polymers

Article Property and Adsorption Kinetics of Reactive for Cotton Textiles in Salt-Free Non-Aqueous Dyeing Systems

Jiping Wang 1,2,3, Yuanyuan Gao 1,2, Lei Zhu 1,2, Xiaomin Gu 1,2,3, Huashu Dou 4 and Liujun Pei 1,2,*

1 Engineering Research Center for Eco-Dyeing and of Textiles, Zhejiang Sci-Tech University, Hangzhou 310018, Zhejiang, China; [email protected] (J.W.); [email protected] (Y.G.); [email protected] (L.Z.); [email protected] (X.G.) 2 National Base for International Science & Technology Cooperation in Textiles and Consumer-Goods Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, Zhejiang, China 3 Key Laboratory of Advanced Textile Materials & Manufacturing Technology, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018, Zhejiang, China 4 Key Laboratory of Fluid Transmission Technology of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou 310018, Zhejiang, China; [email protected] * Correspondence: [email protected]; Tel./Fax: +86-571-8684-3783

 Received: 8 August 2018; Accepted: 13 September 2018; Published: 15 September 2018 

Abstract: In recent years, new concepts in textile dyeing technology have been investigated which aim to decrease the use of chemicals and the emission of water. In this work, dyeing of cotton textiles with reactive dyes has been investigated in a silicone non-aqueous dyeing system. Compared with conventional aqueous dyeing, almost 100% of reactive dyes can be adsorbed on cotton textiles without using any salts in non-aqueous dyeing systems, and the fixation of is also higher (80%~90% for non-aqueous dyeing vs. 40%~50% for traditional dyeing). The pseudo-second-order kinetic model can best describe the adsorption and equilibrium of reactive dyes in the non-aqueous dyeing systems as well as in the traditional water dyeing system. In the non-aqueous dyeing systems, the adsorption equilibrium of reactive dyes can be reached quickly. Particularly in the siloxane non-aqueous dyeing system, the adsorption equilibrium time of reactive dye is only 5–10 min at 25 ◦C, whereas more time is needed at 60 ◦C in the water dyeing system. The surface tension of non-aqueous media influences the adsorption rate of dye. The lower the surface tension, the faster the adsorption rate of reactive dye, and the higher the final uptake of dye. As a result, non-aqueous dyeing technology provides an innovative approach to increase dye uptake under a low dyeing temperature, in addition to making large water savings.

Keywords: non-aqueous medium dyeing; salt-free reactive dyeing; cotton textile; reactive dye; surface tension; adsorption

1. Introduction In recent years, tremendous efforts have been focused on saving water and energy in the textile industry due to environmental pressure [1–4]. Some new dyeing methods [5–8] have been developed to reduce the use of salts and to save water during the dyeing process; for example, supercritical fluid dyeing, solvent dyeing, reverse micelle dyeing, non-aqueous dyeing, ionic liquid dyeing etc. Unfortunately, natural fibers cannot be effectively dyed with conventional water-soluble dyes in normal supercritical fluid [4,5]. Solvent dyeing and reverse micelle dyeing are often carried out using hydrocarbon solvents which are not environmentally friendly, such as hexane, cyclohexane and

Polymers 2018, 10, 1030; doi:10.3390/polym10091030 www.mdpi.com/journal/polymers Polymers 2018, 10, 1030 2 of 16 Polymers 2017, 9, x FOR PEER REVIEW 2 of 16

44 n-heptane,friendly dyeing as continuous technology phase which media uses [ 9non,10].-polar Non-aqueous media to dyeingsubstitute is afor green water and [11 environmentally,12]. Moreover, 45 friendlyYang [9] dyeing and Fu technology [13] believe which that uses non- non-polaraqueous dyeing media tohas substitute been the for most water successful [11,12]. Moreover,attempted 46 Yangsubstitute [9] and for Fu traditional [13] believe water that non-aqueous-based dyeing dyeing in the has textile been the industry most successful. Non-aqueous attempted dyeing substitute media 47 forcannot traditional dissolve water-based water-soluble dyeing dye inbut the can textile transport industry. material Non-aqueous and transfer dyeing energy. media A major cannot advantage dissolve 48 water-solubleof non-aqueous dye dyeing but can technology transport is material that little and water transfer is needed energy. because A major dissolving advantage the of dye non-aqueous and other 49 dyeingchemical technology agents, and is that fiber little swelling water is require needed because only a smalldissolving amount the dye of aqueous and other solution chemical [1 agents,4–16]. 50 andFurthermore, fiber swelling all the require aqueous only solution a small can amount be completely of aqueous absorbed solution by the [14 cotton–16]. Furthermore,textile without all using the 51 aqueousany accelerating solution salts can during be completely the dyeing absorbed process. by As the for cotton the re textile-usability without of no usingn-aqueous any acceleratingmedia, after 52 saltsa short during period the of dyeing static separation process. As non for-aqueous the re-usability media can of non-aqueous be directly used media, for afterthe next a short dyei periodng. Non of- 53 staticaqueous separation media whichnon-aqueous is adsorbed media on can the be directlysurface usedof cotton for the textile next dyeing.can be washed Non-aqueous down media using 54 whichsurfactants is adsorbed and reused on the by surface flotation. of cotton textile can be washed down using surfactants and reused 55 by flotation.In our previous investigations [15,17–19], a non-aqueous dyeing system was favorably prepared 56 usingIn siloxane our previous non-aqueous investigations medium [15 as,17 the–19 dyeing], a non-aqueous medium. Siloxane dyeing systemnon-aqueous was favorably medium prepared is a clear, 57 usingodorless, siloxane colorless, non-aqueous and non medium-oily cyclic as the siloxane dyeing fluid, medium. which Siloxane is widely non-aqueous used in consumer medium andis a 58 clear,industrial odorless, applications. colorless, Research and non-oily has demonstrated cyclic siloxane that fluid, siloxane which non is-aqueous widely usedmedium in consumer is safe to both and 59 industrialhuman health applications. and the environment Research has [ demonstrated20–22]. In recent that years, siloxane siloxane non-aqueous non-aqueous medium medium is safe has to been both 60 humanapplied healthwidely and in dry the cleaning environment as a new [20– 22medium]. In recent [23]. years,Now, w siloxanee have used non-aqueous this non- mediumaqueous hasmedium been 61 appliedto prepare widely a reactive in dry dye/siloxane cleaning as a emulsion new medium dyeing [23]. system Now, wefor have dyeing used cotton this non-aqueoustextiles. As shown medium in 62 toFigure prepare 1, with a reactive the aid dye/siloxane of a surfactant emulsion and co-surfactant, dyeing system the dye for solution dyeing cotton can be textiles. evenly emulsified As shown in 63 Figuresiloxane1, withnon-aqueous the aid ofmedium. a surfactant Since and reactiveco-surfactant, dye is totally the dyeincompatible solution can with be siloxane, evenly emulsified there is a 64 instrong siloxane affinity non-aqueous between the medium. fiber and Since the reactivedye, with dye the is result totally that incompatible nearly 100% with of siloxane,reactive dye there can is 65 adiffuse strong to affinity the surface between of the fiber cotton and textile the dye, under with mechanical the result force.that nearly Therefore, 100% theof reactive final uptake dye can of 66 diffusereactive to dye the surfaceis higher of than the cotton that of textile a conventional under mechanical water dyeing force. Therefore, base, without the final using uptake any ofinorganic reactive 67 dyesalts is in higher the non than-aqueous that of dyeing a conventional base. Furthermore, water dyeing the base,fixation without of dye using is also any higher inorganic than in salts the inwater the 68 non-aqueousbath. As a result, dyeing a lot base. of reactive Furthermore, dyes can the bond fixation with of cotton dye is textiles also higher in non than-aqueous in the waterdyeing bath. systems. As a 69 result,However, a lot information of reactive dyesabout can the bond adsorption with cotton mechanism textiles of in reactive non-aqueous dye solution dyeing in systems. the siloxane However, non- 70 informationaqueous dyeing about system the adsorption is limited; mechanismin particular, of comprehensive reactive dye solution information in the related siloxane to non-aqueous the effect of 71 dyeingthe medium system on is the limited; diffusion in particular, of reactive comprehensive dye and adsorption information models related have to thenot effectbeen ofsystematically the medium 72 onstudied. the diffusion of reactive dye and adsorption models have not been systematically studied.

Dye solution Diffusion Fixation

fiber

fiber fiber siloxane siloxane siloxane media media media

73 74 Figure 1. Schematic diagram of reactive dye in siloxane non-aqueousnon-aqueous dyeingdyeing system.system.

