Preparation of cationic cotton with two-bath pad-bake process and its application in salt-free dyeing

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a zo shan Reactive dyes ed b de a niza to t tai unt . Hi eat ical strength of the dyed fabrics were both evaluated to show applicability of this preparation process of cationic cotton. in tex y, air p rent pr ton du ue. Ho ow bin r sodiu cationizing reagents, such as 2,3-epoxypropyltrimehtylammonium chloride (I in Scheme 1) (Hauser, 2000; Montazer, Malek, & Rahimi, 2007). This compound is usually formed in situ from the reaction of sodium hydroxidewith 3-chloro-2-hydroxypropyltrimethylammo- nium chloride (CHPTAC) (see Scheme 1). CHPTAC is a relatively cheap and low toxic chemical, it can react with cotton under a variety of reaction processes (the reaction pro- the process, the padded fabrics were cationized by wrapping in plastic and batching at room temperature for 12–24 h. This made the cationization inconvenient, lengthy, and not adapted for con- tinuous processing. Pad-bake procedure (Lewis & Lei, 1989, 1991) would be preferable for commercial use, however, from the previous studies, temperature as high as 120–150 �C was em- ployed, so reactant migration occurred during the reaction, which gave rise to non-uniform dyeing. This process still pre- sented the problem of waste of CHPTAC since the reagent and sodium hydroxide were used in one bath. * Corresponding author. Tel.: +86 411 82945527. Carbohydrate Polymers 78 (2009) 602–608 Contents lists availab te els E-mail address: [email protected] (W. Ma). in the dyebath are required to enhance dye–fiber interactions, lead- ing to serious environmental pollution as a large amount of salt- containing effluent is discharged. It has been shown that to add cat- ionic sites to the fibers shows significant advantages of reduced environmental impact following the dyeing process (Ma, Zhang, Tang, & Yang, 2005; Zhang et al., 2005; Xie, Hou, & Wang, 2008; Zhang, Chen, Lin,Wang, & Zhao, 2008; Zhang, Ju, Zhang, Ma, & Yang, 2007). Chemically cationized cotton is usually produced by the etherifying reaction of cottonwith the tertiary amino or quaternary ammonium cationizing reagents, especially quaternary ammonium about 80–120 �C and kept at that temperature for over 20 min for cationization. The reaction efficiency was low and after one-time usage, the reagent has to be discharged due to its hydrolysis (see Scheme 1), which caused significant waste of CHPTAC and pollution in cationization process. Pad-batch process (Kanik, Hauser, Chapman, & Donaldson, 2004; Hauser & Slopek, 2005; Montazer et al., 2007) was proved to enhance reaction efficiency of epoxy compounds, however, it cannot resolve the problem of the waste of the reagent even though the alkali was added to the bath just prior to application. Moreover, in 1. Introduction Cotton fibers are widely applied excellent properties of hygroscopicit ability, no static electricity, etc. In cur predominantly used for dyeing of cot ness, brilliancy and wide range of h cially available reactive dyes show l concentrations of sodium chloride o 0144-8617/$ - see front matter � 2009 Elsevier Ltd. A doi:10.1016/j.carbpol.2009.05.022 � 2009 Elsevier Ltd. All rights reserved. tile industry due to its ermeability, biodegrad- actice, reactive dyes are e to their high wet fast- wever, most commer- ding to cotton, so high m sulfate (30–100 g/L) cedures were shown in Scheme 1), such as exhaust, pad-batch, pad-bake, pad-steam, jig-exhaust, jet-exhaust, etc. Among the pro- cesses mentioned above, exhaust, pad-batch and pad-bake one are usually employed due to application convenience or relatively high reaction efficiency. But till now, no one best procedure has yet been established (Hauser & Tabba, 2001). In the exhaust process (Seong & Ko, 1998), cotton was im- mersed in the bath containing both the cationizing agent CHP- TAC and sodium hydroxide. The temperature was raised to Two-bath pad-bake process Salt-free dyeing properties of the dyes on the cationic fabrics were obtained. Besides, colorimetric properties and mechan- Preparation of cationic cotton with two-b in salt-free dyeing Lili Wang, Wei Ma *, Shufen Zhang, Xiaoxu Teng, Jin State Key Laboratory of Fine Chemicals, Dalian University of Technology, No. 158 Zhong a r t i c l e i n f o Article history: