SYNTHESIS AND CHARACTERISATION OF CROSS-LINKED POLYMERS OF ACRYLIC ACID AND PSYLLIUM MUCILAGE (PSY-CL-AA)

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1 SYNTHESIS AND CHARACTERISATION OF CROSS-LINKED POLYMERS OF ACRYLIC ACID AND PSYLLIUM MUCILAGE (PSY-CL-AA) Deepak Kumar 1, Rakesh Chandra 2, Rashmi Dubey 3 1Research Scholar, Department of Applied Chemistry, Babasaheb Bhimrao Ambedkar Central Government University, Lucknow. 2Research Scholar, Department of Chemistry, Institute of Engineering and Technology, CSJM University, Kanpur. 3Assistant Professor, Department of Chemistry, Chemistry, Institute of Engineering and Technology, CSJM University, Kanpur. ABSTRACT BACKGROUND Psyllium (Psy) mucilage, a food grade polysaccharide is reported as a substrate for the grafted cross-linked copolymerisation of Acrylic Acid (AA) in the presence of cross-linker (N, N`-methylene-bis-acrylamide). Psyllium mucilage was extracted from psyllium husk. Copolymerisation was initiated by ceric ion in aqueous medium under N2 atmosphere. The effect of different reaction parameters such as monomer concentration, initiator concentration, cross-linker concentration, time and temperature on the cross-linking was studied. The progress of the reaction was monitored gravimetrically. Cross-linking of Polyacrylic Acid (PAA) onto psyllium was confirmed by Fourier transform infrared spectroscopy. KEYWORDS Psyllium, Polysaccharides, Copolymer, Cross-Linking. HOW TO CITE THIS ARTICLE: Kumar D, Chandra R, Dubey R. Synthesis and characterisation of cross-linked polymers of acrylic acid and psyllium mucilage (Psy-cl-AA). J. Technological Advances and Scientific Res. 2016; 2(4): , DOI: /jtasr/2016/34 BACKGROUND Natural polysaccharides and their derivatives represent a group of polymers widely used in the pharmaceutical and biomedical field for the controlled release of drugs. The advantages of controlled drug delivery system are mainly the achievement of an optimum concentration usually for prolonged times, the enhancement of the activity of labile drugs due to their protection against hostile environments and the diminishing of side effects due to the reduction of high initial blood concentration. [1-3] The polysaccharides do hold an advantage over the synthetic polymers generally because they are nontoxic, less expensive, biodegradable and freely available compared to their synthetic counterparts. Polysaccharides in their normal form are widely used as flocculants and coagulants, e.g. starch, amylopectin, sodium alginate, xanthan gum, chitosan, guar gum, okra and psyllium mucilage while modified polysaccharides are widely used in various field as super sorbent, antimicrobial, drug delivery, antioxidant in agriculture, textile, etc. Polymers with three-dimensional network structures slightly cross-linked to each other are used to be called gels. Because of the cross-linked structure, they are insoluble in any solvent, but can swell, what leads to macroscopic change in sample dimension. Any gel where the medium is water can be further characterised as a hydrogel, hydrogels are crosslinked polymeric networks that are insoluble in water, but swell to an equilibrium size in the presence of excess of water or biological fluids. [4-8] Hydrophilic gels that are usually referred to as hydrogen are networks of polymer chain that are sometimes found as a colloidal gel in which water in the dispersion medium. In another word, they are water absorbing natural or synthetic polymers Financial or Other, Competing Interest: None. Submission , Peer Review , Acceptance , Published Corresponding Author: Deepak Kumar, Babasaheb Bhimrao Ambedkar Central Government University, Lucknow , Uttar Pradesh, India. dpk.4470@yahoo.in DOI: /jtasr/2016/34 (they may contain over 99% water). Hydrogels have been defined as polymeric materials, which exhibit the ability of swelling in water and retaining a significant fraction of water within their structure without dissolving in water. They possess also a degree of flexibility very similar to natural tissue due to their large water content. Typical simple materials applied for general purpose hydrogels are polyethylene oxide, polyvinyl alcohol, polyvinylpyrrolidone, polyhydroxyethylmethacrylate, polyacrylic acid and poly and polyacrylamide. Hydrophobic materials that swell in water due to presence of hydrophobic groups (like-oh, -COOH, - NH2, etc.) or due to presence of ionic groups (like COO, -NR ++, etc.). [9-13] Several techniques have been reported for the synthesis of hydrogels. The first approach involves copolymerisation/cross-linking of comonomer, which acts as the cross-linking agent. The polymerisation reaction is initiated by chemical initiator. The polymerisation reaction can be