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Degradation of cotton cellulose treated with hydrochloric acid either in water or in ethanol
Food Hydrocolloids 23 (2009) 1548–1553
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Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd
Degradation of cotton cellulose treated with hydrochloric acid either in water or in ethanol Jheng-Hua Lin a, *, Yung-Ho Chang b, You-Hong Hsu b a b
Department of Hospitality Management, MingDao University, #396 Wen-Hwa Road, Peetow 52345, Taiwan Department of Food and Nutrition, Providence University, Shalu 43301, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 September 2008 Accepted 13 October 2008
Cotton cellulose was acid treated either in water or in ethanol, containing 1.39% HCl, at 45 and 65 C for 1–5 h. The morphology and molecular weight distribution of celluloses before and after acid treatments were observed, and the differences in the structure of celluloses treated at different conditions were compared. The soluble sugar contents of celluloses during acid treatment were lower than 6%. Native cellulose showed smooth surface, whereas tiny pin-holes (15–20 nm in diameter) and wrinkles were found on the surface of acid-treated cellulose. Cellulose tended to have pin-holes after treated in ethanol at 65 C. When treated in the same media, the weight-average degree of polymerization (DPw) of cellulose decreased with increasing treatment time or temperature. The degradation rate of cellulose treated in ethanol was faster than that of cellulose treated in water, while the temperature effect on degradation rate was more profound for cellulose treated in water. Nevertheless, the crystallinity of cellulose after acid treatments remained constant or slightly increased. Results indicate that acid treatment in ethanol has more profound effect on the molecular degradation and surface structure of cellulose than the acid treatment in water. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Cellulose Acid treated Medium effect Molecular weight distribution Degradation rate
1. Introduction Cellulose is one of the most abundant polysaccharides on earth. Cellulosic wastes are generated in significant amounts from both industrial and agricultural/forestry activities, and are important potential renewable energy resources (Thanakoses, Black, & Holtzappl, 2003). Generally, a cellulosic material is used to produce glucose by acid treating. For shortening the reaction time, cellulose is treated with concentrated acid at low temperature or with diluted acid solution at high temperature, traditionally temperature higher than 200 C is used in dilute acid cellulose hydrolysis processes (Saeman, 1945; Zhao, Kwak, Wang, Franz, White, & Holladay, 2006). However, cellulose acid treated under violent conditions causes the degradation of glucose (Saeman, 1945; Mok, Antal, & Varhegyi, 1992; Torget, Kim, & Lee, 2000; Xiang, Kim, & Lee, 2003) and produces a substantial amount of byproducts (Tomaya, Yoshichi, & Akira, 1987; Maksinov, Denisov, & Makarov, 1990; Jacques, Andree, & Christion, 1990; Jia & Shen, 2002), subsequently reduces the yield of glucose,. Although, the acid hydrolysis of cellulosic materials to produce glucose has been industrialized for almost a century (Mok et al., 1992), the underlying chemistry is still a focus
* Corresponding author. Tel.: þ886 4 8876660x7827; fax: þ886 4 8879035. E-mail address: [email protected] (J.-H. Lin). 0268-005X/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2008.10.005
of research interest until now. Moreover, the transition products of cellulose during acid hydrolysis, such as cellooligosaccharide (soluble) and microcrystal cellulose (insoluble), have high utilizations and values for many industries in recent years (Iijima & Takeo, 2000; Grodzka, Maciejec, & Krygier, 2005). Thus, the study on improving the controllability and hydrolysis rate of cellulose treated with acid is worth for further investigation. Starch has been treated with acid as cellulose to produce soluble starch, and the yield of soluble starch decreased with increasing concentration of acid and treatment time (Wurzburg, 1986). Small (1919) proposed an acid–alcohol treatment procedure, by refluxing starch granules in 95% ethanol with low acid concentration (0.2– 1.6% HCl) and short treatment time (6–15 min), for obtaining the maximum conversion of raw starch into soluble starch. Results of studies on acid–alcohol treatment of starch indicate that acid degradation of starch molecules occurs in methanol, ethanol, propanol or butanol, and that the degradation rate of starch molecules strongly depends on the type of alcohol (Fox & Robyt, 1992; Chang, Lin, & Chang, 2006). Furthermore, the molecular weight and chain length of starch obviously decrease after acid– alcohol treatment, but the recovery of starch granules in alcohols can be higher than 90% (Lin, Lee, & Chang, 2003; Lin, Lii, & Chang, 2005; Lin & Chang, 2006). The molecular size of acid–alcohol treated starch varies with different conditions, such as reaction time, temperature, acid concentration, alcohol type and alcohol
J.-H. Lin et al. / Food Hydrocolloids 23 (2009) 1548–1553
concentration (Chang et al., 2006; Chang, Lin, & Lii, 2004; Lin et al., 2003, 2005; Robyt, Choe, Hahn, & Fuchs, 1996). Results also indicate that acid–alcohol treatment show a high feasibility in controlling the degradation and molecular size of starch granules (Fox & Robyt, 1992; Lin & Chang, 2006; Lin, Wang, & Chang, 2008). Both cellulose and starch are consisted of glucose and have semi-crystalline structure. Although the acid hydrolysis of native cellulose is much more difficult than that of starch, the acidhydrolysis mechanisms of cellulose and starch are similar. Up to now, most studies on acid treatment of cellulose are performed in the aqueous system, no study has reported the media effect on acid degradation of cellulose. As mentioned, acid–alcohol treatments of starch show high controllability and efficiency in starch degradation, therefore the feasibility of acid–alcohol treatment on cellulose is worth to investigate. In this report, cotton cellulose was treated either in ethanol or in water, containing 1.39% HCl, at 45 and 65 C for 1–5 h. The molecular size distributions of cellulose, before and after treatments, and the degradation rate of cellulose treated at different conditions were determined. Furthermore, the morphology and crystallinity of cellulose were also examined. The media effects on structures, including molecule, surface and crystalline structures, and degradation rate of cellulose treated with acid were compared and discussed. 2. Materials and methods 2.1. Materials Cotton cellulose (No. C6663) was purchased from Sigma– Aldrich (St. Louis, MO, USA). All reagents used were of analytical grade. 2.2. Methods 2.2.1. Acid treatment Acid treatment of cellulose was performed according to Lin et al. (2003) with some modifications. Cotton cellulose (25 g) was suspended in 250 mL distilled water or ethanol. The suspension was stirred at different temperatures (45 and 65 C), and the reaction was started by adding 10 mL (containing 1.39% HCl) of concentrated HCl (36%, w/v) then was allowed to proceed for 1–5 h. The reaction was stopped by neutralizing with 1 M NaHCO3 solution and cooling in an ice-bath for 5 min. The suspension was filtered through a 0.45 mm filter membrane. The filtrate was collected and the soluble sugar content in the supernatant during acid treatment was determined by phenol–sulfuric acid method (Dubois, Gilles, Hamilton, Rebers, & Smith, 1956). Treated cellulose was recovered, washed four times with 50% ethanol and dried at 40 C in an airoven. 2.2.2. Morphology The morphology of cellulose was examined by using of cold cathode field emission scanning electron microscopy (JEOL JSM6700F, Tokyo, Japan). Cellulose samples were mounted on circular aluminum stubs with double sticky tape, coated with gold, and then examined and photographed at an accelerating potential of 3.0 kV. 2.2.3. Molecular weight distribution For enhancing the solubility and detection properties, phenyl isocyanate derivative (tricarbanilated cellulose, CTC) was used for modification of cellulose before molecular weight distribution determination. CTC was prepared following the method proposed by Wood, Conner and Hill (1986). Cellulose sample was dried in a flask at 105 C for 4 h. Air-dried cellulose (0.2 g) was stirred with 50 mL of anhydrous pyridine at 80 C, and the phenyl isocyanate
