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A new strategy for using textile waste as a sustainable source of recovered cotton
Resources, Conservation & Recycling 145 (2019) 359–369
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Full length article
A new strategy for using textile waste as a sustainable source of recovered cotton
T
Samy Yousefa,d, , Maksym Tatariantsb, Martynas Tichonovasb, Zahid Sarwarb, Ilona Jonuškienėc, Linas Kliucininkasb ⁎
a
Department of Production Engineering, Faculty of Mechanical Engineering and Design, Kaunas University of Technology, LT-51424 Kaunas, Lithuania Department of Environmental Technology, Faculty of Chemical Technology, Kaunas University of Technology, LT-50254 Kaunas, Lithuania c Department of Organic Chemistry, Faculty of Chemical Technology, Kaunas University of Technology, LT-50254 Kaunas, Lithuania d Department of Production Engineering and Printing Technology, Akhbar Elyom Academy 6th of October, Egypt b
ARTICLE INFO
ABSTRACT
Keywords: Cotton Textile waste Recycling Cotton fiber recovery Polyester Dimethyl sulfoxide
Cotton is one of the primary resources in many modern industries and with increasing demand rates the current challenge is to find other sources of cotton production with lower prices and higher quality whereas cotton produced only by agriculture is not sufficient for these needs. This is focused on developing a new strategy to make the textile waste a new sustainable source of recovered cotton to face this shortage. This strategy is summarized as development of a chemical technology using sustainable and commercial chemicals to recover cotton from waste textile. The technology consists of three sequential processes: a) textile dye leaching using Nitric Acid as a pretreatment of the original waste, b) dissolution process using Dimethyl Sulfoxide (DMSO) as the main treatment to dissolve the organic materials from the treated fabric, including polyester and remaining organic part from textile dyes, and c) bleaching process using sodium hypochlorite and diluted hydrochloric acid for final recovered cotton purification. Preliminary experiments were performed at a laboratory scale to determine the optimum conditions on a few grams of two different types of denim fabric. To simulate the pilot scale, the main experimental work was conducted for full-size blue and black waste jeans trousers in a developed reactor with capacity 1 kg based on the preliminary experimental results. To close the lifecycle loop of the suggested strategy, rotary evaporator was used to extract the polymeric part and regenerate the spent DMSO, while the acid was regenerated by activated carbon. Additionally, suggestions on treatment of the water contaminated by acid and solvent (obtained after washing) were given. Morphology, thermal behavior, and chemical structure of the recovered cotton, regenerated acid, solvent, and recovered polyester were investigated. Based on the recycling rate (93%), profitability (1466 $/ tonne), greenhouse gas emissions (-1,534 CO2-eq/ tonne), and sustainability assessment, the developed strategy can be seen as a high-potential approach for recovery of cotton.
1. Introduction
situation is further complicated since some of the leading cotton-producing governments have begun to reduce the size of cultivated cotton due to the severe shortage of water resources - cultivation of cotton requires huge amounts of water, consuming 2.6% of global water supply (Chapagain et al., 2006). Moreover, strain on agricultural land is further increased due to the terrible increase in the population size (Chapagain et al., 2006; Oldenborg and Steinman, 2019). On the other hand, artificially produced cellulose does not have the same properties as the cellulose extracted from natural cotton (Kobayashi, 2005). Based on that, the current challenge is to find the other sources for cotton production with low price and sufficient quality. Textile waste recycling
Cellulose is the main component of cotton and according to international statistics in 2017/2018 the world's leading cotton producing countries (India, China, USA, Brazil, Pakistan, Australia, Turkey, Uzbekistan, Turkmenistan, and Burkina Faso) produced around 23.6 million tonnes of cotton; most of this amount of natural fibers was consumed by textile and clothing industry (Anon., 2019a; EsteveTurrillas and de la Guardia, 2017). According to the forecasts, size of textile industry will increase by 20–30% in 2025, requiring governments seek new sources of cellulose production (Anon., 2019b). The
⁎ Corresponding author at: Department of Production Engineering, Faculty of Mechanical Engineering and Design, Kaunas University of Technology, LT-51424 Kaunas, Lithuania. E-mail address: [email protected] (S. Yousef).
https://doi.org/10.1016/j.resconrec.2019.02.031 Received 28 November 2018; Received in revised form 20 February 2019; Accepted 21 February 2019 0921-3449/ © 2019 Elsevier B.V. All rights reserved.
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is one of the essential solutions for tackling this issue and achieving cotton self-sufficiency in many countries as the textile waste mass generated worldwide each year is estimated in millions of tons, while cotton represents 40–50% of its weight on average, reaching > 84% in some of the cases, particularly in waste jeans textile (Esteve-Turrillas and de la Guardia, 2017; Sandin and Peters, 2018a). However, textile waste has not yet been optimally exploited due to the difficulties in certain management and technical aspects during collection, sorting, recycling, and purification of recovered materials. Therefore, the Estonian government organized event “Used textiles: waste or value?” for this purpose with participation of many decision makers and investors to find a serious solution for these aspects (Anon., 2019c). The participants recommended that the life cycle of textile should be transferred from a linear economy to a circular economy by linking these stages together. It should be mentioned that recently a group of researchers worked on solving the textile waste issues and established specific mechanisms for its collection through, firstly, installation of booths and boxes with coding or serial number. The collected waste was sorted manually or semi-automatic/fully automatic based on the product type, manufacturing methods, fiber composition and a product condition assessment (by 17 criteria into 25 categories) followed by recycling process (Luiken and Bouwhuis, 2015; Nørup et al., 2018). Recycling is also a prospective way to decrease the amount of greenhouse gas emissions generated by textile industry. However, in this type of waste cotton is usually mixed with polyester, textile dyes, and some organic materials, making it hard to recover high quality cotton and maintain acceptable recovery cost (Fortuna and Diyamandoglu, 2017). Thus, landfilling and incineration are considered the optimum ways for disposal of such waste. Corroborating that fact, the latest EU reports showed that the textile waste represented ˜6% of the overall municipal solid waste and accounted for more than 3% of the greenhouse gas emissions in the EU (Hu et al., 2018a). In view of the current textile recycling practices, it is clear that most of these practices are focused on using the textiles as a feedstock for energy production, including production of gas, biogas (ethanol), and thermal energy by using combustion or chemical reactions (Gholamzad et al., 2014; Nunes et al., 2018; Bansal et al., 2016; Ge and Li, 2018; Hasanzadeh et al., 2018). Some of these technologies are started by pretreatment to remove textile dyes and polyester and thus improve the yield and product quality by alkaline solutions (e.g. KOH, NaOH), Nmethylmorpholine-N-oxide, phosphate solutions, hydrochloric acid, and other reagents to facilitate the digestion of cotton-containing textiles to avoid generation of waste after all treatment steps. In order to raise the process efficiency, biological reactions for production of clean energy from textile waste were recently used (Hu et al., 2018b). Although the results are promising, the technique requires many additional studies for application at the industrial level while energy production means losing the value of potentially recoverable cotton. Therefore, other researchers selected different direction and attempted to produce glucose from textile waste; the main drawbacks of their approach were many process steps required and a very long reaction time up to 7 weeks (Wang et al., 2018). One more research group focused on recovery of cellulose from textile waste. Fangbing et al. (2015) used dissolution process by ionic liquid 1-allyl-3-methylimidazolium chloride ([AMIM]Cl) to separate cellulose and nylon 6 from waste nylon/cotton blended fabrics (Lv et al., 2015). By this approach, cotton can be separated as cellulose/[AMIM]Cl solution that needs more steps to regenerate cellulose from the liquid phase. In addition, there were no data about textile dyes in the samples and if the steps were taken to properly remove them what is crucial for textile waste recycling as the dyes can contain various heavy metals and organic compounds that pose a threat to public health and environment if left without attention (Khamparia and Jaspal, 2017). Wolkat Circular Textile Recycling is a major company working in the production of textile fabric from textile waste that uses grinding and washing of waste with water without chemical treatment. In spite of the success of this technique, it was
found difficult to control the color of the product and its chemical structure, which varies according to the type of feedstock (Anon., 2019d). Also, this technique requires large amounts of water to remove pigments, therefore producing large amounts of wastewater. Leaching process using different acids, including nitric (HNO3), is used in metal recovery and extraction from waste (Lynn et al., 2018; Li et al., 2018). Therefore, leaching treatment was used by authors to remove heavy metals from textile dyes and obtain treated fabric (cotton fiber and polyester), contaminated only by a small amount of organic materials remaining from textile dyes. Also, during the leaching, it is important to use HNO3 with concentration < 68.4%, since higher concentration of nitric acid can cause irreversible changes in the chemical structure of cellulose through it nitration, Knecht compound formation, etc. (Gert et al., 2000), thus instead of pure cotton, a combination of modified and unmodified fibers can be produced. Therefore, to selectively remove textile dyes without altering the structure of cotton, the textile was processed by 60% HNO3 at mild temperature. Solvent treatment is a typical approach for dissolving polymers and other organic compounds from different wastes with similar structure, such as WPCBs and organic waste (Tatariants et al., 2017; Ozturk et al., 2018). Selection of solvent was the critical point of the dissolution process to avoid or reduce the degradation degree of extracted cotton/cellulose. Solvents, capable of reacting with cellulose can be classified into three types: organic solvents, aqueous solvents, and ionic liquids (Liebert, 2010; Ghasemi et al., 2017; Peng et al., 2017). Among the commercial solvents, Dimethyl Sulfoxide (DMSO) is classified as an organic solvent, ecofriendly and sustainable solvent compared to the other organic solvents like Dimethylformamide, suitable for dissolving polyester and organic residues remaining from dyes in the waste fabrics. Also, DMSO has a high boiling point compared to the other solvents (Byrne et al., 2016). Therefore, DMSO was used to extract polyester from the waste jeans after pretreatment by acid for dye removal, thus liberating cotton fibers that were later purified using bleaching process at pilot scale. The economic benefits of the developed strategy were studied to assess its industrial potential. 2. Experimental 2.1. Materials and textile waste sample preparation Waste jeans were provided by a local clothing repair shop in Lithuania. The waste jeans were chosen depending on the textile dye color: black 100% cotton jeans and blue 80/20 cotton/polyester jeans. Dimethyl Sulfoxide (DMSO) solvent and other reagents for leaching, dissolution, and purification processes were purchased from Sigma-12 Aldrich Corp. To prepare the samples for separation, all the metal and plastic components like rivets and stickers were removed from the samples by suitable mechanical tools. After that, the samples were cleaned by water to remove any contaminants and were dried at room temperature. Later, the dried jeans were shredded into small 50150 mm2 sized pieces. Total weight of the dried samples was measured by laboratory balances (560 g for black and 580 g for blue sample). The weighted samples were divided into two groups: 20 g from each sample for preliminary experiments and the remaining weight (540 g black sample and 560 g blue sample) for the main pilot scale experiments. 2.2. Preliminary experiments Initial tests were conducted on 20 g of waste jeans in ultrasonic bath with 1 L capacity to find the optimal leaching and dissolution conditions (as the needed information is not provided in literature for such specific processes). Preliminary experiments were performed at varying concentrations of HNO3 (0.5–1.0 - 1.5–2 M) at 50 °C and, according to the results, 1.0 M and 1.5 M HNO3 was sufficient to dissolve dyes from blue and black samples with average treatment time 20 min. The optimal solvent treatment conditions were found as follows: 1 g samples of 360
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Fig. 1. Waste denim fabric before and after being subjected to leaching and dissolution treatments: A, E) untreated samples, B, F) bare fabric, C, G) treated fiber at the middle of dissolution process, and C, G) treated fiber at the end of dissolution process.