Received 26 December 2008 Received in revised form 11 April 2009 Accepted 28 May 2009 Available online 6 June 2009 Keywords: Cationic cotton a b s t r a c t Cationic cotton was prepar rimethylammonium chlori tinuous processing of catio ratio of sodium hydroxide for cationization and the ob The structures of both the ning electronic microscopy ton than that on the untr Carbohydra journal homepage: www. ll rights reserved. th pad-bake process and its application ng Yang Road, Dalian 116012, PR China y a designed two-bath pad-bake process with 3-chloro-2-hydroxypropylt- s cationizing reagent to realize recycle utilization of the reagent and con- tion. Experiments showed that 8.0% (o.w.bath) of the reagent, 1:1 of molar he reagent, 60 �C and 6 min of baking temperature and time were selected ned cationic cotton was suitable for application in salt-free reactive dyeing. reated and cationic fibers were investigated by X-ray diffraction and scan- gher dye utilization and color yields could be realized on the cationic cot- ed one in the conventional dyeing. Levelness dyeing and good fastness le at ScienceDirect Polymers evier .com/locate /carbpol agent JFC (fatty alcohol-polyoxyethylene ether, Weifang Auxiliary N H 2 2 4 32 H C.I.Reactive Yellow 145 N N NH NHN N N N R Cl R Cl NH OH NaO3S SO3Na N NR = SO3Na C.I. Reactive Red 120 Fig. 1. Structures of the reactive dyes used in this study. e Po Based on the above research, it is obvious that pad-bake process is more suitable for application, so how to make use of its advan- tages and avoid its disadvantages is a meaningful work needed to be considered. In this study, a two-bath pad-bake process was designed to separate the usage of CHPTAC and alkali in two baths and relatively low reaction temperature and short reaction time were investigated for preparation of cationic cotton to avoid re- agent migration to the great extent. Thus, the recycle utilization of CHPTAC and continuous processing of the preparation of the cat- ionic fabrics may be realized, which will increase cationization effi- ciency and reduce environmental impact. Moreover, X-ray diffraction (XRD) and scanning electronic microscopy (SEM) were used to evaluate the structure properties of the cationic fibers. In addition, the dyeing properties of a variety of reactive dyes on the cationic cotton in the absence of salt were investigated to determine the quality of the cationized substrates and advantages of this preparation process. 2. Experimental 2.1. Materials H2 CCl H C OH H2 C N(CH3)3 Cl OH O H2 C N(CH3)3 Cl CHPTAC 2, 3-epoxyp ropyl- trimethylammonium chloride ( I ) O H2 C N(CH3)3 Cl CH2OCHCH2N(CH3)3 OH Cl OH Cell OH Cell O ( I ) Cotton fiber Cationic cotton Cl H2 C H C OH H2 C N(CH3)3 Cl H2O HO H2 C H C OH H2 C N(CH3)3 Cl OH CHPTAC Hydrolysis product of CHPTAC Scheme 1. Reactions occurred during the cationization process of cotton. L. Wang et al. / Carbohydrat One hundred percent cotton (150 g/m2), bleached, desized and mercerized, was purchased from Testfabrics, Inc., Shanghai. The reactive dyes used (see Fig. 1) were C.I. Reactive Blue 4, C.I. Reac- tive Blue 19, C.I. Reactive Red 195, C.I. Reactive Yellow 145 and C.I. Reactive Red 120; they were obtained from Shanghai Dyestuff Co. and used as received. These dyes were chosen because of their commercial availability, known structures and representative of different types of reactive dyes. CHPTAC which was commercially available as a 65.0% solution in water, was supplied by Weifang Auxiliary Co. and used as re- ceived. Other chemicals used in this study were commercially available sodium hydroxide, sodium sulfate and sodium carbonate, and used as received. 2.2. Preparation of cationic cotton with two-bath pad-bake process Cotton fabric was cationized using the two-bath pad-bake pro- cess. Unless otherwise stated, padding was carried out at a liquor- to-goods ratio of 20:1. The well prepared bleached cotton fabric was separately and continuously dip-nipped in the aqueous solu- tions of 8.0% (o.w.bath) CHPTAC and 1.8% (o.w.bath) sodium hydroxide at room temperature on a TFO/S 350 Laboratory pad mangle (Roaches International Ltd, UK). And 10 mg/L penetrating O O NH2 N SO3Na H N H SO3Na N N N Cl Cl C.I. Reactive Blue 4 O O NH2 N SO2C2H4OSO3Na SO3Na H C.I. Reactive Blue 19 N NaO3S N NN N SO2C2H4OSO3Na Cl N H NaO3S SO3NaOH N H C.I. Reactive Red 195 SO3Na NaO3S SO3Na N NaO3S N N SO C H OSO NaH NOCHN NN N Cl lymers 78 (2009) 602–608 603 Co.) was added in both solutions. The pressure on the mangle was adjusted to give 80% wet pickup. The obtained sample was heated at 60 �C for 6 min in a Rapid baker, and then neutralised by rinsing several times with water. The cationic fabric was ready for dyeing. 