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(4 mL) was added for starting modification. The flask was then sealed with a Teflon stopper. After 48 h, a clear yellow solution was formed and 4 mL of methanol was added to react with the excess phenyl isocyanate. The reaction mixture was transferred to a round bottomed flask and the pyridine was evaporated in a vacuum evaporator at 40 C. The syrupy liquid was dissolved in 150 mL acetone and evaporated at 50 C, and the procedure of dissolved syrupy liquid with 150 mL acetone and evaporated at 50 C was repeated two times to remove the impurity. The final syrupy liquid after dissolving with 100 mL acetone and transferring into a petri dish was dried in a vacuum-oven at 60 C. The molecular weight distribution of CTC was determined by high-performance sizeexclusion chromatography (HPSEC). CTC (5 mg) was dissolved in 5 mL tetrahydrofuran (THF) and filtered through a 0.22 mm filter prior to analysis. The filtrate was injected into an HPSEC system consisting of an LC pump (Series 200, Perkin Elmer, Norwalk, CT) and a UV detector (785A, Perkin Elmer). The columns used were a Shodex KF-G guard column and a KF-805L column (Showa Denko, Tokyo, Japan) connected in series and kept at 25 C. The mobile phase was THF at a flow rate of 0.75 mL/min and the wavelength of detector was 254 nm. Molecular weight of cellulose was obtained using the universal calibration procedure based on narrow polystyrene standards (Pressure Chemical, Pittsburgh, PA). The degree of polymerization of cellulose was obtained from the molecular weight of CTC divided by the molecular mass of the repeating unit of CTC (monomer molecular weight ¼ 519 Da) (Stol, Pedersoli, Poppe, & Kok., 2002). 2.2.4. Cross polarization/magic angle spinning (CP/MAS) 13C solidstate NMR spectra CP/MAS 13C solid-state NMR spectra of cellulose was examined according to the method described by Zhao et al. (2006). Cellulose samples were analysis with Bruker DSX-400 spectrometer (Karlsruhe, Germany) equipped with CP/MAS (cross polarization/magic angle spinning) accessories operating under a static field strength of 2.3 T (100 MHZ 1H) at 25 C. The contact time for CP was 1 ms with a proton pulse of 5.5 ms and decoupling power of 45 kHz. The MAS speed was 3 kHz and the delay time after the acquisition of the FID signal was 2 s. The calibration on crystallinity index (ICr) of cellulose was following the method proposed by Liitia¨, Maunu and Hortling (2000). The ICr was determined from the peak areas assigned to C4 crystalline (86–92 ppm) and C4 noncrystalline (79– 86 ppm) material, and is defined as ICr ¼ A86–92 ppm/(A79– 86 ppm þ A86–92 ppm) 100%, by deconvolution using a Lorenzian line shape. 2.2.5. Statistical analysis The General Linear Model (GLM) procedure of Statistical Analysis System (SAS Institute Inc., Cary, NC, USA) was used for performing statistical analysis. The significant difference of means was analyzed by Duncan’s multiple range test at p < 0.05. 3. Results and discussion 3.1. Soluble sugar content in supernatant The soluble sugar contents in supernatant during acid treatment of cellulose were below 6% (Fig. 1). At 45 C, the soluble sugar content of cellulose treated either in water or in ethanol for 1–5 h was not higher than 1%. While the soluble sugar content during acid treatment at 45 C increased with increasing treatment time. For the same treatment time, cellulose treated in ethanol had lower soluble sugars (0.24–0.29%) than that of cellulose treated in water (0.85–1.00%). Cellulose treated at 65 C showed higher soluble sugar content (1.12–5.04%) than that of cellulose treated at 45 C (0.24–1.00%). Cellulose treated in ethanol at 65 C for 1 h had lower
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J.-H. Lin et al. / Food Hydrocolloids 23 (2009) 1548–1553
Fig. 1. Soluble sugar content of cellulose samples during acid treatment.
soluble sugar content than that of cellulose treated in water at the same conditions (0.84% vs 1.14%), which is similar to that of cellulose treated in 45 C (0.24% vs 0.85%). However, the soluble sugar content of cellulose treated in ethanol at 65 C for longer than 1 h (2.44–5.04%) were higher than that of the respective cellulose treated in water (1.12–1.50%). The discrepancy in soluble sugar content of cellulose treated at 45 and 65 C in ethanol were more obvious than that of cellulose treated in water. Results indicate that cellulose treated in water at low treatment temperature or short treatment time, produced less soluble sugar than cellulose treated in ethanol. While reverse result was found for cellulose treated at relative intense conditions. Moreover, the temperature effect on soluble sugar content of cellulose acid treated in ethanol is more profound than that of cellulose acid treated in water. 3.2. Morphology The morphological structure of cellulose samples during acid treatment was observed using scanning electron microscopy. No obvious difference in shape between cellulose before and after acid treatments was observed, while some alterations on the surface of cellulose were found. The scanning electron micrograms of cellulose (Fig. 2) showed that the most part of the surface of native
cellulose was smooth in spite of some large fissures and wrinkles. Similar result on cotton morphology was observed by Zhao, Kwak, Zhang, Brown, Arey and Holladay (2007). After acid treated in water (Fig. 2), the surface of cellulose treated at 45 C did not show obvious changes and was similar to that of native cellulose. However, after treated at 65 C some tiny wrinkles were found on the surface of cellulose and which was more profound for cellulose with 5 h treatment time. For samples acid treated in ethanol at 45 C, some tiny wrinkles existed on the surface of cellulose (Fig. 3), which was similar to that of cellulose treated in water at 65 C (Fig. 2). While acid treated in ethanol at 65 C, numerous pin-holes (15–20 nm in diameter) presented on the surface of cellulose. The number and size of pin-hole increased with increasing treatment time. Zhao et al. (2007) indicated that the microfibril bundles structure on the surface of acid-treated (0.1–0.4 M H2SO4, 150 C) cotton cellulose was observed when acid hydrolysis ratio was higher than 5%. Results of this study showed that acid treatment caused the occurrence of fissures and pin-holes on the surface of cellulose. No obvious microfibril bundles structure in the surface of cellulose was found. This could be attributed to the relative mild condition of acid treatment used in this study. Moreover, the changes in morphological structure of cellulose depend on the media and treatment temperature, which is more profound for cellulose treated in ethanol than in water. Cellulose treated in ethanol at 65 C had high soluble sugar content and large pin-hole on the surface, and both the soluble sugar content and the number and size of pin-hole obviously increased with increasing treatment time. On the other hand, cellulose treated at other conditions had low soluble sugar contents. Furthermore, the morphological structure of those cellulose samples did not show obvious changes or had some tiny fissures but no pin-holes. This indicates that acid treated of cellulose at intense conditions, such as in ethanol and at 65 C, causes the occurrence of surface pin-hole and the increase of soluble sugar content. The pin-hole structure on the surface of cellulose implies that more soluble sugar released during acid treatment. 3.3. Molecular weight distribution and degradation rate Fig. 4 illustrates the molecular weight distributions of cellulose samples, which shows that native cellulose had a broad molecular weight distribution. After acid treatment, the molecular weight distribution of cellulose shifted toward small molecular fraction,
Fig. 2. Scanning electron micrograms of native cellulose and cellulose samples after acid treated in water containing 1.39% HCl.
