Preparation and Characterization of Cellulose Microcrystalline (MCC) from Fiber of Empty Fruit Bunch Palm Oil

Alpha cellulose which was isolated from cellulose of fiber empty fruit bunch palm oil was hidrolized with hydrochloric acid (2,5N) at 80°C to produce microcrystalline cellulose (MCC). Microcrystalline cellulose is an important additional ingredient in the pharmaceutical, food, cosmetics, and structural composites. In this study, MCC, alpha cellulose, and cellulose were characterized and thereafter were compared. Characterizations were made using some equipment such as x-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM) and thermogravimetry analyzer (TGA). X-ray diffraction and infrared spectroscopy were studied to determine crystallinity and molecular structure of MCC, where scanning electron microscopy images were conducted for information about morfology of MCC. Meanwhile, thermal resistance of MCC was determined using thermogravimetry analyzer (TGA). From XRD and FTIR, the obtained results showed that the crystalline part was traced on MCC, where the –OH and C-O groups tended to reduced as alpha cellulose has changed to MCC. From SEM the image showed the reduction of particle size of MCC, while the thermal resistance of MCC was found lower as compared with cellulose and alpha cellulose as well, which was attributed to the lower molecular weight of MCC.


Introduction
The Empty fruit bunch palm oil (EFBPO) is a renewable agricultural residue represent abundantly, generated from palm oil mills. Each year, the processing produce millions tonnes of residues. This material can be modified for the production of novel materials for environmentally friendly aplications after some chemical modifications. Three major structural polymeric component of EFBPO are lignin, cellulose and hemicellulose. Hemicellulose and lignin are both amorphous subtances, while cellulose forms a microcrystalline structure with high order region (crystalline region) and low order region (amorphous region) [1]. Cellulose, one of the major component in EFBPO is a polydisperse polymer of high molecular weight and comprised long chains of D-glucose units joined together by -1,4 glucosidic bonds [2]. Among other uses such as pulp and paper product, cellulose is also widely employed as a starting material for the production of microcrystalline cellulose. Microcrystalline cellulose (MCC) is a polymer has been widely used in a variety of commercial applications in the food, structural composite, and pharmaceutical industries. This polymer has a high amount of amorphous regions that occurs as a white, odourless, tasteless, crystalline powder composed of porous particles [3]. The MCC was obtained by partially hydrolyzing cellulose with mineral acid to remove amorphouse regions in forming microcrystal. A conventional method for producing MCC from cellulose is acid hydrolysis process. The hydrolysis of cellulose can be accomplished using mineral acid [4][5][6][7][8][9][10], enzymes [11], and microorganism [12]. However, different properties of MCC such as crystallinity, moisture content, molecular weight, surface area and porous structure, thermal resistance were also obtained from different sources of raw material. Reports have shown that MCC can be produced from kenaf fibers [12], rice hull and bin hull [3], cotton linters [13], sawdust [4], rice straw [14], Oil Palm Empty Fruit Bunches [15], groundnut shells [16], corn cobs [17], sisal fibers [5], cotton rags [6].
This article reports the preparation and characterization of MCC by acid hydrolysis method using hydrochloric acid. Characterization was studied by FTIR, XRD, SEM and TGA.

Raw material
Cellulose derived from the EFBPO which was isolated earlier was kindly supplied by Oil Palm Research Centre in Medan, Indonesia. Sodium hydroxide (NaOH), sodium hypochloride (NaOCl), and hydrochloric acid (HCl) (37%) were supplied by Sigma-Aldrich and used as received.

Production of alpha cellulose
Alpha cellulose was obtained from the cellulose using 17,5% sodium hydroxide (NaOH) at 80 o C for 0,5 h. Bleaching was then carried out with 3,2% sodium hypochloride (NaOCl) at 100 o C for 1,5 h.

Production of MCC
The alpha cellulose powder derived from cellulose was hydrolized using 2,5N hydrochloric acid (HCl) at 80 o C for 15 min. The hydrolized cellulose was thoroughly washed with cold distilled water until neutral to litmus paper and then dried. (FTIR). Infrared spectroscopy of cellulose, alpha cellulose and MCC were carried out using Shimadzu IR-Prestige 21. Bands were recorded in the region from 4000 to 500 cm -1 .

X-ray diffraction (XRD)
. X-ray diffractometry patterns of cellulose, alpha cellulose and MCC were pressed to form pellets and recorded in 6100 Shimadzu.
The crystalline index (Ic) was determined by Eq (1) using the intensity of I002 peak at about 2 = 21,9 o and Iam is the intensity corresponding to the peak at about 2 = 12 o -18 o = 100 (1)

Morphologycal characteristic.
Scanning electron microscopy (SEM) was used to examine the microscopic structure and the surface morphology of the prepared cellulose, alpha cellulose and MCC. For SEM measurement the instrument used for morphological observation was SEM EVO MA 10 ZEISS.

