Carbohydrate Polymers 130 (2015) 41–48
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Synthesis of cellulose triacetate from cotton cellulose by using NIS as a catalyst under mild reaction conditions Ahmed El Nemr ∗ , Safaa Ragab, Amany El Sikaily, Azza Khaled Marine Pollution Department, Environmental Division, National Institute of Oceanography and Fisheries, Kayet Bey, El-Anfoushy, Alexandria, Egypt
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Article history: Received 19 November 2014 Received in revised form 13 April 2015 Accepted 27 April 2015 Available online 8 May 2015 Keywords: N-Iodosuccinimide Cellulose triacetate Acetylation Cotton cellulose Raman
a b s t r a c t This research discusses the acetylation of cotton cellulose with acetic anhydride without solvents. The acetylation was done in the presence of different amounts of N-Iodosuccinimide (NIS) as a catalyst; this took place under mild reaction conditions. The extent of acetylation was measured by the weight percent gain (WPG) that varied from 24.71 to 71.83%. Cotton cellulose acetates, with the degree of substitution (DS) that ranged from 0.89 to 2.84, were prepared in one step. The cellulose triacetate, with a degree of substitution (DS) 2.84, was obtained. The WPG and DS were easily controlled by changing the reaction duration (1–5 h), and the concentration of the catalyst (0.05 g, 0.075 g and 0.10 g for 1 g of cellulose) in 25 ml of acetic anhydride. NIS was recognized as a novel and more successful catalyst for the acetylation of hydroxyl groups in cotton cellulose. Formation of the acetates and the calculation of the degree of substitution were performed by FT-IR, Raman, and 1 H NMR. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction Natural organic products, such as cotton, presently attract great attention for the development as they are the main source of cellulose in the production of cellulose acetates. Cotton mainly contains cellulose of high molecular weight ranging from 2.5 × 105 to 1 × 106 or more. Apart from cellulose, the major components of cotton, that make up more than 95% are other constituents that include lignin and hemicelluloses such as xylose or mannose (El Nemr, 2012). Chemical modification of cellulose is one method of the production of value-added products. Acetylation has been the most widely used and most successful chemical modification. It replaces a hydrogen of hydroxyl group with an acetyl group. Cellulose acetate (CA) is one of the most industrial products with widely commercial applications (Bikales & Segal, 1971; Edgar et al., 2001; Heinze, Liebert, & Koschella, 2006; Waheed et al., 2014). Cellulose acetate is used commercially in cigarette filters, textile fibers, photographic films, oil paint, surface coatings (as additives), inks, and plastics (Gedon & Fengl, 2004; Rustemeyer, 2004). It is also a highly efficient adsorbent due to its porosity (Dai, Liu, Jia, & Ru, 2005). It has been found that cellulose diacetate (CDA), that has a degree of
∗ Corresponding author. Tel.: +20 3 4807138; fax: +20 3 4801174; mobile: +20 107801845. E-mail addresses: [email protected], [email protected] (A. El Nemr). http://dx.doi.org/10.1016/j.carbpol.2015.04.065 0144-8617/© 2015 Elsevier Ltd. All rights reserved.
substitution (DS) ranging from 2.2 to 2.7 (Heinze & Liebert, 2001), readily undergoes decomposition by microorganisms (Buchanan, Gardner, & Komarek, 1993; Komarek, Gardner, Buchanan, & Gedon, 1993). This has attracted the attention of biodegradable plastic manufacturers. Cellulose triacetate (CTA), that has an average DS above 2.8 (Heinze & Liebert, 2001), is one of the most important cellulose esters due to its low toxicity and low flammability. It, therefore, has an important role in industrial applications (Goda, Sreekala, Gomes, Kaji, & Ohgi, 2006; He et al., 2015; Jandura, Riedl, & Kokta, 2000; Kiso, Kitao, & Nishimura, 1999; Sun, Sun, & Wen, 2001). CTA could be used in the removal of organic pollutants from water (Dai et al., 2005; Vinturella, Burgess, Coull, Thompson, & Shine, 2004). CTA is also used as protective films in liquid crystalline displays which are widely used in digital devices (Edgar et al., 2001). Cellulose acetates have been prepared by Schatzenberger in 1965 after the reaction of cellulose with acetic anhydride in sealed tubes at 180 ◦ C (Biswas, Shogren, & Willett, 2005). The commercial production of cellulose acetate has been recognized in 1919 and has continued until now. Cellulose acetate is typically made from wood pulp, which is a renewable resource, that then reacts with acetic anhydride and acetic acid in sulfuric acid (Bikales & Segal, 1971; Gedon & Fengl, 1993; Larock, 1989). Recently several methods have been developed for producing cellulose acetates, Biswas reported that Iodine can be used as a catalyst in acetic anhydride for the esterification of cellulose (Biswas et al., 2007, 2009; Biswas et al., 2005). The most commonly used acetylating reagents are acetic anhydride and acetyl chloride (Heinze & Liebert, 2004). Sulfuric acid or perchloric acid could be used as catalysts with an excess
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Table 1 NIS-catalyzed acetylation reaction of cotton cellulose: reaction conditions, weight gain, percentage yield of cellulose acetate and degree of substitution obtained using FTIR and Raman spectrum. Sample no.
