric Acid

Article pubs.acs.org/IECR

Durable Press Finishing of Cotton Fabrics with Citric Acid: Enhancement of Whiteness and Wrinkle Recovery by Polyol Extenders Wenting Yao,†,‡ Bijia Wang,†,‡ Tao Ye,†,‡ and Yiqi Yang*,†,‡,§,∥ †

Key Laboratory of Science & Technology of Eco-Textiles, Ministry of Education and ‡College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai 201620, China § Department of Textiles, Merchandising & Fashion Design and ∥Department of Biological Systems Engineering and Nebraska Center for Materials and Nanoscience, University of NebraskaLincoln, 234 HECO Building, Lincoln, Nebraska 68583-0802, United States ABSTRACT: A durable press finisher formula based on citric acid (CA), featuring polyol extenders, can be made to compare favorably to dimethylol dihydroxyethyleneurea (DMDHEU) or 1,2,3,4-butanetetracarboxylic acid (BTCA) in whiteness and wrinkle recovery performance. Durable press (DP) finishing of cotton fabrics with CA has long been implicated by inferior resilience enhancement and appreciable fabric yellowing, which hinder the industrialization of the technique despite the obvious merits of CA being cost-effective, nontoxic, and renewable. In this research, glycerol was used as the model compound for investigateing the mechanism of polyol’s whitening effect and for obtaining the optimized curing conditions. Then a series of polyols were investigated as extenders for the cross-linking of cotton with CA. Performance indicators such as the wrinkle recovery angle (WRA), CIE whiteness index (WI), tear strength (TS) retention, and DP rating of the treated fabrics were correlated with curing conditions and the structures of the extenders. It was found that the whitening power of the extenders is directly related to the number of primary hydroxyl groups. It was also found that polyols containing both primary and secondary hydroxyl groups are more effective at enhancing the resilience of treated fabrics. By using xylitol as the extender, DP ratings of 3.8−3.9 were imparted to both white and dyed cotton fabrics finished with CA without significant yellowing or discoloration. The addition of the extender was also favorable to the durability of the DP effects so that a DP rating of 3.5 was retained after 20 washing and tumble-drying cycles. It was shown that by using biobased extender xylitol two major drawbacks of DP finishing of cotton with CA could be eliminated, presenting an essentially green alternative to DMDHEU.

1. INTRODUCTION The cross-linking of cellulose has long been used to enhance the wrinkle resistance of cotton fabrics by reducing chain slippage under moist conditions.1 Among the various agents used to replace the formaldehyde-releasing N-methylol crosslinking agent, polycarboxylic acids (PCAs) are believed to be the most promising ones.2−5 The most extensively studied PCA cross-linkers include the proven most effective 1,2,3,4butanetetracarboxylic acid (BTCA),6,7 citric acid (CA),8,9 maleic acid and its oligomers (MA and PMA),10−12 and itaconic acid (IA).13,14 The combination of BTCA and the highly effective activator sodium hypophosphite (SHP) provides the same level of durable-press performance as does conventional dimethylol dihydroxyethyleneurea (DMDHEU).6 However, it still has not been embraced by the textile industry because of the prohibitively high cost. It is widely accepted that cheap, renewable, and essentially edible CA would be the ideal formaldehyde-free cross-linker if the problems of yellowing15,16 and inferior performance to BTCA could be solved. It was proposed that the severe yellowing resulted from unsaturated CA derivatives formed upon dehydration at elevated curing temperatures.15,17 CA has been successfully applied in the low-temperature wet crosslinking of regenerated proteins,18 where dehydration is not a concern. Although the yellowing problem may be reduced by appropriate additives17,19,20 such as triethanolamine hydro© 2013 American Chemical Society

chloride (TEA·HCl), poly(ethylene glycol)s (PEGs), polyols, and boric acid or by using milder curing conditions,15 the improved whiteness is usually at the cost of DP performance. It had been suggested that the addition of PEGs was effective at improving the whiteness of CA-treated fabrics, possibly by assisting reversal of the dehydration reaction.17 However, no experimental evidence was reported to support this hypothesis. In our previous research of cross-linking soy protein with CA,21 it was found that glycerol, added as a plasticizer, led to an appreciable alleviation of yellowing. It was natural to consider using this cheap and regenerable polyol in the cross-linking of cotton with CA to enhance the whiteness of the treated fabrics. It was surprising that despite similar polyols such as sorbitol being tried as whitening agents for CA-treated cotton fabrics,19 glycerol had never been used for this purpose. In this study, the effectiveness of glycerol as a whitener in DP finishing with CA was first examined under various curing conditions. A model reaction of glycerol and CA in the presence of SHP was carried out to investigate the mechanism of glycerol’s whitening effect. Furthermore, systematic studies on how the polyol structure affects the DP rating and whiteness of the finished fabrics were carried out using a series of polyols. Received: Revised: Accepted: Published: 16118

