Synthesis of cellulose-based superabsorbent hydrogels by high-energy irradiation in the presence of crosslinking agent Tamás Fekete a,b , Judit Borsa b,c , Erzsébet Takács a,c,n , László Wojnárovits a a Institute for Energy Security and Environmental Safety, Centre for Energy Research, Hungarian Academy of Sciences, Budapest, Hungary b Faculty of Chemical Technology and Biotechnology, Budapest University of Technology and Economics, Hungary c Faculty of Light Industry and Environmental Engineering, Obuda-University, Hungary HIGHLIGHTS  Cellulose derivative based hydrogels were prepared by radiation-induced crosslinking.  N,N’-methylene-bis-acrylamide was used as a crosslinker to improve gel properties.  The crosslinker improved the gel fraction at the expense of lower water uptake.  The gelation occurred at milder conditions in the presence of crosslinking agent.  The sensitivity to ionic strength decreased with the equilibrium water uptake. article info Article history: Received 24 November 2014 Received in revised form 3 February 2015 Accepted 23 February 2015 Keywords: Cellulose derivative N,N’-methylene-bis-acrylamide Superabsorbent Hydrogel Crosslinking abstract Superabsorbent hydrogels were prepared from aqueous solutions of four cellulose derivatives (carbox- ymethylcellulose Na-salt – CMC, methylcellulose – MC, hydroxyethylcellulose – HEC and hydro- xypropylcellulose – HPC) by gamma irradiation initiated crosslinking. CMC was used for the majority of the measurements. N,N’-methylene-bis-acrylamide (MBA) crosslinking agent was used to modify the gel properties. The crosslink density increased with the MBA concentration, leading to an improved gel fraction and lower water uptake. The crosslinking efficiency was the highest up to 1 w/w polymer % MBA concentration. Very high MBA content (10 w/w polymer %) led to a heterogeneous gel structure. Gelation also occurred under milder conditions in the presence of MBA: good gel properties were achieved at significantly lower doses and solute concentrations as compared to crosslinker-free solutions. The time required to reach maximum water uptake increased with the degree of swelling in equilibrium. Swelling properties of CMC gels with lower water uptake showed lower sensitivity to the ionic strength of the solvent. & 2015 Elsevier Ltd. All rights reserved. 1. Introduction An interesting and growingly popular potential application of cellulose, the most abundant renewable material on earth, is the synthesis of superabsorbent hydrogels. Superabsorbents are three- dimensional polymer networks with very high water absorption capacity. Synthetic-polymer based superabsorbent gels are widely used for practical applications; however, there is an increasing interest in using renewable materials like cellulose. Gel can be produced from pure cellulose, however, it requires special solvents for dissolution (Saito et al., 2003; Li et al., 2009; Kimura et al., 2014). Thus the gel preparation from various water soluble cellulose derivatives is easier. For gel synthesis usually cellulose derivatives containing carboxymethyl, alkyl or hydro- xyalkyl groups are used (Chang and Zhang, 2011). It should be noted that beside the substituent, the polymer properties, such as molecular weight and degree of substitution also affect the poly- mer solubility (Burchard, 2003). Gel formation of cellulose derivatives can be achieved with various methods. While physical gels were also prepared from several derivatives (Haque and Morris, 1993; Sarkar, 1995), che- mical crosslinking is more commonly used (Harsh and Gehrke, 1991). Chemically crosslinked gel can be prepared by free-radical initiation using an initiator compound, or by high energy irradia- tion. In the latter method radicals are formed on the polymer Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/radphyschem Radiation Physics and Chemistry http://dx.doi.org/10.1016/j.radphyschem.2015.02.023 0969-806X/& 2015 Elsevier Ltd. All rights reserved. n Corresponding author at: Institute for Energy Security and Environmental Safety, Centre for Energy Research, Hungarian Academy of Sciences, Budapest, Hungary. Fax: þ36 1 392 2548. E-mail address: erzsebet.takacs@energia.mta.hu (E. Takács). Please cite this article as: Fekete, T., et al., Synthesis of cellulose-based superabsorbent hydrogels by high-energy irradiation in the presence of crosslinking agent. Radiat. Phys. Chem. (2015), http://dx.doi.org/10.1016/j.radphyschem.2015.02.023i Radiation Physics and Chemistry ∎ (∎∎∎∎) ∎∎∎–∎∎∎