Wt. of cotton cellulose (g)
Ac2 O (ml)
Wt of NIS as catalyst
Reaction time (h)
C-1 C-2 C-3 C-4 C-5 C-6 C-7 C-8 C-9 C-10 C-11 C-12 C-13 C-14 C-15 C-16
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 10
25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 250
0.05 0.05 0.05 0.05 0.05 0.075 0.075 0.075 0.075 0.075 0.10 0.10 0.10 0.10 0.10 0.10
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 2
Yield of CA (g) 1.331 1.210 1.502 1.442 1.373 1.299 1.564 1.571 1.494 1.407 1.247 1.718 1.654 1.551 1.433 16.976
WPG (%)
CA yield (%)
WGFTIR (g)
WGRaman (g)
DSFTIR
DSRaman
33.12 21.00 50.21 44.24 37.25 29.94 56.40 57.09 49.44 40.70 24.71 71.83 65.41 55.08 43.33 69.76
46.68 42.05 83.50 65.33 44.30 38.48 86.81 77.72 68.96 56.40 29.58 94.32 88.85 77.33 63.04 92.15
0.327 0.294 0.585 0.457 0.310 0.269 0.606 0.544 0.483 0.395 0.207 0.660 0.623 0.541 0.441 6.941
0.377 0.241 0.525 0.329 0.386 0.332 0.583 0.562 0.481 0.415 0.200 0.700 0.659 0.560 0.490 6.933
1.40 1.26 2.51 1.96 1.33 1.15 2.60 2.33 2.07 1.69 0.89 2.84 2.67 2.32 1.89 2.77
1.61 1.03 2.25 1.41 1.65 1.42 2.49 2.41 2.06 1.77 0.85 3.00 2.82 2.40 2.10 2.75
Wt: weight; CA: cellulose acetate; WPG: weight percentage gain; CA yield: reaction yield percentage of CA; WGFTIR : weight gain calculated using FTIR spectrum; WGRaman : weight gain calculated using FT-Raman spectrum; DSFTIR : degree of substitution calculated using FTIR spectrum; DSRaman : degree of substitution calculated using FT-Raman spectrum.
of acetic anhydride to produce cellulose acetates (Hummel, 2004). Other reported methods for esterification include base-catalyzed transesterification, and ring-opening reactions (Connors & Albert, 1973; Das, Ali, & Hazarika, 2014; Fan et al., 2013; Heinze et al., 2006; Fan et al., 2014). Pyridine and 4-dimethyl-amino pyridine (DMAP) (Hofle, Steglich, & Vorbruggen, 1978) have been used as acylation catalysts in chemical synthesis. In the present work a new method for producing cellulose acetate (CA) from cotton cellulose was investigated. N-Iodosuccinimide was used as a novel and highly effective catalyst in the presence of acetic anhydride under a solvent free system. There have been no reports of its use as a catalyst for the acetylation of cotton cellulose using acetic anhydride. The effects of the reaction’s duration and concentration of the catalyst were investigated too. The structure and properties of acetylated cotton cellulose were characterized by the weight percent gain (WPG). In addition FT-IR, Raman, and 1 H NMR were used to investigate the reaction product that was obtained.
addition of 100 ml of distilled water to decompose the un-reacted acetic anhydride. The reaction mixture was filtered and washed by distilled water followed by ethanol. The products were then dried under vacuum in an oven at 45 ◦ C for 48 h prior to re-weighing. To reduce errors and confirm results, each experiment was repeated in triplicate under the same conditions. Weight percent gain (WPG) of the cotton cellulose due to acetylation was determined according to: WPG% =
weight gain × 100 original weight
2.3. Test of mass production
2. Experimental
A quantity (10 g) of commercial cotton cellulose was placed in a 500 ml round bottom flask that contained 250 ml acetic anhydride and 1 g of N-Iodosuccinaimide (NIS). The flask was then placed in a mantle at the reflux temperature using atmospheric pressure with a fitted reflux condenser. After 2 h of the reaction, the flask was removed. Then the above work method was repeated.
2.1. Chemicals and instruments
2.4. Determination of DS
Cellulose samples were obtained from Fluka analytical (Sigma–Aldrich product). The degree of polymerization of the cellulose DP = 456 (Evans & Wallis, 1989). Acetic anhydride, ethyl alcohol, and N-Iodosuccinaimide (NIS) were supplied by Fluka analytical, and were used without further purification. 1 H NMR was obtained using JEOL Nuclear Magnetic Resonance Spectrometers 400 MHz. FTIR and Raman data were obtained using Bruker VERTEX 70 FT-IR spectrometer coupled to a RAMII FT-Raman module with Germanium detector that provided a spectral range of 3600–50 cm−1 .
The DS values of the cellulose acetates were determined using FT-IR spectra. The DS was further confirmed by Raman spectra and 1 H NMR.
2.2. Acetylation of cotton cellulose A quantity (1.0 g) of commercial cotton cellulose was placed in a 250 ml round bottom flask that contained 25 ml acetic anhydride, and different weights of N-Iodosuccinaimide (NIS) catalyst (0.05, 0.075 and 0.10 g). The flask was then placed in a mantle at the reflux temperature using atmospheric pressure with a fitted reflux condenser. After the reaction took its time (1–5 h), the flask was removed. About 10 ml of ethanol was added, followed by the
3. Results and discussion 3.1. Influence of catalysts and reaction duration on the degree of acetylation This present work shows how cotton cellulose was acetylated in acetic anhydride that contained different concentrations of NIS under the same reaction conditions, at different reaction times. As the data in Table 1 show, it is apparent that the usage of 0.05 g of NIS as a catalyst in 25 ml acetic anhydride for 1, 2, 3, 4, and 5 h in samples 1–3, resulted in an increment in the WPG from 33.12 to 50.50%. In samples 4 and 5, the WPG decreased from 44.24 to 37.25%. In samples 6–10, acetylation of the cotton cellulose was carried out in 0.075 g of NIS that acted as a catalyst under the conditions mentioned above. The WPG increased with an increment in the reaction time 1–3 h from 29.94 to 56.40 and 57.09%. The
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Scheme 1. The proposed reaction mechanism of the acetylation of cotton cellulose using NIS as a catalyst.
WPG decreased with an increment in the reaction time 4–5 h from 49.44 to 40.70%. Table 1 also shows how in samples 11–15, 0.10 g of NIS were used for 1–3 h. This resulted in an increase in the WPG from 24.71 to 71.83 and 65.41%. The WPG decreased from 55.08 to 43.33% as the time increased from 4 to 5 h. The observed higher weight gain (71.83%) was obtained from sample 12, which reacted for 2 h with 0.10 g NIS. These results indicated that prolonging the reaction’s duration has no favorable effect on the acetylation process. That is probably due to the increase in the amount of catalyst
from 0.075 g to 0.10 g NIS, and the de-acetylation mechanism. The DS values (DSFTIR 2.84, DSHNMR 3.1) for sample 12 indicated the formation of cotton cellulose triacetate in excellent yield. About 10 g of cotton cellulose reacted with 1 g NIS as a catalyst, in 250 ml acetic anhydride for 2 h (sample 16) as a test mass production; the result was a WPG of 69.75%. The WPG increased with an increment in the reaction’s time until it reached the maximum value at 3 h. This boost of acetylation by the reaction’s prolongation of time was probably due to
Fig. 1. FT-IR spectra of untreated cotton cellulose fiber and cellulose acetate obtained by reaction of the cellulose and Ac2 O and 0.05 NIS reflux for 1 to 5 h.
