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Production of nanocellulose from lime residues using chemical-free technology
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 5 (2018) 11095–11100
www.materialstoday.com/proceedings
NanoThailand2016
Production of nanocellulose from lime residues using chemical-free technology Saranya Jongaroontaprangsee, Naphaporn Chiewchan* and Sakamon Devahastin Advanced Food Processing Research Laboratory, Department of Food Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi, 126 Pracha u-tid Road, Bangkok 10140, Thailand
Abstract The feasibility of using lime residues after juice extraction as a raw material to produce nanocellulose was determined in this study. Autoclaving at 110-130 °C was performed as a pretreatment to remove hemicellulose and pectin from the native fiber. The pretreated samples were then subjected to high shear homogenizing at 20,000 rpm for 15 min and high pressure homogenizing at 40 MPa for 5 passes. The fiber images obtained from transmission electron microscopy (TEM) technique revealed that the multiple homogenizing steps could effectively disintegrate the pretreated fiber into nanometer scale. X-ray diffraction (XRD) results showed that the prepared nanocellulose possessed much higher crystallinity index (CI) comparing to that of the native fiber; it was noted that the degree of CI was dependent on the processing conditions. The results suggested that there is a potential to produce nanocellulose from citrus by-products via the application of the developed chemical-free technology, which is safely to be used for food applications. © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 5th Thailand International Nanotechnology Conference (NanoThailand2016). Keywords: residues; Nanocellulose; Chemical-free Technology; Autoclaving; Homogenization
* Corresponding author. Tel.: +66-2470-9244. E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 5th Thailand International Nanotechnology Conference (NanoThailand2016).
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1. Introduction Nanocellulose is a natural material extracted from native cellulose and has at least one dimension in a nanometer range. It has gained much attention due to its unique properties, which can be used in numerous applications. Nanocellulose derived from plants is generally produced in the forms of cellulose nanocrystal (CNC) and nanofibrillated cellulose (NFC) depending on the desired applications. CNC is rod like particles and highly crystalline. It can be obtained by hydrolysis using strong acid under strictly controlled conditions [1, 2]. NFC is generally obtained by mechanical disintegration without using strong acid hydrolysis, therefore it exhibits a web-like structure with both amorphous and crystalline parts [3]. NFC possesses very high surface area and very high aspect ratio. It also has ability to form a viscous gel, which can be used as a binder for paper industry or a viscous modifier in paints, cosmetic, pharmaceutical and food products [4, 5]. The mechanical methods for disintegration of native cellulose into nanoscale fiber that have been reported include homogenization, microfluidization, grinding and cyocrushing [6-9]. Pretreatments may be performed as an additional process in order to facilitate the defibrillation and reduce the energy consumption. Mild enzymatic hydrolysis using, for example, endoglucanase, combined with mechanical process has been reported for preparation of NFC from wood pulp and citrus residues [10-12]. Alkaline-acid pretreatment can be used to solubilize noncellulosic components from wood, rice straw, potato tuber and banana peel prior to disintegration [13, 14]. Hydrothermal processing such as steam explosion and autoclaving are also proposed as a promising pretreatment method to reduce the use of chemicals. During steam explosion, the sample is exposed to pressurized steam followed by rapid reduction in pressure resulting in substantial break down of the lignocellulosic structure, hydrolysis of hemicellulose fraction, depolymerization of the lignin components and defibrillation [15]. Using mild acid or alkaline hydrolysis coupled with autoclaving at 110-120 °C for 1-2 h has been suggested for production of NFC from citrus residues, banana fiber and isora fiber [16-18]. Although wood is a main raw material to produce nanocellulose, the agricultural residues are also of interest as they are available in a large quantity and can be prepared into nanocellulose with less energy consumption. In recent years, citrus fruit by-products are proposed as a raw material for production of nanocellulose; approximately 20-40% of cellulose content (dry mass) can be obtained depending on raw materials [19]. This study aimed at producing chemical-free nanocellulose in the form of NFC from lime residues (Citrus aurantifolia Swingle) after juice extraction via the use of autoclaving as a selected pretreatment. The effect of autoclaving conditions on crystallinity and morphology of the produced NFC were determined. 2. Material and methods 2.1. Nanocellulose preparation Lime residues (Citrus aurantifolia Swingle) after juice extraction were obtained from a juice vendor located in Tungkru, Bangkok, Thailand. The residues was collected on the same day of each experiment. The lime residues was squeezed again to remove the remaining juice using a hand press juicer. Only lime residues (i.e., flavedo, albedo, segments and juice sacs) without seeds were used as a starting raw material. The prepared lime residues (80 g) and deionized water (800 mL) were added into a blender jar and then chopped using a blender (Waring Commercial, HGB2WT, Torrington, CT) for 2 min to obtain the particle size in the range of 1-3 mm. After chopping, the slurry was filled into a 1000 mL Duran bottle and autoclaved at the temperatures of 110, 120 and 130 °C for 2 h. After cooling to room temperature (~30 °C), the autoclaved slurry was filtered through a Whatman no. 541 filter paper. The autoclaved sample was collected and prepared into the fiber suspension with the solids content of 0.6% w/w using deionized water. The fiber suspension was passed through a high shear homogenizer (IKA, T25 digital ULTRA-TURRAX®, Staufen, Germany) at 20,000 rpm for 15 min and subsequently passed through a high pressure homogenizer (GEA, NS2006L, Parma, Italy) at 40 MPa for 5 passes. The autoclaved residues and nanocellulose suspension were dried in a hot air oven (Memmert, UF 110, Schwabach, Germany) at 60 °C prior to chemical compositions analysis and XRD analyses.
