A Method for Microwave Assisted Synthesis of Microcrystalline Cellulose from Jute Stick Alpha Cellulose

In India, a huge quantity of jute (Corchorus spp.) stick is being produced as a primary by-product of jute fibre (economic part) cultivation every year, and the common practice in vogue is to burn such resides as firewood for domestic energy purposes. Present study aimed to utilize this jute stick alpha cellulose as raw material for synthesis of microcrystalline cellulose (MCC) under microwave radiation. The samples were characterized by FTIR and degree of polymerization. Effect of various mineral acids under microwave radiation were also tested. This study reported a new method for preparing MCC from jute stick alpha cellulose by microwave radiation (650W for 45 min at 80 oC). The order of finer MCC was HCl>HNO3> H2SO4 whereas, the yield order was HCl>H2SO4> HNO3. The developed MCC could be explored for pharmaceutical and other applications.

Microcrystalline cellulose (MCC) is a partially depolymerised cellulose prepared by treating α-cellulose, obtained as a pulp from fibrous plant with mineral acids. Microcrystalline cellulose is used as a texturizer, an anti-caking agent, a fat substitute, an emulsifier, an extender, and a bulking agent in food production. The most common form is used in vitamin supplements or tablets for pharmaceutical application. The global demand of MCC was around 50,000 T in 2003 (http://www.asahi-kasei.com/asahi/ en/news/2002/e030213.html). Out of which 40 and 60% were shared by the food and pharmaceutical industries, respectively. Presently around 50, 25 and 25% of global MCC demand is from North America, Europe, and, Asia-Africa-others, respectively. The global demand for MCC is growing spontaneously. During 11 th August-11 th Sept, 2014, India exported MCC worth USD 3,081,648 and the major importing countries were Brazil, Vietnam, Yemen, UAE etc (http://www.infodriveindia.com/india-importdata/microcrystalline-cellulose-import-data.aspx). Average value per shipment of microcrystalline cellulose exports in India is USD 47,460. Whereas, during 11 th Aug 2014 to 11 th Sept 2014, India imported microcrystalline cellulose worth USD 9,483,007. Average value per shipment of microcrystalline cellulose imports in India is USD 790,251. The huge difference between import and export, clearly indicated the national and international demand of MCC. The conventional source of MCC is derived from both hardwoods and softwood. However, due to national and international rules related to deforestation issue, researches have started looking for new alternative raw source of MCC preparation (Ahmed et al. 2014). In recent times, several other alternative sources had also been studied like rice husk (Rosa et al. 2012), bamboo (Pachuau et al. 2014), water hyacinth (Murigi et al. 2014), corn cobs (Azubuike, C.P. and Okhamafe, 2012), oil palm (Haafiz et al. 2013) etc.
In India, a huge quantity (around 4 Mt per annum) of jute (Corchorus spp.) stick is being produced as a primary by-product of jute fibre (economic part) cultivation (Nayek et al. 2013). However, the common practice in vogue is to burn such resides as firewood for domestic energy purposes. Though, some small-scale applications include utilization in betel vine cultivation, preparation of particle board and handicrafts. Now the question comes that whether jute stick, the waste materials from jute cultivation and industries, could be explored and utilized as a resource material for better application. Low lingo-cellulosic residues are used for fodder and composting purposes, however, the high lingo-cellulosic residues are treated as 'trouble material'. Generation of huge crop residue/biomass is not only problematic for jute cultivation, but for other crops across India also. Residue generated by different crops was grouped in four categories based on the type of crop, namely cereals (rice, wheat, maize, jowar, bajra, ragi and small millets), oilseeds (groundnut and rapeseed mustard), fibers (jute, mesta and cotton) and sugarcane. The residue to grain ratio varied 1.5-1.7 for cereal crops, 2.15-3.0 for fiber crops, 2.0-3.0 for oilseed crops and 0.4 for sugarcane. Total amount dry crop residue generated by nine major crops was 620.4 Mt. Crop residues (C:N< 20:1) are used as animal feed, thatching for rural homes, residential cooking fuel and industrial fuel.
However, a large portion of the crop residues is not utilized and left in the fields. The disposal of such a large amount of crop residues is a major challenge. To clear the field rapidly and inexpensively and allow tillage practices to proceed unimpeded by residual crop material, the crop residues are burned in situ. According to Street et al. (2003) approximately 730 Tg of biomass burned annually, from both anthropogenic and natural sources in Asia with 18% contribution from India. Farmers opt for burning because it is a quick and easy way to manage the large quantities of crop residues and prepare the field for the next crop well in time.
Utilization of jute stick for new utilities can increase the economic return from jute cultivation system. As a result of numerous studies by various researchers across the world, various methods for conversion of alpha cellulose to MCC were reported. It included mostly physical (ultrasonication), chemical (acidolysis) and biological (enzymatic) means of conversion to MCC. The chemical pathway via acidolysis has been reviewed and reported most frequently. The present study aimed to prepare MCC from jute stick derived alpha-cellulose by acidolysis under microwave irradiation. Microwave irradiation is known for various chemical reaction (Kushniret al. 2015). Effect of various acids (H 2 SO 4 , HNO 3 and HCl) on yield and degree of polymerization of synthesized MCC was also investigated.