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Fig. 2. FT-IR spectra of cellulose acetate obtained by the reaction of cellulose and Ac2 O and 0.075 NIS reflux for 1 to 5 h.
the favorable effect of the reaction’s duration on the adsorption and diffusion of the reactants between cotton cellulose molecules, and the acetic anhydride (Khalil, Hashem, & Hebeish, 1995). There were no significant increases in the observed WPG after 3 h. The level of acetylation decreased due to the de-acetylation mechanism (Adebajo & Frost, 2004). These results were economically favorable because they decreased the energy cost and saved time. It has been reported that the initial step in the reaction of acetic anhydride with a hydroxyl group involved a nucleophilic attack by a lone pair of the alcoholic (OH) group on the acyl carbon center of acetic anhydride; the second step subsequently showed the loss of acetic acid to form the ester (Hill, Jones, Strickland, & Cetin, 1998). When the level of acetylation increased more sharply, the amount of esterifying agent (NIS) was increased. That is because of the role of the NIS as a catalyst which had activated the acyl carbon center of the acetic anhydride molecule, and formed the highly reactive acylating agent (CH3 CO N (OCCH2 CH2 CO ) which then reacted with a lone pair of the hydroxyl groups of cotton cellulose (Scheme 1) (Karimi & Seradj, 2001; Sun, Sun, & Sun, 2004). 3.2. Extent of acetylation The level of acetylation found in the cotton cellulose samples was estimated by the quantitative calculations of the DS and WG values of the resultant CCAs using FT-IR spectroscopy; the results are shown in Table 1. The extent of acetylation in cotton cellulose for these reactions was evaluated by the following calculation: the ratio R between the intensity of the acetyl C O, the stretching band of ester at 1741–1747 cm−1 , the intensity of C O stretching, and the vibration of the cellulose back bone at about 1020–1040 cm−1 . R=
IC=O IC O
WG = R × 0.7
DS =
WG × 3 0.7
The DS, WG values (obtained from FTIR spectra) and WPG are compared in Table 1. We deduced that there was a great agreement between the experimental and calculative values for all samples in which the cotton cellulose triacetate was formed. FTIR spectra were highly sensitive and reliable for the determination of the level of acetylation. 3.3. FT-IR spectra The chemical reaction of cotton cellulose with acetic anhydride in the presence of NIS was monitored by observing FT-IR spectra. Fig. 1 shows FT-IR spectra of un-modified cotton cellulose, and acetylated cotton cellulose. About 0.05 g of NIS was used as a catalyst in samples 6–11. There were principal changes that were observed in the FT-IR spectra of acetylated cotton cellulose samples 1–5 (spectra 2–6) when compared with the un-modified cotton cellulose. A reduced intensity of the areas associated with the stretching bands of the hydroxyls (OH) at 3348–3339 cm−1 was found. An increased intensity in the areas associated with C O stretching bands of ester at 1744–1741 cm−1 , an increased intensity in the areas associated with C H bending bands of acetyl groups at 1370–1369 cm−1 , and an increased intensity in the areas associated with C O stretching bands of ester at 1227–1222 cm−1 , were found. Strong bands in the areas associated with C O stretching in C O C linkages of cellulose, hemicellulose and lignin were also discovered (Sun, Tomkinson, Ma, & Liang, 2000; Sun, Guan, Wen, & Zhu, 2001).
A. El Nemr et al. / Carbohydrate Polymers 130 (2015) 41–48
Fig. 3. FT-IR spectra of cellulose acetate obtained by the reaction of cellulose and Ac2 O and 0.10 NIS reflux for 1 to 5 h.
Fig. 4.
1
H NMR Spectrum of CTA.
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Fig. 5. FT-Raman of cotton cellulose and cellulose triacetate (0.10 g NIS, reflux for 2 h).
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Fig. 6. TGA analysis of cellulose and cellulose acetate (C-11 to C-15).
Fig. 2 shows that the FT-IR spectra of acetylated cotton cellulose samples 6–11 used 0.075 g of NIS as a catalyst. Strong evidences that indicated a successful acetylation were observed in the FTIR spectra of acetylated cotton cellulose samples 6–10 after being compared with the un-modified cotton cellulose. A reduced intensity of the absorption bands at 3335–3338 cm−1 was due to a stretch in the band of the hydroxyl (O H) groups. It was also due to an increase in the intensity of the bands at 1738–1744 cm−1 , which was related to C O stretching band of ester. It was because of an increase in the intensity of the peaks at 1369–1370 cm−1 which was attributed to C H bending band of acetyl groups, and an increase in the intensity of the absorption bands at 1219–1227 cm−1 which corresponded to the C O stretching band of ester and strong peaks at 1034–1040 cm−1 too. It was also the reason behind the rise caused by the C O stretching in C O C linkages of cellulose, hemicellulose and lignin (Sun et al., 2000; Sun, Guan, et al., 2001). Fig. 3 illustrates the FTIR spectra of acetylated cotton cellulose samples 11–15 that were performed at 0.10 g of NIS as a catalyst. All the acetylated cotton cellulose samples 11–15 showed evidence of acetylation with three ester bands enhanced at 1744 (carbonyl C O stretching of ester), 1370 (C H in O(C O) CH3 ) and 1039 cm−1 (C O stretching of acetyl group). They also displayed a low intensity of the OH stretching bands at 3326 cm−1 . 3.4.