Thermal analysis.
Thermogravimetry analysis was utilized using Shimadzu Simultanous TGA/DTA Analyzer DTG-60 to investigate the thermal properties of cellulose, alpha cellulose and MCC.

Infrared spectroscopy
The molecular structure of the cellulose isoated directly from EFBPO, alpha cellulose and MCC. Are shown in Figure 1. FT-IR spectra of the different samples of cellulose were recorded in the range of 4000-500 cm -1 . A slight difference is observed in the region of the intermolecular hydrogen bonding (3200-3400 cm -1 ). The shift of the maximum absorbance band of stretching vibration of OH group of MCC to lower wave number (3340 cm -1 ) as compared with other two samples of cellulose (3363 cm -1 and 3400 cm -1 for alpha cellulose and cellulose, respectively). This shift proves that MCC is more crystalline than both samples. Moreover, the characteristic intermolecular and intramolecular OH stretching vibration band in the spectrum of MCC appeared broader than those of alpha cellulose and cellulose. This is due to the degradation of the hydrogen bond between the cellulosic chains during the hydrolysis process. Here, the first part hydrolyzed and degraded by acid were an amorphous region.
The C-H stretching vibration absorbance intensity in MCC (2892 cm −1 ) is slightly decreased upon acid hydrolysis of alpha cellulose; this is due to the presence of -CH2 moieties in the samples [18]. The absorption bands at 1635 cm −1 corresponds with 1639 cm −1 and 1631 cm −1 were attributed to O-H bending, the vibration of adsorbed water molecules [19]. This peak could be due to the presence of small amounts from hemicellulose. The presence of this peak may be arising from the oxidation of the C-OH groups.
The peaks related to -CH or C-O bending vibrations (1369, 1374 cm −1 ) in the polysacharide aromatic rings (20) are less intense in the spectrum of MCC than those of alpha cellulose and cellulose. The band at 1064 cm -1 corresponds with 1061 and 1053 cm -1 appears is due to -CH2-O-CH2 pyranos ring stretching vibration.In addition, the band at about 898 cm −1 in the spectrum of MCC is attributed to the asymmetric out of plane ring stretching in cellulose due to the  glicosidic linkage between glucose unit in cellulose. It is noted the linkage stands for the increase in crystallinity of the material [21]. Figure 2 shows the x-ray diffraction spectra of cellulose, alpha cellulose and MCC. . The powder x-ray diffraction spectra of the three cellulose samples exhibit different diffraction patterns. Cellulose derived from oil palm empty fruit bunch fibre was highly amorphous, as indicated by the less peaks in the diffractogram (Fig 1a). An amorphous region implies a more disordered structure, resulting in a low crystal region.

X-ray diffraction
The crystallinity is traced on the alpha cellulose diffractogram (Fig. 1b). This is due to removal of hemicellulose and lignin, which existed in amorphous region leading to realignment of cellulose molecules. However, These two peaks are smeared and appear as one broad peak. A smeared out diffractogram was observed for samples, especially the peaks that appeared at diffraction angles ranging from 20 o -24 o for cellulose and from 18 o -24 o for alpha cellulose indicating a low degree of order. This results are similar with the study have reported by Mat Soom et.al [15]. However, the higher peak of alpha cellulose in comparison to cellulose, indicating that the crystalline behaviour of alpha cellulose was higher than for cellulose. The presence of amorphous aromatic compounds such as lignin, polysacharide polymers and many others was attributed to this behaviour. Figure 1c shows the x-ray diffraction spectra of MCC. The highest crystal structure was obtained for MCC due to the removal of the amorphous regions of alpha cellulose by acid hydrolysis, realeasing individual crystallites. It is interesting to note that the MCC in the present case shows doublet in the intensity of the main peaks corroborating the coexistence of cellulose I and cellulose II allomorphs. The large different spectra between MCC with cellulose and alpha cellulose results in the appearance of two significant peaks indicating the highly crystalline structure of MCC. High crystallinity indicates an ordered compact molecuar structure, when the crystalline cellulose content is high, these two peaks are more pronounced. The peak intensity of MCC appeared to be higher than that of alpha cellulose indicating that the MCC is more crystalline than alpha cellulose.The peaks at MCC spectra are more defined suggesting that the hydrolysis acid process removed some of the amorphous material from the alpa cellulose. The process was initiated in the fast removal of amorphous cellulose near the surface of macrofibrils, which leads to the exposure of microfibril bundles. An amorphous cellulose near surface is hydrolyzed first and followed by crystalline cellulose near surface. The amorphous cellulose deeply buried in the bulk leach out from macrofibrils during hydrolysis at slower rates due to barriers caused by the microfibril bundles. This process repeats during the hydrolysis process until cellulose degradation occurs [22]. During processing to MCC, the alpha cellulose was hydrolized and depolymerized to remove a large portion of the amorphous region, leaving the crystalline cellulose.The diffractograms for MCC exhibits diffraction patterns typical of cellulose, with diffraction peaks of the 2 angles at 12,2; 20,2 and 21,9 o . The index crystallinity (CI) which is calculated according to the equation (1) gives a quantitative measure of the crystallinity in powders. Here the crystallinity index of MCC from hydrolization process is 73%. Since cellulose from different source differs in propeties, different properties of MCC obtained from source are expected and the condition of hydrolysis process also affect the properties. Some studies about the effect of sources on the percent crystallinity of MCC have been reported such as Kenaf is 70% [12] cotton linter is 76% [14], groundnut shells is74% [16], baggas is 76% [10], rice straw is 78% [10], cotton stalks is 77% [10] and sisal is 60% [5]. Figure 3 shows the surface morphology of cellulose, alpha cellulose and MCC using SEM. the macrofibril interconnections were occured as the hemicellulose could not well dissolved during treatment.

