Physicochemical characterization of cellulose nanowhiskers extracted from oil palm biomass microcrystalline cellulose

Materials Letters 113 (2013) 87–89

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Physicochemical characterization of cellulose nanowhiskers extracted from oil palm biomass microcrystalline cellulose M.K. Mohamad Haafiz a,b, Azman Hassan a,n, Zainoha Zakaria c, I.M. Inuwa a, M.S. Islam d a

Department of Polymer Engineering, Faculty of Chemical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia School of Industrial Technology, Universiti Sains Malaysia, 11800 Penang, Malaysia c Faculty of Science, Universiti Teknologi Malaysia, UTM, 81310 Skudai, Johor, Malaysia d Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia b

art ic l e i nf o

a b s t r a c t

Article history: Received 26 February 2013 Accepted 5 September 2013 Available online 14 September 2013

Cellulose nanowhiskers are lightweight, inexpensive, biocompatible nanomaterials that have found wide range of applications. One of their important applications is in the development of reinforced polymer nanocomposites (PNC). The aim of this study was to isolate cellulose nanowhiskers from oil palm biomass microcrystalline cellulose (MCC) using chemical swelling treatment. Analysis of Fourier transform infrared spectroscopy (FTIR) indicated that chemical swelling did not change the chemical structure of the cellulosic fragments. The morphology of the swelled MCC was observed using scanning electron microscopy (SEM) and the micrographs showed that the aggregated structure of MCC have broken down. The produced cellulose nanowhiskers (CNW-S) were estimated to have less than 20 nm width and lengths of 300 nm after treatment, which confirm its nanoscale structure. X-ray diffraction analysis indicated that chemical swelling improve slightly the crystallinity of MCC while maintaining the cellulose I structure. Thermogravimetric analysis (TGA) showed that the CNW-S was significantly thermally more stable than MCC, having higher on-set degradation temperature and maximum degradation temperature. & 2013 Elsevier B.V. All rights reserved.

Keywords: Cellulose Nanowhiskers FTIR Crystal structure Thermal properties

1. Introduction Cellulose is the world's most ubiquitous and abundant natural biomacromolecule that is produced by plants, and microorganisms [1,2]. It is a linear homopolymer of glucose (C6H10O5)nchain with repeating units consisting of D-glucose in a 4C1 conformation. It has very attractive properties such as biocompatibility, biodegradability, thermal and chemical stability [1,3]. In nature, the cellulose molecular chains are biosynthesized and self-assembled into microfibrils, which are composed of crystalline and amorphous domains [4,5]. These aggregated cellulose molecules are stabilized laterally by hydrogen bonds between the hydroxyl groups and oxygens of adjacent molecules [4]. The amorphous regions of native cellulose can be readily hydrolyzed, with almost no weight loss, when subjected to strong acid hydrolysis [6]. Typically when wood sources are used, the particles of hydrolyzed cellulose obtained are
100–300 nm in length and
3–10 nm in width [5]. These nanoparticles are referred to as “nanocrystalline cellulose” or “cellulose nanowhiskers” because of their nanoscale cross sectional dimension [7]. n

Corresponding author. Tel.: þ 60 7 5537835; fax: þ60 7 5581 463. E-mail addresses: [email protected], [email protected] (A. Hassan). 0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.09.018

Cellulose nanowhiskers (CNW) are renewable and biocompatible nanomaterials that have evoked much interest in the research world because of its versatility in various applications (e.g. green nanocomposites, tissue engineering scaffolds) [8,9]. CNW are highly ordered crystalline regions of cellulosic materials. Isolated nanowhiskers are rod shaped nanocrystals that have unique electrical, optical, magnetic and conductive properties [5]. Even though CNW can be obtained from a variety of natural resources such as hemp, wheat straw, and wood pulp by acid hydrolysis, these nanoentities however are not as commercially popular as other nanomaterials like carbon nanotubes. One major challenge in the use of CNW in commercial applications is their limited availability and low yield when isolated from natural resources [5]. This study is the first attempt to isolate CNW from the microcrystalline cellulose (MCC) produced from oil palm empty fruit bunch total chlorine free pulp by chemical swelling method using N,N-dimethylacetamide (DMAc) containing 0.5% LiCl solutions as swelling agent. To the best of our knowledge, no study on production of CNW from oil palm biomass MCC has been reported in the open literature. However, studies on the isolation of CNW using different approaches and sources have been reported by previous researchers. Satyamurthy et al. have isolated CNW from cotton fibers by controlled microbial activity which generated

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CNW [10]. In other study by Pan et al. the isolation of CNW from commercial MCC by combination of acid hydrolysis and high pressure homogenization was reported. The combined techniques generated rod like materials with properties which is characteristic of CNW [11]. In this study, molecular structure analysis, crystallinity, morphology, size of particles, and thermal stability of the produced CNW have been characterized.

