Circular Textiles: Closed Loop Fiber to Fiber Wet Spun Process for

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Cite This: ACS Sustainable Chem. Eng. 2019, 7, 11937−11943

Circular Textiles: Closed Loop Fiber to Fiber Wet Spun Process for Recycling Cotton from Denim Yibo Ma,† Beini Zeng,† Xungai Wang,† and Nolene Byrne*,† †

Institute for Frontier Materials, Deakin University, 75 Pigdons Road, Waurn Ponds, Victoria 3216, Australia

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S Supporting Information *

ABSTRACT: Textile waste is a major waste source found in landfills around the world today, due to increases in population, fast fashion cycles, and inefficient recycling technologies. Here we demonstrate a textile recycling process whereby waste denim is dissolved into a binary solvent and a regenerated cellulose fiber is wet spun. We show that using this process the spun fiber can be regenerated whereby the original color of the waste garment is maintained or regenerated in the absence of color. The retention of color can be significant since the regenerated fibers do not need to be redyed, saving considerable water and energy that is typically required in the traditional textile dyeing processes. This process utilized dimethyl sulfoxide (DMSO) as a cosolvent with ionic liquid 1-butyl-3methylimidazolium acetate ([Bmim]OAc) for the dissolution of the denim waste. The addition of the cosolvent allowed fast dissolution of the cellulosic materials while reducing the viscosity of the spinning dope. The regenerated discolored cellulose fibers produced had similar mechanical properties and morphology to that of viscose fibers, a common regenerated cellulose fiber used extensively in the textile industry. Furthermore, the utilization of binary IL solvent with high DMSO concentration (1:4) reduces the overall process cost. Synopsis: Recycling waste denim creating a regenerated cellulose fiber which can retain the color of the starting textile item or the color can be removed leaving a neutral fiber. KEYWORDS: Cellulose, Recycling, Regenerated fibers, DMSO, Ionic liquid

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for regenerated cellulosic fiber owing to its high cellulose content (∼ 95%).10 The regenerated cellulosic fibers, such as rayon and Tencel fibers, are becoming increasingly popular in the textile market and these fibers, as well as cotton, can never be replaced by synthetic fibers due to their unique properties such as superior moisture absorption, breathability, and excellent mechanical properties. Presently, the dominating method for manufacturing regenerated cellulosic fiber is the viscose process. The global viscose fiber output was over 5.3 million tons in 2016 and is still expected to grow in the coming future.11 The major drawback preventing viscose technology from further expansion is its considerable environmental impact, especially for the viscose manufacturer in Asian countries. The viscose process utilizes commercial dissolving grade wood pulp as a cellulose resource and wet spinning technology with carbon bisulphite (CS2) used for the derivatization of cellulose. This process generates highly toxic side products when cellulose xanthate is dissolved in caustic soda and regenerated in a coagulation bath containing sulfuric acid.12,13 Currently, the only commercial alternative regenerated cellulosic fiber method for viscose is the lyocell process,

INTRODUCTION The modern world is facing rapid globalization due to population growth and technology development. The booming population and their prosperity, especially in developing countries, cause a rise in purchasing power that has led to the generation of vast amounts of postconsumer waste.1,2 These global trends drive humankind to look for a solution in order to balance the development of modern society and environmental sustainability. Textiles are one of the major municipal wastes which typically end up in landfill or are cremated for energy.3,4 Such inappropriate waste management methods contribute to greenhouse gases and soil contamination.5 This phenomenon has been recognized as a linear economy, in which a product is made from natural resources, used and dumped without further application.6 In contrast, a circular economy aligns with the future perspectives of global development. A circular economy defines the production and consumption system that extends the lifetime of products by reusing or upcycling with minimum energy input.2,6 Cotton-based textiles, such as denim, represent a significant proportion of textile waste.7 Re/upcycling of these waste materials would facilitate environmental protection. Furthermore, effective reuse of these materials may also reduce the need for cotton production which competes with arable land and demands considerable amounts of fresh water, fertilizer, and pesticides.8,9 Cotton is considered to be a suitable material © 2019 American Chemical Society

