Advances in Polymer Technology
Volume 2022 (2022), Article ID 4255409, 10 pages
https://doi.org/10.1155/2022/4255409

Research Article

Utilization of Waste Textile Cotton by Synthesizing Sodium Carboxymethyl Cellulose: An Approach to Minimize Textile Solid Waste

Md. Samsur Rahaman,1,2 Sultana Shamsun Nahar,¹ Jahid M. M. Islam,³ Rajib Samadder,⁴ Md. Saifur Rahaman,⁵ Rujina Khatun Chadni,¹ Faisal Rahaman Shagor,¹ Md. Latifur Rahman,² Tania Akter Ruhane,² and Mubarak Ahmad Khan1,2

¹Research Lab, Echotex Ltd., Gazipur, Bangladesh
²Bangladesh Jute Mills Corporation, Ministry of Jute and Textiles, Motijheel, Dhaka-1000, Bangladesh
³School of Science, Monash University, Sunway Campus, Subang Jaya, Selangar 47500, Malaysia
⁴Deapartment of Chemistry, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh
⁵Institute of Nuclear Science and Technology, Bangladesh Atomic Energy Commission, Dhaka-3787, Bangladesh

Correspondence should be addressed to Mubarak Ahmad Khan; makhan.inst@gmail.com

Received 31 May 2021; Revised 22 December 2021; Accepted 17 February 2022; Published 11 March 2022

Academic Editor: Yun Yu

Copyright © 2022 Md. Samsur Rahaman et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

This research uses waste textile cotton (WTC) from the textile industry as a raw material to synthesize sodium carboxymethyl cellulose (CMC) by adapting a modified etherification methodology. Yields of technical CMC (TCMC), semipurified CMC (SPCMC), and purified CMC (PCMC) were  g,  g, and  g, respectively, per gram of cotton waste. Degree of substitution (DS) values of PCMC, SPCMC, and TCMC was , , and , respectively. For PCMC, SPCMC, and TCMC, the purity of the prepared different grades of CMC was %, %, and %, respectively. Fourier transform infrared spectroscopy (FTIR) peak values were 3437 cm⁻¹, 1609 cm⁻¹, and 1427 cm⁻¹, proving WTC conversion to CMC. Furthermore, values of X-ray diffraction (XRD) peaks were 9.7 and 20.5, confirming the transformation of WTC to CMC as well. Thermogravimetric analysis (TGA) and scanning electron microscope (SEM) have been assessed to define CMC’s thermal stability and morphology, respectively.

1. Introduction

Bangladesh’s textile industries grew rapidly in response to the country’s rapidly growing population and high global demand for textiles. However, although the vast potentials of the textile industries have become the backbone of the country’s economic growth, they are now raising severe environmental concerns because of their huge waste discharge. The percentage of wastage from different sections of the textile industry includes apparel cutting about 59%, dyeing about 21%, knitting about 13%, sewing about 3%, and others about 4% of total textile waste [1]. In 2014, the fabric waste generation in the textile industry reached approximately 2326 tons per day in Bangladesh [2]. Waste cotton is one of the most prominent extravagances in the textile industry among this dissipation.

The textile industry is vital for economic growth in today’s world. As a result, this industry is increasing all over the world. But the sobering fact is that this industry produces over 100 million tons of waste per year, of which just a fraction is recycled [3]. Due to slow degradation in anaerobic (landfills are sealed and keep out water and oxygen is called anaerobic) conditions, this vast volume of cotton waste is harmful to the earth’s surface. It is a valuable resource for the economy and the environment despite the emissions since this cotton contains 70-94% [4].

Cellulose is an anhydrous-glucose unit’s linear polymer found in nature. At the C-1 and C-4 positions, cellulose is made up of repeating glycosidic bonds. Cellulose can easily be converted to numerous derivatives because there are two secondary OH groups and a primary OH group at C-2 and C-3 and C-6, respectively. CMC is an anionic linear polysaccharide. It is a cellulose derivative with carboxymethyl groups (-CH₂-COOH) bound to some hydroxyl groups that make up the cellulose backbone [5, 6]. It is a water-based, natural, and biodegradable commodity for this carboxymethyl group. All forms of CMC biodegrade at a rate of >60% in one week, suggesting complete biodegradation [7]. When CMC is discharged directly into the water surface, no adverse effects on aquatic life have been observed. Due to its nontoxicity, it is used as a food additive. The downside of CMC is that it does not protect against rot, insects, and light [8–10].

