Article pubs.acs.org/IECR
Heterogeneous Chemical Modification of Cotton Cellulose with Vinyl Sulfone Dyes in Non-Nucleophilic Organic Solvents Bijia Wang,†,‡ Xinhui Ruan,†,‡ Luyi Chen,†,‡ Jiangang Chen,†,‡ and Yiqi Yang*,†,‡,§,∥ †
Key Laboratory of Science & Technology of Eco-Textiles, Ministry of Education, Donghua University, 2999 North Renmin Road, 201620 Shanghai, China ‡ College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, 2999 North Renmin Road, 201620 Shanghai, China § Department of Textiles, Merchandising & Fashion Design, University of Nebraska-Lincoln, HECO Building, Lincoln, Nebraska 68583-0802, United States ∥ Department of Biological Systems Engineering and Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, HECO Building, Lincoln, Nebraska 68583-0802, United States ABSTRACT: Hydrolysis-free heterogeneous modification of cotton cellulose with vinyl sulfone (VS) dyes in non-nucleophilic organic solvents was investigated. Dimethyl sulfoxide was selected to be used in the process based on its superior ability to swell cotton. Dimethylcarbonate was used as a cosolvent to enable dye substantivity adjustment so that dye sorption could be promoted without using inorganic salts. Both solvents are green solvents with excellent environmental health and safety profiles. It was found that the nucleophilic addition of cellulosic hydroxyls to the VS dye required the formation of an activated intermediate of the dye and an amine base, which was distinctive from the general base catalysis observed in conventional wet processing. Diazabicyclo[2.2.2]octane was identified as the most effective base for promoting the reaction. The spent liquor from the solvent-based process was confirmed to be free of hydrolyzed dyes, and multicycle dye bath reuse was demonstrated. The process was also found to be generally applicable to vinyl sulfone dyes with consistently good shade build-up and colorfastness. The problems of insufficient swelling and dye fixation commonly associated with nonaqueous processes were solved without compromising the recyclability.
1. INTRODUCTION Cellulose had been chemically modified to create a large variety of derivatives intended for textile, paper, composites, and biomedical fields.1−3 To preserve the native cellulose structure, the chemical reactions are often carried out in the heterogeneous state. On an industrial scale, such as in pulping and textile processing, cellulose is most often modified in an aqueous medium through wet processes, taking advantage of the similarity of water and cellulose. However, the very similarity inevitably compromises the reaction efficiency because water shares the same reactive functionality with cellulose. Side products from competing hydrolysis would remain in the processing stream and often challenge effluent treatment.4 Consider reactive dyeing of cotton for example: the spent liquor may contain up to 30% of the applied dyes in the nonrecoverable hydrolyzed forms,5,6 making it one of the hardest to treat dyeing effluents.7 Conventional reactive dyeing and other wet processing of cellulose also engage substantial amounts of inorganic salts, which are hard to separate from water.8−10 Moreover, the sheer volume of fresh water consumed by wet processing of cellulose causes environmental concerns.4 The aim of this work was to investigate the possibility of heterogeneous modification of cellulose in a nonaqueous medium with a focus on the nucleophilic addition of cellulosic hydroxyls to vinyl sulfone dyes. Switching the medium to nonnucleophilic organic solvents was expected to eliminate competing hydrolysis so that the process could be made © 2014 American Chemical Society
