In view of biomedical applications of cellulose fibers in orthopedics, dentistry and reconstructive surgery, Luffa cylindrica (LC), a local forest product of Orissa, India, has been used for preparation of alkali treated LC fiber modified with calcium carbonate and calcium phosphate separately by following standard procedures. FTIR and Raman spectra were obtained for these samples at wavelength range 500 - 4000 cm –1 and 300 - 3000 cm –1 respectively. Lattice structures of cellulose i.e., crystalline cellulose and amorphous cellulose were detected using Raman spectroscopy and discussed. The property of cellulose such as its degree of crystallinity was determined from intensity of FT IR peaks and was found to be 74.12%. The presence of calcite and hydroxy apatite, polymorphs of calcium carbonate and calcium phosphate respectively were confirmed in the treated modified LC fibers which can be used as bioactive materials.
At present, it is a challenge before the researchers to develop new materials for biomedical applications. Calcium phosphate based bio-materials such as hydroxy apatite (Hap) and β tri calcium phosphate (β tcp) are extensively used for bone replacement, dental filling, bone tissue engineering, drug delivery, etc. [
Morpho synthesis is an important aspect in the development of new materials in many fields. Such process is used in chemical construction and patterning of inorganic materials with unusual and complex architecture over the surface of any material [
Infrared spectroscopy is nowadays one of the widely used analytical techniques. It is well known that the main constituent in natural fiber is the cellulose which acts as the reinforcing material in the cell wall. The cellulose molecules are held in micro fibrils in which there is extensive hydrogen bonding between cellulose chains, producing a strong crystalline structure. Much work has been reported [
where Xc is the degree of crystallinity of cellulose and I1454 and I893 are the intensity of FTIR peak at 1454 cm−1 and 893 cm−1 respectively.
In a manner similar to FTIR spectroscopy, Raman spectroscopy is based on the existence of a spectrum of normal vibration modes in a given molecular compound. In traditional FTIR spectroscopy the intensity of transmitted radiation was studied whereas in Raman spectroscopy the intensity of scattered radiation is studied. Raman spectrum is generated by directing a laser onto the sample and observing the patterns of light waves which are scattered at higher and lower wavelengths relative to that of the incident laser beam. The shift provides information about vibration, rotational and other low frequency transitions in the given molecules. Therefore vibration spectroscopy like Raman spectroscopy plays an important role in the investigation of cellulose and cellulose based structures. The studies made by many researchers [
In our research, compounds of calcium carbonate and calcium phosphate are artificially synthesized over the surface of LC fibers. Presence of polymorphs of calcium phosphate such as hydroxy apatite and β tri calcium phosphate on the surface of LC fibers are confirmed from Raman spectroscopy. It is interesting to note that the crystallinity index of treated LC fiber was determined from FT IR spectral analysis and it was found to be 74.71%. The high % of crystallinity of cellulose in treated LC fiber was an important result to be considered in this study. The objective of our investigation is to transform the low priced, readily available agricultural waste, i.e. fruit of LC into a high value product. This work may subsequently demonstrate the effectiveness of cellulose nano crystals derived from LC in improving the mechanical, thermal and electrical properties of matrix polymer.
The fruit of LC was collected from local forest area near Barang, Orissa, India. The chemicals such as calcium chloride (CaCl2 2H2O, 97%), sodium carbonate (Na2CO3, 95%), di sodium hydrogen phosphate (Na2HPO4 2H2O, 99.5%), all of AR grade were procured from E. Merck, India.