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2.2. Chemical composition analysis The chemical compositions of the samples were determined in terms of neutral detergent fiber (NDF), aciddetergent fiber (ADF) and acid-detergent lignin (ADL) following the method of Goering and Van Soest [20]. Cellulose, hemicellulose and lignin contents were calculated using the following equations. Cellulose = ADF- ADL (1) Hemicellulose = NDF – ADF (2) Lignin = ADL (3) Galacturonic acid (GalA) content was determined to represent the pectin content in a sample. For GalA determination, sample preparation and analysis procedures were performed following the method described by Ahmed and Labavitch [21] and Kintner and Van Buren [22], respectively. 2.3. X-ray diffraction XRD pattern of samples was determined using an X-ray diffractometer (Bruker AXS GmbH, D8 Discover, Karlsruhe, Germany). The XRD spectra were recorded using a Cu Kα radiation (λ = 0.1546 nm) at 40 kV and 40 mA. Samples were analyzed in the scattering range (2θ) of 10-70° at a scanning rate of 2° 2θ/min. The crystallinity index for each sample was calculated using the following equation: I002 − Iam Crystallinity index = × 100 (4) I002 Where I002 and Iam are the peak intensities of crystalline and amorphous regions, respectively. 2.4. Transmission electron microscopy The nanocellulose suspensions obtained from various pretreatments were diluted and sonicated to achieve a uniform dispersion. A droplet of suspension was placed onto Cu-grid and coated with a thin film of carbon and negatively stained with 1% uranyl acetate solution. All samples were analyzed using a transmission electron microscope (JEOL, JEM-2100HR, Tokyo, Japan). The diameters of nanocellulose were calculated from TEM images using ImageJ. 2.5. Statistical analysis The experiments were designed to be completely random. The data were subject to analysis of variance (ANOVA) and are presented as mean values with standard deviations. Differences between mean values were established using Duncan’s new multiple range tests; values were considered at a confidence level of 95%. All statistical analyses were performed using SPSS software (version 17) (SPSS Inc., Chicago, IL, USA). All experiments were performed in triplicate unless specified otherwise. 3. Results and discussion The contents of solids, cellulose, hemicellulose, lignin and GalA of fresh and autoclaved lime residues are listed in Table 1. The results showed that the solids content of lime residues significantly decreased after autoclaving. Increasing the autoclaving temperatures resulted in a higher reduction in a solids content. Cellulose content of lime residues was similar to those reported for orange and lemon residues after juice extraction [23]. The cellulose content of lime residues significantly increased after autoclaving. These values corresponded to the reduction in the total solids content. Removal of soluble solids such as low-molecular weight carbohydrates and noncellulosic cell wall components resulted in an increase in a cellulose fraction retained in the autoclaved samples. Autoclaving at 110 °C for 2 h seemed to have a minute effect on the lignocellulosic structure; only pectin and other soluble components could be released from the plant tissues leading to an increase in the cellulose content.
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The effect of autoclaving was more pronounced when higher autoclaving temperatures were applied. Higher fraction of cellulose could be obtained with a lesser fractions of hemicellulose and pectin contents. Hydrothermal treatment by autoclaving at the temperatures higher than 110 °C led to a significant reduction of hemicellulose. The autohydrolysis of hemicellulose may occur at the temperature of higher than 110 °C. During autohydrolysis, the acetyl groups of xylan (backbone of hemicellulose) were hydrolyzed to acetic acid, thus decreasing the pH of the autohydrolysate and promoting the autohydrolysis of hemicellulose into water soluble oligomers [24]. Sabiha-Hanim, Noor and Rosma [24] and El Hage, Chrusciel, Desharnais and Brosse [25] also observed the autohydrolysis of hemicellulose in grass and oil palm frond during autoclaving at the temperatures of 121 °C and 130 °C, respectively. It was found that the autoclaving conditions performed in this work did not have a significant effect on lignin content of the pretreated samples. Lignin extraction can occur when using chemical treatments in coupled with autoclaving. For example, diluted alkaline solution combined with autoclaving at 110-120 °C has been reported to be an effective method used for extraction of lignin form banana fiber and pineapple leaf [17, 26]. Chemical compositions of lime residues before and after autoclaving at 110, 120 and 130 °C for 2 h Yield of solids content Content (% dry basis) (% dry basis) Cellulose Hemicellulose Lignin Lime residues 100.00 11.46±1.86a 10.18±5.36b 7.29±1.87a Autoclaving 41.66±3.41b 10.06±0.71b 7.91±1.77a 35.84±1.13b at 110 °C 47.04±2.24c 3.94±1.21a 9.19±0.71a 31.01±0.62a at 120 °C 46.58±2.53c 3.55±1.27a 7.90±1.83a 29.35±0.35a at 130 °C Same letters in the same column indicate that values are not significantly different (p≥0.05). Table 1.