recyclable and more environmentally friendly. For similar reasons, nonaqueous reactive dyeing of cotton cellulose had been attempted employing chlorinated hydrocarbons11,12 and supercritical carbon dioxide (ScCO2).13−18 Poor shade build-up and leveling were the major problems associated with these systems because of insufficient swelling of cotton cellulose and limited solubility of the reactive dyes. For the ScCO2 system, appreciable shades could be achieved by reintroducing water13 or adding lower alcohols14,15 as cosolvents. However, these hydroxyl-containing solvents would inevitably lead to competing solvolysis of the dye and compromise the recyclability of the system. In the current study, nucleophilic solvents that are reactive toward the vinyl sulfone were strictly excluded. All of the three key steps in heterogeneous chemical modification of cellulose, namely swelling, sorption, and reaction, change considerably in an organic medium compared with an aqueous one and deserve careful investigation. The dyeing media were selected based on the ability to swell cotton as well as the environmental friendliness. The sorption and fixation of a representative dye, namely the C.I. Reactive Blue 19 in its vinyl sulfone form (Blue19-VS), were studied in detail. Repeated dyeing with replenished spent dye liquor was conducted to validate the recyclability of the process. The Received: Revised: Accepted: Published: 15802
August 13, 2014 September 18, 2014 September 22, 2014 September 22, 2014 dx.doi.org/10.1021/ie503173m | Ind. Eng. Chem. Res. 2014, 53, 15802−15810
Industrial & Engineering Chemistry Research
Article
Scheme 1. Structures of the Reactive Dyes Investigated in the Study in Their Vinyl Sulfone Forms
optimized solvent dyeing process was applied to five different dyes featuring the vinyl sulfone functionality to demonstrate the generality of the approach. Because vinyl sulfone and related activated vinyls are also frequently featured in other cellulose modifiers such as cross-linking agents, the results from this study have implications for nonaqueous heterogeneous modification of cellulose through nucleophilic additions in general.
temperatures for 1 h. The swollen fabrics were removed from the vessels and placed into centrifuge tubes equipped with steel meshes to hold the sample. After being centrifuged for 3 min at 1600 g, the sample was weighed and swelling was calculated according to eqs 1 and 2.
2. EXPERIMENTAL SECTION 2.1. Materials. Bleached cotton poplin (40 × 40, 133 × 72, 123 g/m2) was kindly supplied by the Esquel Group (Guangdong, China) and used as is. The multifiber adjacent fabrics used for colorfastness assessment were purchased from Testfabrics, Inc. Standard detergent was purchased from Shanghai Textile Industry Institute of Technical Supervision. Dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), 1,2-dichloroethane (DCE), nitrobenzene (PhNO2), chlorobenzene (PhCl), toluene, pyridine, triethylamine (TEA), diazabicyclo[2.2.2]octane (DABCO), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), methyl nicotinate (MeNIC), hexamethylenetetramine (HMTA), tetrabutylammonium bromide (TBABr), sodium bicarbonate, and sodium carbonate were analytical grade and purchased from Sino Reagent Co. Triglyme, diglyme, and dimethylcarbonate (DMC) were analytical grade and purchased from Alfa Aesar. Acetonitrile was HPLC grade purchased from Fischer Scientific. C.I. Reactive Blue 19, Reactive Orange 16, Reactive Black 5, Reactive Yellow 201, and Reactive Yellow 176 were obtained from Shangyu Shunlong Co., Ltd. (Zhejiang, China). The dyes were in the form of unactivated βsulphatoethylsulphone and were converted to the corresponding vinyl sulfones before use. The rest of the chemicals were used as received. 2.2. Measurement of the Swelling of Cotton Cellulose. The swelling of cotton fabrics by various solvents was expressed in terms of centrifugal liquid retention values according to a procedure reported by Seoud.19 Cotton fabrics were cut into pieces weighing about 3.0 g and were conditioned at 105 °C for 2 h. The samples were allowed to cool to room temperature in a sealed desiccator. Each sample was then weighed and placed in a stainless steel vessel filled with 100.0 mL of the solvent to be tested. The vessels were sealed and maintained at proper
