Abstract
Cotton was modified with disodium salt of ethylene diamine tetra acetic acid (EDTA) in presence of potassium sodium tartrate as the esterification catalyst following a pad-dry-cure technique. Treatment of cotton fabric with 8% EDTA in presence of 8% catalyst followed by drying at 95°C for 5 min and curing at 140°C for 5 min produced optimum results in respect of exhaustion and fixation of reactive dyes having chlorotriazine and vinyl sulphone reactive groups when dyeing was accomplished in absence of salt. Colourfastness to wash, light, and rubbing of cotton for application of reactive dyes remain unaltered for such prior modification with EDTA. IR spectroscopy indicated incorporation of amine in polymeric chains of cotton via establishment of ester linkages between carboxyl groups of the EDTA and hydroxyl groups of the cotton cellulose on pad-dry-cure.
Reactive dye is widely used for coloration of cotton due to its ability to produce bright shades and good colorfastness properties at a reasonable cost (Lewis, 1993). The application process of such dye for cotton, however, suffers from the disadvantages of poor exhaustion of dye into the fiber, and the use of large amounts of electrolytes that ultimately create effluent containing a high concentration of color and salt, which causes environmental pollution (Bairagi, Gulrajani, Deopura, & Shrivastava, 2005). Incorporating amino compounds into cotton or viscose prior to dyeing appears to be promising in this respect in view of high exhaustion of reactive dye reported into such modified fibers even in the absence of salt (Burkinshaw, Lei, & Lewis, 1989; Burkinshaw, Mignanelli, Froehling, & Bide, 2000; Evans, Shore, & Stead, 1984; Patino et al., 2011; Shimizu, Dohmayou, Yoshikawa, & Takagishi, 2004). Reports of prior modification of cotton with acrylamide followed by reactive dyeing of acrylamide-modified cotton in the absence of salt for an overall improved result are available in the literature (Fang, Zhang, & Sun, 2013). It has also been reported in the literature that the type of reactive dye used for dyeing cationized cotton does not play any noticeable role in the dye yield and colorfastness properties of prior cationized cotton (Montazer, Malek, & Rahimi, 2007). A commercial cationizing agent of the type quaternized polyglycol ether of fatty amine is also reported to be employed for cationization of cotton. Improvements in the adsorption and fixation of reactive dyes on such cationized cotton have been reported as the result of combined effects of salt and the cationizing agent employed (Ristić & Ristić, 2012). Hercosett 125 prepared from adipic acid diethylenetriamine and epichlorohydrin has been reported to introduce a cationic charge to cotton permanently, owing to its reaction with cotton. Exhaustion and fixation of reactive dyes on such Hercosett 125-modified cotton enhance substantially due to the incorporation of, chiefly, the azetidinium group in cotton (Chattopadhyay, 2001). Reports of improvement in exhaustion and fixation of reactive dyes having chlorotriazinyl groups into aminated cotton are also available in the literature; prior amination of cotton was reported to be accomplished by pretreating cotton with 1,2-dichloroethane followed by treatment with methyl amine (Chattopadhyay, Chavan, & Sharma, 2007). Most of the amines and/or aminating agents reported in the literature and used for prior aminating cotton to improve reactive dyeability are reportedly highly toxic in nature and cause irritation to eyes, skin, and respiratory organs resulting in headache, dizziness, shortness of breath, nausea, and vomiting. Chlorine-containing agents, when used in such aminating processes, give rise to environmental problems in terms of enhancement of adsorbable organo halogens (AOX) in the effluent (Chattopadhyay, 2001).