GalA 32.15±3.86c 24.76±2.48b 18.38±1.77a 15.63±1.29a
Approximately 32% of GalA was found in fresh lime residues. High amount of GalA implies that pectin is an important substance in lime residues. A significant reduction in GalA content was observed after autoclaving; higher temperatures led to the higher removal of pectin from the plant structure. Fig. 1 shows the XRD patterns of fresh and autoclaved lime residues as well as the produced nanocellulose. No clear XRD pattern of typical cellulose was observed for fresh lime residues. The diffractograms of autoclaved lime residues and nanocellulose showed 2 distinct peaks at 2θ = 16° and 22°, which represent the typical native cellulose structure [27]. The CI of fresh and autoclaved lime residues undergoing varying conditions calculated using XRD method are given in Table 2. An increase in CI after autoclaving was observed. Regarding to the chemical compositions given in Table 1, autoclaving led to a release of pectin and hemicellulose from the fiber matrix. The removal of non-crystalline materials, especially pectin and hemicellulose, changed the nature of fiber to be more crystalline [26]. CI of nanocellulose was in the range of 59-65%. CI values greater than 60% have been generally reported for many nanocellulose materials derived from agricultural by-products, for examples, citrus residues, pineapple leaf and banana fiber [8, 11, 28]. It was also observed that CI of nanocellulose samples was greater than those of autoclaved samples. Naturally, the individual polysaccharide chains are arranged in parallel and are bound together by hydrogen bonds to form cellulose microfibrils [29]. Disruption of hydrogen bonds linked between individual fiber during homogenization led to a numerous formation of nanoscale fiber. When the nanocellulose suspension was prepared into the dry form, available hydroxyl groups of each nanofiber moved closer due to the loss of water and formed tight aggregates [30]. This resulted in a crystalline structure, which hence reflected in a higher CI of dried nanocellulose.
Saranya Jongaroontaprangsee et al ./ Materials Today: Proceedings 5 (2018) 11095–11100 700
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Fig. 1. XRD patterns of (a) lime residues and (b) nanofibrillated cellulose (NFC) undergoing different autoclaving conditions Table 2. Crystallinity index of treated lime residues and nanofibrillated cellulose (NFC) undergoing different autoclaving conditions Sample Condition CI (%) Fresh lime residues 24.38 Treated lime residues 54.95 Autoclaving at 110 °C 50.35 Autoclaving at 120 °C 52.53 Autoclaving at 130 °C Nanofibrillated cellulose 58.82 Autoclaving at 110 °C 65.33 Autoclaving at 120 °C 64.48 Autoclaving at 130 °C
TEM image confirmed the presence of nanocellulose in the form of NFC. The diameter of NFC was in the range of 3-10 nm showing that combination of autoclaving and homogenization processes effectively disintegrated the native cellulose into the nanoscale fiber. The diameter of NFC in this study was similar to those previously reported for NFC produced from citrus residues after juice extraction; which was in the range of 2-10 nm [11, 16].
