One-Bath Pretreatment for Enhanced Color Yield of Ink-Jet Prints Using Reactive Inks

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Article One-Bath Pretreatment for Enhanced Color Yield of Ink-Jet Prints Using Reactive Inks

Wei Ma *, Kezhan Shen †, Shuang Li †, Meichen Zhan and Shufen Zhang * State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116023, China; [email protected] (K.S.); [email protected] (S.L.); [email protected] (M.Z.) * Correspondence: [email protected] (W.M.); [email protected] (S.Z.); Tel.: +86-411-8498-6506 (W.M.); +86-411-8498-6265 (S.Z.) † These authors contributed equally to this work.

Received: 30 September 2017; Accepted: 9 November 2017; Published: 13 November 2017

Abstract: In order to facilely increase the color yield of ink-jet prints using reactive inks, one-bath pretreatment of cotton fabrics with pretreatment formulation containing sodium alginate, glycidyltrimethylammonium chloride (GTA), sodium hydroxide, and urea is designed for realizing sizing and cationization at the same time. The pretreatment conditions, including the concentrations of GTA and alkali, baking temperature, and time are optimized based on the result of thecolor yield on cationic cotton for magenta ink. The mechanism for color yield enhancement on GTA-modified fabrics is discussed and the stability of GTA in the print paste is investigated. Scanning electron microscopey, tear strength, and thermogravimetric analysis of the modified and unmodified cotton are studied and compared. Using the optimal pretreatment conditions, color yield on the cationic cotton for magenta, cyan, yellow, and black reactive inks are increased by 128.7%, 142.5%, 71.0%, and 38.1%, respectively, compared with the corresponding color yield on the uncationized cotton. Much less wastewater is produced using this one-bath pretreatment method. Colorfastness of the reactive dyes on the modified and unmodified cotton is compared and boundary clarity between different colors is evaluated by ink-jet printing of colorful patterns.

Keywords: ink-jet printing; cotton modiﬁcation; one-bath pretreatment; reactive dyes

1. Introduction Ink-jet printing of textiles has developed rapidly in recent years because of its rapid response to fashion patterns and satisfactory printing effects [1–6]. This modern printing is suitable for small-scale production to meet personal demand. In the future, it is largely possible that conventional flat, rotary screen or roll printing techniques will be replaced by ink-jet printing [7–10]. Cotton fibers, owing to their soft, hygroscopic, and ventilative properties, have a prevailing position in the present developments of textile materials [11–16]. Unlike in conventional printing, cotton fabrics need to be pretreated in ink-jet printing with a pretreatment formulation containing a thickener, alkali, and urea, and then dried to remove water prior to ink-jet printing. It is impossible to add regular chemicals into the inks due to special requirements on the ink viscosity, stability, and conductivity [17–20]. Reactive dye-based inks are commonly used to print cotton and other cellulosic fabrics due to their wide shade range and excellent fastness properties. Due to limited reactivity and hydrolysis of the reactive groups during dye fixation step, reactive dyes only have a fixation of 50–80%, resulting in producing a large amount of dye wastewater [21]. Moreover, monochloro-s-triazine dyes with low reactivity are commonly used in ink formulation to meet the requirement for stability, resulting in even low color yield of the prints. Therefore, one of the key problems for ink-jet printing of reactive dyes is the unsatisfactory color yield, which restricts the application of reactive ink-jet printing in producing deep colors [22].

Molecules 2017, 22, 1959; doi:10.3390/molecules22111959 www.mdpi.com/journal/molecules Molecules 2017, 22, 1959 2 of 13

Many attempts have been made to improve the color yield of reactive ink-jet prints. PretreatmentMany attempts and modification have been made of cotton to improve to increase the color its reactivity yield of reactive and affinity ink-jet prints.between Pretreatment the fibers and and themodification dyes were ofreported cotton to to be increaseeffective methods, its reactivity such andas pretreatment affinity between with gas the plasma fibers [1], and modification the dyes werewith glycidyltrimethylammonium reported to be effective methods, chloride such (GTA) as or pretreatment 3-chloro-2-hydroxypr with gasopyltrimethylammonium plasma [1], modification withchloride glycidyltrimethylammonium [14,23,24], dendrimer compounds chloride (GTA)[4], an ord chitosan 3-chloro-2-hydroxypropyltrimethylammonium [14,25–28]. With these methods, the colorchloride yield [14 of,23 the,24], prints dendrimer was improved compounds to [a4], certai and chitosann extent. [ 14Among,25–28 ].them, With GTA these is methods, an effective the color agent yield for enhancingof the prints color was yield. improved It undergoe to a certains an extent.etherification Among reaction them, GTA with is the an primary effective agenthydroxyl for enhancinggroups of thecolor fibers, yield. and It undergoes the hydrolysis an etherification side reaction reaction also with occurs the primaryduring the hydroxyl cationization groups of process. the fibers, GTA and is the a relativelyhydrolysis cheap side reactionand low alsotoxic occurs chemical during [29]. the Moreover cationization, as it is process. a small GTAmolecule, is a relativelyand its influence cheap and on dyelow toxicpermeability chemical and [29]. colorfastness Moreover, as is it islow. a small Kanik molecule, et al. [23] and used its influence GTA and on sodium dye permeability hydroxide and to modifycolorfastness the cotton is low. fabrics Kanik at et al.room [23 ]temperature used GTA and for sodium 24 h, which hydroxide were to then modify thoroughly the cotton rinsed fabrics and at driedroom temperatureto remove water for 24 from h, which the fabrics. were then The thoroughly obtained rinsedcationized and driedfabrics to were remove used water in ink-jet from the printing fabrics. Theof reactive obtained inks cationized for enhanced fabrics color were yield. used In in ink-jetthe study, printing cationization of reactive and inks pretreatment for enhanced formulation color yield. pretreatmentIn the study, cationization are separated, and and pretreatment the cationizatio formulationn process pretreatment is long, arewhich separated, makes and the the whole cationization process complex,process is long,and time-and which makes water-consuming. the whole process An complex, additional and cationization time-and water-consuming. step is disadvantageous An additional in practice,cationization which step restricts is disadvantageous its real application. in practice, which restricts its real application. It is found that both GTA cationization and cotton sizing proceed under under alkaline alkaline conditions. conditions. However, the alkali used in the two procedures is different: sodium hydroxide is effective for for GTA GTA cationization and and sodium sodium carbonate carbonate is is commonly commonly used used for for sizing sizing pretreatment. pretreatment. Sodium Sodium hydroxide hydroxide is notis not conventionally conventionally employed employed in pretreatment in pretreatment formulation formulation because because it will it will promote promote hydrolysis hydrolysis of the of reactivethe reactive dyes dyes in ink-jet in ink-jet printing printing and and is isnot not bene beneficialficial for for dye dye fixation. fixation. If If the the cationization and pretreatment procedures are combined, the process will be simpler and there will be significantsignificant time- and water-saving.water-saving. Thus,Thus, inin thisthis study,study, wewe designeddesigned aa one-bathone-bath pretreatment to combine both GTA cationization and and sizing sizing pretreatment. pretreatment. “Sizing” “Sizing” in in this this paper paper refers refers to tothe the surface surface treatment treatment of cottonof cotton with with alginate alginate paste, paste, the the polymeric polymeric compon componentent in in the the pretreatment pretreatment formulation. formulation. With With the method, sodiumsodium alginate,alginate, GTA, GTA, sodium sodium hydroxide, hydroxide, and and urea urea are are uniformly uniformly mixed mixed together together in one in bathone bathfor cotton for cotton pretreatment pretreatment before ink-jetbefore printing.ink-jet prin Figureting.1 showsFigure the1 shows flowchart the offlowchart the ink-jet of printing the ink-jet on printingthe modified on the cotton. modified This papercotton. aims This to paper investigate aims whetherto investigate this method whether is effectivethis method in improving is effective color in improvingyield compared color toyield the previously-reportedcompared to the previously-r two-batheported method two-bath and the influencesmethod and of the pretreatmentinfluences of theparameters, pretreatment including parameters, concentrations including of concentrat GTA andions sodium of GTA hydroxide, and sodium and baking hydroxide, temperature and baking and temperaturetime on the colorand time yield. on The the mechanism color yield. for The color mechanism yield enhancement for color yield and theenhancement stability of and GTA the in stabilitythe pretreatment of GTA in bath the will pretreatment also be studied. bath will In addition,also be studied. a comparison In addition, will be a madecomparison on the surfacewill be mademorphology, on the surface strength, morphology, and thermal strength, properties, and colorfastness, thermal properties, and print colorfastness, quality of the and cationized print quality and ofuncationized the cationized cotton and to comprehensively uncationized cotton evaluate to thecomprehensively applicability of evaluate the one-bath the pretreatmentapplicability methodof the one-bathfor ink-jet pretreatment reactive printing. method for ink-jet reactive printing.