Received: November 26, 2018 Revised: May 21, 2019 Published: May 28, 2019 11937

DOI: 10.1021/acssuschemeng.8b06166 ACS Sustainable Chem. Eng. 2019, 7, 11937−11943

Research Article

ACS Sustainable Chemistry & Engineering

dissolved dyes. After 10 min, 50 g/L sodium chloride was added to the water bath in two portions 10 min apart (totally 20 min). Subsequently, the temperature of the water bath was raised to 70 °C and sodium carbonate (10 g/L) was added and allowed to react for 15 min. Another portion of sodium carbonate (10 g/L) was then added, and the reaction was kept for 60 min. The washing of the dyed fabric was done by rinse the fabric with 35 °C water containing 0.5% acetic acid (pH 5) for 10 min. The fabric was then soaped off with 2 g/L Seriquest CMA for 10 min at 98 °C. The final washing was done by rinsing with warm and then cold water. The fabric was tumbled dried. Pretreatment of Cotton. The cotton, red denim pants, blue denim, and mixed color T-shirt were first ground into powders in a Wiley mill with a mesh size of 0.2 mm. To prepare samples with varying DP, the powdered cotton, red pants were subsequently dispersed and stirred in 10 wt % aqueous NaOH solution in a glass beaker at 80 and 90 °C for varying durations with a total consistency of 1 wt %. The pretreated substrates were washed with distilled water until neutral pH and dried in an oven at 60 °C overnight. The DP of the NaOH treated cotton and red denim pants was analyzed according to the standard test method ASTM D1795−13. The DP was measured in an Ostwald viscometer (1 mm) using CED (cupriethylenediamine hydroxide solution 0.5 N) as the solvent. Table 1 lists the DP of the pretreated cotton and red pants as a function of treatment temperature and duration.

which represents only about four percent of viscose production. In this process, fewer chemicals are involved, and N-methylmorpholine N-oxide monohydrate (NMMO) and water can be recovered efficiently (99%).14−17 Moreover, NMMO is almost nontoxic and biodegradable which makes the process much more sustainable than the viscose process.18 However, the lyocell process operates at relatively high temperature (90−120 °C) and requires the addition of stabilizers (typically propyl gallate) to avoid the runaway reaction and extensive cellulose degradation.15,16 The drawbacks and limitations mentioned above can be bypassed with fiber spinning technology which utilizes ionic liquid (IL) as the solvent. ILs are salts composed solely of ions and have a melting point lower than 100 °C.19 A range of ILs have been recognized as green solvents for both cellulose and lignocellulose thanks to their thermal stability and high solvation power.20 The addition of aprotic solvents, such as DMSO (dimethyl sulfoxide), can accelerate the dissolution of cellulose in IL by preswelling the cellulose, facilitating the penetration of the IL into the cellulose fiber.21−23 Furthermore, the viscosity of the solution can be substantially reduced.23,24 The direct dissolution of cellulosic material in IL enables the shaping of the celluloses into fibers.25 The production of regenerated fibers from cellulose-IL dopes has been reported using both wet and dry-jet wet spinning with a wide range of cellulosic materials and ILs, among which the most successful process is the Ioncell process.26−31 This technology demonstrated the viability of the IL to process not only dissolving grade pulps but also recycled cotton textiles. Spinning with binary solvent (with low DMSO concentration) has also been reported.32,33 The presence of the DMSO reduces the high viscosity of the spinning dope, thus, enhancing the processability of the spinning dope. In the current study, we propose an upcycling routine to convert waste denim into viscose-like regenerated fibers. A binary solution with IL to DMSO ratio up to 1:4 was used as the solvent. The solubility of the binary solvents at different ratios was studied using commercial dissolving pulp. The cellulose with a high degree of polymerization (DP) was prepared from waste cotton and red denim pants and dissolved in the binary system. The effect of the DP and solvent ratio were found to have great influence on the spinning dope rheology. We demonstrate that the regenerated fibers here can be produced with the original garment color or in the absence of original color, resulting in a neutral regenerated fiber. The properties of the fibers produced from the waste denim are characterized here.

