Characteristics of Wood Cellulose Fibers Treated with Periodate and

Oct 10, 2007 - Wood cellulose fibers were oxidized by periodate to obtain dialdehyde cellulose (DAC) fibers. The aldehyde group content, degrees of ...
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Characteristics of Wood Cellulose Fibers Treated with Periodate and Bisulfite Q. X. Hou,* W. Liu, Z. H. Liu, and L. L. Bai Tianjin Key Laboratory of Pulp & Paper, Tianjin UniVersity of Science & Technology, Tianjin 300457, China

Wood cellulose fibers were oxidized by periodate to obtain dialdehyde cellulose (DAC) fibers. The aldehyde group content, degrees of crystallinity and polymerization, and fiber length of treated fibers were characterized. The tensile strength of the test sheets made of treated fibers was also measured. The results show that periodate oxidation significantly increased the aldehyde group content and the dry and rewet tensile strengths of the test sheets. Sulfonation of the oxidized fibers by bisulfite improved the undried fiber water absorbency and the dry and rewet tensile strengths of the test sheets made of sulfonated fibers. Introduction

Table 1. Characteristics of Commercial Bleached Kraft Softwood Pulp

As a natural and renewable resource with high-molecularweight polymer, cellulose is widely used in pulp and paper, textile, and other industries. In recent years much scientific effort has been made to chemically modify cellulose fibers to obtain different functionalities for broad practical applications.1-3 It is known that cellulose can be oxidized by periodate to form dialdehyde cellulose (DAC) through a highly undivided reaction. The highly selective reaction selectively cleaves C-2 and C-3 vicinal hydroxyl groups to yield a product with 2,3dialdehyde units along the cellulose chain.2,4-6 The aldehyde groups of DAC can be easily converted to other functional groups by means of oxidative reaction. Such a chemical modification resulted in a high-molecular-weight polymer possessing fluorescence, energy storing, and biomedically active functions, etc.7-11 Most studies on cellulose periodate oxidation have involved applications either in the biomedical industry or in the textile industry. The raw materials used are mostly pure cellulose such as different kinds of cotton (defatted or not; powder of cotton origin), flax, and so on. Varma and Kulkarni reported a detailed study of the effect of temperature, pH, and the concentration of periodate on the progress of the oxidation reaction with hardwood powder of ∼150 mesh.12 Chavan et al. prepared a series of 2,3-dialdehyde cellulose, 2,3-dicarboxylate cellulose, etc. from commercial cellulose powder and then investigated their morphologies by scanning electron microscopy.13 Few studies have been reported on periodate oxidation of wood fibers produced in the pulp and paper industry. The practical applications of the wood fibers oxidized by periodate have not been explored. Tang et al. studied the influence of ultrasound treatment on periodate oxidation of prehydrolysis eucalyptus sulfate pulp with 97.6% cellulose and 2.4% hemicellulose.14 The R-cellulose content of chemical paper pulp is about 78%. Wood fibers consist of cellulose, hemicellulose, lignin, resin, etc. This complex composition of wood fibers may cause complications during oxidation and affect the characteristics of the oxidized fibers. The present research is to study the sodium periodate oxidation behavior of wood cellulose fibers from commercial bleached kraft softwood pulp produced in the pulp and paper industry. The oxidized fibers were sulfonated to further improve the bonding potential of the fibers. The objective of the study is to improve the absorption ability of cellulose fibers and the dry and rewet tensile strengths of the test sheets. * Corresponding author. Tel.: +86-22-60601293. Fax: +86-2260600300. E-mail: [email protected].

determined item

result

initial beating degree length weighted fiber length ISO brightness pentosan ash resin tensile index (at 45 °SR)