J.-H. Lin et al. / Food Hydrocolloids 23 (2009) 1548–1553
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Fig. 3. Scanning electron micrograms of native cellulose and cellulose samples after acid treated in ethanol containing 1.39% HCl.
especially for cellulose samples after treated at 65 C. Table 1 shows that the weight-average (DPw) and number-average (DPn) degree of polymerization of native cotton cellulose was 2427 and 240 anhydrous glucose unit (AGU), respectively. The polydispersity (DPw/ DPn) of native cotton cellulose was 10.1. Both DPw and DPn of cellulose obviously decreased after acid treated, except for cellulose acid treated in water at 45 C. The DPw, DPn and polydispersity of acid-treated cellulose decreased with increasing treatment time. The degradation extent was more profound for cellulose after acid treated at 65 C than treated at 45 C. For the same treatment temperature and time, cellulose treated in ethanol had significantly lower DPw and DPn than cellulose treated in water. Commonly, the yield of glucose or the residue amount of cellulose is used as the index for studying the degradation rate of cellulose treated with acid (Xiang, Lee, Pettersson & Torget, 2003).
Rare study deliberated the molecular size of acid-treated cellulose during treatment. In this study, the change of DPw of cellulose was used to monitor the degradation extent of cellulose treated with different conditions. The hydrolysis of glycosidic bonds has been demonstrated follows a first-order reaction (Daruwalla, & Shet, 1962; Springer, 1966), consequently the following equation could express the reduction in DPw of polysaccharides during acid treatment (Chang, Tai, & Cheng, 2001; Lin et al., 2003):
1=Mt ¼ 1=M0 þ kt=m ¼ 1=M0 þ k0 t where k and k0 are the rate constants, t is the reaction time, M0 is the DPw of native cellulose, Mt is the DPw of cellulose after treatment time t, and m is the monomer molecular weight. Fig. 5 shows the plots of treatment time against the reciprocal of DPw, and the slopes
Fig. 4. Molecular weight distributions of native cellulose (–) and cellulose samples after acid treated for 1 (C), 3 (:) and 5 h (;), respectively.
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Table 1 Molecular characterizes and crystallinity index of cellulose samples Sample
Native Water, 45 C 1h 3h 5h Ethanol, 45 C 1h 3h 5h Water, 65 C 1h 3h 5h Ethanol, 65 C 1h 3h 5h
Molecular characterizesa
Crystallinity index (%)
DPw
DPn
Polydispersity
2427ab
240a
10.1b
57.4ac
2518a 2282b 1994c
247a 235b 229c
10.2b 9.7 de 8.8g
56.1a 59.2a 60.8a
2221b 1028e 1087e
191d 107g 110g
11.6a 9.6f 9.9c
54.2a 57.8a 57.6a
1565d 964f 759h
163e 117f 101h
9.6ef 8.2h 7.5j
59.4a 59.5a 58.3a
857g 428i 409i
88i 54j 60j
9.7d 7.9i 6.8k
56.1a 58.3a 58.7a
a DPw: Weight-average degree of polymerization; DPn: Number-average degree of polymerization; Polydispersity ¼ DPw/DPn. b Means with different letters in the same parameter differ significantly (p < 0.05), n ¼ 3. c The peak fitting correlation coefficient is at least 0.995, and the maximum standard deviation is less than 5%.
of the regression lines are the degradation rates (k0 ) of cellulose during different acid treatments. Results of Fig. 5 indicate that cellulose treated in ethanol at 65 C had the highest k0 (4.129) among the cellulose samples treated with different conditions. At the same treatment temperature, the k0 of cellulose treated in ethanol was higher than that of cellulose treated in water. Cellulose treated at 65 C had obvious higher k0 than that of cellulose treated at 45 C. As treatment temperature increased from 45 to 65 C, the increment of k0 for samples treated in water (9.4-fold) was more profound than treated in ethanol (3.4-fold). Moreover, the difference in k0 between cellulose treated in ethanol and in water at 45 C (6.2-fold) was more obvious than that at 65 C (2.3-fold). Results imply that the degradation rate of cellulose acid treated in ethanol is faster than that of cellulose treated in water, and which is more profound for cellulose treated at low temperature (45 C). Fox and Robyt (1992) concluded that hydrolysis of the glycosidic linkage of starch granule acid treated in alcohol was taking place exclusively inside the granule with the granule-bound water. Therefore, the hydrogen ion in ethanol more easily penetrates into cellulose and degrades the molecules inside the cellulose. Consequently,
Fig. 6. CP/MAS 13C solid-state NMR spectra of native cellulose and cellulose samples after acid treated for 5 h.
a relative higher degradation rate of cellulose acid treated in ethanol was observed in this study. 3.4. Crystallinity index Fig. 6 shows the typical NMR spectra of cellulose samples studied, and illustrates that the NMR spectra of native cellulose and acid-treated cellulose were similar to each other. Furthermore, no obvious difference in spectra of cellulose samples with different treatment conditions was found. Table 1 shows the crystallinity index calculated from the NMR spectra according to the method proposed by Liitia¨ et al. (2000). The crystallinity of cotton cellulose was 57.4%. After treatment, the crystallinity index of acid-treated cellulose remained constant or slightly increased. While no obvious tendency in changes of crystallinity index for cellulose samples treated in different media or temperatures was found. The acid-catalyzed hydrolysis of cellulose is a complex heterogeneous reaction, which involves physical factors as well as the hydrolytic chemical reaction. Amorphous cellulose was hydrolyzed 100-fold faster than crystalline a-cellulose (Xiang et al., 2003). Since cellulose molecules possess semi-crystalline structure, the hydrolysis rate of cellulose should be a heterogeneous reaction and a two-order hydrolysis pattern and products with low degree of polymerization and high crystallinity should be observed (Nelson, 1960). However, the change in crystallinity of cellulose after treated is not obvious, although the DPw of cellulose decreased dramatically. This could be attributed to the low acid concentration (<2%) and temperature (no
Fig. 5. Plot of treatment time against the reciprocal of DPw of cellulose samples.
