DURABLE-PRESS FINISHING OF COTTON FABRICS WITH MIXTURES OF BTCA,  CA AND SOME ADDITIVES.

M. RAHEEL, C. GUO, G. X. DAI

University of Illinois at Urbana-Champaign, USA

ABSTRACT

The efficacy of polycarboxylic acids, Butanetetracarboxylic acid ( BTCA )  and Citric acid ( CA) as cross-linkers for cotton when used individually, and as mixtures of various ratios  is investigated. Also, the effects of additives such as Triethanolamine ( TEA ) on whiteness index of cotton, and the inclusion of direct dyes in the cross-linking bath on dye fixation and wrinkle recovery are addressed. Dye fixation levels are compared with the conventional two-step dyeing and finishing process.

 INTRODUCTION

The conventional method of durable-press finishing of cotton involves urea-formaldehyde type cross-linking agents. With the recognition of formaldehyde as a probable carcinogen (10, 12) formaldehyde-free durable-press (DP) finishes have been developed which utilize polycarboxylic acids (13, 15, 16) . Butanetetracarboxylic acid ( BTCA) system has been found to be very effective DP finishing agent for cotton, and DP ratings comparable with those finished with dimethyloldihydroxy ethylene urea (DMDHEU) have been achieved (5, 13, 15) .  BTCA is an environmentally friendly cross-linking agent but more expensive than DMDHEU resin. Citric acid (CA) also is a nontoxic cross-linking agent for cotton, and costs much less than BTCA. But one of the draw backs of citric acid is that it produces an off-color on white cotton goods (2 ) and does not achieve the same level of DP rating as BTCA. Thus, it is of interest to  investigate the efficacy of mixtures of BTCA and CA in achieving acceptable levels of wrinkle recovery in cotton, while reducing the cost of finishing system compared to pure BTCA. Since citric acid is an a-hydroxyl carboxylic acid, esterification could occur between the carboxyl groups of BTCA and a-hydroxyl group of CA to form a hexacarboxylic acid which may be even more effective than BTCA. We wanted to explore this hypothesis. Also, the effects of additives, such as Triethanolamine  ( TEA ) on whiteness index as well as wrinkle recovery of cotton is studied. In addition, the feasability of incorporating  direct dyes in the cross-linking bath to achieve a single step dyeing and cross-linking of cotton fabric is explored.

 Saving production cost by reducing energy consumption, production time, dyeing and finishing chemicals,  and water, is an important goal of the textile industry. Dyeing in conjunction with durable-press finishing (single-step) is based on incorporating dyestuff in the finishing bath. Several attempts have been made to incorporate acid or reactive dyes in formaldehyde containing resin finishing agents for this purpose (7, 8, 11). Because of incompatibility between wet, alkaline fixation conditions for most cellulose dyes and dry acid conditions for finishes, the finishing agents explored in single-step processes are limited. Direct dyes, on the other hand, usually are applied under neutral conditions without the addition of alkalis for fixation. Also, direct dyes are stable, less expensive and easy to apply. One-step dyeing and DP finishing has been studied by Choi (6), they showed that excellent color strength and dye fixation were achieved using reactive dyes in conjunction with BTCA. But not much work is reported on DP finishing  of cotton textiles, especially with mixtures of BTCA and CA, in conjunction with dyeing or the presence of other additives.

 Objectives

The objectives of this study were: 

1.      To investigate the efficacy of Butanetetracarboxylic acid ( BTCA )  and Citric acid

      ( CA) as cross-linkers for cotton when used individually, and as mixtures of various   

      ratios.    

2.      To examine the effects of additives such as Triethanolamine  ( TEA ), on whiteness index and wrinkle recovery of durable-press finished  cotton.

 3.      To investigate the feasibility of incorporating direct dyes in the polycarboxylic cross-linking system for  cotton fabric.

  EXPERIMENTAL

Materials

Fabric: Bleached mercerized cotton print cloth from Testfabrics Inc., Middlesex, NJ.

Finishing agents: Polycarboxylic acids were, 1,2,3,4-butanetetracarboxylic acid (BTCA)  from Aldrich Chemical Company Inc., and citric acid ( CA ), from Alfa Company .