Figure 1. Flowchart of ink-jet printing on modified modiﬁed cotton.

2. Results and Discussion 2. Results and Discussion

2.1. Effect of Concentration of GTAGTA onon Color Yield of Magenta Ink In order to investigate the effecteffect ofof thethe GTAGTA concentrationconcentration onon KK//S,, GTA GTA of differentdifferent concentrationsconcentrations were usedused in in pretreatment pretreatment paste paste and eachand fabriceach wasfabric ink-jet was printed ink-jet with printed the magenta with the ink. magenta The concentration ink. The concentrationof sodium hydroxide of sodium was 0.4hydroxide wt % of was pretreatment 0.4 wt % formulation,of pretreatment and allformulation, treated cotton and was all bakedtreated at cotton 90 ◦C

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was baked at 90 °C for 15 min. The printed samples were steamed for 15 min and then thoroughly washed. The obtained K/S on the fabrics is shown in Figure 2a. In Figure 2a, when GTA applied was 0%, 1%, 2%, 3%, 4%, and 5 wt %, K/S of the prints was 10.03, 13.23, 19.56, 22.94, 23.71 and 24.22, respectively. K/S of the prints increased distinctly with increasing GTA concentration. It can be calculated that K/S increased by 31.9%, 95.0%, 128.7%, 136.4% and 141.5% compared with that without addition of GTA when 1%, 2%, 3% and 4% GTA was used, respectively. These results reveal that GTA concentration is a decisive parameter for the increase of the color yield. K/S was enhanced significantly especially when the concentration of GTA was higher than 2 wt %.This one-bath pretreatment method can also effectively increase the color yield as the two bath pretreatment method [30]. One reason for K/S increase could be higher substantivity of the cationic fibers to the dyes and lower dye penetration in the fibers as demonstrated in previous studies, which was caused by strong ionic attraction between the cationic fibers and the anionic dyes [14,22,27]. The other reason that we considered as the main reason for the K/S increase was much higher dye fixation. That means more dyes were covalently bonded to the fibers in the presence of GTA. A color stripping procedure was used to test the covalent bonds between the fibers and the dyes [31]. For the sample with K/S of 24.22, K/S only showed a small decrease to 23.90 after the color stripping test, indicating most of the dyes were covalently bonded to cotton. All of these FigureresultsFigure 2.demonstrate Effects2. Effects of ofthat, ((aa)) GTAafter GTA concentration;pretreatment, concentration; ( bthe) NaOH ( breactivity) NaOH concentration; of concentration; the fibers (c) baking was improved. ( ctemperature;) baking It temperature; is and likely (d) that baking time on the K/S values of magenta ink. andthe secondary (d) baking hydroxyl time on the group,K/S values in the of2-position magenta of ink. the propane side chain when GTA reacts with cellulose, is ionized at a much lower pH value than are the cellulose hydroxyl groups and is highly Innucleophilic Figure2a, (see when Figure GTA 3) [32]. applied This wascould 0%, be responsible 1%, 2%, 3%, for the 4%, higher and 5reactivity. wt %, K/S of the prints was 10.03, 13.23, 19.56, 22.94, 23.71 and 24.22, respectively. K/S of the prints increased distinctly with increasing GTA concentration. It can be calculated that K/S increased by 31.9%, 95.0%, 128.7%, 136.4% and 141.5% compared with that without addition of GTA when 1%, 2%, 3% and 4% GTA was used, respectively. These results revealFigure that3. Reaction GTA concentrationequation of GTA with is a cotton decisive fiber. parameter for the increase of the color yield. K/S was enhanced significantly especially when the concentration of GTA was higher In our study, in order to prove the function of the newly introduced hydroxyl group, a contrast thanexperiment 2 wt %. This was one-bath carried out pretreatment that GTA was method first hy candrolyzed also effectively and then increaseadded in thethe colorpretreatment yield as the two bathformulation. pretreatment Using methodthe same [pretreatment30]. One reason and forink-jetK/S printingincrease processes, could be we higher found substantivity the K/S of the of the cationicprints fibers did tonot the increase, dyes and demonstrating lower dye penetration only grafting in of the GTA fibers onto as cotton demonstrated fibers can in enhance previous fiber studies, which was caused by strong ionic attraction between the cationic fibers and the anionic dyes [14,22,27]. The other reason that we considered as the main reason for the K/S increase was much higher dye fixation. That means more dyes were covalently bonded to the fibers in the presence of GTA. A color stripping procedure was used to test the covalent bonds between the fibers and the dyes [31]. For the sample with K/S of 24.22, K/S only showed a small decrease to 23.90 after the color stripping test, indicating most of the dyes were covalently bonded to cotton. All of these results demonstrate that, after pretreatment, the reactivity of the fibers was improved. It is likely that the secondary hydroxyl group, in the 2-position of the propane side chain when GTA reacts with cellulose, is ionized at a much lower pHFigure value 2. than Effects are of the(a) GTA cellulose concentration; hydroxyl (b) NaOH groups concentration; and is highly (c) baking nucleophilic temperature; (see and Figure (d) 3)[ 32]. This couldbaking be responsible time on the K for/S values the higher of magenta reactivity. ink.

