Synthesis and Superswelling Behavior of Carboxymethylcellulose–Poly(sodium acrylate-co-acrylamide) Hydrogel Mohammad Sadeghi, 1 Hossein Hosseinzadeh 2 1 Department of Chemistry, Science Faculty, Islamic Azad University, Arak Branch, Arak, Iran 2 Polymer Research Laboratory, Department of Chemistry, Sharif University of Technology, Tehran, Iran Received 18 June 2006; accepted 3 March 2007 DOI 10.1002/app.26464 Published online 23 January 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: In this paper, attention is paid to synthesis and swelling behavior of a superabsorbent hydrogel based carboxymethylcellulose (CMC) and polyacrylonitrile (PAN). The physical mixture of CMC and PAN was hydrolyzed in NaOH solution to yield hydrogel, CMC–poly(NaAA-co- AAm). During alkaline hydrolysis, the nitrile groups of PAN were completely converted to a mixture of hydro- philic carboxamide and carboxylate groups followed by in situ crosslinking of the grafted PAN chains. A proposed mechanism for hydrogel formation was suggested and the structure of the product was established using FTIR spec- troscopy. The reaction variables affecting the swelling capacity of the hydrogel were systematically optimized to achieve a hydrogel with swelling capacity as high as possi- ble. Swelling measurements of the synthesized hydrogels in various chloride salt solutions indicated a swelling-loss with increase in the ionic strength of the salt solutions. The pH of the various solutions also affected the swelling of the superabsorbent. Furthermore, the present hydrogels showed a pH-reversible property. Finally, the swelling kinetics of synthesized hydrogels with various absorbent particle sizes was briefly examined. Ó 2008 Wiley Periodicals, Inc. J Appl Polym Sci 108: 1142–1151, 2008 Key words: hydrogel; superabsorbent; carboxymethylcel- lulose; polyacrylonitrile; swelling behavior; crosslinking INTRODUCTION In recent years, interest in natural-based superab- sorbent hydrogel has increased, mainly due to high hydrophilicity, biocompatibility, nontoxicity, and biodegradability of biopolymers. These materials are defined as crosslinked macromolecular networks that can absorb water or physical fluids up to many times of their own weight in a short time, but are not dissolved when brought into contact with water. 1 The absorbed fluids are hardly removable even under some pressure. Because of excellent char- acteristics, superabsorbent hydrogels are widely used in many fields, such as agricultural and horti- cultural, disposable diapers, feminine napkins, phar- maceuticals, and medical applications. 2–4 This ac- counts for increase in the worldwide production of superabsorbent polymers (SAPs) from 6000 tons in 1983 to 450,000 tons in 1996. 1 Nowadays, the world- wide production of SAPs is more than one million tons in year. Hence, synthesis and investigation of specific and new superabsorbent hydrogels with high absorbency, mechanical strength, and initial absorption rate has been the goal of several research groups in the past decades. 5–8 Because of their exceptional properties, i.e., bio- compatibility, biodegradability, renewability, and nontoxicity, polysaccharides are the main part of the natural-based superabsorbent hydrogels. Carboxy- methylcellulose (CMC), an anionic water-soluble polysaccharide, is the most modified cellulose, which is used in various fields such as detergent, food, pa- per, and textile industries. The application potential of CMC has been demonstrated because of its prom- ising characteristics including those of mentioned above. Most of ionic hydrogels sometimes undergo a vol- ume phase transition in response to a little change in surrounding conditions such as heat, pH, electric field, chemical environments, etc. The hydrogels that respond to external stimuli are often referred to as ‘‘intelligent’’ or ‘‘smart’’ hydrogels. They have im- portant applications in the field of medicine, phar- macy, and biotechnology. Among these, pH-sensitive hydrogels have been extensively investigated for potential use in site-specific delivery of drugs to spe- cific regions of the gastrointestinal tract and have been prepared for delivery of low molecular weight (MW) protein drugs. 9,10 Free radical graft copolymerization of vinylic monomers onto polysaccharide backbones followed Correspondence to: M. Sadeghi (m-sadeghi@iau-arak. ac.ir). Journal of Applied Polymer Science, Vol. 108, 1142–1151 (2008) V V C 2008 Wiley Periodicals, Inc.