O R I G I N A L P A P E R
Synthesis and characterization of microcrystalline cellulose powder from corn husk fibres using bio-chemical route
Nishant D. Kambli .V. Mageshwaran.Prashant G. Patil.Sujata Saxena. Rajendra R. Deshmukh
Received: 3 June 2017 / Accepted: 6 October 2017 ÓSpringer Science+Business Media B.V. 2017
Abstract In the present study low cost microcrys- talline cellulose (MCC) powder was prepared from cornhusk fibres, extracted chemically followed by anaerobic consortium treatment. Cornhusk fibres were treated with 10% alkali at 120 °C for 60 min followed by anaerobic consortium treatment for 3 days. It was then bleached with hydrogen peroxide and finally washed. Bleached pulp was hydrolysed using 4 N HCl to get the MCC. In the present investigation, we have characterized the MCC prepared from cornhusk fibres thoroughly for its physico-chemical properties and compared with AvicelÒ-PH 101, a commercial grade MCC. Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Powder Diffraction (XRD) and Differential Scanning Calorimetry (DSC) were used for characterization of samples. Similarly the powder and flow properties of the MCC prepared from cornhusk fibres were also investigated and the results were compared with AvicelÒ-PH 101. Our results showed that various properties and the purity of MCC prepared from
cornhusk fibres are comparable to the commercial grade MCC. Since, cornhusk is an agricultural waste product, MCC obtained from cornhusk fibres will be from cheaper raw materials than current market MCC.
Keywords Cornhusk fibresExtractionAnaerobic consortium treatmentMicrocrystalline cellulose Physico-chemical and flow properties
Introduction
In the present scenario, researchers from all over the world are focusing on utilization of agro wastes generated from food and fibre crops for various industrial applications. Corn (Zea mays) is from Graminacea family referred as Miracle crop and Queen of the Cereals. It is the third most important cereal crop after rice and wheat in the world. The cultivation of maize is continuously increasing due to its diversified usage in sectors like food, feed and ethanol production.
In India, on an average 24.5 million tons of cornhusk are produced annually. Cornhusk is mainly used as animal feed and for decorations in natural crafts. It is also used for wrapping different types of seafood, such as fish, prawns and crabs for its easy roasting. Inspite of all these uses, substantial quantities of cornhusk are being incinerated. Instead of burning, the left over cornhusk can be used for synthesis of N. D. KambliR. R. Deshmukh (&)
Institute of Chemical Technology, Nathalal Parekh Marg, Matunga, Mumbai 400 019, India
e-mail: [email protected];
N. D. KambliV. MageshwaranP. G. PatilS. Saxena ICAR- Central Institute for Research on Cotton Technology, Adenwala Road, Matunga, Mumbai 400 019, India
DOI 10.1007/s10570-017-1522-4
MCC, as cornhusk is rich in cellulose content (Reddy and Yang2005; Kambli et al.2016).
Microcrystalline cellulose (MCC) is partially puri- fied de-polymerized crystalline cellulose having potential industrial applications. Cellulose, a biopoly- mer is the basic and major constituent of plants. It is the most abundant polymer in nature. The basic method for preparing MCC from purified pulps was first described in Battista and Smith (1962) (US. Pat.
No. 2978446) which still represents the basis for many conventional MCC manufacturing processes. For over 50 years MCC is prepared from available cellulosic material or pulp by acid hydrolysis. Commercially available MCC is mostly derived from wood pulp and also cotton based materials by treating with acids like hydrochloric acid (HCl) (Brittain et al.1993). In well- known commercial process for making MCC by using partial acid hydrolysis of purified cellulose, at which only the amorphous areas of the polysaccharides are hydrolyzed, dissolved and removed. The crystalline cellulose areas are not hydrolyzed and are recovered.
The quality MCC has high demands in the field of cosmetics, food and pharmaceutical industries because it can be used as good suspension stabilizer and a reinforcing agent for final products such as medical tablets and capsules (Ruan et al.1996; Laka and Chernyavskaya2007). Due to its low cost, MCC prepared from cornhusk can be a potential excipient in the preparation of pharmaceutical dosage forms (Vora and Shah2015). MCC is used as bulking agent and fat substitute in food products such as baked foods, dairy products, desserts, frozen foods etc. It helps in enhancing mouthfeel, texture and consistency of the food product. In pharmaceutical industry, use of MCC is demandable as it exhibits chemical inertness and has no taste and odor. MCC is used an excipient in almost every kind of oral dosage like pellets, tablets, capsules, sachets and others. Commercially available MCC is derived from costly wood pulp and also purified cotton. The need for cheaper sources of MCC has led to the investigation of other lignocellulosic materials based on different agricultural residues (Suesal and Suwanruji2011).