Ethylenediaminetetraacetic acid (EDTA) is an innocuous, biodegradable, sequestering agent that forms a complex with a bivalent metal present in water, such as calcium or magnesium, and has wide applications in textiles for dyeing and bleaching. EDTA has been used as an electrolyte for promoting the exhaustion of reactive dye into cotton. Improved exhaustion of reactive dye into cotton is reportedly achieved as a consequence of neutralizing the negative-charge potential of cotton and enhancing the degree of aggregation of the dye molecules in the solution by common ion effect. The tetrasodium salt of EDTA has also been reported to promote the fixation of reactive dye by providing a necessary alkaline pH in the dye bath, favorable for the fixation of reactive dye on cotton (Ahmed, 2005).
Polycarboxylic acid compounds such as butanetetracarboxylic acid (Welch, 1992) and carboxyl-containing vinyl monomers such as methacrylic acid (Das & Munshi, 2006) and itaconic acid (Das, Datta, & Bhattacharya, 2014) have been reported to be esterified with the hydroxyl groups of cotton in the presence of suitable catalysts. EDTA, being a tetracarboxylic acid compound, has the possibility of being esterified with cotton under suitable conditions. Also, as EDTA is an amine, a positive charge on EDTA-modified cotton can be induced consequently to protonation of EDTA moieties under acidic pH for attracting negatively charged reactive dye toward EDTA-modified cotton. Moreover, no report so far is available in the literature stating the prior amination of cotton that employs such biodegradable and environmentally friendly aminating agents for improving the reactive dyeability of cotton. In view of this, we thought it would be of interest to modify the cotton fabric with EDTA, following a pad-dry-cure technique under the influence of a suitable esterification catalyst prior to the application of reactive dye on cotton and assess the reactive dyeability of such EDTA-modified cotton. The results of related investigations done on bleached cotton fabric under the catalytic influence of potassium sodium tartrate are reported in the present article.
Method
Materials
Mill-bleached plain weave cotton fabric obtained from National Textile Corporation (Kolkata, West Bengal, India) with 262 ends/dm, 315 picks/dm, 13 Tex warp count, 15 Tex weft count, and having an average areal density of 106 g/m2 was considered for the present study. Procion Red M5B (Color Index Reactive Red 2) and Procion Yellow H4C (Color Index Reactive Yellow 84) were obtained from M/s ATIC Industries Limited (Valsaad, Gujarat, India). Remazol blue R (Color Index Reactive Blue 19) was obtained from M/s Ashwini International (Kolkata, West Bengal, India). The above dyes were used without any purification for the study. All other chemicals including EDTA and potassium sodium tartrate used in the study are of laboratory reagent grade.
Experimental Procedures
Application of EDTA on bleached cotton was done by the padding technique in a laboratory two-bowl padding mangle. After two successive dippings in the aqueous formulation containing different specified doses of EDTA, the pressure between the squeezing rollers was adjusted to enable an overall wet pickup of 100%. The aqueous formulations also contained potassium sodium tartrate as an esterification catalyst as indicated in Table 1. The padded and squeezed cotton fabrics were dried at a temperature of 95°C for 5 min and subsequently oven-cured at 140°C for 5 min; soap-washed following the International Standard Organization (ISO) II method; washed further with water; and air-dried. The soap wash following the ISO II method was performed by treating the EDTA-cured cotton fabric in an aqueous solution containing 5 g/l of soap at a material/liquor ratio of 1:50 for a period of 45 min at 50°C temperature in a wash wheel having 40
Effect of Application of Ethylenediaminetetraacetic Acid (EDTA) on the Properties of Cotton.
Note. The data given in the parentheses refer to the coefficient of variation % (CV%) of the corresponding property parameters.
Applications of Procion Red M5B and Procion Yellow H4C on unmodified cotton were done following conventional methods at a material/liquor ratio of 1:20 with a starting dye bath temperature of 30°C and 50° C, respectively. Both dye baths had a common salt concentration of 70 g/l, and fixation of (dichlorotriazenyl) Procion Red M5B and (monochlorotriazenyl) Procion Yellow H4C was achieved after 40 min of dyeing at dye bath temperatures of 30°C and 80°C, respectively. Fixation of such reactive dyes was commonly effected by employing 10 g/l sodium carbonate and dyeing further for a period of 60 min. Application of (vinyl sulfone) Remazol blue R reactive dye on unmodified cotton was accomplished at a material/liquor ratio of 1:20 at 60°C, employing 50 g/l Glauber salt and 10 g/l sodium carbonate. Dyeing was done for a period of 60 min.