carried out in bulk, in solution or in suspension. [14-17] The second method involves cross-linking of linear polymers by irradiation or by chemical compound. The monomers used in the preparation of the ionic polymer network contain an ionizable group, a group that can be ionized or a group that can undergo a substitution reaction after the polymerisation is completed. As a result, hydrogels synthesised contain weakly acidic groups like carboxylic acids, or a weakly basic group like substituting amines or a strong acidic and basic group like sulphonic acids and quaternary ammonium compounds. Some of the commonly used cross-linking agents include N,N`-methylene-bisacrylamide (N,N`-MBA Am), divinylbenzene and ethylene glycol dimethacrylate are Used N,N`-methylene-bisacrylamide. [11-12] Psyllium is obtained from the seed of the Plantago ovata plant. It is also famous as ispaghula and isabgol and mucilage is a white fibrous material that is of hydrophilic nature and forms the clear colourless mucilaginous gel by absorbing water. It is composed of natural arabinoxylan (arabinose 22.6%, xylose 74.6%) shown in Figure 1. Psyllium is pharmaceutically significant polysaccharide and it has been reported for the treatment of diabetes, diarrhoea, J. Technological Advances and Scientific Res./eISSN , pissn / Vol. 2/ Issue 04/ Oct-Dec Page 185

2 constipation, inflammation bowel diseases-ulcerative colitis, obesity, high cholesterol and cancer. In view of the pharmacological significance of gel-forming psyllium polysaccharides and drug delivery devices based on hydrogels, psyllium, if suitably tailored to synthesise the hydrogels can work as the double possible candidates to improve drug delivery systems. [8,15,16] required amount of ceric ion solution (vitamin C) was injected through the stopper by hypodermic syringe. The nitrogen flushing was continued for another 20 minutes; then, the needles were taken out and the flask was further sealed with Teflon tape. The reaction temperature was maintained at requisite temperature. The reaction mixture was stirred occasionally. The reaction was continued for required time and then terminated by injecting 0.5 ml of saturated aqueous hydroquinone solution. [17] The reaction product was precipitated in excess of isopropanol and filtered through filter paper. The precipitate was again slurried in acetone followed by filtration and finally the precipitate was dried in vacuum oven at 40ºC. The homopolymer was extracted from the cross-linked product using acetone as solvent until a constant weight was obtained. The % cross-linking was calculated by the equation- Figure 1. Structure of Psyllium In the present research program, we wish to report the cross-link copolymerisation of acrylic acid onto psyllium using ceric ammonium nitrate as the initiator. The graft copolymerisation was studied by varying the initiator, time, temperature and concentration of monomer. The crosslinked polymers were characterised by SEM, FTIR and TGA studies. Experimental Materials Acrylic acid was purchased from Aldrich Chemical Co. (USA) and used without further purification. Acetic acid (99.5%) methyl alcohol, Ceric Ammonium Nitrate (CAN) and acetone are purchased from Merck (Germany). Nitrogen gas was used for maintaining the inert atmosphere during synthesis of copolymers. Compressed nitrogen cylinders were purchased. This gas may contain traces of oxygen, which is removed by passing it through Fieser s solution. Fieser s solution consists of an alkaline solution of sodium dithionite to which sodium anthraquinone-2-sulphonate is added. Synthesis of (Psy-cl-PAA) Half gram of psyllium was dissolved in distilled water (150 ml) in an Erlenmeyer flask. Then, the required amount of acrylic acid was added into the solution through the stopper by hypodermic syringe with constant stirring using magnetic stirrer. The flask was then sealed with septum stopper and nitrogen gas was flushed into the solution through hypodermic needle for 20 minutes. The solution was stirred for 30 minutes while being bubbled with nitrogen. The Sample Characterisation FTIR Spectroscopy The pure psyllium and Psy-cl-PAA are grinding into powder and KBr discs are prepared. FTIR spectra of psyllium and Psycl-PAA are recorded by Perkin Elmer FTIR spectrophotometer using KBr pellets. FTIR spectra of the psyllium and Psy-cl-PAA are taken in the range of cm -1 with a resolution of 2 cm -1. Scanning Electron Microscopy (SEM) The surface morphology of the psyllium and Psy-cl-PAA is studied with the help of SEM. SEM analysis is prepared on JEOL scanning electron spectroscopy machine. Before focusing electron beam on the samples, the samples were gold-sputtered in order to make them conducting. Thermogravimetric Analysis