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Fig. 2. TEM of nanofibrillated cellulose (NFC) prepared using different autoclaving conditions; (a) 110 °C, (b) 120 °C and (c) 130 °C
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Saranya Jongaroontaprangsee et al./ Materials Today: Proceedings 5 (2018) 11095–11100
Overall, the results suggested that it was possible to produce the nanoscale fiber without the use of chemicals. Autoclaving was proven to be an effective method to segregate cellulose from plant structure. Autoclaving followed by recommended defibrillation condition could provide the nanocellulose with high CI similar to those produced from citrus waste via the use of chemical treatments such as mild acid hydrolysis and alkaline hydrolysis [11, 16]. 4. Conclusion The feasibility study of nanocellulose production from lime residues after juice extraction in the form of NFC via chemical-free process was investigated. Autoclaving temperature in the range of 110-130 °C effectively removed hemicellulose and pectin from the lime fiber matrix leaving the higher content of cellulose in the pretreated samples. The CI of the produced NFC was in the range of 59-65%. Autoclaving at 120 °C for 2 h followed by high shear and high pressure homogenization was suggested as an optimum condition for preparation of NFC from lime residues. The chemical-free process can produce nanocellulose with similar properties to chemical treated nanocellulose. The redisperisble NFC production and its properties are being further investigated. Acknowledgements The authors express their sincere appreciation to Engineering faculty, King Mongkut’s University of Technology Thonburi for supporting the study financially. Miss Saranya Jongaroontaprangsee thanks the TRF, through its Royal Golden Jubilee (RGJ) Scholarship program, for supporting her doctoral study. References [1] W. Bai, J. Holbery, A. K. Li, Cellulose 16 (2009) 455-465. [2] Y. Hu, L. Tang, Q. Lu, S. Wang, X. Chen, B. Huang, Cellulose 21 (2014) 1611-1618 [3] N. Lavoine, I. Desloges, A. Dufresne, J. Bras, Carbohyd. Polym. 90 (2012) 735-764. [4] C. Gómez, A. Serpa, J. Velásquez-Cock, P. Gañán, C. Castro, L. Vélez, R. Zuluaga, Food Hydrocolloids. 57 (2016) 178-186 [5] M. Börjesson, G. Westman, Crystalline nanocellulose - Preparation, modification, and properties. In: Poletto M, editor. Cellulose Fundamental aspects and current trends, 2015. [6] H.P.S. Abdul Khalil, Y. Davoudpour, M.N. Islam, A. Mustapha, K. Sudesh, R. Dungani, M. Jawaid, Carbohyd. Polym. 99 (2014) 649-665. [7] Q.Q. Wang, J.Y. Zhu, R. Gleisner, T.A. Kuster, U. Baxa, S.E. McNeil, Cellulose 19 (2012) 1631-1643. [8] M. Jonoobi, N.K. Oksman, J. Harun, M. Misra, BioResources 4 (2009) 626-639. [9] T. Winuprasith, M. Suphantharika, Food Hydrocolloids. 32 (2013) 383-394. [10] M. Henriksson, G. Henriksson, L.A. Berglund, T. Lindström, Eur. Polym. J. 43 (8) (2007) 3434-3441. [11] M. Mariño, L. Lopes da Silva, N. Durán, L. Tasic, Molecules 20 (2015) 5908-5923. [12] M. Pääkkö, M. Ankerfors, H. Kosonen, A. Nykänen, S. Ahola, M. Österberg, J. Ruokolainen, J. Laine, P.T. Larsson, O. Ikkala, T. Lindström, Biomacromolecules 8 (2007) 1934-1941. [13] F.M. Pelissari, P.J.dA Sobral, F.C. Menegalli, Cellulose 21 (2014) 417-432. [14] K. Abe, H. Yano, Cellulose 16 (2009) 1017-1023. [15] H.P.S. Abdul Khalil, A.H. Bhat, A.F. Ireana Yusra, Carbohyd. Polym. 87 (2012) 963-979. [16] S. Hiasa, S. Iwamoto, T. Endo, Y. Edashige, Ind. Crops. Prod. 62 (2014) 280-285. [17] B. Deepa, E. Abraham, B.M. Cherian, A. Bismarck, J.J. Blaker, L.A. Pothan, A.L. Leao, S.F. de Souza, M. Kottaisamy, Bioresour. Technol. 102 (2011) 1988-1997. [18] C.J. Chirayil, J. Joy, L. Mathew, M. Mozetic, J. Koetz, S. Thomas, Ind. Crops. Prod. 59 (2014) 27-34. [19] F.R. Marín, C. Soler-Rivas, O. Benavente-García, J. Castillo, J.A. Pérez-Alvarez, Food Chem. 100 (2007) 736-741. [20] H.K. Goering, P.J. Van Soest, Forage fiber analysis. Agricultural handbook no. 379, Washington DC: US Department of Agriculture, 1970. [21] E.A. Ahmed, J.M. Labavitch, J. Food Biochem. 1 (1978) 361-365. [22] P.K. Kintner, J.P. Van Buren, J. Food Sci. 47 (1982) 756-759. [23] C. Ververis, K. Georghiou, D. Danielidis, D.G. Hatzinikolaou, P. Santas, R. Santas, V. Corleti, Bioresour. Technol. 98 (2007) 296-301. [24] S. Sabiha-Hanim, M.A.M. Noor, A. Rosma, Bioresour. Technol. 102 (2011) 1234-1239. [25] R. El Hage, L. Chrusciel, L. Desharnais, N. Brosse, Bioresour. Technol. 101 (2010) 9321-9329. [26] B.M. Cherian, A.L. Leão, S.F. de Souza, S. Thomas, L.A. Pothan, M. Kottaisamy, Carbohyd. Polym. 81 (2010) 720-725. [27] W. Chen, H. Yu, Y. Liu, Y. Hai, M. Zhang, P. Chen, Cellulose 18 (2011) 433-442. [28] F. Jiang, Y.L. Hsieh, Carbohyd. Polym. 95 (2013) 32-40. [29] R.J. Moon, A. Martini, J. Nairn, J. Simonsen, J. Youngblood, Chem. Soc. Rev. 40 (2011) 3941-3994. [30] Y. Peng, D.J. Gardner, Y. Han, A. Kiziltas, Z. Cai, M.A. Tshabalala, Cellulose 20 (2013) 2379-2392.