Dyeing was commenced at 30°C at a material/liquor ratio of 1:20, with a starting pH in the range of 4–7 as specified and employing a drop-wise addition of different doses of formic acid. The pH of the dye bath was subsequently brought from 10 to 12 by the addition of sodium carbonate after 25 min of dyeing. After the addition of sodium carbonate for fixation of the reactive dyes used in this study, the dyeing was continued for a further 60 min. Fixation temperatures kept for reactive dyes with dichlorotriazenyl, monochlorotriazenyl, and vinyl sulfone reactive groups were 30°C, 80°C, and 60°C, respectively. The dye bath did not contain any salt during the application of reactive dye unless otherwise specified. The dyed fabrics were thereafter soap washed (80°C), hot washed, cold washed, and finally dried in air. For the assessment of fixation of dye on cotton, dyed cotton was extracted further with 50%V/V dimethyl formamide (DMF)–water mixture in a Soxhlet apparatus for 30 min, washed with water, and air-dried. The exhaustion and fixation of reactive dye were determined by taking dyes present in exhaust liquor, wash liquor, and Soxhlet extract appropriately into consideration. The dye in each of the above liquors was estimated color-metrically by employing a U-2000 Hitachi UV-Vis absorbance spectrophotometer (Hitachi, Japan) as also described in Cheek’s (1982) research.
Evaluation of Dyeing and Other Textile Properties
For the determination of weight gain upon application of EDTA in the pad-dry-cure technique, the modified fabric was soap washed following the ISO II method as detailed before. The washed fabric sample was then dried to a constant weight (W 1) at 100°C. The weight gain (%) was calculated on the basis of initial dry weight of scoured cotton (W 2) using the following relationship as indicated in Equation 1.
Dye uptake of EDTA-modified and unmodified cotton fabrics was estimated in terms of K/S (ratio of coefficient of absorbtion to coefficient of scattering) employing a Macbeth 2020 + reflectance spectrophotometer, Macbeth (USA), interfaced with a computer (Kubelka–Munk function).
The tenacity of some selected fabric samples was measured in an Instron tensile testing machine 4411, Instron (USA), according to a method prescribed by ASTM D 5034. The results obtained were based on an average of 10 tests in the warp direction of each sample. The size of the test specimen was 50 mm × 20 mm, and tests were performed with a traverse speed of 40 mm/min.
Infrared spectra of unmodified and selectively modified cotton samples were obtained following the KBr pellet technique as detailed elsewhere, using a Bomem FTIR spectrometer of ABB Analytical Measurements (formerly Bomem Inc., Canada). The dried fabric samples were crushed to a size finer than 20 mesh before pelletizing with KBr. The test KBr pellet contained about 1% powdered fiber.
Colorfastness tests to wash (ISO: 105 C06), rubbing (ISO: 105 X12), and light (ISO: 105 B02) were done following the standard procedures and approaches described by the ISO. Colorfastness to wash was done employing a Launder-Ometer obtained from SDL Atlas, China. The test for colorfastness to light was done employing a lightfastness tester obtained from Shirley Development Limited (Bradford, UK). Colorfastness to rubbing was done by employing a digital crockmeter obtained from Shirley Development Limited (Bradford, UK).
Moisture regain of selected samples was assessed following a method prescribed in ASTM D 2495-07. The results given are the average of 10 tests done for each sample. The wrinkle recovery angle (warp + weft) of the selected fabric samples was measured using a SASMIRA wrinkle recovery tester obtained from silk and art silk mills research association (SASMIRA; Mumbai, Maharashtra, India), following a test method prescribed in ASTM D 1295-67. Results recorded for analysis are the averages of 10 tests.