2. Experimental method Materials: Microcrystalline cellulose (MCC) was produced from oil palm empty fruit bunch (OPEFB) chlorine free pulps. The production of MCC was described in detail in our previous paper [12]. All chemicals used were secured from Merck, Malaysia. Method: Swelling and separation of MCC: MCC was swelled and partly separated to whiskers by chemical and ultra sonification treatments using same method described by Pereda et al. based on original procedures described by Oksman et al. [13,14]. A N,Ndimethylacetamide (DMAc) with 0.5% LiCl solution was used as a swelling agent. The initial concentration of MCC in DMAc/LiCl was 10 wt%. MCC was agitated using a mechanical stirrer inside the water bath for 12 h at 70 1C. Then the slightly swelled particles were sonicated in Branson 2510 bransonic bath for 3 h over a period of 5 days with long intervals between each sonication treatment, to separate the cellulose nanowhiskers. The resultant cellulose nanowhiskers were repeatedly washed with distilled water then freeze-dried and noted as CNW-S. Fourier transform infrared spectroscopy: Fourier transform infrared spectroscopy (FTIR) was performed on a Perkin Elmer 1600 infrared spectrometer using the KBr method. FTIR spectra of the samples were recorded by using Nicolet's AVATAR 360 at 32 scans with a resolution of 4 cm  1 and between wave number ranges of 4000–370 cm  1.

Fig. 1. Typical FTIR spectra obtained from MCC and CNW-S.

Morphological analysis: The morphology of samples was observed using scanning electron microscopy (SEM). SEM was carried out using a SEM-EDX Oxford INCA 400 model at an acceleration voltage of 15 kV. Transmission electron microscope (TEM) model LEOLIBRA was used to observe the size distribution of the sample. X-ray diffraction: X-ray diffraction (XRD) analysis was carried out to study the crystallinity of the samples using an X'Pert X-ray diffractometer (SIEMENS XRD D5000) and Ni-fltered Cu Kα radiation at an angular incidence of 5–501 (2θ angle range). The operating voltage and current were 40 kV and 50 mA, respectively. The crystallinity of the samples was calculated from diffraction intensity data using the empirical method for native cellulose [15]. The crystalline-to-amorphous ratio of materials was determined using the following equation.   C Ir ð%Þ ¼ ðI 200 I am Þ=I 200  100% ð1Þ Thermogravimetric analysis (TGA): The thermal stability of samples was characterized using a thermogravimetric analyzer, model 2050 (TA Instruments, New Castle, DE). The specimens were scanned from 30 1C to 900 1C at a rate of 20 1C min  1 under a nitrogen gas atmosphere.

3. Results and discussions In this study, isolation and characterization of CNW-S by chemical swelling treatment of MCC has been conducted. The significance of this method is that the CNW generated is free from chemical modifications (as observed in FTIR analysis) that is normally associated with acid hydrolysis. Without such chemical modifications and couple with high thermal stability, the CNW-S produced from the MCC is suitable in composites formulation and pharmaceutical applications. Characterization of its structure and properties are discussed below. FTIR spectroscopic analysis: Typical FTIR spectra of MCC and CNW-S are shown in Fig. 1. The FTIR spectroscopy revealed the similarities between both spectra which is an indication that both samples have similar chemical compositions. Similar result is also obtained by Fatma et al. using different concentrations of sulfuric acid (H2SO4) to isolate nanofibers from OPEFB [16]. The broad absorption band located from 3400 to 3500 cm  1 and absorption at 2900 cm  1 is due to stretching of –OH groups and CH2 groups respectively [15,17]. The absorption at 1645 cm  1 in both samples is indicative of absorption of water. According to previous studies, this band is related to the bending modes of water molecules due to a strong interaction between cellulose and water [15,17]. The absorption band at 1425 cm  1 is associated to the intermolecular

Fig. 2. Typical SEM of (a) MCC, (b) CNW-S and (c) typical TEM of CNW-S.

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temperature (Tmax) were 275 1C and 326 1C respectively, while for CNW-S the on-set and maximum degradations took place at 329 1C and 418 1C respectively. This increase could be attributed the rearrangement and reorientation of the crystals in cellulose and it also applies to the higher degree of crystallinity observed for CNW-S [17,20]. Based on these results, we conclude that the thermal stability of the MCC was increased by the chemical swelling treatments. Therefore, it could be used as a potential reinforcing material for polymeric materials, where good thermal properties are required. Fig. 3. X-ray diffractograms from MCC and CNW-S.