August 21, 2013 October 21, 2013 October 24, 2013 October 24, 2013 dx.doi.org/10.1021/ie402747x | Ind. Eng. Chem. Res. 2013, 52, 16118−16127

Industrial & Engineering Chemistry Research

Article

Figure 1. (a) WRA and weight gain of CA/glycerol-treated fabrics cured at various temperatures. (b) Tear strength retention and whiteness index of CA/glycerol-treated fabrics cured at various temperatures.

softener CT208 were obtained from the Waker Chemical Company. Laundry detergent was a nonbleaching product from Shanghai White Cat Co. Ltd. 2.2. Fabric Treatment. Fabric treatments were carried out on a laboratory-scale rapid M-TENTER tenter frame. Preweighed fabrics were padded with two dips and two nips using a finishing bath containing a cross-linking agent, catalyst, softener, and one or more polyol additives to about 70% wet pickup (DMDHEU-treated controls were padded to 55% wet pickup). Padded fabrics were dried at 85 °C for 5 min and cured at 150 to 180 °C for 1 to 10 min. The cured fabrics were machine washed and tumble dried using a XQG50-1 washer− dryer according to AATCC Test Method 124 before testing. 2.3. Fabric Testing. The wrinkle recovery angle (WRA) was measured according to the American Association of Textile Chemists and Colorists (AATCC) Testing Method 66-2003. A home laundering washing/drying procedure was used, and a durable press rating was measured according to AATCC Testing Method 124-2006. CIE whiteness index (WI) and color difference (ΔE) measurements were made according to AATCC Testing Methods 11-2005 and 173-2005 respectively. The tear strength of the treated fabrics was measured according to the American Society of Testing Materials (ASTM) Testing Method D-1424-1996 using a Thwing-Albert Elmendorf tearing tester. The strip breaking strength was measured according to ASTM-D-5035-06 using Tinius Olesen benchtop tester

The best extender was identified and subjected to optimization. The optimized conditions were applied to both white and colored cotton fabrics and compared to DMDHEU and BTCA finished fabrics, respectively. It was shown, for the first time, that discoloration and poor DP performance of CA finished fabrics could be fixed simultaneously by using an appropriate polyol extender.

2. EXPERIMENTAL SECTION 2.1. Materials. The fabrics used in this study were desized, scoured, and bleached 40 × 40 cotton poplin weighing 123 g/ m2, reactively dyed yellow 40 × 40 cotton cloth weighing 113 g/m2, and reactively dyed navy 50 × 50 cotton cloth weighing 105 g/m2 kindly provided by the Esquel Group. Citric acid monohydrate, sodium hypophosphite monohydrate, ethylene glycol, 1,4-butanediol, 1,5-pentadiol, 1,6hexadiol, pentaerythritol, sorbitol, glycerol, cyclohexanol, benzyl alcohol, PEG 200, PEG 400, and PEG 600 were purchased from Sinopharm Chemical Reagent Co. Ltd. 1,3Propanediol was purchased from Tokyo Chemical Industry Co. Ltd. BTCA, xylitol, and cyclohexylmethanol were purchased from Adamas-Beta Reagent. 1,2-Propanediol and tris(methylol)ethane were purchased from Alfa Aesar. All chemicals used were reagent grade and used as received. DMDHEU was a commercial product containing 55% solid, kindly supplied by the Esquel Group. Wetting agent JFC and 16119

dx.doi.org/10.1021/ie402747x | Ind. Eng. Chem. Res. 2013, 52, 16118−16127


Article

Figure 2. Performances of CA/glycerol-treated fabrics cured at 180 °C for various times.