Many R&D reports are also available for the preparation of MCC using other methods such as radiation degradation with deposited electron energy, reactive extrusion, two-step radiation-enzymatic depolymerisation process, etc. (Stupinska et al.
2006,2007; US patent No. US6228213 B12001). It
is generally understood that the differences in the properties of MCC between different manufacturers are due to the type of pulp used as raw material, and processing conditions. Since cellulose from different sources has different properties, for example crys- tallinity, moisture content, surface area and porous structure, molecular weight, and so on. It is expected that MCC obtained from different sources would also have different properties. The combination of anaer- obic method with chemical for preparation of MCC will reduce the cost and also help in reducing the toxic effluents released in environment (Shaikh2000).
In the present study, cornhusk fibres were subjected to chemical and anaerobic consortium treatment to prepare MCC. Also, we compared the properties of the prepared MCC with commercial grade MCC.
Materials and methods
Materials
For the fiber extraction the required cornhusks (maize cob sheaths) were collected from local market, Mumbai, India. The peeled cornhusks from maize cobs were manually cleaned to remove foreign materials. Both the ends of the cornhusks were removed and air dried. These air dried cornhusks were chemically treated to extract fibres. For chemical extraction of fibres, sodium hydroxide (98%, Merck Specialties Private Limited, India) was used. AvicelÒ- PH 101 (a commercial brand of microcrystalline cellulose) was used for the comparison of prepared MCC. Hydrochloric acid (HCl) (35%, Fishers Scien- tific, India) was used for acid hydrolysis. CIRCOT, India, anaerobic consortium was used for anaerobic consortium treatment in the preparation of MCC.
Procedure for fibre extraction
The cornhusk fibres were extracted at 120°C for 60 min by using 10% w/w concentration of sodium hydroxide. Fifty g of corn husk was taken in one liter of alkali solution with the material to liquor ratio 1:20.
The extracted fibres were then neutralized with dilute acetic acid 0.1% (w/v) and air dried. The chemical composition of cornhusk fibres used in the present study is reported in our previous work (Kambli et al.
2016). The fibre contain 7.5% lignin, 50–55% cellu- lose and 39.39% hemicellulose.
Procedure for the preparation of microcrystalline cellulose powder
The anaerobic consortium was prepared by adding 4%
(w/v) papaya pulp, 2.5% (w/v) paste of spinach leaves to 40% (w/v) cow dung slurry in 5 L glass bottle. The anaerobic condition was created by sealing the top of glass bottle with rubber cork and the gas outlet was connected inside water. The extracted corn husk fibres were cut into 2 cm size and 1 kg of these fibres was transferred to anaerobic digester containing 4 L of 30 days old anaerobic consortium. Thus, the material to liquor ratio was 1:4. The digester was kept under anaerobic condition for 3 days. The pulp obtained after 3 days was washed thoroughly. This pulp was bleached at 85°C for 60 min using hydrogen peroxide (0.3% w/v), sodium hydroxide (0.1% w/v) and sodium silicate (0.15% w/v) as a stabilizer with material to liquor ratio 1:20. The bleached sample was acid hydrolyzed by using 2.5 N HCl (1:10 material to liquor ratio). Hydrolysis was done by passing steam through the material for 20 min, then hydrolyzed pulp was cooled and finally washed thoroughly with water till it was free of acid (pH 6.5–7.0). The material was dried in incubator at 37°C for 30 h then pulverized (0.053 mm mesh size) to obtain MCC powder.
Physico-chemical characterization of MCC The physico-chemical properties of MCC prepared from cornhusk fibres were compared with commercial grade MCC (AvicelÒ-PH 101).
Determination of moisture content
In a tared weighing bottle, 2 g of sample (A) was taken. The weighing bottles carrying the sample was kept in oven at 105°±1 °C (4 h) for drying. After drying, it was cooled in desiccator and weighed accurately until a constant weight (B) was obtained.
The following formula was used to calculate moisture content:
Moisture contentð Þ ¼% ½ðABÞ=A 100
Determination of ash content
By using ASTM (E 1755-01) test method, the ash content in the sample was determined. The sample (5 g) was placed in a crucible and accurately weighed.
The sample was carbonized by igniting over the bunsen flame. After carbonization, the crucible was transferred to a muffle furnace along with the sample.