2.3. Dyeing procedures All dyeings were carried out in XW-PDR Laboratory Dyeing Ma- chine with 12 shaking baths and a temperature and time control unit using a liquor-to-goods ratio of 20:1. The dye applied was 3% (o.w.f) for C.I. Reactive Blue 4 and C.I. Reactive Blue 19, 2% (o.w.f) for C.I. Reactive Red 195 and C.I. Reactive Red 120, and 1% (o.w.f) for C.I. Reactive Yellow 145. Dyebaths were prepared by dis- solving the dye in distilled water and the temperature was raised to 30 �C for C.I. Reactive Blue 4, 45 �C for C.I. Reactive Blue 19, and 60 �C for C.I. Reactive Red 195, C.I. Reactive Yellow 145 and C.I. Reactive Red 120. Both the untreated and cationic fabric sam- ples were then added to the dyebaths. For conventional dyeing of the untreated cotton, 60 g/L of anhydrous sodium sulphate was added to the dyebaths. The dyeing procedure for cationic cotton was chosen to allow dyeing in the absence of electrolyte. After dye- ing at the temperatures mentioned above for 30 min, the temper- ature was gradually increased at 2 �C/min to dye fixation e Po temperature, it was 45 �C for C.I. Reactive Blue 4, 85 �C for C.I. Reac- tive Blue 19, and 90 �C for C.I. Reactive Red 195, C.I. Reactive Yellow 145 and C.I. Reactive Red 120, respectively. Sodium carbonate (10 g/L) was then added in each dyebath and dyeing continued at the fixation temperatures for 40 min. After dyeing, the cotton fabrics were removed from the dyebaths and rinsed thoroughly in tapwater. The rinsewas collected formea- surement of dye exhaustion. Then the dyed fabric was subjected to boiling in a solution containing 2 g/L anionic detergent LS (Shanghai Auxiliary Co.) at a liquor-to-goods ratio of 25:1 for 15 min until no dye was removed off, and then rinsed and allowed to air dry. 2.4. Determination of nitrogen content Nitrogen content of cationic cotton was determined in triplicate by the Kjeldahl method. The samples were dried under vacuum at the temperature of 50 �C before measurement. In this study, the nitrogen content of the cationic cotton obtained under the prepa- ration method illustrated above was 0.65% (wt%). 2.5. X-ray diffraction The X-ray diffraction (XRD) patterns of the fibers were mea- sured stepwise in 2 h between 0� and 55� by a Rigaku diffractom- eter D/max-2400 (Rigaku, Japan). Monochromatic (Graphite monochromator) Cu-Ka1-radiation (40 kV, 100 mA) was used. 2.6. Scanning electron microscope (SEM) The cotton fabric samples were coated by gold sputtering at room temperature. Scanning electron micrographs of the samples were taken by JSM-5600LV Electron Microscope (JEOL, Japan). 2.7. Color strength (K/S) and dye fixation (F%) measurement The color strength expressed as K/S value is calculated from Kubelka-Munk equation as shown below: K=S ¼ ð1� RÞ2=2R ð1Þ The reflectance R of the dyed sample was determined on Ultra- Scan XE Color Measuring and Matching Meter (Roaches Co.) at the wavelengths of minimum reflectance (maximum absorbance) of each dyestuff. Dyebath exhaustion (E%) of both the untreated and cationized cotton was measured by sampling the dyebath before and after dyeing process using Eq. (2). E% ¼ 100� ð1� A1=A0Þ ð2Þ where A0 is the absorbance of the dyebath before dyeing, and A1 is the absorbance of the dyebath after dyeing, the absorbance of the dyebath was measured at maximum absorbance of each dye using HP 8453 UV–vis spectrophotometer. The percentage of the total dye fixed (F%) on both the untreated and cationized cotton was determined by measuring K/S values of the dyed samples before and after soaping, which was calculated using Eq. (3). F% ¼ E%� C2=C1 ð3Þ C1 is K/S value of dyed sample before soaping and C2 is K/S value of dyed sample after soaping. 2.8. Color measurement * * * * 604 L. Wang et al. / Carbohydrat CIE L , a , b , C and h of the dyed samples were measured with UltraScan XE Color Measuring and Matching Meter (Roaches Co.) at the wavelengths of minimum reflectance (maximum absorbance) of each dyestuff. 