Figure 3. Comparison of 13C NMR spectra of major products formed by baking CA and SHP in the absence and presence of glycerol.

H10KS. All mechanical tests were carried out in the warp direction. All tests were carried out after one home laundering if not specified. 2.4. Model Reactions without the Fabrics. CA, SHP, and glycerol in a 1:1:1 or 1:1:0.5 molar ratio were combined and made into a concentrated aqueous solution. The solution was then placed in an evaporating dish, dried at 85 °C to constant weight, and cured at 180 °C for 10 min. The products were extracted into methanol, dried, and subjected to NMR and

TGA analyses. A control without glycerol was subjected to the same treatments. 2.5. Characterization of Model Reaction Products. 13C nuclear magnetic resonance (13C NMR) spectra were recorded on a Bruker AM-400 spectrometer. The samples (100 mg) were dissolved in 0.5 mL of d4-methanol. Chemical shifts were referenced to the solvent peak at 49.3 ppm. Thermogravimetric analysis (TGA) was performed with a TG-209-F1 manufactured by Netzsch at a heating rate of 10 °C/min from 30 to 600 °C under a nitrogen atmosphere. The 16120



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Scheme 1. Possible Mechanism for SHP-Promoted Formation of 2-Methyl Succinic Acid

Scheme 2. Possible Mechanism for Reaction between Cellulose and Glycerol Dicitrate II as an Extended Cross-Linker

shown in Figure 1b. The curing temperature was chosen to be 180 °C for the rest of the experiments to avoid a significant decomposition of citric acid. The effect of curing time on the performances of treated fabrics was investigated, and the results are shown in Figure 2. The fabric resilience indicated by WRA peaked at a curing time of 5 min. Both the whiteness and TS retention of the treated fabric continued to decrease with elongated curing time. Therefore, curing the fabric at 180 °C for 5 min seemed to impart the best performance. Under this condition, the CIE whiteness index measured after one home laundering improved substantially from 24.6 to 59.7 with the addition of one equivalent of glycerol. A whiteness index close to 60 is generally

weight of the samples was 4 to 5 mg; the rate of gas consumption was 40 mL/min.

3. RESULTS AND DISCUSSION 3.1. Glycerol as the Extender in CA Cross-Linking. Figure 1a shows the percentage weight gain and fiber performances of CA/glycerol-treated fabrics cured at different temperatures for 90 s. A 1:1:1 molar ratio of CA, SHP, and glycerol was used. Although the fiber resilience kept increasing with curing temperature, the weight gain peaked at 180 °C, indicating the dominance of undesirable decompositions at higher temperatures. A higher curing temperature also led to aggravated yellowing and a loss of tear strength of samples as 16121



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Figure 4. TGA curves of products from model reactions.

considered to be acceptable for unbleached cotton fabric.19 The addition of glycerol also increased the TS retention of the treated fabric from 63.2 to 69.9 without significantly lowering its resilience. 3.2. Mechanism of the Whitening Effect Imparted by Glycerol. To understand better the mechanism behind the whitening effect of glycerol, the reaction of CA, SHP, and glycerol was studied under conditions resembling the curing process. The 1:1:1 mixture of CA, SHP, and glycerol yielded an off-white gummy material after being baked at 180 °C for 10 min. The control containing a 1:1 mixture of CA and SHP gave a yellow powdered product. It was clear that the control (Figure 3, spectrum on top) contained a significant quantity of unsaturated species as indicated by the characteristic peaks of CC double bonds from 110 to ∼150 ppm. The yellow appearance of the product was most likely caused by these unsaturated species. It was unexpected that 2-methyl succinic acid rather than cyclic CA anhydride was the major product identified in the mixture (Figure 3, spectrum on top). When CA was heated alone, less than 10% decomposition was observed after heating at 180 °C for 10 min. Therefore, SHP appeared to have promoted the decarboxylation and dehydration of CA. A possible mechanism of the reaction is shown in Scheme 1. Adding 1 equiv of glycerol resulted in the formation of glycerol citrate I as the major product (Figure 3, spectrum on bottom). The bottom spectrum was much cleaner with no characteristic peaks of CC double bonds (110−150 ppm). This indicated that the undesirable dehydration of CA leading to unsaturated species was effectively suppressed by adding 1 equiv of glycerol. When the amount of added glycerol was halved, the product appeared to be slightly yellow and gummy and was only partially soluble in methanol. Multiple peaks showed up in the carbonyl and CC bond regions in the 13C NMR spectrum of this product, indicating that monocitrate I was no longer the dominant product and a small amount of unsaturated CA derivatives had formed. Although it was hard to identify the major product in this case, glycerol dicitrate II (Scheme 2) would be expected. Compared to CA, compound II is more likely to react twice with neighboring hydroxyl groups on cellulose because its reactive carboxylic groups are well spaced by the flexible extender backbone. A possible reaction of glycerol dicitrate II and cellulose is shown in Scheme 2. Likewise, other oligomeric esters of glycerol and CA featuring citrates at both ends would also be able to act as