75 To study the the influence influence of of non non-aqueous-aqueous media media surface surface tension tension on the on theadsorption adsorption of reactive of reactive dye, 76 dye,vinyl vinylsulphone sulphone reactive reactive dye (blue dye 19) (blue and 19) a combinati and a combinationon of cyanuric of cyanuricchloride and chloride vinyl and sulphone vinyl 77 sulphonereactive dye reactive (red dye195) (redwere 195) selected. were selected. The influences The influences of dyeing of dyeingmedia mediaand surface and surface tension tension of non of- 78 non-aqueousaqueous media media on the on theadsorption adsorption kinetics kinetics of ofreactive reactive dye dye were were investigated investigated with with a a model model on the 79 adsorption kinetics of reactive dye. In addition, the influenceinfluence of surface tension on reactive dyeing 80 levellevel propertyproperty waswas systematicallysystematically discussed.discussed. 81

Polymers 2017, 9, x FOR PEER REVIEW 3 of 16

82 2. Materials and Methods

83 2.1. Materials Polymers 2018, 10, 1030 3 of 16 84 Cotton woven fabric (130.5 g/m2, yarn count: 42S × 42S, yarn density: 148 × 285) was dyed with 85 reactive dye which was obtained from Haitong Printing&Dyeing Co., Ltd, (Hangzhou, China). 2. Materials and Methods 86 Siloxane non-aqueous medium (purity>98%) was purchased from Wynca. Paraffin (Jiande, China), 87 C2.1.8H Materials18 (isooctane) and M-oil (white oil) withpurity above 99.7% were purchased from Hangzhou Mick 88 Chemical Co., Ltd (Hangzhou, China) The parameters of different dyeing media are shown in Table 2 89 1. Cotton woven fabric (130.5 g/m , yarn count: 42S × 42S, yarn density: 148 × 285) was dyed with reactive dye which was obtained from Haitong Printing&Dyeing Co., Ltd, (Hangzhou, China). 90 Siloxane non-aqueous mediumTable (purity>98%)1. The parameters was of purchased different dyeing from media. Wynca. Paraffin (Jiande, China), C8H18 (isooctane) and M-oil (white oil) withpurity above 99.7% were purchased from Hangzhou Mick Medium Surface Tension (dyn/cm) Boiling Point(°C) Viscosity(mm2/s) Chemical Co., Ltd (Hangzhou, China) The parameters of different dyeing media are shown in Table1. Siloxane 18.13 210 5.63 Table 1. The parameters of different dyeing media. Paraffin 19.45 330 16.34 Medium Surface Tension (dyn/cm) Boiling Point (◦C) Viscosity (mm2/s) SiloxaneC8H18 23.34 18.13 126 210 0.77 5.63 Paraffin 19.45 330 16.34 MC8-HOil18 31.2323.34 200 126 4.20 0.77 M-Oil 31.23 200 4.20 H2O 72.04 100 1.00 H2O 72.04 100 1.00

91 Reactive dyes (red 195 and blue 19) were purchased from Aladdin Reagent (Shanghai, (Shanghai, China). China). 92 The molecular structures of these dyes are shownshown inin FigureFigure2 .2. Non-ionicNon-ionic surfactantsurfactant (AEO-3,(AEO-3, fattyfatty 93 alcohol polyoxyethylene ether ether)) was obtai obtainedned from from Jiangsu Jiangsu Haian Haian Petrochemical Petrochemical Plant Plant (Haian, (Haian, China) China).. 94 n--octanoloctanol (A.R.) was purchased from AladdinAladdin ReagentReagent (Shanghai,(Shanghai, China).China). SodiumSodium carbonatecarbonate (Na(Na22COCO33,, 95 A.R.) and sodium chloride (NaCl, A.R.) were purchased from Cangzhou Haolong Chemical Products 96 Co., Ltd (Cangzhou, China) China)..

Cl

SO3Na N N O HN N SO CH CH OSO Na N H 2 2 2 3 OH NH SO2CH2CH2OSO3Na N=N

SO3Na SO3Na NH NaO3S SO3Na O 2

C. I. Reactive Red 195 C. I. Reactive Blue 19 97 Figure 2. Molecular structure of C. I. (Color Index) Reactive Red 195 and C. I. Reactive Blue 19. 98 Figure 2. Molecular structure of C. I. (Color Index) Reactive Red 195 and C. I. Reactive Blue 19. 2.2. Determination of Surface Tension 99 2.2. Determination of Surface Tension A Krüss GmbH DAS20 using the captive drop method was used to measure the surface tension 100 of differentA Krüss non-aqueous GmbH DAS20 media. using In the the captive testing conditions,drop method the was needle used diameter to measure was the 1.820 surface mm and tension flow 101 ofrate different was 60.2 non mm/min.-aqueous media. In the testing conditions, the needle diameter was 1.820 mm and 102 flow rate was 60.2 mm/min. 2.3. Cotton Textile Dyeing 103 2.3. Cotton Textile Dyeing 2.3.1. Non-Aqueous System 104 2.3.1. Non-Aqueous System 5.0 g cotton fabric was dyed with reactive dye (2%, o.w.f.) in 100 mL (mililitro) non-aqueous 105 medium5.0 g (liquorcotton ratiofabric = was 20:1) dyed using with a dyeing reactive machine dye (2%, (Sanjing o.w.f.) Technologyin 100 mL (mililitro) Company, non Hangzhou,-aqueous 106 mediumChina). First, (liquor 2% ratio (o.w.f.) = 20:1) of reactive using dyewas a dyeing added machine to 130% (Sanjing (o.w.f) Technology of water. After Company, stirring Hangzhou, for 5 min, 107 China)7.5% (o.w.f). First, of 2% sodium (o.w.f. carbonate) of reactive was dye addedwas added to reactive to 130% dye (o solution.w.f) of water. and stirred After forstirring another for 5 5 min, min. 108 7.5%Finally, (o. thew.f) dye of sodium solution carbonate obtainedin was the added previous to stepreactive was dye added solution into 100 and mL stirred of non-aqueous for another medium. 5 min. ◦ After adding the cotton fabric, dyeing began at a lower temperature (25 C) for 15 min, and then the temperature was increased to 70 ◦C for 30 min, with a heating rate of 2◦C/min. After dyeing, the dyed fabric was washed in a soap solution containing 2.0 g/L sodium carbonate and 2.0 g/L Polymers 2018, 10, 1030 4 of 16 standard detergent for 10 min, rinsed again with warm (50 ◦C) water and cold water, and finally dried at ambient temperature.

2.3.2. Aqueous Dyeing For comparison with the conventional water-base dyeing, the same cotton fabric (5 g) was dyed with reactive dye (2%, o.w.f) in water base at a liquor ratio of 20:1. The amounts of NaCl and Na2CO3 were 40 and 15 g/L, respectively. First, reactive dye and the cotton fabric were added into 100 mL of water at room temperature, and then the temperature was increased to 60 ◦C. After 10 min, half of the NaCl was added into the dye bath, and the rest of the NaCl was added in the next 10 min. ◦ ◦ After adsorption (30 min), the temperature was increased to 70 C at 2 C/min, then the Na2CO3 was added into the dye bath and left for 30 min. After fixation, the dyed fabric samples were soaped and rinsed.

2.4. Determination of Adsorption Rate The dyeing rate was monitored using the dye concentration. Small samples (1 mL) were taken at different times during the dyeing process. The concentration of dye was determined with a UV-vis spectrometer (Lambda 35, Perkin Elmer, Waltham, MA, USA). Prior to dyeing, standard solutions of the two dyes were made and the absorbance was measured from 380~680nm wavelengths; therefore, a plot of absorbance versus wavelength could be obtained. Maximum adsorption wavelength of the dye was determined with a UV-vis spectrometer (C.I. Reactive Red 195 in 550 nm; C.I. Reactive Blue 19 in 596 nm). Calibration curves of absorbance vs. dye concentration (Beer-Lambert law) were performed separately for the two dyes. The calibration plot revealed a linear relationship in the range of dye concentration from 0 to 0.19 g/L. Therefore, it was necessary to dilute the sample with a higher concentration. For the non-aqueous dyeing system, the dye solution (1 mL) was diluted with 9 mL of ethyl alcohol. For the traditional system, distilled water was used for dilution. Samples of dye solutions were taken at different times (0, 1, 3, 5, 10, 15, 20, 25, 30, 40, 50, 60 and 70 min) for UV measurements.