Ashing was done at 575±25°C, till it attained a constant weight. The ash content was calculated based on dry weight basis.
Determination of cellulose content
Halliwel method (Halliwell 1959) was used to estimate the cellulose content in the MCC. About 2 g of the samples in duplicates were extracted for 6 h with ether in a soxhlet assembly. For 1 h these defatted samples were boiled in 0.5% ammonium oxalate in the ratio of 1:50 (material to liquor ratio) to remove water soluble matter and pectin. To remove lignin, samples were bleached with 1% sodium chlorite solution and 0.05 N acetic acid in the ratio of 1:50 in a boiling water bath for 1 h. The obtained holocellulose was then treated with 5% potassium hydroxide (KOH) initially for 2 h which was then again treated with 24% KOH for 2 h to remove hemicellulose. The resultant cellu- lose was stirred with a 20 fold volume of phosphoric acid (90%) for 2 h at 1°C, washed with 1% solution of sodium carbonate and finally with water. The residue was completely dried in incubator at 37 °C and weighed to constant weight. Thus the actual weight of pure cellulose was obtained by subtracting the ash content from the residual weight.
Determination of starch content
Presence of starch in the MCC was determined qualitatively using the standard method (United States Pharmacopeia1980a,b). To obtain starch suspension, 2 g of sample was added in 100 ml distilled water (USP 1980a, b). In a 20 ml of prepared starch suspension, few drops of iodine solution (1%) was added and mixed thoroughly. The presence of starch was determined by the development of blue colour.
Determination of pH
Cellulose powder (1 g) was added in 500 ml distilled water. This suspension was then kept in shaking condition for 30 min at room temperature. Then the pH of this suspension was read by using micropro- cessor based pH Meter (United States Pharmacopeia 1980a,b).
Solubility characteristics
To observe the solubility of the sample in water (Battista1975) 4.0 g of sample was mixed with 80 ml of water for 10 min. Then the filtration was carried out using Whatman filter paper, sample was collected into a pre-weighed beaker and evaporated on a steam bath at 105°C for 1 h till it was completely dry.
To observe the solubility of the sample in alkali (1%), 2.0 g of sample was added to 1% of NaOH (100 ml) and heated on a water bath for 1 h. The insoluble residue present in the beaker was filtered through glass crucible followed by washing with 1.0%
acetic acid and finally with hot water. The content was dried to constant weight. The weight loss of the dry sample was calculated as material soluble in 1%
NaOH.
To observe the solubility of the sample in HCl (1%), 2.0 g of sample was added to 100 ml of HCl (1%) for 1 h in shaking condition at room temperature.
The content was filtered through glass crucible. The residue was washed with 0.1 N NaOH and finally with hot water, it was then dried to constant weight. The weight loss of the sample was calculated as the material soluble in 1% acid.
To observe the solubility of the sample in organic solvent, 2.0 g of sample was extracted with distilled petroleum ether having the boiling point range between 40 and 60°C, for 6 h in soxhlet extractor.
Extracted sample was then taken in a beaker and the remaining solvent was evaporated by heating in a water bath. The sample was finally dried to constant weight at 105°C.
To observe the solubility of the sample in oil, 2.0 g of sample was mixed with 50 ml of groundnut oil in shaking conditions for 4 h at room temperature.
Thereafter insoluble residue was filtered through glass crucible. The residue was washed with water and dried till it attained constant weight. The weight loss of the sample was calculated as material soluble in oil.
Degree of polymerization
The degree of polymerization (DP) is defined as the number of monomeric units in a macromolecule or polymer. DP of MCC obtained from cornhusk fibres and AvicelÒ-PH 101, a commercial grade MCC was estimated as per the standard method (Sundaram 1979) using Shirley type Viscometer. The following formula was used to calculate DP
DP¼2160 log½ ðgrþ1Þ 0:267 Where,gr=Relative Viscosity.
Determination of particle size
The particle size of MCC was analyzed using particle size analyzer (Mastersizer, Malvern Instruments, United Kingdom).
Bulk and tapped density
10 g of the cellulose powder was accurately weighed and poured into a 50 ml clean, dry graduated measur- ing cylinder. The cylinder was stoppered and the bulk density Dbulk, was recorded without tapping it.
For tapped density Dtap, the same cylinder was tapped 500 times from a height of 2.5 cm on a hard surface to a constant volume (i.e., until no more settling of the material occurred). The final (constant) volume was noted and the tapped density was calculated. The bulk density, Dbulk, and tapped density, Dtap, were determined using the following equations (Ohwoavworhua et al.2004).