extended cross-linkers. The larger span of the extended crosslinkers might also be the reason for the lower tensile strength loss observed for fabrics treated with extenders added. The thermal stability of the model reaction products was studied using TGA as shown in Figure 4. The onsets of the decomposition temperature (at a weight loss of 10%) were improved by about 28 and 55 °C with loadings of 0.5 and 1 equiv of glycerol, respectively. A second decomposition stage was observed at about 320 °C for the two products with glycerol added, which could be attributed to the decomposition of the thermally more stable glycerol citrates. TGA of 1 equiv of grounded cotton mixed with 1:1 CA/SHP is also shown in Figure 4. This mixture showed only about a 12 °C improvement in the onset decomposition temperature (at a weight loss of 10%). This suggested that despite being a polyol, cellulose was not as effective in suppressing the unfavorable decomposition of CA. The reactivity of a hydroxyl group on a polymer would be hampered by its lack of flexibility to adopt the favorable orientation. At 180 °C, cellulose barely reacts with CA or other PCAs without a catalyst, whereas the uncatalyzed esterification of CA with monomeric polyols is feasible. Therefore, the higher reactivity of the monomeric polyols was crucial to suppressing the undesirable decompositions. The greater reactivity of the monomeric polyol extenders was also crucial to allowing the extended cross-linkers, such as compound II, to form in a rich environment of cellulose. From the mechanistic study, it was learned that the whitening effect of a polyol was likely due to the formation of polyol citrates, which were less prone to decomposition under the curing conditions. The addition of an appropriate amount of a polyol would also lead to the formation of extended cross-linkers, or esters featuring citrates at either end, that were more likely to react with cellulose multiple times. It was also noticed from the model reactions that instead of catalyzing the formation of cyclic CA anhydride, SHP was more active in promoting the formation of 2-methyl succinic acid. 2Methyl succinic acid has one less carboxylic group and would not be able to cross-link cellulose, which might be the reason that excess SHP led to a lower WRA of the treated fabric. 3.3. Polyols of Varying Structures as Extenders. Using the optimized curing condition for glycerol, we conducted a systematic investigation on the relationship between the structures of polyols and their performance as cross-linking extenders by using a series of polyols. These included the previously reported ethylene glycol, tris(methylol)ethane, 16122



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Table 1. Effect of Polyol Extenders on Textile Properties Imparted by 10% CA and 5% SHPa extender ethylene glycol 1,2-propanediol 1,3-propanediol 1,4-butanediol 1,5-pentanediol 1,6-hexanediol PEG 200 PEG 400 PEG 600 glycerol Tris(methylol)ethane pentaerythritol xylitol sorbitol

extender/CA (molar ratio)

−OH/−COOH

WRA (w + f)b

TS%(w)c

WId

3:2 3:16 3:2 3:16 3:2 3:16 3:2 3:16 3:2 3:16 3:2 3:16 3:2 3:16 3:2 3:16 3:2 3:16 1:1 1:8 1:1 1:8 3:4 3:32 3:5 3:40 1:2 1:16

1:1 1:8 1:1 1:8 1:1 1:8 1:1 1:8 1:1 1:8 1:1 1:8 1:1 1:8 1:1 1:8 1:1 1:8 1:1 1:8 1:1 1:8 1:1 1:8 1:1 1:8 1:1 1:8

252 271 260 271 257 282 252 274 238 274 248 272 232 273 209 271 197 273 257 268 255 274 252 279 265 287 255 272 261 131