J.-H. Lin et al. / Food Hydrocolloids 23 (2009) 1548–1553
higher than 65 C) used in this study. Therefore, the degradation of cellulose preferentially occurred in the amorphous regions, consequently only one-order degradation pattern was observed. 4. Conclusions The soluble sugar content, changes in morphological structure and degradation rate of cellulose after acid treated either in water or in ethanol at 45 or 65 C were found depended on the media and treatment temperature. The temperature effect on soluble sugar content of cellulose treated in ethanol was more profound than that of cellulose treated in water. Tiny wrinkles or pin-holes were found on the surface of cellulose after acid treated. Cellulose treated in ethanol at 65 C obviously formed pine-holes on the surface, while treated under other conditions the surface of cellulose did not show obvious changes or tended to form wrinkles. The degradation rate of cellulose treated in ethanol was obviously faster that that treated in water, especially treated at 45 C. Results suggest that acid treated in ethanol showed more obvious effect on degradation, of both surface structure and molecular size of cellulose, than acid treated in water. Results also reveal that cellulose acid treated in media other than water, such as ethanol, could improve the degradation efficiency. Nevertheless, investigations on the degradation of cellulose acid treated in media other than water and ethanol are needed for further elucidating the controllability and efficiency of acid degradation of cellulose. Acknowledgment We thank the National Science Council, Taiwan, for financial support (NSC 96-2313-B-451-004). References Chang, K. L. B., Tai, M. C., & Cheng, F. H. (2001). Kinetics and products of the degradation of chitosan by hydrogen peroxide. Journal of Agricultural and Food Chemistry, 49(10), 4845–4851. Chang, Y. H., Lin, J. H., & Chang, S. Y. (2006). Physicochemical properties of waxy and normal corn starches treated in different anhydrous alcohols with hydrochloric acid. Food Hydrocolloids,, 20(2/3), 332–339. Chang, Y. H., Lin, J. H., & Lii, C.-Y. (2004). Effect of ethanol concentration on the physicochemical properties of waxy corn starch treated by hydrochloric acid. Carbohydrate Polymers, 57(1), 89–96. Daruwalla, E. H., & Shet, R. T. (1962). Heterogeneous acid hydrolysis of alpha– cellulose from Sudanese cotton. Textile Research Journal, 32(11), 942–954. Dubois, M., Gilles, K. A., Hamilton, J. K., Rebers, P. A., & Smith, F. (1956). Colorimetric method for determination of sugars and related substances. Analytical Chemistry, 28(3), 350–356. Fox, J. D., & Robyt, J. F. (1992). Modification of starch granules by hydrolysis with hydrochloric acid in various alcohols, and the formation of new kinds of limit dextrins. Carbohydrate Research, 227(1), 163–170. Grodzka, K., Maciejec, A., & Krygier, K. (2005). Attempts to apply microcrystalline cellulose as a fat replacer in low fat mayonnaise emulsions. Zywnosc, 12(1), 52–61. Iijima, H., & Takeo, K. (2000). Microcrystalline cellulose: an overview. In G. O. Phillips, & P. A. Williams (Eds.), Handbook of hydrocolloids (pp. 331–346). Boca Raton, Florida: CRC Press.
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Jacques, D., Andree, G., & Christion, P. (1990). Prepaaration of b-(1-6)oligomers of 2acetamido-2-deoxyglacoses and galactose as drugs. FR 2640628. Jia, Z., & Shen, D. (2002). Effect of reaction temperature and reaction time on the preparation of low-molecular-weight chitosan using phosphoric acid. Carbohydrate Polymers, 49(4), 393–396. Liitia¨, T., Maunu, S. L., & Hortling, B. (2000). Solid state NMR studies on cellulose crystallinity in fines and bulk fibres separated from refined kraft pulp. Holzforschung, 54(6), 618–624. Lin, J. H., & Chang, Y. H. (2006). Molecular degradation rate of rice and corn starches during acid–methanol treatment and its relation to the molecular structure of starch. Journal of Agricultural and Food Chemistry, 54(16), 5880–5886. Lin, J. H., Lee, S. Y., & Chang, Y. H. (2003). Effect of acid–alcohol treatment on the molecular structure and physicochemical properties of maize and potato starches. Carbohydrate Polymers, 53(4), 475–482. Lin, J. H., Lii, C.-Y., & Chang, Y. H. (2005). Chang of granular and molecular structures of waxy maize and potato starch after treated in alcohols with or without hydrochloric acid. Carbohydrate Polymers, 59(4), 507–515. Lin, J. H., Wang, S. W., & Chang, Y. H. (2008). Effect of molecular size on gelatinization thermal properties before and after annealing of rice starch with different amylose contents. Food Hydrocolloids, 22(1), 156–163. Maksinov, V.I., Denisov, V.M., & Makarov, N.V. (1990). Preparation of water-soluble oligosaccharides. SU 1571047. Mok, W. S. L., Antal, M. J., & Varhegyi, G. (1992). Productive and parasitic pathways in dilute acid-catalyzed hydrolysis of cellulose. Industrial and Engineering Chemistry Research, 31(1), 94–100. Nelson, M. L. (1960). Apparent activation energy of hydrolysis of some cellulosic materials. Journal of Polymer Science, 43(142), 351–371. Robyt, J. F., Choe, J. Y., Hahn, R. S., & Fuchs, E. B. (1996). Acid modification of starch granules in alcohols: effects of temperature, acid concentration, and starch concentration. Carbohydrate Research, 281(2), 203–218. Saeman, J. F. (1945). Kinetic of wood saccharification. Hydrolysis of cellulose and decomposition of sugars in dilute acid at high temperature. Industrial and Engineering Chemistry, 37(1), 43–52. Small, J. C. (1919). A method for the preparation of soluble starch. Journal of American Chemical Society, 41(1), 113–120. Springer, E. L. (1966). Hydrolysis of aspenwood with aqueous solutions of hydrochloric acid. Tappi, 49(3), 102–106. Stol, R., Pedersoli, J. L., Poppe, H., & Kok, W. T. (2002). Application of size exclusion electrochromatography to the microanalytical determination of the molecular mass distribution of celluloses from objects of cultural and historical value. Analytical Chemistry, 74(10), 2314–2320. Thanakoses, P., Black, A. S., & Holtzappl, M. T. (2003). Fermentation of corn stover to carboxylic acids. Biotechnology and Bioengineering, 83(2), 191–200. Tomaya, T., Yoshichi, A., & Akira, A. (1987). Manufacture of water soluble lowmolecular weight chitosan with narrow molecular weight distribution. JP 62 184002. Torget, R. W., Kim, J. S., & Lee, Y. Y. (2000). Fundamental aspects of dilute acid hydrolysis/fractionation kinetics of hardwood carbohydrates. 1. Cellulose hydrolysis. Industrial and Engineering Chemistry Research, 39(8), 2817– 2825. Wood, B. F., Conner, A. H., & Hill, C. G. J. (1986). The effects of precipitation on the molecular weight distribution of cellulose tricarbanilate. Journal of Applied Polymer Science, 32(2), 3703–3712. Wurzburg, O. B. (1986). Converted starches. In O. B. Wurzburg (Ed.), Modified starches: Properties and uses (pp. 17–40). Boca Raton, Florida: CRC Press. Xiang, Q., Kim, J. S., & Lee, Y. Y. (2003). A comprehensive kinetic model for diluteacid hydrolysis of cellulose. Applied Biochemistry and Biotechnology, 106(1-3), 337–352. Xiang, Q., Lee, Y. Y., Pettersson, P. O., & Torget, R. W. (2003). Heterogeneous aspects of acid hydrolysis of a-cellulose. Applied Biochemistry and Biotechnology, 107(1– 3), 505–514. Zhao, H., Kwak, J. H., Wang, Y., Franz, J. A., White, J. M., & Holladay, J. E. (2006). Effects of crystallinity on dilute acid hydrolysis of cellulose by cellulose ballmilling study. Energy and Fuels, 20(2), 807–811. Zhao, H., Kwak, J. H., Zhang, Z. C., Brown, H. M., Arey, B. W., & Holladay, J. E. (2007). Studying cellulose fiber structure by SEM, XRD, NMR and acid hydrolysis. Carbohydrate Polymers, 68(2), 235–241.
