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Cellulose (2008) 15:141­147 DOI 10.1007/s10570-007-9147-7

Investigation of the physicochemical properties of microcrystalline cellulose from agricultural wastes I: orange mesocarp

Paul Madus Ejikeme

Received: 2 February 2007 / Accepted: 6 July 2007 / Published online: 9 August 2007 Ó Springer Science+Business Media B.V. 2007

Abstract Orange mesocarp was obtained after removal of the epicarp and the endocarp from oranges. It was dried, pulverized and digested with 2% w/v sodium hydroxide at 80°C for 3 h. Alphaand micro-crystalline celluloses were extracted from the pulp using 17.5% w/v and 2.5 N hydrochloric acid, respectively. The physicochemical and powder properties of the extracted material were evaluated. Results obtained showed that the yield of a-cellulose from the orange mesocarp was 62.5% and that of microcrystalline cellulose 25.3%. The total watersoluble substances were 0.0018 g/g, ash 0.00035 g/g and the true density 1.760 g cmÀ1, while the pH and hydration capacity are 6.61 and 2.916, respectively. Elemental analysis of the cellulose ash shows the absence of Pb and Mn and the preponderance of K, Na and Fe. The water sorption profile of the microcrystalline cellulose was also studied. Keywords Orange mesocarp Á Microcrystalline cellulose Á Lignocellulosic material Á Tabletting Á Elemental analysis

Introduction Microcrystalline cellulose (MCC) is a purified partially depolymerised non-fibrous form of cellulose that occurs as a white, odourless, tasteless, crystalline powder composed of porous particles. It is widely used in pharmaceuticals, primarily as a binder/ diluents in oral tablet and capsule formulations where it is used in both wet or dry formulation and direct compression processes like spheronization/ pelletisation (Kibbe 2000; Enezian 1972; Chilamkurti et al. 1982; Wallace et al. 1983). It also has some lubricant and disintegrant properties (Omray and Omray 1986) and can be used in cosmetics and food products, especially as fat replacers. MCC, produced from a naturally occurring substance (cellulose) has proven to be stable, safe, and physiologically inert and has revolutionized tabletting. Microcrystalline cellulose is one of the few materials used in tabletting that combines two properties of tablet vehicle; it can produce very hard tablets and yet these tablets disintegrate rapidly in water due to swelling of the MCC particles and destruction of the bonding forces holding them together (Lachman et al. 1990). Woody plants and cotton were the major sources of MCC, but cost has made it imperative that other materials be investigated as potential sources. MCC can be made from any material that is high in cellulose ranging from pure cellulose, commercial grade cellulose to lignocellulosic materials. Reports have shown that MCC can be produced from soybean, oath and rice

P. M. Ejikeme (&) Department of Pure and Industrial Chemistry, University of Nigeria, Nsukka, Nigeria e-mail: [email protected]

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hulls as well as sugar beet pulp (Hanna et al. 2000), bagasse and corn cob (Okhamafe and Azubike 1994; Okhamafe et al. 1995), wheat, barley and oath straw (Proencal 1999), groundnut shell and rice husks (Okhamafe et al. 1991), reed stalks (Saleh and El-Ashmay 1978), and cereal straw (Jain et al. 1993). Indian bamboo (Ofoefule and Chukwu 1999) and luffa cylindrica (Ohwoavworhua et al. 2004) have also been studied as potential sources of MCC. Except for the work in which cellulose derivatives were made from orange mesocarp (Akaranta and Osuji 1997; Akaranta and Amadi 2000), no record is available yet to the knowledge of the author on production and characterization of microcrystalline cellulose from the domestic waste, orange mesocarp. This work therefore is aimed at exploring the potentials of making microcrystalline cellulose from orange mesocarp and characterizing for its tabletting and other properties.