two jeans types were treated at a constant temperature 50 °C in the range 10 to 80 ml of solvent with step 10 ml. Minimal dissolution time was found as the time needed to fully liberate cotton from polyester and other organic components. The experiments showed that full optimal separation of black sample could be reached after 7 h. with 40 ml of solvent whereas the blue sample required 9 h. and 60 ml. of solvent. Fig.1 shows the images of untreated/treated black (Fig. 1(A–D)) and blue (Fig. 1(E–H)) samples at different periods.
feedstock or from solvent and chemicals remaining or attached on the reactor walls and ease the cleaning process), attached to the main body through two rotary hinges (indicated by orange circles) to give the chamber possibility to move freely when the body is filled with vibrating fluid (distilled water). At the bottom of the reaction chamber, there are four outlets with valves connected to four separate tanks used for storing the reaction solutions. Two of the tanks are used for spent acid and solvent, while the other two are used for spent water obtained after washing the treated denim material after leaching and dissolution. The main reason behind the implementation of separate storage vessels for the spent water was the fact that water after the leaching is contaminated by reactive acid, whereas water after the dissolution is contaminated by much more safe eco-friendly solvent, thus these effluents require different handling. Inside the reaction chamber there is a fixed plastic basket with sieve at the bottom used for filtration and washing of the fabric and cotton fibers after all treatment stages. The upper part of the reactor is closed by cover to prevent any leakage of harmful fumes. There are two feeders on the back side of the reactor: first one for feeding solvent or acid, while the second one is designed for taking samples from reaction
2.3. Pilot scale experiments The main experiments were done for the remaining samples (540 g black jeans and 560 g blue jeans) in a developed reactor at the conditions obtained from preliminary experiments. 2.3.1. Design of the pilot scale reactor Fig. 2 shows the full design and image of the developed reactor; as shown in the sketch, the outer frame of 2 L ultrasonic bath was used as a main body of the reactor. A cylindrical glass reaction chamber is installed inside the main frame (to avoid any waste particles from
Fig. 2. A) Full design of the developed reactor and B) Image of the developed reactor. 361
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Finally, the cover was opened to extract the plastic basket with recovered fibers from the reactor and begin the refining of the fibers and the regeneration of spent chemicals. The cotton fibers were bleached with Sodium Hypochlorite (the chlorine content is about 1.5% from the weight of cotton) and dilute hydrochloric acid (˜2% from the weight of cotton), (Zhou et al., 2016) to remove the remaining impurities under soundwave treatment for 2 h. at 40 °C. To close the loop of the technology, used chemicals (Acid, solvent) were regenerated using a rotary evaporator at 150 °C and activated carbon with mass ratio 20 ml (solution): 5 g (activated carbon).
solution for investigation. There is one more feeder in the right side of the reactor for feeding water to compensate the water that evaporates during the treatment. In addition, there is a spindle with a pressure plate supported by a bearing in the reactor cover used as a manual press at the end of leaching, dissolution, and washing stages to effectively separate the spent solvent, acid, or water from solid samples through compressing the pulp and directing the spent solution to its tank by opening the specified valve. The tanks are connected with four regeneration units for acid, solvent and spent acidic/solvent water. The acid regeneration unit is a glass flask with capacity 2 L that contains activated carbon, absorbing the heavy metals and organic dyes from the acid within several days (based on the jeans type). Rotary evaporator with capacity 2 L is used as a solvent regeneration unit to extract the polymeric part from the spent solvent at 150 °C. Regarding the spent water, in the implemented system there were units only to collect it, and at the end of this article the authors suggested some techniques to treat the spent water based on the approaches used in the literature. Finally, all connected components are tightly sealed by a silicone sealant to avoid leakage of any gases or other substances.
3. Results and discussions Fig. 4 shows images of cotton fiber obtained after the bleaching process. Optical Microscope was used for analysis of morphology, Thermogravimetric Analysis (TGA) – for determining thermal properties, and Fourier-Transform Infrared Spectroscopy (FTIR) – for finding the chemical structure of the fibers and to investigate the mechanism of processes taking place at all technology stages. Chemical structure and thermal behavior of the extracted polymers were investigated in order to determine their types, thus evaluate the recycling rate as well as its economic performance. In addition, the chemical properties of the spent acid, solvent were analyzed to evaluate the sustainability of the suggested technology.
2.3.2. Waste textile separation procedure using the developed reactor As mentioned above, the approach developed during the preliminary experiments consisted of two main steps: leaching using acid and dissolution using DMSO; both main steps are followed by water washing. To apply the same concept on the pilot scale using the new reactor, the reaction chamber containing waste textile was filled with acid from the side feeder with solid to liquid ratio 1:50 and samples were treated for 20 min. at 50 °C. At the end of this process, the valve of the spent acid tank was opened to withdraw the spent acid by compressing the pulp and the tank was locked again. To clean the obtained fabric and remove the remaining acid, water was added into the chamber and the spent water was collected afterwards in the second tank by using the manual press again. To dissolve the polyester and other organic contaminants in the textile, the reaction chamber loaded by fabric was filled with solvent (according to the optimum solid to liquid ratio) and dissolution process was performed at 50 °C for 6 h. for blue and 10 h. for black sample. The spent solvent was collected in the third tank and spent solvent-containing water was collected in the last tank as shown in Fig. 3.
3.1. Separation mechanism Original cotton is usually characterized by its bright white color. Once the cotton fiber is colored by textile dyes and mixed with synthetic fibers, its color changes according to the dye color (black and blue in the current case). This change in matrix color is difficult to observe by SEM because the images obtained by SEM are monochromatic(greyscale). USB Microscope (USB 8 LED Light Digital Microscope Endoscope Camera Magnifier) has a color imaging feature, which eases observation and verification of fiber layer separation as well as verification of the cotton structure. Based on this, the morphology of denim fabric was investigated by using the color imaging feature of USB microscope. Fig. 5 shows the photographies of the untreated jeans, treated
Fig. 3. A schematic drawing of the textile separation using the developed reactor: (A–C) Leaching process and (D–F) Dissolution process. 362
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Fig. 4. Photographies of the cotton obtained from A, B) blue and black sample, respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
fabric, liberated cotton fiber, and purified cotton fiber from the samples. As shown in the images, the untreated samples (Fig. (5 A, E)) were coated by black and blue textile dyes. At the end of leaching process, after breakage of chemical bonds between fabric and textile dye layer by acid the dyes were removed, and the surface of the samples became bare. The color of the fabric changed to brown, especially for black sample (Fig. (5 B, F)); the dyes contain significant amounts of heavy metals and organic materials (e.g. iron and nickel) and while the metals are easily dissolved, the organic part of dyes are not easily removed by acid, what causes the change of the color to brown (Sandin and Peters, 2018b). The organic part of dyes was dissolved together with polyester by the selected solvent DMSO through breaking the internal van der Waals bonds of the molecules of organic materials; after this step the treated fabric became more white (Fig. (5 C, G)). By applying the bleaching process as final treatment, all remaining organic contaminants were removed from the liberated cotton fibers, then pure cotton fiber was obtained as shown in Fig. (5 D, H).