MATERIALS AND METHODS
Alpha cellulose from jute stick was collected from CBP laboratory, ICAR-NIRJAFT, Kolkata, India. The purity was >99%. Analytical grade chemicals namely mineral acids (H 2 SO 4 , HNO 3 and HCl) were procured from Merck India. De-ionized water was used in experimental studies.
Jute stick alpha cellulose was mixed different mineral acid solutions at solid to solution ratio of 1:20 (w/v). The samples were heated at 80 o C under microwave irradiation of 650W for 45 min. The Microwave treatments were carried out with a microwave digester (Catalyst system, Pune, India). Then samples were washed to neutral pH and analysed for degree of polymerization (DP). The number-average DPn was calculatedas the ratio of glucosyl monomer concentration determined by the phenol-sulfuric acid method divided bythe reducing-end concentration determined by the modified 2,2'-bicinchoninate (BCA) method (Zhang and Lynd, 20015). All chemicals used in modified BCA method were of analytical grade and supplied by Himedia, India.

RESULTS AND DISCUSSION
The conversion of alpha cellulose to MCC varied with varying the mineral acids, while all other condition under microwave radiation remained same. MCC yields were 84.6, 81 and 79.3% for HCL, H 2 SO 4 and HNO 3 , respectively. FTIR analysis was used to study the physico-chemical and conformational properties of developed MCCs. Print ISSN : 1974ISSN : -1712 Online ISSN : 2230-732X FTIR showed the changes in the functional groups present in the structure of cellulose (Fig. 1). Peaks at 3200 -3450 cm -1 are assigned to stretching of -H bond of -OH group. The study showed that theses absorption of these peaks in MCCs were higher as compared to that of the parent alpha cellulose. Further, peaks at 1430, 1158, 1109, 1025, 1000 and 970 cm -1 are typical characteristic peaks of cellulose. Peak around at 2885-2890 cm -1 is attributed to the C-H stretching. Peak due -C-Ostretching of the carboxyl and acetyl groups inhemicelluloses of lignocellulosic biomasses was not absent which indicated the purity of the samples. The peaks around 1420-1428 and 1362-1370 cm -1 were characteristic for the asymmetric -CH2 bending and wagging. Peak around 1150-1158 cm -1 was associated with the -C-O-C-stretch of the β-1,4-glycosidic linkage of cellulose. This band has a lower intensity in R-MCC spectrum which could be due to the presence of trace amounts of noncellulosic constituents in R-MCC. The absorption peak at 892 cm -1 is assigned to -C-O asymmetric stretching. A weak shoulder around 700 cm -1 was associated with the Iα (tricyclic) cellulose. The data clearly indicated that during chemical conversion under the microwave radiation the intensity of all these peaks increased as compared to the initial raw jute stick cellulose. The data indicated the purity of synthesized MCCs as compared to the commercial MCC. These samples were analysed for estimation of DP. The DP also varied with varying mineral acids. The DP were 100, 140, 149and 212 for HCL, HNO 3 , H 2 SO 4 and commercial MCC, respectively. Therefore, the order of finer MCC was HCl>HNO 3 > H 2 SO 4 whereas, the yield order was HCl>H 2 SO 4 > HNO 3. Table 1 showed comparative analysis of MCC prepared from different sources via-vis present products.

CONCLUSION
The present study indicated that microwave radiation can be successfully used for converting alpha cellulose to MCC. The DP of MCC varied with nature of mineral acids. However, under studied condition of microwave irradiation of 650W for 45 min at 80 o C resulted best MCC by HCL acidolysis from JS-alpha cellulose. The FTIR analysis and DP testing indicated purity of the products as compared to commercial one.