stainless steel vessel was raised and held at 80°C for l h. with constant stirring to obtain the a-cellulose of the orange mesocarp. It was again consecutively bleached with hypochlorite and hydrogen peroxide, washed and dried. The cellulose obtained was subjected to the hydrolytic action of 2.5 M HCl (which is able to specifically cleave 1­4 glucosidic linkages) at the boiling temperature of about 105°C for 15 min. During treatment with dilute mineral acids, the acid penetrates the amorphous regions relatively fast and hydrolyses these regions, yielding water-soluble fragments or oligomers (Osol 1980). The time allowed for the hydrolysis to take place is just enough such that it will not penetrate the crystalline regions appreciably to destroy the crystallites. The MCC was collected by filtration, washed with distilled water to neutral pH, dried at 69°C for 1 h. and stored in an airtight container in a desicator. Determination of phsicochemical properties of the MCC

Materials and methods Sodium hydroxide (NaOH) is a product of Loba Chemie Pvt. Ltd, Mumbai India and HCl a product of Fluka Chemie GmbH, Switzerland. All other reagents are of analytical grade unless otherwise stated. Sweet oranges were bought from Afor-Ojoto market in Anambra State of Nigeria and the epicarp removed by peeling. The juice was squeezed out and the tissues containing the juice removed according to the methods of Akaranta et al (Akaranta and Osuji 1997; Akaranta and Amadi 2000). Pulping of the orange mesocarp The mesocarp obtained was cut into pieces, ovendried at 105°C until brittle to touch, ground with a milling machine and delignified with a 2.67 l 4% (w/w) sodium hydroxide for about 180 min at 80°C. The pulp obtained was washed with distilled water, bleached consecutively with 5.3% (w/w) sodium hypochlorite and 9.3% (w/w) hydrogen peroxide, to obtain an off-white fibrous product. Preparation of microcrystalline cellulose The temperature of a mixture of the fibrous product and 1.6 l of 17.5% (w/w) sodium hydroxide in a Some of the properties determined were total ash, elemental analysis of the ash, pH, water-soluble substances, solubility, starch and dextrin and identification. Total ash The residue on ignition of 1 g of the sample placed in a tarred dish at a temperature of 450°C in a furnace (The International Pharmacopoeia 1979) for 3 h is taken as the total ash. Ashing is normally completed in a muffle furnace with a controlled temperature that starts at 250°C and is raised within about 1 h. gradually to 450°C where it is held until the decomposition of the organic matter is complete (Pomeranz and Meloan 1994). pH The pH of the sample was determined as that of the supernatant after shaking 1 g in 30 ml of distilled water for 10 min with a pH meter. Water-soluble substances About 5 g of the sample in 80 ml of water was shook for 10 min. and vacuum filtered using Whatman No1

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filter paper. The filtrate in a tarred flask was evaporated to dryness, dried at 100­105°C for 1 h and weighed. A blank determination was carried out under the same conditions and the difference noted. The experiment was performed in triplicates and the average of three determinations taken. Solubility The solubility test was carried out with 0.4 g of the sample in 10 ml of the following solvents; water, 2.5 M HCl, 2.5 M H2SO4, acetone, ethanol, toluene and ammoniacal tetramine solution. Starch and dextrin The exhibition or otherwise of dark-blue coloration characteristic of starch and simpler dextrin as well as red coloration of the more complex dextrin with iodine solution was tested for, following the methods in British Pharmacopoeia (British Pharmacopoeia 1993b). Identification Into a solution made by dissolving 20 g of zinc chloride (ZnCl2) and 6.5 g of potassium iodide (KI) in 10.5 ml of water was added 0.5 g of iodine and shaken for 15 min. 0.1 g of the sample was placed on a watch glass and dispersed with the solution prepared above and the colour change recorded (British Pharmacopoeia 1993a). Elemental analysis of the MCC ash This was carried out as outlined by Ohwoavworhua et al. (2004). 1 g of the MCC was ashed at 450°C in a muffle furnace and the residue mixed with concentrated trioxonitrate IV acid and ashed again. The final residue was dissolved in water and made up to 100 ml. The concentration of the elements present were determined using Atomic absorption/Flame emission spectrophotometers. Scanning Electron Microscopy The microstructure of the orange mesocarp microcrystalline cellulose was determined using a wild Heerbrugg 9435 electron microscope at different magnifications.