Contents lists available at ScienceDirect
Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd
Degradation of cotton cellulose treated with hydrochloric acid either in water or in ethanol Jheng-Hua Lin a, *, Yung-Ho Chang b, You-Hong Hsu b a b
Department of Hospitality Management, MingDao University, #396 Wen-Hwa Road, Peetow 52345, Taiwan Department of Food and Nutrition, Providence University, Shalu 43301, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 September 2008 Accepted 13 October 2008
Cotton cellulose was acid treated either in water or in ethanol, containing 1.39% HCl, at 45 and 65 C for 1–5 h. The morphology and molecular weight distribution of celluloses before and after acid treatments were observed, and the differences in the structure of celluloses treated at different conditions were compared. The soluble sugar contents of celluloses during acid treatment were lower than 6%. Native cellulose showed smooth surface, whereas tiny pin-holes (15–20 nm in diameter) and wrinkles were found on the surface of acid-treated cellulose. Cellulose tended to have pin-holes after treated in ethanol at 65 C. When treated in the same media, the weight-average degree of polymerization (DPw) of cellulose decreased with increasing treatment time or temperature. The degradation rate of cellulose treated in ethanol was faster than that of cellulose treated in water, while the temperature effect on degradation rate was more profound for cellulose treated in water. Nevertheless, the crystallinity of cellulose after acid treatments remained constant or slightly increased. Results indicate that acid treatment in ethanol has more profound effect on the molecular degradation and surface structure of cellulose than the acid treatment in water. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Cellulose Acid treated Medium effect Molecular weight distribution Degradation rate
1. Introduction Cellulose is one of the most abundant polysaccharides on earth. Cellulosic wastes are generated in significant amounts from both industrial and agricultural/forestry activities, and are important potential renewable energy resources (Thanakoses, Black, & Holtzappl, 2003). Generally, a cellulosic material is used to produce glucose by acid treating. For shortening the reaction time, cellulose is treated with concentrated acid at low temperature or with diluted acid solution at high temperature, traditionally temperature higher than 200 C is used in dilute acid cellulose hydrolysis processes (Saeman, 1945; Zhao, Kwak, Wang, Franz, White, & Holladay, 2006). However, cellulose acid treated under violent conditions causes the degradation of glucose (Saeman, 1945; Mok, Antal, & Varhegyi, 1992; Torget, Kim, & Lee, 2000; Xiang, Kim, & Lee, 2003) and produces a substantial amount of byproducts (Tomaya, Yoshichi, & Akira, 1987; Maksinov, Denisov, & Makarov, 1990; Jacques, Andree, & Christion, 1990; Jia & Shen, 2002), subsequently reduces the yield of glucose,. Although, the acid hydrolysis of cellulosic materials to produce glucose has been industrialized for almost a century (Mok et al., 1992), the underlying chemistry is still a focus
* Corresponding author. Tel.: þ886 4 8876660x7827; fax: þ886 4 8879035. E-mail address: [email protected] (J.-H. Lin). 0268-005X/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2008.10.005
of research interest until now. Moreover, the transition products of cellulose during acid hydrolysis, such as cellooligosaccharide (soluble) and microcrystal cellulose (insoluble), have high utilizations and values for many industries in recent years (Iijima & Takeo, 2000; Grodzka, Maciejec, & Krygier, 2005). Thus, the study on improving the controllability and hydrolysis rate of cellulose treated with acid is worth for further investigation. Starch has been treated with acid as cellulose to produce soluble starch, and the yield of soluble starch decreased with increasing concentration of acid and treatment time (Wurzburg, 1986). Small (1919) proposed an acid–alcohol treatment procedure, by refluxing starch granules in 95% ethanol with low acid concentration (0.2– 1.6% HCl) and short treatment time (6–15 min), for obtaining the maximum conversion of raw starch into soluble starch. Results of studies on acid–alcohol treatment of starch indicate that acid degradation of starch molecules occurs in methanol, ethanol, propanol or butanol, and that the degradation rate of starch molecules strongly depends on the type of alcohol (Fox & Robyt, 1992; Chang, Lin, & Chang, 2006). Furthermore, the molecular weight and chain length of starch obviously decrease after acid– alcohol treatment, but the recovery of starch granules in alcohols can be higher than 90% (Lin, Lee, & Chang, 2003; Lin, Lii, & Chang, 2005; Lin & Chang, 2006). The molecular size of acid–alcohol treated starch varies with different conditions, such as reaction time, temperature, acid concentration, alcohol type and alcohol
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concentration (Chang et al., 2006; Chang, Lin, & Lii, 2004; Lin et al., 2003, 2005; Robyt, Choe, Hahn, & Fuchs, 1996). Results also indicate that acid–alcohol treatment show a high feasibility in controlling the degradation and molecular size of starch granules (Fox & Robyt, 1992; Lin & Chang, 2006; Lin, Wang, & Chang, 2008). Both cellulose and starch are consisted of glucose and have semi-crystalline structure. Although the acid hydrolysis of native cellulose is much more difficult than that of starch, the acidhydrolysis mechanisms of cellulose and starch are similar. Up to now, most studies on acid treatment of cellulose are performed in the aqueous system, no study has reported the media effect on acid degradation of cellulose. As mentioned, acid–alcohol treatments of starch show high controllability and efficiency in starch degradation, therefore the feasibility of acid–alcohol treatment on cellulose is worth to investigate. In this report, cotton cellulose was treated either in ethanol or in water, containing 1.39% HCl, at 45 and 65 C for 1–5 h. The molecular size distributions of cellulose, before and after treatments, and the degradation rate of cellulose treated at different conditions were determined. Furthermore, the morphology and crystallinity of cellulose were also examined. The media effects on structures, including molecule, surface and crystalline structures, and degradation rate of cellulose treated with acid were compared and discussed. 2. Materials and methods 2.1. Materials Cotton cellulose (No. C6663) was purchased from Sigma– Aldrich (St. Louis, MO, USA). All reagents used were of analytical grade. 2.2. Methods 2.2.1. Acid treatment Acid treatment of cellulose was performed according to Lin et al. (2003) with some modifications. Cotton cellulose (25 g) was suspended in 250 mL distilled water or ethanol. The suspension was stirred at different temperatures (45 and 65 C), and the reaction was started by adding 10 mL (containing 1.39% HCl) of concentrated HCl (36%, w/v) then was allowed to proceed for 1–5 h. The reaction was stopped by neutralizing with 1 M NaHCO3 solution and cooling in an ice-bath for 5 min. The suspension was filtered through a 0.45 mm filter membrane. The filtrate was collected and the soluble sugar content in the supernatant during acid treatment was determined by phenol–sulfuric acid method (Dubois, Gilles, Hamilton, Rebers, & Smith, 1956). Treated cellulose was recovered, washed four times with 50% ethanol and dried at 40 C in an airoven. 2.2.2. Morphology The morphology of cellulose was examined by using of cold cathode field emission scanning electron microscopy (JEOL JSM6700F, Tokyo, Japan). Cellulose samples were mounted on circular aluminum stubs with double sticky tape, coated with gold, and then examined and photographed at an accelerating potential of 3.0 kV. 2.2.3. Molecular weight distribution For enhancing the solubility and detection properties, phenyl isocyanate derivative (tricarbanilated cellulose, CTC) was used for modification of cellulose before molecular weight distribution determination. CTC was prepared following the method proposed by Wood, Conner and Hill (1986). Cellulose sample was dried in a flask at 105 C for 4 h. Air-dried cellulose (0.2 g) was stirred with 50 mL of anhydrous pyridine at 80 C, and the phenyl isocyanate