1H
NMR analysis
A 1 H NMR spectrum of acetylated cotton cellulose (sample 12) took place in 2 h with 0.10 g of NIS. Fig. 4 shows that there were two clusters of hydrogen atom signals. The first was proton resonance signals of the glucose ring (ı = 3.53–5.06 ppm), and the second was methyl protons resonance signals of the acetate group (ı = 1.93–2.11 ppm) (Kono, Hashimoto, & Shimizu, 2015). The DS of cotton cellulose acetates can be calculated by 1 H NMR spectroscopy according to the following equation (Cao et al., 2007): DS =
7 × Iacetyl 3 × IAGU
where, Iacetyl is the integral of methyl protons of acetyl groups, IAGU is the integral of all protons of anhydroglucose unit. The DS
value obtained from 1 H NMR spectrum was 3.0, in excellent agreement with DSFTIR , and experimental value. It was clear that cotton cellulose triacetate was formed. 3.5. Raman spectra The degree of acetylation can be determined by using Raman spectroscopic technique too; it was estimated by calculating the ratios R1 and R2 . R1 and R2 are the ratios between the intensity of the acetyl C O stretching vibration of ester at 1736–1751 cm−1 . The intensity of COC ˇ-glycosidic link, with asymmetric and symmetric stretching bands, was found to be about 1087–1100 and 1121–1135 cm−1 , respectively. R1 =
IC=O I1094
WG = R1 × 0.7 DS =
WG × 3 0.7
The most Raman bands that affirm successful acetylation were observed at about 1736–1751, 1434–1461, 826–878 and 634–698 cm−1 . These bands are associated with (C O stretching vibration of ester), (CH3 -symmetric deformation), (H3 C C stretching), and (O C O in plane deformation), respectively. Fig. 5 shows Raman spectra of un-modified cotton cellulose (spectrum 1); the acetylated cotton cellulose of sample 12 took place in 2 h with 0.10 g NIS. Table 1 shows all the DS which was obtained from Raman spectra for samples 1–16. The DS calculated from Raman data was also found to fit with DSFTIR , DSH NMR , and experimental value (Adebajo, Frost, Kloprogge, & Kokot, 2006). 3.6. TGA analysis The thermal gravimetric analysis (TGA) was performed on the selected cellulose acetate (C-11 to C-15) and for cotton cellulose in order to examine the influence of their structural differences
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on their degradation behavior. Investigation of thermal gravimetric analysis (TGA) of the prepared acetate (C-11 to C-15) is presented in Fig. 6. It is seen that the degradation of all synthetic cellulose acetate occurs as more acetates degrade at higher temperature than less acetate. For example, triacetate C-12 and C-13 degrade at higher temperature than mono- (C-11) and diacetate (C-14 and C-15). This difference in the mass loss is possibly ascribed to the replacement of hydroxyl groups with acetyl groups. 4. Conclusions In this study we provided a new method to prepare cotton cellulose acetates in good yields from cotton cellulose. This was done using acetic anhydride and in the presence of different amounts of NIS which was used as an elegant catalyst. By using 0.05 g of NIS as a catalyst, and increasing the reaction time from 1 to 3 h, an increased in the WPG from 33.12 to 50.21%, respectively, resulted. To enhance yields of cotton cellulose acetates, we increased the concentration of the catalyst (0.075 g NIS) and the time of the reaction from 1–3 h. This caused the WPG to increase from 29.94 to 57.09%. About 0.10 g of NIS was used for 1–3 h, the WPG then increased from 24.71 to 65.41%, and cellulose acetates reached a DS of 2.84 in 2 h. The acetylation of cotton cellulose was successfully performed with increment reaction time and amount of catalyst at 0.10 g, 3 h. As the reaction time increased from 4–5 h, the WPG decreased from 55.08 to 43.33%. The optimum conditions to prepare cellulose triacetate were determined at 2 h and 0.10 g NIS. Under those conditions, the WPG was found to be 71.83%. FTIR, Raman, and NMR data were used to investigate the level of acetylation of cotton cellulose. Acknowledgements We are grateful to Science and Technological Development Fund (STDF) of Egypt for financial support for the project no. 4788. References Adebajo, M. O., & Frost, R. L. (2004). Infrared and 13 C MAS nuclear magnetic resonance spectroscopic study of acetylation of cotton. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 60, 449–453. Adebajo, M. O., Frost, R. L., Kloprogge, J. T., & Kokot, S. (2006). Raman spectroscopic investigation of acetylation of raw cotton. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 64(2), 448–453. Bikales, N. M., & Segal, L. (1971). Cellulose and cellulose derivatives, high polymers: Series V. New York: Wiley-Interscience. Biswas, A., Selling, G., Appell, M., Woods, K. K., Willett, J. L., & Buchanan, C. M. (2007). Iodine catalyzed esterification of cellulose using reduced levels of solvent. Carbohydrate Polymers, 68, 555–560. Biswas, A., Selling, G. S., Shogren, R. L., Willett, J. L., Buchanan, C. M., & Cheng, H. N. (2009). Iodine-catalyzed esterification of polysaccharides. Chemistry Today, 27(4), 4–6. Biswas, A., Shogren, R. L., & Willett, J. L. (2005). A solvent-less method to prepare cellulose or starch acetate. Biomacromolecules, 6, 1843–1845. Buchanan, C. M., Gardner, R., & Komarek, R. J. (1993). Aerobic biodegradation of cellulose acetate. Journal of Applied Polymer Science, 47, 1709–1719. Cao, Y., Wu, J., Meng, T., Zhang, J., He, J., Li, H., et al. (2007). Acetone-soluble cellulose acetates prepared by one-step homogeneous acetylation of cornhusk cellulose in an ionic liquid 1-allyl-methylimidazolium chloride (AmimCl). Carbohydrate Polymers, 69, 665–672. Connors, K. A., & Albert, K. S. (1973). Determination of hydroxyl compounds by 4dimethylaminopyridine-catalyzed acetylation. Journal of Pharmaceutical Science, 62, 845–846. Dai, R. H., Liu, H. J., Jia, J. H., & Ru, J. (2005). Preparation and characterization of novel adsorbent made by cellulose acetate. Environmental Science, 26, 111–113. Das, A. M., Ali, A. A., & Hazarika, M. P. (2014). Synthesis and characterization of cellulose acetate from rice husk: Eco-friendly condition. Carbohydrate Polymers, 112, 342–349.