ScienceDirect Materials Today: Proceedings 5 (2018) 11095–11100
www.materialstoday.com/proceedings
NanoThailand2016
Production of nanocellulose from lime residues using chemical-free technology Saranya Jongaroontaprangsee, Naphaporn Chiewchan* and Sakamon Devahastin Advanced Food Processing Research Laboratory, Department of Food Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi, 126 Pracha u-tid Road, Bangkok 10140, Thailand
Abstract The feasibility of using lime residues after juice extraction as a raw material to produce nanocellulose was determined in this study. Autoclaving at 110-130 °C was performed as a pretreatment to remove hemicellulose and pectin from the native fiber. The pretreated samples were then subjected to high shear homogenizing at 20,000 rpm for 15 min and high pressure homogenizing at 40 MPa for 5 passes. The fiber images obtained from transmission electron microscopy (TEM) technique revealed that the multiple homogenizing steps could effectively disintegrate the pretreated fiber into nanometer scale. X-ray diffraction (XRD) results showed that the prepared nanocellulose possessed much higher crystallinity index (CI) comparing to that of the native fiber; it was noted that the degree of CI was dependent on the processing conditions. The results suggested that there is a potential to produce nanocellulose from citrus by-products via the application of the developed chemical-free technology, which is safely to be used for food applications. © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 5th Thailand International Nanotechnology Conference (NanoThailand2016). Keywords: residues; Nanocellulose; Chemical-free Technology; Autoclaving; Homogenization
* Corresponding author. Tel.: +66-2470-9244. E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 5th Thailand International Nanotechnology Conference (NanoThailand2016).
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Saranya Jongaroontaprangsee et al./ Materials Today: Proceedings 5 (2018) 11095–11100
1. Introduction Nanocellulose is a natural material extracted from native cellulose and has at least one dimension in a nanometer range. It has gained much attention due to its unique properties, which can be used in numerous applications. Nanocellulose derived from plants is generally produced in the forms of cellulose nanocrystal (CNC) and nanofibrillated cellulose (NFC) depending on the desired applications. CNC is rod like particles and highly crystalline. It can be obtained by hydrolysis using strong acid under strictly controlled conditions [1, 2]. NFC is generally obtained by mechanical disintegration without using strong acid hydrolysis, therefore it exhibits a web-like structure with both amorphous and crystalline parts [3]. NFC possesses very high surface area and very high aspect ratio. It also has ability to form a viscous gel, which can be used as a binder for paper industry or a viscous modifier in paints, cosmetic, pharmaceutical and food products [4, 5]. The mechanical methods for disintegration of native cellulose into nanoscale fiber that have been reported include homogenization, microfluidization, grinding and cyocrushing [6-9]. Pretreatments may be performed as an additional process in order to facilitate the defibrillation and reduce the energy consumption. Mild enzymatic hydrolysis using, for example, endoglucanase, combined with mechanical process has been reported for preparation of NFC from wood pulp and citrus residues [10-12]. Alkaline-acid pretreatment can be used to solubilize noncellulosic components from wood, rice straw, potato tuber and banana peel prior to disintegration [13, 14]. Hydrothermal processing such as steam explosion and autoclaving are also proposed as a promising pretreatment method to reduce the use of chemicals. During steam explosion, the sample is exposed to pressurized steam followed by rapid reduction in pressure resulting in substantial break down of the lignocellulosic structure, hydrolysis of hemicellulose fraction, depolymerization of the lignin components and defibrillation [15]. Using mild acid or alkaline hydrolysis coupled with autoclaving at 110-120 °C for 1-2 h has been suggested for production of NFC from citrus residues, banana fiber and isora fiber [16-18]. Although wood is a main raw material to produce nanocellulose, the agricultural residues are also of interest as they are available in a large quantity and can be prepared into nanocellulose with less energy consumption. In recent years, citrus fruit by-products are proposed as a raw material for production of nanocellulose; approximately 20-40% of cellulose content (dry mass) can be obtained depending on raw materials [19]. This study aimed at producing chemical-free nanocellulose in the form of NFC from lime residues (Citrus aurantifolia Swingle) after juice extraction via the use of autoclaving as a selected pretreatment. The effect of autoclaving conditions on crystallinity and morphology of the produced NFC were determined. 2. Material and methods 2.1. Nanocellulose preparation Lime residues (Citrus aurantifolia Swingle) after juice extraction were obtained from a juice vendor located in Tungkru, Bangkok, Thailand. The residues was collected on the same day of each experiment. The lime residues was squeezed again to remove the remaining juice using a hand press juicer. Only lime residues (i.e., flavedo, albedo, segments and juice sacs) without seeds were used as a starting raw material. The prepared lime residues (80 g) and deionized water (800 mL) were added into a blender jar and then chopped using a blender (Waring Commercial, HGB2WT, Torrington, CT) for 2 min to obtain the particle size in the range of 1-3 mm. After chopping, the slurry was filled into a 1000 mL Duran bottle and autoclaved at the temperatures of 110, 120 and 130 °C for 2 h. After cooling to room temperature (~30 °C), the autoclaved slurry was filtered through a Whatman no. 541 filter paper. The autoclaved sample was collected and prepared into the fiber suspension with the solids content of 0.6% w/w using deionized water. The fiber suspension was passed through a high shear homogenizer (IKA, T25 digital ULTRA-TURRAX®, Staufen, Germany) at 20,000 rpm for 15 min and subsequently passed through a high pressure homogenizer (GEA, NS2006L, Parma, Italy) at 40 MPa for 5 passes. The autoclaved residues and nanocellulose suspension were dried in a hot air oven (Memmert, UF 110, Schwabach, Germany) at 60 °C prior to chemical compositions analysis and XRD analyses.