                    H₂C-COOH

                        ½

                     HC-COOH                                                        H₂C-COOH           

                        ½                                                                         ½

                     HC-COOH                                                       HOC-COOH

                        ½                                                                         ½

                    H₂C-COOH                                                       H₂C-COOH

1,2,3,4,- butanetetracarboxylic acid (BTCA)                      Citric acid (CA)

Catalyst: Sodium hypophosphite monohydrate (NaHPO₂.H₂O), Sigma Chemical Co.

Additives:

Direct Dyes: Two direct dyes from Crompton & Knowles Industrial Products Division were used in this study. The dyes were:

1. Direct Red 81, a class A dye   

2. Direct Green 26, a class B dye

3.  Reagent grade 98% Triethanolamine ( TEA ) from Aldrich Co.        

                               CH₂CH₂OH

                    N          CH₂ CH₂OH

                               CH₂CH₂OH

Other chemicals and water:

Wetting agent: Triton X-100(Alkyle phenoxy polyethoxy ethanol), Rohm and Haas Co.

Softener: Protolube Pe, by National Starch and Chemical Co.

Water: Distilled water for all dyeing and finishing solutions.

METHODS AND PROCEDURES

Cross-linking Treatments With and Without Additives:

Cross-linking treatments were done using BTCA system and CA system individually, and as mixtures of various ratios. Also, additives  such as triethanolamine, and direct dyes were included in the finishing bath for single step dyeing and finishing ( SDF ) process.

Cotton specimens ( 38x61 cm ) were padded in a solution containing 6.5% owb cross-linking  agent,  the catalyst, sodium hypophosphite ( SHP) was one-to-one mole ratio Vs finishing agent. The cross-linking bath also contained 1% owb Triton X-100 and 1% owb Protolube Pe. Additives such as dyes, and triethanolamine were 2% owf ,  when called for. The cross-linking agents were pure 1,2,3,4-butanetetrecarboxylic acid ( BTCA ), pure citric acid ( CA ), and  mixtures of CA/BTCA in 5:1, 2:1, 1:1, 1:2, 1:5 ratio respectively. The liquor-to-goods ratio was 10:1. Two-dips and two-nips gave a wet pickup of about 100%. The specimens were dried for 5 min. at 85 °C and cured at 190 °C for 90 sec., then washed and dried. For comparison of wrinkle recovery, or dyeing efficacy, a set of specimens was treated with finishing agents without the addition of triethanolamine, or dyeing . Also, results were compared with the conventional two step dyeing and cross-linking process.

Two-step Dyeing and Finishing Process:

Dyeing: Dyeing was done in a Darlten AATCC standard dyeing machine. Dye bath was prepared with 2% owf direct dye and 20% owb sodium chloride at a 40:1 liquor-to-goods

ratio. Fabric specimens ( 38x61 cm) were entered into the dye bath at 40-50 °C and then the liquor temperature was raised to 60 °C for C.I. Direct Red and 100 °C for C.I. Direct Green over a period of 30-40 min. and dyeing process was continued for 60 min. The samples were washed in cold running water for 10 min. and then air dried.

Durable-press Finishing: Dyed cotton specimens were padded with cross-linking

agents using two-dips and two-nips giving a wet pickup of 100%, then dried at 80 °C for 5 min. and cured at 190 °C for 90 sec., after which they were washed and dried. The paddding bath contained 6.5% owb BTCA or CA, NaH2PO2.H2O ( one-to-one mole ratio Vs. BTCA or CA ), 1% owb Triton  X-100, and 1% owb Protolube Pe when Triethanolamine (TEA) was used (1: 0.5 mole ratio Vs BTCA or CA). The liquor-to-goods ratio was 10:1.

Fabric Performance Tests:

Wrinkle recovery of fabrics was evaluated according to AATCC Test Method 66-1990 (1).  Dye Fixation (wash colorfastness ) as per AATCC Test Method 153-1985 using  Hunter Labscan 6000 Spectro-colorimeter, and Whiteness Index ( WI ) was measured according to AATCC Test Method 110-1989 (1).

