Sugarcane bagasse whiskers: Extraction and characterizations

Industrial Crops and Products 33 (2011) 63–66 Contents lists available at ScienceDirect Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop Sugarcane bagasse whiskers: Extraction and characterizations Eliangela de Morais Teixeira a , Thalita Jessika Bondancia a,b , Kelcilene Bruna Ricardo Teodoro a,b , Ana Carolina Corrêa a , José Manoel Marconcini a , Luiz Henrique Caparelli Mattoso a,∗ a b National Nanotechnology Laboratory for Agriculture (LNNA), Embrapa Agricultural Instrumentation, P. O. Box 741, CEP: 13560-970, São Carlos, SP, Brazil Federal University of São Carlos (UFSCar), Chemistry Department, P. O. Box: 676, CEP: 13565-905, São Carlos, SP, Brazil a r t i c l e i n f o Article history: Received 15 June 2010 Received in revised form 13 August 2010 Accepted 28 August 2010 Keywords: Sugarcane bagasse Sugarcane bagasse whiskers Acid hydrolysis a b s t r a c t This work evaluates the use of sugarcane bagasse (SCB) as a source of cellulose to obtain whiskers. These fibers were extracted after SCB underwent alkaline peroxide pre-treatment followed by acid hydrolysis at 45 ◦ C. The influence of extraction time (30 and 75 min) on the properties of the nanofibers was investigated. Sugarcane bagasse whiskers (SCBW) were analyzed by transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) in air atmosphere. The results showed that SCB could be used as source to obtain cellulose whiskers and they had needle-like structures with an average length (L) of 255 ± 55 nm and diameter (D) of 4 ± 2 nm, giving an aspect ratio (L/D) around 64. More drastic hydrolysis conditions (75 min) resulted in less thermally stable whiskers and caused some damage on the crystal structure of the cellulose as observed by XRD analysis. © 2010 Elsevier B.V. All rights reserved. 1. Introduction There has been increasing interest in cellulose based-materials due to the abundance, renewable and eco-friendly nature of cellulose (Hubbe et al., 2008). Currently, by diversifying the use of cellulosic fibers, a new research trend has been seen for obtaining whiskers from several cellulose sources, whether from animal origin (such as tunicin) (Anglès and Dufresne, 2000), cotton plant fibers (Dong et al., 1998), sisal (De Rodriguez et al., 2006; Morán et al., 2008; Siqueira et al., 2009a) and capim dourado (Siqueira et al., 2009b). One way to obtain such whiskers is by acid hydrolysis where the cellulose is exposed to sulfuric acid for a controlled period of time and temperature. This process removes the amorphous parts of the cellulose, leaving single and well-defined crystals in a stable colloidal suspension. The negative sulfate groups on the surface of the nanofibers guarantee the stability of this suspension due to the electrostatic repulsion (Lima and Borsali, 2004; Dufresne, 2006). The whiskers’ high stiffness, surface area and crystallinity are suitable for applications in polymeric matrices, acting as reinforcing elements (Gardner et al., 2008). Sugarcane bagasse (SCB) is a residue from the refining process of sugarcane that contains about 40–50% of cellulose in its composition (Sun et al., 2004). This characteristic suggests the possibility of using the SCB as a source of cellulose fibers for the extraction of whiskers structures. Agroindustrial residues have been used for the production of nano-sized cellulose-like microfibrils, such as banana residues (Zuluaga et al., 2007) and wheat straw (Alemdar and Sain, 2008) and nanofibrils from cassava bagasse (Teixeira et al., 2009). Bhattacharya et al. (2008) obtained microfibrils from sugarcane bagasse by acid hydrolysis through the use of sulfuric acid at 60 ◦ C for 2.5 h, after bleaching the sugarcane bagasse with sodium chlorite and glacial acetic acid. The aim of this work was to isolate and characterize cellulose whiskers from sugarcane bagasse pre-bleached with alkaline peroxide solution (free-chlorine reagent) by acid hydrolysis conditions at a mild temperature (45 ◦ C), and to investigate the influence of extraction time (30 and 75 min) on the morphology, crystallinity and thermal stability in air atmosphere of the resulting whiskers. 