SW% =
Msc − Mcc × 100% Mcc
(1)
nSW =
SW% × 1.77 MWsolvent
(2)
Msc, Mcc, and MWsolvent represent the mass of swollen cellulose, mass of the conditioned cellulose, and molecular weight of the solvent, respectively. The experiment was repeated strictly at least three times. 2.3. Preparation of Vinyl Sulfone Dyes. The appropriate dye in its β-sulphatoethylsulphone form (30.0 mmol) was dissolved in 120.0 mL of deionized water. The pH of the solution was adjusted to 8.5 by addition of sodium carbonate and sodium bicarbonate. The buffered solution was then heated to and maintained at 60 °C with stirring. The progress of the βsulphatoethylsulphone elimination reaction was monitored by thin-layer chromatography. For all five dyes studied, the reactions were completed in 1 h. The reaction mixture was then neutralized with hydrogen chloride, and 50.0 g of sodium chloride was added to precipitate out the vinyl sulfone (VS) product. The crude product was dried and extracted with acetone, and the solvents were removed under reduced pressure to yield the purified VS dye (45−60%). The purified dyes were confirmed to have purity greater than 95% by 1H NMR and HPLC. Structures of the VS dyes prepared are shown in Scheme 1. 2.4. Treatment of Cotton Cellulose in DMSO/DMC and in Water. 2.4.1. Treatment in Solvents. Cotton fabrics were cut into pieces of approximately 3.0 g and swollen in DMSO for 1 h at 25 °C. Each preswollen sample was drained and transferred to a vessel containing dye liquor consisted of 0.09 g of the appropriate dye (VS form) and 0.20 g of DABCO dissolved in 57.0 mL of DMC and 3.0 mL of DMSO (DMSO: DMC, 1:19; liquor ratio, 20:1). The vessel was sealed and heated to and maintained at 65 °C for 2 h with mechanical agitation. The vessel was then cooled to room temperature, and the sample was removed from the dye bath, extracted with 30.0 15803
dx.doi.org/10.1021/ie503173m | Ind. Eng. Chem. Res. 2014, 53, 15802−15810
Industrial & Engineering Chemistry Research
Article
Figure 1. Swelling of cotton by selected organic solvents: %SW, swelling as measured by percentage weight gain; nSW, swelling as measured by the number of solvent molecules per anhydroglucose units (mol/AGU).
until it was completely dissolved. The amount of fixed dyes on the fabric was determined spectroscopically using a Shimadzu UV-1800 spectrophotometer. Colorimetric measurements were performed using a Datacolor 650 benchtop spectrophotometer. The color strength (K/ S) was measured at the maximum absorption wavelengths (λmax), which were 595, 406, 490, 600, and 416 nm for C.I. Reactive Blue 19, Reactive yellow 201, Reactive Orange 16, Reactive Black 5, and Reactive Yellow 176, respectively. High-performance liquid chromatography (HPLC) analysis was done on an Elite P230 II liquid chromatography equipped with a C-18 reversed phase column (ODS-BP 5 μm, 205 mm × 4.6 mm, Eliter, Dalian, China) and a UV−vis detector. A heated dye bath containing Blue19-VS and 10 mol equiv of an amine base was diluted 50 times using DI water. The diluted sample (25 μL) was injected and eluted at a flow rate of 0.9 mL/min and ambient temperature. The mobile phase was a solution of TBABr (25 mM) and NH4OAc (50 mM) in a 55:45 v/v mixture of acetonitrile and DI water. The UV−vis detector was set at 593 nm. Colorfastness to laundering was determined according to American Association of Textile Chemists and Colorists (AATCC) Test Method 61-1986(2A) using a Darong SW-12 washing colorfastness tester. Dry and wet colorfastness to crocking was examined according to AATCC Test Method 81988 using an Atlas AATCC Mar CM-5 Tester. Lightfastness was determined according to AATCC Test Method 16-2004 using an Atlas-150S+ lightfastness tester.