Dbulk¼w=vo Dtap¼w=v1
wherewis the weight of the powder, andvo andv1 are the volumes of the bulk and tapped powders, respec- tively. The arithmetic mean of five replicate determi- nations were taken in each case.
Determination of true density
The specific gravity bottled method was used to determine the true density of MCC powder. Xylene was used as displacement fluid. A cleaned glass bottle
was filled with xylene followed by wiping off all spilled over xylene with a tissue paper and then its weight was noted (a). The same bottle was emptied and cleaned thoroughly, now 2 g of MCC powder was added into it. The weight of the MCC powder was noted as (w). The bottle was then half filled with xylene, stirred with glass rod to release air bubbles and was allowed to stands for 10 min. Finally the bottle was completely filled with xylene and the weight of bottle was noted as (b). True density of MCC was calculated using the following equation (Ohwoav- worhua et al.2005)
Dt¼w=½ðaþwÞ b S
where, Dtis the true density of MCC and the specific gravity of xylene, S=0.86.
Porosity
The porosity of MCC powder (E) was calculated using the method of Ohwoavworhua et al. (2007) as follows:
E¼½1ðBd=DtÞ 100
where, Bdis bulk density, Dtis true density of MCC.
Determination of flow properties of MCC Angle of repose
Fixed funnel and free standing cone method was used to measure the static angle of repose (h) (Train David 1958). A graph paper was placed on a flat horizontal surface and the funnel was clamped with its tip 2 cm above it. The powders were carefully poured through the funnel without disturbing its position until the apex of the cone thus formed just reached the tip of the funnel. The mean diameters of formed powder cones were determined and the tangent of the angle of repose was calculated using the equation:
tanh¼h=r
where, h is the height of the heap of powder and r is the radius of the base of the powder heap obtained on the graph paper.
Carr’s index and Hausner ratio
Carr’s index and Hausner ratio for MCC were determined from the bulk (Dbulk) and tapped densities
(Dtap)using the following equations (Ohwoavworhua et al.2004).
Carr’s Index¼DtapDbulk
Dtap
100
Hausner Ratio¼ Dtap Dbulk
Hydration capacity
The method of Kornblum and Stoopak (1973) was used to determine the hydration capacity of MCC powder. In each 15 ml graduated centrifugal tubes 1.0 g of the samples was placed and 10 ml of distilled water was added. The tubes were stop- pered and vortex for 2 min on a vortex mixer. The tubes with the contents were allowed to stand for 10 min and immediately centrifuged for 10 min at 1000 rpm in a centrifuge (Remi, India). The sediment was then weighed after decanting the supernatant carefully. The ratio of weight of the sediment to the dry sample weight was taken as the hydration capacity.
Swelling capacity
This was measured at the same time as the hydration capacity determination using the method (Okhamafe et al.1991) and computed according to the following equation:
S¼V2V1
V1
100
where S is the % swelling capacity, V2is the volume of the hydrated or swollen material after the centrifu- gation and V1 is the tapped volume of the material prior to hydration.
Moisture sorption capacity
Accurately weighed 2 g MCC powder was evenly distributed over the petri dish of 70 mm diameter. A large desiccator containing distilled water in its reservoir (RH=100%) was used to place the samples at room temperature. The weight gained was recorded at regular time interval of 24 h for five-days. The weight difference was used to calculate the amount of
water absorbed using the following equation (Oh- woavworhua et al.2005)
W2W1
W1
100
Where W1is the weight of the sample before exposure.
W2is the weight of the sample after exposure.
X-ray crystallinity
The degree of crystallinity of cellulose powder prepared from cornhusk fibres was determined using the X-ray diffractometry technique (Make:
Shimadzu).
The crystallite height 002 (I002) and amorphous height (Iam) were used to calculate the apparent crystallinity index (apparent Cr.I.) and was calculated by Eq. (i). The apparent crystallite size (L) of the refection of plane was calculated from the Scherrer equation based on the width of the diffraction patterns Eq. (ii). The surface chains occupy a layer approxi- mately 0.57 nm thick, so the proportion of crystallite interior chains (X) calculated using Eq. (iii),
Cr:I¼ I002Iam
I002
100% ðiÞ
The apparent crystallite size L of the refection of plane was calculated from the Scherrer equation based on the width of the diffraction patterns.