2.5. Dyeing Evaluations

2.5.1. Color Depth of Dyed Fabric The color strength of dyed fabric samples were measured with a Datacolor SF600X spectrophotometer (Datacolor, Lawrenceville, NJ, USA), then the K/S values were evaluated at λmax using the Kubelka-Munk equation: K (1 − R)2 = (1) S 2R where R is the reflectance of the dyed fabric sample at the λmax absorption and K and S are the absorption and scattering coefficients, respectively.

2.5.2. Dye Uptake of Reactive Dye The final uptake of reactive dye was calculated by the following equation. The amount of dye in the dyeing residues solution was determined using a UV-vis spectrometer.

Sorption% = (1 − C1V1/C0V0) × 100% (2) where sorption refers to the dye uptake, C0 and C1 refer to the concentration (g/L) of initial dye solution and dyeing residues, respectively; and V0 and V1 refer to the volume (mL) of initial dye solution and dyeing residues, respectively. Polymers 2017, 9, x FOR PEER REVIEW 5 of 16

147 where sorption refers to the dye uptake, C0 and C1 refer to the concentration (g/L) of initial dye 148 solution and dyeing residues, respectively; and V0 and V1 refer to the volume (mL) of initial dye 149 solution and dyeing residues, respectively.

150 2.Polymers5.3. Fixation2018, 10, Rate 1030 of Reactive Dye 5 of 16 151 Consideration of the percentage of fiber-reactive dyes is necessary to evaluate the dye fixation 152 during2.5.3. Fixation the non Rate-aqueous of Reactive dyeing Dyesystems and in the traditional water dyeing system. The fixation ratio 153 of reactive dye was calculated based on the following equation: Consideration of the percentage of fiber-reactive dyes is necessary to evaluate the dye fixation during the non-aqueous dyeing systems and in the traditional water dyeing system. The fixation ratio C1122 VCV of reactive dye was calculated basedT on(1)100% the following equation: (3) CV 00 C V + C V = ( − 1 1 2 2 ) × 154 where T refers to the fixation rate ofT reactive1 dye, and C0, C1, 100%C2 refer to the concentration (g/L) of the (3) C0V0 155 initial dye solution, dyeing residues and soaping solution, respectively. V0, V1, and V2 refer to the 156 wherevolumeT (mL)refers of to the the initial fixation dye rate solution, of reactive dyeing dye, residues and C0, andC1, Csoaping2 refer tosolution, the concentration respectively. (g/L) of the initial dye solution, dyeing residues and soaping solution, respectively. V0, V1, and V2 refer to the 157 2.5.volume4. Leve (mL)l Dyeing of the Property initial dye solution, dyeing residues and soaping solution, respectively.

158 2.5.4.Twelve Level Dyeing points on Property the fabric surface were randomly selected, and the K/S values of these points 159 were tested with a Datacolor SF600X spectrophotometer (Datacolor, Lawrenceville, NJ, USA). The Twelve points on the fabric surface were randomly selected, and the K/S values of these points 160 level dyeing property was calculated using the following equation, where the lower the value of Sγ(λ), 161 werethe better tested the with level aDatacolor dyeing property: SF600X spectrophotometer (Datacolor, Lawrenceville, NJ, USA). The level dyeing property was calculated using the following equation, where the lower the value of Sγ(λ),

the better the level dyeing property: 2 n KS/  i v 1  2 (4) ui1nKS/  i  u (K/S)iλ S ()  u ∑ − 1 t = (Kn/S)i1λ S (λ) = i 1 (4) γ n − 1

162 3. Results and Discussion

163 3.1. Comparisons between thethe DyeingDyeing PropertyProperty ofof ReactiveReactive Dye Dye in in Different Different Non-Aqueous Non-Aqueous Dyeing Dyeing Systems Systems and 164 anda Traditional a Traditional Water Water Dyeing Dyeing System System 165 Four different nonnon-aqueous-aqueous dyeing media were selected to study their influenceinfluence on reactive 166 dyeing for cotton fabric, and the color depth depthss of the dyed fabric are plotted in Figure 33.. DyeingDyeing inin aa 167 water base was also included for comparison. I Inn the traditional water dyeing system, the color depth 168 of cotton fabricsfabrics ( K/SS value)value) dye dyedd with with reactive reactive blue blue 19 19 and and red red 195 195 w wereere 12 12 and and 13, respectively respectively;; 169 while in non-aqueousnon-aqueous media,media, thethe color color depth depth of of dyed dyed cotton cotton fabric fabric samples samples dyed dyed with with reactive reactive blue blue 19 170 19and and reactive reactive red red 19 were19 were above above 15 and15 and 21, 21, respectively. respectively.

(a):blue 19 (b):red 195 25 25

20 20

15 15

10 10 K/S value K/S

K/S value K/S 5 5

0 0 Siloxane C H Paraffin M-Oil H O C H Paraffin H O 8 18 2 Siloxane 8 18 M-Oil 2 171 Media Media

172 Figure 3. ColorColor depth depth of of fabric fabric in in different different non non-aqueous-aqueous emulsion emulsion systems systems and and traditional traditional water water base: base: 173 (a) C. I. Reactive Blue 19; (b) C. I. Reactive RedRed 195.195.

Comparing the different dyes, the color depth of the cotton fabric dyed with reactive 195 was deeper than that of the fabric dyed with reactive blue 19. This was mainly because the reactive red 195 molecular structure contains two different active groups; namely, the homogeneous chlorotriazine and vinyl sulfone active groups, with the result that the reaction between fiber and dye was higher than Polymers 2017, 9, x FOR PEER REVIEW 6 of 16

174 Comparing the different dyes, the color depth of the cotton fabric dyed with reactive 195 was

175 deeperPolymers 2018than, 10 that, 1030 of the fabric dyed with reactive blue 19. This was mainly because the reactive6 ofred 16 176 195 molecular structure contains two different active groups; namely, the homogeneous 177 chlorotriazine and vinyl sulfone active groups, with the result that the reaction between fiber and dye 178 wasthat higher of a single than functional that of a single group functional (blue 19) group [24–26 (blue]. Furthermore, 19) [24–26]. the Furthermore, molar extinction the molar coefficients extinction of 179 coefficientsdye might be of adye reasonable might be guide a reasonable to the color guide depth to the of dyedcolor fabricdepth [ 27of]. dyed Reactive fabric red [27] 195. Reactive may absorb red 180 195more may light absorb andreflect more light less light. and reflect Therefore, less light. the color Therefore, depth ofthe fabric color after depth dyeing of fabric with after reactive dyeing red with 195 181 reactivewas significantly red 195 was deeper significantly than that deeper of cotton than fabric that dyed of cotton with fabric reactive dyed blue with 19. reactive blue 19. 182 As shown shown in in Figure Figure4, the 4, uptake the uptake of reactive of reactive dye in dyenon-aqueous in non-aqueous media was medi abovea was 95%, above indicating 95%, ◦ 183 indicatingthat almost that all almost of the dye all of could the dye diffuse could to diffuse the cotton to the fabric cotton without fabric addingwithout any adding electrolyte any electrolyte at 25 C 184 atduring 25 °C dyeing.during dyeing. However, However, in the conventionalin the conventional aqueous aqueous dyeing dyeing system, system, the final the uptakefinal uptake of these of ◦ 185 thesetwo reactive two reactive dyes wasdyes only was 70%~75% only 70%~7 when5% when using using an accelerating an accelerating agent agent (sodium (sodium chloride) chloride) at 60 atC. 186 6Considering0 °C. Considering removal removal of these of saltsthese issalts a major is a major challenge challenge for the for treatment the treatment of dyeing of dyeing wastewater wastewater [25]; 187 [however,25]; however, there isthere a little is a wastewater little wastewater after dyeing after indyeing the non-aqueous in the non- mediaaqueous dyeing media systems. dyeing Therefore, systems. 188 Therefore,non-aqueous non dyeing-aqueous systems dyeing are systems green and are recyclablegreen and dyeingrecyclable systems. dyeing systems.

(a): blue 19 (b): red 195 120 100 120 100 Uptake Fixation Uptake Fixation 100 100 80 80

80 80 60 60 60 60 40 40 40 40

Fixation (%) Fixation (%) 20 20

Dye uptake (%) 20 Dye uptake (%) 20

0 0 0 0 Siloxane C H Paraffin M-Oil H O Siloxane C H Paraffin M-Oil H O 8 18 2 8 18 2 189 Media Media

190 Figure 4. 4. UptakeUptake and and fixation fixation of reactive of reactive dye in dye different in different non-aqueous non-aqueous emulsion emulsion systems and systems traditional and 191 traditionalwater base: water (a) C. base: I. Reactive (a) C. BlueI. Reactive 19; (b )Blue C. I. 19; Reactive (b) C. RedI. Reactive 195. Red 195.