66 59.2 63 58.8 72.5 62.9 68.4 58.1 68.6 58.9 69.5 62.7 62.7 58.7 61.2 58.8 61.8 57.9 69.9 64.5 64.5 59.6 65.6 61 63.5 60.4 62.5 62.2 63.2 100

53.8 29.3 51.8 31.1 59.9 32.3 60.9 34.5 61.2 35.8 62.2 38.2 60.6 35.6 54.9 38.2 57.6 39.4 59.7 35.0 66.3 35.2 72.4 38.9 58.2 34.5 56.3 33.9 24.6 67.3

no extender controle

a All finishing baths contained 10% CA, 5% SHP, 2% softener, and 0.2% JFC. Padded fabrics were predried at 85 °C for 5 min and cured at 180 °C for 5 min. bWrinkle recovery angle. cWarp direction tear strength. dWhiteness index. eThe control was subjected to the same pad−dry−cure procedure as the other samples with no chemicals added.

Figure 5. Effects of polyols featuring various numbers of 1° hydroxyl groups on whiteness index of fabrics finished with CA.

pentaerythritol, and three PEGs of varying sizes. In the previous reports, the added polyols were usually kept at the same weight percentage with respect to the fabric, leading to dramatic differences in molarity for polyols of various sizes. In this study, the quantity of polyols added was adjusted so that the molar ratios of hydroxyls from the polyol and carboxyls from CA were 1:1 and 1:8, respectively. This arrangement allowed us to study the whitening and resilience enhancement effects of the polyols separately. The results are summarized in Table 1.

All of the polyols studied imparted a substantial improvement in whiteness when a sufficient amount was used to give a 1:1 ratio of hydroxyl and carboxyl groups. It was worth noticing that although the whiteness enhancement was not satisfactory at a lower OH/COOH ratio of 1:8, an appreciable increase in fabric resilience was achieved with most polyols in this ratio. The most effective whitener was found to be pentaerythritol, which features four primary hydroxyl groups. Figure 5 compared the whitening power of the polyols with one to four primary hydroxyl groups and showed a positive correlation 16123



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Figure 6. Effects of diols of varying sizes on the properties of fabrics finished with CA.

between the number of primary hydroxyls on the polyol and its whitening power. Primary hydroxyls are the most reactive ones to form an ester linkage with CA, leading to the suppressed formation of colored unsaturated derivatives from dehydration. The results also showed that despite the differences in the number of total hydroxyls, ethylene glycol, glycerol, xylitol, and sorbitol led to similar WI values. This was likely due to the fact that all of them are in possession of two primary hydroxyl groups. The performances of linear terminal diols of various lengths added at a molar ratio of 3:2 were compared in Figure 6 to investigate the effect of the bridging length. It was clear that at this dosage most of these diols were effective at enhancing the whiteness of the treated fabrics, except for ethylene glycol and PEG 400. However, all of the diols inevitably decreased the WRAs in this case. The three poly(ethylene glycol)s caused the largest drop in WRA without imparting a particularly high WI. The results seemed to indicate that longer bridges were less effective at keeping the cellulose chain from slipping. The optimum length of the extender seemed to lie between three and six carbons. It was surprising to notice from Figure 6 that 1,3-propanediol gave not only the highest WRA but also the highest TS retention of all of the diols. This was unexpected because the accepted theory states that a high level of cross-linking leads to a higher WRA but a severe drop in TS. This result seemed to suggest that the high WRA of 1,3-propanediol-treated fabrics was not necessarily a result of high cross-linking. This might be general for polyol-added PCA cross-linking systems because throughout the data in Table 2 no definitive relationship between WRA and the TS retention of the treated fabrics was observed. The mechanism behind this phenomenon is under further investigation. The performances of the three C3 polyols, namely, 1,2propanediol, 1,3-propanediol, and glycerol in a 1:1 OH/COOH ratio were compared in Figure 7. The difference in performance was within experimental error for 1,3-propanediol and glycerol. The two differ only in that glycerol has an additional secondary hydroxyl group, suggesting that secondary hydroxyls are not involved in CA esterification. 1,2-Propanediol imparted a similar WRA but was less effective at improving the WI because it has only one primary hydroxyl group.