RESULTS AND DISCUSSION

Effect of CA/BTCA Mixture Ratio on Dry Wrinkle Recovery Angle:

Since citric acid is much less expensive than BTCA, the efficacy of CA and BTCA mixture in different ratios on dry wrinkle recovery angle (WRA) of cotton fabric was studied. The ratios included, CA: BTCA  5: 1, 2: 1, 1: 1, 1: 2, and 1: 5. Results of dry wrinkle recovery angle (WRA) of cotton fabric cross-linked with pure BTCA and CA as well as mixtures of the two reagents in various ratios are given in Table 1. It is apparent that 100%BTCA imparted a higher level of dry wrinkle recovery than 100%CA. It appears that WRA increased significantly  with increasing concentration of BTCA in the mixture upto 1 : 1 ratio, and then leveled off. It is suggested that a tetracarboxylic acid

( BTCA ) can esterify the hydroxyl group of an alpha-hydroxy  di- or tricarboxylic acid to yield, in situ, a penta or hexacarboxylic acid (14),  which would be a very efficient cross-linking agent for cotton cellulose. The formation of hexacarboxylic acid is related to the concentration of BTCA and CA in the mixture, therefore, the reaction rate would form a curve with a certain maximum point and then level off. Thus, from a practical point of view acceptable level of WRA is achieved with a 1:1 ratio mixture of BTCA and CA.

Effect of Triethanolamine Additive on Dry Wrinkle Recovery Angle:

Dry wrinkle recovery  data, with and without the addition of Triethanol amine (TEA) in the cross-linking bath also are given in Table 1. In general, TEA hindered the efficacy of both cross-linkers when used individually or as mixtures in various ratios. Hence a decrease in dry wrinkle recovery angle. Esterification of carboxylic acid and cotton is effective at low pH values. Because of the basic nature of TEA, its presence in the cross-linking bath increased the pH , which hindered the esterification reaction.

Table 1. Dry Wrinkle Recovery Angle (WRA) of Cotton Treated

              With Mixtures of BTCA and CA in Different Ratios

              a: TEA = Triethanolamine, b: WRA = Wrinkle Recovery Angle

Effect of Triethanolamine Additive on Whiteness Retention:

Cotton fabrics crosslinked with citric acid have the drawback of yellowing. Even BTCA produces some yellowing of white fabrics but to a much lower extent than CA. Andrew

et al.,  (3,4 ) have demonstrated that the cause of yellowing of CA finished fabrics is dehydration of citric acid with the production of aconitic acid from abscission of hydroxyl group and an adjacent hydrogen. Triethanolamine ( TEA ), as an additive to citric acid crosslinker enhances the whiteness retention of cotton fabric as well as the strength and abrasion resistance of treated cotton ( 9) . The mechanism by which TEA operates is not 

clear, a possible explanation is that TEA acts as an etherifying agent,  etherifies the

hydroxyl group of citric acid and protects it from abscission. As shown in Fig. 1. The

presence of TEA as an additive enhanced the whiteness index of cotton fabric

significantly when the fabric was cross-linked with pure CA, or BTCA, as well as with mixture of the two reagents in various ratios. If the explanation of the hydroxyl group of citric acid being etherified and protected  from abscission is correct, then in the BTCA-CA mixture cross-linking system, BTCA could react with hydroxyl group of CA and also protect it from abscission. In other words, as the ratio of BTCA in the mixture is increased whiteness retention should increase. In this study, as shown in Fig. 1. the presence of BTCA  in the mixture did improve the whiteness index of cross-linked cotton relative to pure CA, both without  TEA, especially up to 2:1 CA/BTCA ratio, and in the presence of TEA.

Effect of Direct Dyes as Additives on Dry Wrinkle Recovery Angle:

When dyeing step was incorporated in the durable-press finishing step, recovery angles were found to be  different in the one-step and the conventional two-step processes as a function of the dye type. As shown in Table 2., in the presence of Direct Red 81, both

BTCA and CA showed higher WRA in the two-step process than in the single step process (SDF). But in the presence of Direct Green 26 the conventional two step process with BTCA cross-linker showed significantly lower WRA than the single step process. However the reverse was true with CA cross-linker. It is theorized that in the conventional process (dyeing then DP finishing), dye molecules seem to block

the reaction sites of cotton cellulose that would otherwise be available for cross-linking with carboxylic acids. This influence is more apparent when large molecular size finishing agent ( BTCA ) as well as dyestuff with many nucleophilic groups,  such as Direct Green 26 were used. The effect of the two dyes as additives in the single step process is shown in Fig. 2, where both dyes enhanced the WRA of DP finished fabric.

