Carbohydrate Polymers 78 (2009) 602–608

Contents lists available at ScienceDirect

Carbohydrate Polymers

journal homepage: www.elsevier .com/locate /carbpol

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

Lili Wang, Wei Ma *, Shufen Zhang, Xiaoxu Teng, Jinzong YangState Key Laboratory of Fine Chemicals, Dalian University of Technology, No. 158 Zhongshan Road, Dalian 116012, PR China

a r t i c l e i n f o a b s t r a c t

Article history:Received 26 December 2008Received in revised form 11 April 2009Accepted 28 May 2009Available online 6 June 2009

Keywords:Cationic cottonTwo-bath pad-bake processSalt-free dyeingReactive dyes

0144-8617/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.carbpol.2009.05.022

* Corresponding author. Tel.: +86 411 82945527.E-mail address: weima@dlut.edu.cn (W. Ma).

Cationic cotton was prepared by a designed two-bath pad-bake process with 3-chloro-2-hydroxypropylt-rimethylammonium chloride as cationizing reagent to realize recycle utilization of the reagent and con-tinuous processing of cationization. Experiments showed that 8.0% (o.w.bath) of the reagent, 1:1 of molarratio of sodium hydroxide to the reagent, 60 �C and 6 min of baking temperature and time were selectedfor cationization and the obtained cationic cotton was suitable for application in salt-free reactive dyeing.The structures of both the untreated and cationic fibers were investigated by X-ray diffraction and scan-ning electronic microscopy. Higher dye utilization and color yields could be realized on the cationic cot-ton than that on the untreated one in the conventional dyeing. Levelness dyeing and good fastnessproperties of the dyes on the cationic fabrics were obtained. Besides, colorimetric properties and mechan-ical strength of the dyed fabrics were both evaluated to show applicability of this preparation process ofcationic cotton.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Cotton fibers are widely applied in textile industry due to itsexcellent properties of hygroscopicity, air permeability, biodegrad-ability, no static electricity, etc. In current practice, reactive dyes arepredominantly used for dyeing of cotton due to their high wet fast-ness, brilliancy and wide range of hue. However, most commer-cially available reactive dyes show low binding to cotton, so highconcentrations of sodium chloride or sodium sulfate (30–100 g/L)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 reducedenvironmental 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 theetherifying reaction of cotton with the tertiary amino or quaternaryammonium cationizing reagents, especially quaternary ammoniumcationizing reagents, such as 2,3-epoxypropyltrimehtylammoniumchloride (I in Scheme 1) (Hauser, 2000; Montazer, Malek, & Rahimi,2007). This compound is usually formed in situ from the reaction ofsodium hydroxide with 3-chloro-2-hydroxypropyltrimethylammo-nium chloride (CHPTAC) (see Scheme 1).

CHPTAC is a relatively cheap and low toxic chemical, it can reactwith cotton under a variety of reaction processes (the reaction pro-

ll rights reserved.

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 areusually employed due to application convenience or relatively highreaction efficiency. But till now, no one best procedure has yetbeen 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 toabout 80–120 �C and kept at that temperature for over 20 minfor cationization. The reaction efficiency was low and afterone-time usage, the reagent has to be discharged due to itshydrolysis (see Scheme 1), which caused significant waste ofCHPTAC and pollution in cationization process. Pad-batch process(Kanik, Hauser, Chapman, & Donaldson, 2004; Hauser & Slopek,2005; Montazer et al., 2007) was proved to enhance reactionefficiency of epoxy compounds, however, it cannot resolve theproblem of the waste of the reagent even though the alkaliwas added to the bath just prior to application. Moreover, inthe process, the padded fabrics were cationized by wrapping inplastic and batching at room temperature for 12–24 h. This madethe cationization inconvenient, lengthy, and not adapted for con-tinuous processing. Pad-bake procedure (Lewis & Lei, 1989,1991) would be preferable for commercial use, however, fromthe 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 andsodium hydroxide were used in one bath.

