Preparation and characterization of regenerated cellulose using ionic liquid.
Cellulose is the most abundant bio-renewable material, with a long and well-established technological base  and almost inexhaustible source of raw material for the increasing demand for environmentally friendly and biocompatible products . Cellulose is one of the most widespread biopolymer found globally, existing in a variety of living species such as plant, animals, bacteria and some amoebas . As shown in Fig.1, it has a highly crystalline polymer of D-an-hydroglucopyranose units joined together in long chains by [beta]-1,4-glycosidic bonds .
However, processing and derivatization of cellulose are difficult in general, because this natural polymer is neither meltable nor soluble in conventional solvents due to its hydrogen bonded and partially crystalline structure. Therefore, present industrial production of regenerated cellulose and cellulose derivatives are in long time dominated by polluting viscose process and heterogeneous processes, respectively (Klemm et al., 1998). With increasing governmental regulations in industries, the need to implement "green" processes for cellulose processing and to explore alternative routes for the functionalization of cellulose with simpler reagents and less steps is getting increasingly important .
Since cellulose is difficult to process in solution or as a melt, because of its large proportion of intra- and intermolecular hydrogen bonds, which strictly limit its processing and applications [1,23]. Therefore, many organic and inorganic solvent systems such as N-methyl morpholine N-oxide (NMMO)  lithium chloride/1,3dimethyl-2-imidazolidinone (LiCl/DMI)  lithium chloride/N,N dimethylacetamide (LiCl/DMAc)  and phosphoric acid  have been investigated for regenerated cellulose fiber production. Nevertheless, most of the systems still seem to be unsuccessful from an industrial viewpoint because of their toxicity and difficult solvent recovery. Recently, ionic liquids (ILs), which are considered as desirable green solvents, have been reported to be effective and promising cellulose solvents. [21,25,26,32]. Nowadays, ILs used for manufacturing regenerated cellulose fibers are arousing considerable commercial interest because of their superior dissolving capacity, environmentally friendly properties, easy recycling and good recoverability [20,31,32].
In this research to investigated the effect of MCC content on tensile properties and X-ray diffraction of regenerated cellulose using ionic liquid.
In this research, microcrystalline cellulose (MCC) with particle size of 50pm was supplied by SigmaAldrich, USA. Lithium Chloride (LiCl) and N, N Dimethylacetamide (DMAc) was obtained from Across, Belgium. Acetone was supplied by Sigma-Aldrich.
Preparation of Regenerated Cellulose:
Cellulose was dissolve using DMAc/LiCl initially, involves an activation step in which the cellulose structure is first swollen via solvent exchange. Microcrystalline cellulose (MCC) was immersed in distilled water, twice in acetone and in DMAc for 40 minutes each, dried for 3 hrs at 80[degrees]C. The dissolution occurred by immersing the MCC in DMAc solution with addition of 8 wt. % LiCl and stirred using magnetic stirrer at room temperature for 30 minutes until the LiCl completely dissolved. The transparent gel film had formed after removal of DMAc was immersed in distilled water for 30 minutes to regenerate cellulose and extract the DMAC/LiCl co-solvent. Then the samples were dried at room temperature for 1 day.
X-ray diffraction (XRD):
XRD analysis was carried out using Bruked Ds Advance diffractometer equipped with X-ray Tube: Cu-K[alpha] ([lambda]=1.5418A[degrees]), analysed under normal atmospheric condition at room temperature. The relative amount of crystallinity of the specimens was evaluated using crystallinity index (CI) 
Crystallinity Index(CI) = 100 (I - I') / I
where I is the height of the peak assigned to (200) planes, typically located in the range 2[theta] = 21[degrees]-22[degrees]. I' is the height of the peak assigned to (110) planes measured at 2[theta] = 18[degrees]-19[degrees], which is where the maximum occurs in a diffractogram for fully-amorphous cellulose.
Tensile test was carried out using ASTM D882, and Instron Universal Testing Machine model 5569 was used. The tensile specimens with dimensions of 15 mm x 100 mm were used. The cross-head speed used was 10 mm/min and the test was performed at 25 [+ or -] 3[degrees]C.
RESULTS AND DISCUSSIONS
Typical stress-strain curves for regenerated cellulose is shown in Figure 2. It is noted that these stress-strain curves are all non-linear. The non-linearity is typical for a regenerated cellulose film, as previously reported by [6,7]. The result indicates MCC had significant effects on tensile properties of regenerated cellulose. The tensile properties of the regenerated cellulose increased with increasing cellulose content, and reduced at cellulose content of 4 wt%.
