Journal of Water Resource and Protection, 2011, 3, 380-386 doi:10.4236/jwarp.2011.36048 Published Online June 2011 (http://www.scirp.org/journal/jwarp) Optimization of Ceric Ammonium Nitrate Initiated Graft Copolymerization of Acrylonitrile onto Chitosan Arumugam Shanmugapriya1, Ramya Ramammurthy2, Venkatachalam Munusamy3 , Sudha N. Parapurath4 1Bharathiar University, Coimbatore, Tamil Nadu, India 2Department of Chemistry, Manonmaniam Sundaranar University, Tirunelveli, Tamil Nadu, India 3Department of Chemistry, Dravidian University, Kuppam, Andhra Pradesh, India 4DKM College, Thiruvalluvar University, Vellore, Tamil Nadu, India E-mail: [email protected] Received March 14, 2011; revised April 21, 2011; accepted May 25, 2011 Abstract In the present work, graft copolymerization of polyacrylonitrile onto chitosan has been carried out in the pre- sence of ceric ammonium nitrate redox initiator. Optimization of grafting of polyacrylonitrile onto chitosan was performed by varying the process parameters such as ceric ammonium nitrate (CAN) concentration, polyacrylonitrile concentration and reaction time to study their influence on percent grafting and grafting ef- ficiency. The optimum reaction conditions obtained for grafting of acrylonitrile onto chitosan were reaction time 55 mins, CAN concentration 1% in Con. HNO3, and polyacrylonitrile concentration 0.75 mol/L. The characterization of the grafted products by means of FTIR, thermal analysis, X-ray diffraction and scanning electron microscopy furnished the evidence of grafting of polyacrylonitrile onto chitosan. Keywords: Chitosan-g-polyacrylonitrile, Ceric ammonium nitrate, Grafting efficiency, Grafting yield 1. Introduction synthetic polymers increased its properties tremendously. Besides these applications chitosan has few drawbacks Chitosan is a unique basic polysaccharide and partially such as acidic solubility, low thermal and mechanical deacetylated polymer of glucosamine obtained after alka- stability. To improve these drawbacks, chitosan can be line deacetylation of the chitin [1]. It consists of mainly modified physically and also chemically. Now days, a lot of β-[1-4]-2-acetamido-2-deoxy-D-glucose units and is of attention has been paid on chemical modification of the second most abundant biopolymer on earth after cell- chitosan. One such important modification is graft ulose, widely distributed in crustacean shells and cell copolymerization [6-9]. Of all possible modifications, walls of fungus [2,3]. Chitosan is soluble in dilute acids. graft copolymerisation of vinyl monomers onto natural The solubility occurs by the protonation of the –NH2 polysaccharides is quite promising [10,11]. function on the C-2 position of the D-glucosamine repeat Grafting onto chitosan and its derivatives has been the unit, where by the polysaccharide is converted to a thrust of researchers. In chitosan, both hydroxyl and polyelectrolyte in acidic media. Chitosan is the only pse- amino groups are possible sites for the reaction to incorp- udonatural cationic polymer and thus it finds applications orate new and desired functional groups. Graft copolym- in the wastewater treatment. A few review articles on the erization of synthetic polymers onto chitosan can potential applications of chitosan for pharmaceutical, introduce desired properties and enlarge the field of the veterinary medicine, and biomedicine. Chitin and applications by choosing various types of side chains. chitosan are widely used for wastewater treatments of In recent years, a number of initiator systems such as polymers experimentally proven that decrease the APS (ammonium per sulphate), PPS (potassium per chemical oxygen demand, total nitrogen and destroy the sulphate), CAN (ceric ammonium nitrate), FAS (ferrous microbial population [4,5]. However, due to its low ammonium sulphate) have been developed to initiate mechanical strength and flexible behaviour, chitosan has graft copolymerization [6,12-14]. Many investigations limited application of water treatment, while addition of have been carried out on the grafted copolymerization of Copyright © 2011 SciRes. JWARP A. SHANMUGAPRIYA ET AL. 381 chitosan and it is considered to be a promising approach Wi = weight of homopolymer (polyacrylonitrile), respec- for designing a wide variety of molecular matrices. Graft tively copolymerization of acrylamide on chitosan using ammonium persulfate as an initiator, was prepared [15]. 