INTRODUCTION Highly swelling polymers, i.e. super absorbent hydrogels, are hydrophilic, three dimensional networks that can absorb water in the amount from 10% up to thousands of times their dry weight. They are widely used in various applications such as hygienic, foods, cosmetics, and agriculture 1 . This accounts for increase in the worldwide production of superabsorbent polymers (SAPs) from 6000 tons in 1983 to 450000 tons in 1996 2-4 . Nowadays, the worldwide production of SAPs is more than one million tons in year. Hence, synthesis and characterization of superabsorbent hydrogels is the main goal of the several research groups in the world 3-6 . Pectin is a naturally occurring biopolymer that is finding increasing applications in the pharmaceutical and biotechnology industry. It has been used successfully for many years in the food and beverage industry as a thickening agent, a Current World Environment Vol. 7(1), 69-77 (2012) Synthesis and Investigation of a Novel pH- and Salt-Responsive Superabsorbent Hydrogel Based on Pectin MOHAMMAD SADEGHI*, ESMAT MOHAMMADINASAB and FATEMEH SHAFIEI Department of Chemistry, Science Faculty, Islamic Azad University, Arak Branch, Arak (Iran). (Received: March 25, 2012; Accepted: April 13, 2012) ABSTRACT In the present paper, attention is paid to synthesis and investigates swelling behavior of a superabsorbent hydrogel based on Pectin (Pec) and polyacrylic acid (PAcA). acrylic acid (AcA) was graft copolymerized onto Pectin backbones by a free radical polymerization technique using ammonium persulfate (APS) as initiator and methylene bisacrylamide (MBA) as a crosslinker. A proposed mechanism for hydrogel formation was suggested and the structure of the product was established using FTIR and SEM spectroscopies. Under the optimized conditions concluded, maximum capacity of swelling in distilled water was found to be 348 g/g. Absorbency of the synthesized hydrogels was also measured in NaCl and CaCl 2 salt solutions. Results indicated that the swelling ratios in compare to water decreased with an increase in the ionic strength of solution. In addition, swelling capacity was conducted in solutions with pH ranged from 1 to 13. The H-Pec- poly(sodium acrylate) hydrogel exhibited a pH-responsiveness character so that a swelling- deswelling pulsatile behavior was recorded at pHs 3 and 9. Key words: Pectin, Hydrogel, pH- and salt-responsive, Acrylic acid monomer. gelling agent and a colloidal stabiliser. Pectin also has several unique properties that have enabled it to be used as a matrix for the entrapment and/or delivery of a variety of drugs, proteins and cells. The modification of natural polymers is a promising method for the preparation of superabsorbt hydrogels. Graft copolymerization of vinyl monomers onto natural polymers is an efficient approach to achieve these materials. Superabsorbing resins were first developed with a view to utilizing agricultural materials, and are typed by the hydrolyzed starch-g-poly(acrylonitrile), H- SPAN 6 . Since then, starches from different resources as well as other polysaccharides, for example, cellulose 8 , hydroxyethyl cellulose, agar , sodium alginate and guar gum were graft copolymerized to achieve water absorbing polymers. Polyacrylonitrile (PAN), polyacryamide, and poly(acrylic acid) 10-11 have been frequently grafted, mostly onto starch, using different initiators especially the ceric-saccharide redox system 12 .