leaching process in terms of metal dissolution and prove that the recovered materials are not polluted with heavy metals, 2 g of each jeans sample was grinded into fine powder and digested by aqua regia under microwave treatment. After that Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) measurements were used to precisely determine the concentrations of elements in the grinded jeans samples. These results as a reference during the concentration comparison in the next section. All results were summarized in Table 1. Carbon titration was used to check the organic carbon concentration in each sample and ICP spectroscopy was used to detect the presence of metallic components (in particular heavy metals) and their concentrations in the leaching solutions. According to the titration analysis, the original leaching solutions had high concentrations of organic carbon in the range 200–500 mg/L. These values were decreased significantly by adding activated carbon, up to 10–30 mg/L, meaning the activated carbon effectively remove dyes from the acidic solution. Absorption rate was > 88% (according to the concentrations of virgin and regenerated acid). Table 1 shows the heavy metals concentrations (Pb, Cu, Al, Ni, Cr, Fe, and Si) in the pure acid and leached dye solutions from the samples. The ICP measurements showed that the leached solutions were rich in heavy metals, thus the leaching process succeeded in metal removal from the textile samples. Also, ICP results demonstrated that landfilling of such textile waste would cause serious environmental problems related to soil, water pollution etc. In addition, 96.4% of the heavy metals were leached from the selected samples, meaning the recovered materials have high purity and are practically free from heavy metal contamination. Moreover, usage of untreated
3.2. Analysis of the leached solutions Since the treatment was started by leaching process, the analysis began from investigating the output of this process. Fig. 6 shows the images of spent acid, solvent from black/blue samples after completion of all respective treatment steps. As shown, the leaching solution from the black sample was notably darker than from the blue sample, whereas after addition of the activated carbon the color of the solutions became completely black. In order to evaluate the performance of
Fig. 5. Morphology of the waste denim fabric during the leaching, dissolution, and bleaching treatment of the black (A–D) and blue (E–H) samples. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article). 363
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Fig. 6. Photographies of spent and regenerated acid.
3.3. Analysis of the DMSO solution
Table 1 Heavy metals concentrations in control and leached solutions. Sample
Dissolution of the polyester in the treated fabric was the second process in the developed technology and Fig. 8 shows the DMSO solutions received as one of the outputs of treatment process and after leaving the solution overnight for cooling in ambient until the room temperature. According to the figure (A, B), DMSO solutions consisted of two main components - liquid and precipitate fractions. The spent solvent had a transparent brown-yellow color with a very low viscosity, meaning that most of the polyester was precipitated and the color was a result of dye oxidation during the leaching process. Filtration was used to extract the precipitated part followed by regeneration of the solvent (liquid phase) using a rotary evaporator. FTIR was used to analyze the chemical structure of solid residues recovered from solvent, precipitate, and regenerated solvent. The residue was additionally examined in terms of its thermal stability.
Element concentration (mg/L) Pb
Cu
Al
Ni
Pure NHO3 — 0.010 0.015 0.050 Heavy metals concentrations in grinded samples Crushed blue 0.93 9.33 41.86 0.054 sample Crushed black 0.78 65.32 93.37 0.938 sample Heavy metals concentrations in leached solutions Original blue 0.860 8.640 37.77 0.051 Original black 0.630 62.24 92.27 0.875 Average leaching rate (concentrations in leached solutions/ concentrations in grinded samples)
Cr
Fe
Si
0.850
4.570
14.97
1.23
32.8
88.64
1.3657
35.86
67.84
0.960 1.320 96.4%
31.75 34.76
86.56 66.67
textile waste in a role of feedstock for gas and fuel generation can lead to contamination of final products by many of these metals, decreasing the quality and value of the products (Otłowska et al., 2018). After completion of leaching, spent activated carbon was washed with distilled water and dried at 40 °C to reuse it again, thus increase the sustainability in the framework of present experiment. The chemical structure and purity of the regenerated activated carbon as well as raw activated carbon for comparison was examined by FTIR spectroscopy. As shown in FTIR analysis Fig. 7, the raw and regenerated samples had similar vibration band characteristics with five main functional groups found at 3335 cm−l, 3040, cm−l, 2928 cm-1, (1732, 1440) cm−l, and 1012 cm−l resulting from NeH stretching vibration, OeH groups, stretching vibrations of aliphatic groups eCH2, CeO axial deformation, respectively. These functional groups play a significant role in adsorption of contaminant ions. This meaning that the regenerated activated carbon had a high purity. The obtained results correspond to the data of Shu et al. (2017) (Shu et al., 2017). Also, Scanning Electron Microscopy (SEM) images (Fig. 7) showed that the surface features of the regenerated activated carbon were almost the same as for the pure sample, meaning all contaminated components were removed by washing what corresponds to FITR results. A research is in progress to purify the leaching solution by extracting metals and recover the spent water used for washing after leaching and solvent treatment.
3.3.1. Regenerated solvent analysis Fig. 9 illustrates the FTIR spectra of the pure and regenerated solvent from blue and black sample. The spectra indicated that the samples had a high degree of chemical similarity with bands at 1300 and 1426 cm−1 that are assigned to the vibrational peaks of methyl groups in DMSO molecules. Two weak bands at 3428 and 1655 cm−1 were caused by the OH stretching of absorbed water. Bands at 2996 and 2912 cm−1 corresponded to CH3 stretching vibrations of residual DMSO. It was apparent that the solvent did not degrade since obtained readings were practically identical to the literature-described bands of pure DMSO (Wang et al., 2017). This means the rotary evaporator process was sufficient to regenerate high purity DMSO and thus achieve the goals of sustainability concept, having positive economic and environmental effect. 3.3.2. Analysis of the precipitate fraction Fig. 10 shows the FTIR readings of the precipitate after extraction from solvent by filtration. The spectra of blue and black samples showed that the specimens had the same vibrational bands at 3330 cm−l (broadband), 1725 cm-1 (carboxylic end groups of polyester), and 1065 cm-l (phenyl ring deformation and CH2 bending group vibration). These functional groups mean that the precipitated fraction consisted of
Fig. 7. FTIR spectra and SEM images of pure and used activated carbon. 364
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Fig. 8. Photographies of the spent solvent at the end of dissolution process of A) blue, B) black sample, and C) regenerated solvent. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
Fig. 9. FTIR spectra of pure and regenerated DMSO.
Fig. 11. TGA-DTG measurements of the polyester from: A) black, B) blue textile sample. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article). Fig. 10. FTIR spectra of the precipitate of black, blue samples. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
photographies and FTIR spectra of the fibers. As shown in FTIR analysis, the samples had several similar functional groups: CeO, CeH and OeH stretching vibrations at 1016 cm−1, 3027 cm−1, 3364 cm−1, respectively, and SeO bond stretching at 1004–820 cm−1 due to the sulfate groups present on the surface of the treated fiber. These functional groups showed that the cotton was strongly represented in all samples (Gaspar et al., 2014; Memon et al., 2017). Also, in the untreated samples, strong vibrations were observed at 1710 cm−1, 1249 cm−1, and 1124 cm−1. These vibrations are associated with dyes, which can be Sulfur and Indigo dyes that are used by industry during the production of black and blue jeans (Lee et al., 2013). This means that leaching, dissolution, and bleaching successfully removed all dyes and any contaminated materials and recovered fiber was composed of high purity cotton. Finally, TGA-DTG was used to investigate degradation degree and thermal stability of the obtained fibers as shown in Fig. 13. Both samples were similar in terms of thermal degradation features with weight loss ˜93% in the temp. range 380 °C–470 °C. As shown in TGA-DTG analysis, degradation was occurring in five stages: water evaporation,
polyester (Kusuktham, 2010). Fig. 11 shows thermal degradation and stability trends of the precipitate analyzed by Thermogravimetric/Derivative Thermogravimetric analysis (TGA-DTG). As is evident, both of the samples had similar decomposition mechanisms observed in the range 80 °C–365 °C and nearly identical total mass loss. The results are easily comparable with results reported in the literature for raw and modified polyester (decomposition range 70 °C–320 °C, weight loss (˜82%) (Rahimi et al., 2011). As can be seen, the proposed technology can provide dissolution of the polyester and its extraction from different grades of waste jeans with high thermal stability. 3.4. Recovered fiber analysis The chemical structure of the fiber samples (before and after the treatment) was investigated by FTIR spectroscopy. Fig. 12 shows the 365
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Fig. 14. Boundaries of the new strategy.
technologies, the developed strategy was assessed based on the recycling rate, profitability, carbon footprint, and sustainability. Quantification of profits could encourage entrepreneurs in adopting circular economy principles in practice and increase the amount of competitive sustainable technologies in the market. Therefore, recovery of cotton fiber from textile waste represents a significant economic opportunity in the circular economy framework. 3.5.1. Recycling rate and sustainability evaluation Fig. 14 shows the flowsheet of the developed strategy, including the consumables and electrical power required for all treatment stages, while Table 2 illustrates the rates of secondary raw material (Polyester and Cotton fibers) recycling and regeneration and consumables (acid and solvent) regeneration in the technology, determined based on average the mass balances of recycled denim fabric to increase the accuracy of the final results. As shown, the suggested strategy has a high recycling rate ˜93% - this value is resultant from all treatments including washing process. Sustainability of the present strategy was evaluated based on the regeneration rates of the consumable chemicals; acid and solvent can be regenerated with high performance, while the chemicals used for bleaching process should be reconsidered to find more sustainable and green alternative. This part is researched by authors in order to find a sustainable bleaching process. The share of cotton fiber was 77 wt.% of recovered materials after bleaching and washing steps, while polyester fraction represented 16.2 wt.%.