O

O

NH2

N

SO3Na

HNH

SO3NaN N

N Cl

ClC.I. Reactive Blue 4

O

O

NH2

N

SO2C2H4OSO3Na

SO3Na

H

C.I. Reactive Blue 19

N

NaO3S

NNN

N

SO2C2H4OSO3Na

ClN

H

NaO3S SO3NaOH N

H

C.I. Reactive Red 195

SO3Na

NaO3S SO3Na

NNaO3S

N

NH

N SO2C2H4OSO3NaH2NOCHN

NNN

Cl

HC.I.Reactive Yellow 145

N N

NHNHN

NN

NR

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.

H2CClHCOH

H2C N(CH3)3 Cl

OH

O

H2C N(CH3)3 Cl

CHPTAC 2, 3-epoxyp ropyl- trimethylammonium chloride ( I )

O

H2C N(CH3)3 Cl CH2OCHCH2N(CH3)3

OHCl

OHCell OH Cell O

( I ) Cotton fiber Cationic cotton

ClH2CHCOH

H2C N(CH3)3 Cl

H2OHO

H2CHCOH

H2C N(CH3)3 Cl

OH

CHPTAC Hydrolysis product of CHPTAC

Scheme 1. Reactions occurred during the cationization process of cotton.

L. Wang et al. / Carbohydrate Polymers 78 (2009) 602–608 603

Based on the above research, it is obvious that pad-bake processis more suitable for application, so how to make use of its advan-tages and avoid its disadvantages is a meaningful work neededto be considered. In this study, a two-bath pad-bake process wasdesigned to separate the usage of CHPTAC and alkali in two bathsand relatively low reaction temperature and short reaction timewere investigated for preparation of cationic cotton to avoid re-agent migration to the great extent. Thus, the recycle utilizationof 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-raydiffraction (XRD) and scanning electronic microscopy (SEM) wereused to evaluate the structure properties of the cationic fibers. Inaddition, the dyeing properties of a variety of reactive dyes onthe cationic cotton in the absence of salt were investigated todetermine the quality of the cationized substrates and advantagesof this preparation process.

2. Experimental

2.1. Materials

One hundred percent cotton (150 g/m2), bleached, desized andmercerized, was purchased from Testfabrics, Inc., Shanghai. Thereactive 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 andC.I. Reactive Red 120; they were obtained from Shanghai DyestuffCo. and used as received. These dyes were chosen because of theircommercial availability, known structures and representative ofdifferent types of reactive dyes.

CHPTAC which was commercially available as a 65.0% solutionin water, was supplied by Weifang Auxiliary Co. and used as re-ceived. Other chemicals used in this study were commerciallyavailable 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 fabricwas separately and continuously dip-nipped in the aqueous solu-tions of 8.0% (o.w.bath) CHPTAC and 1.8% (o.w.bath) sodiumhydroxide at room temperature on a TFO/S 350 Laboratory padmangle (Roaches International Ltd, UK). And 10 mg/L penetrating

agent JFC (fatty alcohol-polyoxyethylene ether, Weifang AuxiliaryCo.) was added in both solutions. The pressure on the manglewas adjusted to give 80% wet pickup. The obtained sample washeated at 60 �C for 6 min in a Rapid baker, and then neutralisedby rinsing several times with water. The cationic fabric was readyfor 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 controlunit using a liquor-to-goods ratio of 20:1. The dye applied was3% (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 raisedto 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 andC.I. Reactive Red 120. Both the untreated and cationic fabric sam-ples were then added to the dyebaths. For conventional dyeing ofthe untreated cotton, 60 g/L of anhydrous sodium sulphate wasadded to the dyebaths. The dyeing procedure for cationic cottonwas 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

604 L. Wang et al. / Carbohydrate Polymers 78 (2009) 602–608

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 Yellow145 and C.I. Reactive Red 120, respectively. Sodium carbonate(10 g/L) was then added in each dyebath and dyeing continued atthe fixation temperatures for 40 min.