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Table 1. DP of Substrates as Functions of Treatment Temperature and Time substrate

DP

cotton cotton cotton cotton cotton cotton cotton red denim pants red denim pants red denim pants red denim pants wood pulp

3313 2180 2111 1558 1265 1213 945 2047 1732 1270 1099 821

treatment temp. °C

duration (h)

80 80 80 90 90 90

3 4 18 12 14.5 23

90 90 90

5 10 15

Pulp Dissolution and Fiber Spinning. Pretreated substrates from cotton and red denim pants were dissolved in [Bmim]OAc and DMSO mixture at designated ratios using a Thinky mixer at elevated temperature for 30 min (max. temperature controlled at 80 °C). Multifilaments were spun using a lab scale customized wet spinning line (Dissol, Korea). The spinning dope was transferred to the barrel attached to a gear pump. The pump was equipped with a spinneret with 100 holes (Ø = 100 μm). The barrel was heated to 70 °C during spinning. The filaments were extruded (at 1 m/min) through the spinneret to a coagulation bath containing tap water at room temperature. After coagulation, the filaments passed through the first godet followed by washing in a warm water bath (60 °C). The filaments were then guided by the second godet and led to the winder. The fibers were washed offline in warm water (60 °C) for 2 h and airdried at room temperature. The draw ratio (DR) of the filaments is defined as Ve/Vt1, where Ve is the extrusion speed of the filaments from the spinneret. Vt1 stands for the speed of the first godet. The spinning scheme is illustrated in Figure S1 in the Supporting Information (SI). Rheological Measurement. The rheology of the spinning dopes was analyzed by a Discovery HR-1 Rheometer with 40 mm/2° cone to plate geometry and a Peltier plate with temperature control. The measuring gap was 49 μm. The dynamic frequency sweep was performed with a strain of 0.5% within the angular velocity range of 0.01−100 s−1 at 70 °C. The complex viscosity of the spinning dope was recorded.

EXPERIMENTAL SECTION

Materials. Ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim]OAc) was purchased from Iolitec, Germany. The sodium hydroxide and dimethyl sulfoxide were purchased from Merck, Australia. The wood pulp (birch prehydrolyzed kraft pulp) was acquired from Department of Bioproducts and Biosystems in Aalto University, Finland. Waste cotton was kindly provided by Cotton Research & Development Corporation (CRDC), Australia. The waste red pants and mixed color T-shirt belonged to an author. The denim dyed with indigo was provided by Chris Hurren in Institute for the Frontier Materials, Deakin University, Australia. The pink fabric was received from RMIT University, Australia. The dyeing process was done as follow: 100% cotton fabric (110 mg/m2) was used as raw material. Reactive dyes Levafix Red E-4BA (conc. 1.5%) and Levafix Yellow E-3RL (conc. 0.5%) were used to dye the fabric. The fabric was placed in water bath at 40 °C followed by addition of the 11938

DOI: 10.1021/acssuschemeng.8b06166 ACS Sustainable Chem. Eng. 2019, 7, 11937−11943

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Figure 1. Optical microscopy images of the dissolution of the wood pulp at different concentration in [Bmim]OAc and DMSO solvent system.

Figure 2. Polarized microscopy images of the cellulose solutions in B/D 20:80 as a function of DP.