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Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol
Synthesis of cellulose triacetate from cotton cellulose by using NIS as a catalyst under mild reaction conditions Ahmed El Nemr ∗ , Safaa Ragab, Amany El Sikaily, Azza Khaled Marine Pollution Department, Environmental Division, National Institute of Oceanography and Fisheries, Kayet Bey, El-Anfoushy, Alexandria, Egypt
a r t i c l e
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Article history: Received 19 November 2014 Received in revised form 13 April 2015 Accepted 27 April 2015 Available online 8 May 2015 Keywords: N-Iodosuccinimide Cellulose triacetate Acetylation Cotton cellulose Raman
a b s t r a c t This research discusses the acetylation of cotton cellulose with acetic anhydride without solvents. The acetylation was done in the presence of different amounts of N-Iodosuccinimide (NIS) as a catalyst; this took place under mild reaction conditions. The extent of acetylation was measured by the weight percent gain (WPG) that varied from 24.71 to 71.83%. Cotton cellulose acetates, with the degree of substitution (DS) that ranged from 0.89 to 2.84, were prepared in one step. The cellulose triacetate, with a degree of substitution (DS) 2.84, was obtained. The WPG and DS were easily controlled by changing the reaction duration (1–5 h), and the concentration of the catalyst (0.05 g, 0.075 g and 0.10 g for 1 g of cellulose) in 25 ml of acetic anhydride. NIS was recognized as a novel and more successful catalyst for the acetylation of hydroxyl groups in cotton cellulose. Formation of the acetates and the calculation of the degree of substitution were performed by FT-IR, Raman, and 1 H NMR. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction Natural organic products, such as cotton, presently attract great attention for the development as they are the main source of cellulose in the production of cellulose acetates. Cotton mainly contains cellulose of high molecular weight ranging from 2.5 × 105 to 1 × 106 or more. Apart from cellulose, the major components of cotton, that make up more than 95% are other constituents that include lignin and hemicelluloses such as xylose or mannose (El Nemr, 2012). Chemical modification of cellulose is one method of the production of value-added products. Acetylation has been the most widely used and most successful chemical modification. It replaces a hydrogen of hydroxyl group with an acetyl group. Cellulose acetate (CA) is one of the most industrial products with widely commercial applications (Bikales & Segal, 1971; Edgar et al., 2001; Heinze, Liebert, & Koschella, 2006; Waheed et al., 2014). Cellulose acetate is used commercially in cigarette filters, textile fibers, photographic films, oil paint, surface coatings (as additives), inks, and plastics (Gedon & Fengl, 2004; Rustemeyer, 2004). It is also a highly efficient adsorbent due to its porosity (Dai, Liu, Jia, & Ru, 2005). It has been found that cellulose diacetate (CDA), that has a degree of
∗ Corresponding author. Tel.: +20 3 4807138; fax: +20 3 4801174; mobile: +20 107801845. E-mail addresses: [email protected], [email protected] (A. El Nemr). http://dx.doi.org/10.1016/j.carbpol.2015.04.065 0144-8617/© 2015 Elsevier Ltd. All rights reserved.
substitution (DS) ranging from 2.2 to 2.7 (Heinze & Liebert, 2001), readily undergoes decomposition by microorganisms (Buchanan, Gardner, & Komarek, 1993; Komarek, Gardner, Buchanan, & Gedon, 1993). This has attracted the attention of biodegradable plastic manufacturers. Cellulose triacetate (CTA), that has an average DS above 2.8 (Heinze & Liebert, 2001), is one of the most important cellulose esters due to its low toxicity and low flammability. It, therefore, has an important role in industrial applications (Goda, Sreekala, Gomes, Kaji, & Ohgi, 2006; He et al., 2015; Jandura, Riedl, & Kokta, 2000; Kiso, Kitao, & Nishimura, 1999; Sun, Sun, & Wen, 2001). CTA could be used in the removal of organic pollutants from water (Dai et al., 2005; Vinturella, Burgess, Coull, Thompson, & Shine, 2004). CTA is also used as protective films in liquid crystalline displays which are widely used in digital devices (Edgar et al., 2001). Cellulose acetates have been prepared by Schatzenberger in 1965 after the reaction of cellulose with acetic anhydride in sealed tubes at 180 ◦ C (Biswas, Shogren, & Willett, 2005). The commercial production of cellulose acetate has been recognized in 1919 and has continued until now. Cellulose acetate is typically made from wood pulp, which is a renewable resource, that then reacts with acetic anhydride and acetic acid in sulfuric acid (Bikales & Segal, 1971; Gedon & Fengl, 1993; Larock, 1989). Recently several methods have been developed for producing cellulose acetates, Biswas reported that Iodine can be used as a catalyst in acetic anhydride for the esterification of cellulose (Biswas et al., 2007, 2009; Biswas et al., 2005). The most commonly used acetylating reagents are acetic anhydride and acetyl chloride (Heinze & Liebert, 2004). Sulfuric acid or perchloric acid could be used as catalysts with an excess
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Table 1 NIS-catalyzed acetylation reaction of cotton cellulose: reaction conditions, weight gain, percentage yield of cellulose acetate and degree of substitution obtained using FTIR and Raman spectrum. Sample no.