Figure 3 present the effect of MCC content on tensile strength of regenerated cellulose. It can be observed that the addition of MCC increased tensile strength of the films. The highest tensile strength is contributed by 3 wt% of MCC concentration. As the content of MCC is further increased, the MCC/LiCl/DMAc mixture becomes very viscous and the cellulose dissolution is incomplete. Therefore, at MCC content above 3wt% the tensile strength is reduced. The decreament of tensile strength of regenerated cellulose with further MCC content due to aggregation of MCC particles occurred. The similar result had been reported by Mahmoudian et al., 2012; Roder et al., 2002; Ishii et al., 2003. They found that cellulose/LiCl/DMAc systems, when the phase separation is slow, cellulose prefer to form molecular aggregates which caused reduction in tensile strength.
Figure 4 shows the effect of MCC content on elongation at break of regenerated cellulose. The elongation at break of regenerated cellulose decreased with increasing MCC content. This attributed that increases of MCC content increased the rigidity of regenerated cellulose. An increase in the crystalline content leads to an increase in tensile strength and stiffness, but caused the detriment of the ductility. The similar result had been reported by . They found that when MCC content increased, elongation at break is reduced.
Figure 5 illustrates the Young's modulus of regenerated cellulose with different MCC content. Young's modulus of the regenerated cellulose increased directly proportional with increasing MCC content. Addition of cellulose content in regenerated cellulose film caused increased in stiffness which leads to modulus improvement. As reported in previous study, Pullawan et al.,2010 stated that this reinforcement is thought to be due to the presence of the stiff and strong MCC.
X-ray diffraction (XRD):
The XRD diffraction intensity curves of regenerated cellulose with different cellulose content is shown in Fig. 6. Table 1 shows the XRD of regenerated cellulose. The diffractograms of regenerated cellulose exhibit sharp diffraction peaks with increasing cellulose concentration. The diffraction peaks at 2[theta] = 18[degrees]- 19[degrees] and 21[degrees]22[degrees] which were assigned to lattices  and . From the Table 1, the crystallinity index of regenerated cellulose is increased from 41.86% to 52.70% with increasing MCC content. The increased in MCC content caused increased in transformation of cellulose I to cellulose II structure which is the reason of increased in crystallinity. The similar results had been reported by [14,11] that the dissolution and regeneration of cellulose produced different cellulose polymorphs: type I, type II cellulose and amorphous cellulose. Regeneration of cellulose in [H.sub.2]O caused reorganisation and immobilisation of cellulose I into type II and amorphous cellulose. Figure 7 illustrate the schematic structure of cellulose I and cellulose II.
In summary, an ionic liquid of DMAc/LiCL was found to be effective since it act as non-derivatizing single-component solvent for cellulose. Tensile strength and Young's modulus of regenerated cellulose increased with increasing MCC content, while the elongation at break decreased. The crystallinity index is increased with increased MCC concentration in regenerated cellulose. The transformation of cellulose I to cellulose II was observed by X-ray diffraction for the regenerated cellulose.
Received 28 February 2014
Received in revised form 25 May 2014
Accepted 6 June 2014
Available online 20 June 2014
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Vaniespree Govindan, Salmah Hussiensyah, Teh Pei Leng, Faisal Amri
Universiti Malaysia Perlis, Division of Polymer Engineering, School of Materials Engineering, 02600 Jejawi, Perlis, Malaysia.
Corresponding Author: Salmah Hussiensyah. Universiti Malaysia Perlis, Division of Polymer Engineering, School of Materials Engineering, 02600 Jejawi, Perlis, Malaysia.
Fax: 604-9798178. Email: email@example.com
Table 1: XRD data for regenerated cellulose at different MCC content. Crystallinity MCC (wt%) 2[theta](110) 2[theta](200) index, CI (%) 1 18.28 22.20 41.86 2 18.16 22.12 44.70 3 18.28 22.12 52.40 4 18.11 22.06 52.70
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|Author:||Govindan, Vaniespree; Hussiensyah, Salmah; Leng, Teh Pei; Amri, Faisal|
|Publication:||Advances in Environmental Biology|
|Date:||Jun 5, 2014|
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