CMC is one of the most industrially relevant and commercially demanded derivatives [11]. It is used in different industries, including food processing, pharmaceuticals, detergents, cosmetics, textiles, paper production, and oil drilling [12, 13]. It is a widely used product in biomedical applications such as drug delivery, biosensors, implants, wound dressing, and bone cement. It is a low-cost, low-impact binder. As a result, supercapacitors and battery electrodes are made out of it. It is also used in agricultural products as a heavy ion remover, thickener, emulsifier, stabilizer, and UV shield [14–17]. Because of the low toxicity, fugitive handling, and economic performance, etherification is the most widely used method for producing CMC [18]. In this phase, this process requires strict temperature and reaction time control.

Until now, scientists have been working hard to find a less costly way to make CMC. It has been stated that CMC can be made from a variety of cellulosic sources, such as knitted rag, cotton gin waste, corncob, cornstalk, and corn husk [19–23]. The techniques to prepare CMC include a cellulose isolation stage, which increases the manufacturing cost of CMC. Another challenge for scientists to minimize total alkalization and etherification time is to produce CMC. Alkalization and etherification were done separately to prepare CMC, where these took 4 h, 5 h, 4 h, 2.5 h, and 4.5 h [19–23]. As a result, it consumes much time during alkalization and etherification.

This study is aimed at finding a long-term solution for reducing textile cotton waste by generating various grades of CMC. No research has been published on the conversion of cellulose to CMC without isolating it. The first goal, in this case, was to use cellulose without any isolation. This research is unique because alkalization and etherification were performed in the same reactor vessel. Alkalization and etherification were done in one step, another benefit of the research. On the other hand, this method was carried out simultaneously with the recovered IPA, ethanol, and acetone, an excellent way to save cost. As a result, the focus of this study is to develop a cost-efficient and environmentally friendly method for synthesizing different grades of CMC with a fair DS and excellent solubility.

2. Experimental

2.1. Materials

Echotex PVT. Ltd. provided the WTC for this experiment. According to a statistics conducted by this factory, 1500 tons of WTC are produced annually on average. It is approximately 35% of total fabric production. The cost per kilogram of WTC is only 6.00 BDT which is very negligible compared to the cost of CMC. Price of per kg CMC of PCMC, SPCMC, and TCMC are around 650, 450, and 150 BDT, respectively, in the local market (i.e., Midford, Dhaka) of Bangladesh. The chemicals used in this research work were sodium hydroxide (Merck, Germany), monochloroacetic acid (Qualikem, India), isopropyl alcohol (Chem-lab, Belgium), ethanol (Merck, Germany), acetone (Chem-lab, Belgium), acetic acid (Scharlau, Spain), sodium chloride (Merck, India), 2, 7-dihydroxy naphthalene (Merck, Germany), and sodium glycolate (Merck, India). All of the chemicals used in this experiment were reagent grade and unmodified before use.

2.2. Synthesis of CMC

The preparation methodology of CMC from WTC is shown in Scheme 1. Firstly, 1 g of WTC was taken in beaker and mixed with isopropyl alcohol at a proportion of 1 : 22 (). A total of 4 mL of NaOH solution at a concentration of 40% and 4 mL of monochlroacetic acid solution 40%, 45%, and 50% was added drop wise to the solution under mechanical stirring continuously for 30 minutes at room temperature. Then, the solution containing WTC was heated in a water bath under stirring for one hour. The residue was then washed with 70% ethanol and dried at 60°C in an oven until it reached a constant weight. Technical grade CMC was the name given to this residue.

Scheme 1: Synthesis of CMC from WTC.

It has adjusted the pH to 7 in the case of semipurified grade CMC by adding acetic acid during the washing process with 70% ethanol. After washing several times, the sample was filtered once more and dried in an oven at 60°C until it reached a constant weight. The semipurified grade CMC was dissolved in water and precipitated with acetone for the purified grade CMC. The precipitation accumulated was washed the last time by 70% ethanol and dried at 60°C in an oven until it reached a constant weight.