Powder properties Density The true density was determined by the liquid displacement method using xylene (a non-polar liquid) as the immersion fluid. For the bulk and tapped densities, 20 g of the sample was carefully put in a dry 100 ml measuring cylinder and the volume occupied by the sample noted. After 500 taps at the bottom of the cylinder, the new volume, V500 was also noted and the densities determined as the ratio of the weight and volume of sample in each case. The densities were determined in triplicates. The powder porosity, PB (%), that is the ratio of inter-particle void space to the total volume of the packing was estiminated for the orange mesocarp MCC using the expression: PB = 1À.B/.T where .B and .T are bulk and true particle densities, respectively (Bean et al. 1967). Moisture content This was done by successive drying of the sample at 105°C in a dryer, cooling in a desicator and weighing until the difference became negligible after 6 h of total heating. Results are expressed as the mean of three paralled determinations Moisture sorption profile Exactly 1 g of sample was evenly distributed in a 5 cm petri dish and placed in a large desiccator containing distilled water at the base. The weight of the exposed sample was monitored at 12-hourly intervals and the weight gain noted. Hydration capacity This was determined by the method of Kornblum and Stoopak (1973) 0.5 g of the sample was placed in a weighed 12 ml centrifuge tube and 8 ml of distilled water added. The system was agitated for about 2 min, left to stand for 10 min and centrifuged at 1,000 rpm, equivalent to NRe = 20,667 using a Gallenkamp bench centrifuge. The weight of the sediment was obtained after decanting the supernatant and the average of its ratio to the weight of original material for three determinations taken as the hydration capacity.

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Particle size analysis A representative sample (40 g) of the MCC produced was obtained and put in a BS No 410 wire mesh type sieve in which the coarsest sieve is placed on top and was shaken for 3 min. The weight of the sample retained in each sieve mesh was measured. The particle sizes of each quantity retained was estimated using a semi-log graph having the particle size and the equivalent sieve mesh numbers on the logarithmic scale and the material passing through plotted on the arithmetic scale (Carter 2000). Angle of repose The MCC sample was filled into an open-ended cylinder with the bottom resting on a horizontal surface. On withdrawing the cylinder vertically, the powder formed a heap on the horizontal with the mean diameters of the base of the powder heaps and the tangent of the angle of repose (x) obtained using the expression. tan x ¼ 2h=D; where, h is the height of heap and D is the diameter of base of sample heap. Results of angle of repose are expressed as the mean of 4 determinations.

Results and discussion The dried mesocarp had moisture content of 8.3%. The yield of cellulose or a-cellulose from the orange mesocarp was 62.5% and that of MCC 25.3%. The 25.3% reported in this work is lower than the 27 and 29%, respectively reported for corncob (Hanna et al. 2000) and luffa cylindrica (Ohwoavworhua et al. 2004). The microcrystalline cellulose obtained from orange mesocarp was almost white in colour, tasteless, crystalline and odorless. The identification test gave a violet-blue colour, indicating an MCC. The test for starch and dextrin did not give any colour change and the two were thus adjudged absent in the sample. The MCC produced was insoluble in most solvents tested except ammoniacal solution of copper tetramine in which it dissolved completely. The pH, total ash and water-soluble substances obtained are 6.61, 0.00035 g/g (0.035%) and 0.0018 g/g (1.8 mg/g), respectively.