192 The effect effect of of the the non non-aqueous-aqueous media media on on the the fixation fixation of ofthe the reactive reactive dye dye was was also also investigated, investigated, as 193 shownas shown in inFigure Figure 4.The4. The fixation fixation rates rates for for the the non non-aqueous-aqueous dyeing dyeing systems systems were were higher higher than for thethe 194 traditional process (80%~90% for for siloxane non non-aqueous-aqueous dyeing sys systemtem vs. 40%~50% 40%~50% for for traditional). traditional). 195 Fixation is also affected by the sorption of dye, dyeing time, etc. [1010,28,28].]. The apparent sorption of 196 reactive dye was over 95% in non-aqueousnon-aqueous dyeing system systems,s, indicat indicatinging that that a a l lotot of the dyesdyes could ◦ 197 react with cotton fabri fabrics.cs. Furthermore, the dyeing temperature is lower (25 °CC in non non-aqueous-aqueous media ◦ 198 vs. 60 60 °CC in in water base), and and the hydrolysis rate of reactive dye in non non-aqueous-aqueous dyeing system systemss is 199 slower than that in the traditional water base [15,16 [15,16]].. As a a result, result, a a lot lot of of re reactiveactive dyes can bond with 200 cotton textiles, and a higher fixation fixation rate rate can can be be obtained obtained in in the the non non-aqueous-aqueous dyeing dyeing systems systems [29,30 [29,30]].. 201 As can be seen, this dyeing technology can solve some some of of major major problems problems of of a a traditional traditional water water bath, bath, 202 such as difficultdifficult wastewaterwastewater treatment treatment due due to to the the high high residue residue amounts amounts of dyeof dye and and electrolytes, electrolytes, low low dye 203 dyeefficiency, efficiency, etc. etc. 3.2. Dye Adsorption in Different Non-Aqueous Dyeing Systems 204 3.2. Dye Adsorption in Different Non-Aqueous Dyeing Systems The degree of dye adsorption (qt) can be calculated using the following equation: 205 The degree of dye adsorption (qt) can be calculated using the following equation:

1000 × (C0 − Ct) qt = V (5) 1000W (CC0 t ) qV (5) t W where qt (mg/g) refers to the mass of dye adsorbed on cotton fabric at given times during the dyeing 206 wprocess,here qt C(mg/g)0 refers refers to the to initialthe mass dye of concentration dye adsorbed (g/L) on cotton in the fabric dye bath,at givenCt referstimes toduring the residue the dyeing dye 207 process,concentration C0 refers (g/L) to atthe given initial times, dye Vconcentrationis the volume (g/L) of dye in solutionthe dye bath, (mL), C andt refersW is to the the mass residue of cotton dye fabric (g). ◦ As shown in Figure5, the fastest equilibrium was observed at 25 C in the siloxane non-aqueous dyeing system. In other non-aqueous dyeing systems, adsorption equilibrium was established within Polymers 2017, 9, x FOR PEER REVIEW 7 of 16

208 concentration (g/L) at given times, V is the volume of dye solution (mL), and W is the mass of cotton 209 fabric (g). Polymers 2018, 10, 1030 7 of 16 210 As shown in Figure 5, the fastest equilibrium was observed at 25 °C in the siloxane non-aqueous 211 dyeing system. In other non-aqueous dyeing systems, adsorption equilibrium was established within 212 20–3020–30 min. This is mainlymainly because the surfacesurface tensiontension ofof non-aqueousnon-aqueous mediamedia isis lowlow (18.13(18.13 mN/m),mN/m), 213 whichwhich makes them highly hydrophobic,hydrophobic, and reactive dye solution is easily adsorbed on the cotton 214 fabric surfacesurface underunder mechanicalmechanical force [[31,3231,32].]. The Therefore,refore, salt-freesalt-free adsorption could be realized by 215 non-aqueousnon-aqueous media dyeing.

(a):red 195 (b):blue 19

20 20

15 15

10 10

(mg/g) (mg/g)

t t

q 5 Siloxane Paraffin q 5 Siloxane Paraffin C H M-Oil 8 18 C H M-Oil H O 8 18 0 2 0 H O 2 -10 0 10 20 30 40 50 60 70 80 -10 0 10 20 30 40 50 60 70 80 time (min) 216 time (min)

217 Figure 5.5. Adsorption of reactive dye in differentdifferent non-aqueousnon-aqueous dyeing systemssystems and traditionaltraditional water 218 base: (a) C. I. Reactive Red 195; (b)) C.C. I.I. ReactiveReactive BlueBlue 19.19.

In addition to the faster equilibrium, the highest uptake of dye (20 mg/g) was achieved after 219 In addition to the faster equilibrium, the highest uptake of dye (20 mg/g) was achieved after dyeing for 10 min in the siloxane non-aqueous dyeing system. For other non-aqueous dyeing media, 220 dyeing for 10 min in the siloxane non-aqueous dyeing system. For other non-aqueous dyeing media, the uptake of dye was also above 94%, which was significantly higher than that of the traditional 221 the uptake of dye was also above 94%, which was significantly higher than that of the traditional water base. The distribution of reactive dye solution between the dyeing bath and the cotton fabric 222 water base. The distribution of reactive dye solution between the dyeing bath and the cotton fabric depends on its relative solubility in the dyeing media and fabric. Since reactive dye solution is totally 223 depends on its relative solubility in the dyeing media and fabric. Since reactive dye solution is totally incompatible with non-aqueous media, there is a strong affinity between fiber and dye, with the 224 incompatible with non-aqueous media, there is a strong affinity between fiber and dye, with the result that nearly 100% of reactive dye can diffuse to the surface of cotton textile under mechanical 225 result that nearly 100% of reactive dye can diffuse to the surface of cotton textile under mechanical force [18,33]. 226 force [18,33]. 3.3. Dye Adsorption Kinetics 227 3.3. Dye Adsorption Kinetics 3.3.1. Fitting of Pseudo-First-Order Kinetic Model 228 3.3.1. Fitting of Pseudo-First-Order Kinetic Model In order to assess the adsorption performance of reactive dye in different non-aqueous 229 dyeingIn order systems, to assess the adsorption the adsorption dynamics performance of the of reactive reactive dye dye were in different evaluated non using-aqueous Lagergren dyeing 230 equationssystems, the [34 adsorption–37]. dynamics of the reactive dye were evaluated using Lagergren equations [34– 231 37]. ln(qe − qt) = ln qe − k1t (6) ln(qe  qt)  ln qe  k1t (6) where qe (mg/g) and qt (mg/g) denote the masses of dye adsorbed on cotton fabric at equilibrium sate and at given times t (min) respectively, and k refers to the rate constant of the pseudo-first-order 232 where qe (mg/g) and qt (mg/g) denote the masses 1of dye adsorbed on cotton fabric at equilibrium sate kinetic model. 233 and at given times t (min) respectively, andk1 refers to the rate constant of the pseudo-first-order 2 234 kineticAccording model. to Equation (6), R (correlation coefficient) was calculated using plots of ln(qe − qt) versus adsorption time (t). 235 According to Equation (6), R2 (correlation coefficient) was calculated using plots of ln(qe − qt) 236 versusThe adsorption fitted line time plots (t). of equations in non-aqueous dyeing systems and conventional water are 2 237 shownThe in fitted Figure line6. Table plots2 shows of equations the values in non of R-aqueousfor cotton dyeing fabric systems dyed with and red conventional 195 and blue water 19. Both are 238 non-aqueousshown in Figure dyeing 6. Table systems 2 shows and the the aqueous values systemof R2 for showed cotton afabric low correlationdyed with coefficient,red 195 and indicating blue 19. 239 thatBoth the non pseudo-first-order-aqueous dyeing kinetic systems model and did the not aqueous fit well system for the showed adsorption a low or reactive correlation dye incoefficient, different 240 non-aqueousindicating that dyeing the pseudo systems.-first-order kinetic model did not fit well for the adsorption or reactive dye 241 in different non-aqueous dyeing systems.

Polymers 2018, 10, 1030 8 of 16 Polymers 2017, 9, x FOR PEER REVIEW 8 of 16

(a):red 195 (b):blue19 4 4

2 2

0 0 ) )

t -2 t

-2 -q -q

e -4 e q q

( ( -4 Siloxane Paraffin Siloxane Paraffin ln -6 ln C H M-Oil C H M-Oil 8 18 -6 8 18 H O -8 2 H O -8 2 -10 -10 0 10 20 30 40 50 60 70 80 -10 0 10 20 30 40 50 60 70 80 242 time (min) time (min)

243 Figure 6. KineticsKinetics of of pseudo pseudo-first-order-first-order model for adsorption of reactive dyes: ( a) red 195; ( b) blue 19.