Table 2. Comparison of the Optimized DP Finish with CA to DMDHEU and BTCA Treatmentsa finishing agent d

CA/xylitol BTCA DMDHEU CA controle

WRA

DPb

WI

TS%(w)

BS%(w)c

270 277 275 257 125

3.9 3.9 4.0 3.3 1

57.8 62.8 64.2 38.6 70.7

62.3 64.8 49.6 63.6 100

60.5 56.2 37.0 59.4 100

All finishing baths contained 2% softener and 0.2% JFC. Padded fabrics were predried at 85 °C for 5 min and cured at 180 °C for 3 min, except that fabrics treated with DMDHEU were cured at 150 °C for 3 min. Add-ons for CA, BTCA, and DMDHEU were 10, 6, and 8%, respectively. SHP (50% of PCAs) and MgCl2·6H2O (1.5%) were used as catalysts. bDurable press rating after one standard laundering. cWarp direction breaking strength. d1.1% xylitol was added. eThe control was subjected to the same pad−dry−cure procedure as the CA/xylitol finished sample with no chemicals added. a

The effects of polyols with varying ratios of 2° to 1° hydroxyls on WRA for treated fabrics are plotted in Figure 8. When sufficient polyols are present (1:1 OH/COOH), then WRA appears to increase with the ratio of 2° to 1° hydroxyls with the exception of sorbitol. Because the total quantity of hydroxyl groups added was kept constant and 1° hydroxyl is much more reactive than 2° hydroxyl, polyols featuring a higher secondary hydroxyl ratio left more free carboxyls to react with cotton. The results at low polyol loading (1:8 OH/COOH) did not follow any trend, indicating that competition between polyols and cotton to esterify CA could be neglected in this case. In both cases, xylitol was the most effective resilience enhancer with which the WRA could be raised from 261 to 287°. At high polyol loading (1:1 OH/COOH), xylitol was the only polyol that imparted a higher WRA than the control. These results suggested that the fabric resilience was very sensitive to the structure of the extenders. Although 2° hydroxyls are less likely to be involved in esterification, their presence may enhance the fiber resilience through hydrogen bonding with cellulosic hydroxyls. This non-cross-linking enhancement of fabric resilience was not expected to impair 16124



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Figure 7. Performance of the C3 polyols on DP finishing with CA (1:1 OH/COOH).

Figure 8. Effects of polyols with a varying ratio of 2° to 1° hydroxyls on WRA of treated fabrics.

Figure 9. Performance of varying amounts of xylitol on DP finishing with CA.

offers a DP finishing formula that is essentially green. Further studies were carried out to examine the CA/xylitol cross-linking system. Figure 9 shows the performance of treated fabric with varying amounts of added xylitol. The initial addition of xylitol substantially increased the WRA to 287°. WRA decreased gradually as more xylitol was added. Up to a load of 1.2 equiv, xylitol yielded WRAs no worse than the control. As expected,

the TS retention, which was consistent with what was observed in this study. 3.4. Xylitol as an Extender for DP Finishing of White and Colored Cotton Fabrics with CA. As the most effective extender identified by this research, xylitol has an additional advantage of being a renewable biobased product. The industrial production of xylitol starts from xylan, which is extracted from hardwoods. The combination of CA with xylitol 16125



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WI of the treated fabrics continued to increase as more xylitol was added. In all cases, the tear strength retention was greater than 58%. The optimum resilience was achieved by applying 0.075 equiv of the xylitol extender. Unfortunately, the whiteness of the fabric was far from acceptable under this condition. When whiteness was brought up to the acceptable range, the WRA of the fabric was only slightly better than the control. Acceptable WI and WRA could be achieved by adding 0.3 equiv of xylitol and shortening the curing time to 3 min. Tables 2 and 3 compare the performance of white cotton poplin

Table 4. Comparison of Properties of Dyed Fabrics Finished with Various Cross-Linking Systemsa fabric yellow

blue

Table 3. Comparison of DP Durability of Fabrics Finished with Various Cross-Linking Systemsa WRA after n washings N=1

5

10

20

N=1

5

10

20

CA CA/xylitolb BTCA DMDHEU controlc

257 270 277 275 125

252 262 269 262

245 260 263 256

234 250 254 253

3.3 3.9 3.9 4.0 1

3.2 3.8 3.8 3.8

3.0 3.6 3.7 3.6

2.8 3.5 3.5 3.5

WRA

DP rating

TS% (w)