Table 2. Dry Wrinkle Recovery Angle (WRA) of Cotton Treated by SDF (one step) 

              and Conventional Process (two step) Using BTCA , CA, and Different Direct    

              Dyes with and without TEA^a

a: TEA = Triethanolamine.

 Effect of Dyes in Conjunction  with TEA on Wrinkle Recovery: 

The results of dry wrinkle recovery angle when TEA was used as an additive in conjunction with dyed in the single-step  process  are shown in Table 2.  when CA  and BTCA were used individually. Also, in Fig. 3. when used as a mixture in different ratios.

Results indicate that the presence of  TEA suppressed both the wrinkle recovery angle and percent dye fixation as will be explained in the later section on dye fixation. Thus TEA did not play a positive role in the single-step dyeing and durable-press finishing process. 

Effect of Crosslinker on Dye Fixation:

After both single-step and two-step dyeing and cross-linking processes, fabrics were washed according to AATCC Method 61-1989, and % dye fixation was measured. Results are given in Fig. 4. Dye fixation was higher in cross-linked cotton than untreated fabric. In both processes % dye fixation was greater for BTCA cross-linker than CA.

However the two-step process achieved a higher level of wash colorfastness than single step process.

This could be explained on the basis of two effects, one, formation of cross-links with cotton and its blocking effect on dye movement, and the second, due to the reaction between dye and finishing agent thus fixing it to cotton. Better wash colorfastness was expected with C.I. Direct Green 26 than C.I. Direct Red 81 in both processes since the former has good exhaustion and a large number of nucleophilic groups and larger molecular size. However, the results revealed the opposite in the single-step ( SDF) process. This indicates that unlike the conventional process, dye molecule size plays an important role in the SDF process. The smaller molecular size dyestuff( C.I. Red 81) showed better penetration in the fiber before crosslinking takes place. Besides the molecular size, steric configuration and high aggregation properties of direct dyes may also have contributed to this difference. The large molecular size of the dye  influenced not only  penetration of the dyestuff but also on crosslinking ability of the finishing agents because of its blocking effect. This result is in line with data shown in Table 2. where  wrinkle recovery angle ( WRA ) of fabric dyed and finished in the single step ( SDF )process using Direct Green 26 is lower compared to Direct Red 81.

Effect of CA/BTCA Mixture Ratio on dye fixation:

Results of Dye fixation when CA/BTCA cross-linkers were in different ratios is given in Fig. 5. As shown in Fig. 5 dye fixation increased at higher BTCA concentration, but the increase was not dramatic after 1: 2 ratio. The increase in BTCA concentration generated

more free carboxylic groups into the system to react with direct dyes. Again, dye fixation was higher for Direct Red 81 at all CA/BTCA mixture ratios.

 CONCLUSIONS

Polycarboxylic acids are gaining recognition as a new class of formaldehyde-free durable-press ( DP ) agents. Butanetetracarboxylic acid( BTCA ) is a very effective DP agent for cotton textiles compared to citric acid ( CA ), a much less expensive crosslinker. With the goal of saving cost, we investigated the efficacy of mixtures of CA and BTCA crosslinkers in different ratios. Also, a single-step dyeing and durable-press finishing process ( SDF ) using direct dyes was explored to assess the feasability of the process and indirectly  saving processing time, energy and water consumption. Some of the findings are as follows:

·        Mixture of CA and BTCA in 1:1 ratio achieved good wrinkle recovery  values close to pure BTCA. It is postulated that the reaction between BTCA and CA to form a very efficient crosslinker, hexacarboxylic acid is responsible for this result. Also, dye fixation increased as the ratio of BTCA increased in the mixture but after 1: 1 ratio further increase in dye fixation was not very significant.

·        Excellent dye fixation and wrinkle recovery were achieved by BTCA in the single-step dyeing and finishing process compared to CA.

·        Because of competition and repellence between polycarboxylic acids and direct dyes, percent dye fixation and wrinkle recovery values in the SDF process were somewhat lower than the conventional two-step process.

·        In the SDF process molecular weight of the dye played an important role. C.I. Direct Red 81 with smaller molecule showed better dye fixation and wrinkle recovery than the larger size C.I. Direct Green 26.

1.      Addition of triethanolamine to the crosslinking bath improved the whiteness retention of cotton but there was a decrease in dye fixation and wrinkle recovery values.

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