Thermogravimetric analysis were performed with an SII 6300 EXSTAR TG-DTA (Japan). Samples of 5 mg were placed in the TGA furnace and the measurements were carried out under a nitrogen atmosphere with a heating rate of 10 C/mins. from 0 to 700 o C. Weight losses of the samples were determined with respect to temperature. RESULT AND DISCUSSION The effect of different reaction parameters such as monomer concentration, initiator concentration, cross-linker concentration, time and temperature on the cross-linking was shown in Table 1. Sample No. Moles of Acrylic Acid [AA] Moles of [Ce IV] 103 [MBAM] x 103 mol/l Time (hours) Temp. ( C) Percentage Cross-Linking (%) J. Technological Advances and Scientific Res./eISSN , pissn / Vol. 2/ Issue 04/ Oct-Dec Page 186

3 Table 1. Details of Cross-Link Reactions Effect of Monomer Concentration The effect of monomer concentration on cross-linking shown in Figure 2. The best PG was obtained for moles of AA. The increase of PG till moles was expected with increase in AA concentration due to the availability of AA monomer with respect to polysaccharide macro radicals leading to larger possibility of cross-linking. When more than moles of AA was taken in the reaction medium, the formation of homopolymers, i.e. PAA hindered the rates of penetration of monomer molecules to the polysaccharide free radicals resulting in decrease in PG. Effect of Cross-Linker Concentration The effect of cross-linker concentration on percentage of cross-linking is shown in Figure 4. On increasing the concentration of cross-linker from 0.8 moles to 2.4 x 10-3 moles, PG increased due to increase in the free radicals on polysaccharide chain. With further increase in cross-linker Concentration up to 3.2 x 10-3 moles, PG decreased. Figure 2. Effect of Monomer Concentration Effect of Initiator (CAN) Concentration The effect of initiator concentration (CAN) on percentage of grafting is shown in Figure 3. On increasing the concentration of initiator, i.e. CAN from 0.5 x 10-3 moles to 1.5 x 10-3 moles, PG increased due to increase in the free radicals on polysaccharide chain. With further increase in CAN concentration up to 2.0 x 10-3 moles, PG decreased. The falling of PG at higher CAN concentration is a well-known phenomenon and ascribed to the increasing participation of the ceric ion in the termination of the growing cross-linked chains. Figure 4. Effect of Cross-Linker (N, N -MBAAm) Concentration on Cross-Linking (%) [AA] = mol/l; [CAN] = x 10-3 mol/l; reaction time = 2 hrs. Effect of Reaction Temperature Reaction temperature is an important reaction condition in the cross-link copolymerisation. The effect of temperature on percentage of cross-link is shown in Figure 5. Percentage cross-link increased with increase in the temperature. Figure 3. Effect of Initiator (CAN) Concentration Figure 5. Effect of Temperature on Cross-Linking (%) J. Technological Advances and Scientific Res./eISSN , pissn / Vol. 2/ Issue 04/ Oct-Dec Page 187

4 [AA] = mol/l; [CAN] = 0.15 x 10-3 mol/l; reaction time = 3 hrs. Effect of Time The effect of time on % crosslinking is shown in Figure 6. The percentage cross-link increased with an increase in the reaction time. This agrees with the earlier observation with free radical initiated polymerisation. Figure 7b. IR Spectrum of Psy-cl-PAA Figure 6. Effect of Time on Cross-Linking (%) [AA] = 0.18 mol/l; [CAN] = 0.15 x 10-3 mol/l Characterisation of Psy-cl-PAA/FTIR The FTIR spectra of pure psyllium and Psy-cl-PAA are shown in Figure 7a and 7b, respectively. The FTIR spectra of purified psyllium shows characteristic peaks of -OH between 3472 cm -1, -CH stretching between 2923 cm -1, -CO stretching at 1040 and 1644 cm -1 and -CH3 at 2923 cm -1. In the crosslinked sample of Psy-cl-PAA, the characteristic absorption at cm -1 of C=O (Figure 7b) indicates cross-linking of PAA with psyllium. The O-H stretching frequency at 3420cm -1 in the cross-linked product is broader as compared to that in the spectrum of psyllium. This is due to unequal hydrogen bonding in the cross-linked product again attributing to the fact that cross-linking has occurred. SEM Analysis of Psyllium and Psy-cl-AA The surface morphology of the pure psyllium and Psy-cl-AA is studied with the help of SEM. SEM analysis is made on JEOL scanning electron spectroscopy machine. Before focusing the electron beam on the samples, the samples were goldsputtered in order to make them conducting. Figure 8a,b shows the morphology of pure psyllium and Psy-cl-AA at different magnifications. The SEM micrograph of the psyllium matrix was rather a smooth, porous and heterogeneous surface as shown in (Figure 8a). It has been confirmed that cross-linked polymerisation of acrylic acid improved the surface morphology of psyllium. The SEM images clearly indicated the smooth and homogeneous morphology structure of the Psy-cl-AA shown in Figure 8b. The effective cross-linking of poly (AA) with psyllium has also been confirmed. Scanning Electron Micrographs (SEM) image designated the uniform distribution of poly (AA) modified the native properties of psyllium. Figure 7a. IR Spectrum of Psyllium Mucilage Figure 8. SEM Images of the (a) Psyllium (Insert), (b) Psy-cl-AA J. Technological Advances and Scientific Res./eISSN , pissn / Vol. 2/ Issue 04/ Oct-Dec Page 188