2. Experimental 2.1. Materials Unpurified sugarcane bagasse (SCB) containing about 43.6, 27.7 and 27.7% of cellulose, lignin and hemicelluloses, respectively, were kindly supplied by Edra Eco Sistemas (Ipeúna-SP, Brazil). Hydrogen peroxide (Nuclear) and NaOH (Qhemis) was used for bleaching the bagasse. The cellulose was hydrolyzed with sulfuric acid (Synth) and the cellulose membrane (Sigma–Aldrich: D9402) was used to dialyze the products. 2.2. Purification of cellulose from sugarcane bagasse ∗ Corresponding author. Tel.: +55 1621072804. E-mail address: [email protected] (L.H.C. Mattoso). 0926-6690/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.indcrop.2010.08.009 The sugarcane bagasse (used as received) was submitted to a bleaching process. This process was adapted by Sun et al. (2004) 64 E.d.M. Teixeira et al. / Industrial Crops and Products 33 (2011) 63–66 Fig. 1. Images of SCB (a) before and (b) after the bleaching with alkaline peroxide solution. and is describes below. About 5 g of SCB were sonified in 300 mL of distilled water for 30 min. Next, the SCB was filtered to remove the excess of water. Then, this pre-washed material was put in a flask containing 100 mL of NaOH 5 wt% solution at 55 ◦ C. Next, 100 mL of hydrogen peroxide solution (11%, v/v) was added to the flask. The system was vigorously stirred for 90 min. After that, the SCB was filtered and washed with distilled water until neutral pH. The SCB was dried at 50 ◦ C until constant weight. This product was submitted again to the same bleaching process for a more effective discoloration. 2.6. X-ray diffraction (XRD) The X-ray diffraction patterns were obtained in an X-ray diffractometer (VEB Carl Zeiss-Jena URD-6 Universal Diffractometer), ´ at 40 kV and 20 mA. Scattered using CuK␣ radiation ( = 1.5406 Å) radiation was detected in the range of 2 = 5–40◦ , at a scan rate of 2◦ /min. The extent of crystallinity (CI% ) was estimated on the basis of areas under crystalline and amorphous peaks after an appropriate baseline correction and the applying of a devolution technique through the use of the Origin 7.5 software and a Gaussian line shape to the peaks. 2.3. Determination of residual lignin 2.7. Thermogravimetric analysis (TGA) The residual lignin content of bleached SCB was analyzed by reaction with sulfuric acid, using a standard method as recommended by TAPPI-T222 om-88. Dried whiskers were subjected to TGA in a TA Q500 thermal analyzer (TA Instruments, New Castle, DE, USA). The samples (10.0 ± 1.0 mg) were heated in a Pt crucible from 25 to 600 ◦ C in air flowing at 60 mL min−1 . The heating rate was 10 ◦ C min−1 . 2.4. Preparation of the cellulose nanofibers from SCB 3. Results and discussion About 5.0 g of bleached SCB were dispersed in 100 mL of 6 M sulfuric acid at 45 ◦ C and vigorously stirred for 30 min or 75 min. Next, 500 mL of cold distilled water was added to stop the reaction. The sulfuric acid was partially removed from the resulting suspension by centrifugation at 10,000 rpm for 10 min. The non-reactive sulfate groups were removed by centrifugation followed by dialysis in tap water with a cellulose membrane, until the pH reached 6 to 7. The neutral suspension was ultrasonicated for 5 min and stored in a refrigerator after adding chloroform drops. The cellulose whiskers were labeled SCBW30 or SCBW75 depending on the time of extraction. The yield of whiskers was determined by weighting an aliquot of 10 mL of the supernatant of the suspension after standing overnight to dry. The yield (%) was calculated from the difference between the initial and final weight. For XRD and TG analysis an aliquot of 25 mL was dried at 35 ◦ C for 12 h in an air-circulating oven. Fig. 1 shows the physical aspect of the original SCB and after the bleaching with alkaline peroxide solution. The great effectiveness of the process was observed because a white colored SCB was obtained. The lignin content after the bleaching was calculated to be 5.8 wt%, indicating that a great part of the initial lignin was removed, resulting in a purer cellulose, hence more suitable for extracting whiskers. The resulting suspensions and the morphology of whiskers are shown in Fig. 2. After acid hydrolysis, the suspensions were stable but the sample hydrolyzed for 75 min (SCBW75 ) presented a brown coloring in the suspension, indicating some level of cellulose degradation. TEM micrographs presented needle-like whiskers, especially sample SCBW30 . The dimensions were calculated with the