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(4 mL) was added for starting modification. The flask was then sealed with a Teflon stopper. After 48 h, a clear yellow solution was formed and 4 mL of methanol was added to react with the excess phenyl isocyanate. The reaction mixture was transferred to a round bottomed flask and the pyridine was evaporated in a vacuum evaporator at 40 C. The syrupy liquid was dissolved in 150 mL acetone and evaporated at 50 C, and the procedure of dissolved syrupy liquid with 150 mL acetone and evaporated at 50 C was repeated two times to remove the impurity. The final syrupy liquid after dissolving with 100 mL acetone and transferring into a petri dish was dried in a vacuum-oven at 60 C. The molecular weight distribution of CTC was determined by high-performance sizeexclusion chromatography (HPSEC). CTC (5 mg) was dissolved in 5 mL tetrahydrofuran (THF) and filtered through a 0.22 mm filter prior to analysis. The filtrate was injected into an HPSEC system consisting of an LC pump (Series 200, Perkin Elmer, Norwalk, CT) and a UV detector (785A, Perkin Elmer). The columns used were a Shodex KF-G guard column and a KF-805L column (Showa Denko, Tokyo, Japan) connected in series and kept at 25 C. The mobile phase was THF at a flow rate of 0.75 mL/min and the wavelength of detector was 254 nm. Molecular weight of cellulose was obtained using the universal calibration procedure based on narrow polystyrene standards (Pressure Chemical, Pittsburgh, PA). The degree of polymerization of cellulose was obtained from the molecular weight of CTC divided by the molecular mass of the repeating unit of CTC (monomer molecular weight ¼ 519 Da) (Stol, Pedersoli, Poppe, & Kok., 2002). 2.2.4. Cross polarization/magic angle spinning (CP/MAS) 13C solidstate NMR spectra CP/MAS 13C solid-state NMR spectra of cellulose was examined according to the method described by Zhao et al. (2006). Cellulose samples were analysis with Bruker DSX-400 spectrometer (Karlsruhe, Germany) equipped with CP/MAS (cross polarization/magic angle spinning) accessories operating under a static field strength of 2.3 T (100 MHZ 1H) at 25 C. The contact time for CP was 1 ms with a proton pulse of 5.5 ms and decoupling power of 45 kHz. The MAS speed was 3 kHz and the delay time after the acquisition of the FID signal was 2 s. The calibration on crystallinity index (ICr) of cellulose was following the method proposed by Liitia¨, Maunu and Hortling (2000). The ICr was determined from the peak areas assigned to C4 crystalline (86–92 ppm) and C4 noncrystalline (79– 86 ppm) material, and is defined as ICr ¼ A86–92 ppm/(A79– 86 ppm þ A86–92 ppm) 100%, by deconvolution using a Lorenzian line shape. 2.2.5. Statistical analysis The General Linear Model (GLM) procedure of Statistical Analysis System (SAS Institute Inc., Cary, NC, USA) was used for performing statistical analysis. The significant difference of means was analyzed by Duncan’s multiple range test at p < 0.05. 3. Results and discussion 3.1. Soluble sugar content in supernatant The soluble sugar contents in supernatant during acid treatment of cellulose were below 6% (Fig. 1). At 45 C, the soluble sugar content of cellulose treated either in water or in ethanol for 1–5 h was not higher than 1%. While the soluble sugar content during acid treatment at 45 C increased with increasing treatment time. For the same treatment time, cellulose treated in ethanol had lower soluble sugars (0.24–0.29%) than that of cellulose treated in water (0.85–1.00%). Cellulose treated at 65 C showed higher soluble sugar content (1.12–5.04%) than that of cellulose treated at 45 C (0.24–1.00%). Cellulose treated in ethanol at 65 C for 1 h had lower
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Fig. 1. Soluble sugar content of cellulose samples during acid treatment.
soluble sugar content than that of cellulose treated in water at the same conditions (0.84% vs 1.14%), which is similar to that of cellulose treated in 45 C (0.24% vs 0.85%). However, the soluble sugar content of cellulose treated in ethanol at 65 C for longer than 1 h (2.44–5.04%) were higher than that of the respective cellulose treated in water (1.12–1.50%). The discrepancy in soluble sugar content of cellulose treated at 45 and 65 C in ethanol were more obvious than that of cellulose treated in water. Results indicate that cellulose treated in water at low treatment temperature or short treatment time, produced less soluble sugar than cellulose treated in ethanol. While reverse result was found for cellulose treated at relative intense conditions. Moreover, the temperature effect on soluble sugar content of cellulose acid treated in ethanol is more profound than that of cellulose acid treated in water. 3.2. Morphology The morphological structure of cellulose samples during acid treatment was observed using scanning electron microscopy. No obvious difference in shape between cellulose before and after acid treatments was observed, while some alterations on the surface of cellulose were found. The scanning electron micrograms of cellulose (Fig. 2) showed that the most part of the surface of native
cellulose was smooth in spite of some large fissures and wrinkles. Similar result on cotton morphology was observed by Zhao, Kwak, Zhang, Brown, Arey and Holladay (2007). After acid treated in water (Fig. 2), the surface of cellulose treated at 45 C did not show obvious changes and was similar to that of native cellulose. However, after treated at 65 C some tiny wrinkles were found on the surface of cellulose and which was more profound for cellulose with 5 h treatment time. For samples acid treated in ethanol at 45 C, some tiny wrinkles existed on the surface of cellulose (Fig. 3), which was similar to that of cellulose treated in water at 65 C (Fig. 2). While acid treated in ethanol at 65 C, numerous pin-holes (15–20 nm in diameter) presented on the surface of cellulose. The number and size of pin-hole increased with increasing treatment time. Zhao et al. (2007) indicated that the microfibril bundles structure on the surface of acid-treated (0.1–0.4 M H2SO4, 150 C) cotton cellulose was observed when acid hydrolysis ratio was higher than 5%. Results of this study showed that acid treatment caused the occurrence of fissures and pin-holes on the surface of cellulose. No obvious microfibril bundles structure in the surface of cellulose was found. This could be attributed to the relative mild condition of acid treatment used in this study. Moreover, the changes in morphological structure of cellulose depend on the media and treatment temperature, which is more profound for cellulose treated in ethanol than in water. Cellulose treated in ethanol at 65 C had high soluble sugar content and large pin-hole on the surface, and both the soluble sugar content and the number and size of pin-hole obviously increased with increasing treatment time. On the other hand, cellulose treated at other conditions had low soluble sugar contents. Furthermore, the morphological structure of those cellulose samples did not show obvious changes or had some tiny fissures but no pin-holes. This indicates that acid treated of cellulose at intense conditions, such as in ethanol and at 65 C, causes the occurrence of surface pin-hole and the increase of soluble sugar content. The pin-hole structure on the surface of cellulose implies that more soluble sugar released during acid treatment. 3.3. Molecular weight distribution and degradation rate Fig. 4 illustrates the molecular weight distributions of cellulose samples, which shows that native cellulose had a broad molecular weight distribution. After acid treatment, the molecular weight distribution of cellulose shifted toward small molecular fraction,
Fig. 2. Scanning electron micrograms of native cellulose and cellulose samples after acid treated in water containing 1.39% HCl.