13.8 °SR 2.32 mm 88.6% g5.5% e0.3% e0.9% 85.08 N‚m/g

Experimental Section Materials. Commercial elemental chlorine free (ECF) bleached kraft softwood pulp sheets imported from Chile were used. The pulp was prepared from softwood (radiate pine) and with a kraft pulping process and ECF bleaching sequence. The characteristics of the pulp are shown in Table 1. The pulp sheets were torn by hand into small pieces of roughly 25 mm2 area and soaked in tap water for 4 h. Then the wet pulp was dispersed thoroughly in a disintegrator at about 1.2% consistency, and filtered and washed with distilled water three times in a Bu¨chner funnel with a diameter of 200 mm. The pulp was not refined mechanically. All chemicals used in the experiment were analytical-grade products and were obtained from commercial sources in China. The methanol solution with 0.01 mol/L sodium hydroxide was prepared by adding 0.400 g of sodium hydroxide into 1 L of methanol. The methanol solution with 20 g/L hydroxylamine hydrochloride was obtained by adding 20 g of hydroxylamine hydrochloride into 1 L of methanol. During the experimentation, a fixed volume of sodium periodate (NaIO4) solution of 857 mL was used. This volume includes the moisture of the prepared fibers used in reaction, equivalent to a total liquid volume of a 30 g (oven-dry) fiber suspension at 3.5% consistency. Three different concentration solutions with sodium periodate of 0.04, 0.08, and 0.16 mol/L were prepared for reacting with wood pulp at different dosages. Similarly, a fixed volume of sodium bisulfite (NaHSO3) solution of 750 mL was used to further treat the sodium periodate fibers. This volume includes the moisture of the fibers, and is equivalent to a total liquid volume of a 30 g (oven-dry) fiber suspension at 4.0% consistency. The concentration of the sodium bisulfite solution is 0.096 mol/L. Apparatus. The standard pulp disintegrator and tensile strength tester are from Lorentzen & Wettre, Sweden. They were used for dispersing fibers thoroughly in water and for measurement of tensile strength of test sheets. The laboratory handsheet maker is from Frank Co., Germany. Fourier transform infrared

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Figure 1. Effect of periodate oxidation on the content of aldehyde groups in treated fibers.

Figure 2. Effect of periodate oxidation on dry and rewet tensile indices of the test sheets prepared from treated fibers.

Scheme 1. Reaction for Periodate Oxidation of Cellulose Fibers

Scheme 2. Sulfonation Reaction of Dialdehyde Cellulose Fibers

spectroscopy (FTIR), VECTOR 22 (Bruck Co., Germany), was used to obtain 4 cm-1 resolution spectra in the 375-4000 cm-1 region at ambient temperature. A Kajaani FS-100 fiber analysis tester (Kajaani Co., Finland) was used for fiber length measurements. A fiber quality analyzer (FQA; Optest Equipment Inc., Canada) was used to measure the fiber curl index. A JSPM5200 atomic force microscope (AFM) (Japan Electron Optics Laboratory Co., Ltd.) was used for analyzing the topographic images of test sheets prepared from treated and untreated cellulose fibers. This operation was performed at ambient temperature in the tapping mode with a silicon nitride tip and a resolution of 512 pixels × 512 pixels. Periodate Oxidation of Cellulose Fibers. A 1 L filter flask was used as a reaction kettle. The kettle was put in a water

bath after addition of 30 g of fibers and 857 mL of sodium periodate solution. The pH of the solution was adjusted to about 3.5 using dilute sulfuric acid. The oxidation reaction conditions were temperature 45 °C, pulp consistency 3.5%, and stirring speed 310 rpm. The stirring elements are made of 304 stainless steel. The shaft design is suited to all overhead stirrer motors with a standard chuck, and its size is 8 mm × 400 mm. The size of each of the two extendable blades is 18 mm × 62 mm, and the maximum extended diameter of the stirrer is 116 mm. Three different concentrations of sodium periodate of 0.04, 0.08, and 0.16 mol/L were used, giving a sodium periodate charge on wood fiber (oven-dry) of 25%, 50%, and 100%, respectively. The reaction duration times were 10, 30, 60, 120, 240, 360,

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Figure 3. Effect of NaIO4 oxidation on the degree of crystallinity.

Figure 4. Effect of NaIO4 oxidation on the degree of polymerization.

and 480 min, respectively. The kettle was wrapped with several layers of aluminum foil to prevent exposure to light. The inside of the kettle was also isolated from ambient air by bottled nitrogen through the exhaust opening of the filter flask while the reaction was in progress. The nitrogen pressure in the kettle was just slightly higher than that of ambient air. These measures were to avoid NaIO4 decomposition and photooxidation15 and to avoid the influence of oxygen from ambient air on fiber reaction with periodate oxidation. The shaft of the stirrer passed through the center hole of the rubber plug of the filter flask to keep the pulp suspension well mixed during reaction. The clearance between the inside of the center hole of the rubber plug and the outside of the shaft was used as the exhaust opening of the kettle. At the end of each preset reaction duration time, the pulp was washed thoroughly with distilled water. The reaction for the periodate oxidation of cellulose fibers can be described in Scheme 1.16 Analysis for Aldehyde Group Content in Treated Fibers. FTIR was used for validating the presence of aldehyde groups in the treated fibers. Approximately 1 mg of dry fibers was

pressed into a small slice with 100 mg of potassium bromide. The slice was dried under the condition of 80 °C in a vacuum oven for 6 h to eliminate the impact of moisture of the test sample on measurements. Since the DAC can be converted to oximes by Schiff base reaction with hydroxylamine hydrochloride,17 the content of aldehyde groups was determined using the method of hydroxylamine hydrochloride.18-20 The reactions and calculation formula are expressed as follows:

-CHO + NH2OH‚HCl f -CHNOH + HCl + H2O HCl + NaOH f NaCl + H2O A)

10X (µmol/g of oven-dry fibers) w

(1) (2) (3)

where A is the content of aldehyde groups, X is the consumed volume of the methanol solution with 0.01 mol/L sodium hydroxide, in milliliters, and w is the weight of oven-dry treated fibers, in grams.

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Figure 5. Influence of NaIO4 oxidation on the treated fiber length.

Figure 6. Influence of NaIO4 oxidation on the mean curl of treated fibers.

Degrees of Crystallinity and Polymerization of the Treated Fibers. The degree of crystallinity was determined using FTIR measurements based on the O’KI index described by the O’Connor empirical formula21

O’KI ) a1429 cm-1/a893 cm-1

(4)

where a is the spectral intensity. The degree of polymerization (DP) was estimated by the intrinsic viscosity [η] using the following equation.21

DP0.905 ) 0.75[η]

(5)

Sulfonation of the Treated Fibers. Sodium bisulfite was used as a sulfonation agent to sulfonate the periodate-treated fibers in a beaker with a 2000 mL volume under the following conditions: temperature of 20-25 °C, fiber suspension consistency of 4%, pH 4.5, reaction duration time of 180 min, a chemical charge of 30 wt % in fiber (oven-dry) weight, and

stirring speed of 310 rpm. After finishing the reaction, the fibers were filtered and thoroughly washed with distilled water. The sulfonation reaction can be described in Scheme 2.22 Testing of the Physical Properties of Test Sheets. The test sheets were made of untreated fibers, fibers treated with periodate, and fibers treated with periodate followed by bisulfite, respectively. The test sheet preparation and the measurements of the physical properties of cellulose fibers such as water retention value (WRV) and the dry or rewet tensile strength were performed according to literature methods.21 Results and Discussion FTIR Verification of Aldehyde Groups in PeriodateTreated Fibers. The samples of commercial bleached kraft softwood pulp fibers before and after treatment using NaIO4 (25% NaIO4 for 8 h and 50% NaIO4 for 6 h, respectively) were scanned by FTIR. FTIR spectra between 375 and 2000 cm-1 were obtained. The characteristic peak of aldehydic carbonyl

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Figure 7. Effect of oxidation extent on water absorbency property of sulfonated cellulose fibers.

Figure 8. Effect of NaIO4 oxidation on dry and rewet tensile indices of test sheets prepared from sulfonated cellulose fibers.

groups at 1732 cm-1 can be clearly seen in the spectrum of the treated fibers. The characteristic peaks for the hydroxyl groups at 1059 and 1164 cm-1 of the treated fibers were weakened. These results agree with those of literature reports.3,15,19 The FTIR spectra indicated the presence of aldehyde groups in the treated fibers. Effect of Periodate Charge and Oxidation Duration Time on the Content of Aldehyde Groups. The content of aldehyde groups can be used as a quantitative measure of the oxidative extent of cellulose fibers by periodate.23 The effect of periodate oxidation on the content of aldehyde groups in the treated fibers is shown in Figure 1. The content of aldehyde groups increases as oxidant charge and oxidation duration time increase. However, the rate of aldehyde group formation decreases as reaction proceeds, especially at a high oxidant charge. An asymptotic value of aldehyde groups is obtained at an oxidation duration time of 240 min with NaIO4 charge of 100%. Beyond this oxidation time, the condensation reaction between the aldehyde and hydroxyl groups in the cellulose molecular chains could occur, which may prohibit the further formation of DAC and