After dyeing, the cotton fabrics were removed from the dyebathsand rinsed thoroughly in tap water. The rinse was collected for mea-surement of dye exhaustion. Then the dyed fabric was subjected toboiling in a solution containing 2 g/L anionic detergent LS (ShanghaiAuxiliary Co.) at a liquor-to-goods ratio of 25:1 for 15 min until nodye 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 triplicateby the Kjeldahl method. The samples were dried under vacuum atthe temperature of 50 �C before measurement. In this study, thenitrogen 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 (Graphitemonochromator) Cu-Ka1-radiation (40 kV, 100 mA) was used.

2.6. Scanning electron microscope (SEM)

The cotton fabric samples were coated by gold sputtering atroom temperature. Scanning electron micrographs of the sampleswere 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 fromKubelka-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 thewavelengths of minimum reflectance (maximum absorbance) ofeach dyestuff.

Dyebath exhaustion (E%) of both the untreated and cationizedcotton was measured by sampling the dyebath before and afterdyeing process using Eq. (2).

E% ¼ 100� ð1� A1=A0Þ ð2Þ

where A0 is the absorbance of the dyebath before dyeing, and A1 isthe absorbance of the dyebath after dyeing, the absorbance of thedyebath was measured at maximum absorbance of each dye usingHP 8453 UV–vis spectrophotometer.

The percentage of the total dye fixed (F%) on both the untreatedand cationized cotton was determined by measuring K/S values ofthe dyed samples before and after soaping, which was calculatedusing Eq. (3).

F% ¼ E%� C2=C1 ð3Þ

C1 is K/S value of dyed sample before soaping and C2 is K/S value ofdyed sample after soaping.

2.8. Color measurement

CIE L*, a*, b*, C* and h of the dyed samples were measured withUltraScan 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 ISO105-B01:1994 using S-1002 two-bath dyeing and testing appara-tus (Roaches Co., UK). Rub fastness was tested according to ISO105-X12:1993 using Y(B) 571-II crockmeter. Light fastness wastested 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 weretested according to ISO 13934-1-1999 and ASTM D 5734-1995using YG (B) 026H weave-force machine (Wenzhou, China), YG(B) 033A tearing instrument (Wenzhou, China), respectively. Eachsample 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 leasteffect on the fiber properties and at the same time achieve high dyeutilization on the obtained cationic cotton. Thus, the conditionscould not be severe and they were considered to be good if the to-tal dye fixed (F%) in salt-free dyeing could be improved comparedwith that in the conventional dyeing. Therefore, in this study, thepreparation conditions of the two-bath pad-bake process wereinvestigated and the optimal conditions were determined basedon the percentage of the total dye fixed (F%) of C.I. Reactive Blue19 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 oncationic cotton

To optimize the preparation conditions, the effect of the con-centration of CHPTAC was first investigated and the results werepresented in Fig. 2(a). Wherein, the molar ratio of sodium hydrox-ide to CHPTAC was 2:1, baking temperature was 90 �C and bakingtime was 10 min. Addition of high concentration of cationizing re-agent could achieve high cationization degree of cotton, as well ashigh dye exhaustion and the percentage of total dye fixed on thecationic 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% to84.1%, indicating that cationization efficiently supplies increasedcationic 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% wasobserved. This could be explained by that sufficient cationic siteshad been provided for this dye when 8.0% of the reagent was used.Thereafter 8.0% of CHPTAC was selected in the followinginvestigation.

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 examinedand the results were shown in Fig. 2(b). The cationic reagent con-centration was 8.0% (o.w.bath), baking temperature was 90 �C andbaking time was 10 min. The results showed that F% increased withincreasing molar ratio at the beginning, however, when the ratiowas higher than 1.0 and further increased to 2.0, F% of C.I. Reactive

2 4 6 8 1065

70

75

80

85

90

F %

Concentration of CHPTAC, %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

50 60 70 80 90 10065

70

75

80

85

90

Baking temperature,

F %

2 4 6 8 1060

65

70

75

80

85

90

F %

Baking time, min

a b

c d

Fig. 2. Effect of CHPTAC concentration (a), molar ratio of sodium hydroxide to CHPTAC (b), baking temperature (c) and time (d) on F% of C.I. Reactive Blue 19 on cationiccotton.