Table 2. R2 of pseudo-first-order model for cotton fabric in non-aqueous dyeing media and 244 Table 2. R2 of pseudo-first-order model for cotton fabric in non-aqueous dyeing media and water water system. 245 system. Media Dye Media Dye Siloxane Paraffin C8H18 M-Oil H2O Red-195 0.757Siloxane 0.819Paraffin C 0.8258H18 M-Oil 0.916 H2O 0.696 Blue-19 0.961 0.830 0.929 0.942 0.655 Red-195 0.757 0.819 0.825 0.916 0.696

3.3.2. Fitting of Pseudo-Second-OrderBlue-19 0.961 Kinetic Model0.830 0.929 0.942 0.655 The pseudo-second-order kinetic model is expressed as the following equation [38–41]: 246 3.3.2. Fitting of Pseudo-Second-Order Kinetic Model t 1 1 = + 2 t (7) 247 The pseudo-second-order kinetic modelqt is kexpre2qe ssedqe as the following equation [38–41]: t 11 where k2 (g/mg·min) denotes the adsorption rate constant of reactive dye, and qe and qt denote 2 t (7) the masses of dye which react with cottonqkqqtee fabric2 samples at equilibrium state and at given times t, respectively. 248 where k2 (g/mg·min) denotes the2 adsorption rate constant of reactive dye, and qe and qt denote the As shown in Equation (7), R was calculated using plots of t/qt versus adsorption time (t).We can 249 masses of dye which react with cotton fabric samples at equilibrium state and at given times t, use the slopes and intercepts of these plots to calculate the adsorption rate of reactive dye (k2) and the 250 respectively. adsorption equilibrium (qe), as shown in Equation (8): 251 As shown in Equation (7), R2 was calculated using plots of t/qt versus adsorption time (t).We can

252 use the slopes and intercepts of these plots toq ecalculate= 1/ tan theα adsorption rate of reactive dye (k2) and the (8) 253 adsorption equilibrium (qe), as shown in Equationk = (81): 2 bqe2 q 1/ tan where tan α and b denote the slope and intercepte of the linear equation, respectively. (8) The dyeing rate can also be expressed by the half-dyeing time (t0.5) which is the time required for k 2  1 half of the dye to reach equilibrium adsorption amount.bqe2 The t0.5 was calculated using Equation (9):

254 where tan α and b denote the slope and intercept of the1 linear equation, respectively. t0.5 = (9) 255 The dyeing rate can also be expressed by the khalf· qe-dyeing time (t0.5) which is the time required 256 for half of the dye to reach equilibrium adsorption amount. The t0.5 was calculated using Equation (9): Figure7 shows the fitting curves of the pseudo-second-order model and Table3 lists the results of rate constant studies for different non-aqueous dyeing1 systems and the conventional water dyeing t 0.5  (9) system with the pseudo-second-order model. Bothkq non-aqueouse dyeing systems and the aqueous system showed a high correlation coefficient value (>0.991). Furthermore, the equilibrium adsorption 257 Figure 7 shows the fitting curves of the pseudo-second-order model and Table 3 lists the results capacities, qe,cal, fit well with the experimental adsorption capacities, qe,exp, in the non-aqueous dyeing 258 ofsystems rate constant and the studies traditional for different aqueous non system.-aqueous These dyeing results systems suggest thatand the conventional adsorption kinetics water ofdyei theseng 259 systemtwo reactive with dyesthe pseudo on a cotton-second fabric-order surface model. can Both be described non-aqueous by the dyeing pseudo-second-order systems and the adsorption aqueous 260 systemmechanism showed in non-aqueous a high correlation dyeing coefficient systems andvalue a traditional(>0.991). Furthermore, aqueous system. the equilibrium adsorption 261 capacities, qe,cal, fit well with the experimental adsorption capacities, qe,exp, in the non-aqueous dyeing 262 systems and the traditional aqueous system. These results suggest that the adsorption kinetics of

Polymers 2017, 9, x FOR PEER REVIEW 9 of 16

263 Polymersthese two2018 ,reactive10, 1030 dyes on a cotton fabric surface can be described by the pseudo-second-9order of 16 264 adsorption mechanism in non-aqueous dyeing systems and a traditional aqueous system.

(a):red 195 (b):blue 19 6 9 8 5 Siloxane Paraffin Siloxane Paraffin 7 C H M-Oil C H M-Oil 8 18 8 18 4 6 H O H O 2 2 5

3 t

t

4 t/q t/q 2 3 2 1 1 0 0 0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 265 time (min) time (min)

266 Figure 7. Kinetics ofof pseudo-second-orderpseudo-second-order model model for for adsorption adsorption of of reactive reactive dyes: dyes: (a) ( reda) red 195; 195; (b) ( blueb) blue 19. 267 19. The results in Table3 also show k2, t0.5, as a main factor in the adsorption rate. For the adsorption 268 rate, theThe rate results constant in Table in non-aqueous 3 also show dyeingk2, t0.5, as systems a main was factor significantly in the adsorption faster than rate. that For of the the adsorption traditional 269 waterrate, the bath. rate Especially constant in in the non siloxane-aqueous non-aqueous dyeing systems dyeing was system, significantly the rate faster constants than of that these of twothe 270 reactivetraditional dyes water were bath. 5~6 Especially times those in ofthe the siloxane conventional non-aqueous aqueous dyeing bath. system, In addition, the rate the constant half-dyeings of 271 time,these ttwo0.5, wasreactive significantly dyes were lower 5~6 intimes non-aqueous those of the dyeing conventional systems aqueous than in the bath. aqueous In addition, dyeing the system. half- 272 Thesedyeing results time, t indicated0.5, was significantly that the adsorption lower in ofnon reactive-aqueous dye dyeing in non-aqueous systems than dyeing in the systems aqueous was dyeing faster 273 thansystem. in theThese conventional results indicated water system. that the adsorption of reactive dye in non-aqueous dyeing systems 274 was faster than in the conventional water system. Table 3. Kinetic parameters of pseudo-second-order for adsorption of reactive red 195 and blue 19 in 275 non-aqueousTable 3. Kinetic dyeing parameters systems of and pseudo traditional-second water-order bath. for adsorption of reactive red 195 and blue 19 in 276 non-aqueous dyeing systems and traditional water bath. Medium Dye Parameter Siloxane Paraffin C8H18 M-Oil H2O −2 Medium k2×10 Parameter Siloxane2.88 Paraffin 1.08 C 1.168H18 M- 1.52Oil H2 0.46O Dye (g/mg·min)−2(min−1) qe,exp (mg/g) 19.97 18.81 19.08 18.97 12.86 Red-195 −2 qe,calk(mg/g)2×10 20.59 20.47 20.37 10.11 14.61 t0.5 (min) 1.572.88 4.941.08 1.16 4.52 1.52 3.48 0.46 17.02 (g/mg·min)R2 −2(min−1) 0.999 0.998 0.998 0.999 0.997 k ×10−2 q2e,exp (mg/g) 19.973.18 18.81 1.62 19.08 1.82 18.97 1.74 12.86 0.63 Red-195 (g/mg·min)−2(min−1) qe,expqe,cal(mg/g) (mg/g) 19.9920.59 18.3520.47 20.37 18.83 10.11 18.50 14.61 8.72 Blue-19 qe,cal (mg/g) 20.64 19.33 19.80 19.54 11.30 t0.5t0.5(min) (min) 1.741.57 3.384.94 4.52 2.92 3.48 3.11 17.02 18.19 R2 0.999 0.999 0.999 0.999 0.991 R2 0.999 0.998 0.998 0.999 0.997