may consume a great deal of oxidant.3 Some of the effect of condensation reaction can be indirectly seen from the tensile strength of the test sheets made of the treated fibers, as shown in Figure 2. When the oxidation duration time was 240 min and the oxidant charge was over 30 wt %, both the dry and rewet tensile indices of the test sheets prepared from the treated fibers were much higher than those of the control. Besides the contribution of the carboxyl groups formed on the fibers, it is also probable that the condensation reaction closes the distance between the adjacent fibers due to the linkages between different anhydroglucose units either in the same chain or between different chains. As a result, the number of hydrogen bonds between the contiguous fibers was increased. This explanation can be validated by AFM topographical imaging, as will be discussed later. Effect of Oxidation Process on the Degrees of Crystallinity and Polymerization and the Fiber Length. The degrees of crystallinity and polymerization of cellulose can reflect the physical and chemical properties of cellulose fibers. The crystallinity represents the highly ordered structure of the

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Figure 9. AFM analysis of control test sheets (8.00 µm × 8.00 µm × 939 nm).

Figure 10. AFM analysis of test sheets made of fibers treated with periodate (8.00 µm × 8.00 µm × 484 nm). Oxidation conditions: 50% NaIO4, 4 h.

cellulose compared to the less-ordered amorphous region of the cellulose. In general, a high degree of polymerization indicates that the cellulose has a low extent of damage in the main chain and can form sheets with high tensile strength. An increase in the degree of crystallinity increases the tensile strength, specific gravity, and size stability of cellulose fibers, but decreases the stretchability, absorbency, chemical reactivity, and pliability. As summarized in Figures 3 and 4, an increase in the oxidation duration time decreases the degrees of both crystallinity and polymerization of the treated fibers. The degree of polymerization decreases rapidly immediately after the oxidation reaction with periodate. This is because the weak acid medium can easily access the amorphous regions of the cellulose and a rapid initial hydrolytic degradation took place. The weak acid medium is

relatively difficult to penetrate and diffuse into the microcrystalline and crystalline regions. The reduction in the degree of polymerization can facilitate the cleavage of the glycosidic linkage of cellulose, which could result in the shortening of fiber length as shown in Figure 5. It should be pointed out that the shortening of mean fiber length shown may be overstated because many factors, such as fiber curling, could influence the measured fiber length using available commercial instruments such as the Kajaani FS-100 used in this study that measures the projected length of a fiber. A highly curled fiber has a short projected length, or a short fiber length as measured by Kajaani, and vice versa. For the sample treated with 25 wt % oxidant charge, the FQA measured profile of the mean fiber curl index vs oxidation time (Figure

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Figure 11. AFM analysis of test sheets made of sulfonated fibers (8.00 µm × 8.00 µm × 231 nm). Oxidation conditions: 50% NaIO4, 6 h. Sulfonation conditions: 30% NaHSO3, 4 h.

6) has a convex shape; i.e., curl index increases with oxidation time to a maximal value of about 0.29 at about 240 min and then decreases. The Kajaani measured fiber length profile of the same sample (Figure 5) has a concave shape; i.e., mean fiber length decreases with oxidation time to a minimal value of about 1.88 mm at about 240 min and then increases slightly, opposite the shape of the mean fiber curl index profile. This indicates that the shortening of mean fiber length shown in Figure 5 may be partly due to the change of fiber curling (morphology) through oxidation, which will be verified by image analysis in the future. Fiber shortening is apparent for samples treated with oxidant dosage higher than 25% at longer treatment times. Both lower fiber curl indices and shorter mean fiber lengths than those of the untreated control sample were measured under those conditions. Physical Properties of Sulfonated Cellulose Fibers. The DAC has a higher chemical reactivity due to the presence of the dialdehyde groups. It can be used as an intermediate to react with other functional groups such as bisulfite to yield absorbent sulfonated cellulose fibers (Scheme 2). Because sulfonate groups have a higher hydrophilicity than hydroxyl groups, periodate oxidation prior to sulfonation can increase the water absorbency and fiber swelling capacity after sulfonation treatment, as shown in Figure 7. For the sample treated with 100 wt % NaIO4 charge, the highest WRV of 2.76 g/g was achieved at 240 min of oxidation time. In addition, the never-dried sulfonated fibers apparently have a silky luster and feel satiny. Furthermore, with an increase in oxidation time beyond 240 min, the cellulose chain degrades, which resulted in short fibers as shown in Figure 5. The degradation may also result in a reduced bonding area between the adjacent fibers and fewer interactions among the hydrophilic groups of sulfonated cellulose fibers. As a result, the WRV decreases as shown in Figure 7. The effects of periodate oxidation on the dry and rewet tensile indices of test sheets prepared from the sulfonated cellulose fibers are summarized in Figure 8. Both dry and rewet tensile indices of the test sheets made of sulfonated fibers that were oxidized for 240 min before sulfonation can increase except