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Fig. 3. Scanning electron micrograms of native cellulose and cellulose samples after acid treated in ethanol containing 1.39% HCl.
especially for cellulose samples after treated at 65 C. Table 1 shows that the weight-average (DPw) and number-average (DPn) degree of polymerization of native cotton cellulose was 2427 and 240 anhydrous glucose unit (AGU), respectively. The polydispersity (DPw/ DPn) of native cotton cellulose was 10.1. Both DPw and DPn of cellulose obviously decreased after acid treated, except for cellulose acid treated in water at 45 C. The DPw, DPn and polydispersity of acid-treated cellulose decreased with increasing treatment time. The degradation extent was more profound for cellulose after acid treated at 65 C than treated at 45 C. For the same treatment temperature and time, cellulose treated in ethanol had significantly lower DPw and DPn than cellulose treated in water. Commonly, the yield of glucose or the residue amount of cellulose is used as the index for studying the degradation rate of cellulose treated with acid (Xiang, Lee, Pettersson & Torget, 2003).
Rare study deliberated the molecular size of acid-treated cellulose during treatment. In this study, the change of DPw of cellulose was used to monitor the degradation extent of cellulose treated with different conditions. The hydrolysis of glycosidic bonds has been demonstrated follows a first-order reaction (Daruwalla, & Shet, 1962; Springer, 1966), consequently the following equation could express the reduction in DPw of polysaccharides during acid treatment (Chang, Tai, & Cheng, 2001; Lin et al., 2003):
1=Mt ¼ 1=M0 þ kt=m ¼ 1=M0 þ k0 t where k and k0 are the rate constants, t is the reaction time, M0 is the DPw of native cellulose, Mt is the DPw of cellulose after treatment time t, and m is the monomer molecular weight. Fig. 5 shows the plots of treatment time against the reciprocal of DPw, and the slopes
Fig. 4. Molecular weight distributions of native cellulose (–) and cellulose samples after acid treated for 1 (C), 3 (:) and 5 h (;), respectively.
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Table 1 Molecular characterizes and crystallinity index of cellulose samples Sample
Native Water, 45 C 1h 3h 5h Ethanol, 45 C 1h 3h 5h Water, 65 C 1h 3h 5h Ethanol, 65 C 1h 3h 5h
Molecular characterizesa
Crystallinity index (%)
DPw
DPn
Polydispersity
2427ab
240a
10.1b
57.4ac
2518a 2282b 1994c
247a 235b 229c
10.2b 9.7 de 8.8g
56.1a 59.2a 60.8a
2221b 1028e 1087e
191d 107g 110g
11.6a 9.6f 9.9c
54.2a 57.8a 57.6a
1565d 964f 759h
163e 117f 101h
9.6ef 8.2h 7.5j
59.4a 59.5a 58.3a
857g 428i 409i
88i 54j 60j
9.7d 7.9i 6.8k
56.1a 58.3a 58.7a
a DPw: Weight-average degree of polymerization; DPn: Number-average degree of polymerization; Polydispersity ¼ DPw/DPn. b Means with different letters in the same parameter differ significantly (p < 0.05), n ¼ 3. c The peak fitting correlation coefficient is at least 0.995, and the maximum standard deviation is less than 5%.
of the regression lines are the degradation rates (k0 ) of cellulose during different acid treatments. Results of Fig. 5 indicate that cellulose treated in ethanol at 65 C had the highest k0 (4.129) among the cellulose samples treated with different conditions. At the same treatment temperature, the k0 of cellulose treated in ethanol was higher than that of cellulose treated in water. Cellulose treated at 65 C had obvious higher k0 than that of cellulose treated at 45 C. As treatment temperature increased from 45 to 65 C, the increment of k0 for samples treated in water (9.4-fold) was more profound than treated in ethanol (3.4-fold). Moreover, the difference in k0 between cellulose treated in ethanol and in water at 45 C (6.2-fold) was more obvious than that at 65 C (2.3-fold). Results imply that the degradation rate of cellulose acid treated in ethanol is faster than that of cellulose treated in water, and which is more profound for cellulose treated at low temperature (45 C). Fox and Robyt (1992) concluded that hydrolysis of the glycosidic linkage of starch granule acid treated in alcohol was taking place exclusively inside the granule with the granule-bound water. Therefore, the hydrogen ion in ethanol more easily penetrates into cellulose and degrades the molecules inside the cellulose. Consequently,
Fig. 6. CP/MAS 13C solid-state NMR spectra of native cellulose and cellulose samples after acid treated for 5 h.
a relative higher degradation rate of cellulose acid treated in ethanol was observed in this study. 3.4. Crystallinity index Fig. 6 shows the typical NMR spectra of cellulose samples studied, and illustrates that the NMR spectra of native cellulose and acid-treated cellulose were similar to each other. Furthermore, no obvious difference in spectra of cellulose samples with different treatment conditions was found. Table 1 shows the crystallinity index calculated from the NMR spectra according to the method proposed by Liitia¨ et al. (2000). The crystallinity of cotton cellulose was 57.4%. After treatment, the crystallinity index of acid-treated cellulose remained constant or slightly increased. While no obvious tendency in changes of crystallinity index for cellulose samples treated in different media or temperatures was found. The acid-catalyzed hydrolysis of cellulose is a complex heterogeneous reaction, which involves physical factors as well as the hydrolytic chemical reaction. Amorphous cellulose was hydrolyzed 100-fold faster than crystalline a-cellulose (Xiang et al., 2003). Since cellulose molecules possess semi-crystalline structure, the hydrolysis rate of cellulose should be a heterogeneous reaction and a two-order hydrolysis pattern and products with low degree of polymerization and high crystallinity should be observed (Nelson, 1960). However, the change in crystallinity of cellulose after treated is not obvious, although the DPw of cellulose decreased dramatically. This could be attributed to the low acid concentration (<2%) and temperature (no
Fig. 5. Plot of treatment time against the reciprocal of DPw of cellulose samples.