Results and Discussion
Effect of Variation of Dose Level of EDTA
The effect of applying different doses of EDTA in the absence and presence of potassium sodium tartrate as the esterification catalyst expressed in terms of percentage of EDTA on the weight of 100 g of a cotton fabric sample following a pad-dry-cure technique is shown in Table 1. Also shown is that the potential of EDTA to self-catalyze the esterification process under the given condition is poor or simply marginal, giving poor weight gain and nitrogen content. Improvement in the wrinkle recovery of such cotton fabric modified with EDTA in the absence of catalysts is also observed to be poor, with the highest retention of tenacity among the cotton samples listed in Table 1. When increasing the dose level of EDTA, the weight gain and nitrogen content of the cotton fabric follow a common increasing trend. A higher degree of esterification of cellulose chains of cotton via incorporated EDTA moieties in the presence of higher doses of esterification catalyst evidently tends to produce higher weight gain and nitrogen content for a given system as shown in Table 1. When no catalyst is used, both weight gain and nitrogen content achieved in the treatment with EDTA are expectedly low, indicating that the potential for carboxylic acid groups of EDTA to self-catalyze the esterification process is marginal. Tenacity of the fabric, however, was shown to decrease as dose levels of EDTA increased, as evident from relevant data given in Table 1. Such a reduction of tenacity in cotton modified with EDTA is the consequence of the hydrolytic degradation of cotton during EDTA curing at elevated temperatures under the influence of the potassium sodium tartrate used as the esterification catalyst. Relevant data given in Table 1 also indicate that with increasing application levels of EDTA, the wrinkle recovery of cotton fabric tends to increase, leveling off at a 10% application level of EDTA.
Infrared Analysis
The infrared spectra for (a) unmodified bleached cotton and (b) bleached cotton modified with EDTA in the presence of potassium sodium tartrate used as the esterification catalyst following a pad-dry-cure technique are shown in Figure 1. A strong absorption band at 3,340 cm−1 is common to both the spectra; such common spectra account for the intermolecular hydrogen-bonded OH stretching of cotton cellulose. Other common absorption bands appearing in different intensities in both spectra are 2,358 cm−1 and 1,436 cm−1, characteristics of –CH2– stretching and –CH2– symmetrical bending, respectively. Two new notable absorption bands appearing in spectrum (b) in strong-to-medium intensities at 1,214 cm−1 and at 1,736 cm−1 are the characteristics of C–N stretching of amine and ester stretching vibrations, respectively. Such absorption bands, however, are practically nonexistent in the spectrum of bleached unmodified cotton, spectrum (a). Treatment of cotton with EDTA in the presence of potassium sodium tartrate as esterification catalyst resulted in the incorporation of EDTA moieties into cotton cellulose, consequent to the establishment of ester linkages between the carboxyl groups of EDTA and the hydroxyl groups of cotton cellulose. A description of a reaction that took place between EDTA and cotton under the catalytic influence of potassium sodium tartrate in the pad-dry-cure technique is presented in Figure 2 for better appreciation of the findings of infrared analysis described above.
Infrared spectra of (a) unmodified bleached cotton and (b) bleached cotton treated with ethylenediaminetetraacetic acid.
Reaction of cotton with ethylenediaminetetraacetic acid in the presence of potassium sodium tartrate catalyst.