2.3. Characterization The effect of temperature, pH of the medium and concentrations of initiator, chitosan and acrylamide on 2.3.1. FTIR Spectral Studies grafting kinetics and efficiency were established. Graft Fourier Transform infrared (FTIR) spectral analyses of copolymerization of mixtures of acrylic acid and acryla- the copolymer samples were performed with Thermo mide onto chitosan using potassium per sulphate as initia- Nicolet AVATAR 330 spectrophotometer in 4000-400 tor and methylenebisacrylamide as a cross-linker was carr- cm–1 wave length range, using KBr pellet method. ied [16]. Semi-interpenetrating polymer network hydrogel was pre-pared to recognize hemoglobin, by molecularly 2.3.2. Thermo Gravimetric Analysis imprinted method, in mild aqueous media of chitosan Thermogravimetric analysis was conducted to measure and acylami-de in the presence of N, N’-methylenebisa- the thermal weight loss of the copolymers on a SDT crylamide as the cross linking agent [17]. Q600 V8.0 Build 95 instrument at a heating rate of In the present study chitosan has been graft copolyme- 100˚C per minute in nitrogen atmosphere. The weight rized with acrylonitrile with an aim to develop a product, losses at different stages were analysed. which could be used for wastewater treatment. The effect of reaction conditions such as monomer concentration, 2.3.3. Differential Scanning Calorimetry initiator concentration and time of reaction have been The differential scanning calorimeter (DSC) was used to optimized at constant temperature of 70˚C. examine the thermal property of the copolymers. The measurements were performed with NETZSCH DSC 2. Methods and Materials 200 PC in a pan Al, pierced lid in the N2 atmosphere at a heating rate of 100 K /min. The results were recorded 2.1. Materials and analysed. Chitosan was received from India seafoods, Cochin. 2.3.4. X – Ray Diffraction Studies Ceric ammonium nitrate, concentrated nitric acid and X–ray diffraction (XRD) patterns of the Chito- acrylonitrile were of analytical grade and used as re- san-g-acrylonitrile copolymer was studied using X-ray ceived. The copolymer was characterized using FTIR, powder diffractometer (XRD – SHIMADZU XD – D1) TGA, DSC, SEM and XRD. Chitosan-g-polyacrylonitrile using a Ni – filtered Cu K X–ray radiation source. The was prepared in the presence of UV light assisted oxida- relative intensities were recorded within the range of 100 tive polymerisation using CAN as an initiator. -900 (2) at a scanning rate of 50 min–1. 2.2. Preparation of Copolymer 2.3.5. Scanning Electron Microscopy (SEM) The surface morphology and cross sectional morphology A 2% w/v solution of chitosan was prepared in 2% of the copolymer was observed with scanning electron aqueous acetic acid. A solution of 0.1 M CAN in 10 ml microscopy to verify the compatibility. For the analysis, of 1 N nitric acid was added followed by a known the samples were cut into pieces of various sizes and amount of acrylonitrile drop by drop with continuous wiped with a thin gold-palladium layer by a sputter stirring. After a specified time, the reaction was stopped coater unit (VG-microtech, UCK field, UK) and the and the product was precipitated using sodium hydroxide cross section topography was analysed with a Cambridge solution with vigorous stirring. The precipitate was stereoscan 440 scanning electron microscope (SEM, washed with distilled water for several times and filtered. Leica, Cambridge, UK). The percent grafting yield (GY%) and percent grafting efficiency (GE%) were calculated as follows: 3. Results and Discussion Wg Grafting efficiency (GE%) = 100 The grafting of zwitterionic monomer, N, N-dimethyl-N- WWgi methacryloxy-N-(3-sulfopropyl) ammonium onto chito- WWgi Grafting yield (GY%) = 100 san using CAN as redox initiator in acetic acid solution Wi under nitrogen atmosphere was investigated [18]. The where, effect of reaction condition on the rate of poly (acryloni- Wg = weight of grafted copolymer; trile) grafting onto chitosan under inert atmosphere using Copyright © 2011 SciRes. JWARP 382 A. SHANMUGAPRIYA ET AL. CAN as initiator was studied [19]. CAN is also reported change in graft efficiency with increase in reaction time, as a suitable initiator for grafting poly (acryloamide), whereas, grafting yield is significantly changed with re- acrylic acid, poly (4-vinylpyridine) onto chitosan [6]. action time. As a result, the maximum yield has been found at 55 min. Hence 55 min was found to be rate of 3.1. Mechanism grafting [20, 21]. Graft copolymerization of vinyl monomers onto chitosan 3.3 Effect of Initiator (CAN) Concentration is also carried out using redox initiator system such as CAN. This system is used to produce free radical sites Figure 2 shows the effect of concentration of CAN on the which may improve the properties of chitosan material graft copolymerization of polyacrylonitrile onto chitosan and hence the graft polymerization of acrylonitrile onto by keeping other reaction conditions constant. Both graft chitosan at 60˚C by using CAN as a initiator is reported. yield and grafting efficiency showed an increase with in-