−2 Based on the amount of reactivek2×10 dye (2%, o.w.f) added to the dyeing system, if all of the dye −2 −1 3.18 1.62 1.82 1.74 0.63 was adsorbed on the cotton(g/mg·min) fabric,(min the adsorption) capacity was 20 mg/g. For reactive red 195,

the equilibrium adsorption, qqe,expe,exp (mg/g), at 10 min reached19.99 above18.35 18.81 mg/g18.83 in the18.50 non-aqueous 8.72 dyeing systems, indicatingBlue-19 that at least 94.05% of dye had been adsorbed on the cotton fabric. However, only qe,cal (mg/g) 20.64 19.33 19.80 19.54 11.30 13.75 mg/g (68.75%) of dye was adsorbed in the water bath after dyeing for 70 min. We also observed

a similar phenomenon in the adsorptiont0.5 (min) of reactive1.74 blue 19. These3.38 results2.92 suggest 3.11 that the18.19 equilibrium time of reactive dye in non-aqueous dyeing systems was shorter than in the water bath, and almost all R2 0.999 0.999 0.999 0.999 0.991 the dye could be adsorbed on the fabric in the non-aqueous dyeing systems. For different dyes, the rate constant value of red 195 was lower than that of blue 19 under the same dyeing conditions. The reason 277 may beBased that on the the molecular amount of structure reactive of dye red (2%, 195 iso.w.f) complex added and to itsthe molecular dyeing sy weightstem, if is all higher of thethan dye was that 278 ofadsorbed blue 19 [on42 – the44], cotton so the adsorption fabric, the rate adsorption of the dye capacity is influenced was 20 by mg/g. the molecular For reactive structure. red 195, the 279 equilibrium adsorption, qe,exp, at 10 min reached above 18.81 mg/g in the non-aqueous dyeing systems, 280 indicating that at least 94.05% of dye had been adsorbed on the cotton fabric. However, only 13.75

Polymers 2017, 9, x FOR PEER REVIEW 10 of 16 Polymers 2017, 9, x FOR PEER REVIEW 10 of 16 281 mg/g (68.75%) of dye was adsorbed in the water bath after dyeing for 70 min. We also observed a 281282 mg/gsimilar (68.75 phenomenon%) of dye wasin the adsorbed adsorption in theof reactive water bath blue after 19. These dyeing results for 70 suggest min. We that also the observedequilibrium a 282283 similartime of phenomenon reactive dye inin thenon adsorption-aqueous dyeing of reactive systems blue was 19. Theseshorter results than insuggest the water that bath,the equi andlibrium almost 283284 timeall the of reactivedye could dye be in adsorbed non-aqueous on the dyeing fabric systems in the non was-aqueous shorter thandyeing in thesystems. water For bath, different and almost dyes, 284285 allthe the rate dye constant could be value adsorbed of red on195 the was fabric lower in than the nonthat- aqueousof blue 19 dyeing under systems. the same For dyeing different conditions. dyes, 285286 theThe rate reason constant may value be that of redthe 195molecular was lower structure than tofhat red of blue195 is 19 complex under the and same its moleculardyeing conditions. weight is 286287 Thehigher reason than may that be of thatblue the 19 [42molecular–44], so structurethe adsorption of red rate 195 ofis thecomplex dye is and influenced its molecular by the weightmolecular is 287 higher than that of blue 19 [42–44], so the adsorption rate of the dye is influenced by the molecular 288 Polymersstructur2018e., 10, 1030 10 of 16 288 structure. 289 3.3.3. Effect of Non-Aqueous Media on the Dyeing Level Property 289 3.3.3.3.3.3. EffectEffect ofof Non-AqueousNon-Aqueous MediaMedia on on the the Dyeing Dyeing Level Level Property Property 290 Compared with a conventional aqueous bath, reactive dye has a faster adsorption rate in non- 290291 aqueousComparedCompared dyeing with with systems, a conventionala conventional which might aqueous aqueous influence bath, bath, reactive their reactive dyeing dye has dye property. a fasterhas a adsorptionfaster As shown adsorption rate in in Figures non-aqueous rate in 8 andnon -9, 291 aqueous dyeing systems, which might influence their dyeing property. As shown in Figures 8 and 9, 292 dyeingfor the systems, dyeing which property might of influence reactive their red dyeing195 and property. blue 19, As their shown values in Figures of Sγ8(λ) and were9 , for higher the dyeing in non- 292 for the dyeing property of reactive red 195 and blue 19, their values of Sγ(λ) were higher in non- 293 propertyaqueous of media reactive than red in 195 the and traditional blue 19, theirwater values bath, ofbutSγ were(λ) were less higherthan 1, in indicating non-aqueous that mediareactive than dye 293294 inaqueouscan the obtain traditional media a good than water level in bath, the dyeing traditional but wereproperty less water thanby mechanicalbath, 1, indicating but were fo thatrce less during reactive than 1, the dyeindicating dyeing can obtain processthat areactive good. level dye 294 can obtain a good level dyeing property by mechanical force during the dyeing process. dyeing property by mechanical force during the dyeing process. 1.2 1.2 red 195 1.0 red blue 195 19 1.0 blue 19 0.8 0.8

) 0.6

)

( 0.6

(

Sγ Sγ 0.4

Sγ Sγ 0.4 0.2 0.2 0.0 0.0 Siloxane C H Paraffin M-Oil H O C H8 18 H O2 Siloxane 8 18 Paraffin M-Oil 2 295 Media 295 Media 296 Figure 8. Level dyeing property of reactive dye in different non-aqueous dyeing systems and water Figure 8. Level dyeing property of reactive dye in different non-aqueous dyeing systems and 296297 Figurebath. 8. Level dyeing property of reactive dye in different non-aqueous dyeing systems and water 297 waterbath. bath. (a) (b) (c) (d) (a) (b) (c) (d)

298 298 299 FigureFigure 9. 9.Level Level dyeing dyeing property property of of reactive reactive dye dye in in siloxane siloxane non-aqueous non-aqueous dyeing dyeing system system and and water water 299300 bath:Figurebath (a: )(9.a red) Levelred 195 195 indyeing in water water property base; base; (b )(ofb blue) reactiveblue 19 19 in in waterdye water in base; siloxane base; (c )(c red )non red 195- aqueous195 in in siloxane siloxane dyeing non-aqueous non system-aqueous and dyeing waterdyeing 300301 system;bathsystem: (a ()d ; red)(d blue) 195blue 19 in 19 in water in siloxane siloxane base; non-aqueous ( nonb) blue-aqueous 19 in dyeing waterdyeing system. base; system. (c) red 195 in siloxane non-aqueous dyeing 301 system; (d) blue 19 in siloxane non-aqueous dyeing system. 3.4. Influence of Non-Aqueous Media Surface Tension on Dye Adsorption Kinetics 302 3.4. Influence of Non-Aqueous Media Surface Tension on Dye Adsorption Kinetics 302 3.4. Influence of Non-Aqueous Media Surface Tension on Dye Adsorption Kinetics 3.4.1. Non-Aqueous Media with Different Surface Tension 303 3.4.1. Non-Aqueous Media with Different Surface Tension 303 3.4.1.Siloxane Non-Aqueous was formulated Media with with Differ M-oilent or Surface paraffin Tension in a mass ration of 6:1, 4:1, 2:1, 1:1, 1:2, 1:4, and 304 1:6. DifferentSiloxane surface was formulated tensions of with the non-aqueous M-oil or paraffin media in are a mass shown ration in Figure of 6:1, 10 4:1,. 2:1, 1:1, 1:2, 1:4, and 304305 1:6. SiloxaneDifferent was surface formulated tensions with of the M non-oil -oraqueous paraffin media in a mass are shown ration inof Figure 6:1, 4:1, 1 02:1,. 1:1, 1:2, 1:4, and 305 1:6. Different surface tensions of the non-aqueous media are shown in Figure 10.

Polymers 2018, 10, 1030 11 of 16 Polymers 2017, 9, x FOR PEER REVIEW 11 of 16 Polymers 2017, 9, x FOR PEER REVIEW 11 of 16