for an oxidation chemical charge of 100%. At 50 wt % oxidant charge and 240 min oxidation duration time, the rewet tensile index of the test sheets made of sulfonated fibers could reach 8.30 N‚m/g, about 10 times higher than that of the control ones. This increase of dry and rewet tensile indices of the test sheets was most likely attributed to the powerful bonding strength formed between the sulfonate groups in a fiber and the hydroxyl groups in the vicinal one, and the subsequent resistance to rewetting. As a result, they greatly benefit the increased formation of hydrogen bonding between the adjacent fibers, owing to the large increase of the relative bonding areas between the fibers. It should be emphasized that the increased rewet and dry tensile strengths were achieved without refining of the original pulp. This could be advantageous by eliminating mechanical refining in chemical modification of wood fibers. AFM Topographical Image Analysis. To further explore various effects of periodate and sulfonate treatments in the cellulose fibers, a series of the test sheets of control fibers, treated fibers, and sulfonated ones were subjected to AFM analysis (Figures 9-11). The AFM topographical images acquired show dramatic changes in fiber morphology. Figure 9 presents an AFM micrograph of a small piece of control test sheet prior to periodate oxidizing. Most of the fiber surface is nearly flat and relatively smooth and has fewer microfibrils exposed to the fiber surface. Its Z-direction depth is the deepest among the three topographical images, which may be a disadvantage to producing a great bonding area between the fibers. Figure 10 displays a topographical image of the test sheet following periodate oxidizing. Orientated, wrinkled, closely interwoven microfibrils can be clearly seen as a result of periodate oxidizing, hydration, and drying. These fiber surface features and the closely interwoven microfibrils can enlarge the fiber bonding area and therefore bonding strength (assuming fiber conformability is not affected), which explains the increase in tensile strength by periodate oxidation as shown in Figure 2. Oxidizing followed by sulfonation produced sheets with a grainlike topography as exhibited in Figure 11. It is probable that ester compounds were produced, induced by the sulfonate

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and hydroxyl groups in the cellulose covered fiber surface during sheet dewatering and drying, which is greatly beneficial to both the dry and rewet tensile strengths of the test sheets. Perhaps this kind of cross-link in the ester compounds has presented in a hydration phase prior to drying. Conclusions This study demonstrates that cellulose fibers can be oxidized by periodate to yield DAC fibers. The content of aldehyde groups increases as the oxidant charge and oxidation duration time increase. At the oxidant charge of 100 wt % and oxidation reaction duration time of 240 min, the content of aldehyde groups reached an asymptotic value of 4.7 mmol/g of oven-dry fibers. Within the range of oxidant charge from 30 to 50 wt % and oxidation duration time of 240 min, periodate oxidation improved both the dry and rewet tensile indices of test sheets and reduced the degrees of crystallinity and polymerization and the length of the treated fibers. Sulfonation treatment of the oxidation-treated fibers with sodium bisulfite not only improved the undried fiber water absorbency and fiber swelling but also increased the dry and rewet tensile strengths of test sheets. At 50 wt % oxidant charge and 240 min oxidation duration time the highest values of 8.30 and 62.94 N‚m/g for both rewet and dry tensile indices of the test sheets can be obtained after sulfonation, respectively. For some paper grades, this may be a potential advantage because no refining of the original pulp is required. The shortening of the fiber length, however, may occur partially due to the cellulose degradation. AFM topographical images of the test sheets revealed special surface features that validate the observed increase in bonding strength of test sheets made of oxidated fibers and sulfonated ones. The treated fibers with improved properties can be used in a wide variety of special paper products such as specialty tissue, wet wipes, and tissue wraps in personal care products and the like. Acknowledgment This work was financially supported by the Tianjin Education Committee (2004ZD16) and from National Ministry of Education for scientific research startup. The authors would like to express their appreciation to Dr. J. Y. Zhu (USDA, U.S. Forest Service, Forest Products Laboratory, Madison, WI) for conducting a thorough review of this paper. Literature Cited (1) Princi, E.; Vicini, S.; Pedemonte, E.; et al. Physical and chemical characterization of cellulose based textiles modified by periodate oxidation. Macromol. Symp. 2004, 218 (1), 343. (2) Vicini, S.; Princi, E.; Luciano, G.; et al. Thermal analysis and characterisation of cellulose oxidised with sodium methaperiodate. Thermochim. Acta 2004, 418 (1-2), 123.