Wt. of cotton cellulose (g)
Ac2 O (ml)
Wt of NIS as catalyst
Reaction time (h)
C-1 C-2 C-3 C-4 C-5 C-6 C-7 C-8 C-9 C-10 C-11 C-12 C-13 C-14 C-15 C-16
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 10
25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 250
0.05 0.05 0.05 0.05 0.05 0.075 0.075 0.075 0.075 0.075 0.10 0.10 0.10 0.10 0.10 0.10
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 2
Yield of CA (g) 1.331 1.210 1.502 1.442 1.373 1.299 1.564 1.571 1.494 1.407 1.247 1.718 1.654 1.551 1.433 16.976
WPG (%)
CA yield (%)
WGFTIR (g)
WGRaman (g)
DSFTIR
DSRaman
33.12 21.00 50.21 44.24 37.25 29.94 56.40 57.09 49.44 40.70 24.71 71.83 65.41 55.08 43.33 69.76
46.68 42.05 83.50 65.33 44.30 38.48 86.81 77.72 68.96 56.40 29.58 94.32 88.85 77.33 63.04 92.15
0.327 0.294 0.585 0.457 0.310 0.269 0.606 0.544 0.483 0.395 0.207 0.660 0.623 0.541 0.441 6.941
0.377 0.241 0.525 0.329 0.386 0.332 0.583 0.562 0.481 0.415 0.200 0.700 0.659 0.560 0.490 6.933
1.40 1.26 2.51 1.96 1.33 1.15 2.60 2.33 2.07 1.69 0.89 2.84 2.67 2.32 1.89 2.77
1.61 1.03 2.25 1.41 1.65 1.42 2.49 2.41 2.06 1.77 0.85 3.00 2.82 2.40 2.10 2.75
Wt: weight; CA: cellulose acetate; WPG: weight percentage gain; CA yield: reaction yield percentage of CA; WGFTIR : weight gain calculated using FTIR spectrum; WGRaman : weight gain calculated using FT-Raman spectrum; DSFTIR : degree of substitution calculated using FTIR spectrum; DSRaman : degree of substitution calculated using FT-Raman spectrum.
of acetic anhydride to produce cellulose acetates (Hummel, 2004). Other reported methods for esterification include base-catalyzed transesterification, and ring-opening reactions (Connors & Albert, 1973; Das, Ali, & Hazarika, 2014; Fan et al., 2013; Heinze et al., 2006; Fan et al., 2014). Pyridine and 4-dimethyl-amino pyridine (DMAP) (Hofle, Steglich, & Vorbruggen, 1978) have been used as acylation catalysts in chemical synthesis. In the present work a new method for producing cellulose acetate (CA) from cotton cellulose was investigated. N-Iodosuccinimide was used as a novel and highly effective catalyst in the presence of acetic anhydride under a solvent free system. There have been no reports of its use as a catalyst for the acetylation of cotton cellulose using acetic anhydride. The effects of the reaction’s duration and concentration of the catalyst were investigated too. The structure and properties of acetylated cotton cellulose were characterized by the weight percent gain (WPG). In addition FT-IR, Raman, and 1 H NMR were used to investigate the reaction product that was obtained.
addition of 100 ml of distilled water to decompose the un-reacted acetic anhydride. The reaction mixture was filtered and washed by distilled water followed by ethanol. The products were then dried under vacuum in an oven at 45 ◦ C for 48 h prior to re-weighing. To reduce errors and confirm results, each experiment was repeated in triplicate under the same conditions. Weight percent gain (WPG) of the cotton cellulose due to acetylation was determined according to: WPG% =
weight gain × 100 original weight
2.3. Test of mass production
2. Experimental
A quantity (10 g) of commercial cotton cellulose was placed in a 500 ml round bottom flask that contained 250 ml acetic anhydride and 1 g of N-Iodosuccinaimide (NIS). The flask was then placed in a mantle at the reflux temperature using atmospheric pressure with a fitted reflux condenser. After 2 h of the reaction, the flask was removed. Then the above work method was repeated.
2.1. Chemicals and instruments
2.4. Determination of DS
Cellulose samples were obtained from Fluka analytical (Sigma–Aldrich product). The degree of polymerization of the cellulose DP = 456 (Evans & Wallis, 1989). Acetic anhydride, ethyl alcohol, and N-Iodosuccinaimide (NIS) were supplied by Fluka analytical, and were used without further purification. 1 H NMR was obtained using JEOL Nuclear Magnetic Resonance Spectrometers 400 MHz. FTIR and Raman data were obtained using Bruker VERTEX 70 FT-IR spectrometer coupled to a RAMII FT-Raman module with Germanium detector that provided a spectral range of 3600–50 cm−1 .
The DS values of the cellulose acetates were determined using FT-IR spectra. The DS was further confirmed by Raman spectra and 1 H NMR.
2.2. Acetylation of cotton cellulose A quantity (1.0 g) of commercial cotton cellulose was placed in a 250 ml round bottom flask that contained 25 ml acetic anhydride, and different weights of N-Iodosuccinaimide (NIS) catalyst (0.05, 0.075 and 0.10 g). The flask was then placed in a mantle at the reflux temperature using atmospheric pressure with a fitted reflux condenser. After the reaction took its time (1–5 h), the flask was removed. About 10 ml of ethanol was added, followed by the
3. Results and discussion 3.1. Influence of catalysts and reaction duration on the degree of acetylation This present work shows how cotton cellulose was acetylated in acetic anhydride that contained different concentrations of NIS under the same reaction conditions, at different reaction times. As the data in Table 1 show, it is apparent that the usage of 0.05 g of NIS as a catalyst in 25 ml acetic anhydride for 1, 2, 3, 4, and 5 h in samples 1–3, resulted in an increment in the WPG from 33.12 to 50.50%. In samples 4 and 5, the WPG decreased from 44.24 to 37.25%. In samples 6–10, acetylation of the cotton cellulose was carried out in 0.075 g of NIS that acted as a catalyst under the conditions mentioned above. The WPG increased with an increment in the reaction time 1–3 h from 29.94 to 56.40 and 57.09%. The
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Scheme 1. The proposed reaction mechanism of the acetylation of cotton cellulose using NIS as a catalyst.
WPG decreased with an increment in the reaction time 4–5 h from 49.44 to 40.70%. Table 1 also shows how in samples 11–15, 0.10 g of NIS were used for 1–3 h. This resulted in an increase in the WPG from 24.71 to 71.83 and 65.41%. The WPG decreased from 55.08 to 43.33% as the time increased from 4 to 5 h. The observed higher weight gain (71.83%) was obtained from sample 12, which reacted for 2 h with 0.10 g NIS. These results indicated that prolonging the reaction’s duration has no favorable effect on the acetylation process. That is probably due to the increase in the amount of catalyst
from 0.075 g to 0.10 g NIS, and the de-acetylation mechanism. The DS values (DSFTIR 2.84, DSHNMR 3.1) for sample 12 indicated the formation of cotton cellulose triacetate in excellent yield. About 10 g of cotton cellulose reacted with 1 g NIS as a catalyst, in 250 ml acetic anhydride for 2 h (sample 16) as a test mass production; the result was a WPG of 69.75%. The WPG increased with an increment in the reaction’s time until it reached the maximum value at 3 h. This boost of acetylation by the reaction’s prolongation of time was probably due to
Fig. 1. FT-IR spectra of untreated cotton cellulose fiber and cellulose acetate obtained by reaction of the cellulose and Ac2 O and 0.05 NIS reflux for 1 to 5 h.