Crystallite sizeL¼ Kk bcosh
ðiiÞ where K, the dimensionless shape factor of value 0.94;
k—the X-ray wavelength (0.1542 nm); b—the line broadening at half the maximum intensity; h—the Bragg angle corresponding to the planes.
The proportion of crystallite interior chains and the interlayer distances d was calculated as follows:
Crystallite interior chainsX¼ L2h L
2
ðiiiÞ where L - the crystallite size for the reflection of plane;
h - the layer thickness of the surface chain is 0.57 nm.
The X value was used as estimates of the fraction of MCC chains contained in the interior of the crystallites.
Infrared spectroscopy
To study the functional groups and chemical structure of MCC prepared from cornhusk fibres, Fourier transform infrared (FT-IR) spectroscopy was done.
Shimadzu IR Prestige 21 analyzer was used to carry out the spectroscopy. MCC (0.5 mg) was mixed with 200 mg KBr (spectroscopy grade) and pelletized in a KBr press. A pressure of approximately 8 tons was used to form 13 mm diameter pellets. To eliminate air and moisture from the KBr powder degassing was done. The scanning range was 500 to 4500 cm-1. Scanning electron microscopy (SEM)
The morphological structure of the cellulose powder was studied using a scanning electron microscope (SEM), Philips XL-30, with an accelerating voltage of 10 kV. Before SEM analysis the sample was coated with a thin layer of conducting material (gold/palla- dium) using a sputter coater to render them electrically conductive.
Thermal analysis
The thermal properties of the commercial MCC and MCC prepared from cornhusk fibres were analyzed by differential scanning calorimeter (DSC) on a thermal analyzer (Mettler-Toledo, Germany) instrument. Sam- ples weighing between 4 to 6 mg were used. Each sample was heated from room temperature to 450 °C at a rate of 10 °C/min under nitrogen atmosphere.
Results and discussion
The present study dealt with preparation of MCC from cornhusk fibres by chemical and anaerobic consortium treatment and characterization of prepared MCC.
Figure1 depicts the steps followed in the process of preparation of MCC (Fig. 1a–d). The corn husk was separated from corn cobs, cleaned and subjected for fibre extraction.
The MCC was prepared from extracted fibres by anaerobic consortium treatment. The present study is an attempt to replace NaOH with anaerobic consor- tium in the pulping process. The previous results showed that similar anaerobic consortium was used for retting of banana pseudostem fibre. It was found that
the anaerobic consortium consists of mixture of anaerobic and facultative anaerobic bacteria which includes Eubacterium, Bacillus, Cellulomonas, Methanomicrobium andMethanospirillum that aided in the degradation of pectin and the other adhering substances during the retting of banana pseudostem fibre (Ghorpade and Balasubramanya 2013). The present results showed that the pulp was made from cornhusk fibre under anaerobic consortium treatment in three days which might be due to the presence of the activity of pectinolytic and lignolytic enzymes in anaerobic consortium as reported earlier in retting of banana pseudostem fibre.
The comparison of various physico-chemical prop- erties of MCC prepared from cornhusk fibres with
commercial MCC are presented in Table1. The moisture content of MCC prepared from cornhusk fibre was 5.2% while it was 5.3% in commercial MCC.
In a similar study, the moisture content of MCC from soybean hulls and banana fibres was found to be 7.2%
and 5.3% respectively (Mageshwaran et al. 2015;
Shanmugam et al. 2015). Various studies also con- firmed that the moisture content of MCC has an effect on compaction properties, tensile strength and vis- coelastic properties (Doelker 1993; Sun 2008). The storage conditions of the MCC also play an important role, as relative humidity increases tablet strength decreases (Williams et al.1997).
The ash content of cellulose powder from cornhusk fibre was found to be 0.05% which is in close Fig. 1 aCorn,bcornhusk,cchemically extracted cornhusk fibres anddMCC from cornhusk fibres
Table 1 Properties of MCC prepared from cornhusk fibres and its comparison with commercial MCC
S. No. Property MCC prepared from cornhusk fibres Commercial MCC Standards as per USP/IP
1. Moisture content (%) 5.2 5.3 \10
2. Ash content (%) 0.05 0.06 \0.1
3. Cellulose content (%) 98.2 98.5* [97
4. Starch Absent Absent Absent
5. pH value 6.7 7 –
6. Solubility
Distilled water Partially soluble Partially soluble Partially soluble
1% NaOH Partially soluble Partially soluble Partially soluble
1% HCl Insoluble Insoluble Insoluble
Petroleum ether Completely insoluble Completely insoluble Completely insoluble
Acetone Completely insoluble Completely insoluble Completely insoluble
Ground nut oil Completely insoluble Completely insoluble Completely insoluble
7. Degree of polymerization 282 157 –
8. Particle size inlm 35–45 30–50 10–50
9. Degree of compressibility (%) 21.4 11.0 –
10. X-ray crystallinity 80.9% 89% –
* Estimated by standard method
agreement with ash content (0.06%) of commercial sample and according to U.S. Pharmacopeia1980a,b, ash content should not be more than 0.1%. While the ash content reported was 0.085% and 0.07% in case of MCC prepared from soybean hulls and banana fibres respectively (Mageshwaran et al. 2015; Shanmugam et al.2015).