ImageJ software. Both whiskers had a length (L) of around 255 ± 55 nm and the diameters (D) of 4 ± 2 and 8 ± 3 nm for SCBW30 and SCBW75 , respectively. No significant difference in length or diameter among the whiskers could be detected by STEM among the whiskers, if the standard deviation of each value is taken into account. A slight larger diameter for SCBW75 sample could be due to some small agglomerations of whiskers. The diameters measured were similar to the nano-sized structures derived from other sources of agro-residues such as nanofibrils from cassava bagasse (2–11 nm) (Teixeira et al., 2009) and banana residues (5 nm) (Zuluaga et al., 2007) and smaller than microfibrils from wheat straw (10–80 nm) (Alemdar and Sain, 2008) and sugarcane bagasse (30 nm) (Bhattacharya et al., 2008). The yield was 58% for SCBW30 and 50% for SCBW75 . 2.5. Scanning transmission electron microscopy (STEM) The whiskers samples were examined by TEM in a TecnaiTM G2 F20 equipment. The images were acquired in STEM (scanning transmission electron microscopy) mode, with a bright-field (BF) detector. A droplet of diluted suspension was deposited on a carbon microgrid (400 mesh) and allowed to dry. The grid was stained with a 1.5% solution of uranyl acetate and dried at room temperature. E.d.M. Teixeira et al. / Industrial Crops and Products 33 (2011) 63–66 Fig. 2. Suspensions of SCB whiskers: (a) extracted at 30 min (SCBW30 ) and (b) extracted at 75 min (SCBW75 ). The X-ray diffraction patterns of the bleached SCB and their respective nanofibers are shown in Fig. 3 and the crystallinity values are shown in Table 1. The diffractograms display a mixture of polymorphs of cellulose I (typical peaks at 2 ∼ 15◦ and 22.6◦ ) and cellulose II (peaks at 12.3◦ and 22.1◦ ) (Klemm et al., 2005). An increase in crystallinity of SCBW30 with respect to bleached SCB was observed, indicating that the hydrolysis was effective. The sample SCBW75 presented a decrease in crystallinity and a little change in the diffractogram profile, with the disappearance of the peak at 2 = 15.3◦ . This observation, added to the physical aspect of SCBW75 suspension (brown coloration, Fig. 2), suggests that the extraction time of 75 min was severe enough to remove not only the amorphous phase but also to destroy part of the cellulose crystalline Table 1 Crystallinity index (CI% ) and initial temperature of thermal degradation (Tid , air atmosphere) for SCB bleached and their whiskers. Sample CI% (%) Tid (◦ C) SCB bleached SCBW30 SCBW75 76.0 87.5 70.5 270.0 255.0 210.0 Fig. 3. X-ray diffraction patterns of bleached SCB, SCBW30 and SCBW75 . 65 66 E.d.M. Teixeira et al. / Industrial Crops and Products 33 (2011) 63–66 the environment reagent (alkaline peroxide solution). SCB whiskers were obtained at a mild temperature (45 ◦ C) and at a shorter extraction time (30 min). The SCB whiskers presented a length (L) of around 255 ± 55 nm and average diameter (D) of 4 nm, and good thermal stability (255 ◦ C) and high crystallinity (87.5%). SCB whiskers obtained by a longer extraction time (75 min) damaged the crystalline structure of cellulose, resulting in a decrease of their thermal stability. Acknowledgements The authors gratefully acknowledge the financial support provided by FAPESP (Process No. 07/50863-4), FINEP, MCT, CNPq and EMBRAPA. References Fig. 4. The TG (a) and DTG (b) curves of bleached SCB and whiskers. Analysis in air atmosphere, heated at 10 ◦ C min−1 . regions. Similar effect of hydrolysis time in excess was observed by Chen et al. (2009) for whiskers from pea hull fibers, although the rod-like structures were maintained. The TG curves for the bleached SCB and nanofibers (Fig. 4a) in air atmosphere exhibit an initial small drop between 50 and 150 ◦ C, which corresponds to absorbed moisture, with a mass loss of approximately 5%. The initial temperatures of thermal degradation (Tid ) of the samples are presented in Table 1 and were attributed to cellulose depolymerisation. In this step, the thermal degradation of nanofibers proceeded at lower temperatures than for the bleached SCB. This behavior was expected given that the introduction of sulfate groups in the cellulose diminishes the thermostability of cellulose crystals (Roman and Winter, 2004). As observed in the data of Table 1, sample SCBW75 had lower thermal stability than sample