2.3. Measurement of CMC Yield

Determination of the yield of CMC was performed on a dry-weight basis. According to Rachtanapun (2009) and Silva et al. (2004), the net weight of dried CMC was measured [24, 25]. Equation (1) was utilized to calculate the yield.

2.4. Determination of the Degree of Substitution

The average number of hydroxyl groups in the cellulose structure, substituted by carboxymethyl groups, is known as CMC’s degree of substitution (DS) [9]. Rosnah et al. (2004) defined a potentiometric back titration method for determining DS values [26]. It follows the ASTM D 1439 (ASTM 2015) [27]. CMC’s DS value was determined using Equations (2) and (3), respectively.

where is the consumed acid per gram of specimen, is the volume of NaOH, is the concentration of NaOH, is the volume of HCl, is the concentration of HCl, and is the weight of the sample. Here, 0.162 is the molecular weight of anhydrous glucose unit, and 0.058 is the net increment in the anhydrous glucose unit for each substituted carboxymethyl group.

4 g of dried CMC of various grades was placed in separate beakers. Each beaker received 75 mL of 95% ethanol, which was stirred for 5 minutes. Then, 5 mL of 2 N HNO₃ was added to the mixture and stirred for 10 minutes. The mixture was allowed to boil for a few minutes in a water bath and then stirred for 10 minutes before cooling. The liquid solution was decanted from the suspended CMC using a vacuum pump and washed the residue five times with ethanol. The alcohol was removed using a vacuum pump after the residue was washed again with methanol. Finally, the washed CMC was dried for 3 hours at 105°C. Following that, 1 g dried CMC was put in a beaker and then dissolved in a 100 mL distilled water mixture and 25 mL 0.5 N NaOH solution. The beaker was boiled for 15 minutes in a water bath. After cooling the solution, 0.3 N HCl was used to titrate it. As an indicator, phenolphthalein was used. The endpoint was shown when the color changed from dark pink to colorless.

2.5. Viscosity Measurement

The viscosity of CMC is a very important industrial parameter since it tests the flow characteristics in product processing operations using various CMC concentrations. The viscosity of the prepared CMC solutions was measured using a Brookfield viscometer (model: LVDV-E, USA). 1% of CMC solution was used to determine the viscosity of CMC. The spindle used here was 61, and the temperature was 21°C during operation.

2.6. Determination of Intrinsic Viscosity and Average Molecular Weight

The intrinsic viscosity of CMC of various grades was calculated using an Ostwald viscometer. CMC was dissolved in a 0.78 M NaOH solution to measure intrinsic viscosity. The “Mark–Houwink–Sakurada” Equation (4) was used to calculate the molecular weight of CMC described in Alam and Mondal (2013) [19].

where is the constant for a specific solvent ( dL/gm), is the polymer shape factor (0.61), is the intrinsic viscosity, and is the molecular weight.

2.7. Water and Oil Retention Capacity

1 g of dried CMC of various grades was placed in two different beakers. 25 mL of distilled water (for water retention capacity) and 25 mL extra virgin olive oil (for oil retention capacity) were added in two respective beakers. After that, they were stirred and incubated at 40°C for 1 hour. Then, the residues were centrifuged and measured water retention capacity (WRC) and oil retention capacity (ORC) [28].

2.8. Moisture Content

The moisture content of different grades of CMC was measured using KERN moisture analyzer (Model: DBS 60-3, Germany).

2.9. Gel Content of CMC

According to Alam and Mondal (2013), the gel content was estimated and measured using the following equation [19]:

where (g) is the weight before extraction and (g) is the weight after extraction.

Soxhlet extraction with hot toluene was used to assess the gel content of films made from various grades of CMC. The films were weighed and put in the Soxhlet extractor after being cut into . In this method, 250 mL toluene was used. The solvent extraction was run for 6 hours to complete the process. The samples were then vacuum dried and weighed again until they reached a consistent weight.

2.10. CMC Content

The method of CMC content was summarized in Togrul and Arslan (2003), which was measured by using [29]

where (g) is the weight of the sample before washing and (g) is the weight of the washed sample.