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higher than 65 C) used in this study. Therefore, the degradation of cellulose preferentially occurred in the amorphous regions, consequently only one-order degradation pattern was observed. 4. Conclusions The soluble sugar content, changes in morphological structure and degradation rate of cellulose after acid treated either in water or in ethanol at 45 or 65 C were found depended on the media and treatment temperature. The temperature effect on soluble sugar content of cellulose treated in ethanol was more profound than that of cellulose treated in water. Tiny wrinkles or pin-holes were found on the surface of cellulose after acid treated. Cellulose treated in ethanol at 65 C obviously formed pine-holes on the surface, while treated under other conditions the surface of cellulose did not show obvious changes or tended to form wrinkles. The degradation rate of cellulose treated in ethanol was obviously faster that that treated in water, especially treated at 45 C. Results suggest that acid treated in ethanol showed more obvious effect on degradation, of both surface structure and molecular size of cellulose, than acid treated in water. Results also reveal that cellulose acid treated in media other than water, such as ethanol, could improve the degradation efficiency. Nevertheless, investigations on the degradation of cellulose acid treated in media other than water and ethanol are needed for further elucidating the controllability and efficiency of acid degradation of cellulose. Acknowledgment We thank the National Science Council, Taiwan, for financial support (NSC 96-2313-B-451-004). References Chang, K. L. B., Tai, M. C., & Cheng, F. H. (2001). Kinetics and products of the degradation of chitosan by hydrogen peroxide. Journal of Agricultural and Food Chemistry, 49(10), 4845–4851. Chang, Y. H., Lin, J. H., & Chang, S. Y. (2006). Physicochemical properties of waxy and normal corn starches treated in different anhydrous alcohols with hydrochloric acid. Food Hydrocolloids,, 20(2/3), 332–339. Chang, Y. H., Lin, J. H., & Lii, C.-Y. (2004). Effect of ethanol concentration on the physicochemical properties of waxy corn starch treated by hydrochloric acid. Carbohydrate Polymers, 57(1), 89–96. Daruwalla, E. H., & Shet, R. T. (1962). Heterogeneous acid hydrolysis of alpha– cellulose from Sudanese cotton. Textile Research Journal, 32(11), 942–954. Dubois, M., Gilles, K. A., Hamilton, J. K., Rebers, P. A., & Smith, F. (1956). Colorimetric method for determination of sugars and related substances. Analytical Chemistry, 28(3), 350–356. Fox, J. D., & Robyt, J. F. (1992). Modification of starch granules by hydrolysis with hydrochloric acid in various alcohols, and the formation of new kinds of limit dextrins. Carbohydrate Research, 227(1), 163–170. Grodzka, K., Maciejec, A., & Krygier, K. (2005). Attempts to apply microcrystalline cellulose as a fat replacer in low fat mayonnaise emulsions. Zywnosc, 12(1), 52–61. Iijima, H., & Takeo, K. (2000). Microcrystalline cellulose: an overview. In G. O. Phillips, & P. A. Williams (Eds.), Handbook of hydrocolloids (pp. 331–346). Boca Raton, Florida: CRC Press.
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Jacques, D., Andree, G., & Christion, P. (1990). Prepaaration of b-(1-6)oligomers of 2acetamido-2-deoxyglacoses and galactose as drugs. FR 2640628. Jia, Z., & Shen, D. (2002). Effect of reaction temperature and reaction time on the preparation of low-molecular-weight chitosan using phosphoric acid. Carbohydrate Polymers, 49(4), 393–396. Liitia¨, T., Maunu, S. L., & Hortling, B. (2000). Solid state NMR studies on cellulose crystallinity in fines and bulk fibres separated from refined kraft pulp. Holzforschung, 54(6), 618–624. Lin, J. H., & Chang, Y. H. (2006). Molecular degradation rate of rice and corn starches during acid–methanol treatment and its relation to the molecular structure of starch. Journal of Agricultural and Food Chemistry, 54(16), 5880–5886. Lin, J. H., Lee, S. Y., & Chang, Y. H. (2003). Effect of acid–alcohol treatment on the molecular structure and physicochemical properties of maize and potato starches. Carbohydrate Polymers, 53(4), 475–482. Lin, J. H., Lii, C.-Y., & Chang, Y. H. (2005). Chang of granular and molecular structures of waxy maize and potato starch after treated in alcohols with or without hydrochloric acid. Carbohydrate Polymers, 59(4), 507–515. Lin, J. H., Wang, S. W., & Chang, Y. H. (2008). Effect of molecular size on gelatinization thermal properties before and after annealing of rice starch with different amylose contents. Food Hydrocolloids, 22(1), 156–163. Maksinov, V.I., Denisov, V.M., & Makarov, N.V. (1990). Preparation of water-soluble oligosaccharides. SU 1571047. Mok, W. S. L., Antal, M. J., & Varhegyi, G. (1992). Productive and parasitic pathways in dilute acid-catalyzed hydrolysis of cellulose. Industrial and Engineering Chemistry Research, 31(1), 94–100. Nelson, M. L. (1960). Apparent activation energy of hydrolysis of some cellulosic materials. Journal of Polymer Science, 43(142), 351–371. Robyt, J. F., Choe, J. Y., Hahn, R. S., & Fuchs, E. B. (1996). Acid modification of starch granules in alcohols: effects of temperature, acid concentration, and starch concentration. Carbohydrate Research, 281(2), 203–218. Saeman, J. F. (1945). Kinetic of wood saccharification. Hydrolysis of cellulose and decomposition of sugars in dilute acid at high temperature. Industrial and Engineering Chemistry, 37(1), 43–52. Small, J. C. (1919). A method for the preparation of soluble starch. Journal of American Chemical Society, 41(1), 113–120. Springer, E. L. (1966). Hydrolysis of aspenwood with aqueous solutions of hydrochloric acid. Tappi, 49(3), 102–106. Stol, R., Pedersoli, J. L., Poppe, H., & Kok, W. T. (2002). Application of size exclusion electrochromatography to the microanalytical determination of the molecular mass distribution of celluloses from objects of cultural and historical value. Analytical Chemistry, 74(10), 2314–2320. Thanakoses, P., Black, A. S., & Holtzappl, M. T. (2003). Fermentation of corn stover to carboxylic acids. Biotechnology and Bioengineering, 83(2), 191–200. Tomaya, T., Yoshichi, A., & Akira, A. (1987). Manufacture of water soluble lowmolecular weight chitosan with narrow molecular weight distribution. JP 62 184002. Torget, R. W., Kim, J. S., & Lee, Y. Y. (2000). Fundamental aspects of dilute acid hydrolysis/fractionation kinetics of hardwood carbohydrates. 1. Cellulose hydrolysis. Industrial and Engineering Chemistry Research, 39(8), 2817– 2825. Wood, B. F., Conner, A. H., & Hill, C. G. J. (1986). The effects of precipitation on the molecular weight distribution of cellulose tricarbanilate. Journal of Applied Polymer Science, 32(2), 3703–3712. Wurzburg, O. B. (1986). Converted starches. In O. B. Wurzburg (Ed.), Modified starches: Properties and uses (pp. 17–40). Boca Raton, Florida: CRC Press. Xiang, Q., Kim, J. S., & Lee, Y. Y. (2003). A comprehensive kinetic model for diluteacid hydrolysis of cellulose. Applied Biochemistry and Biotechnology, 106(1-3), 337–352. Xiang, Q., Lee, Y. Y., Pettersson, P. O., & Torget, R. W. (2003). Heterogeneous aspects of acid hydrolysis of a-cellulose. Applied Biochemistry and Biotechnology, 107(1– 3), 505–514. Zhao, H., Kwak, J. H., Wang, Y., Franz, J. A., White, J. M., & Holladay, J. E. (2006). Effects of crystallinity on dilute acid hydrolysis of cellulose by cellulose ballmilling study. Energy and Fuels, 20(2), 807–811. Zhao, H., Kwak, J. H., Zhang, Z. C., Brown, H. M., Arey, B. W., & Holladay, J. E. (2007). Studying cellulose fiber structure by SEM, XRD, NMR and acid hydrolysis. Carbohydrate Polymers, 68(2), 235–241.