FigureFigure 3. 3.Reaction Reaction equationequation of GTA GTA with with cotton cotton fiber. ﬁber.

In ourIn study,our study, in order in order to proveto prove the the function function ofof thethe newly newly introduc introduceded hydroxyl hydroxyl group, group, a contrast a contrast experimentexperiment was was carried carried out out that that GTA GTA was was ﬁrstfirst hydrolyzedhydrolyzed and and then then added added in the in thepretreatment pretreatment formulation.formulation. Using Using the the same same pretreatment pretreatment andand ink-jet printing printing processes, processes, we wefound found the K the/S ofK/S theof the prints did not increase, demonstrating only grafting of GTA onto cotton fibers can enhance fiber

Molecules 2017, 22, 1959 4 of 13 prints did not increase, demonstrating only grafting of GTA onto cotton fibers can enhance fiber reactivity and, finally, realizing a much higher dye fixation. This clearly presents that the main reason for enhancing the color yield were the more reactive hydroxyl groups. In addition, Figure2a also shows that when GTA concentration increases from 3% to 5%, the increase of K/S was not very high. As K/S increased by 128.7% when 3% GTA was used, it is already very beneficial to commercial use, and 3% of GTA was selected to be used in the following investigation.

2.2. Effect of NaOH Concentration Similar to the conventional printing process, alkali is used in ink-jet printing to ionize the cellulose hydroxyl groups for reactive dye fixation [26]. In ink-jet printing, alkali is added in the pretreatment formulation and pretreated on the cotton fibers together with sizing agent. For cationization of cotton with GTA, alkaline conditions are also required for the reaction. Due to this reason, we to combined sizing and cationization processes in one step. However, it is found that the alkali commonly used in ink-jet printing was not that used for GTA modification. Sodium carbonate is the preferred alkali in reactive dye printing because its alkalinity is suitable for dye fixation [19]. However, for GTA modification, sodium hydroxide is the most effective alkali to promote the reaction. It is always considered that sodium hydroxide accelerates hydrolysis of reactive dyes owing to its strong alkalinity and is not suitable for reactive dyeing and printing. In this study, we first tried different concentrations of sodium hydroxide for investigation. The effect of NaOH concentration on K/S of the prints is shown in Figure2b. A baking temperature of 90 ◦C and baking time of 10 min were used for investigation. It can be seen from the figure, when alkali concentration was 0, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5 wt %, K/S value was 3.07, 12.70, 17.16, 19.84, 22.94 and 21.71, respectively. K/S of the prints increased distinctly with increasing GTA concentration. It can be seen from the data that NaOH addition in pretreatment formulation is very important for the color yield of the ink. Without alkali, the dye almost cannot fix to the cotton, and the color yield is very limited, only 3.07; with a 0.1% alkali addition, the K/S significantly increased to 12.70; with a further increase to 0.2%, 0.3% and 0.4%, the K/S further greatly increased to 17.16, 19.84 and 22.94, respectively. Addition of NaOH activates the cotton fibers and promotes reaction of GTA with cotton, and further promotes dye fixation. So we can conclude that the K/S value is strongly dependent on and very sensitive to the concentration of NaOH. As the concentration further increases from 4% to 5%, K/S does not show obvious enhancement, even showing a slight decrease to 21.71. As a further increase in the alkali concentration will accelerate the hydrolysis of reactive dyes and GTA, and show an adverse effect on the formed covalent bonds between the dyes and the fibers, this is not beneficial for achieving a high color yield. For comparison, 0.4% Na2CO3 was used instead of NaOH, and the K/S value on the modified fabrics reached 17.21, which was much lower than that obtained with the addition of the same concentration of NaOH. From the above investigation, it can be concluded that better fixation of GTA on cotton is a prerequisite for higher dye fixation. As NaOH is more effective for the GTA reaction and dye fixation, it is better than Na2CO3 in the designed one-bath pretreatment.