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Color Strength and Whiteness. The color strength and whiteness of the red denim pants, NaOH treated red denim pulp and the spun fiber with and without color were analyzed using Datacolor 600 Spectrophotometer with a light source D65. For the fiber samples, the fiber bundles were opened to yield a fluffy form and then the opened fibers were tightly tied on a cardboard prior to analysis. The whiteness with CIE standard and color strength (K/S) at wavelength of the max. absorbance were recorded. For each sample, 5 spots were selected for the measurement. The color strength K/S is calculated from the reflectance% (R%) measured by the instrument. The relationship between K/S and the R% is shown in eq 1: ÄÅ É ÅÅ (1 − R )2 ÑÑÑ ÑÑ K /S = ÅÅÅÅ Ñ ÅÅÇ 2R ÑÑÑÖ

RESULTS AND DISCUSSION Solubility Studies. The solubilizing power of a solvent with respect to the substrate is critically important for spinning, incomplete dissolution may result in a dope with poor spinnability and weak filaments.29 The solubility of cellulose in the binary [Bmim]OAc/DMSO solvent at different ratios was studied by using wood pulp (DP 821) as a model substrate. Solvents with [Bmim]OAc to DMSO (B/D) ratio of 20:80, 30:70, and 50:50 were selected to evaluate the influence of solvent composition on cellulose dissolution. As shown in Figure 1, the solubility of the mixture reduced as DMSO content increased. When there are equal amounts of IL and DMSO, the wood pulp readily dissolved in the solvent until 18 wt % dope concentration was reached. Aggregation of short undissolved fibers could be observed. Due to the high polymer concentration, a gel-state solution was formed that limited the accessibility of the solvent to the cellulose. Gradually raising the DMSO concentration led to dilution of the anion of IL which resulted in the reduced solubility. At B/D ratio of 30:70, complete dissolution was achieved at 12 wt %. As shown in Figure 1, higher pulp concentration resulted in partial dissolution with a balloon structure which indicated the swelling of cellulose fiber. Ultimately, the binary solvent with 20 wt % [Bmim]OAc was able to dissolve up to 8 wt % of the wood pulp. A pronounced swelling of the wood pulp fibers could be observed when the loading increased to 10 wt %. The reduction of the cellulose solubility in the IL/DMSO mixture is in agreement with previous studies.34,35 It has been reported that the IL anion is key in the dissolution of cellulose by

(1)

where R is the reflectance%, K is the absorbance, and S is the scattering. Mechanical Properties. The linear density (dtex) of the spun fiber was analyzed by Favimat+ with a pretension of 1.1 cN/tex at 2 mm/min. The mechanical properties of the spun fiber were conducted by Instron with a 5N load cell. The gauge length and speed were set as 20 mm and 10 mm/min, respectively. SEM. SEM imaging was performed using a Zeiss Sigma VP with variable pressure. For cross-section imaging, the fiber was prepared by cryo-fracture. A bundle of fiber was first dipped into liquid nitrogen and snapped. The fractured fiber bundle was then glued onto the conductive support. The samples were sputter-coated with gold to ensure electric conductivity. The images were taken at 3 kV operating voltage. 11939

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Figure 3. Rheological properties of spinning dopes at 70 °C: A. cotton with high DP and B. cotton and wood pulp dopes with lower DP.

Figure 4. Schematic highlighting the process for closed loop fiber to fiber recycling. Fibers produced without color are first treated with NaOH solution whereas fibers produced with color are directly dissolved into the [Bmim]OAc/DMSO solvent.