34 34 32 32 Siloxane:Paraffin 30 Siloxane:ParaffinSiloxane:M-Oil 30 Siloxane:M-Oil 28 28 26 26 24 24 22 22 20 20 Surface tension (mN/m) Surface 18 Surface tension (mN/m) Surface 18 Siloxane 6:1 4:1 2:1 1:1 1:2 1:4 1:6 M-Oil/Paraffin Siloxane 6:1 4:1 2:1 1:1 1:2 1:4 1:6 M-Oil/Paraffin 306 Mass Ratio 306 Mass Ratio 307 Figure 10.Different surface tensions of non-aqueous media after compounding siloxane with M-oil or 307 Figure 1 10.0.DifferentDifferent surface surface tensions tensions of of non non-aqueous-aqueous media media after after compounding compounding siloxane siloxane with with M- M-oiloil or 308 paraffin. 308 paraffin.or paraffin. 309 As shown in Figure 10, the surface tension of non-aqueous media increased with the increase of 309 As shown in in Figure Figure 1 100, ,the the surface surface tension tension of of non non-aqueous-aqueous media media increased increased with with the the increase increase of 310 M-oil or paraffin. For example, when the mass ratio of siloxane to M-oil was 4:1, 1:1, and 1:4, the 310 Mof- M-oiloil or orparaffin. paraffin. For Forexample, example, when when the themass mass ratio ratio of siloxane of siloxane to M to-oil M-oil was was4:1, 4:1,1:1, 1:1,and and1:4, the 1:4, 311 surface tensions of the mixed media were 22.83, 25.73, and 28.16 mN/m respectively. To study the 311 surfthe surfaceace tensions tensions of the of themixed mixed media media were were 22.83, 22.83, 25.73, 25.73, and and 28.16 28.16 mN/m mN/m respectively. respectively. To To study study the 312 influence of surface tension on reactive dye adsorption in non-aqueous dyeing systems, several mass 312 influenceinfluence of surface tension on reactive dye adsorption in non non-aqueous-aqueous dyeing systems, several mass 313 ratios of siloxane to M-oil (4:1, 1:1, 1:4) were chosen in this investigation. 313 ratios of siloxane to M-oilM-oil (4:1, 1:1, 1:4) were chosen in this investigation.investigation. 314 3.4.2. Effect of Surface Tension onon ReactiveReactive DyeDye AdsorptionAdsorption 314 3.4.2. Effect of Surface Tension on Reactive Dye Adsorption 315 As shown in in Figure Figure 1111, ,in in different different surface surface tension tension non non-aqueous-aqueous dyeing dyeing systems, systems, the the uptake uptake of 315 As shown in Figure 11, in different surface tension non-aqueous dyeing systems, the uptake of 316 ofreactive reactive dyes dyes was was almost almost the thesame same and and was was close close to 100%, to 100%, indicating indicating that the that surface the surface tension tension of non of- 316 reactive dyes was almost the same and was close to 100%, indicating that the surface tension of non- 317 non-aqueousaqueous media media had hadlittle little influence influence on onthe the final final adsorption adsorption capacity capacity of of reactive reactive dye. dye. In In the the siloxane 317 aqueous media had little influence on the final adsorption capacity of reactive dye. In the siloxane 318 non-aqueousnon-aqueous dyeing system, the reactive dye completes the adsorption process in 5–105–10 min. If M-oilM-oil 318 non-aqueous dyeing system, the reactive dye completes the adsorption process in 5–10 min. If M-oil 319 was addedadded totosiloxane siloxane to to increase increase the the media medi surfacea surface tension, tension, the the adsorption adsorption rate rate of the of reactivethe reactive dye wasdye 319 was added to siloxane to increase the media surface tension, the adsorption rate of the reactive dye 320 decreasedwas decreased which which meant meant it needed it needed 10–15 min10–15 to min reach to the reach adsorption the adsorption equilibrium. equilibrium. Moreover, Moreover, reactive 320 was decreased which meant it needed 10–15 min to reach the adsorption equilibrium. Moreover, 321 dyereactive took dye more took time more (close time to (close 20 min) to to20 accomplishmin) to accomplish the adsorption the adsorption process inprocess M-oil in non-aqueous M-oil non- 321 reactive dye took more time (close to 20 min) to accomplish the adsorption process in M-oil non- 322 dyeingaqueous media, dyeing in media, which in the which surface the tension surface was tension 31.23 was mN/m. 31.23 mN/m. 322 aqueous dyeing media, in which the surface tension was 31.23 mN/m.

(a):red 195 (b):blue 19 (a):red 195 (b):blue 19 20 20 20 20

15 15 15 15 19.74mN/m 19.74mN/m 10 19.74mN/m 10 19.74mN/m

22.83mN/m 22.83mN/m 10 10

22.83mN/m 22.83mN/m25.73mN/m

(mg/g) 25.73mN/m (mg/g)

t t 25.73mN/m

(mg/g) 25.73mN/m (mg/g)

q 5 28.16mN/m q 5 28.16mN/m

t t

q 5 28.16mN/m31.23mN/m q 5 28.16mN/m31.23mN/m 31.23mN/m 31.23mN/m 0 0 0 0 -10 0 10 20 30 40 50 60 70 80 -10 0 10 20 30 40 50 60 70 80 -10 0 10 20time30 (min)40 50 60 70 80 -10 0 10 20time30 (min)40 50 60 70 80 323 time (min) time (min) 323 Figure 11. Adsorption rate of reactive dye in different surface tension non-aqueous dyeing media: 324 Figure 11. Adsorption rate of reactive dye in different surface tension non-aqueous dyeing media: (a) 324 (Figurea) red 195;11. Adsorption (b) blue 19. rate of reactive dye in different surface tension non-aqueous dyeing media: (a) 325 red 195; (b) blue 19. 325 red 195; (b) blue 19. Thus, the above results reveal that, for dyeing with reactive dye in non-aqueous media, the higher 326 Thus, the above results reveal that, for dyeing with reactive dye in non-aqueous media, the 326 surfaceThus, tension the above of non-aqueous results reveal media that, is a for possible dyeing reason with for reactive the longer dye adsorption in non-aqueous time. media,This is due the 327 higher surface tension of non-aqueous media is a possible reason for the longer adsorption time. This 327 higherto the insolubilitysurface tension of reactive of non-aqueous dye in non-aqueous media is a possible media, reason and the for strong the longer affinity adsorption of reactive time. dye This to 328 is due to the insolubility of reactive dye in non-aqueous media, and the strong affinity of reactive dye 328 iscotton due to fabric the insolubility [45,46]. Therefore, of reactive reactive dye in dye non can-aqueous quickly media, diffuse and to the the fabric strong surface affinity and of completereactive dye the 329 to cotton fabric [45,46]. Therefore, reactive dye can quickly diffuse to the fabric surface and complete 329 toadsorption cotton fabric process [45,46 [47]–. 49Th].erefore, When thereactive surface dye tension can quickly of non-aqueous diffuse to mediathe fabric is increased, surface and the complete repulsive 330 the adsorption process [47–49]. When the surface tension of non-aqueous media is increased, the 330 the adsorption process [47–49]. When the surface tension of non-aqueous media is increased, the 331 repulsive force between the reactive dye and non-aqueous media may decrease, which will influence 331 repulsive force between the reactive dye and non-aqueous media may decrease, which will influence 332 the adsorption rate of the dye. 332 the adsorption rate of the dye.

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force between the reactive dye and non-aqueous media may decrease, which will influence the Polymersadsorption 2017, rate9, x FOR of thePEER dye. REVIEW 12 of 16

333 3.4.3.3.4.3. F Fittingitting of of Pseudo Pseudo-First-Order-First-Order Kinetic Kinetic Model Model 334 ItIt can can be be seen seen from from the the results results obtained obtained in in the the above above section, section, the the salts salts can can be be eliminated eliminated and and 335 reactivereactive dye dye can can quickly quickly diffuse diffuse to to the the cotton cotton fabric fabric surface surface in in different different surface surface tension tension non non-aqueous-aqueous 336 dyeingdyeing processes. processes. In In order order to to thoroughly thoroughly understand understand the the effect effect of of non non-aqueous-aqueous surface surface tension tension on on the the 337 adsorptionadsorption kinetics, kinetics, the the fitted fitted line line plots plots of of equations equations for for diffe differentrent surface surface tension tension non non-aqueous-aqueous dyeing dyeing 338 mediamedia provide provide the the values values of of RR22.. As As shown shown in in Figure Figure 1 122 andand Table Table 44,, thethe correlationcorrelation coefficientscoefficients forfor 339 differentdifferent surface surface tension tension non non-aqueous-aqueous dyeing dyeing systems systems were were above above 0.744. 0.744. However, However, the the linearity linearity was was 340 notnot good, good, indicati indicatingng that that the the pseudo pseudo-first-order-first-order kinetic kinetic model model did did not not fit fit well well to to the the adsorption adsorption or or 341 reactivereactive dye dye in in different different non non-aqueous-aqueous dyeing systems.