2.3. Effect of Baking Temperature As the reaction temperature shows a significant influence on the reaction of GTA on cotton fibers [14], the baking temperature is studied. According to the references for the reaction of GTA with polysaccharide derivatives, baking temperatures of 70 ◦C, 80 ◦C, 90 ◦C, 100 ◦C, and 110 ◦C were chosen for investigation to determine the optimum temperature, the results were shown in Figure2c. In the study, the concentration of GTA and sodium hydroxide was 3 wt % and 0.4 wt %, respectively. Baking time was 15 min. It could be seen from Figure2c that K/S of magenta ink gradually increased from 15.34 to 22.94 as the baking temperature was raised from 70 ◦C to 90 ◦C. However, when the temperature further increased to 100 ◦C and 110 ◦C, K/S showed slight decrease to 22.78 and 21.32, respectively. As the aim of baking process is to dry the fabrics within a short time, high temperature Molecules 2017, 22, 1959 5 of 13 is usually employed. For the one-bath pretreatment, high temperature baking is also beneficial for reaction between GTA and cotton, so we just chose temperature range of 70 ◦C to 110 ◦C. It was found that, for the selected temperature range, the dependence of the color yield on baking temperature is not as high as that on GTA and NaOH concentrations. Molecules 2017, 22, 1959 5 of 13 2.4. Effect of Baking Time on K/S of Magenta Ink found that, for the selected temperature range, the dependence of the color yield on baking temperature Inis not order as high to obtain as that theon GTA optimum and NaOH baking concentrations. time for the reaction between GTA and cotton fibers, the baking time was set to be 5, 10, 15, 20, and 25 min, and its influence on color yield was shown in Figure2.4. Effect2d. Wherein,of Baking Time the on concentration K/S of Magenta of Ink GTA and sodium hydroxide was 3 wt % and 0.4 wt %, ◦ respectively.In order The to baking obtain temperaturethe optimum baking was 90 timeC. fo Fromr the reaction Figure2 betweend, it can GT beA observed and cotton that fibers, when the the bakingbaking time time was was prolonged set to be from5, 10, 515, to 20, 15 min,and 25 the min,K/S andvalue its influence of the cationized on color yield cotton was increased shown in from 19.85Figure to 22.94 2d., respectively.Wherein, the concentration However, when of GTA further and sodium prolonging hydroxide the baking was 3 wt time % toand 20 0.4 and wt 25%, min, K/S valuerespectively. a little decreasedThe baking totemperature 21.28 and was 20.33, 90 respectively.°C. From Figure Further 2d, it extendingcan be observed the baking that when time the shows adversebaking effect time on was the prolonged covalent bondsfrom 5 formed,to 15 min, causing the K/S avalue slight of decreasethe cationized in K/S cottonof the increased prints. from Based on the results,19.85 to it22.94, could respectively. be observed However, that 5when min further is already prolonging a good the choice baking fortime baking to 20 and time 25 min, when K/S other conditionsvalue a have little been decreased determined, to 21.28 prolongingand 20.33, respectively. the baking timeFurther to 15extending min can the just baking achieve time better shows results. adverse effect on the covalent bonds formed, causing a slight decrease in K/S of the prints. Based on Accordingly, it can be concluded that the color yield of the dye is much less sensitive to baking time the results, it could be observed that 5 min is already a good choice for baking time when other comparedconditions with have other been conditions. determined, prolonging the baking time to 15 min can just achieve better Basedresults. onAccordingly, above data it can analysis, be concluded it could that be the summarized color yield of that theK/S dyevalue is much of less the dyesensitive is strongly to dependentbaking ontime the compared concentrations with other of conditions. GTA and NaOH, moderately dependent on baking temperature and muchBased less dependenton above data on analysis, baking time.it could According be summarized to the datathat K in/S Figurevalue 2of, wethe chosedye is 3strongly wt % GTA, 0.4 wtdependent % NaOH on, baking the concentrations temperature of ofGTA 90 ◦andC, andNaOH baking, moderately time of dependent 15 min as on the baking optimized temperature conditions for one-bathand much pretreatment less dependent application. on baking time. According to the data in Figure 2, we chose 3 wt % GTA, 0.4 wt % NaOH, baking temperature of 90 °C, and baking time of 15 min as the optimized conditions 2.5. Stabilityfor one-bath of the pretreatment Pretreatment application. Agent

In2.5. industrial Stability of production,the Pretreatment the Agent stability of the pretreatment agent is essential for the stability of the ink-jet printing. The agent with excellent stability contributes to the continuity of production and In industrial production, the stability of the pretreatment agent is essential for the stability of prolongs the pretreatment agent replacement cycle. GTA is sensitive to alkali due to existence of its the ink-jet printing. The agent with excellent stability contributes to the continuity of production and epoxyprolongs group. the In thepretreatment designed agent one-bath replacement pretreatment cycle. GT method,A is sensitive GTA and to alkali NaOH due are to dissolvedexistence of together its in theepoxy pretreatment group. In formulation, the designed so theone-bath stability pret ofreatment GTA in themethod, pretreatment GTA and formulation NaOH are isdissolved an important factortogether to be evaluated. in the pretreatment The baths formulation, were placed so forthe differentstability of time GTA before in the pretreatment usage. K/S values formulation of the is prints with differentan important pretreatment factor to be baths evaluated. were measured The baths andwere the placed results for were different presented time before in Figure usage.4. ItK shows/S that thevalues color of the yield prints of the with prints different almost pretreatment does not baths change were when measured standing and timethe results was 0,were 0.5, presented 1 and 1.5 h at roomin temperature, Figure 4. It shows the K/S thatvalues the color of prints yield wasof the 22.94, prints 23.00, almost 22.65, does 22.73, not change respectively. when standing Then K/S timevalues experiencedwas 0, 0.5, a slight 1 and decrease1.5 h at room to 22.04 temperature, after standing the K/S for values 2 h. Aof furtherprints was increase 22.94, of23.00, standing 22.65, time22.73, to 3 h respectively. Then K/S values experienced a slight decrease to 22.04 after standing for 2 h. A further further showed decrease in K/S value to 20.64. Thus, with this one-bath pretreatment method, it is increase of standing time to 3 h further showed decrease in K/S value to 20.64. Thus, with this better to use the bath within 2 h to maintain the continuity of production, and NaOH should be added one-bath pretreatment method, it is better to use the bath within 2 h to maintain the continuity of just beforeproduction, the pretreatment and NaOH should process. be added just before the pretreatment process.

Figure 4. K/S values of the prints when pretreatment bath standing for 0, 0.5, 1, 1.5, 2, 3, and 5 h. Figure 4. K/S values of the prints when pretreatment bath standing for 0, 0.5, 1, 1.5, 2, 3, and 5 h.

Molecules 2017, 22, 1959 6 of 13 Molecules 2017, 22, 1959 6 of 13

2.6. Surface Morphology 2.6. Surface Morphology In order to study the influence of cationization on the surface morphology of the fibers, the cotton In order to study the influence of cationization on the surface morphology of the fibers, the was dip-padded pretreatment formulation, with and without GTA, and baked at 90 ◦C for 15 min, cotton was dip-padded pretreatment formulation, with and without GTA, and baked at 90 °C for 15 min, and then rinsed thoroughly. The surface morphology of thus-obtained uncationized and cationized and then rinsed thoroughly. The surface morphology of thus-obtained uncationized and cationized cotton fibers was examined by SEM (see Figure5). Additionally, the SEM of the raw fibers was cotton fibers was examined by SEM (see Figure 5). Additionally, the SEM of the raw fibers was also also shown for comparison. It can be seen no obvious difference among the raw, uncationized and shown for comparison. It can be seen no obvious difference among the raw, uncationized and cationized cotton fibers. There seems to be some impurity on the raw fibers, the surfaces of the cationized cotton fibers. There seems to be some impurity on the raw fibers, the surfaces of the uncationzied and cationized cotton fibers seem much cleaned after pretreatment under alkaline and uncationzied and cationized cotton fibers seem much cleaned after pretreatment under alkaline and high-temperature conditions, and rinsing. No damage was detected on the surface of alkali-treated high-temperature conditions, and rinsing. No damage was detected on the surface of alkali-treated and GTA-treated fibers, indicating the pretreatment conditions did not show any adverse effect on the and GTA-treated fibers, indicating the pretreatment conditions did not show any adverse effect on surface morphology of the cotton fibers. the surface morphology of the cotton fibers.