The values respectively fall within the acceptable limits of between 5 and 7, <0.05% and <12.0 mg/g (United States Pharmacopaea 2004; British Pharmacopoeia 2004). The low percentage of ash in the product may be as a result of very low inorganic materials usually present in cellulosic materials and care in the MCC preparation. Results of other properties are shown in Table 1. The 4.9% moisture obtained in the work though by far higher than 1.5 reported for Avicel PH-112 and 113 (Hanna et al. 2000) and 4.3 for luffa cylindrica (Ohwoavworhua et al. 2004), is less than 5.2 reported for Avicel PH101 and ultimately less than the maximum allowable limit of 8% (British Pharmacopoeia 1993a). Bhimte and Tayade (2007) reported values of 3.96 to 5.06 after heating at 105°C for 8 h. The weight of water absorbable by the orange mesocarp MCC is about 300%, indicating that it can absorb about three times its weight of water. The swelling of the cellulose particle, in water speeds up the disintegration of the ingested tablets made with them (Osol 1980), by two mechanisms of capillary or wicking due to interparticulate water and swelling (Ohwoavworhua 2004). The bulk density of 0.424 is higher than 0.25 and 0.31 reported for luffa and Avicel PH101, respectively (Ohwoavworhua 2004), as well as 0.325, 0.321 and 0.238 reported for Avicel PH102, Flocel-102 and sisal fibre MCC (Bhimte and Tayade 2007) respectively. Small particle size and low moisture content has been suggested to lead to increased bulk density (Korhonen 2002). The compressibility and Hausner indices were estimated as the ratios of the difference between tapped and bulk densities. The Carr's compressibility index gives an idea of how much a powder can be

Table 1 Physicochemical/powder properties of the orange mesocarp MCC Moisture Content (%) Hydration Capacity Compressibility Index (%) Hausner Index Porosity (%) Angle of repose (degrees) True density (g/cm ) Bulk density (g/cm3) Tapped density (g/cm3)

3

4.9 2.916 28.86 1.41 76 38.66 1.76 0.424 0.596

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145 Table 2 Particle sizes of the cellulose Retained in sieve no 10 16 25 300 Particle size (lm) 1200 1000 600 53 Weight (g) Weight (%)

compressed while Hausner index measures/estimates cohesion between particles, and the values for both varies inversely with particle flow. Thus, the lower ` values obtained in this work vis-a-vis that of another author (Ohwoavworhua 2004), 39 and 1.64, respectively, shows that orange mesocarp MCC flows better. Compressibility indices and angles of repose less than 15% and 35o, respectively, are indicative of very free flowing powders; indices and angles of repose greater than 38% and 45o, respectively usually correspond to very poor flow (Carr 1970; Carr 1965). The angle of repose of 38.66o reported in this work lays between the theoretical minimums of 20o for uniform spheres that flow very well and the maximum of 45o for powders that flow poorly (Bean et al. 1967). The value is higher than 34.4o reported for Emcol 90 M (Celic and Okutgen 1993). The observed angle of repose, which is on the average, correlates the average values too of Hausner and compressibility indices and the consequent average or moderate flow behaviour for the orange mesocarp MCC. Poor flow properties in any powder may be due to one or more of the following reasons; surface forces existing between the particles, interparticulate friction and interlocking of particles (Carter 2000). From the result obtained for true density, Table 1, it could be inferred that the material is highly crystalline in nature, as the degree of crystallinity of cellulose has been reported (Stamm 1964) to increase directly with true density determined in a non-polar solvent. The total porosity of a porous powder is made up of voids between the particles as well as pores within the particles. This as estimated for the orange mesocarp MCC is high suggesting poly-sized particles and easily compressible powder during tabletting. This also correlates the high tapped density obtained in this work. Particle size analysis The result of one of the two fundamental properties of a collection of particles, the particles size analysis, is shown in Table 2. It is observed that 24.49 g or 62.4% of the 40 g sample passed through sieve no 25. This shows that more of the particles have sizes less than 600 lm while the coarsest portion has the least quantity.

2.240 5.636 7.177 24.49

5.6 14.1 17.9 62.4

Moisture sorption profile The moisture sorption profile of the MCC is shown in Fig. 1. It is evident from the graph that after the first 12 h that the material adsorbed minimal quantity of water. The 31.65% moisture adsorbed in the first 12 h appears high. This apparently is at variance with the results obtained for compressibility and Hausner indices as well as that of true density that suggested high degree of crystallinity for the sample. It has been

60

Weight Gain(%)

50 40 30 20 10 0 0 50 100 150

Time(h.)