Effect of Variation of Dye Bath pH on Dyeability of EDTA-Modified Cotton
When coloring wool with reactive dye, an initial acidic dye bath pH distinctly favored a higher incorporation of reactive dye in the protein substrate, owing to a strong mutual attraction between the protonated, positively charged protein fiber and the negatively charged reactive dye (Lewis, 1993). Keeping this in mind, the effects of variation of the starting dye bath pH for applications of different specified reactive dyes on EDTA-modified cotton were studied; the results are given in Figures 3 –5. Results indicate that, with a decrease in dye bath pH, the exhaustion of reactive dye tends to increase for EDTA-modified cotton fabrics dyed with different reactive dyes as specified in Figures 3 –5. This suggests that the protonation of EDTA-modified cotton favors an increase in reactive dye uptake. Also, the exhaustion points of all reactive dyes considered in our study (Figures 3 –5) reach their respective maximum at a common dye bath pH of 4. The appreciable exhaustion observed for the above three colorants at a starting dye bath pH of 4 is considered to be of practical significance for the dyeing of cotton with reactive dyes. Such changes of exhaustion with dye bath pH are also found to be common for cotton modified with different dose levels of EDTA (as indicated in Figures 3 –5), expressed in terms of nitrogen content of EDTA-modified samples. Dye–fiber attraction in this reactive dye and EDTA-modified system in the absence of salt is expected to depend chiefly on the ionic attraction between negatively charged reactive dyes and electron-deficient protonated amine groups of EDTA duly bound to cotton via ester linkage. The above exhaustion patterns of reactive dyes for EDTA-modified cotton are the consequence of such force of attraction between protonated, pendant, prior-grafted, amine groups of cotton, and negatively charged reactive dyes that ultimately led to improved levels of dye transfer into the EDTA-modified cotton substrates from an aqueous dye bath. Also, a higher exhaustion is achieved for cotton previously modified with a higher dose level of EDTA, as evident from Figures 3 –5. However, a final, almost-leveling-off trend for the exhaustion of reactive dyes appears in most of the cases for the application of EDTA just beyond 8%; this corresponds to an EDTA-modified cotton sample having 4.83% nitrogen content as shown in Figures 3 –5. This leveling off observed for higher doses of EDTA application (>8%) is due to the physical barrier offered by the grafted-on EDTA to the approaching dye anions from the aqueous phase of dyeing the EDTA-modified cotton with a reactive dye.
Bar chart showing exhaustion of reactive dye Procion Red M5B with respect to nitrogen content in modified cotton fabric at different pH levels of the dye bath.
Bar chart showing exhaustion of reactive dye Procion Yellow H4C with respect to nitrogen content in modified cotton fabric at different pH levels of the dye bath.
Bar chart showing exhaustion of reactive dye Remazol blue R with respect to nitrogen content in modified cotton fabric at different pH levels of the dye bath.
Fixation of the above reactive dyes on cotton samples previously modified with different specified dose levels of EDTA was also studied at various specified fixation pHs (pH 9–12), and results are also given in Figures 6 –8 in the form of a bar chart for fixation against nitrogen content of the EDTA-modified cotton samples. In such studies, different fixation pHs as specified in the figure were achieved by adding appropriate doses of sodium carbonate to the dye bath following a procedure described in the experimental section. Results suggest that the fixation of all dyes as specified follows a common increasing trend, with increases in the fixation pH of the dye bath maxing out at a common dye bath pH of 11 for all cotton samples, even for those with different dose levels of EDTA. It is also worth mentioning that the fixation of all the reactive dyes follows a common increasing trend, with increases in nitrogen content of the EDTA-modified cotton fabric showing a common maximum for 6.65% nitrogen content, even for different fixation pHs considered in our study. However, higher incorporation of EDTA into cotton via esterification evidently caused a higher extent of fixation of reactive dyes at all pHs of fixation, consequent to a higher initial transfer of reactive dyes. The fixation of reactive dyes in the quantitative sense therefore appears to be dependent on the initial absorption of reactive dyes on EDTA-modified cotton, and reasonably high values of fixation appear to be achievable for cotton modified with 8–10% EDTA.
Bar chart showing fixation of reactive dye Procion Red M5B with respect to nitrogen content in modified cotton fabric at different pH levels of the dye bath.
Bar chart showing fixation of reactive dye Procion Yellow H4C with respect to nitrogen content in modified cotton fabric at different pH levels of the dye bath.