Fig. 12. Photographies and FTIR spectra of the original textile and cotton fibers recovered from black, blue samples. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
solvent evaporation, organic residue decomposition (dyes or polyester impurities), primary decomposition of fiber, and char devolatilization/ decomposition. Due to the fact that the samples were left for overnight for drying, most of the water evaporated and only very small amount remained besides the humidity from ambient. Most of the solvent was extracted during the treatment, thus amount of evaporated solvent was also very low. Based on the weight loss during the primary stage, especially for the black sample, it can be concluded that the recovered fibers had thermal stability closer to raw cotton and can be used as a new source of cotton after spinning using wet or melt spinning limited by minimum degradation (Karthik and Murugan, 2013; Rajkumar et al., 2016).
3.5.2. Economic performance of the developed strategy The economic performance of the developed strategy was evaluated based on the input costs (Chemicals and Electric Energy) and two output costs (Purified cotton and Polyester) presented in Fig. 14. Since some studies were developed to regenerate HNO3 and DMSO using membrane and rotary evaporator, cost of these agents was not taken account during the calculations (Yang et al., 2017). The total electrical energy required for treating 1 ton of denim fabric waste and regenerate spent solvent using the developed strategy was calculated taking into account the capacity of the developed reactor (5 kg) and total treatment
3.5. Recycling rate and profitability assessment of the new strategy In order to support companies involved in reverse logistic chains during the evaluation of investments in textile waste recycling
Fig. 13. TGA-DTG analysis of the fibers from A) black and B) blue specimens. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article). 366
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Table 2 Recycling, Regeneration rates, and economic performance of the proposed strategy. Process
Leaching Dissolution Bleach
Treated substrate average weight (g) Average weight before treatment
Average weight after treatment
295 284 276
284 276 274
Average recycling rate (%) 0.964 × 0.972 × 0.993
Recycling rate (%)
96.4 97.2 99.3 93%
Sustainability evaluation Chemical material
Regeneration Rate (%)
Acid DMSO NaOCl, HCl
99.4 99.5 ——
time as illustrated in Eqs. ((1)–(5)). The energy consumed in evaporation process was estimated as 32 kW h/ 1 t of fabric waste. Finally, the profitability assessment of the developed strategy revealed that the profits from technology can reach up to 1466 $/ tonne of waste (price of recovered materials: Cotton – 2000 $/ tonne, Polyester - 1000 $/ tonne; price of consumables: Activated carbon - 2$/kg, Electricity - 0.23 $/KWh [Alibaba.com], (Anon., 2019e)) as illustrated in Eq. (5).
Fig. 15. System boundaries of the developed strategy scenarios.
Total treatment time = leaching time (0.5 h.) + dissolution time (8 h.) + bleaching time (2 h.) = 10.5 h. (1)
Energy consumption of 5 kg of fabric waste = 74
calculated based on the energy consumption during the treatment and amount of recovered metals of 1 ton of textile waste. Based on these values, applying the developed strategy on an industrial scale gives a possibility to decrease GGE by -1,534 kg CO2-eq/ tonne. Despite the fact that preliminary environmental assessment (Based on GHG factor) of the developed strategy showed high performance (-1,534 kg CO2-eq/ tonne), it is very important to assess more environmental impact categories (e.g. Climate Change, Human Toxicity, Particulate Matter Formation, Environmental Toxicity, Land Occupation, and Fossil fuels Depletion) as mentioned in detailed ISO standard doctrines, such as (ISO-14067, 2013), which is characterized by a specific requirement, accuracy, strength, and transparency (Garcia and Freire, 2014). According to the specified protocol, the analysis should be conducted on one ton of feedstock (textile waste in the present research) as a Functional Unit (FU) taking into account collection, transportation, and sorting practices. In addition, based on the Cradleto-Gate approach, all input processes should be simulated to cover plant requirements in terms of auxiliaries and energy as well as all outputs from the treatment system such as mass/energy recovery and releases into the environment (Huang et al., 2017). Fig. 15 shows the physical boundaries of the developed strategy based on the Cradle-to-Gate concept, including average weight of the recovered secondary raw materials and electricity consumption. As shown in the layout, the emissions (into air, water, and soil) of the technology and production of solid wastes were represented only by wastewater, while the output was represented by cotton and polyester. Regarding the heavy metals, which ate considered a very critical point and have a major effect on the environmental impacts (Sandin and Peters, 2018c; Anon., 2019f), the recovery of heavy metals under research by our research group using pH control. Therefore, the environmental impacts would be calculated
J × 3600 × 10.5 s (2)
= 2797200 J (0.777 KWh) Energy consumption for 1 tonne of fabric waste
(3)
= (0.777 KWh × 1000 kg )/5 = 155 KWh
Total Energy cost for 1 tonne = (155 KWh + 32 KWh) × 0.23
$ = 43 $ KWh (4)
Profitability per tonne = [Output cost – Electricity cost – Raw material cost] = [0.768 × 2000$ (Cotton)+ 0.162 × 1000 $ (Polyester)] – 43 $ – 83 $ = 1466 $ (5) 3.5.3. Environmental assessment of the new strategy The Life Cycle Assessment (LCA) is a standardized global approach recognized as a valuable screening tool to support basic and applied researches in the field of environmental studies and sustainable industries. Specifically, its application to the end-of-life management of textile products represents a consolidated way to evaluate improvements, reached because of a process implementation, or to compare several viable treatment solutions in terms of environmental footprint (Chen et al., 2018). A life cycle analysis was applied to determine environmental performances of the new strategy in terms of Greenhouse Gas (GHG) emissions, according to ISO standard 14040 and based on the average values reported in the literature (Turner et al., 2015). Table 3 shows GHG emissions of the developed strategy, which were Table 3 GHGE from the treated cotton fiber using the new strategy. Recovered material/Energy
Kg or kWh/ tonne of textile waste
Average (kgCO2-eq/ tonne or 1000 kW h) (Agarwal and Jeffries, 2013; EEA, 2014; Zamani et al., 2015)
Polyester 162 −4,060 Cotton fiber 768 −1,500 Electricity 187 +1475 CO2-eq reduction by the developed strategy (kgCO2-eq/ tonne)
kgCO2-eq / tonne of textile waste −658 −1,152 +276 −1,534
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Fig. 16. The developed recycling technology within the sustainability system.
without considering the heavy metals, leading to results lacking precision and credibility. Accordingly, the authors merely present the physical boundaries of the developed strategy in the present research, while the full LCA of strategy, including all impacts will be evaluated using SimaPro software after heavy metal extraction and wastewater treatment to ensure the developed strategy is integrated and sustainable. The integrated-sustainable technology will be compared with three alternative textile waste treatment scenarios: incineration, pyrolysis, and landfilling (as a worst waste treatment solution), which require additional research and estimation as well (Silva et al., 2019; Li and Feng, 2018). Finally, the recovered materials, especially cotton can be used as a new source of material for facing the high demand and lack of supply for cotton and thus achieve the core principles of Circular Economy for textile waste (Fig. 16). 4. Conclusions In the context of facing a high demand for cotton and lack of its supply, in this research, the authors developed a sustainable strategy to recover cotton from textile waste to make it a new source of material taking into account the quality of product and economic issues. The new strategy is composed of three main processes: leaching using Nitric Acid, dissolution using Dimethyl Sulfoxide, and bleaching by Sodium Hypochlorite and dilute Hydrochloric Acid dosage, respectively. These processes were employed to remove textile dyes followed by dissolving the polymeric part, then the cotton fiber was liberated. The pilot scale experiments showed that the developed strategy can help achieve selfsufficiency in raw cotton fiber for many and accelerate transition to Critical Economy; recovery rate, economic performance, and carbon footprint of the technology were estimated as 93%, 1466 $/ tonne, and -1,534 kg CO2-eq/ tonne. The authors closed the loop of the strategy by regenerating the spent acid and solvent as well as extracting the polyester, thus the proposed strategy can be considered highly sustainable. References Agarwal, B., Jeffries, B., 2013. Cutting Cotton Carbon Emissions: Findings from Warangal, India. http://awsassets.wwfindia.org/downloads/wwf___cotton_carbon_emission.pdf. https://www.statista.com/statistics/263055/cotton-production-worldwide-by-topcountries/. https://www.grandviewresearch.com/industry-analysis/cellulose-fibers-market. https://www.sei.org/events/used-textiles-waste-or-value/. https://wolkat.com/en. Energy Price Statistics. (Accessed 1 November 2017). http://ec.europa.eu/eurostat/ statistics-explained/index.php/Energy_price_statistics. Environmental impacts of the use of bottom ashes from municipal solid waste incineration: A review. Bansal, A., Illukpitiya, P., Tegegne, F., Singh, S.P., 2016. Energy efficiency of ethanol production from cellulosic feedstock. Renew. Sustain. Energy Rev. https://doi.org/ 10.1016/j.rser.2015.12.122. Byrne, F.P., Jin, S., Paggiola, G., Petchey, T.H.M., Clark, J.H., Farmer, T.J., Hunt, A.J., Robert McElroy, C., Sherwood, J., 2016. Tools and techniques for solvent selection: green solvent selection guides. Sustain. Chem. Process. https://doi.org/10.1186/ s40508-016-0051-z. Chapagain, A.K., Hoekstra, A.Y., Savenije, H.H.G., Gautam, R., 2006. The waterfootprint of cotton consumption: an assessment of the impact of worldwideconsumption of
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Full length article
A new strategy for using textile waste as a sustainable source of recovered cotton
T
Samy Yousefa,d, , Maksym Tatariantsb, Martynas Tichonovasb, Zahid Sarwarb, Ilona Jonuškienėc, Linas Kliucininkasb ⁎
a
Department of Production Engineering, Faculty of Mechanical Engineering and Design, Kaunas University of Technology, LT-51424 Kaunas, Lithuania Department of Environmental Technology, Faculty of Chemical Technology, Kaunas University of Technology, LT-50254 Kaunas, Lithuania c Department of Organic Chemistry, Faculty of Chemical Technology, Kaunas University of Technology, LT-50254 Kaunas, Lithuania d Department of Production Engineering and Printing Technology, Akhbar Elyom Academy 6th of October, Egypt b
ARTICLE INFO
ABSTRACT
Keywords: Cotton Textile waste Recycling Cotton fiber recovery Polyester Dimethyl sulfoxide
Cotton is one of the primary resources in many modern industries and with increasing demand rates the current challenge is to find other sources of cotton production with lower prices and higher quality whereas cotton produced only by agriculture is not sufficient for these needs. This is focused on developing a new strategy to make the textile waste a new sustainable source of recovered cotton to face this shortage. This strategy is summarized as development of a chemical technology using sustainable and commercial chemicals to recover cotton from waste textile. The technology consists of three sequential processes: a) textile dye leaching using Nitric Acid as a pretreatment of the original waste, b) dissolution process using Dimethyl Sulfoxide (DMSO) as the main treatment to dissolve the organic materials from the treated fabric, including polyester and remaining organic part from textile dyes, and c) bleaching process using sodium hypochlorite and diluted hydrochloric acid for final recovered cotton purification. Preliminary experiments were performed at a laboratory scale to determine the optimum conditions on a few grams of two different types of denim fabric. To simulate the pilot scale, the main experimental work was conducted for full-size blue and black waste jeans trousers in a developed reactor with capacity 1 kg based on the preliminary experimental results. To close the lifecycle loop of the suggested strategy, rotary evaporator was used to extract the polymeric part and regenerate the spent DMSO, while the acid was regenerated by activated carbon. Additionally, suggestions on treatment of the water contaminated by acid and solvent (obtained after washing) were given. Morphology, thermal behavior, and chemical structure of the recovered cotton, regenerated acid, solvent, and recovered polyester were investigated. Based on the recycling rate (93%), profitability (1466 $/ tonne), greenhouse gas emissions (-1,534 CO2-eq/ tonne), and sustainability assessment, the developed strategy can be seen as a high-potential approach for recovery of cotton.