dopes in this study was measured at the same temperature as the spinning temperature (70 °C) using an amplitude sweep method. To avoid high dope viscosity which deteriorates the spinnability, the concentration of the spinning dope was controlled at 6 wt %. Spinning dopes were prepared with pretreated cotton with varying DP and solvent B/D ratios. Figure 3 illustrates the viscoelastic properties of the spinning dopes prepared from cotton and wood pulp. Like the other polymer solutions, the cellulose IL solutions in this study exhibited shear thinning behavior at higher shear rate/angular frequencies. Whereas, a Newtonian plateau can usually be observed at lower angular frequency.40,44 This effect is confirmed in the current study, especially with solutions containing lower DP substrates. As shown in Figure 3A, the complex viscosity of the dopes was governed by both the DP of the substrates and the concentration of DMSO. The DP has an obvious effect on the complex viscosity of the spinning dope. Without altering the solvent ratio, a lower DP resulted in dopes with less complex viscosity. Reduction of the viscosity was attributed to reduced entanglement of the short cellulose chains which enhanced the motion of the solution. DMSO concentration also has a pivoting effect on the viscoelastic properties of the dopes. The viscosity of the aprotic DMSO is considerably lower than the IL, therefore the addition of DMSO reduced the viscosity of the spinning dope. Figure 3B illustrates the effect of the B/D ratio on the rheology of the spinning dopes. At a given substrate DP (954), the viscosity of the solution reduced gradually with lower B/D ratio. Technology Demonstration: Conversion of Waste Denim into Regenerated Fibers. Here a pair of red denim pants was recycled into fibers with and without the original red color. The fibers are wet spun at a polymer concentration of 6 wt % in the binary IL solvent system with B/D ratio of 20:80. To produce the fibers without the color the waste textile was

interrupting the inter- and intrahydrogen bonds. When IL is solvated in DMSO, the solubility of the IL/DMSO mixture undergoes an incremental rise first at relatively low DMSO concentration as more anion of the IL is freed due to the interaction between DMSO and the cations of the IL.23,36 The increased concentration of anion enhances the dissolution capacity. Further addition of DMSO reduces the overall concentration of IL and anions, thus leading to a reduced dissolution capacity.34 The solubility of a solvent system is also strongly influenced by the DP of the cellulose.10,37 Since until now, the majority of textile is still produced using cotton with high DP (as opposed to viscose fiber), the influence of DP was investigated for the selected solvent system which was B/D 20:80. The solution at this ratio minimized the amount of IL used, reducing the cost of the spinning process. A polymer concentration of 6 wt % was chosen as this ensured a solution with excellent spinnability (discussed in the next sections). Figure 2 illustrates the influence of the cellulose DP on the solubility when using the mixed solvent system at a B/D 20:80 ratio. Cellulose pulps derived from red denim pants were used as substrates (see Table 1). In agreement with previous studies,38,39 the solubility of cellulose reduced with increasing DP. A clear, transparent solution can be obtained with cotton DP of 1099. Complete dissolution was suppressed at cellulose DP of 1270 and distinct undissolved cellulose fibers can be observed at DP 1732 and DP 2047. Dope Properties. Rheological properties of the dope play a key role in their spinnability as such the viscoelastic properties of the spinning dope (from cotton and wood pulp) were assessed. The rheology of the spinning dope can be influenced by several factors, e.g., temperature, polymer concentration, DP of the polymer, and the addition of cosolvent.21,40−43 The complex viscosity of the spinning 11940

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Table 2. Whiteness (CIE), Reflectance% (R%) and Color Strength (K/S) and of the Red Denim Pants, NaOH Treated Red Denim Pulp and the Spun Fibers sample

R%

whiteness −65.55 56.92 50.20 −46.71

red denim pants NaOH treated red denim pulp fiber without color fiber with red color

± ± ± ±

0.56 0.96 2.28 5.44

6.07 67.35 68.16 8.35

± ± ± ±

K/S 0.07 0.65 2.92 0.66

7.27 0.08 0.08 5.07

± ± ± ±

0.10 0.01 0.02 0.48

Table 3. Mechanical Properties of Regenerated Fibers and Viscose Fiber DP 1099 DP 1099 viscosea

DR

titer (dtex)

dry elongation (%)

dry tenacity (cN/tex)

elastic modulus (GPa)

wet elongation (%)

wet tenacity (cN/tex)

