Some Physical Characteristics of Microcrystalline Cellulose Obtained from Raw Cotton of Cochlospermum planchonii

Purpose: The microcrystalline cellulose is an important ingredient in pharmaceutical, food, cosmetic and other industries. This study aimed at evaluating the physical characteristics of microcrystalline cellulose (CP-MCC), obtained from the raw cotton of Cochlospermum planchonii. Methods: CP-MCC was obtained from the raw cotton by a two-stage sodium hydroxide treatment process followed by sodium hypochlorite bleaching and acid hydrolysis. It was examined for its physicochemical and powder properties. The powder properties of CP-MCC were compared to those of the well-known commercial microcrystalline cellulose grade, Avicel PH 101. Results: The extraction yield of CP-MCC was approximately 21%. The cellulose material was composed of irregularly shaped fibrous cellulose particles with a moisture content of 7.2% and total ash of 0.12%. The true density was 1.38. The flow indices showed that CP-MCC has poor flow. The hydration, swelling and moisture sorption capacities were 4.7, 83.3 and 22%, respectively. Conclusion: The cellulose product, CP-MCC, obtained from the raw cotton of Cochlospermum planchonii conformed to the official specifications in the British Pharmacopoeia (2004). The flow properties of a powder are critical in direct compression tableting; consequently, for the materials to be used for this purpose, it would require the addition of a glidant. Furthermore, the swelling parameters indicate that CP-MCC would be a better disintegrant than Avicel PH 101.


INTRODUCTION
Microcrystalline cellulose, (MCC), is described as purified, partially depolymerised cellulose prepared by treating α-cellulose, obtained as a pulp from fibrous plant with mineral acids.It is one of the most used filler-binders in direct tablet compression.
Its popularity in direct compression is due to its excellent binding properties when use as a dry binder.It also works as a disintegrant and lubricant and has a high dilution potential in direct compression formulations.In addition to its use in direct compression formulations, MCC is used as a diluent in tablets prepared by wet granulation as well as a filler for capsules and spheres 1 .
Commercially available MCC is derived from both gymnosperms (generally conifers) and other softwoods, and from hardwood dicotyledons.These woods differ considerably in chemical composition (proportions of cellulose, hemicelluloses and lignin) and structural organization which affect the composition of the α-cellulose extracted and the composition and crystallinity of MCC finally produced 2 .Besides the wood pulp as a source of cellulose and its derivatives, the purified cotton linters obtained from Gossypium species are also a common source 3 .
Cochlospermum planchonii is a low shrubby savanna plant which grows up to 2.5m high and reproduces from seeds and rhizomes.It is a common weed of cultivated fields in both Guinea and Sudan savanna zones 4 .It produces 3-to 5 celled capsules containing numerous seeds whose epidermal trichomes are cotton.Although it has long been known that cotton linters from different plants are sources of cellulose and cellulose derivatives, there is paucity of information on the physical and tableting properties of microcrystalline cellulose obtained from these sources.Hence this study aims to evaluate the physical and tableting properties of microcrystalline cellulose obtained from raw cotton of C. planchonii.This paper reports on some of the physical characteristics of the obtained microcrystalline cellulose, here code named CP-MCC, in comparison with the wellknown microcrystalline cellulose, Avicel PH 101.
Matured bolls of C. planchonii were identified and collected in the herbarium unit of National Institute for Pharmaceutical Research and Development, Abuja, Nigeria.Microcrystalline cellulose, CP-MCC, was prepared in our laboratory as described below under 'Methods'.

Isolation of α-cellulose
The bolls were properly air dried, the hairs manually separated from the seeds and impurities such as immature and broken seeds and fragments of leaves removed.Isolation of αcellulose was as described earlier 5 , with a slight modification.An 80 g quantity of this material was placed in a stainless steel container to which was added 4.0 L of 2% w/v sodium hydroxide and digestion effected for 4 h at 80 0 C in a water bath (FGL 1083.Karl Kolb Scientific, West Germany).Following thorough washing and filtration, it was bleached with 2.0 L of a 1:1 aqueous dilution of sodium hypochlorite for 15 min at 80 0 C. The material was then washed sufficiently with water and treated with 2.0 L of 17.5% w/v sodium hydroxide at 80 0 C for 1 h.The resulting α-cellulose was washed thoroughly with water.The extraction process was then completed by whitening with a 1:2 aqueous dilution of sodium hypochlorite for 15 min at 80 0 C and subsequent washing with water until neutral.The cellulose material was filtered, and the water manually squeezed out using calico cloth to obtain small lumps, which were dried in a fluidized-bed dryer at an inlet air temperature of 57-60 o C for 1 h.