Figure 5. SEM images of different cotton fibers: (a) raw cotton, ×3000; (b) uncationized cotton, ×3000; Figure 5. SEM images of different cotton fibers: (a) raw cotton, ×3000; (b) uncationized cotton, ×3000; (c) cationized, ×3000; (d) raw cotton, ×6000; (e) unmodified, ×6000; and (f) modified, ×6000. (c) cationized, ×3000; (d) raw cotton, ×6000; (e) unmodified, ×6000; and (f) modified, ×6000. 2.7. Tear Strength 2.7. Tear Strength Tear strength of cotton fabrics was measured to investigate the mechanical strength of the fabricsTear (Table strength 1). Table of cotton 1 shows fabrics the was tear measured strength toof investigatethe raw fabric the mechanicalis 12.4 N in strength warp and of the10.2 fabrics N in weft,(Table that1). Tableof the1 showsuncationized the tear cotton strength is 12.2 of the N rawin wa fabricrp and is 12.49.8 N N in in weft, warp indicating and 10.2 N a inslight weft, decrease that of inthe tear uncationized strength cottonafter alkali is 12.2 and N in high-temperature warp and 9.8 N in weft,treatment. indicating For athe slight cationized decrease fabric, in tear strengthits tear strengthafter alkali presents and high-temperature further decrease treatment. to 12.1 N in For warp the cationizedand 9.5 N in fabric, weft. its Even tear though strength the presents tear decrease further ofdecrease the cationic to 12.1 cotton N in warpis quite and small 9.5 Ncompared in weft. Evento that though of the the uncationized tear decrease one, of it the can cationic still show cotton a certainis quite influence small compared of the pretreatment to that of the with uncationized GTA. one, it can still show a certain influence of the pretreatment with GTA. Table 1. Tear strength of raw, uncationized, and cationized cotton. Table 1. Tear strength of raw, uncationized, and cationized cotton. Cotton Warp (N) Weft (N) RawCotton Warp12.4 (N) Weft10.2 (N) Uncationized 12.2 9.8 Raw 12.4 10.2 CationizedUncationized 12.1 12.2 9.8 9.5 Cationized 12.1 9.5 2.8. Determination of Thermal Properties 2.8. DeterminationThermogravimetric of Thermal analysis Properties was used to investigate the thermal properties of different cotton fabrics.Thermogravimetric Figure 6 presents analysisthe thermal was degradation used to investigate of the raw, the thermaluncationized, properties and cationized of different cotton. cotton Thefabrics. stability Figure of 6the presents raw cotton the thermalwas better degradation than the cotton of the treated raw, uncationized, with pretreatment and cationized formulation cotton. as a significantThe stability weight of the loss raw happened cotton was at 340 better °C thanfor raw the cottoncotton, treatedwhile at with 290 pretreatment°C for uncationized formulation and cationizedas a significant cotton. weight This difference loss happened may be at due 340 to◦C th fore corrosion raw cotton, effect while of Na atOH 290 on◦C cotton for uncationized under high baking temperature. However, no distinct change was detected between uncationized and cationized fabrics. This result indicated that the effect of GTA on the thermal property of cotton was not obvious.

Molecules 2017, 22, 1959 7 of 13 and cationized cotton. This difference may be due to the corrosion effect of NaOH on cotton under high baking temperature. However, no distinct change was detected between uncationized and Molecules 2017, 22, 1959 7 of 13 Moleculescationized 2017 fabrics., 22, 1959 This result indicated that the effect of GTA on the thermal property of cotton7 of was 13 Allnot cotton obvious. samples All cotton began samplesto produce began char toat producehigher temperature. char at higher Carbon temperature. and charred Carbon residues and increased charred All cotton samples began to produce char at higher temperature. Carbon and charred residues increased inresidues this process increased because in this of processdewatering because and ofcharring dewatering reactions and [33,34]. charring reactions [33,34]. in this process because of dewatering and charring reactions [33,34].

Figure 6. Thermogravimetric analysis of raw, uncationized, and cationized cotton. FigureFigure 6. 6. ThermogravimetricThermogravimetric analysis analysis of of raw, raw, uncationized, and cationized cotton. 2.9. Effect of GTA Modification on Different Colors of Ink and Colorfastness 2.9.2.9. Effect Effect of of GTA GTA Modification Modification on Different Colors of Ink and Colorfastness Magenta, yellow, cyan, and black inks are the four basic colors for ink-jet reactive printing in this Magenta,Magenta, yellow, yellow, cyan, and black inks are the four basicbasic colors for ink-jet reactive printing in this study. They are ink-jet printed on cotton pretreated with and without GTA under the above optimal study.study. They are ink-jet printed on cotton pretreated with with and without GTA under the above optimal conditions to show the applicability of the one-bath pretreatment method. The digital pictures of the conditionsconditions to to show show the the applicability applicability of of the the one-bath one-bath pretreatment pretreatment method. method. The The digital digital pictures pictures of the of prints and the washing and soaping wastewater are presented in Figures 7 and 8, respectively. From printsthe prints and andthe washing the washing and soaping and soaping wastewater wastewater are presented are presented in Figures in Figures 7 and 78, and respectively.8, respectively. From Figure 7, the distinct K/S increase of the cationized fabrics for all four colors can be observed. The FigureFrom Figure 7, the7 distinct, the distinct K/S increaseK/S increase of the of cationized the cationized fabrics fabrics for all for four all colors four colors can be can observed. be observed. The contrast of washing and soaping wastewater between the uncationized and cationized fabrics is contrastThe contrast of washing of washing and andsoaping soaping wastewater wastewater between between the theuncationized uncationized and and cationized cationized fabrics fabrics is quite obvious in Figure 8, revealing much less dye wastewater is produced with the designed one-bath quiteis quite obvious obvious in Figure in Figure 8, revealing8, revealing much much less dye less wastewater dye wastewater is produced is produced with the with designed the designed one-bath pretreatment method. Although the comparison of soaping residue (See Figure 8c,d) is not as significant pretreatmentone-bath pretreatment method. Although method. Althoughthe comparison the comparison of soaping ofresidue soaping (See residue Figure (See 8c,d) Figure is not8 asc,d) significant is not as as that of washing waste water(See Figure 8a,b), the difference between the uncationized (Figure 8c) and assignificant that of washing as that waste of washing water(See waste Figure water(See 8a,b), th Figuree difference8a,b), thebetween difference the uncationized between the (Figure uncationized 8c) and cationized (Figure 8d) results is still easily detected for all the colors. The results demonstrate that cationized(Figure8c) and(Figure cationized 8d) results (Figure is still8d) easily results detected is still easilyfor all detectedthe colors. for The all results the colors. demonstrate The results that higher dye fixation is achieved and much less dye wastewater is produced with the one-bath higherdemonstrate dye fixation that higher is achieved dye fixation and is much achieved less and dye much wastewater less dye wastewateris produced is with produced the one-bath with the pretreatment method, which greatly reduces the adverse effect of ink-jet reactive printing on pretreatmentone-bath pretreatment method, method,which greatl whichy reduces greatly reducesthe adverse the adverse effect effectof ink-jet of ink-jet reactive reactive printing printing on environment. Accordingly, it is considered that the one-bath pretreatment is a much cleaner and environment.on environment. Accordingly, Accordingly, it is it considered is considered that that the the one-bath one-bath pretreatment pretreatment is is a a much much cleaner cleaner and water-saving process. water-saving process.