L. Wang et al. / Carbohydrate Polymers 78 (2009) 602–608 605

Blue 19 on the cationic cotton changed quite a little. Based on thereaction procedure shown in Scheme 1, the main function of so-dium hydroxide was to promote the formation of epoxy groupand neutralize the acid produced in the process. In the reaction be-tween the epoxy agent and cotton, although alkaline condition wasrequired to activate the cotton, it was found in the experiment thatonly quite a little amount of sodium hydroxide was needed asmuch stronger organic alkali was formed in the process to promotethe cationization reaction of cotton. Therefore, nearly equal mole ofsodium 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 cationiccotton.

For baking temperature determination, CHPTAC concentrationused 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 shownin Fig. 2(c). It was evident from the data that in this process, theetherification reaction was unsuitable at much lower temperatureas 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 etherificationreaction, 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. Reactiveblue 19 had been obtained under the condition of 60 �C. In addi-tion, much higher temperature was not suitable for applicationin cationization of cotton because it might cause degradation ofthe 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 1:1and 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 increasewith longer baking time. This result confirmed that good F% resultcould be obtained by using 6-min reaction time, since enough cat-ionic sites had been provided under the conditions for C.I. ReactiveBlue 19.

Based on the above investigations, it can be concluded that un-der much milder two-bath pad-bake conditions, especially muchlower baking temperature (60 �C) and shorter baking time(6 min), F% of about 84.0% of C.I. Reactive Blue 19 could be yieldedon 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 werebased on C.I. Reactive Blue 19, it was proved that other reactivedyes used in this paper also give promising effects on the cottoncationized 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 preparationmethod for cationic cotton should not influence its structure prop-erties. In this section, X-ray diffraction and scanning electronmicroscope were used to examine the physical structure propertiesof 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 ofthe cationic cotton and the control one were made (as shown inFig. 3). The results showed that the X-ray spectra of the cotton be-fore and after cationization are the same, a typical diffraction peakexisted at 2h = 18.6� in both Fig. 3(a) and (b). It demonstrated thatcationization occurred just on the surface of the fiber; it had no ef-fect on its crystal structure.

0 10 20 30 40 50 60 0 10 20 30 40 50 60

a b

Fig. 3. X-ray diffraction patterns of untreated cotton fiber (a) and cationic cotton fiber (b).

Fig. 4. SEM photos of untreated cotton fiber (a 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.

606 L. Wang et al. / Carbohydrate Polymers 78 (2009) 602–608

3.2.2. Surface morphologyThe 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 thesurface of the cationic fiber was a little rougher (d) compared withthat of the untreated one (b), no distinct change could be detectedbetween them. As the extent of cationization was small under theselected conditions, the physical structure of the cotton was almostnot influenced and the obtained cationic cotton was suitable forfurther 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 (preparedunder the optimized conditions) and untreated cotton. Due to theintroduction of the cationic groups to cotton, reactive dyes easilyabsorbed on the cationic cotton without addition of sodium sul-phate or sodium chloride in the dye-bath. Comparing the fixationresults for dyeing the cationic cotton with those from the conven-tional dyeing of the untreated cotton, it could be seen that in all thecases, F% of the dyeings obtained on the former was higher than

that on the latter. These results indicated that with the cationiccotton prepared under the optimized conditions, dye utilizationefficiency was enhanced and savings in dye consumption may bemade in salt-free dyeing process. It was also found that good phys-ical appearance and levelness of the dyed fabrics were achieved.

Table 1Fastness properties of the reactive dyes and mechanical strength of the dyed cotton.