Scanning Electron Microscopy (SEM)
The SEM micrographs for the alpha cellulose (Figure 3b), showed a smaller diameter as compared to the cellulose (Figure 34a). On subsequent treatment with alkali, the hemicelluloses, which was still remain in cellulose, was hydrolyzed and becomes water soluble. These help in defibrillation of the fibrils and result in micrograph, whereby the diameter of the fibrils is reduced to a great extent. However, the interconnections amongst fibrils were still occured.
On the other hand, the MCC image shows a fibrous structure and individualized (Figure 3c). The MCC obtained showing fibers strands which appear like rod-shaped. The MCC appeared to be irregular fiber fragments and also show a network-structure (13). In this case, after macrofibrils were hydrolyzed and rinsed, the volume of amorphous cellulose was occupied by water molecules that were then removed; the remaining macrofibrils contain large amounts of naked microfibril bundles. Figure 4 below shows the thermal resistance of cellulose, alpha cellulose and MCC. The thermogravimetry curve for cellulose and alpha cellulose follow similar degradation pattern. The first stage degradation for cellulose and alpha cellulose occurs at a temperature range of 225-350 o C and 220-355 0 C, respectively with a total weight loss of 80% for cellulose and 75% for alpha cellulose. The second stage started at about 350 o C for cellulose and 355 o C for alpha cellulose and reached a maximum at 480 o C for both samples with a total weight loss of 85%. In the alpha cellulose the removal of all non cellulosic materials helps to make the cellulose structure more dense and compact and hence a slightly rise in the temperature of degradation have occured. The degradation of MCC appears to follow different mechanism where the temperature at a range of 285-340 o C with a total weight loss of 85%, which is due to the degradation of cellulose. The rest of degradation occured during heating at 340-480 o C with a total weight loss of 90%.

Thermal Resistance
A notable difference, in particular between MCC sample and two other samples (cellulose and alpha cellulose), is observed at the temperature at which 20% weight loss of the samples is degraded. This temperature is lower for cellulose and alpha cellulose (275 o C) as compared to the MCC (285 o C). This result might be attributed to the higher crystallinity and lower moisture contents of the MCC. The rearangement and reorientation of the crystals in MCC offers to raise the onset temperature of degradation. Additionally higher onset temperature are associated with high thermal stability. However, start at a temperature of 325 o C the degradation of MCC shows more drastic as compared with two other samples. This temperature correspons with 40% weight loss of MCC, while the other two samples (cellulose and alpha cellulose) show 35% of weight losses. It may attributed to the reduction in molecular weight of MCC during hydrolysis process.. Hydrolysis process have made the MCC is more susceptible to degrade when temperature increases. It is also believed that hydrolysis of cellulose not only dissolves the amorphous regions, but also some crystalline regions (21). Similar results have been reported by El-Sakhawy and Hassan (10) when producing MCC from baggase fibers.

Conclusion
The microcrystalline cellulose (MCC) was obtained from alpha cellulose which was isolated from cellulose derived from EFBPO. The three samples were then compared in terms of molecule structure, crystallinity, morphology and thermal stability. MCC was prepared by hydrolysis acid using hydrochloric acid (2,5N). Some structures of the molecules have been changed due to the hydrolysis process. In addition, the x-ray diffractograms proved that the MCC samples are more crystalline compared to two other samples (cellulose and alpha cellulose). On the other hand, it was noticed by the SEM that hydrolysis treatment affected the morphological structure of the resulting microfibrillated cellulose. However, the thermal stability of the MCC samples starting at temperature at 325 o C were lower as compared to the corresponding other two samples which was attributed to the reduction of molecular weight of MCC.