Figure 7. Cont. Figure 7. Cont. Figure 7. Cont.

Molecules 2017, 22, 1959 8 of 13 Molecules 2017, 22, 1959 8 of 13 Molecules 2017, 22, 1959 8 of 13

Figure 7. (a) K/S values on uncationized and cationized cotton with magenta, yellow, cyan, and black Figure 7. (a) K/S values on uncationized and cationized cotton with magenta, yellow, cyan, and black Figureinks; and 7. ( digitala) K/S values photos on of uncationized uncationized an (bd) andcationized cationized cotton (c )with cotton magenta, printed yellow, with magenta, cyan, and yellow, black inks; and digital photos of uncationized (b) and cationized (c) cotton printed with magenta, yellow, inks;cyan, and and digital black inks. photos of uncationized (b) and cationized (c) cotton printed with magenta, yellow, cyan, and black inks. cyan, and black inks.

Figure 8. Washing wastewater of the ink-jet printed uncationized (a); and cationized cotton (b). Soaping Figureresidue 8. of Washing the ink-jet wastewater printed uncationized of the ink-jet printed(c); and uncationizedcationized cotton (a); and (d) cationized(uncationizedand cotton (b cationized). Soaping Figure 8. Washing wastewater of the ink-jet printed uncationized (a); and cationized cotton (b). Soaping residuecotton were of the washed ink-jet printedand soaped uncationized under the (c );same and cationizedconditions. cotton The volume (d) (uncationizedand of water was 200cationized mL for residue of the ink-jet printed uncationized (c); and cationized cotton (d) (uncationizedand cationized cottonwashing were and washed 120 mL andfor soaping). soaped under the same conditions. The volume of water was 200 mL for cotton were washed and soaped under the same conditions. The volume of water was 200 mL for washing and 120 mL for soaping). washing and 120 mL for soaping). Color yield, and colorimetric and colorfastness properties of the prints are listed in Table 2. K/S valuesColor of all yield, four and prints colorimetric on modified and cotton colorfastness were mu propertiesch higher. of L thevalues prints of tharee printslisted inon Table the cationic 2. K/S valuescottonColor ofwere all yield, fourlower prints and than colorimetric onthe modified corresponding and cotton colorfastness valueswere mu onch the properties higher. uncationized L values of the one, of prints th indicatinge prints are listed on that the in the cationic Table color2. cottonK/Slooksvalues darker.were oflower allThere four than were prints the alsocorresponding on changes modified in cottonvalues redness-greenness wereon the much uncationized higher. (a) and Lone, yellowness-blueness values indicating of the that prints the (b) on color thefor looksdifferentcationic darker. cottondyes. ThereOne were of were lowerthe main also than reaschanges theons corresponding for in the redn colormetricess-greenness values difference on the(a) uncationizedand is the yellowness-blueness different one, color indicating yield (b) on that forthe differentfabrics;the color however, dyes. looks One darker. it ofis thedifficult There main weretoreas accountons also for changesfor the the colormetric direct in redness-greenness effect difference of the cationicis the (a) different and quanternary yellowness-blueness color yieldammonium on the fabrics;(b)groups for differenthowever,on the color dyes.it is ofdifficult One the ofdyes to the account associating main reasonsfor the with direct for them. the effect colormetric This of maythe cationic suggest difference quanternary some is the difference different ammonium in color the groupsphysicalyield on on theenvironment the fabrics; color however,of of the the dyes dyes it is associating difficulton the modified to accountwith them. and for unmodified theThis direct mayeffect suggestfabrics. ofthe someFor cationic practical difference quanternary purposes, in the physicaltheammonium color environmentdifference groups oncould theof the colorbe accommodateddyes of theon dyesthe modified associating in the formulationand with unmodified them. of This the fabrics. mayink recipes. suggest For practical some difference purposes, in thethe color physicalTable difference 2 environmentalso shows could that ofbe theaccommodatedwash, dyes crock on the and modified in light the formulationfast andness unmodified properties of the ink fabrics.of therecipes. inks For practicalon cationized purposes, and uncationizedthe colorTable difference 2 also fabrics. shows could The that bewash wash, accommodated fast crockness of and the in light inks the formulationfast on nessthe cationicproperties of the cotton ink of the recipes. was inks all onassessed cationized as good, and uncationizedreachingTable 42 or also fabrics.4–5 shows grade. The that Drywash wash, and fast wet crockness crock of and the lightfastness inks fastness on of the the cationic properties inks on cotton the of thecationized was inks all onassessed fabrics cationized aswas good, andalso reachingcomparableuncationized 4 or with fabrics.4–5 thatgrade. Theobtained Dry wash and from fastness wet uncationized crock of the fastness inks ones. on of the Inthe the cationic inks case on of cottonthe magenta cationized was alland assessed fabricsyellow wasinks, as good, also the comparablewetreaching fastness 4 orwith on 4–5 the that grade. cationic obtained Dry cotton and from was wet uncationized 1 crock and 0.5 fastness grade ones. of higher, In the the inks caserespectively. on of the magenta cationized Moreover, and yellow fabrics light inks, wasfastness alsothe wetofcomparable the fastness prints with onon the the that cationic cationic obtained cotton cotton from was uncationizedwas 1 muchand 0.5 sa grade ones.tisfactory. Inhigher, the For case respectively. cyan, of magenta magenta, Moreover, and and yellow yellow light inks, inks,fastness the wetthe oflightfastness the fastness prints on the on was cationicthe even cationic cotton0.5, cotton1 and was was1.5 1 and grades much 0.5 grade sahighertisfactory. higher, with Forthe respectively. cyan,one-bath magenta, Moreover,pretreatment and yellow light method. fastness inks, Thethe of lightabovethe prints fastness results on the wasdemonstrate cationic even 0.5, cotton 1that and was the 1.5 much designedgrades satisfactory. higher pretreatment with For cyan,the one-bathmethod magenta, haspretreatment and a yellowgood effect inks,method. theon lightThethe abovecolorfastnessfastness results was evenof demonstrate the 0.5, inks. 1 and that 1.5 gradesthe designed higher withpretreatment the one-bath method pretreatment has a good method. effect The on above the results demonstrate that the designed pretreatment method has a good effect on the colorfastness of colorfastness of the inks. the inks.