C.I. Reactive Fabric K/S Wash fastness Rub fastness Light fastness Tensile strength (N) Tear strength (N)

Change Staining Dry Wet Warp Weft Warp Weft

Cotton Wool

Blue 4 Cationic 4.3 4–5 4–5 4 4 4 6 711.0 404.0 11.4 9.0Untreated 3.4 4 4 4 4 3–4 6 735.9 415.8 11.7 9.2

Blue 19 Cationic 9.1 4 4 3 4 3–4 5–6 781.3 424.1 11.4 8.8Untreated 7.9 3–4 3–4 4 4 3–4 5–6 805.3 456.7 12.0 8.8

Red 195 Cationic 8.1 4–5 4–5 4–5 4 4 4 733.9 418.5 11.7 9.6Untreated 7.9 3–4 3 4–5 4–5 4 4 768.2 428.0 12.6 10.2

Yellow 145 Cationic 4.5 4–5 4–5 4–5 4–5 3–4 4 753.1 404.0 11.6 8.3Untreated 4.0 4 4–5 4–5 4–5 4 4–5 765.8 429.9 12.4 8.6

Red 120 Cationic 14.4 4 3–4 4–5 4 3–4 4 777.2 413.4 9.3 8.2Untreated 10.0 3–4 3–4 4–5 4 3 4 804.1 421.6 12.0 9.6

Table 2Colorimetric 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 30.7 257.3Untreated 54.2 �7.7 �29.8 30.8 255.4

Blue 19 Cationic 37.4 0.9 �35.6 35.6 271.6Untreated 40.8 �0.4 �37.2 37.2 269.4

Red 195 Cationic 45.9 53.3 �6.1 53.6 353.5Untreated 49.4 47.2 �9.3 48.1 348.9

Yellow 145 Cationic 74.3 24.3 61.4 66.1 68.4Untreated 75.1 24.8 59.9 64.9 67.5

Red 120 Cationic 44.1 59.1 9.8 59.9 9.4Untreated 48.8 55.0 3.9 55.1 4.1

L. Wang et al. / Carbohydrate Polymers 78 (2009) 602–608 607

3.4. Recycle utilization of CHPTAC

At atmospheric temperature, the solution of CHPTAC is stableand can be stored for quite a long time. However, addition of alkalispeeds up the hydrolysis of the reagent to form inactive material,especially at high temperature. It was reported that dependingon 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 bathand continuously dip-nipped in alkali bath at room temperature,thus no alkali was mixed into the bath of CHPTAC during the wholeprocess and the hydrolysis of the cationic reagent was effectivelyrestrained. As a result, recycle utilization of CHPTAC could berealized.

In this section, ten times’ recycle of 50 mL solutions of CHPTACand sodium hydroxide was made for successively padding of 10pieces 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’ usageof the solutions without addition of the agents. The value of F% foreach recycle was between 81.7% and 86.3% and the nitrogen con-tents of the cationic fabrics were also measured to be all between0.6% and 0.7% (wt%). This demonstrated good repeatability of thispretreatment process. Owing to the relatively low substantivityof CHPTAC to cotton fibers, the concentration of it almost did notchange by each pad procedure, therefore, the amount of the re-agent padded on the fabric each time was almost the same, whichdefinitely resulted in close F% in each application cycle. Accord-ingly, with this two-bath pad-bake process, the cationizing reagentCHPTAC 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 propertiesand mechanical strength of the dyeings in both salt-free dyeingand conventional dyeing. K/S values of all 5 reactive dyes in salt-free dyeing were higher. The wash fastness of the dyeings on thecationic 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 dyeingprocess. Dry and wet rub fastness of the dyes on the cationic fab-rics was also comparable with that obtained from conventionaldyeing. In the cases of C.I. Reactive Blue 4 and C.I. Reactive Red120, the wet fastness on the cationic cotton was even 0.5 gradehigher. Moreover, light fastness testing of the dyeings on the cat-ionic fabrics showed satisfactory results compared with that inthe 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 thedyes.