1 6

5.89 ± 0.14 1.15 ± 0.13 1.80 ± 0.10

14.53 ± 0.78 5.11 ± 0.71 19.20 ± 2.20

18.15 ± 0.87 27.44 ± 3.85 20.70 ± 1.50

18.06 ± 0.15 21.82 ± 0.32 6.90 ± 0.50

23.71 ± 2.59 11.18 ± 2.23 16.50 ± 1.30

10.00 ± 1.17 21.52 ± 2.34 7.50 ± 1.30

a

Values adopted from Michud et al.,28 the DP of pulp before xanthation for viscose production is 270 to 35049

first powered and mechanically milled into a powder (⩽0.2 mm). Subsequently, the powder was treated with a 10% NaOH solution aimed at degrading the DP of the waste textile to ∼1000 (Figure 4). It was noticed that the red color of the waste denim was discolored during the NaOH treatment after 5 h. The evolution of the discoloration over time is demonstrated in Figure S2 in the SI. It is likely that under the alkaline conditions, both cotton and the dye tended to degrade which eventually lead to the whitening of the cotton fibers. Further discoloration tests have also been carried out for blue (indigo) denim powder, a pink fabric with known dye history and a mixed color t-shirt representing waste textile (the dye history of the mixed color T-shirt is unknown). It was shown that the indigo dye could also be readily discolored using the NaOH treatment, requiring treatment time of 10 h, whereas the pink fabric with known dye history required at least 30 h and the mixed color T-shirt required 10 h for complete discoloration of the dye. (Figures S3, S6, and S5 in the SI). The difference in the time required to decolor is highly dye dependent with reactive dyes such as those used in the pink fabric (Levafix Red E-4BA and Levafix Yellow E-3RL) requiring longer treatment times than indigo. Powdering of the textile material is an important step to achieving decoloration, since the dye could not be efficiently decolored from nonshredded red denim pants and mixed color T-shirt (Figures S4 and S5 in the SI). The color in the regenerated fiber can be maintained if the powder is added directly to the spinning solvent instead of pretreating the powder in a decoloring solution The color strength and the CIE whiteness of the spun fibers and their starting materials were analyzed using a Datacolor 600 Spectrophotometer, and the results are listed in Table 2. The NaOH treated red denim pulp showed a whiteness of 56.92 which indicated the red denim is bleached. The resulting fiber from this pulp had a whiteness of 50.2. The slight reduction of the whiteness may be a result of the ionic liquid itself that showing light yellowish color. The white fiber has lower whiteness (CIE) compared to viscose fiber which could be higher than 60 depending on the source of the pulp used.45 However, it has to be noted that the commercial viscose process may have a bleaching step that improves the whiteness of the fiber.46 The color variation between the red denim pants and red regenerated fiber can be better extrapolated by the color strength (K/S value). The red fiber demonstrated a lower K/S value compared to the original red pants. This effect

indicates partial discoloration may be performed during the dissolution in IL and spinning process. Table 3 presents the tensile properties of the regenerated fiber from the alkaline treated red denim pants (discolored) spun under different draw ratios (DR). The spinning dope possessed a significantly higher draw ratio than what has been reported previously for the wet spinning of cellulose-IL dope.47,48 The mechanical strength was analyzed under a fully conditioned environment for textiles. The spun fiber had a dry tenacity of 27.44 cN/tex and a wet tenacity of 21.82 cN/ tex at the highest draw ratio. The mechanical strength of the regenerated fiber is comparable to the viscose fiber, albeit with a lower elongation and higher wet tenacity which owes to the high DP of the cellulose. Morphology of the Spun Fibers. Figure 5 shows SEM images of the regenerated fiber from the waste textile garment.

Figure 5. SEM images of fiber spun from DR 1 and 6.

