Modern Applied Science; Vol. 7, No. 8; 2013 ISSN 1913-1844 E-ISSN 1913-1852 Published by Canadian Center of Science and Education 22 Synthesis of Hydrogel Film Based on Carrageenan Extracted from Kappaphycus alvarezii Sperisa Distantina 1,2 , Rochmadi 1 , Mohammad Fahrurrozi 1 & Wiratni 1 1 Department of Chemical Engineering, Gadjah Mada University, Yogyakarta, Indonesia 2 Department of Chemical Engineering, Sebelas Maret University, Surakarta, Indonesia Correspondence: Sperisa Distantina, Department of Chemical Engineering, Sebelas Maret University, Jl. Ir. Sutami 36 A, Surakarta 57126, Indonesia. Tel: 62-274-632-112. E-mail: distantina@uns.ac.id Received: May 3, 2013 Accepted: June 27, 2013 Online Published: July 5, 2013 doi:10.5539/mas.v7n8p22 URL: http://dx.doi.org/10.5539/mas.v7n8p22 Abstract Hydrogel based on kappa carrageenan extracted from Kappaphycus alvarezii was synthesized by film immersion in glutaraldehyde solution (GA 4% w/w) as crosslinker for 2 min and then followed by thermal curing at 110 o C for 25 min. The obtained crosslinked films were washed using ethanol to remove the unreacted crosslinker and finally dried to constant weight. The aim of this research was to investigate the effect of carrageenan recovery method on the prepared hydrogel properties. The method of carrageenan extraction strongly determined the swelling properties of crosslinked carrageenan. Hydrogel obtained from alkali treated carrageenan showed higher swelling ability compared to hydrogel from nonalkali treated carrageenan. Hydrogel from alkali treated carrageenan showed the ability of sensitive to pH media. Swelling degree of alkali treated carrageenan based hydrogels increased by increasing pH solution from about 5 g/g for neutral pH to 20 g/g for pH~13. Keywords: hydrogel, kappa carrageenan, glutaraldehyde, swelling, Kappaphycus alvarezii 1. Introduction Hydrogels are tridimensional networks of hydrophilic polymers which are able to swell in water. Hydrogel ability to swell in response to external stimuli as pH, ionic strength, temperature, electric fields depends on the nature of polymer chains and allows hydrogels useful in application such as controlled drug delivery, separation process or agricultural application (Hoffman, 2002; Gerlach et al., 2005; Peppas, 2004; Samchenko et al., 2011). Nowadays, preparation of hydrogels based on natural polymers especially polysaccharides have been explored extensively. Compared to synthetic polymer, the polysaccharides-based hydrogels exhibit several advantages, such as renewability, biodegradability and cheaperness because the raw materials are locally abundant. The biocompatibility of polysaccharides is very interesting characteristic of material, mainly on biomedical applications. In this research, we converted polysaccharide extracted from seaweed into hydrogel. Kappa carrageenans are linear polysaccharides sulfated galactan extracted from red seaweed (Rhodophyta), such as Kappaphycus alvarezii (known as Eucheuma cottonii in industry) which is well cultivated in Indonesia. This natural polymers comprise of repeating units of (1,3)-D-galactopyranose and (1,4)-3,6-anhidro-α-D- galactopyranose with sulfate groups in a certain amount and position (Campo et al., 2009). The presence of hydroxyl groups and sulfate groups in carrageenan structure cause the carageenan tend to be hydrophilic. Kappa carageenans have ability to form thermoreversible gel. Because of their gelling ability, carrageenans are widely used as agent for thickening and gelling in food and nonfood industries (Van de Velde et al., 2002), and potent as raw materials of hydrogels (Hoffman, 2002). Some gel applications need hydrogel properties which mainly can absorb and keep water without dissolution. For improving the stability in aqueous, the kappa carrageenan structures must be chemically crosslinked to produce hydrogel structure. Preparation of hydrogel of kappa carrageenan graft polyacrylamide has been studied by Abd El-Mohdy and Abd El-Rehim (2009). Previous studies reported the preparation of kappa carrageenan base hydrogel by crosslinking with epichlorohydrine (Keppeler et al., 2009), CaCl 2 (Pascalau et al., 2012), and genipin (Meena et al., 2007). To our best knowledgde, crosslinking carrageenan with glutaraldehyde into hydrogel film has not been reported. In this work, glutaraldehyde was chosen as the crosslinker. Glutaraldehyde is easily available and inexpensive. Its aqueous solution is known as an effective crosslinker for natural polymer, such as guargum (Cunha et al., 2005),