1. Introduction
situation is further complicated since some of the leading cotton-producing governments have begun to reduce the size of cultivated cotton due to the severe shortage of water resources - cultivation of cotton requires huge amounts of water, consuming 2.6% of global water supply (Chapagain et al., 2006). Moreover, strain on agricultural land is further increased due to the terrible increase in the population size (Chapagain et al., 2006; Oldenborg and Steinman, 2019). On the other hand, artificially produced cellulose does not have the same properties as the cellulose extracted from natural cotton (Kobayashi, 2005). Based on that, the current challenge is to find the other sources for cotton production with low price and sufficient quality. Textile waste recycling
Cellulose is the main component of cotton and according to international statistics in 2017/2018 the world's leading cotton producing countries (India, China, USA, Brazil, Pakistan, Australia, Turkey, Uzbekistan, Turkmenistan, and Burkina Faso) produced around 23.6 million tonnes of cotton; most of this amount of natural fibers was consumed by textile and clothing industry (Anon., 2019a; EsteveTurrillas and de la Guardia, 2017). According to the forecasts, size of textile industry will increase by 20–30% in 2025, requiring governments seek new sources of cellulose production (Anon., 2019b). The
⁎ Corresponding author at: Department of Production Engineering, Faculty of Mechanical Engineering and Design, Kaunas University of Technology, LT-51424 Kaunas, Lithuania. E-mail address: [email protected] (S. Yousef).
https://doi.org/10.1016/j.resconrec.2019.02.031 Received 28 November 2018; Received in revised form 20 February 2019; Accepted 21 February 2019 0921-3449/ © 2019 Elsevier B.V. All rights reserved.
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is one of the essential solutions for tackling this issue and achieving cotton self-sufficiency in many countries as the textile waste mass generated worldwide each year is estimated in millions of tons, while cotton represents 40–50% of its weight on average, reaching > 84% in some of the cases, particularly in waste jeans textile (Esteve-Turrillas and de la Guardia, 2017; Sandin and Peters, 2018a). However, textile waste has not yet been optimally exploited due to the difficulties in certain management and technical aspects during collection, sorting, recycling, and purification of recovered materials. Therefore, the Estonian government organized event “Used textiles: waste or value?” for this purpose with participation of many decision makers and investors to find a serious solution for these aspects (Anon., 2019c). The participants recommended that the life cycle of textile should be transferred from a linear economy to a circular economy by linking these stages together. It should be mentioned that recently a group of researchers worked on solving the textile waste issues and established specific mechanisms for its collection through, firstly, installation of booths and boxes with coding or serial number. The collected waste was sorted manually or semi-automatic/fully automatic based on the product type, manufacturing methods, fiber composition and a product condition assessment (by 17 criteria into 25 categories) followed by recycling process (Luiken and Bouwhuis, 2015; Nørup et al., 2018). Recycling is also a prospective way to decrease the amount of greenhouse gas emissions generated by textile industry. However, in this type of waste cotton is usually mixed with polyester, textile dyes, and some organic materials, making it hard to recover high quality cotton and maintain acceptable recovery cost (Fortuna and Diyamandoglu, 2017). Thus, landfilling and incineration are considered the optimum ways for disposal of such waste. Corroborating that fact, the latest EU reports showed that the textile waste represented ˜6% of the overall municipal solid waste and accounted for more than 3% of the greenhouse gas emissions in the EU (Hu et al., 2018a). In view of the current textile recycling practices, it is clear that most of these practices are focused on using the textiles as a feedstock for energy production, including production of gas, biogas (ethanol), and thermal energy by using combustion or chemical reactions (Gholamzad et al., 2014; Nunes et al., 2018; Bansal et al., 2016; Ge and Li, 2018; Hasanzadeh et al., 2018). Some of these technologies are started by pretreatment to remove textile dyes and polyester and thus improve the yield and product quality by alkaline solutions (e.g. KOH, NaOH), Nmethylmorpholine-N-oxide, phosphate solutions, hydrochloric acid, and other reagents to facilitate the digestion of cotton-containing textiles to avoid generation of waste after all treatment steps. In order to raise the process efficiency, biological reactions for production of clean energy from textile waste were recently used (Hu et al., 2018b). Although the results are promising, the technique requires many additional studies for application at the industrial level while energy production means losing the value of potentially recoverable cotton. Therefore, other researchers selected different direction and attempted to produce glucose from textile waste; the main drawbacks of their approach were many process steps required and a very long reaction time up to 7 weeks (Wang et al., 2018). One more research group focused on recovery of cellulose from textile waste. Fangbing et al. (2015) used dissolution process by ionic liquid 1-allyl-3-methylimidazolium chloride ([AMIM]Cl) to separate cellulose and nylon 6 from waste nylon/cotton blended fabrics (Lv et al., 2015). By this approach, cotton can be separated as cellulose/[AMIM]Cl solution that needs more steps to regenerate cellulose from the liquid phase. In addition, there were no data about textile dyes in the samples and if the steps were taken to properly remove them what is crucial for textile waste recycling as the dyes can contain various heavy metals and organic compounds that pose a threat to public health and environment if left without attention (Khamparia and Jaspal, 2017). Wolkat Circular Textile Recycling is a major company working in the production of textile fabric from textile waste that uses grinding and washing of waste with water without chemical treatment. In spite of the success of this technique, it was
found difficult to control the color of the product and its chemical structure, which varies according to the type of feedstock (Anon., 2019d). Also, this technique requires large amounts of water to remove pigments, therefore producing large amounts of wastewater. Leaching process using different acids, including nitric (HNO3), is used in metal recovery and extraction from waste (Lynn et al., 2018; Li et al., 2018). Therefore, leaching treatment was used by authors to remove heavy metals from textile dyes and obtain treated fabric (cotton fiber and polyester), contaminated only by a small amount of organic materials remaining from textile dyes. Also, during the leaching, it is important to use HNO3 with concentration < 68.4%, since higher concentration of nitric acid can cause irreversible changes in the chemical structure of cellulose through it nitration, Knecht compound formation, etc. (Gert et al., 2000), thus instead of pure cotton, a combination of modified and unmodified fibers can be produced. Therefore, to selectively remove textile dyes without altering the structure of cotton, the textile was processed by 60% HNO3 at mild temperature. Solvent treatment is a typical approach for dissolving polymers and other organic compounds from different wastes with similar structure, such as WPCBs and organic waste (Tatariants et al., 2017; Ozturk et al., 2018). Selection of solvent was the critical point of the dissolution process to avoid or reduce the degradation degree of extracted cotton/cellulose. Solvents, capable of reacting with cellulose can be classified into three types: organic solvents, aqueous solvents, and ionic liquids (Liebert, 2010; Ghasemi et al., 2017; Peng et al., 2017). Among the commercial solvents, Dimethyl Sulfoxide (DMSO) is classified as an organic solvent, ecofriendly and sustainable solvent compared to the other organic solvents like Dimethylformamide, suitable for dissolving polyester and organic residues remaining from dyes in the waste fabrics. Also, DMSO has a high boiling point compared to the other solvents (Byrne et al., 2016). Therefore, DMSO was used to extract polyester from the waste jeans after pretreatment by acid for dye removal, thus liberating cotton fibers that were later purified using bleaching process at pilot scale. The economic benefits of the developed strategy were studied to assess its industrial potential. 2. Experimental 2.1. Materials and textile waste sample preparation Waste jeans were provided by a local clothing repair shop in Lithuania. The waste jeans were chosen depending on the textile dye color: black 100% cotton jeans and blue 80/20 cotton/polyester jeans. Dimethyl Sulfoxide (DMSO) solvent and other reagents for leaching, dissolution, and purification processes were purchased from Sigma-12 Aldrich Corp. To prepare the samples for separation, all the metal and plastic components like rivets and stickers were removed from the samples by suitable mechanical tools. After that, the samples were cleaned by water to remove any contaminants and were dried at room temperature. Later, the dried jeans were shredded into small 50150 mm2 sized pieces. Total weight of the dried samples was measured by laboratory balances (560 g for black and 580 g for blue sample). The weighted samples were divided into two groups: 20 g from each sample for preliminary experiments and the remaining weight (540 g black sample and 560 g blue sample) for the main pilot scale experiments. 2.2. Preliminary experiments Initial tests were conducted on 20 g of waste jeans in ultrasonic bath with 1 L capacity to find the optimal leaching and dissolution conditions (as the needed information is not provided in literature for such specific processes). Preliminary experiments were performed at varying concentrations of HNO3 (0.5–1.0 - 1.5–2 M) at 50 °C and, according to the results, 1.0 M and 1.5 M HNO3 was sufficient to dissolve dyes from blue and black samples with average treatment time 20 min. The optimal solvent treatment conditions were found as follows: 1 g samples of 360
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Fig. 1. Waste denim fabric before and after being subjected to leaching and dissolution treatments: A, E) untreated samples, B, F) bare fabric, C, G) treated fiber at the middle of dissolution process, and C, G) treated fiber at the end of dissolution process.