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Fig. 2. FT-IR spectra of cellulose acetate obtained by the reaction of cellulose and Ac2 O and 0.075 NIS reflux for 1 to 5 h.
the favorable effect of the reaction’s duration on the adsorption and diffusion of the reactants between cotton cellulose molecules, and the acetic anhydride (Khalil, Hashem, & Hebeish, 1995). There were no significant increases in the observed WPG after 3 h. The level of acetylation decreased due to the de-acetylation mechanism (Adebajo & Frost, 2004). These results were economically favorable because they decreased the energy cost and saved time. It has been reported that the initial step in the reaction of acetic anhydride with a hydroxyl group involved a nucleophilic attack by a lone pair of the alcoholic (OH) group on the acyl carbon center of acetic anhydride; the second step subsequently showed the loss of acetic acid to form the ester (Hill, Jones, Strickland, & Cetin, 1998). When the level of acetylation increased more sharply, the amount of esterifying agent (NIS) was increased. That is because of the role of the NIS as a catalyst which had activated the acyl carbon center of the acetic anhydride molecule, and formed the highly reactive acylating agent (CH3 CO N (OCCH2 CH2 CO ) which then reacted with a lone pair of the hydroxyl groups of cotton cellulose (Scheme 1) (Karimi & Seradj, 2001; Sun, Sun, & Sun, 2004). 3.2. Extent of acetylation The level of acetylation found in the cotton cellulose samples was estimated by the quantitative calculations of the DS and WG values of the resultant CCAs using FT-IR spectroscopy; the results are shown in Table 1. The extent of acetylation in cotton cellulose for these reactions was evaluated by the following calculation: the ratio R between the intensity of the acetyl C O, the stretching band of ester at 1741–1747 cm−1 , the intensity of C O stretching, and the vibration of the cellulose back bone at about 1020–1040 cm−1 . R=
IC=O IC O
WG = R × 0.7
DS =
WG × 3 0.7
The DS, WG values (obtained from FTIR spectra) and WPG are compared in Table 1. We deduced that there was a great agreement between the experimental and calculative values for all samples in which the cotton cellulose triacetate was formed. FTIR spectra were highly sensitive and reliable for the determination of the level of acetylation. 3.3. FT-IR spectra The chemical reaction of cotton cellulose with acetic anhydride in the presence of NIS was monitored by observing FT-IR spectra. Fig. 1 shows FT-IR spectra of un-modified cotton cellulose, and acetylated cotton cellulose. About 0.05 g of NIS was used as a catalyst in samples 6–11. There were principal changes that were observed in the FT-IR spectra of acetylated cotton cellulose samples 1–5 (spectra 2–6) when compared with the un-modified cotton cellulose. A reduced intensity of the areas associated with the stretching bands of the hydroxyls (OH) at 3348–3339 cm−1 was found. An increased intensity in the areas associated with C O stretching bands of ester at 1744–1741 cm−1 , an increased intensity in the areas associated with C H bending bands of acetyl groups at 1370–1369 cm−1 , and an increased intensity in the areas associated with C O stretching bands of ester at 1227–1222 cm−1 , were found. Strong bands in the areas associated with C O stretching in C O C linkages of cellulose, hemicellulose and lignin were also discovered (Sun, Tomkinson, Ma, & Liang, 2000; Sun, Guan, Wen, & Zhu, 2001).
A. El Nemr et al. / Carbohydrate Polymers 130 (2015) 41–48
Fig. 3. FT-IR spectra of cellulose acetate obtained by the reaction of cellulose and Ac2 O and 0.10 NIS reflux for 1 to 5 h.
Fig. 4.
1
H NMR Spectrum of CTA.
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Fig. 5. FT-Raman of cotton cellulose and cellulose triacetate (0.10 g NIS, reflux for 2 h).
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Fig. 6. TGA analysis of cellulose and cellulose acetate (C-11 to C-15).
Fig. 2 shows that the FT-IR spectra of acetylated cotton cellulose samples 6–11 used 0.075 g of NIS as a catalyst. Strong evidences that indicated a successful acetylation were observed in the FTIR spectra of acetylated cotton cellulose samples 6–10 after being compared with the un-modified cotton cellulose. A reduced intensity of the absorption bands at 3335–3338 cm−1 was due to a stretch in the band of the hydroxyl (O H) groups. It was also due to an increase in the intensity of the bands at 1738–1744 cm−1 , which was related to C O stretching band of ester. It was because of an increase in the intensity of the peaks at 1369–1370 cm−1 which was attributed to C H bending band of acetyl groups, and an increase in the intensity of the absorption bands at 1219–1227 cm−1 which corresponded to the C O stretching band of ester and strong peaks at 1034–1040 cm−1 too. It was also the reason behind the rise caused by the C O stretching in C O C linkages of cellulose, hemicellulose and lignin (Sun et al., 2000; Sun, Guan, et al., 2001). Fig. 3 illustrates the FTIR spectra of acetylated cotton cellulose samples 11–15 that were performed at 0.10 g of NIS as a catalyst. All the acetylated cotton cellulose samples 11–15 showed evidence of acetylation with three ester bands enhanced at 1744 (carbonyl C O stretching of ester), 1370 (C H in O(C O) CH3 ) and 1039 cm−1 (C O stretching of acetyl group). They also displayed a low intensity of the OH stretching bands at 3326 cm−1 . 3.4.
