The effects of concentrations of peroxymonosulphate, mercaptosuccinic acid, hydrogen ion, acrylic acid, and carrageenan on grafting parameters were studied to find out the maximum grafting ratio. The corresponding values were found to be , , , ？mol？dm？3, and ？g？dm？3, respectively. The optimal reaction time duration and reaction temperature were found to be 120？min and 40°C, respectively. The effect of hydrogen ion variation from 5.0 up to ？mol？dm？3 shows prompt changes on grafting parameter. The grafted copolymer was found more thermally stable than the ungrafted substrate. Also the grafted copolymer absorbed more water, namely hazardous metal cations. Hg2+, Pb2+, and Cd2+, showed better flocculation behavior than carrageenan. 1. Introduction Currently the commercial application of natural polymers and their derivatives is most captivating and immeasurably investigated. For this purpose, biodegradable natural polymers, such as polysaccharides and protein, have been widely used [1, 2]. Amongst the natural polysaccharides, carrageenan is widely applied due to its anionic nature. It is extracted from red seaweed and obtained from the cell wall of Rhodophyceae (red algae) belonging mainly to the genera Chondrus, Gigartina, Kappaphycus, and Eucheuma [3, 4]. Carrageenan is a linear polymer of about 25,000 galactose derivatives with regular but imprecise structures, depending on the source and extraction conditions. Carrageenans are usually classified according to their sulphate content. From an industrial application point of view, the most important configurations are the (kappa), (iota), and (lambda) forms; their structures differ mostly in the number of sulphated groups per disaccharide: one, two, or three for , , and , respectively. They are composed of alternation-( )- -D-galactopyranose-4-sulfate-( )-3,6-anhydro- -D-galactopyranose-( ) (Figure 1) which are well documented [5–9]. The presence of 3,6-anhydro-D-galactose and conformation of the pyranoside ring are responsible for their interesting rheological properties. -carrageenan is widely used as a thickening and gelling agent in food industry [10–12]. -carrageenan undergoes a coil (disordered state) to helix (ordered) transition, depending on temperature and ionic environment. Gelation is achieved through junction zones formed by the helices, leading to a three-dimensional network [5]. Figure 1: Structure of -carrageenan[-(1,3)- -D-galactopyranose-4-sulphate-(1,4)-3,6-anhydro- -D-galactopyranasoe(1,3)-]. Gelation of -carrageenan is enhanced mainly by calcium, and -carrageenan is enhanced by
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