5 Thermal Study Thermal behaviour of the pure psyllium and Psy-cl-AA are analysed by thermal gravimetric analysis and results has been shown in Figure 9. As shown in Figure 4a, psyllium show two thermal degradation stages and Psy-cl-AA also show two thermal degradation stages. It indicates the thermal stability of psyllium increased after the cross-linking of acrylic acid on to the psyllium. Figure 9. TGA Curves of Psyllium and Psy-cl-AA. CONCLUSION Cross-linking of psyllium mucilage to prepare its acrylic acid grafted copolymer has been done successfully by using a CAN/Vit C redox initiator system. The maximum percent cross-linking (90%) was obtained when acrylic acid and CAN concentrations in reaction mixture were mol/l and 0.15 x 10-3 moles, respectively. The FTIR spectrum, SEM, TGA confirmed the cross-linking of acrylic acid onto the psyllium mucilage chains. REFERENCES 1. Hosseini M, Salari M, Salari R. Psyllium seed may be effective in the treatment of gastroesophageal reflux disease (GERD) in patients with functional constipation. Journal of Medical Hypotheses and Ideas 2015;9(2):S4- S7. 2. Ladjevardi ZS, Gharibzahedi SMT, Mousavi M. Development of a stable low-fat yogurt gel using functionality of psyllium (plantago ovate forsk) husk gum. Carbohydrate Polymers 2015;125: Rao MRP, Warrier DU, Gaikwad SR, et al. Phosphorylation of psyllium seed polysaccharide and its characterization. International Journal of Biological Macromolecules 2016;85: Belščak-Cvitanović A, Komes D, Karlović S, et al. Improving the controlled delivery formulations of caffeine in alginate hydrogel beads combined with pectin, carrageenan, chitosan and psyllium. Food Chemistry 2015;167: Farahnaky A, Askari H, Majzoobi M, et al. The impact of concentration, temperature and ph on dynamic rheology of psyllium gels. Journal of Food Engineering 2010;100(2): Guo Q, Cui SW, Wang Q, et al. Microstructure and rheological properties of psyllium polysaccharide gel. Food Hydrocolloids 2009;23: Kaith BS, Kumar K. In vacuum synthesis of psyllium and acrylic acid based hydrogels for selective water absorption from different oil-water emulsions. Desalination 2008;229(1-3): Thakur VK, Thakur MK. Recent trends in hydrogels based on psyllium polysaccharide: a review. Journal of Cleaner Production 2014;82: Singh B, Chauhan GS, Kumar S, et al. Synthesis, characterization and swelling responses of ph sensitive psyllium and polyacrylamide based hydrogels for the use in drug delivery (I). Carbohydrate Polymers 2007;67(2): Singh B, Chauhan N, Kumar SR. Radiation crosslinked psyllium and polyacrylic acid based hydrogels for use in colon specific drug delivery. Carbohydrate Polymers 2008;73(3): Singh B, Chauhan N, Kumar S, et al. Psyllium and copolymers of 2-hydroxylethylmethacrylate and acrylamide-based novel devices for the use in colon specific antibiotic drug delivery. International Journal of Pharmaceutics 2008;352(1-2): Singh B, Kumar S. Synthesis and characterization of psyllium-nvp based drug delivery system through radiation crosslinking polymerization. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 2008;266(15): Singh B, Sharma N, Chauhan N. Synthesis, characterization and swelling studies of ph responsive psyllium and methacrylamide based hydrogels for the use in colon specific drug delivery. Carbohydrate Polymers 2007;69(4): Levin EG, Miller VT, Stoy DB, et al. Comparison of psyllium hydrophilic mucilloid and cellulose as adjuncts to a prudent diet in the treatment of mild to moderate hypercholesterolemia. Journal of the American College of Cardiology 1990;15(2s1):A Singh B, Chauhan N. Release dynamics of tyrosine from dietary fiber psyllium based hydrogels for use in Parkinson s disease. Food Research International, 2010;43(4): Singh B, Sharma V. Design of psyllium-pva-acrylic acid based novel hydrogels for use in antibiotic drug delivery. International Journal of Pharmaceutics 2010;389 (1-2): Kumar D, Khan N, Kumar P. Improve the native characteristics of polysaccharides by grafting through the gamma radiation: a review. Green Chemistry & Technology Letters 2016;2(3): J. Technological Advances and Scientific Res./eISSN , pissn / Vol. 2/ Issue 04/ Oct-Dec Page 189