Production of microcrystalline cellulose (CP-MCC)
The procedure reported earlier 5 , with a slight modification, was used.A 50 g quantity of the αcellulose obtained was placed in a glass container and hydrolyzed with 0.8 L of 2.5 N hydrochloric acid at a boiling temperature of 105 o C for 15 min.The hot acid mixture was poured into 2.5 L of cold tap water which was followed by vigorous stirring with a spatula and allowed to stand overnight.The microcrystalline cellulose obtained by this process was filtered, washed with water until neutral, filtered, pressed and dried in a fluidised bed dryer at an inlet air temperature of 57 -60 o C for 60 min.Following further milling and sieving, the fraction passing through 650µm sieve aperture was used for the characterization.

Physicochemical properties of CP-MCC
The organoleptic characteristic, identification, organic impurities, starch and dextrin, solubility, total ash and water-soluble substances were carried out in accordance with British Pharmacopoeia 6 specifications.An optical microscope, model Larphot 2 (Nikon Inc., Japan) was used for preliminary assessment of the nature of particles in CP-MCC powder particles.The combination of low and high power objective lenses of x100 and x400 magnification, respectively, were used.
pH determination: This was done by shaking 2 g of the powder material with 100 ml of distilled water for 5 min and the pH of the supernatant liquid was determined using a pH meter (Corning, model 10 England) 5 .
Total ash determination: The method 5 described in an earlier study was adopted.Ash content was estimated by the measurement of the residue left after combustion in a furnace at 550 o C.

Powder Properties Particle size analysis
A sieve-shaker, (Retak 3D, Retsch GmbH and Co KG, Haan, Germany) was used for this assessment.Test sieves ranging from 850 to 150 µm were arranged in a descending order.A 20 g quantity of CP-MCC powder was placed on the top sieve and the set-up was shaken at an amplitude of 1.50 mm/'g' for 5 min.The weight of material retained on each sieve was determined.The average diameter was computed as reported by Ansel et al 7 using the following equation:

True Density
The true densities (D t ), of cellulose powders were determined by the liquid displacement method using xylene as the immersion fluid 8 and computed according to the following equation: Where w is the weight of powder, SG is specific gravity of solvent, a is weight of bottle + solvent and b is weight of bottle + solvent + powder.

Angle of Repose
The static angle of repose, a, was measured according to the fixed funnel and free standing cone method 9 .A funnel was clamped with its tip 2 cm above a graph paper placed on a flat horizontal surface.The powders were carefully poured through the funnel until the apex of the cone thus formed just reached the tip of the funnel.The mean diameters of the base of the powder cones were determined and the tangent of the angle of repose calculated using the equation: Where h is the height of the heap of powder and D is the diameter of the base of the heap of powder.

Bulk and Tap Densities
A 10 g quantity each of the powder samples was, placed in a 50 ml clean, dry measuring cylinder and the volume, V o , occupied by each of the samples without tapping was determined.

Trop J Pharm Res, December 2005; 4 (2)
After 500 taps using Stampfvolumeter (Model STAV 2003 JEF, Germany), occupied volumes, V 500, were determined.The bulk and tap densities were calculated as the ratio of weight to volume (V 0 and V 500 respectively) 5 .

Hausner Index
This was calculated as the ratio of tap density to bulk density of the samples 5 .

Powder Porosity
This was derived from the values of true and bulk densities when fitted into the equation: Where S is the % swelling capacity, V e = 1-B b /D t x 10 .... ( 5) Where B b is the bulk density , D t is the true density and e is the porosity 2 g of the cellulose material was accurately weighed and evenly distributed over the surface of a 70 mm tarred Petri dish.The samples were then placed in a large desiccator containing distilled water in its reservoir (RH = 100%) at room temperature and the weight gained by the exposed samples at the end of a five-day period was recorded and the amount of water sorbed was calculated from the weight difference 5 .