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2.2. Chemical composition analysis The chemical compositions of the samples were determined in terms of neutral detergent fiber (NDF), aciddetergent fiber (ADF) and acid-detergent lignin (ADL) following the method of Goering and Van Soest [20]. Cellulose, hemicellulose and lignin contents were calculated using the following equations. Cellulose = ADF- ADL (1) Hemicellulose = NDF – ADF (2) Lignin = ADL (3) Galacturonic acid (GalA) content was determined to represent the pectin content in a sample. For GalA determination, sample preparation and analysis procedures were performed following the method described by Ahmed and Labavitch [21] and Kintner and Van Buren [22], respectively. 2.3. X-ray diffraction XRD pattern of samples was determined using an X-ray diffractometer (Bruker AXS GmbH, D8 Discover, Karlsruhe, Germany). The XRD spectra were recorded using a Cu Kα radiation (λ = 0.1546 nm) at 40 kV and 40 mA. Samples were analyzed in the scattering range (2θ) of 10-70° at a scanning rate of 2° 2θ/min. The crystallinity index for each sample was calculated using the following equation: I002 − Iam Crystallinity index = × 100 (4) I002 Where I002 and Iam are the peak intensities of crystalline and amorphous regions, respectively. 2.4. Transmission electron microscopy The nanocellulose suspensions obtained from various pretreatments were diluted and sonicated to achieve a uniform dispersion. A droplet of suspension was placed onto Cu-grid and coated with a thin film of carbon and negatively stained with 1% uranyl acetate solution. All samples were analyzed using a transmission electron microscope (JEOL, JEM-2100HR, Tokyo, Japan). The diameters of nanocellulose were calculated from TEM images using ImageJ. 2.5. Statistical analysis The experiments were designed to be completely random. The data were subject to analysis of variance (ANOVA) and are presented as mean values with standard deviations. Differences between mean values were established using Duncan’s new multiple range tests; values were considered at a confidence level of 95%. All statistical analyses were performed using SPSS software (version 17) (SPSS Inc., Chicago, IL, USA). All experiments were performed in triplicate unless specified otherwise. 3. Results and discussion The contents of solids, cellulose, hemicellulose, lignin and GalA of fresh and autoclaved lime residues are listed in Table 1. The results showed that the solids content of lime residues significantly decreased after autoclaving. Increasing the autoclaving temperatures resulted in a higher reduction in a solids content. Cellulose content of lime residues was similar to those reported for orange and lemon residues after juice extraction [23]. The cellulose content of lime residues significantly increased after autoclaving. These values corresponded to the reduction in the total solids content. Removal of soluble solids such as low-molecular weight carbohydrates and noncellulosic cell wall components resulted in an increase in a cellulose fraction retained in the autoclaved samples. Autoclaving at 110 °C for 2 h seemed to have a minute effect on the lignocellulosic structure; only pectin and other soluble components could be released from the plant tissues leading to an increase in the cellulose content.
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The effect of autoclaving was more pronounced when higher autoclaving temperatures were applied. Higher fraction of cellulose could be obtained with a lesser fractions of hemicellulose and pectin contents. Hydrothermal treatment by autoclaving at the temperatures higher than 110 °C led to a significant reduction of hemicellulose. The autohydrolysis of hemicellulose may occur at the temperature of higher than 110 °C. During autohydrolysis, the acetyl groups of xylan (backbone of hemicellulose) were hydrolyzed to acetic acid, thus decreasing the pH of the autohydrolysate and promoting the autohydrolysis of hemicellulose into water soluble oligomers [24]. Sabiha-Hanim, Noor and Rosma [24] and El Hage, Chrusciel, Desharnais and Brosse [25] also observed the autohydrolysis of hemicellulose in grass and oil palm frond during autoclaving at the temperatures of 121 °C and 130 °C, respectively. It was found that the autoclaving conditions performed in this work did not have a significant effect on lignin content of the pretreated samples. Lignin extraction can occur when using chemical treatments in coupled with autoclaving. For example, diluted alkaline solution combined with autoclaving at 110-120 °C has been reported to be an effective method used for extraction of lignin form banana fiber and pineapple leaf [17, 26]. Chemical compositions of lime residues before and after autoclaving at 110, 120 and 130 °C for 2 h Yield of solids content Content (% dry basis) (% dry basis) Cellulose Hemicellulose Lignin Lime residues 100.00 11.46±1.86a 10.18±5.36b 7.29±1.87a Autoclaving 41.66±3.41b 10.06±0.71b 7.91±1.77a 35.84±1.13b at 110 °C 47.04±2.24c 3.94±1.21a 9.19±0.71a 31.01±0.62a at 120 °C 46.58±2.53c 3.55±1.27a 7.90±1.83a 29.35±0.35a at 130 °C Same letters in the same column indicate that values are not significantly different (p≥0.05). Table 1.