The mechanical strength of the cationic cotton affected theapplication of it, so the tensile strength and tear strength of thecationic and untreated cotton were measured and compared (seeTable 1). As the data shown, the tear strength of the dyed cationiccotton was lower than that obtained from the untreated one. Thetensile strength of the cationic cotton was also reduced. Higherdye fixation F% may have certain responsibility for the strength de-crease of the fibers. The reduction in tear strength was not muchexcept that of the fabrics dyed with C.I. Reactive Red 120, andthe reduction in warp tensile strength was 0.7–4.5% and in wefttensile strength was 1.9–7.1%, which were still comparable to theresults 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 thecolorimetric data of the reactive dyes was evaluated. Table 2 showsthat L� values for all five dyes on cationic cotton are lower than thecorresponding values on untreated cotton, indicating that cationiccotton colors are darker than untreated one. There were alsochanges in redness-greenness (a�), yellowness-blueness (b�), chro-ma (C�) and hue (h) values between dyed cationic and untreatedcotton, and the differences for different dyes were not the same.

In fact, the color differences were difficult to account for the di-rect effect of the cationic groups on the color of the dyes associatedwith them. The darker influence suggested a difference in physicalenvironment 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 differencecould impose minor limitations on application of this dyeing meth-

608 L. Wang et al. / Carbohydrate Polymers 78 (2009) 602–608

od, which could be accommodated in the reformulation of the dyerecipes.

4. Conclusions

By studying the preparation method of cationic cotton with de-signed two-bath pad-bake process, it was shown that this processwas beneficial for recycle utilization of CHTPAC and continuousprocessing of cationization, and by this method, effluent dischargein cationization was greatly diminished to reduce its impact onenvironment. XRD and SEM results showed cationization occurredonly on the surface of the cotton fibers and surface morphology ofthe 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 fixationand color yield of the reactive dyes in salt-free dyeing process, anduniform dyeing was achieved. So by this cationization method, notonly pollution from salt addition was eliminated, dye utilizationefficiency was also enhanced. Besides, the colorfastness andmechanical strength of the fabrics were all good and can meetthe need for use. While by cationization, a little darker shadewas 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-bathpad-bake process was suitable for preparation of cationic cottonused for salt-free reactive dyeing to achieve both effluent reductionand satisfactory application properties.

Acknowledgements

The authors gratefully thank the financial support of the Na-tional Nature Science Funds for Distinguished Young Scholar ofChina (No. 20525620), the National Nature Science Funds of China

(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 fiberreactive dyes and cationized cotton. Colourage, 52(61–62), 64–66.

Hauser, P. J., & Tabba, A. H. (2001). Improving the environmental and economicaspects of cotton dyeing using a cationised cotton. Coloration Technology, 117,282–288.

Kanik, M., Hauser, P. J., Chapman, L. P., & Donaldson, A. (2004). Effect ofcationization on inkjet printing properties of cotton fabrics. AATCC Review, 4,22–25.

Kitkulnumchsi, Y., Ajavakom, A., & Sukwattanasinitt, M. (2008). Treatment ofoxidized cellulose fabric with chitosan and its surface activity towards anionicreactive dyes. Cellulose, 15, 599–608.

Lewis, D. M., & Lei, X. P. (1989). Improved cellulose dyeability by chemicalmodification of fiber. Textile Chemist and Colorist, 21, 23–29.

Lewis, D. M., & Lei, X. P. (1991). New methods for improving the dyeability ofcellulose 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 withpoly(vinylamine chloride) for salt-free dyeing with reactive dyes. ColorationTechnology, 121, 193–197.

Montazer, M., Malek, R., & Rahimi, A. (2007). Salt free reactive dyeing of cationizedcotton. Fibers and Polymers, 8, 608–612.

Seong, H. S., & Ko, S. W. (1998). Synthesis, application and evaluation of cationisingagents 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 ofmodified novel cellulose with triazine derivatives containing cationic andanionic groups. Carbohydrate Polymers, 72, 646–651.

Zhang, F., Chen, Y. Y., Lin, H., Wang, H., & Zhao, B. (2008). HBP-NH2 grafted cottonfiber: 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 cationichydrolyzed 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. ColorationTechnology, 121, 183–186.