BS% (w)

ΔEb

CA CA/xylitolc BTCA DMDHEU control CA CA/xylitol BTCA DMDHEU controle

268 278 274 272 127 265 275 281 291 158

3.4 3.8 3.9 3.8 1.3 3.5 3.9 3.8 3.8 1.7

59.8 61.7 57.2 44.8 100

56 57 53.1 36 100 51.4 57.2 55.1 41.5 100

0.81 0.56 0.83 0.32 0 0.61 0.86 0.56 0.28 0

d

60.8 59 d

100

a All finishing baths contained 2% softener and 0.2% JFC. Padded fabrics were predried at 85 °C for 5 min and cured at 180 °C for 3 min, except that fabrics treated with DMDHEU were cured at 150 °C for 3 min. Add-ons for CA, BTCA, and DMDHEU were 10, 6, and 8%, respectively. SHP (50% of PCAs) and MgCl2·6H2O (1.5%) were used as catalysts. bColor difference in cmc units. c1.1% xylitol was added. d The tear strength of the treated fabric is beyond the lower limit of the tester. eThe control was subjected to the same pad−dry−cure procedure as the CA/xylitol finished sample with no chemicals added.

DP rating after n washings

finishing agent

finishing agent

a All finishing baths contained 2% softener and 0.2% JFC. Padded fabrics were predried at 85 °C for 5 min and cured at 180 °C for 3 min, except that fabrics treated with DMDHEU were cured at 150 °C for 3 min. Add-ons for CA, BTCA, and DMDHEU were 10, 6, and 8%, respectively. SHP (50% of PCAs) and MgCl2·6H2O (1.5%) were used as catalysts. b1.1% xylitol was added. cThe control was subjected to the same pad−dry−cure procedure as the CA/xylitol finished sample with no chemicals added.

xylitol substantially enhanced the DP rating with a subtle enhancement of TS and BS as well. BS was measured because TS dropped below the testing limit after DMDHUE and CA treatment for the feeble blue cotton fabric. In practice, lower curing temperatures had to be used for DMDHEU-based industrial finishes to ensure sufficient strength retention for this particular fabric, in which case the DP performance is inevitably compromised. Data in Table 4 clearly showed that fabrics treated with CA/ xylitol have appreciably better strength retention compared to DMDHEU-treated fabrics. This is an unexpected plus for this newly developed CA-based finishing system. Overall, comparable DP performance to DMDHEU and BTCA treatments can be imparted to the dyed cotton fabrics using CA/xylitol with minor discoloration and strength loss.

finished using this optimized condition to several controls. Conditions used for the BTCA control were based on previously reported optimized conditions. Conditions used for the DMDHEU control were suggested by the Esquel group. By examining Tables 2 and 3, we can conclude that CA/ xylitol offers comparable DP performance and DP durability to BTCA. After 20 standard home laundering cycles, the DP rating of the CA/xylitol finished fabric did not drop below 3.5, whereas that for the fabric finished with only CA fell to 2.8. The whiteness of the CA/xylitol finished fabric was comparable to that of the control similarly treated (pad−dry−cure) with DI water. As little as 1.1% o.w.f. of xylitol was needed to achieve these appreciable improvements. It was also noticed that the fabric treated with PCAs clearly had a higher TS retention than did the DMDHEU-treated one. Because CA costs only oneeighth of what BTCA costs, the overall cost could be cut appreciably even though a slightly higher loading of CA was needed. Both CA and xylitol are listed among the 12 renewable chemicals by the U.S. Department of Energy as nontoxic renewable resources and biologically safe nutrients,22 making the CA/xylitol formula advantageous compared to petroleumbased PCAs such as BTCA and MA. 3.5. DP Finishing of Dyed Cotton Fabrics with CA/ Xylitol. DP finishing of dyed cotton fabrics with PCAs was reported to give rise to coloration changes with ΔE = 4−6.23 In this study, the effects of CA/xylitol treatment on two dyed cotton fabrics were also examined. The results are summarized in Table 4. For both the yellow and the blue cotton fabrics, the treatment of DMDHEU gave the lowest ΔE. In all cases, ΔEs were within the acceptable range of

Durable Press Finishing of Cotton Fabrics with Citric Acid

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