Molecules 2017, 22, 1959 9 of 13

MoleculesTable 2017 2., 22Colorfastness, 1959 and the L, a, b of the four kinds of inks printed on cotton fabrics treated in the9 of 13 absence and presence of GTA, respectively. Table 2. Colorfastness and the L, a, b of the four kinds of inks printed on cotton fabrics treated in the absence and presence of GTA, respectively. Wash Fastness Crock Fastness Light Color Cotton K/S L a b Staining Crock ChangeWash Fastness Dry Wet Fastness Fastness Light Color Cotton K/S L a b Cotton Wool Staining Fastness I 10.03 39.86 47.95 23.90Change 4–5 4–5 4–5 4–5Dry Wet 3–4 3–4 Magenta Cotton Wool II 22.94 35.91 48.60 19.57 4–5 4–5 4–5 4–5 4–5 5 I 10.03 39.86 47.95 23.90 4–5 4–5 4–5 4–5 3–4 3–4 Magenta III 22.94 10.07 35.91 84.00 −48.6011.28 19.57 87.16 4–5 5 4–5 4–5 4–5 4–5 4–5 4–5 4–5 4 5 5 Yellow − III 10.07 18.22 84.00 79.07 −11.2813.27 87.16 82.53 5 4–5 4–5 4 4–5 4–5 4–5 4–5 4–5 4 5 6 Yellow III 18.22 8.00 79.07 34.11 −13.27 13.37 82.53−31.46 4–5 4–5 4–5 4 4–5 4–5 4–5 4–5 4–5 4 6 3 Cyan III 8.00 19.40 34.11 24.72 13.37 12.37 −31.46−32.09 4–5 4–5 4–5 4–5 4–5 4–5 4–54–5 3–44 33–4 Cyan III 19.40 18.83 24.72 18.30 12.37 –0.39 −32.09−3.54 4–5 4–5 4–5 4–5 4–5 4–5 4–5 5 3–4 4 3–4 4 Black I 18.83 18.30 –0.39 −3.54− 4–5 4–5 4–5 5 4 4 Black II 26.01 15.96 0.11 3.45 4–5 4–5 4–5 4–5 3–4 4 II 26.01 15.96 0.11 −3.45 4–5 4–5 4–5 4–5 3–4 4 I: Cotton treated in the absence of GTA; II: Cotton treated in the presence of GTA. I: Cotton treated in the absence of GTA; II: Cotton treated in the presence of GTA.

2.10. Colorful Pictures 2.10. Colorful Pictures A flatflat colorfulcolorful picturepicture and and a a three three dimensional dimensional magic magic cube cube (Figure (Figure9) were 9) were ink-jet ink-jet printed printed on both on bothuncationized uncationized and cationizedand cationized fabrics fabrics to study to study the colorthe color and and boundary boundary properties. properties. For For each each color color of ofthe the pictures, pictures, it isit is produced produced from from several several colors, colors, a a result result of of color color match. match. ItIt cancan bebe clearly seen from Figure 99a,ba,b thatthat thethe red,red, orange,orange, green,green, blue,blue, andand blackblack colorscolors areare allall muchmuch deeperdeeper onon thethe modifiedmodified cotton. The The boundary boundary between between different different colors colors is is ve veryry clear. clear. For For the the picture of the three dimensional magic cube in Figure9c,d, Figure9c,d, the small squares with red, orange, green, andand blueblue colorscolors allall looklook deeperdeeper on the modified modified cotton, cotton, while while the the squares squares with with yellow yellow color color do do not not look look that that deeper deeper due due to to that that it itis isa mucha much lighter lighter color, color, and and all all white white square square parts parts ar aree neat. neat. The The whole whole picture picture on on the the cationic cotton bring us visual enjoyment. From From th thee above results, results, it can be conclu concludedded that the one-bath pretreated cotton fabrics shows very good applicability in ink-jet printing of colorful pictures. Color difference produced with this method can be corrected by making some adjustment in the ink formulation or ink-jetink-jet printing equipment.

FigureFigure 9. ColorfulColorful pictures pictures of of ink-jet ink-jet printing printing on uncationized ( a,,c) and cationized cotton ( b,d).

3. Experimental

3.1. Materials

Bleached, desized, and mercerized 100% cotton (150 g/m2), was purchased from Test Fabrics, Inc. (Shanghai, China). Magenta, yellow, cyan, and black reactive dye inks were supplied by Fancell International Co. (Shanghai, China). Glycidyltrimethylammonium chloride (GTA) was purchased from Saen Chemical Technology Co. (Shanghai, China). Sodium hydroxide (NaOH) was purchased

Molecules 2017, 22, 1959 10 of 13

3. Experimental

3.1. Materials Bleached, desized, and mercerized 100% cotton (150 g/m2), was purchased from Test Fabrics, Inc. (Shanghai, China). Magenta, yellow, cyan, and black reactive dye inks were supplied by Fancell International Co. (Shanghai, China). Glycidyltrimethylammonium chloride (GTA) was purchased from Saen Chemical Technology Co. (Shanghai, China). Sodium hydroxide (NaOH) was purchased from Tianli Chemical Reagent Co. (Tianjin, China). Urea was obtained from Damao Chemical Reagent Co. (Tianjin, China). Sodium carbonate anhydrous was purchased from Bodi Chemical Reagent (Tianjin, China). All the solvents were analytically pure. Sodium alginate was obtained from Runlong Marine Biopharmacy Co. (Yantai, China), which is a medium-viscosity, printinganddyeing-class.