1H
NMR analysis
A 1 H NMR spectrum of acetylated cotton cellulose (sample 12) took place in 2 h with 0.10 g of NIS. Fig. 4 shows that there were two clusters of hydrogen atom signals. The first was proton resonance signals of the glucose ring (ı = 3.53–5.06 ppm), and the second was methyl protons resonance signals of the acetate group (ı = 1.93–2.11 ppm) (Kono, Hashimoto, & Shimizu, 2015). The DS of cotton cellulose acetates can be calculated by 1 H NMR spectroscopy according to the following equation (Cao et al., 2007): DS =
7 × Iacetyl 3 × IAGU
where, Iacetyl is the integral of methyl protons of acetyl groups, IAGU is the integral of all protons of anhydroglucose unit. The DS
value obtained from 1 H NMR spectrum was 3.0, in excellent agreement with DSFTIR , and experimental value. It was clear that cotton cellulose triacetate was formed. 3.5. Raman spectra The degree of acetylation can be determined by using Raman spectroscopic technique too; it was estimated by calculating the ratios R1 and R2 . R1 and R2 are the ratios between the intensity of the acetyl C O stretching vibration of ester at 1736–1751 cm−1 . The intensity of COC ˇ-glycosidic link, with asymmetric and symmetric stretching bands, was found to be about 1087–1100 and 1121–1135 cm−1 , respectively. R1 =
IC=O I1094
WG = R1 × 0.7 DS =
WG × 3 0.7
The most Raman bands that affirm successful acetylation were observed at about 1736–1751, 1434–1461, 826–878 and 634–698 cm−1 . These bands are associated with (C O stretching vibration of ester), (CH3 -symmetric deformation), (H3 C C stretching), and (O C O in plane deformation), respectively. Fig. 5 shows Raman spectra of un-modified cotton cellulose (spectrum 1); the acetylated cotton cellulose of sample 12 took place in 2 h with 0.10 g NIS. Table 1 shows all the DS which was obtained from Raman spectra for samples 1–16. The DS calculated from Raman data was also found to fit with DSFTIR , DSH NMR , and experimental value (Adebajo, Frost, Kloprogge, & Kokot, 2006). 3.6. TGA analysis The thermal gravimetric analysis (TGA) was performed on the selected cellulose acetate (C-11 to C-15) and for cotton cellulose in order to examine the influence of their structural differences
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on their degradation behavior. Investigation of thermal gravimetric analysis (TGA) of the prepared acetate (C-11 to C-15) is presented in Fig. 6. It is seen that the degradation of all synthetic cellulose acetate occurs as more acetates degrade at higher temperature than less acetate. For example, triacetate C-12 and C-13 degrade at higher temperature than mono- (C-11) and diacetate (C-14 and C-15). This difference in the mass loss is possibly ascribed to the replacement of hydroxyl groups with acetyl groups. 4. Conclusions In this study we provided a new method to prepare cotton cellulose acetates in good yields from cotton cellulose. This was done using acetic anhydride and in the presence of different amounts of NIS which was used as an elegant catalyst. By using 0.05 g of NIS as a catalyst, and increasing the reaction time from 1 to 3 h, an increased in the WPG from 33.12 to 50.21%, respectively, resulted. To enhance yields of cotton cellulose acetates, we increased the concentration of the catalyst (0.075 g NIS) and the time of the reaction from 1–3 h. This caused the WPG to increase from 29.94 to 57.09%. About 0.10 g of NIS was used for 1–3 h, the WPG then increased from 24.71 to 65.41%, and cellulose acetates reached a DS of 2.84 in 2 h. The acetylation of cotton cellulose was successfully performed with increment reaction time and amount of catalyst at 0.10 g, 3 h. As the reaction time increased from 4–5 h, the WPG decreased from 55.08 to 43.33%. The optimum conditions to prepare cellulose triacetate were determined at 2 h and 0.10 g NIS. Under those conditions, the WPG was found to be 71.83%. FTIR, Raman, and NMR data were used to investigate the level of acetylation of cotton cellulose. Acknowledgements We are grateful to Science and Technological Development Fund (STDF) of Egypt for financial support for the project no. 4788. References Adebajo, M. O., & Frost, R. L. (2004). Infrared and 13 C MAS nuclear magnetic resonance spectroscopic study of acetylation of cotton. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 60, 449–453. Adebajo, M. O., Frost, R. L., Kloprogge, J. T., & Kokot, S. (2006). Raman spectroscopic investigation of acetylation of raw cotton. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 64(2), 448–453. Bikales, N. M., & Segal, L. (1971). Cellulose and cellulose derivatives, high polymers: Series V. New York: Wiley-Interscience. Biswas, A., Selling, G., Appell, M., Woods, K. K., Willett, J. L., & Buchanan, C. M. (2007). Iodine catalyzed esterification of cellulose using reduced levels of solvent. Carbohydrate Polymers, 68, 555–560. Biswas, A., Selling, G. S., Shogren, R. L., Willett, J. L., Buchanan, C. M., & Cheng, H. N. (2009). Iodine-catalyzed esterification of polysaccharides. Chemistry Today, 27(4), 4–6. Biswas, A., Shogren, R. L., & Willett, J. L. (2005). A solvent-less method to prepare cellulose or starch acetate. Biomacromolecules, 6, 1843–1845. Buchanan, C. M., Gardner, R., & Komarek, R. J. (1993). Aerobic biodegradation of cellulose acetate. Journal of Applied Polymer Science, 47, 1709–1719. Cao, Y., Wu, J., Meng, T., Zhang, J., He, J., Li, H., et al. (2007). Acetone-soluble cellulose acetates prepared by one-step homogeneous acetylation of cornhusk cellulose in an ionic liquid 1-allyl-methylimidazolium chloride (AmimCl). Carbohydrate Polymers, 69, 665–672. Connors, K. A., & Albert, K. S. (1973). Determination of hydroxyl compounds by 4dimethylaminopyridine-catalyzed acetylation. Journal of Pharmaceutical Science, 62, 845–846. Dai, R. H., Liu, H. J., Jia, J. H., & Ru, J. (2005). Preparation and characterization of novel adsorbent made by cellulose acetate. Environmental Science, 26, 111–113. Das, A. M., Ali, A. A., & Hazarika, M. P. (2014). Synthesis and characterization of cellulose acetate from rice husk: Eco-friendly condition. Carbohydrate Polymers, 112, 342–349.
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