2.9. Fastness testing Wash fastness of the dyed cotton was tested according to ISO 105-B01:1994 using S-1002 two-bath dyeing and testing appara- tus (Roaches Co., UK). Rub fastness was tested according to ISO 105-X12:1993 using Y(B) 571-II crockmeter. Light fastness was tested according to ISO 105-B01:1994 using Xenotext 150s Weath- erometer (Heraeus Co., Germany). 2.10. Mechanical property testing The tensile strength and tear strength of the dyed cotton were tested according to ISO 13934-1-1999 and ASTM D 5734-1995 using YG (B) 026H weave-force machine (Wenzhou, China), YG (B) 033A tearing instrument (Wenzhou, China), respectively. Each sample was tested five times and the average value was used. 3. Results and discussion 3.1. Optimization of the preparation conditions of the cationic cotton The preparation conditions need to be studied to show the least effect on the fiber properties and at the same time achieve high dye utilization on the obtained cationic cotton. Thus, the conditions could not be severe and they were considered to be good if the to- tal dye fixed (F%) in salt-free dyeing could be improved compared with that in the conventional dyeing. Therefore, in this study, the preparation conditions of the two-bath pad-bake process were investigated and the optimal conditions were determined based on the percentage of the total dye fixed (F%) of C.I. Reactive Blue 19 on the cotton cationized under different conditions (see Fig. 2). 3.1.1. Effect of CHPTAC concentration on F% of C.I. Reactive Blue 19 on cationic cotton To optimize the preparation conditions, the effect of the con- centration of CHPTAC was first investigated and the results were presented in Fig. 2(a). Wherein, the molar ratio of sodium hydrox- ide to CHPTAC was 2:1, baking temperature was 90 �C and baking time was 10 min. Addition of high concentration of cationizing re- agent could achieve high cationization degree of cotton, as well as high dye exhaustion and the percentage of total dye fixed on the cationic cotton. As expected, Fig. 2(a) shows that as the concentra- tion of CHPTAC was increased from 2.0% (o.w.bath) to 8.0% (o.w.bath), F% of C.I. Reactive Blue 19 increased from 69.8% to 84.1%, indicating that cationization efficiently supplies increased cationic sites on cotton with increasing cationic reagent concentra- tion. However, when the reagent concentration was further in- creased to 10.0% (o.w.bath), no significant increase in F% was observed. This could be explained by that sufficient cationic sites had been provided for this dye when 8.0% of the reagent was used. Thereafter 8.0% of CHPTAC was selected in the following investigation. 3.1.2. Effect of molar ratio of sodium hydroxide to CHPTAC on F% of C.I. Reactive Blue 19 on cationic cotton The effect of molar ratio of sodium hydroxide to CHPTAC on F% of C.I. Reactive Blue 19 on the modified substrates was examined and the results were shown in Fig. 2(b). The cationic reagent con- centration was 8.0% (o.w.bath), baking temperature was 90 �C and baking time was 10 min. The results showed that F% increased with lymers 78 (2009) 602–608 increasing molar ratio at the beginning, however, when the ratio was higher than 1.0 and further increased to 2.0, F% of C.I. Reactive b d TAC e Po Blue 19 on the cationic cotton changed quite a little. Based on the reaction procedure shown in Scheme 1, the main function of so- dium hydroxide was to promote the formation of epoxy group 2 4 6 8 10 65 70 75 80 85 90 F % Concentration of CHPTAC, % 50 60 70 80 90 100 65 70 75 80 85 90 Baking temperature, F % a c Fig. 2. Effect of CHPTAC concentration (a), molar ratio of sodium hydroxide to CHP cotton. L. Wang et al. / Carbohydrat and neutralize the acid produced in the process. In the reaction be- tween the epoxy agent and cotton, although alkaline condition was required to activate the cotton, it was found in the experiment that only quite a little amount of sodium hydroxide was needed as much stronger organic alkali was formed in the process to promote the cationization reaction of cotton. Therefore, nearly equal mole of sodium hydroxide and the cationic reagent could meet the require- ment for cationization. 