In 100 mL of 80% methanol solution, 1.5 g of different grades of CMC was added. Those slurries were allowed to sit for 10 minutes before being filtered. The residues were washed again with 100 mL of fresh 80% methanol and then dried to obtain pure CMC.

2.11. Sodium Glycolate Content

5 mL glacial acetic acid and 5 mL water were used to wet 0.5 g of CMC. Then, 50 mL acetone and 1 g sodium chloride were added to the mixture and stirred for several minutes to ensure complete CMC precipitation. Following that, the mixture was filtered, and the clear supernatant was used for making the test solution. A similar blank solution was made just by using reagents. Acetone was removed from the test and blank solutions by heating them in a boiling water bath for 20 minutes. The solutions were cooled before being used. After that, each solution received 20 mL of 2,7-dihydroxy naphthalene. A UV–vis spectrophotometer was used to compare the absorbance of the test solution to that of the blank solution at 540 nm (model: T 60, England). The unknown quantity of sodium glycolate in the solution was determined using the following formula [29], where 1.29 is a factor for converting glycolic acid into sodium glycolate, is mg of glycolic acid read from the calibration curve, and is the dry weight of sample in g:

2.12. NaCl Content in CMC

Latif et al. (2007) defined the method for determining NaCl content, calculated using [30]

where (mL) is the volume of AgNO₃ solution and (g) is the weight of the dried sample.

2 g of various grades of CMC was mixed with 250 mL of 65% methanol for 5 hours. 0.1 N HNO₃ solution was used to neutralize, which were then titrated with 0.1 N AgNO₃ solution.

2.13. FTIR Spectroscopy

A Fourier transform infrared spectrometer (model: Prestige-21, Shimadzu, Japan) was used to record the functional groups of CMC and WTC in the range of 4000 cm⁻¹ to 400 cm⁻¹. The samples were dried in a 60°C oven. 0.2 gm powder samples were mixed with 2 g of KBr, to make pellets.

2.14. X-Ray Diffraction

XRD (X-ray diffraction) analysis was used to determine WTC and CMC’s crystal and amorphous structures. Using an X-ray diffractometer (model: Smart Lab SE, Rigaku, Australia), this experiment was conducted at room temperature. Cu-Kα radiation with a range of -40° and a scanning rate of 0.25° min⁻¹ were used.

2.15. Thermogravimetric Analysis

The thermal properties of WTC and CMC were investigated by using a thermogravimetric analyzer (model: STA 449 F3 Jupiter, NETZSCH, Germany). In a nitrogen atmosphere, the samples were heated at a constant rate of 1.5°C/min up to 700°C.

2.16. Scanning Electron Microscopy

A scanning electron microscope (Model: PV25MK, EDWARDS, England) was used to investigate the surface morphology of the WTC and CMC samples. The dried samples were coated with gold before being examined. There was a voltage of 15.00 kV.

3. Results and Discussion

3.1. Yield of CMC

Cellulose is composed of a repeating unit of glucose anhydride in which the carboxymethyl groups replace the hydroxyl groups during CMC synthesis. Several methods are found in the literature to synthesize CMC [31–33]. A few methods were found to be reported about the synthesis of CMC from WTC [19, 20]. However, all of the reported methods consist of more than one step needing too many chemicals.

In this present work, we report a one-step facile synthesis method to produce CMC (Scheme 2>). The prime target for the CMC production from cellulose is the hydroxyl groups of cellulose which are shown to be active under alkaline conditions. The alkali cellulose is reactive towards monochloroacetate acid (MCA), which converts cellulose to carboxymethyl cellulose ethers [34]. NaOH reacts simultaneously with MCA to form two by-products, which are sodium glycolate and sodium chloride.

Scheme 2: Reaction mechanism of prepared CMC.

The drawback of previous research was the pretreatment of cellulose before the basification and etherification process [19, 20]. Through pretreatment and basification step is considered a necessary step to make CMC. Those separate steps were skipped in this process and successfully prepared CMC from WTC. Preparation of purified grade CMC from cotton ginning waste was a four-step process that included pretreatment. This procedure yielded 1.437 g/g, according to Haleem et al. (2014) [20]. A seven-step technique including pretreatment based on Fakhrul et al. (2013) was used to make purified grade CMC from the knitted rag, and the yield was reported to be 1.494 g/g [19].