two jeans types were treated at a constant temperature 50 °C in the range 10 to 80 ml of solvent with step 10 ml. Minimal dissolution time was found as the time needed to fully liberate cotton from polyester and other organic components. The experiments showed that full optimal separation of black sample could be reached after 7 h. with 40 ml of solvent whereas the blue sample required 9 h. and 60 ml. of solvent. Fig.1 shows the images of untreated/treated black (Fig. 1(A–D)) and blue (Fig. 1(E–H)) samples at different periods.
feedstock or from solvent and chemicals remaining or attached on the reactor walls and ease the cleaning process), attached to the main body through two rotary hinges (indicated by orange circles) to give the chamber possibility to move freely when the body is filled with vibrating fluid (distilled water). At the bottom of the reaction chamber, there are four outlets with valves connected to four separate tanks used for storing the reaction solutions. Two of the tanks are used for spent acid and solvent, while the other two are used for spent water obtained after washing the treated denim material after leaching and dissolution. The main reason behind the implementation of separate storage vessels for the spent water was the fact that water after the leaching is contaminated by reactive acid, whereas water after the dissolution is contaminated by much more safe eco-friendly solvent, thus these effluents require different handling. Inside the reaction chamber there is a fixed plastic basket with sieve at the bottom used for filtration and washing of the fabric and cotton fibers after all treatment stages. The upper part of the reactor is closed by cover to prevent any leakage of harmful fumes. There are two feeders on the back side of the reactor: first one for feeding solvent or acid, while the second one is designed for taking samples from reaction
2.3. Pilot scale experiments The main experiments were done for the remaining samples (540 g black jeans and 560 g blue jeans) in a developed reactor at the conditions obtained from preliminary experiments. 2.3.1. Design of the pilot scale reactor Fig. 2 shows the full design and image of the developed reactor; as shown in the sketch, the outer frame of 2 L ultrasonic bath was used as a main body of the reactor. A cylindrical glass reaction chamber is installed inside the main frame (to avoid any waste particles from
Fig. 2. A) Full design of the developed reactor and B) Image of the developed reactor. 361
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Finally, the cover was opened to extract the plastic basket with recovered fibers from the reactor and begin the refining of the fibers and the regeneration of spent chemicals. The cotton fibers were bleached with Sodium Hypochlorite (the chlorine content is about 1.5% from the weight of cotton) and dilute hydrochloric acid (˜2% from the weight of cotton), (Zhou et al., 2016) to remove the remaining impurities under soundwave treatment for 2 h. at 40 °C. To close the loop of the technology, used chemicals (Acid, solvent) were regenerated using a rotary evaporator at 150 °C and activated carbon with mass ratio 20 ml (solution): 5 g (activated carbon).
solution for investigation. There is one more feeder in the right side of the reactor for feeding water to compensate the water that evaporates during the treatment. In addition, there is a spindle with a pressure plate supported by a bearing in the reactor cover used as a manual press at the end of leaching, dissolution, and washing stages to effectively separate the spent solvent, acid, or water from solid samples through compressing the pulp and directing the spent solution to its tank by opening the specified valve. The tanks are connected with four regeneration units for acid, solvent and spent acidic/solvent water. The acid regeneration unit is a glass flask with capacity 2 L that contains activated carbon, absorbing the heavy metals and organic dyes from the acid within several days (based on the jeans type). Rotary evaporator with capacity 2 L is used as a solvent regeneration unit to extract the polymeric part from the spent solvent at 150 °C. Regarding the spent water, in the implemented system there were units only to collect it, and at the end of this article the authors suggested some techniques to treat the spent water based on the approaches used in the literature. Finally, all connected components are tightly sealed by a silicone sealant to avoid leakage of any gases or other substances.
3. Results and discussions Fig. 4 shows images of cotton fiber obtained after the bleaching process. Optical Microscope was used for analysis of morphology, Thermogravimetric Analysis (TGA) – for determining thermal properties, and Fourier-Transform Infrared Spectroscopy (FTIR) – for finding the chemical structure of the fibers and to investigate the mechanism of processes taking place at all technology stages. Chemical structure and thermal behavior of the extracted polymers were investigated in order to determine their types, thus evaluate the recycling rate as well as its economic performance. In addition, the chemical properties of the spent acid, solvent were analyzed to evaluate the sustainability of the suggested technology.
2.3.2. Waste textile separation procedure using the developed reactor As mentioned above, the approach developed during the preliminary experiments consisted of two main steps: leaching using acid and dissolution using DMSO; both main steps are followed by water washing. To apply the same concept on the pilot scale using the new reactor, the reaction chamber containing waste textile was filled with acid from the side feeder with solid to liquid ratio 1:50 and samples were treated for 20 min. at 50 °C. At the end of this process, the valve of the spent acid tank was opened to withdraw the spent acid by compressing the pulp and the tank was locked again. To clean the obtained fabric and remove the remaining acid, water was added into the chamber and the spent water was collected afterwards in the second tank by using the manual press again. To dissolve the polyester and other organic contaminants in the textile, the reaction chamber loaded by fabric was filled with solvent (according to the optimum solid to liquid ratio) and dissolution process was performed at 50 °C for 6 h. for blue and 10 h. for black sample. The spent solvent was collected in the third tank and spent solvent-containing water was collected in the last tank as shown in Fig. 3.
3.1. Separation mechanism Original cotton is usually characterized by its bright white color. Once the cotton fiber is colored by textile dyes and mixed with synthetic fibers, its color changes according to the dye color (black and blue in the current case). This change in matrix color is difficult to observe by SEM because the images obtained by SEM are monochromatic(greyscale). USB Microscope (USB 8 LED Light Digital Microscope Endoscope Camera Magnifier) has a color imaging feature, which eases observation and verification of fiber layer separation as well as verification of the cotton structure. Based on this, the morphology of denim fabric was investigated by using the color imaging feature of USB microscope. Fig. 5 shows the photographies of the untreated jeans, treated
Fig. 3. A schematic drawing of the textile separation using the developed reactor: (A–C) Leaching process and (D–F) Dissolution process. 362
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Fig. 4. Photographies of the cotton obtained from A, B) blue and black sample, respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
fabric, liberated cotton fiber, and purified cotton fiber from the samples. As shown in the images, the untreated samples (Fig. (5 A, E)) were coated by black and blue textile dyes. At the end of leaching process, after breakage of chemical bonds between fabric and textile dye layer by acid the dyes were removed, and the surface of the samples became bare. The color of the fabric changed to brown, especially for black sample (Fig. (5 B, F)); the dyes contain significant amounts of heavy metals and organic materials (e.g. iron and nickel) and while the metals are easily dissolved, the organic part of dyes are not easily removed by acid, what causes the change of the color to brown (Sandin and Peters, 2018b). The organic part of dyes was dissolved together with polyester by the selected solvent DMSO through breaking the internal van der Waals bonds of the molecules of organic materials; after this step the treated fabric became more white (Fig. (5 C, G)). By applying the bleaching process as final treatment, all remaining organic contaminants were removed from the liberated cotton fibers, then pure cotton fiber was obtained as shown in Fig. (5 D, H).