4. Conclusion

Fig. 4. Typical TGA for MCC and CNW-S.

hydrogen of aromatic ring group [18]. The absorption band at 1163 cm  1 and the peak at 896 cm  1 corresponds to C–O–C stretching and associated to C–H rock vibration of cellulose (anomeric vibration, specific for β-glucosides) observed in MCC and CNW-S samples [15,19]. The FTIR spectra confirm that the chemical swelling performed to obtain CNW-S from MCC did not change the chemical structure of the cellulosic fragments. Morphological analysis: The morphology of MCC was investigated using SEM. The SEM micrographs show changes in the morphology of the MCC after chemical swelling as shown in Fig. 2. Fig. 2(a) shows irregular shaped aggregated fibrils with rough surface. Meanwhile, Fig. 2(b) shows that the aggregationhas broken down after chemical swelling giving rise to intermittent fibrillar structure and further reduction in intrafibrillar diameter. Similar result has been reported by Oksman et al. [14]. TEM technique was used to observe the dispersion of individual crystallites or whiskers. Typical TEM images of CNW-S are shown in Fig. 2(c). The figure shows the separation of whiskers in nanometer scale. The size of whiskers was estimated to be less than 20 nm width and 300 nm in length. X-ray diffraction: The X-ray diffraction (XRD) patterns of MCC and CNW-S are presented in Fig. 3. The crystallinity value of CNWS increased slightly to 88% (Fig. 3a), as compared to MCC, which exhibited 87% crystallinity (Fig. 3b). An increase in the crystallinity is related to increases in the rigidity of the cellulose structure, which can lead to a higher tensile strength of fibers [14]. XRD diffraction data suggested the both samples were highly crystalline native cellulose I, with no cellulose II present; indicated by the absence of the doublet located at 22.61 [15]. CNW-S produced from chemical swelling method in our study possess ahigher degree of crystallinity compared to nanocellulose produced from OPEFB by a chemo-mechanical technique (69%) [17]. Thermogravimetric analysis: Fig. 4 reports thermogravimetric analysis (TGA) for MCC and CNW-S. In the case of the MCC, the onset degradation temperature (Ton) and maximum decomposition

Cellulose nanowhiskers were successfully isolated from oil palm biomass MCC by chemical swelling treatment. Structural characterization and morphological studies of the generated CNWS have confirmed its nanostructured nature. The size of whiskers produced were found to be less than 20 nm width and 300 nm in length with a relatively higher degree of crystallinity when compared to nanocellulose produced from OPEFB by chemomechanical technique. Improvement in thermal stability of MCC was also observed using the chemical swelling method. The present studies have shown the potentials of MCC as a reinforcing agent in the development of polymer composites.

Acknowledgment The author would like to thank University Sains Malaysia, Ministry of Higher Education Malaysia and Research University Grant 05H22 sub-code Q.J130000.3509.05H22 for financial support. References [1] Deng M, Zhou Q, Du A, Kasteren JV, Wang Y. Materials Letters 2009;63:1851–4. [2] Klemm D, Heublein B, Fink HP, Bohn A. Angewandte Chemie International Edition 2005;44:3358–93. [3] Li R, Fei J, Cai Y, Li Y, Feng J, Yao J. Carbohydrate Polymers 2009;76:94–9. [4] Nishiyama YJ. Wood Science 2009;55:241–9. [5] Herrera MA, Mathew AP, Oksman K. Materials Letters 2010;71:28–31. [6] Rånby BG. Discussions of the Faraday Society 1951;11:158–64 (Discussion 20813). [7] Bras J, Hassan ML, Bruzesse C, Hassan EA, El-Wakil NA, Dufresne A. Industrial Crops and Products 2010;32:627–33. [8] Cao X, Ding B, Yu J, Al-Deyab SS. Carbohydrate Polymers 2012;90:1075–80. [9] Salavati-Niasari M, Davar F, Fereshteh Z. Journal of Alloys and Compounds 2010;494:410–4. [10] Satyamurthy P, Jain P, Balasubramanya RH, Vigneshwaran N. Carbohydrate Polymers 2011;83:122–9. [11] Pan M, Zhou X, Chen M. BioResources 2013;8(1):933–43. [12] Haafiz MKM, Eichhorn SJ, Hassan A, Jawaid M. Carbohydrate Polymers 2013;93:628–34. [13] Pereda M, Amica G, Rácz I, Marcovich NE. Journal of Food Engineering 2011;103:76–83. [14] Oksman K, Mathew AP, Bondeson D, Kvien I. Composites Science and Technology 2011;66:2776–84. [15] Rosa SML, Rehman N, De Miranda MIG, Nachtigall SMB, Bica CLD. Carbohydrate Polymers 2012;87:1131–8. [16] Fahma F, Iwamoto S, Hori N, Iwata T, Takemura A. Cellulose 2010;17:977–85. [17] Jonoobi M, Harun J, Tahir PM, Shakeri A, Azry SS, Makinejad MD. Materials Letters 20111098–100. [18] Kumar V, Maria De La LRM, Yang D. International Journal of Pharmaceutics 2002;235:129–40. [19] Alemdar A, Sain M. Bioresource Technology 2008;99:1664–71. [20] Mandal A, Chakrabarty D. Carbohydrate Polymers 2011;86:1291–9.