3.1.3. Effect of baking temperature and baking time on F% of C.I. Reactive Blue 19 on cationic cotton Baking temperature and time were both important for the cati- onization process and the application properties of the cationic cotton. For baking temperature determination, CHPTAC concentration used was 8.0% (o.w.bath), molar ratio of sodium hydroxide to CHP- TAC was 1:1 and baking time was 10 min. The results were shown in Fig. 2(c). It was evident from the data that in this process, the etherification reaction was unsuitable at much lower temperature as 50 �C. It was presented that F% of C.I. Reactive Blue 19 was im- proved with increasing baking temperature from 50 to 60 �C. Although higher temperature was beneficial for the etherification reaction, further increase of baking temperature even to 100 �C al- most did not give rise to F% enhancement. This result demon- strated that sufficient cationic sites for exhaustion of C.I. Reactive blue 19 had been obtained under the condition of 60 �C. In addi- tion, much higher temperature was not suitable for application in cationization of cotton because it might cause degradation of the cotton under alkaline condition. So 60 �C was used in the fol- lowing investigation. For baking time investigation, CHPTAC concentration was 8.0% (o.w.bath), molar ratio of sodium hydroxide to CHPTAC was 1:1 and baking temperature was 60 �C. Fig. 2(d) shows that prolonging baking time from 2 to 6 min has a beneficial effect on F% of C.I. Reactive Blue 19, whereas, F% showed almost no further increase with longer baking time. This result confirmed that good F% result 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 65 70 75 80 85 90 F % Molar ratio of NaOH to CHPTAC 2 4 6 8 10 60 65 70 75 80 85 90 F % Baking time, min (b), baking temperature (c) and time (d) on F% of C.I. Reactive Blue 19 on cationic lymers 78 (2009) 602–608 605 could be obtained by using 6-min reaction time, since enough cat- ionic sites had been provided under the conditions for C.I. Reactive Blue 19. Based on the above investigations, it can be concluded that un- der much milder two-bath pad-bake conditions, especially much lower baking temperature (60 �C) and shorter baking time (6 min), F% of about 84.0% of C.I. Reactive Blue 19 could be yielded on the cationic cotton, and at the same time good physical appear- ance and levelness of the dyed fabrics were obtained. Although the optimized preparation conditions outlined were based on C.I. Reactive Blue 19, it was proved that other reactive dyes used in this paper also give promising effects on the cotton cationized under the selected conditions. 3.2. Analysis of physical structures of cationic cotton fibers Cationization of cotton may affect the structure of the fiber (Kit- kulnumchsi, Ajavakom, & Sukwattanasinitt, 2008), which will fur- ther affect the wearability of it. Therefore, a good preparation method for cationic cotton should not influence its structure prop- erties. In this section, X-ray diffraction and scanning electron microscope were used to examine the physical structure properties of the cationic cotton. 3.2.1. X-ray diffraction analysis (XRD) Chemical modification of cotton fibers may change the crystal form and crystallinity of the fibers, so X-ray diffraction spectra of the cationic cotton and the control one were made (as shown in Fig. 3). The results showed that the X-ray spectra of the cotton be- fore and after cationization are the same, a typical diffraction peak existed at 2h = 18.6� in both Fig. 3(a) and (b). It demonstrated that cationization occurred just on the surface of the fiber; it had no ef- fect on its crystal structure. 0 10 20 30 40 50 60 b d cotton fiber (a) and cationic cotton fiber (b). e Polymers 78 (2009) 602–608 0 10 20 30 40 50 60 a Fig. 3. X-ray diffraction patterns of untreate 606 L. Wang et al. / Carbohydrat 3.2.2. Surface morphology The scanning electron microscope (SEM) is usually used to intu- itively investigate the surface structure of the solid. In this study, SEM was employed to examine the surface structure of the pre- pared cationic cotton fibers at the micro-level, which could esti- mate the influence of cationization process on the fibers. Fig. 4(a) and (b) were SEM photos of the untreated fibers and (c) and (d) were that of the cationic ones. Based on the photos, although the surface of the cationic fiber was a little rougher (d) compared with that of the untreated one (b), no distinct change could be detected between them. As the extent of cationization was small under the selected conditions, the physical structure of the cotton was almost not influenced and the obtained cationic cotton was suitable for further application in dyeing process. 