3.2. Pretreatment of Cotton Fabrics One-bath pretreatment of cotton fabrics was carried out with a dip-pad procedure. The printing phase was prepared by first mixing a certain amount of sodium hydroxide, 1.25 g of sodium alginate and 2.5 g of urea, and added deionized water to weight of 40 g in total. The mixture was then heated to 50 ◦C under stirring for dissolving. After that, 10 g GTA solution, which was obtained by dissolving a certain amount of GTA in deionized water, was mixed uniformly with the pretreatment formulation before use. In the control pretreatment bath, no GTA was added. The cotton fabrics were dipped in the pretreatment bath, and then padded using a two-roll padder (MU 505T; Beijing Textile Equipment Institute, Beijing, China) with a 0.3 MPa roll pressure to give a wet pick-up of 80%. The fabrics were subsequently baked at a certain temperature for some time using a rapid baker. Baking is an important step in pretreatment for drying the cotton and promoting the reaction between cotton fibers and GTA. Then the treated fabrics were ready for ink-jet printing. In our experiment, alternative cationic agent-hydrolyzed GTA was also used in the one-bath pretreatment of cotton fibers for comparison for mechanism study. GTA was hydrolyzed in 12.5% of ◦ Na2CO3 solution at 50 C for 40 min. The pH of the solution was then adjusted to neutral and ready to use. The procedure for preparation of the pretreatment formulation containing hydrolyzed GTA was the same as that of GTA-containing paste; only hydrolyzed GTA solution was used, instead of the GTA solution.

3.3. Ink-Jet Printing A square 3 × 5 inch picture was printed with an ink-jet printer (L310; Epson, Suwa, Japan) at a resolution of 5760 × 1440 dpi for each single color. Color parameters (RGB) were (255, 0, 0) for magenta, (255, 255, 0) for yellow, (0, 0, 255) for cyan, and (0, 0, 0) for black. After being printed, the samples were air-baked and then steamed for 15 min.

3.4. Wash-Off Procedure The printed and steamed cotton fabrics were consecutively washed with cold water, warm water, and cold water. They were then soaped in a 0.1 wt % soap solution at 95 ◦C with a goods-to-liquor ratio of 1:30 for 10 min, and eventually washed thoroughly with cold water and warm water, and then air dried. For color stripping, a four-step process was employed using Höechst agents of (1) acetic acid and ethanol (1:1, v/v); (2) 1 wt % aqueous ammonia; (3) a mixture of N,N-Dimethylformamide (DMF) and water (1:1, v/v); and (4) DMF. In each step, the samples were boiled in the each agent for 4 min, and rinsed with cold water between the steps.

3.5. Measurement of Color Yield The color yield (K/S) of the ink-jet printed fabrics were measured using a UltraScan XE color Measuring and Matching Meter (HunterLab Co., Reston, VA, USA) at room temperature. The color Molecules 2017, 22, 1959 11 of 13 yield ranging from the wavelength of 400 nm to 700 nm with 10 nm interval was measured and calculated using Equation (1) [14]. All K/S values were determined at λmax and average values were obtained at ﬁve different positions for each cotton:

K/S = (1 − R)2/2R (1) where K is the light absorption coefficient of the fabric, S is the light scattering coefficient, and R is the light reflectance at the maximum wavelength of the fabric.

3.6. Determination of Nitrogen Content The samples were dried under vacuum at room temperature for 24 h before measurement. Nitrogen content of cationic cotton was determined by the Kjeldahl method with a KDY-9820 Kjeldahl nitrogen apparatus (Tongrun Electrical and Mechanical Technology Co., Ltd., Beijing, China). For each condition, nitrogen content of three samples were measured to obtain the average. In this study, the nitrogen content of the uncationized and cationized cotton obtained under the optimal conditions was 0.58 wt % and 0.77 wt %, respectively.

3.7. Scanning Electronic Microscopy The surface morphology of the pretreated fibers was investigated using a Quanta 200 (FEI instruments company, Hillsboro, OR, USA) scanning electron microscope (SEM). The cotton fiber samples were coated with gold sputtering at room temperature before measurement.

3.8. Thermogravimetric Analysis The thermal degradation property of the samples was performed on a Q500 thermoanalyzer from the TA instrument company (New Castle, DE, USA). A certain weight of sample was tested under N2 at a heating rate of 10 ◦C/min with the temperature ranging from 30 ◦C to 800 ◦C.

3.9. Tear Strength Testing The tear strength of the printed cotton fabrics was tested according to ASTM D 5734-1995 using a YG(B)033A tearing instrument (Wenzhou, China). Each sample was tested three times and the average value was used.

3.10. Colorfastness Properties The wash fastness of the reactive prints on cotton was tested according to AATCC Test Method 61-2001 with an S-1002 two-bath dyeing and testing apparatus (Roaches Co., West Yorkshire, UK). The crock fastness was tested according to AATCC Test Method 8-2001 using Y(B)571-II crockmeter (Darong Standard Textile Apparatus Co. Ltd., Wenzhou, China). The light fastness was tested according to AATCC Test Method 16-2001using a YG(B)611-V lightfastness tester (Darong Standard Textile Apparatus Co. Ltd., Wenzhou, China) [35].

4. Conclusions One-bath pretreatment of cotton fabrics with a GTA-containing pretreatment formulation is effective in improving the color yield of the reactive ink-jet prints. Sodium hydroxide, instead of sodium carbonate, in the pretreatment formulation can promote both GTA and reactive ink ﬁxation. Optimal pretreatment conditions for magenta ink was 3 wt % GTA, 0.4 wt % NaOH, baking temperature of 90 ◦C, and baking time of 15 min. With these conditions, K/S on the cationic cotton for magenta, cyan, yellow, and black reactive inks are 22.94, 18.22, 19.40 and 26.01, respectively. These results are increased by 128.7%, 142.5%, 80.9% and 38.1%, respectively, compared with the corresponding color yield on the uncationized cotton. All colorfastness of the dyes are satisfactory, and lightfastness of magenta, yellow, and cyan inks on the cationic cotton is even higher than that on the uncationized one. Colorful ink-jet Molecules 2017, 22, 1959 12 of 13 prints with this one-bath pretreatment method exhibit higher color yield and good boundary clarity. Therefore, using one-bath pretreatment for reactive ink-jet printing has considerable potential in terms of high dye utilization ratio and reduction in efﬂuent. Further work is underway to investigate how to increase the stability of GTA in the pretreatment formulation for reactive ink-jet printing.

Acknowledgments: This work was supported in part by the National Science Foundation of China (21376042 and 21536002), the program for Changjiang Scholars and Innovative Research Team in the University (IRT-13R06) and Specific Fund of Central University Fundamental Research of China (DUT15ZD224). Author Contributions: W.M. designed the study, analyzed the data and wrote the paper; K.S. and S.L. searched the literatures, performed the experiments, analyzed the data and wrote the paper; M.Z. performed the experiments and analyzed the data. S.Z. contributed to study design and data analysis. Conflicts of Interest: The authors declare no conflicts of interest.

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Sample Availability: Ink-jet printed samples of this paper are available from the authors.

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