The cellulose content in MCC prepared from cornhusk fibres is 98.2% which is comparable to commercial MCC (98.5%) (Table1). According to U.S. Pharmacopeia [27] cellulose content should not be less than 97%. In case of MCC prepared from soybean hulls and banana fibres it was 97.5% and 99.0% respectively (Mageshwaran et al.2015; Shan- mugam et al. 2015). Hence the MCC prepared from cornhusk fibres is well in agreement with U.S.P.
specifications.
The starch content is absent in cellulose powder prepared from cornhusk fibres which is comparable to the specification given in U.S.P. for MCC. Even the pH value of prepared MCC is very much close to commercial material.
As per standards of Pharmacopeia of India charac- teristics such as solubility in water, dilute alkali and dilute acid, organic solvent and groundnut oil for prepared MCC were comparable with commercial MCC (Pharmacopeia of India1985).
The degree of polymerization (DP) helps to under- stand the number of repeating units in polymer. The DP of MCC prepared from cornhusk fibres was found to be 282 (\350). Tommi et al. have reported that the DP of MCC derived from hemp stalks and rice husks as 125 and 245 respectively (Virtanen et al.2012). DP is used as an identity test, as pharmacopoeial MCC is defined by a DP below 350 glucose units, compared to DPs in the order of 10,000 units for the original native cellulose (Carlin2008; Dybowski1997).
Particle size analysis
The particle size of the prepared MCC is in the range of 30-45lm whereas commercial MCC is having 35–50 lm range as seen in the Fig.2. Particle size depends upon the extent of degradation of cellulose molecule (Agblevor et al. 2007). Finer particle size MCC promotes tablet (compact) strength as confirmed by the researchers. Variability in excipient particle size and content uniformity impacts on tablet
hardness, friability and disintegration (Agblevor et al.2007; Kushner et al.2011).
The MCC powder properties prepared from corn- husk fibres and AvicelÒPH 101 are presented in Table 2. The bulk and tap densities of the MCC from cornhusk fibres were slightly lesser than the AvicelÒ- PH 101 as given in Table2. The ability of a material to flow into the die cavity of a rotary compression tablet machine from its hopper is estimated by bulk density.
On repeated packing how well a MCC powder can be packed into a confined space is determined by its tap density. Generally, higher the bulk and tap densities, better is the potential of a material to flow and to rearrange under compression. This suggests that both the MCC samples might have good flow properties. In case of MCC derived from Sorgum caudatum and from groundnut shells, bulk densities were 0.27 and 0.31 g/ml whereas tapped densities were 0.48 and 0.37 g/ml respectively (Ohwoavworhua and Adelakun 2010; Chukwuemeka et al.2012).
The true density of MCC powder prepared from cornhusk fibres was comparable to that of AvicelÒPH 101 (Table 2). According to Stamm (1964) there is a
(a)
(b)
0 50 100
10
5
Parcle size (μm)
Differenal Intensity (%)
100 Parcle size (μm)
0 50
5 10
Differenal Intensity (%)
Fig. 2 Particle size analysis ofaMCC prepared from cornhusk fibres,bcommercial MCC
direct correlation between the degree of crystallinity of cellulose and its true density when determined in a non-polar liquid. From the obtained values of true density it can be said both the MCC powders might have the same degree of crystallinity (Table1, 2).
MCC prepared from Indian Bamboo (Bambusa vul- garis) had true density of 1.642 g/ml (Umeh et al.
2014) and it was 1.38 g/ml when prepared from raw cotton (Ohwoavworhua and Adelakun2005).
The voids and pores within the particles make up the total porosity of a porous powder. The results obtained for both the MCC powders (Table2) were almost similar which indicates that poly sized particles are easily compressible during tableting.