3.3. Comparison of F% on cationic and untreated cotton Fig. 5 shows F% of 5 reactive dyes on both the cationic (prepared under the optimized conditions) and untreated cotton. Due to the introduction of the cationic groups to cotton, reactive dyes easily absorbed on the cationic cotton without addition of sodium sul- phate or sodium chloride in the dye-bath. Comparing the fixation results for dyeing the cationic cotton with those from the conven- tional dyeing of the untreated cotton, it could be seen that in all the cases, F% of the dyeings obtained on the former was higher than Fig. 4. SEM photos of untreated cotton fiber (a that on the latter. These results indicated that with the cationic cotton prepared under the optimized conditions, dye utilization efficiency was enhanced and savings in dye consumption may be made in salt-free dyeing process. It was also found that good phys- ical appearance and levelness of the dyed fabrics were achieved. and b) and cationic cotton fiber (c and d). 0 20 40 60 80 100 F % salt-free dyeing Conventional C.I. Reactive Blue 4 C.I. Reactive Blue 19 C.I. Reactive Red 195 C.I. Reactive Yellow 145 C.I. Reactive Red 120 Fig. 5. Comparison of F% of 5 reactive dyes on cationic and untreated cotton. b fastness Light fastness Tensile strength (N) Tear strength (N) Wet Warp Weft Warp Weft 4 6 711.0 404.0 11.4 9.0 3–4 6 735.9 415.8 11.7 9.2 3–4 5–6 781.3 424.1 11.4 8.8 3–4 5–6 805.3 456.7 12.0 8.8 4 4 733.9 418.5 11.7 9.6 5 4 4 768.2 428.0 12.6 10.2 5 3–4 4 753.1 404.0 11.6 8.3 5 e Polymers 78 (2009) 602–608 607 3.4. Recycle utilization of CHPTAC At atmospheric temperature, the solution of CHPTAC is stable and can be stored for quite a long time. However, addition of alkali speeds up the hydrolysis of the reagent to form inactive material, especially at high temperature. It was reported that depending on the specific reactions, 20–50% of the epoxy groups would hydro- lyze to be inactive (Hauser, 2000). In the designed two-bath pad- bake process, cotton fabric was first dip-nipped in CHPTAC bath and continuously dip-nipped in alkali bath at room temperature, thus no alkali was mixed into the bath of CHPTAC during the whole process and the hydrolysis of the cationic reagent was effectively restrained. As a result, recycle utilization of CHPTAC could be realized. In this section, ten times’ recycle of 50 mL solutions of CHPTAC and sodium hydroxide was made for successively padding of 10 pieces of 1.0 g cotton. The recycle utilization test showed that F% of C.I. Reactive Blue 19 did not change much after 10 times’ usage of the solutions without addition of the agents. The value of F% for each recycle was between 81.7% and 86.3% and the nitrogen con- tents of the cationic fabrics were also measured to be all between 0.6% and 0.7% (wt%). This demonstrated good repeatability of this pretreatment process. Owing to the relatively low substantivity of CHPTAC to cotton fibers, the concentration of it almost did not change by each pad procedure, therefore, the amount of the re- agent padded on the fabric each time was almost the same, which definitely resulted in close F% in each application cycle. Accord- Table 1 Fastness properties of the reactive dyes and mechanical strength of the dyed cotton. C.I. Reactive Fabric K/S Wash fastness Ru Change Staining Dry Cotton Wool Blue 4 Cationic 4.3 4–5 4–5 4 4 Untreated 3.4 4 4 4 4 Blue 19 Cationic 9.1 4 4 3 4 Untreated 7.9 3–4 3–4 4 4 Red 195 Cationic 8.1 4–5 4–5 4–5 4 Untreated 7.9 3–4 3 4–5 4– Yellow 145 Cationic 4.5 4–5 4–5 4–5 4– Untreated 4.0 4 4–5 4–5 4– Red 120 Cationic 14.4 4 3–4 4–5 4 Untreated 10.0 3–4 3–4 4–5 4 L. Wang et al. / Carbohydrat ingly, with this two-bath pad-bake process, the cationizing reagent CHPTAC could be recycled and continuous processing of the prep- aration of the cationic cotton could be realized. 