Bar chart showing fixation of reactive dye Remazol blue R with respect to nitrogen content in modified cotton fabric at different pH levels of the dye bath.
The above results justify the alternate dyeing method followed in our study as described in the experimental section and necessitate commencement of dyeing from an acidic dye bath (pH 4) followed by a change of dye bath pH to alkaline (pH 11), so that results will be useful concerning the fixation of the mostly absorbed reactive dye molecules on the cellulosic substrate. A fixation pH of 11 appears to produce a common fixation level of more than 90%. A dye bath fixation pH of 12 commonly causes a lowering of the fixation value for the cotton samples previously modified with different dose levels of EDTA, in the case of application of Procion dyes. However, for application of Remazol dyes, such effect is not as pronounced, which is evident from the data given in Figure 8. Results also suggest that reactive dyes are fixed on EDTA-modified cotton under the alkaline fixation conditions employed in this study in such a manner that the majority of incorporated dyes in the modified cotton could not be removed from the substrate when the EDTA-modified reactive dyed substrates were extracted with a DMF–water mixture at the estimated time of reactive dye fixation. From the results, it appears that a fixation pH of 11 gives the optimum effect in regard to fixation of reactive dyes on EDTA-modified cotton.
Properties of Reactive-Dyed Cotton Priorly Modified With EDTA
A comparison of reactive-dyed EDTA-modified cotton and reactive-dyed unmodified cotton with respect to their property parameters is shown in Table 2. Prior treatment of cotton with EDTA following a pad-dry-cure technique increases the fixation of reactive dyes and moisture regain as evident from the data given in Table 2. Colorfastness to light, rubbing, and wash remains undiminished for prior modification of cotton with EDTA. Such results of the colorfastness properties of EDTA-modified cotton vis-à-vis that of unmodified cotton indicate that a modified dyeing process employed for EDTA-modified cotton having a starting acidic dye bath pH and a final alkaline fixation pH appears to have no significant adverse effect on the fixation process of reactive dye for EDTA-modified cotton. On overall assessment, reactive-dyed EDTA-modified cotton appears to be superior to reactive-dyed unmodified cotton with respect to the fixation of reactive dye and moisture regain for achieving comparable colorfastness properties for the dyeing of cotton with reactive dyes in the total absence of salt. Wrinkle recovery of EDTA-modified cotton also appears to be enhanced somewhat for applications of different dose levels of EDTA under the influence of potassium sodium tartrate as the esterification catalyst. The establishment of ester linkages between carboxyl groups of EDTA and hydroxyl groups of cotton also led to some degree of cross-linking of chain polymers of cotton, promoting wrinkle recovery of the fabric as evident from the data given in Table 1.
Comparison of Some Important Functional Properties of Reactive Dyed Unmodified Cotton and Reactive Dyed Ethylenediaminetetraacetic Acid (EDTA)-Modified Cotton.
Note. The data given in the parentheses refer to the CV% of the corresponding property parameters.
Conclusion
The appropriate modification of cotton prior to dyeing with EDTA in the presence of potassium sodium tartrate rendered the cotton fabric suitable for improved fixation of reactive dyes, when reactive dyes with chlorotriazinyl and vinyl sulfone groups were applied in the absence of salt. Prior modification of cotton with EDTA followed by dyeing of EDTA-modified cotton with reactive dyes led to balanced improvements in the properties of the dyed substrates with respect to the fixation of reactive dyes; retention of tenacity; improvement in wrinkle recovery; and colorfastness to light, wash, and rubbing. A prior modification of cotton with 8–10% EDTA and 8–10% potassium sodium tartrate following a pad-dry-cure technique made the cotton fabric sufficiently aminated to be dyed with the above dyes for a final dye fixation of more than 90%. An acidic starting dye bath pH (∼4) followed by an alkaline fixation pH (∼11) for the application of above reactive dyes on EDTA-modified cotton produced optimum effects.
Footnotes
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.