Fig. 1 Moisture sorption profile of orange mesocarp MCC Table 3 Elemental Composition of the MCC Ash Element K Na Fe Zn Cu Ca Al Mn Pb Weight Composition (mg/g) 2.0 · 10À2 6.3 · 10À3 4.15 · 10À4 9.0 · 10À5 7.0 · 10À5 7.0 · 10À5 2.0 · 10À5 Not detected Not detected.

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146 Fig. 2 Scanning electron micrograph of orange mesocarp microcrystalline cellulose; (a) 500· (b) 100·

Cellulose (2008) 15:141­147

reported (Stamm 1964) that the extent of water adsorbed by cellulose should be proportional to the amount of amorphous cellulose present. This seeming contradtion may be explained by the preponderance (62.4%) of the smallest particle size 53 lm, Table 2, in the MCC sample as particle size reduction or small particle size (increased surface area) has been reported (Ono et al. 1998) to lead to water immobilization. Element analysis of the orange mesocarp MCC ash Result of the elemental analysis of the ash is shown in Table 3. The absence of lead (Pb) from the MCC extracted from orange mesocarp is a welcome development as it has been reported to accumulate throughout life in the bones (Barry 1975) leading to lead encephalopathy, which manifests in the long run, in loss of memory. Microcrystalline cellulose generally is not absorbed systemically following oral administration, and thus has little toxic potential. Again since cellulose is not exclusively used in drug formulation as excipient due to the prohibitive cost, the levels for the other metals reported in this work may not likely pose major health problems. The electron micrographs at 500 and 100 magnifications, Fig. 2a and b, show the MCC produced to be spherical in shape and to exist mainly as discrete particles.

The absence of lead in the sample rules out possibility of lead poisoning. Despite the slightly lower percent ` content of MCC in orange mesocarp vis-a-vis that of luffa cylindrica, its flow properties that is better than that of luffa makes it a better alternative to luffa as an MCC source. Furthermore, with many fruit drink companies that use orange and treat the mesocarp as a waste material, it would ultimately be cheap to collect that `waste material' and turn it into the costly MCC. This may help to reduce the cost of MCC, especially in areas where orange is readily available.

Acknowledgements The author greatly acknowledges the assistance of Chime Chizoba who helped in doing some of the practical work.

References

Akaranta O, Amadi EA (2000) The plasticisation of a Jatropha oil Alkyd of a nitrocellulose coating material based on Musanga Ceropiodes wood and orange mesocarp. Surf Coatings Int 5:243­245 Akaranta O, Osuji IC (1997) Carboxymethylation of orange mesocarp and the utilisation in drilling mud formulations. Cellulose Chem Technol 31:193­197 Barry PSI (1975) A comparison of concentration of lead in human tissues. Br J Ind Med 32:119­139 Bean HS, Becket AE, Carless JE (eds) (1967) Advances in Pharm Sci. vol 2. Academic Press, London, p 198 Bhimte NA, Tayade PT (2007) Evaluation of microcrystalline cellulose prepared from sisal fibres as a tablet excipient. AAPS Pharm Sci Tech 8(1). DOI 10.1208/pt0801008 British Pharmacopoeia (1993a) HMSO Press, London, vol 1, p 53 British Pharmacopoeia (1993b) HMSO Press, London, vol 1, pp 119­120 British Pharmacopoeia (2004) Stationary office. The Department of Health, pp 405­407 Carr RL (1965) Evaluating flow properties of solids. Chem Eng 18:163­166 Carr RL (1970) Particle behaviour, storage, and flow. Bri Chem Eng 15:1541­1549

Conclusion The microcrystalline cellulose prepared in this work has been shown to possess properties that could make its source, orange mesocarp, another addition to the ever-growing new sources of the costly material.

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