In this method, the caustic concentration and reaction time were fixed but the concentration of MCA varied. Table 1 shows the yield of CMC increases with the increase of MCA; the optimum concentration MCA was 45%. At optimum concentration, yield of different grades of CMC was  g,  g, and  g per gram of cotton waste for TCMC, SPCMC, and PCMC, respectively, using a one-step technique. Temperature, reaction time, NaOH concentration, and MCA concentration all significantly impact the percentage of CMC yield percentage. Hence, these parameters were maintained strictly.

Table 1: Yield, purity, NaCl, moisture, and gel contents of different grades of CMC.

% MCA
Yield of technical grade CMC (g/g of WTC)
Yield of semi-purified grade CMC (g/g of WTC)
Yield of semipurified grade CMC (g/g of WTC)

40% MCA

45% MCA

50% MCA

3.2. CMC, Sodium Glycolate, and NaCl Contents

Table 2 shows the purity, sodium glycolate, and NaCl contents of CMC of various grades. With an increase in CMC content and a decrease in NaCl content, the purity of CMC rises. The percentage of CMC, sodium glycolate, and NaCl contents can be used to classify CMC grades.

Table 2: CMC, sodium glycolate, and NaCl contents of different grades of CMC.

CMC grade
CMC content or % purity
Sodium glycolate content
NaCl content

Technical

Semipurified grade

Purified

For example, when the CMC content is less than 72%, and the salt content is more than 25%, it can be called TCMC, which can be utilized in detergents and mining flotation. SPCMC, which has a CMC content of 75-85% and a salt content of 15-25%, is used in oil and gas drilling. PCMC is a pure grade with more than 98% CMC content and less than 2% impurities of NaCl and sodium glycolate that can be utilized in paper coating, textile sizing, printing, ceramic glazing, oil drilling, and other applications [23].

3.3. Gel and Moisture Contents of CMC

The high gel content indicates a high level of reactivity. The reactivity of different grades of CMC is shown in Table 3 as PCMC>SPCMC>TCMC.

Table 3: Gel and moisture contents of different grades of CMC.

CMC grade
Gel content
Moisture content

Technical

Semipurified grade

Purified

Furthermore, as the moisture content rises, CMC’s water solubility increases, the moisture content should not exceed 12%, according to the FAO/WHO Expert Committee (2011) [35]. In this study, the moisture content of PCMC was , SPCMC was , and TCMC was , which depicts the standard moisture content requirements are obtained. According to Table 2, the moisture content of various grades of CMC is PCMC>SPCMC>TCMC [23].

3.4. Water and Oil Retention Capacity

In the etherification process, the hydroxyl groups of cellulose were replaced by carboxymethyl groups, converted into the CMC. The grade of CMC and its hydrophilic characteristics improve as the number of carboxymethyl groups increases. This hydrophilic quality is shown by the water retention capacity (WRC). Because of WRC, the structure of CMC molecules and hydrophilic interactions via hydrogen bonding is also effective.

The appearance of CMC, on the other hand, becomes sticky as the WRC value rises. The sticky appearance of different grades of CMC can be represented as PCMC> SPCMC>TCMC, according to Table 4. The hydrophobic property is linked to oil retention capacity (ORC). As per Table 3, the hydrophobicity of different grades of CMC is supposed to be TCMC>SPCMC> PCMC [23].

Table 4: Water retention capacity and oil retention capacity of different grades of CMC.

CMC grade
WRC (g/g)
ORC (g/g)

Technical

Semipurified grade

Purified

3.5. Degree of Substitution and Viscosity

Table 5 exhibits the degree of substitution (DS), the viscosity of prepared CMC. CMC’s solubility, stability, acid resistance, and salt tolerance are all affected by the DS. The other properties of CMC can be enhanced accordingly increase with DS [32, 36, 37]. The DS range of commercially available CMC produced by alkalization and carboxymethylation is usually between 0.4 and 1.3 [30]. CMC is swellable but insoluble when the DS is less than 0.4, but above that, it is completely soluble in water and its hydro affinity increases as the DS increases. In water, CMC having the DS range of 1.5-2.5 is highly soluble [38]. In this study, the DS value for CMC from WTC was in the solubility range and was completely soluble in water.