At a draw ratio of 1, no fibril orientation is observed which is typical for low draw ratio fibers. Furthermore, a smooth surface with only slight defects can be observed, again typical morphology for wet spun fibers at low DR. The DR6 fibers exhibited an irregular, serrated cross-section. This unique structure is likely caused by the pressure difference between the fiber and the coagulation media due to the osmotic solvent exchange which eventually leads to the collapse of the regenerated filament surface (skin) and also the radial orientation of the fiber cross-section. The morphology of the DR 6 fiber was similar to that of viscose fiber which is also produced by wet spinning. Furthermore, the surface shows 11941

DOI: 10.1021/acssuschemeng.8b06166 ACS Sustainable Chem. Eng. 2019, 7, 11937−11943

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ACS Sustainable Chemistry & Engineering grooves caused by stretching of the fiber under high draw conditions.

(4) Asaadi, S.; Hummel, M.; Hellsten, S.; Härkäsalmi, T.; Ma, Y.; Michud, A.; Sixta, H. Renewable High-Performance Fibers from the Chemical Recycling of Cotton Waste Utilizing an Ionic Liquid. ChemSusChem 2016, 9 (22), 3250−3258. (5) Allesch, A.; Brunner, P. H. Assessment Methods for Solid Waste Management: A Literature Review. Waste Manage. Res. 2014, 32 (6), 461−473. (6) Korhonen, J.; Honkasalo, A.; Seppälä, J. Circular Economy: The Concept and Its Limitations. Ecol. Econ. 2018, 143, 37−46. (7) Paul, R. Denim and Jeans: An Overview. Denim 2015, 1−11. (8) Hämmerle, F. M. The Cellulose Gap (the Future of Cellulose Fibres). Lenzinger Berichte 2011, 89, 12−21. (9) Eichinger, D. A Vision of the World of Cellulosic Fibers in 2020. Lenzinger berichte 2012, 90, 4−10. (10) De Silva, R.; Byrne, N. Utilization of Cotton Waste for Regenerated Cellulose Fibres: Influence of Degree of Polymerization on Mechanical Properties. Carbohydr. Polym. 2017, 174, 89−94. (11) Lenzing, A. G. Global fiber market in 2016 http://www.lenzing. com/en/investors/equity-story/global-fiber-market.html (accessed Jan 10, 2018). (12) Hermanutz, F.; Gähr, F.; Uerdingen, E.; Meister, F.; Kosan, B. New Developments in Dissolving and Processing of Cellulose in Ionic Liquids. In Macromol. Symp.; 2008; Vol. 262, pp 23−27. (13) Bywater, N. The Global Viscose Fibre Industry in The 21st CenturyThe First 10 Years. Lenzinger Berichte 2011, 89, 22−29. (14) Eichinger, D.; Eibl, M. Lenzing Lyocell-an Interesting Cellulose Fibre for the Textile Industry. Chem. Fibers Int. 1996, 46 (1), 28−30. (15) Rosenau, T.; Hofinger, A.; Potthast, A.; Kosma, P. On the Conformation of the Cellulose Solvent N-Methylmorpholine-NOxide (NMMO) in Solution. Polymer 2003, 44 (20), 6153−6158. (16) Fink, H. P.; Weigel, P.; Purz, H. J.; Ganster, J. Structure Formation of Regenerated Cellulose Materials from NMMOSolutions. Prog. Polym. Sci. 2001, 26 (9), 1473−1524. (17) Schuster, K. C.; Rohrer, C.; Eichinger, D.; Schmidtbauer, J.; Aldred, P.; Firgo, H. Environmentally Friendly Lyocell Fibers. In Natural Fibers, Plastics and Composites; Wallenberger, F. T., Weston, N. E., Eds.; Springer: Boston, MA, 2004; pp 123−146. (18) Meister, G.; Wechsler, M. Biodegradation of N-Methylmorpholine-N-Oxide. Biodegradation 1998, 9 (2), 91−102. (19) Welton, T. Room-Temperature Ionic Liquids. Solvents for Synthesis and Catalysis. Chem. Rev. 1999, 99 (8), 2071−2084. (20) Zhang, J.; Wu, J.; Yu, J.; Zhang, X.; He, J.; Zhang, J. Application of Ionic Liquids for Dissolving Cellulose and Fabricating CelluloseBased Materials: State of the Art and Future Trends. Mater. Chem. Front. 2017, 1 (7), 1273−1290. (21) Li, X.; Zhang, Y.; Tang, J.; Lan, A.; Yang, Y.; Gibril, M.; Yu, M. Efficient Preparation of High Concentration Cellulose Solution with Complex DMSO/ILs Solvent. J. Polym. Res. 2016, 23 (2), 1−8. (22) Kuzmina, O.; Jankowski, S.; Fabiańska, A.; Sashina, E.; Wawro, D. Preswelling of Cellulose Pulp for Dissolution Inionic Liquid. Cellul. Chem. Technol. 2014, 48 (1−2), 45−51. (23) Andanson, J. M.; Bordes, E.; Devémy, J.; Leroux, F.; Pádua, A. A. H.; Gomes, M. F. C. Understanding the Role of Co-Solvents in the Dissolution of Cellulose in Ionic Liquids. Green Chem. 2014, 16 (5), 2528−2538. (24) Lu, F.; Wang, L.; Zhang, C.; Cheng, B.; Liu, R.; Huang, Y. Influence of Temperature on the Solution Rheology of Cellulose in 1Ethyl-3-Methylimidazolium Chloride/Dimethyl Sulfoxide. Cellulose 2015, 22 (5), 3077−3087. (25) Hummel, M.; Michud, A.; Tanttu, M.; Asaadi, S.; Ma, Y.; Hauru, L. K. J.; Parviainen, A.; King, A. W. T.; Kilpel?inen, I.; Sixta, H. Ionic Liquids for the Production of Man-Made Cellulosic Fibers: Opportunities and Challenges. In Advances in Polymer Science; Springer International Publishing, 2015; Vol. 271, pp 133−168. (26) De Silva, R.; Vongsanga, K.; Wang, X.; Byrne, N. Understanding Key Wet Spinning Parameters in an Ionic Liquid Spun Regenerated Cellulosic Fibre. Cellulose 2016, 23 (4), 2741−2751.