GalA 32.15±3.86c 24.76±2.48b 18.38±1.77a 15.63±1.29a
Approximately 32% of GalA was found in fresh lime residues. High amount of GalA implies that pectin is an important substance in lime residues. A significant reduction in GalA content was observed after autoclaving; higher temperatures led to the higher removal of pectin from the plant structure. Fig. 1 shows the XRD patterns of fresh and autoclaved lime residues as well as the produced nanocellulose. No clear XRD pattern of typical cellulose was observed for fresh lime residues. The diffractograms of autoclaved lime residues and nanocellulose showed 2 distinct peaks at 2θ = 16° and 22°, which represent the typical native cellulose structure [27]. The CI of fresh and autoclaved lime residues undergoing varying conditions calculated using XRD method are given in Table 2. An increase in CI after autoclaving was observed. Regarding to the chemical compositions given in Table 1, autoclaving led to a release of pectin and hemicellulose from the fiber matrix. The removal of non-crystalline materials, especially pectin and hemicellulose, changed the nature of fiber to be more crystalline [26]. CI of nanocellulose was in the range of 59-65%. CI values greater than 60% have been generally reported for many nanocellulose materials derived from agricultural by-products, for examples, citrus residues, pineapple leaf and banana fiber [8, 11, 28]. It was also observed that CI of nanocellulose samples was greater than those of autoclaved samples. Naturally, the individual polysaccharide chains are arranged in parallel and are bound together by hydrogen bonds to form cellulose microfibrils [29]. Disruption of hydrogen bonds linked between individual fiber during homogenization led to a numerous formation of nanoscale fiber. When the nanocellulose suspension was prepared into the dry form, available hydroxyl groups of each nanofiber moved closer due to the loss of water and formed tight aggregates [30]. This resulted in a crystalline structure, which hence reflected in a higher CI of dried nanocellulose.
Saranya Jongaroontaprangsee et al ./ Materials Today: Proceedings 5 (2018) 11095–11100 700
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Fig. 1. XRD patterns of (a) lime residues and (b) nanofibrillated cellulose (NFC) undergoing different autoclaving conditions Table 2. Crystallinity index of treated lime residues and nanofibrillated cellulose (NFC) undergoing different autoclaving conditions Sample Condition CI (%) Fresh lime residues 24.38 Treated lime residues 54.95 Autoclaving at 110 °C 50.35 Autoclaving at 120 °C 52.53 Autoclaving at 130 °C Nanofibrillated cellulose 58.82 Autoclaving at 110 °C 65.33 Autoclaving at 120 °C 64.48 Autoclaving at 130 °C
TEM image confirmed the presence of nanocellulose in the form of NFC. The diameter of NFC was in the range of 3-10 nm showing that combination of autoclaving and homogenization processes effectively disintegrated the native cellulose into the nanoscale fiber. The diameter of NFC in this study was similar to those previously reported for NFC produced from citrus residues after juice extraction; which was in the range of 2-10 nm [11, 16].