Table 5: Degree of substitution (DS), viscosity of prepared CMC.

CMC grade
DS value
Viscosity (mPas)

Technical

Semipurified grade

Purified

Additionally, the level of purity increases with the increase of DS. This incidence demonstrates that more MCA molecules are substituted to the cellulose polymer structure during the etherification process. Besides, this substitution minimizes the possibility of MCA and NaOH reactions with each other, which lowers the probability of byproduct generation [30].

The viscosity has a major impact on the water solubility of CMC. Usually, it is 25 mPas–8000 mPas for a 1% CMC solution. Many factors can influence viscosity, including concentration, pH, temperature, and DS. In the pH range of 6.5-9.0, the viscosity of the 1% solution becomes most stable. As the pH value falls below 6.0, the viscosity of CMC decreases. But, the viscosity rapidly decreases as the pH value exceeds 11.5. It occurs because the unsubstituted hydroxyl group and alkaline molecules aid in cellulose dispersion. On the other side, higher viscosity is caused by an increase in DS. The carboxymethyl groups in cellulose polymers replaced the hydroxyl groups. Carboxymethyl groups are hydrophilic groups that enhance CMC’s capacity to retain water when DS increases [39].

3.6. Intrinsic Viscosity and Average Molecular Weight

Intrinsic viscosity, defined as the hydrodynamic volume occupied by a molecule, is a measure of a polymer molecule’s ability to increase viscosity [29]. The intrinsic viscosity and molecular weight of the synthesized CMC are shown in Table 6. The intrinsic viscosity and average molecular weight of CMC increased with increasing of DS. It is due to the increased amount of carboxymethyl groups replaced on the cellulose polymer’s hydroxyl groups [39]. Furthermore, these carboxymethyl groups function as a hydrophilic group, allowing CMC to trap additional water in the solution [30].

Table 6: Intrinsic viscosity and molecular weight of prepared CMC.

CMC grade
Intrinsic viscosity
Average molecular weight (kg/kmol)

Technical

Semipurified grade

Purified

The molecular weight of cellulose and synthesized CMC is a major factor that influences their structure, characteristics, and solubility. The molecular weight of the carboxymethyl group is higher than the OH group. As a result, the molecular weight of CMC increases with the increase of grades [19]. The concentration and molecular weight of the dissolved polymer play a significant role in the intrinsic viscosity of a polymer solution.

3.7. Physiological Parameters

The prepared CMC are white, fine powdered, odorless, freely soluble in water, and insoluble in alcohol. The pH of 1% CMC solution of various grades ranged from 7 to 9.5. No layer of foam appeared after shaking a 0.1% solution of the CMC sample. Using this test, CMC is distinguished from other cellulose ethers, alginates, and natural gums [40].

3.8. FTIR Analysis

Figure 1 shows the FTIR spectra of WTC and CMC. The absorption band at 3393 cm⁻¹ is due to the intermolecular and intramolecular hydrogen bonds in cellulose. C-H stretching vibration is responsible for the 2921 cm⁻¹ band. Bands at 1435 cm⁻¹ and 1338 cm⁻¹, which are assigned to -CH₂ scissoring and -OH bending vibrations, respectively, are another evidence of cellulose. A band at 1060 cm⁻¹ is due to >CH-O-CH₂. Two absorption bands at 1515 cm⁻¹ and 1250 cm⁻¹ must be highlighted particularly. The band at 1515 cm⁻¹ is absent in purified cellulose spectra, and the band at 1250 cm⁻¹ is reduced. The absence of these two absorption bands in the extracted cellulose spectra strongly suggests almost no lignin present [41]. At 894 cm⁻¹, the 1,4-glycoside of cellulose is observed [42].

Figure 1: FTIR spectra of waste textile cotton (black), technical grade CMC (red), aemi-purified grade CMC (green), and purified grade CMC (blue).

The strong absorption band at 3437 cm⁻¹ indicates the OH group stretching frequency substituted during the etherification reaction. A band at 2902 cm⁻¹ is a stretching vibration of the C-H group. An absorption band at 1609 cm⁻¹ confirms the existence of COO- and 1427 cm⁻¹ allocated to carboxyl groups [43]. The bands about 1310 cm⁻¹ and 1113 cm⁻¹, respectively, describe OH bending vibration and- C-O-C stretching. For WTC and CMC, the peak at 1059 cm⁻¹ refers to >CH-O-CH₂ stretching in glucose units.