leaching process in terms of metal dissolution and prove that the recovered materials are not polluted with heavy metals, 2 g of each jeans sample was grinded into fine powder and digested by aqua regia under microwave treatment. After that Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) measurements were used to precisely determine the concentrations of elements in the grinded jeans samples. These results as a reference during the concentration comparison in the next section. All results were summarized in Table 1. Carbon titration was used to check the organic carbon concentration in each sample and ICP spectroscopy was used to detect the presence of metallic components (in particular heavy metals) and their concentrations in the leaching solutions. According to the titration analysis, the original leaching solutions had high concentrations of organic carbon in the range 200–500 mg/L. These values were decreased significantly by adding activated carbon, up to 10–30 mg/L, meaning the activated carbon effectively remove dyes from the acidic solution. Absorption rate was > 88% (according to the concentrations of virgin and regenerated acid). Table 1 shows the heavy metals concentrations (Pb, Cu, Al, Ni, Cr, Fe, and Si) in the pure acid and leached dye solutions from the samples. The ICP measurements showed that the leached solutions were rich in heavy metals, thus the leaching process succeeded in metal removal from the textile samples. Also, ICP results demonstrated that landfilling of such textile waste would cause serious environmental problems related to soil, water pollution etc. In addition, 96.4% of the heavy metals were leached from the selected samples, meaning the recovered materials have high purity and are practically free from heavy metal contamination. Moreover, usage of untreated
3.2. Analysis of the leached solutions Since the treatment was started by leaching process, the analysis began from investigating the output of this process. Fig. 6 shows the images of spent acid, solvent from black/blue samples after completion of all respective treatment steps. As shown, the leaching solution from the black sample was notably darker than from the blue sample, whereas after addition of the activated carbon the color of the solutions became completely black. In order to evaluate the performance of
Fig. 5. Morphology of the waste denim fabric during the leaching, dissolution, and bleaching treatment of the black (A–D) and blue (E–H) samples. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article). 363
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Fig. 6. Photographies of spent and regenerated acid.
3.3. Analysis of the DMSO solution
Table 1 Heavy metals concentrations in control and leached solutions. Sample
Dissolution of the polyester in the treated fabric was the second process in the developed technology and Fig. 8 shows the DMSO solutions received as one of the outputs of treatment process and after leaving the solution overnight for cooling in ambient until the room temperature. According to the figure (A, B), DMSO solutions consisted of two main components - liquid and precipitate fractions. The spent solvent had a transparent brown-yellow color with a very low viscosity, meaning that most of the polyester was precipitated and the color was a result of dye oxidation during the leaching process. Filtration was used to extract the precipitated part followed by regeneration of the solvent (liquid phase) using a rotary evaporator. FTIR was used to analyze the chemical structure of solid residues recovered from solvent, precipitate, and regenerated solvent. The residue was additionally examined in terms of its thermal stability.
Element concentration (mg/L) Pb
Cu
Al
Ni
Pure NHO3 — 0.010 0.015 0.050 Heavy metals concentrations in grinded samples Crushed blue 0.93 9.33 41.86 0.054 sample Crushed black 0.78 65.32 93.37 0.938 sample Heavy metals concentrations in leached solutions Original blue 0.860 8.640 37.77 0.051 Original black 0.630 62.24 92.27 0.875 Average leaching rate (concentrations in leached solutions/ concentrations in grinded samples)
Cr
Fe
Si
0.850
4.570
14.97
1.23
32.8
88.64
1.3657
35.86
67.84
0.960 1.320 96.4%
31.75 34.76
86.56 66.67
textile waste in a role of feedstock for gas and fuel generation can lead to contamination of final products by many of these metals, decreasing the quality and value of the products (Otłowska et al., 2018). After completion of leaching, spent activated carbon was washed with distilled water and dried at 40 °C to reuse it again, thus increase the sustainability in the framework of present experiment. The chemical structure and purity of the regenerated activated carbon as well as raw activated carbon for comparison was examined by FTIR spectroscopy. As shown in FTIR analysis Fig. 7, the raw and regenerated samples had similar vibration band characteristics with five main functional groups found at 3335 cm−l, 3040, cm−l, 2928 cm-1, (1732, 1440) cm−l, and 1012 cm−l resulting from NeH stretching vibration, OeH groups, stretching vibrations of aliphatic groups eCH2, CeO axial deformation, respectively. These functional groups play a significant role in adsorption of contaminant ions. This meaning that the regenerated activated carbon had a high purity. The obtained results correspond to the data of Shu et al. (2017) (Shu et al., 2017). Also, Scanning Electron Microscopy (SEM) images (Fig. 7) showed that the surface features of the regenerated activated carbon were almost the same as for the pure sample, meaning all contaminated components were removed by washing what corresponds to FITR results. A research is in progress to purify the leaching solution by extracting metals and recover the spent water used for washing after leaching and solvent treatment.
3.3.1. Regenerated solvent analysis Fig. 9 illustrates the FTIR spectra of the pure and regenerated solvent from blue and black sample. The spectra indicated that the samples had a high degree of chemical similarity with bands at 1300 and 1426 cm−1 that are assigned to the vibrational peaks of methyl groups in DMSO molecules. Two weak bands at 3428 and 1655 cm−1 were caused by the OH stretching of absorbed water. Bands at 2996 and 2912 cm−1 corresponded to CH3 stretching vibrations of residual DMSO. It was apparent that the solvent did not degrade since obtained readings were practically identical to the literature-described bands of pure DMSO (Wang et al., 2017). This means the rotary evaporator process was sufficient to regenerate high purity DMSO and thus achieve the goals of sustainability concept, having positive economic and environmental effect. 3.3.2. Analysis of the precipitate fraction Fig. 10 shows the FTIR readings of the precipitate after extraction from solvent by filtration. The spectra of blue and black samples showed that the specimens had the same vibrational bands at 3330 cm−l (broadband), 1725 cm-1 (carboxylic end groups of polyester), and 1065 cm-l (phenyl ring deformation and CH2 bending group vibration). These functional groups mean that the precipitated fraction consisted of
Fig. 7. FTIR spectra and SEM images of pure and used activated carbon. 364
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Fig. 8. Photographies of the spent solvent at the end of dissolution process of A) blue, B) black sample, and C) regenerated solvent. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
Fig. 9. FTIR spectra of pure and regenerated DMSO.
Fig. 11. TGA-DTG measurements of the polyester from: A) black, B) blue textile sample. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article). Fig. 10. FTIR spectra of the precipitate of black, blue samples. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
photographies and FTIR spectra of the fibers. As shown in FTIR analysis, the samples had several similar functional groups: CeO, CeH and OeH stretching vibrations at 1016 cm−1, 3027 cm−1, 3364 cm−1, respectively, and SeO bond stretching at 1004–820 cm−1 due to the sulfate groups present on the surface of the treated fiber. These functional groups showed that the cotton was strongly represented in all samples (Gaspar et al., 2014; Memon et al., 2017). Also, in the untreated samples, strong vibrations were observed at 1710 cm−1, 1249 cm−1, and 1124 cm−1. These vibrations are associated with dyes, which can be Sulfur and Indigo dyes that are used by industry during the production of black and blue jeans (Lee et al., 2013). This means that leaching, dissolution, and bleaching successfully removed all dyes and any contaminated materials and recovered fiber was composed of high purity cotton. Finally, TGA-DTG was used to investigate degradation degree and thermal stability of the obtained fibers as shown in Fig. 13. Both samples were similar in terms of thermal degradation features with weight loss ˜93% in the temp. range 380 °C–470 °C. As shown in TGA-DTG analysis, degradation was occurring in five stages: water evaporation,
polyester (Kusuktham, 2010). Fig. 11 shows thermal degradation and stability trends of the precipitate analyzed by Thermogravimetric/Derivative Thermogravimetric analysis (TGA-DTG). As is evident, both of the samples had similar decomposition mechanisms observed in the range 80 °C–365 °C and nearly identical total mass loss. The results are easily comparable with results reported in the literature for raw and modified polyester (decomposition range 70 °C–320 °C, weight loss (˜82%) (Rahimi et al., 2011). As can be seen, the proposed technology can provide dissolution of the polyester and its extraction from different grades of waste jeans with high thermal stability. 3.4. Recovered fiber analysis The chemical structure of the fiber samples (before and after the treatment) was investigated by FTIR spectroscopy. Fig. 12 shows the 365
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Fig. 14. Boundaries of the new strategy.
technologies, the developed strategy was assessed based on the recycling rate, profitability, carbon footprint, and sustainability. Quantification of profits could encourage entrepreneurs in adopting circular economy principles in practice and increase the amount of competitive sustainable technologies in the market. Therefore, recovery of cotton fiber from textile waste represents a significant economic opportunity in the circular economy framework. 3.5.1. Recycling rate and sustainability evaluation Fig. 14 shows the flowsheet of the developed strategy, including the consumables and electrical power required for all treatment stages, while Table 2 illustrates the rates of secondary raw material (Polyester and Cotton fibers) recycling and regeneration and consumables (acid and solvent) regeneration in the technology, determined based on average the mass balances of recycled denim fabric to increase the accuracy of the final results. As shown, the suggested strategy has a high recycling rate ˜93% - this value is resultant from all treatments including washing process. Sustainability of the present strategy was evaluated based on the regeneration rates of the consumable chemicals; acid and solvent can be regenerated with high performance, while the chemicals used for bleaching process should be reconsidered to find more sustainable and green alternative. This part is researched by authors in order to find a sustainable bleaching process. The share of cotton fiber was 77 wt.% of recovered materials after bleaching and washing steps, while polyester fraction represented 16.2 wt.%.