(a):red 195 (b):blue19 4 4

2 2

0 0

) )

t -2 t -2

-q -q

e e 19.74mN/m

q 19.74mN/m q

( -4 ( -4 22.83mN/m 22.83mN/m

ln ln 25.73mN/m -6 25.73mN/m -6 28.16mN/m 28.16mN/m -8 31.23mN/m -8 31.23mN/m

-10 0 10 20 30 40 50 60 70 80 -10 0 10 20 30 40 50 60 70 80 time (min) 342 time (min) Figure 12. Kinetics of pseudo-first-order model for adsorption of reactive dyes in different surface 343 Figure 12. Kinetics of pseudo-first-order model for adsorption of reactive dyes in different surface tension non-aqueous dyeing systems: (a) red 195; (b) blue 19. 344 tension non-aqueous dyeing systems: (a) red 195; (b) blue 19. Table 4. R2 of pseudo-first-order model for cotton fabric in different surface tension non-aqueous 345 Tabledyeing 4. system. R2 of pseudo-first-order model for cotton fabric in different surface tension non-aqueous 346 dyeing system. Dye Siloxane:W-Oil R2 Dye Siloxane:W-Oil R2 1:0 0.852 4:1 0.847 Reactive 1:0 0.852 1:1 0.918 red 195 4:11:4 0.847 0.838 Reactive 0:1 0.916 1:11:0 0.918 0.962 red 195 4:1 0.782 Reactive 1:41:1 0.838 0.744 blue 19 1:4 0.868 0:10:1 0.91 0.9426

1:0 0.962 3.4.4. Fitting of Pseudo-Second-Order Kinetic Model 4:1 0.782 From the data in Table5 and asReactive shown in Figure 13, the plots provide higher correlation coefficients of more than 0.998, and excellent linearity for different1:1 surface0.744 tension non-aqueous dyeing systems. Moreover, the equilibrium adsorptionblue 19 capacities, qe,cal, fit well with the experimental adsorption 1:4 0.868 capacities, qe,exp, in non-aqueous dyeing systems and in the traditional aqueous system. Therefore, the pseudo-second-order adsorption kinetic model0:1 was suitable0.942 to describe the adsorption kinetics of reactive dyes on cotton fabrics in different surface tension non-aqueous dyeing systems [50–52].

347 3.4.4. Fitting of Pseudo-Second-Order Kinetic Model 348 From the data in Table 5 and as shown in Figure 13, the plots provide higher correlation 349 coefficients of more than 0.998, and excellent linearity for different surface tension non-aqueous 350 dyeing systems. Moreover, the equilibrium adsorption capacities, qe,cal, fit well with the experimental 351 adsorption capacities, qe,exp, in non-aqueous dyeing systems and in the traditional aqueous system. 352 Therefore, the pseudo-second-order adsorption kinetic model was suitable to describe the adsorption

Polymers 2018, 10, 1030 13 of 16

Table 5. R2 of pseudo-second-order model for cotton fabric in different surface tension non-aqueous dyeing systems.

Surface Tension Second-Order Kinetic Model Dye qe,exp (g/mg) (mN/m) −2 2 k2×10 (g/mg·min) qe,cal (mg/g) t0.5 (min) R 19.74 19.97 3.18 20.59 1.57 0.998 22.83 19.55 2.47 20.19 2.07 0.999 Red 195 25.73 19.26 2.29 20.11 2.27 0.998 28.16 19.06 2.11 20.00 2.49 0.998 31.23 18.97 1.52 20.11 3.48 0.999 19.74 19.98 2.88 20.64 1.74 0.999 Polymers 2017, 9, x FOR PEER22.83 REVIEW 19.28 2.62 19.82 1.9813 0.999 of 16 Blue19 25.73 18.83 2.24 19.25 2.37 0.999 353 kinetics of reactive dye28.16s on cotton fabric 18.61s in different surface 2.14 tension non 19.19-aqueous dyeing 2.51 sys 0.999tems 354 [50–52]. 31.23 18.50 1.74 19.54 3.11 0.999

(a):red 195 (b):blue 19 5 5 19.74mN/m 19.74mN/m 4 4 22.83mN/m 22.83mN/m 25.73mN/m 25.73mN/m 3 28.16mN/m 3 28.16mN/m

31.23mN/m 31.23mN/m

t

t

2 2

t/q t/q

1 1

0 0 0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 time (min) time (min) 355 Figure 13. Kinetics of pseudo-second-order model for adsorption of reactive dyes in different surface 356 Figure 13. Kinetics of pseudo-second-order model for adsorption of reactive dyes in different surface tension non-aqueous dyeing systems: (a) red 195; (b) blue 19. 357 tension non-aqueous dyeing systems: (a) red 195; (b) blue 19. For the adsorption rate, the rate constant of reactive dye in lower surface tension non-aqueous 358 Table 5. R2 of pseudo-second-order model for cotton fabric in different surface tension non-aqueous dyeing systems was significantly faster than in higher surface tension systems. For example, 359 dyeing systems. the adsorption rate of reactive red 195 decreased from 3.18×10−2 to 2.11×10−2/(g/mg·min) when the non-aqueous surface tension increased from 19.74 toSecond 28.16- mN/m.Order Kinetic In addition, Model the half-dyeing qe,exp time, t Dyewas significantlySurface Tension lower (mN/m) in lower surface tension non-aqueous−2 dyeing systems. These results 0.5, (g/mg) k2×10 qe,cal t0.5 R2 indicated that the lower the surface tension of non-aqueous(g/mg·min) media, the(mg/g) faster was(min) the adsorption rate of reactive dye, as well as the higher the final uptake of dye. 19.74 19.97 3.18 20.59 1.57 0.998

4. Conclusions 22.83 19.55 2.47 20.19 2.07 0.999

ReactiveRed 195 dyeing for25.73 cotton fabric19.26 and the adsorption2.29 kinetics20.11 ofdye in2.27 non-aqueous 0.998 dyeing systems, and a traditional water base, were investigated in this study. Salts were eliminated throughout 28.16 19.06 2.11 20.00 2.49 0.998 the dyeing process because reactive dye was completely non-miscible with non-aqueous media, but had strong affinity to cotton31.23 fabric. Compared18.97 with reactive1.52 dyeing in a20.11 traditional 3.48 water 0.999 base, a higher

(>94%) uptake of dye19.74 rendered the entire19.98 media recyclable.2.88 Moreover,20.64 the fixation1.74 of0.999 reactive dye was also higher (80%~90% for non-aqueous dyeing vs. 40%~50% for traditional dyeing), resulting in cotton fabric achieving22.83 a deeper shade19.28 after dyeing.2.62 The pseudo-second-order19.82 1.98 kinetic0.999model can adequatelyBlue19 describe the25.73 adsorption and18.83 equilibrium of2.24 reactive dyes19.25 in non-aqueous 2.37 dyeing0.999 systems as well as in a traditional water dyeing system. In non-aqueous dyeing systems, the adsorption rate 28.16 18.61 2.14 19.19 2.51 0.999 of reactive dye was significantly faster than in a traditional water bath. In the siloxane non-aqueous dyeing system, the adsorption31.23 equilibrium18.50 time of reactive1.74 dye was only19.545–10 min3.11 at 250.999◦C, whereas it needed more time at 60 ◦C in the water dyeing system. The surface tension of non-aqueous media affected the adsorption rate of the dye. The lower the surface tension of non-aqueous media, the faster 360 For the adsorption rate, the rate constant of reactive dye in lower surface tension non-aqueous 361 dyeing systems was significantly faster than in higher surface tension systems. For example, the 362 adsorption rate of reactive red 195 decreased from 3.18×10−2 to 2.11×10−2/(g/mg·min) when the non- 363 aqueous surface tension increased from 19.74 to 28.16 mN/m. In addition, the half-dyeing time, t0.5, 364 was significantly lower in lower surface tension non-aqueous dyeing systems. These results indicated 365 that the lower the surface tension of non-aqueous media, the faster was the adsorption rate of reactive 366 dye, as well as the higher the final uptake of dye.

367 4. Conclusions 368 Reactive dyeing for cotton fabric and the adsorption kinetics of dye in non-aqueous dyeing 369 systems, and a traditional water base, were investigated in this study. Salts were eliminated 370 throughout the dyeing process because reactive dye was completely non-miscible with non-aqueous 371 media, but had strong affinity to cotton fabric. Compared with reactive dyeing in a traditional water

Polymers 2018, 10, 1030 14 of 16 was the adsorption rate of reactive dye, and the higher the final uptake of dye. These favorable results have implications for reducing the environmental pressure from reactive dyeing for cotton textiles in a source-control manner through being salts-free, with higher dye uptake, lower dyeing temperature, and large water savings.

Author Contributions: Y.G. and L.Z. designed the experiments; J.W. and L.P. performed the experiments and analyzed the data; L.P. and X.G. wrote the paper; L.P. and H.D. revised the paper. All authors discussed the results and improved the final text of the paper. Funding: This work was supported by the National Key Research and Development Program of China (2017YFB0309600), Key Technology Research and Development Project of Zhejiang Province (2017C03016) and The Young Researchers Foundation of Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education, Zhejiang Sci-Tech University (18050132251812). Acknowledgments: The authors are thankful to the Engineering Research Center for Eco-Dyeing and Finishing of Textiles for providing financial help and to the National Base for International Science & Technology Cooperation in Textiles and Consumer-Goods Chemistry, Key Laboratory of Advanced Textile Materials & Manufacturing Technology, Ministry of Education, for supporting this research. Conflicts of Interest: The authors declare no conflicts of interest.

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