3.9. XRD Analysis

Figure 2 depicts the crystalline characteristic peaks of WTC and CMC, which are and , respectively. The crystalline phase is represented by the sharp and narrow peaks, while the remaining peaks represent the amorphous phase. The microstructure of CMC is influenced by hydrogen bonding strength and crystallinity. When compared to WTC, CMC had a lower value in a peak of intensity (au). According to He et al. (2009), the CI (crystallinity index) is very effective for CMC solubility, with a high CI resulting in low solubility where the innate peaks of WTC almost disappeared [34].

Figure 2: XRD pattern of waste textile cotton (blue) and CMC (DS—, red).

It is because of the alkalization when NaOH and water entered the crystal region, which indicates the amorphous phase’s transition from crystalline to amorphous [33]. The faster substitution of the hydroxyl group of cellulose macromolecules by monochloroacetic acid (MCA) molecules led to a larger aperture among cellulose polymer molecules. It is also a cause of decreasing crystallinity index [24]. In this study, WTC and CMC have CIs of 68.09% and 16.67%, respectively, demonstrating CMC’s high solubility.

3.10. Thermogravimetric Analysis

The TG curves of WTC and CMC are shown in Figure 3. At 700°C, the TGA of WTC and CMC revealed weight losses of 84.21% and 64.26%, respectively, indicating that they contain nonvolatile components. WTC and CMC both lost weights initially in the 30°C–310°C and 30°C–290°C temperature ranges, respectively. For both WTC and CMC, the first weight loss is evaporating physically bounded water, but only for CMC with some volatile organic matter. In the temperature ranges of 310°C-395°C and 290°C–305°C, the second weight loss occurred in WTC and CMC consequently. On the other hand, the major weight loss of CMC at 305°C was shifted to a lower temperature than WTC’s at 395°C, indicating CMC’s lower thermal stability due to the inter and intramolecular hydrogen bonds between cellulose fibers [44].

Figure 3: TG curves of waste textile cotton (Red) and CMC (DS—, Green).

The amorphous structure of CMC was increased by alkalization with NaOH during its preparation. For WTC and CMC, final weight loss occurred from 395°C to 700°C and 305°C to 700°C, and the weight loss was 7.11% and 11.81%, gradually.

3.11. Morphology Analysis

Figure 4 displays SEM microphotographs of WTC and the CMC. WTC has a rough and layered surface structure, which was twisted and ruptured due to different types of chemicals and high temperature during the bleaching, scouring, dyeing, and finishing stages [38, 45].

(a)

(b)

(c)

(d)

Figure 4: SEM micrograph of waste textile cotton (a, b) and CMC (DS—; c, d).

On the other side, the smooth fibrous structure of the CMC surface is arrayed in a woven network [46]. This change is probably due to the alkaline solution reducing the strength of the structure, the stability of the molecular orientation, and loss of the crystallinity of the cellulose; thus, the etherifying agents have more access to the cellulose molecule during CMC synthesis [24, 32, 37].

4. Conclusion

WTC as a sustainable source of cellulose for synthesizing various grades of CMC with high water solubility was introduced in this study. The reaction was carried out by infusing WTC with NaOH and monochloroacetic acid. Although no initial treatment was given to the raw material, the total time of alkalization and etherification was reduced to 1.5 hours. This way, this process saves time and reduces costs, which would be ideal for industrial production. The results showed total impurity of different grades of CMC are within the range of standard data, e.g., , , and , for TCMC, SPCMC, and PCMC, respectively, which can be used in various industries like detergent, textile, oil drilling, packaging, and paper making. Furthermore, the developed method of producing a value-added product by utilizing textile solid waste may help to alleviate environmental issues.

Data Availability

The data used to support the findings of this study are available within the article.

Conflicts of Interest

The authors declare that they have no competing interests that could have influenced the work reported in this paper.

Acknowledgments

The authors are very grateful to Echotex Ltd. for providing waste textile cotton.

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