Fig. 12. Photographies and FTIR spectra of the original textile and cotton fibers recovered from black, blue samples. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
solvent evaporation, organic residue decomposition (dyes or polyester impurities), primary decomposition of fiber, and char devolatilization/ decomposition. Due to the fact that the samples were left for overnight for drying, most of the water evaporated and only very small amount remained besides the humidity from ambient. Most of the solvent was extracted during the treatment, thus amount of evaporated solvent was also very low. Based on the weight loss during the primary stage, especially for the black sample, it can be concluded that the recovered fibers had thermal stability closer to raw cotton and can be used as a new source of cotton after spinning using wet or melt spinning limited by minimum degradation (Karthik and Murugan, 2013; Rajkumar et al., 2016).
3.5.2. Economic performance of the developed strategy The economic performance of the developed strategy was evaluated based on the input costs (Chemicals and Electric Energy) and two output costs (Purified cotton and Polyester) presented in Fig. 14. Since some studies were developed to regenerate HNO3 and DMSO using membrane and rotary evaporator, cost of these agents was not taken account during the calculations (Yang et al., 2017). The total electrical energy required for treating 1 ton of denim fabric waste and regenerate spent solvent using the developed strategy was calculated taking into account the capacity of the developed reactor (5 kg) and total treatment
3.5. Recycling rate and profitability assessment of the new strategy In order to support companies involved in reverse logistic chains during the evaluation of investments in textile waste recycling
Fig. 13. TGA-DTG analysis of the fibers from A) black and B) blue specimens. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article). 366
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Table 2 Recycling, Regeneration rates, and economic performance of the proposed strategy. Process
Leaching Dissolution Bleach
Treated substrate average weight (g) Average weight before treatment
Average weight after treatment
295 284 276
284 276 274
Average recycling rate (%) 0.964 × 0.972 × 0.993
Recycling rate (%)
96.4 97.2 99.3 93%
Sustainability evaluation Chemical material
Regeneration Rate (%)
Acid DMSO NaOCl, HCl
99.4 99.5 ——
time as illustrated in Eqs. ((1)–(5)). The energy consumed in evaporation process was estimated as 32 kW h/ 1 t of fabric waste. Finally, the profitability assessment of the developed strategy revealed that the profits from technology can reach up to 1466 $/ tonne of waste (price of recovered materials: Cotton – 2000 $/ tonne, Polyester - 1000 $/ tonne; price of consumables: Activated carbon - 2$/kg, Electricity - 0.23 $/KWh [Alibaba.com], (Anon., 2019e)) as illustrated in Eq. (5).
Fig. 15. System boundaries of the developed strategy scenarios.
Total treatment time = leaching time (0.5 h.) + dissolution time (8 h.) + bleaching time (2 h.) = 10.5 h. (1)
Energy consumption of 5 kg of fabric waste = 74
calculated based on the energy consumption during the treatment and amount of recovered metals of 1 ton of textile waste. Based on these values, applying the developed strategy on an industrial scale gives a possibility to decrease GGE by -1,534 kg CO2-eq/ tonne. Despite the fact that preliminary environmental assessment (Based on GHG factor) of the developed strategy showed high performance (-1,534 kg CO2-eq/ tonne), it is very important to assess more environmental impact categories (e.g. Climate Change, Human Toxicity, Particulate Matter Formation, Environmental Toxicity, Land Occupation, and Fossil fuels Depletion) as mentioned in detailed ISO standard doctrines, such as (ISO-14067, 2013), which is characterized by a specific requirement, accuracy, strength, and transparency (Garcia and Freire, 2014). According to the specified protocol, the analysis should be conducted on one ton of feedstock (textile waste in the present research) as a Functional Unit (FU) taking into account collection, transportation, and sorting practices. In addition, based on the Cradleto-Gate approach, all input processes should be simulated to cover plant requirements in terms of auxiliaries and energy as well as all outputs from the treatment system such as mass/energy recovery and releases into the environment (Huang et al., 2017). Fig. 15 shows the physical boundaries of the developed strategy based on the Cradle-to-Gate concept, including average weight of the recovered secondary raw materials and electricity consumption. As shown in the layout, the emissions (into air, water, and soil) of the technology and production of solid wastes were represented only by wastewater, while the output was represented by cotton and polyester. Regarding the heavy metals, which ate considered a very critical point and have a major effect on the environmental impacts (Sandin and Peters, 2018c; Anon., 2019f), the recovery of heavy metals under research by our research group using pH control. Therefore, the environmental impacts would be calculated
J × 3600 × 10.5 s (2)
= 2797200 J (0.777 KWh) Energy consumption for 1 tonne of fabric waste
(3)
= (0.777 KWh × 1000 kg )/5 = 155 KWh
Total Energy cost for 1 tonne = (155 KWh + 32 KWh) × 0.23
$ = 43 $ KWh (4)
Profitability per tonne = [Output cost – Electricity cost – Raw material cost] = [0.768 × 2000$ (Cotton)+ 0.162 × 1000 $ (Polyester)] – 43 $ – 83 $ = 1466 $ (5) 3.5.3. Environmental assessment of the new strategy The Life Cycle Assessment (LCA) is a standardized global approach recognized as a valuable screening tool to support basic and applied researches in the field of environmental studies and sustainable industries. Specifically, its application to the end-of-life management of textile products represents a consolidated way to evaluate improvements, reached because of a process implementation, or to compare several viable treatment solutions in terms of environmental footprint (Chen et al., 2018). A life cycle analysis was applied to determine environmental performances of the new strategy in terms of Greenhouse Gas (GHG) emissions, according to ISO standard 14040 and based on the average values reported in the literature (Turner et al., 2015). Table 3 shows GHG emissions of the developed strategy, which were Table 3 GHGE from the treated cotton fiber using the new strategy. Recovered material/Energy
Kg or kWh/ tonne of textile waste
Average (kgCO2-eq/ tonne or 1000 kW h) (Agarwal and Jeffries, 2013; EEA, 2014; Zamani et al., 2015)
Polyester 162 −4,060 Cotton fiber 768 −1,500 Electricity 187 +1475 CO2-eq reduction by the developed strategy (kgCO2-eq/ tonne)
kgCO2-eq / tonne of textile waste −658 −1,152 +276 −1,534
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Fig. 16. The developed recycling technology within the sustainability system.
without considering the heavy metals, leading to results lacking precision and credibility. Accordingly, the authors merely present the physical boundaries of the developed strategy in the present research, while the full LCA of strategy, including all impacts will be evaluated using SimaPro software after heavy metal extraction and wastewater treatment to ensure the developed strategy is integrated and sustainable. The integrated-sustainable technology will be compared with three alternative textile waste treatment scenarios: incineration, pyrolysis, and landfilling (as a worst waste treatment solution), which require additional research and estimation as well (Silva et al., 2019; Li and Feng, 2018). Finally, the recovered materials, especially cotton can be used as a new source of material for facing the high demand and lack of supply for cotton and thus achieve the core principles of Circular Economy for textile waste (Fig. 16). 4. Conclusions In the context of facing a high demand for cotton and lack of its supply, in this research, the authors developed a sustainable strategy to recover cotton from textile waste to make it a new source of material taking into account the quality of product and economic issues. The new strategy is composed of three main processes: leaching using Nitric Acid, dissolution using Dimethyl Sulfoxide, and bleaching by Sodium Hypochlorite and dilute Hydrochloric Acid dosage, respectively. These processes were employed to remove textile dyes followed by dissolving the polymeric part, then the cotton fiber was liberated. The pilot scale experiments showed that the developed strategy can help achieve selfsufficiency in raw cotton fiber for many and accelerate transition to Critical Economy; recovery rate, economic performance, and carbon footprint of the technology were estimated as 93%, 1466 $/ tonne, and -1,534 kg CO2-eq/ tonne. The authors closed the loop of the strategy by regenerating the spent acid and solvent as well as extracting the polyester, thus the proposed strategy can be considered highly sustainable. References Agarwal, B., Jeffries, B., 2013. Cutting Cotton Carbon Emissions: Findings from Warangal, India. http://awsassets.wwfindia.org/downloads/wwf___cotton_carbon_emission.pdf. https://www.statista.com/statistics/263055/cotton-production-worldwide-by-topcountries/. https://www.grandviewresearch.com/industry-analysis/cellulose-fibers-market. https://www.sei.org/events/used-textiles-waste-or-value/. https://wolkat.com/en. Energy Price Statistics. (Accessed 1 November 2017). http://ec.europa.eu/eurostat/ statistics-explained/index.php/Energy_price_statistics. Environmental impacts of the use of bottom ashes from municipal solid waste incineration: A review. Bansal, A., Illukpitiya, P., Tegegne, F., Singh, S.P., 2016. Energy efficiency of ethanol production from cellulosic feedstock. Renew. Sustain. Energy Rev. https://doi.org/ 10.1016/j.rser.2015.12.122. Byrne, F.P., Jin, S., Paggiola, G., Petchey, T.H.M., Clark, J.H., Farmer, T.J., Hunt, A.J., Robert McElroy, C., Sherwood, J., 2016. Tools and techniques for solvent selection: green solvent selection guides. Sustain. Chem. Process. https://doi.org/10.1186/ s40508-016-0051-z. Chapagain, A.K., Hoekstra, A.Y., Savenije, H.H.G., Gautam, R., 2006. The waterfootprint of cotton consumption: an assessment of the impact of worldwideconsumption of
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