The angle of repose of MCC powder gives a quantitative assessment of its internal and cohesive frictions. In this study, there was no significant difference in the angles of repose of both the MCC powders. In general angle of repose around 35°for the MCC samples indicates good flow (Fowler 2000).
Researchers reported 52.17 and 57.44°angle of repose for MCC prepared fromSorgum caudatum(Ohwoav- worhua and Adelakun 2010) and Indian Bamboo respectively (Umeh et al.2014).
In order to determine the suitability of a material to be used as a direct compression excipient its flow properties are important. The flow properties of a powder can be indirectly determined by measuring its angle of repose, Hauser’s index and Carr’s percent compressibility (Staniforth 1996). The Hausner’s index indicate interparticle friction and measures cohesion between particles. The compressibility of a powder can be measured by Carr’s index. The values for Hausner’s index and Carr’s index vary inversely
with particle flow. As the values of these indices increases, the flow of powder decreases. It is accepted that Hausner index ratio greater than 1.25 indicates poor flow and Carr’s compressibility index less than 16% indicates good flowability of the powders. The values more than 35% indicate cohesiveness (Stani- forth1996). The flow indices of MCC from cornhusk fibres and AvicelÒPH 101 powders have showed poor flow as indicated in by their Carr’s compressibility index in Table 2. Whereas, in case of MCC prepared from Sorgum caudatum, Hausner index and Carr’s compressibility index was 1.71 and 43.75 respectively (Ohwoavworhua and Adelakun2010).
The hydration capacity value shows that MCC obtained from cornhusk fibres was able to absorb more water compared to that of AvicelÒPH 101. Also value obtained from cornhusk fibres indicated that it was capable of absorbing about four times of water to that of its own weight (Table2). Whereas in case of MCC obtained from Indian bamboo, water absorption capacity was one and half times of its own weight (Umeh et al.2014).
Disintegration ability of a tablet can be determined by its swelling capacity (Caramella 1991). The swelling capacity for MCC from cornhusk fibres was 30% (Table 2) which reflects the increase in the volume of cellulose due to water absorption. Earlier Stamm reported in his study that the amorphous portion in the cellulose is responsible for uptake of water and swelling (Stamm1964).
The measurement of moisture sensitivity of a material gives its moisture sorption capacity. The moisture sorption capacity value for MCC prepared from cornhusk powder slightly differ than that of Table 2 Properties of
Microcrystalline cellulose powder prepared from cornhusk fibres and commercial MCC AvicelÒ- PH 101
S. No. Parameters MCC from Cornhusk fibres AvicelÒ-PH 101
1 Bulk density (g/ml) 0.28 0.31
2 Tapped density (g/ml) 0.40 0.42
3 True density (g/ml) 1.51 1.54
4 Porosity (%) 32.43 30.19
Flow properties
5 Angle of repose (degree) 41° 39°
6 Hausner index ratio 1.42 1.35
7 Carr’s Compressibility index (%) 30.93 26.19
8 Hydration capacity 3.85 3.49
9 Swelling capacity (%) 30 24
10 Moisture sorption capacity (%) 5.85 6.05
AvicelÒPH 101 value as seen in Table2. In the previous works it is reported that the water is not absorbed by the crystallite portion of cellulose but only amorphous region is responsible for the moisture absorption (Stamm1964). Hence the extent of water absorption by cellulose should be proportional to the amount of amorphous region present in the material.
The interest in water sorption of material is because it determines the relative physical stability of tablets when stored under humid conditions. The sensitivity of cellulose powders to atmospheric moisture makes it necessary to store it in air tight containers.
The moisture sorption profile of MCC prepared from cornhusk fibres and AvicelÒPH 101as shown in Fig.3explains their moisture sensitivity. MCC from cornhusk fibres showed higher rates of moisture sorption capacity compared to that of AvicelÒPH 101 in the first 24 h. Since MCC prepared from cornhusk fibre absorbs moisture, it is obvious that it will show decrease in moisture absorption when kept for longer period as compared to commercial MCC.
As reported by Stamm the extent of water adsorbed by cellulose is proportional to the amount of amorphous cellulose present in it (Stamm 1964). It is observed from Fig.3that the percentage moisture absorption in both the samples is comparable and just 6% (after 5 days), which in turn indicate that there may be a high crystallinity in both the materials.
XRD analysis
The powder X-ray diffraction spectra of the two cellulose samples are shown in Fig.4which showed typical of Cellulose I structure with diffraction peaks of the 2hangles.