The fibers of LC were cut into small pieces of length around 2 cm. These were washed thoroughly with deionized water to remove impurities like oil, dust, part of leaf, etc. These were then dried at 70˚C in vacuum oven for 20 minutes. The dried LC fibers are subjected to chemical treatment such as treatment with alkali followed by bleaching and acid hydrolysis, For alkali treatment, the LC fibers were soaked in a 5% NaOH solution at 80˚C for 1 h. The soaked LC fibers were then washed with fresh water for 30 minutes to remove any excess NaOH sticking to the surface of LC fiber. The fibers were then dried at room temperature for 48 h followed by drying in oven at 60˚C for 6 h. During alkali treatment given to the natural fibers the hemicelluloses and lignin present in the natural fibers are extracted. In this way the number of -OH groups present in the fiber is reduced. The decrease in -OH groups increases hydrophobicity of natural fibers which strengthen the bonding between fiber and matrix. There is disruption of hydrogen bonds in the network structure of cellulose due to the alkali treatment. Thus it increases the surface roughness and the adhesion between fiber and matrix. This treatment depolymerizes cellulose and exposes the short length crystallites of cellulose. The alkali treated LC fibers were bleached with 2% sodium hypochlorite solution. The mixture was continuously stirred for 2 h at 80˚C. After this the mixture was poured through a filter paper in a funnel. The solid fibers were trapped by the filter paper. After filtration the fibers were washed with distilled water till neutral pH was obtained. The pulp obtained after bleaching is termed usually as micro crystalline cellulose (MCC). The colour of the bleached LC fibers appear yellowish from black. The bleached LC fiber/water suspension was prepared and kept on an ice bath. H2SO4 was added slowly under continuous stirring to the suspension placed in an ice water bath, until the final concentration of 60% H2SO4 was reached. The obtained suspension was then heated at 45˚C under continuous stirring for 2 h. In order to remove excess acid the mixture was washed and centrifuged using an ultracentrifuge at 30˚C for 20 minutes with 7000 rpm.
The treated LC fiber were then immersed in CaCl2 solution for 12 h at room temperature and then washed with distilled water for removing excess calcium deposited on it. Now, the LC fiber modified with CaCl2, were re-immersed in Na2HPO4 solution for 12 h at room temperature to deposit compounds of calcium phosphate over it. Another set of the LC fiber modified with CaCl2 were reimmersed in Na2Co3 solution for 12 h to deposit compounds of calcium carbonate on its surface. Thus two separate sets of modified LC fibers were prepared. One set of treated LC fibers are modified by calcium carbonate. The other set of treated LC fibers are modified with calcium phosphate. After 12 h the modified LC fibers were washed again with distilled water.
A mixture of 5.0 mg of dried sample and 200 mg of KBr was pressed into a disk for FTIR measurement. The amount of mixture was kept constant to obtain repeatable transmission from the sample. KBr pellet is used because KBr does not absorb in the IR wavelengths between 4000 - 400 wave numbers (cm−1) and in this way the material could be easily dispersed. All the samples were examined by FTIR spectroscopy (FTIR Nicolet 6700/ Thermofisher Scientific) using KBr pellet technique in the region 500 cm−1 - 4000 cm−1 to identify the functional groups in the samples. A Raman spectrum is generated by directing a laser beam onto the sample and observing the patterns of light waves which are scattered at higher and lower wavelengths relative to that of the incident laser beam. Raman measurements were performed with a HORIBA Jobin Yvon, France Lab RAM HR 800 apparatus. A He-Ne laser source of 632 nm was used. The laser spot diameter was about 1 μm and spectral resolution was 2 cm−1. The measurements were performed between 300 cm−1 and 3000 cm−1.
The Raman spectra of alkali treated LC fiber are shown in
Infrared (IR) radiations normally alters the electric dipole moment of the molecule, on the other hand Raman spectroscopy is dependent on electric polarizability. Raman spectroscopy measures the vibrational modes of non polar bands. Non polar functional groups give rise to a strong band in Raman spectra where as polar functional groups give rise to strong IR bands. The polar -OH groups present in LC fibers are strongly reflected in IR bands at around 3400 cm−1. However in
The additional peak observed at 710 cm−1 and 1074 cm−1 in
is characteristic of calcite, which is a polymorph of calcium carbonate [
A close perusal of
Wave number (cm−1) | Assignments |
---|---|
2902 | C-H,CH2 stretching in cellulose |
1471 | H-C-H bending in cellulose |
1337 | H-O-C bending in cellulose |
1091 | β-1,4-glycosidic linkages |
380.88 | Amorphous cellulose |
979 | Hydroxy apatite |
583 | Hydroxy apatite |
1074 | Calcium carbonate |
710 | Calcium carbonate |
is absent in
Alkali treated LC fiber modified with calcium phosphate and calcium carbonate was prepared and analyzed by using Raman and FTIR spectra for phase identification. From Raman spectra, the presence of polymorphs of calcium carbonate and calcium phosphate was confirmed. The peak at 979 cm−1 indicates presence of hydroxy apatite. Hydroxy apatite is a polymorph of calcium phosphate having chemical formula Ca10 (PO4)6 (OH)2 which is an important bio mineral. It is chemically similar to the mineral component of bone and hard tissues in mammals. It is one of few materials that are classed as bioactive, meaning that it will support bone in growth and Osseo integration when used in orthopedic, dental and maxillofacial applications [