3.5. Fastness properties and mechanical strength Table 1 shows that the color strength (K/S), fastness properties and mechanical strength of the dyeings in both salt-free dyeing and conventional dyeing. K/S values of all 5 reactive dyes in salt- free dyeing were higher. The wash fastness of the dyeings on the cationic cotton was all good, change of shade and staining of adja- cent fabrics both being assessed higher or equal to the values ob- tained on the untreated cotton in the conventional dyeing process. Dry and wet rub fastness of the dyes on the cationic fab- rics was also comparable with that obtained from conventional dyeing. In the cases of C.I. Reactive Blue 4 and C.I. Reactive Red 120, the wet fastness on the cationic cotton was even 0.5 grade higher. Moreover, light fastness testing of the dyeings on the cat- ionic fabrics showed satisfactory results compared with that in the conventional dyeing. The above results indicated that pretreat- ment with the cationizing reagent using the improved pad-bake method had no adverse effect on the fastness properties of the dyes. The mechanical strength of the cationic cotton affected the application of it, so the tensile strength and tear strength of the cationic and untreated cotton were measured and compared (see Table 1). As the data shown, the tear strength of the dyed cationic cotton was lower than that obtained from the untreated one. The tensile strength of the cationic cotton was also reduced. Higher dye fixation F% may have certain responsibility for the strength de- crease of the fibers. The reduction in tear strength was not much except that of the fabrics dyed with C.I. Reactive Red 120, and the reduction in warp tensile strength was 0.7–4.5% and in weft tensile strength was 1.9–7.1%, which were still comparable to the results obtained from untreated cotton and could meet the appli- cation requirements for the dyed fabrics. 3.6. Colorimetric properties of the reactive dyes In this section, the effect of cationization of the cotton on the colorimetric data of the reactive dyes was evaluated. Table 2 shows that L� values for all five dyes on cationic cotton are lower than the corresponding values on untreated cotton, indicating that cationic cotton colors are darker than untreated one. There were also changes in redness-greenness (a�), yellowness-blueness (b�), chro- ma (C�) and hue (h) values between dyed cationic and untreated cotton, and the differences for different dyes were not the same. In fact, the color differences were difficult to account for the di- 4 4–5 765.8 429.9 12.4 8.6 3–4 4 777.2 413.4 9.3 8.2 3 4 804.1 421.6 12.0 9.6 rect effect of the cationic groups on the color of the dyes associated with them. The darker influence suggested a difference in physical environment of the dyes on the cationic and untreated cotton, which resulted in different states of dye–dye aggregation or asso- ciation in the two cases. For practical purpose, the color difference could impose minor limitations on application of this dyeing meth- Table 2 Colorimetric data for the dyed cotton with different reactive dyes. C.I. Reactive Fabric L* a* b* C* h Blue 4 Cationic 48.3 �6.7 �29.9 30.7 257.3 Untreated 54.2 �7.7 �29.8 30.8 255.4 Blue 19 Cationic 37.4 0.9 �35.6 35.6 271.6 Untreated 40.8 �0.4 �37.2 37.2 269.4 Red 195 Cationic 45.9 53.3 �6.1 53.6 353.5 Untreated 49.4 47.2 �9.3 48.1 348.9 Yellow 145 Cationic 74.3 24.3 61.4 66.1 68.4 Untreated 75.1 24.8 59.9 64.9 67.5 Red 120 Cationic 44.1 59.1 9.8 59.9 9.4 Untreated 48.8 55.0 3.9 55.1 4.1 od, which could be accommodated in the reformulation of the dye recipes. 4. Conclusions By studying the preparation method of cationic cotton with de- signed two-bath pad-bake process, it was shown that this process was beneficial for recycle utilization of CHTPAC and continuous processing of cationization, and by this method, effluent discharge in cationization was greatly diminished to reduce its impact on environment. XRD and SEM results showed cationization occurred only on the surface of the cotton fibers and surface morphology of the cationic fiber was almost no change as the extent of cationiza- tion was small under the selected preparation conditions. The ob- tained cationic cotton was very effective in improving the fixation and color yield of the reactive dyes in salt-free dyeing process, and uniform dyeing was achieved. So by this cationization method, not only pollution from salt addition was eliminated, dye utilization efficiency was also enhanced. Besides, the colorfastness and mechanical strength of the fabrics were all good and can meet the need for use. While by