× 3 mL of warm DMSO (65 °C) and washed with 30.0 × 3 mL of DMC to remove unfixed dyes. The fabric samples were finally dried under reduced pressure to constant weight. For the reuse experiments, 3% on the weight of fabric (owf) of the dye was used. After the dyeing was finished, the spent dye bath was poured into a graduated cylinder to determine its volume and was subsequently subjected to 1H NMR and UV− vis analysis to quantify the amount of solvents and dye remaining in solution. Appropriate amounts of fresh solvents and the dye were then added to compensate for the consumption during the previous dyeing cycle. The replenished dye liquor was directly used for dyeing without further treatment. The process was repeated 20 times. 2.4.2. Treatment in Water. Treatment of cotton with commercial β-sulphatoethylsulphone dyestuff in water was done according to the procedure suggested by the manufacturer. Cotton fabrics were cut into pieces of 3.0 g and introduced to 60.0 mL (liquor ratio, 20:1) of aqueous solution of 0.09 g of the appropriate dye and 6.0 g of sodium chloride. The dye bath was heated with agitation at 60 °C for 30 min before 1.2 g of Na2CO3 was added in small portions. Dyeing was continued at the same temperature for another 45 min. After the dyeing was completed, the samples were removed from the dye bath, rinsed with 20.0 × 3 mL of cold water, boiled in 180.0 mL of aqueous solution containing 2.0 g/L sodium carbonate and 2.0 g/L standard detergent for 10 min, rinsed again with 20.0 × 3 mL of cold water, and finally dried at ambient temperature. 2.5. Measurements. Dye sorption was calculated according to eq 3. The amount of the dyes in solution before (C0) and after (C1) dyeing were measured spectroscopically using a Shimadzu UV-1800 spectrophotometer. Sorption% =
C0 − C1 × 100% C0
3. RESULTS AND DISCUSSION 3.1. Swelling of Cotton by Polar Non-Nucleophilic Organic Solvents. Ten organic solvents were tested for their efficiency to swell cotton at room temperature, and the results are plotted in Figure 1. Swelling by water was also included for comparison. The solvents selected for screening were all nonnucleophilic so that they would not compete with cellulose in reacting with VS dyes. The results showed that none of the solvents came close to water in terms of number of solvent molecules per anhydrous glucose unit, or nSw. This was because none of the solvents contained hydrogen bonding
(3)
Percentage dye fixation was measured according to a procedure reported by Kissa.20 The dyed fabrics were cut into small pieces, conditioned at 105 °C for 2 h, and cooled to room temperature in a desiccator. A 0.1 g portion of the sample was weighed out and treated with 5 mL of 70% sulfuric acid 15804
dx.doi.org/10.1021/ie503173m | Ind. Eng. Chem. Res. 2014, 53, 15802−15810
Industrial & Engineering Chemistry Research
Article
solvents mostly consisting of DMC were not able to sufficiently swell cotton. The results indicated that a minimum volume ratio of 60/40 DMC/DMSO was required for an appreciable change in sorption to be observed. Beyond this ratio, dye sorption kept increasing with DMC content and reached the maximum of 51% at 95/5 DMC/DMSO ratio. Blue19-VS was practically insoluble in DMC, and large dye aggregates formed when pure DMC was used, leading to a decrease in dye sorption. The moderate exhaustion value was considered acceptable because the spent dye bath was potentially recyclable. The optimized binary solvent system of 95/5 DMC/DMSO was used for the further dyeing experiments. The sorption-rate curves of Blue19-VS in 95/5 DMC/ DMSO were measured at 45, 65, and 85 °C and are plotted in Figure 3. The fastest equilibrium was observed at 85 °C, and
donor and were not able to form strong interactions with cellulose to compensate for the energy loss from breaking up the cellulosic hydrogen bonds. Among the 10 solvents investigated, DMSO gave the highest nSw value of 1.02. The percentage weight gain of cotton from swelling (%Sw) by DMSO was measured to be 45.23%, which was even slightly higher than that of water (36.82%). DMF also led to considerable swelling of cotton with an nSw of 0.59 and %Sw of 24.31. Swelling of cellulose is an important initial step providing sufficient sites for both dye uptake and fixation. Insufficient swelling was a major challenge for dyeing cotton in nonaqueous systems such as supercritical carbon dioxide (ScCO2).16 DMSO was selected to be the dyeing medium on the basis of the swelling results and the fact that it is much less toxic than DMF.21,22 3.2. Sorption of Blue19-VS. The vinyl sulfone of C.I. Reactive Blue 19 (Blue19-VS) was used as the model compound to investigate dye sorption and fixation in the water-free organic medium. The dye was chosen for being one of the most extensively used reactive dyes of the vinyl sulfone type. Preliminary results showed that exhaustion of Blue19-VS in pure DMSO was very poor (