SCBW30 . The DTG curves of the nanofibers (Fig. 4b) show a large peak at the range of 235–365 ◦ C for SCBW30 and multiples peaks of around 200–370 ◦ C for SCBW75 , respectively. This reveals a greater heterogeneity of the samples due to the different content of sulfate groups incorporated on the cellulose surface. More sulfated regions of cellulose degrade at lower temperatures, while regions less accessed by the sulfate groups of the acid tend to be more thermally stable (Wang et al., 2007; Li et al., 2009). Thus, the condition of hydrolysis for 75 min resulted in a major cellulose sulfonation, also contributing to the cellulose degradation by dehydration reactions, hence causing damages in the crystal structure of cellulose, as was verified by XRD analysis. Because less sulfonation occurred when hydrolysis was carried out for 30 min, this effect was minimized. 4. Conclusions SCB could be the source of cellulose for the attainment of whiskers. SCB was successfully bleached by a less aggressive to Anglès, M.N., Dufresne, A., 2000. Plasticized starch/tunicin whiskers nanocomposites. 1. Structural analysis. Macromolecules 33, 8344–8353. Alemdar, A., Sain, M., 2008. Biocomposites from wheat straw nanofibers: morphology, thermal and mechanical properties. Compos. Sci. Technol. 68, 557–565. Bhattacharya, D., Germinario, L.T., Winter, W.T., 2008. Isolation, preparation and characterization of cellulose microfibers obtained from bagasse. Carbohydr. Polym. 73, 371–377. Chen, Y., Liu, C., Chang, P.R., Cao, x., Anderson, D.P., 2009. Bionanocomposites based on pea starch and cellulose nanowhiskers hydrolyzed from pea hull fibre: effect of hydrolysis time. Carbohydr. Polym. 76, 607–615. De Rodriguez, N.L.G., Thielemans, W., Dufresne, A., 2006. Sisal cellulose whiskers reinforced polyvinyl acetate nanocomposites. Cellulose 13, 261–270. Dong, X.M., Revol, J.-F., Gray, D.G., 1998. Effect of microcrystallite preparation conditions on the formation of colloid crystal of cellulose. Cellulose 5, 19–32. Dufresne, A., 2006. Comparing the mechanical properties of high performances polymer nanocomposites from biological sources. J. Nanosci. Nanotechnol. 6, 322–330. Gardner, D.J., Oporto, G.S., Mills, R., Samir, M.A.S.A., 2008. Adhesion and surface issues in cellulose and nanocellulose. J. Adhes. Sci. Technol. 22, 545–567. Hubbe, M.A., Rojas, O.J., Lucia, L.A., Sain, M., 2008. Cellulosic nanocomposites: a review. BioResources 3, 929–980. Klemm, D., Heublein, B., Fink, H.P., Bohn, A., 2005. Cellulose: fascinating biopolymer and sustainable raw material. Angew. Chem. Int. 44, 2–37. Li, R., Fei, J., Cai, Y., Li, Y., Feng, J., Yao, J., 2009. Cellulose whisker extracted from mulberry: a novel biomass production. Carbohydr. Polym. 76, 94–99. Lima, M.M.S., Borsali, R., 2004. Rodlike cellulose microcrystals: structure, properties, and applications. Macromol. Rapid Commun. 25, 771–787. Morán, J.I., Alvarez, V.A., Cyras, V.P., Vázquez, A., 2008. Extraction of cellulose and preparation of nanocellulose from sisal fibers. Cellulose 15, 149–159. Roman, M., Winter, W.T., 2004. Effect of sulfate groups from sulfuric acid hydrolysis on the thermal degradation behavior of bacterial cellulose. Biomacromolecules 5, 1671–1677. Siqueira, G., Bras, J., Dufresne, A., 2009a. Cellulose whiskers versus microfibrils: influence of nature of the nanoparticle and its surface functionalization on the thermal mechanical properties of nanocomposites. Biomacromolecules 10, 425–432. Siqueira, G., Abdillahi, H., Bras, J., Dufresne, A., 2009b. High reinforcing capability cellulose nanocrystals extracted from Syngonanthus nitens (Capim Dourado). Cell 17, 289–298. Sun, J.X., Sun, X.F., Zhao, H., Sun, R.C., 2004. Isolation and characterization of cellulose from sugarcane bagasse. Polym. Degrad. Stabil. 84, 331–339. Teixeira, E.M., Pasquini, D., Curvelo, A.A.S., Corradini, E., Belgacem, M.N., Dufresne, A., 2009. Cassava bagasse cellulose nanofibrils reinforced thermoplastic cassava starch. Carbohydr. Polym. 78, 422–431. Wang, N., Ding, E., Cheng, R., 2007. Thermal degradation behavior of spherical cellulose nanocrystals with sulfate groups. Polymer 48, 3486–3493. Zuluaga, R., Putaux, J.L., Restrepo, A., Mondragon, I., Gañán, P., 2007. Cellulose microfibrils from banana farming residues: isolation and characterization. Cellulose 14, 585–592.