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CONCLUSIONS We have demonstrated a closed loop fiber to fiber approach for recycling waste cotton from denim via a dissolution wet spinning approach. The use of a binary solvent containing a low IL amount reduces the drawbacks (e.g., high dope viscosity) generally associated with spinning cellulose from IL solvents. Furthermore, it reduces the cost of the solvent by 77% (900 $/kg for neat [Bmim]OAc and 202 $/kg for [Bmim]OAc/DMSO with ratio of 20:80). The solvent can be recovered and reused via distillation making this a closed loop system. Depending on the pretreatment of the waste textile the color can be maintained or removed. Compared to wet spinning process using neat ionic liquid, this process improves the draw ratio of the filaments by which a max. draw ratio 6 has been achieved. The mechanical properties and the morphology of the spun fibers were similar to viscose fibers. This work reveals the potential of using high DP waste cellulosic material (specifically denim) and binary IL solvent with high DMSO concentration for production of man-made cellulose fibers.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.8b06166. The schematic spinning process; evolution of the decoloration of red pants powder, blue denim powder, red pants thread, mixed color T-shirt, and pink fabric powder (with known dye history) in 10% NaOH solution (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Yibo Ma: 0000-0001-9031-6460 Nolene Byrne: 0000-0002-9474-7644 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by the Australian Research Council (ARC) Research Hub for Future Fibers (IH140100018) and funded by the Australian Government. The authors acknowledge Dr. Xin Liu (from Institute for Frontier Materials, Deakin University, Australia) for the kind assistance on the whiteness and color strength analysis.

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REFERENCES

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DOI: 10.1021/acssuschemeng.8b06166 ACS Sustainable Chem. Eng. 2019, 7, 11937−11943