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Fig. 2. TEM of nanofibrillated cellulose (NFC) prepared using different autoclaving conditions; (a) 110 °C, (b) 120 °C and (c) 130 °C
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Saranya Jongaroontaprangsee et al./ Materials Today: Proceedings 5 (2018) 11095–11100
Overall, the results suggested that it was possible to produce the nanoscale fiber without the use of chemicals. Autoclaving was proven to be an effective method to segregate cellulose from plant structure. Autoclaving followed by recommended defibrillation condition could provide the nanocellulose with high CI similar to those produced from citrus waste via the use of chemical treatments such as mild acid hydrolysis and alkaline hydrolysis [11, 16]. 4. Conclusion The feasibility study of nanocellulose production from lime residues after juice extraction in the form of NFC via chemical-free process was investigated. Autoclaving temperature in the range of 110-130 °C effectively removed hemicellulose and pectin from the lime fiber matrix leaving the higher content of cellulose in the pretreated samples. The CI of the produced NFC was in the range of 59-65%. Autoclaving at 120 °C for 2 h followed by high shear and high pressure homogenization was suggested as an optimum condition for preparation of NFC from lime residues. The chemical-free process can produce nanocellulose with similar properties to chemical treated nanocellulose. The redisperisble NFC production and its properties are being further investigated. Acknowledgements The authors express their sincere appreciation to Engineering faculty, King Mongkut’s University of Technology Thonburi for supporting the study financially. Miss Saranya Jongaroontaprangsee thanks the TRF, through its Royal Golden Jubilee (RGJ) Scholarship program, for supporting her doctoral study. References [1] W. Bai, J. Holbery, A. K. Li, Cellulose 16 (2009) 455-465. [2] Y. Hu, L. Tang, Q. Lu, S. Wang, X. Chen, B. Huang, Cellulose 21 (2014) 1611-1618 [3] N. Lavoine, I. Desloges, A. Dufresne, J. Bras, Carbohyd. Polym. 90 (2012) 735-764. [4] C. Gómez, A. Serpa, J. Velásquez-Cock, P. Gañán, C. Castro, L. Vélez, R. Zuluaga, Food Hydrocolloids. 57 (2016) 178-186 [5] M. Börjesson, G. Westman, Crystalline nanocellulose - Preparation, modification, and properties. In: Poletto M, editor. Cellulose Fundamental aspects and current trends, 2015. [6] H.P.S. Abdul Khalil, Y. Davoudpour, M.N. Islam, A. Mustapha, K. Sudesh, R. Dungani, M. Jawaid, Carbohyd. Polym. 99 (2014) 649-665. [7] Q.Q. Wang, J.Y. Zhu, R. Gleisner, T.A. Kuster, U. Baxa, S.E. McNeil, Cellulose 19 (2012) 1631-1643. [8] M. Jonoobi, N.K. Oksman, J. Harun, M. Misra, BioResources 4 (2009) 626-639. [9] T. Winuprasith, M. Suphantharika, Food Hydrocolloids. 32 (2013) 383-394. [10] M. Henriksson, G. Henriksson, L.A. Berglund, T. Lindström, Eur. Polym. J. 43 (8) (2007) 3434-3441. [11] M. Mariño, L. Lopes da Silva, N. Durán, L. Tasic, Molecules 20 (2015) 5908-5923. [12] M. Pääkkö, M. Ankerfors, H. Kosonen, A. Nykänen, S. Ahola, M. Österberg, J. Ruokolainen, J. Laine, P.T. Larsson, O. Ikkala, T. Lindström, Biomacromolecules 8 (2007) 1934-1941. [13] F.M. Pelissari, P.J.dA Sobral, F.C. Menegalli, Cellulose 21 (2014) 417-432. [14] K. Abe, H. Yano, Cellulose 16 (2009) 1017-1023. [15] H.P.S. Abdul Khalil, A.H. Bhat, A.F. Ireana Yusra, Carbohyd. Polym. 87 (2012) 963-979. [16] S. Hiasa, S. Iwamoto, T. Endo, Y. Edashige, Ind. Crops. Prod. 62 (2014) 280-285. [17] B. Deepa, E. Abraham, B.M. Cherian, A. Bismarck, J.J. Blaker, L.A. Pothan, A.L. Leao, S.F. de Souza, M. Kottaisamy, Bioresour. Technol. 102 (2011) 1988-1997. [18] C.J. Chirayil, J. Joy, L. Mathew, M. Mozetic, J. Koetz, S. Thomas, Ind. Crops. Prod. 59 (2014) 27-34. [19] F.R. Marín, C. Soler-Rivas, O. Benavente-García, J. Castillo, J.A. Pérez-Alvarez, Food Chem. 100 (2007) 736-741. [20] H.K. Goering, P.J. Van Soest, Forage fiber analysis. Agricultural handbook no. 379, Washington DC: US Department of Agriculture, 1970. [21] E.A. Ahmed, J.M. Labavitch, J. Food Biochem. 1 (1978) 361-365. [22] P.K. Kintner, J.P. Van Buren, J. Food Sci. 47 (1982) 756-759. [23] C. Ververis, K. Georghiou, D. Danielidis, D.G. Hatzinikolaou, P. Santas, R. Santas, V. Corleti, Bioresour. Technol. 98 (2007) 296-301. [24] S. Sabiha-Hanim, M.A.M. Noor, A. Rosma, Bioresour. Technol. 102 (2011) 1234-1239. [25] R. El Hage, L. Chrusciel, L. Desharnais, N. Brosse, Bioresour. Technol. 101 (2010) 9321-9329. [26] B.M. Cherian, A.L. Leão, S.F. de Souza, S. Thomas, L.A. Pothan, M. Kottaisamy, Carbohyd. Polym. 81 (2010) 720-725. [27] W. Chen, H. Yu, Y. Liu, Y. Hai, M. Zhang, P. Chen, Cellulose 18 (2011) 433-442. [28] F. Jiang, Y.L. Hsieh, Carbohyd. Polym. 95 (2013) 32-40. [29] R.J. Moon, A. Martini, J. Nairn, J. Simonsen, J. Youngblood, Chem. Soc. Rev. 40 (2011) 3941-3994. [30] Y. Peng, D.J. Gardner, Y. Han, A. Kiziltas, Z. Cai, M.A. Tshabalala, Cellulose 20 (2013) 2379-2392.