From X-ray analysis, it was observed that crys- tallinity Index (%) in prepared MCC is 80.9% whereas in commercial MCC it is 89%. In case of MCC prepared from banana fibres it was 72.1% (Shan- mugam et al. 2015) and in jute it was 74.9% (Jahan et al. 2011). MCC prepared from an environment- friendly two step radiation-enzymatic process reported crystallinity index 64% (Shlieout et al. 2002). It is reported that due to the chemical modifications such as delignification, bleaching and hydrolysis, MCC exhi- bits higher crystallinity because of more efficient removal of non-cellulosic components of amorphous zones (Sim et al. 2016). It has been showed that modifying the hydrolysis conditions, including tem- perature, time and acid concentration, also have very little impact on the degree of crystallinity. This indicates that crystallinity cannot be controlled at the hydrolysis stage. Crystallinity appears to be more dependent on pulp source rather than on processing condition (Shlieout et al.2002; Landin et al.1993).
Fig. 3 Moisture sorption profile for MCC from cornhusk fibres
FTIR spectroscopy
FT-IR spectroscopy has the capability to calculate structural differences not seen by other analytical methods. To understand the chemical groups present in commercial MCC and MCC prepared from corn- husk fibres, FTIR spectra of both the samples were studied. No major differences were observed between
the FT-IR spectra of the MCC samples prepared from cornhusk fibres and AvicelÒ-PH 101. Figure5shows the general characteristic spectrum of typical cellu- losic material. For example, absorption bands are clearly observed at 900, 2900 and 3300–3500 cm-1 which are corresponding tob-glycosidic linkages, C–
H asymmetric and symmetric tensile vibration and – OH stretching respectively (Azubuike and Okhamafe Fig. 4 XRD analysis of
commercial MCC and MCC prepared from cornhusk
Fig. 5 FT-IR spectra ofacommercial MCC,bMCC prepared from cornhusk fibres
2012). Both samples showed a strong broad absorption band in the range of 3170–3360 cm-1corresponding to O–H stretching of hydroxyl groups of cellulose. A sharp medium band appeared in both the samples at its normal position of 2900 cm-1is due to C–H stretching in cellulose molecule. The sharp peak at 1640 cm-1 may be attributed to the stretching vibrations of C=C.
A strong and broad band observed at around 1400 cm-1 in both the samples corresponds to C-H bending vibrations. Whereas, peak at 1050 cm-1 is attributed to C–O stretching. This study shows that both the samples are same in terms of functional groups presents and crystallanity as the peaks for crystallanity observed at 924 cm-1 are of same strength.
SEM analysis
The study of SEM micrographs for cornhusk MCC and commercial MCC are presented in Fig.6a, b respec- tively. It can be observed from the SEM micrographs
that cornhusk MCC surface is plain and uniform in size as compared to commercial MCC. Whereas commercial MCC shows a mixture of plated shaped, complex and ribbon like structure.
Thermal property
Both the curves are showing initial endothermic peak at around 60–100 °C, due to the evaporation of the moisture. Next endothermic peak observed at around 350 °C is responsible for the pyrolysis of cellulose.
Indeed, this endothermic peak is responsible for the heat absorption by the cellulose polymer, depolymeri- sation of the polymer and the production of the flammable gases. Only difference is, commercial grade MCC is showing pyrolysis endotherm at 20–25 °C lower temperature than the other one. It may be due to the difference of the maturity or variety/grade of the cotton fibre which affect the fineness of the cotton fibre. However, as per
Fig. 6 SEM micrographs ofaMCC prepared from cornhusk fibres,bcommercial MCC
conclusion, technically no significant difference has been observed between the two samples (Fig.7).
Conclusion
Cornhusk fibres are rich in cellulose and annually available agro residue waste and thus can be a potential raw material for MCC production. The present study revealed that MCC prepared by chem- ical and biological treatment yielded cellulose content of 98.2%. The physico-chemical characterization studies showed that the quality of MCC prepared from cornhusk is at par with commercial grade MCC and also meets the national and international stan- dards. To conclude, the present study reveals a high quality MCC could be prepared from cornhusk by following bio-chemical route and thus the use of environmentally toxic chemicals would be reduced.
Further work may be carried out on development of a green technology for MCC preparation with very minimum chemical usage.
Acknowledgments The authors would like to acknowledge the support from the Institute of Chemical Technology (ICT), Mumbai and ICAR-Central Institute for Research on Cotton Technology (CIRCOT), Mumbai. Thanks are also expressed to the staff members of CIRCOT for their help to carry out various characterizations of MCC.
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