Hydration Capacity
The method of Kornblum and Stoopak 10 was used.A 1.0 g each of the samples was placed in each of four 15 ml plastic centrifuge tubes and 10 ml distilled water was added from a 10 ml measuring cylinder and then stoppered.The contents were mixed on a vortex mixer (Vortex-Gennie Scientific Industry, USA) for 2 min.The mixture was allowed to stand for 10 min and immediately centrifuged at 1000 rpm for 10 min on a bench centrifuge (Gallenkamp, England).
The supernatant was carefully decanted and the sediment weighed.The hydration capacity was taken as the ratio of the weight of the sediment to the dry sample weight.

Complete and no residue
Water -soluble substance Total ash (%) Microscopy < 0.2% 0.12 (0.004) Irregularly shaped fibrous particles which are mixture of primary particles and spherical aggregates.

Swelling capacity
This was measured at the same time as the hydration capacity determination using the method of Okhamafe et al 8 and computed according to the following equation: 2 is the volume of the hydrated or swollen material and V 1 is the tapped volume of the material prior to hydration.

Loss on drying
Trop J Pharm Res, December 2005; 4 (2) The powder sample (5 g) was transferred, each, into a Petri dish and then dried in an oven at 105 o C until a constant weight was obtained.The % moisture content was then determined as the ratio of weight of moisture loss to weight of sample expressed as a percentage 5 .

RESULTS AND DISCUSSION
The yield of α-cellulose was approx.32 % w/w of the original material.The yield of the microcrystalline, CP-MCC, obtained from αcellulose was 67 % w/w.Thus the yield of CP-MCC was 21 % w/w of the starting raw cotton material.
The results of the physicochemical properties investigated are shown in Table 1.The results indicate a high level of purity of the cellulose material.This is expected as raw cotton is regarded the purest form of cellulose, consisting of cellulose approximately 90% and moisture 7%, the remainder being wax, fat, remains of protoplasm and ash 3 .
The organoleptic qualities of the CP-MCC produced were good as the material was odourless, tasteless, white and granular in texture.The value obtained for the total ash was very low.The total ash figure is of importance and probably indicates, to some extent, the level of care taken in the preparation of the substance 3 .In general, the results were as specified in the British Pharmacopoeia 2004.

POWDER PROPERTIES
The powder properties of CP-MCC and Avicel PH 101 are presented in Table 2 while the result of particle size analysis is shown in Fig. 1.The figure represents a unimodal frequency distribution which is positively skewed.The particle size is in the range of 70-1000 µm.Thus, CP-MCC powder belongs to the classification, 'conventional powder' 11 .Over 85 % of the particle population is less than 250 µm, and the calculated average diameter was 113 µm.
The loss on drying of CP-MCC was about 7.2%.This is slightly above the official limit of 6 % stated in British Pharmacopoeia 2004 6 .Consequently, CP-MCC would need to be dried further if it is to be used as a diluent in the formulation of hydrolysable drugs such as aspirin.
The flow properties of a powder are essential in determining its suitability as a direct compression excipient.The angle of repose, Hausner index and Carr's % compressibility are considered as indirect measurements of powder In all, this property showed that the cellulose powders are sensitive to atmospheric moisture and should therefore be stored in air-tight container.

CONCLUSION
The cellulose product, CP-MCC, obtained from the raw cotton of Cochlospermum planchonii conformed to the official specifications in the British Pharmacopoeia (2004).The flow properties of a powder are critical in direct compression tableting; consequently, for the materials to be used for this purpose, it would require the addition of a glidant.Furthermore, the swelling parameters indicate that CP-MCC would be a better disintegrant than Avicel PH 101.

Figure 1 :
Figure 1: Particle size distribution of microcrystalline cellulose powder (CP-MCC) obtained from raw cotton of C.planchonii

Table 2 :
Powder properties of microcrystalline cellulose and Avicel PH 101