cationization, a little darker shade was obtained on the cationic cotton compared with that on the un- treated fabric when the same amount of reactive dyes was used. Based on the above results, it can be concluded that the two-bath pad-bake process was suitable for preparation of cationic cotton used for salt-free reactive dyeing to achieve both effluent reduction and satisfactory application properties. (No. 20806013) and the Program for Changjiang Scholars and Inno- vative Research Team in University (IRT0711). References Hauser, P. J. (2000). Reducing pollution and energy requirements in cotton dyeing. Textile Chemist and Colorist & American Dyestuff Reporter, 32, 44–48. Hauser, P. J., & Slopek, R. P. (2005). Energy, water and pollution reduction with fiber reactive dyes and cationized cotton. Colourage, 52(61–62), 64–66. Hauser, P. J., & Tabba, A. H. (2001). Improving the environmental and economic aspects of cotton dyeing using a cationised cotton. Coloration Technology, 117, 282–288. Kanik, M., Hauser, P. J., Chapman, L. P., & Donaldson, A. (2004). Effect of cationization on inkjet printing properties of cotton fabrics. AATCC Review, 4, 22–25. Kitkulnumchsi, Y., Ajavakom, A., & Sukwattanasinitt, M. (2008). Treatment of oxidized cellulose fabric with chitosan and its surface activity towards anionic reactive dyes. Cellulose, 15, 599–608. Lewis, D. M., & Lei, X. P. (1989). Improved cellulose dyeability by chemical modification of fiber. Textile Chemist and Colorist, 21, 23–29. Lewis, D. M., & Lei, X. P. (1991). New methods for improving the dyeability of cellulose fibers with reactive dyes. Journal of the Society of Dyers and Colorists, 107, 102–109. Ma, W., Zhang, S. F., Tang, B. T., & Yang, J. Z. (2005). Pretreatment of cotton with poly(vinylamine chloride) for salt-free dyeing with reactive dyes. Coloration Technology, 121, 193–197. Montazer, M., Malek, R., & Rahimi, A. (2007). Salt free reactive dyeing of cationized cotton. Fibers and Polymers, 8, 608–612. Seong, H. S., & Ko, S. W. (1998). Synthesis, application and evaluation of cationising agents for cellulosic fibers. Journal of the Society of Dyers and Colorists, 114, 124–129. Xie, K. L., Hou, Ai. Q., & Wang, X. J. (2008). Dyeing and diffusion properties of modified novel cellulose with triazine derivatives containing cationic and anionic groups. Carbohydrate Polymers, 72, 646–651. Zhang, F., Chen, Y. Y., Lin, H., Wang, H., & Zhao, B. (2008). HBP-NH2 grafted cotton 608 L. Wang et al. / Carbohydrate Polymers 78 (2009) 602–608 Acknowledgements The authors gratefully thank the financial support of the Na- tional Nature Science Funds for Distinguished Young Scholar of China (No. 20525620), the National Nature Science Funds of China fiber: Preparation and salt-free dyeing properties. Carbohydrate Polymers, 74, 250–256. Zhang, M., Ju, B. Z., Zhang, S. F., Ma, W., & Yang, J. Z. (2007). Synthesis of cationic hydrolyzed starch with high DS by dry process and use in salt-free dyeing. Carbohydrate Polymers, 69, 123–129. Zhang, S. F., Ma, W., Ju, B. Z., Dang, N. Y., Zhang, M., Wu, S. L., et al. (2005). Continuous dyeing of cationised cotton with reactive dyes. Coloration Technology, 121, 183–186. Preparation of cationic cotton with two-bath pad-bake process and its application in salt-free dyeing Introduction Experimental Materials Preparation of cationic cotton with two-bath pad-bake process Dyeing procedures Determination of nitrogen content X-ray diffraction Scanning electron microscope (SEM) Color strength (K/S) and dye fixation (F%) measurement Color measurement Fastness testing Mechanical property testing Results and discussion Optimization of the preparation conditions of the cationic cotton Effect of CHPTAC concentration on F% of C.I. Reactive Blue 19 on cationic cotton Effect of molar ratio of sodium hydroxide to CHPTAC on F% of C.I. Reactive Blue 19 on cationic cotton Effect of baking temperature and baking time on F% of C.I. Reactive Blue 19 on cationic cotton Analysis of physical structures of cationic cotton fibers X-ray diffraction analysis (XRD) Surface morphology Comparison of F% on cationic and untreated cotton Recycle utilization of CHPTAC Fastness properties and mechanical strength Colorimetric properties of the reactive dyes Conclusions Acknowledgements References


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