(3) Xiong, J.; Ye, J.; He, X.; Wu, Z. The improved heterogeneous reaction of the oxidation of cellulose by periodic acid. Polym. Mater. Sci. Eng. 2000, 16 (3), 172. (4) Maekawa, E.; Koshijima, T. Properties of 2,3-dicarboxy cellulose combined with various metallic ions. J. Appl. Polym. Sci. 1984, 29 (7), 2289. (5) Varma, A. J.; Chavan, V. B. A study of crystallinity changes in oxidised celluloses. Polym. Degrad. Stab. 1995, 49 (2), 245. (6) Guthrie, R. D. In AdVances in carbohydrate chemistry; Wolfram, M. L., Ed.; Academic Press: New York, 1961; p 105. (7) Rahn, K.; Heinze, T. New cellulosic polymers by subsequent modification of 2,3-dialdehyde cellulose. Cellul. Chem. Technol. 1998, 32 (3-4), 173. (8) Sarymsakova, A.; Nadzhimutdinov; Tashpulatov, Y. T. Chemical transformation is the chains of cellulose dialdehydes and cellulose ethers. Chem. Nat. Compd. 1998, 34 (2), 170. (9) Ye, J.; Xiong, J.; Liang, W. Effect of the pH on the synthesis of o-phenylenediimido cellulose and its fluorescence behavior. Gongneng Gao Fenzi Xuebao 1998, 11 (4), 539. (10) Varma, A. J.; Kennedy, J. F.; Galgali, P. Synthetic polymers functionalized by carbohydrates: A review. Carbohydr. Polym. 2004, 56 (4), 429. (11) Kim, U.-J.; Kua, S. Ion-exchange chromatography by dicarboxyl cellulose gel. J. Chromatogr., A 2001, 919 (1), 29. (12) Varma, A. J.; Kulkarni, M. P. Oxidation of cellulose under controlled conditions. Polym. Degrad. Stab. 2002, 77 (1), 25. (13) Chavan, V. B.; Sarwade, B. D.; Varma, A. J. Morphology of cellulose and oxidized cellulose in powder form. Carbohydr. Polym. 2002, 50 (1), 41. (14) Tang, A.; Zhang, H.; Chen, G.; et al. Influence of ultrasound treatment on accessibility and regioselective oxidation reactivity of cellulose. Ultrason. Sonochem. 2005, 12 (6), 467. (15) Fan, Q. G.; Lewis, D. M.; Tapley, K. N. Characterization of cellulose aldehyde using Fourier transform infrared spectroscopy. J. Appl. Polym. Sci. 2001, 82 (5), 1195. (16) Liu, Y.; Feng, Y.; Li, X.; Zhang, W. Studies on the preparation of dialdehyde cellulose. Chem. Eng. (China) 2002, 30 (6), 54. (17) Kim, U.-J.; Kuga, S.; et al. Periodate Oxidation of Crystalline Cellulose. Biomacromolecules 2000, 1 (3), 488. (18) Marte, R. L.; Owens, M. L. Rapid determination of carbonyl content in acrylonitrile. Anal. Chem. 1956, 28, 1312. (19) Qian, J.; Li, X. Study on oxidation of cellulose to oxycellulose by sodium periodate. Mod. Chem. Ind. 2001, 21 (7), 27. (20) Allan, G. G.; Reif, W. M. Fibre Surface ModificationsThe Stereotopochemistry of Ionic Bonding in Paper. SVen. Papperstidn. Arg. 1971, 74, 563. (21) Shi, S.; He, F. Pulping & Papermaking Analysis and Testing; China Light Industry Press: Beijing, 2003. (22) Shet, R. T. Sulphonated cellulose having improved absorbent properties. U. S. Patent 5,703,225, 1997. (23) Zhao, X.; Xia, W. Research on the Reaction Conditions of Cloth Fibre Oxidized by Sodium Periodate. J. Cellul. Sci. Technol. 2003, 11 (3), 17.

ReceiVed for reView April 2, 2007 ReVised manuscript receiVed August 2, 2007 Accepted August 9, 2007 IE0704750