Radiation crosslinking of methylcellulose and hydroxyethylcellulose in concentrated aqueous solutions Radoslaw A. Wach a, * , Hiroshi Mitomo a , Naotsugu Nagasawa b , Fumio Yoshii b a Department of Biological and Chemical Engineering, Faculty of Engineering, Gunma University, Kiryu 376-8515, Japan b Takasaki Radiation Chemistry Research Establishment, Japan Atomic Energy Research Institute, Takasaki 370-1292, Japan Received 24 February 2003; received in revised form 19 May 2003 Abstract The effects of ionizing radiation on aqueous solutions of cellulose ethers, methylcellulose (MC) and hydroxyethylcel- lulose (HEC) were investigated. The well-established knowledge states that cellulose and its derivatives belong to degrading type of polymers. However, in our study intermolecular crosslinking initiated by gamma rays or electron beam leaded to the formation of insoluble gel. This is an opposite effect of irradiation to the degradation. Paste-like form of the initial specimen, i.e. concentration 20–30%, when water plasticizes the bulk of polymer; and a high dose rate were favorable for hydrogel formation. Gel fraction up to 60% and 70% was obtained from solutions of HEC and MC, respectively. Produced hydrogels swell markedly in aqueous media by imbibing and holding the solvent. Radiation parameters of irradiation, such as yields of degradation and crosslinking and the gelation dose, were evaluated by sol–gel analysis on the basis of Char- lesby–Rosiak equation. Despite of the crosslinked structure, obtained hydrogels can be included into the group of bio- degradable materials. They undergo decomposition by the action of cellulase enzyme or microorganisms from compost. Ó 2003 Elsevier B.V. All rights reserved. PACS: 61.25.H; 61.82.P; 81.05; 82.70.G Keywords: Hydrogels; Methylcellulose; Hydroxyethylcellulose; Crosslinking; Radiation yield; Biodegradation 1. Introduction Irradiation of polymeric materials generates some effects depending on the kind of polymer, parameters of irradiation, the state of the material under processing, etc. The two main reactions, which determine the final properties of the poly- mer, include (a) scission of main chain, leading to the diminishing of the molecular weight of mac- romolecules and (b) crosslinking, the opposite process ending with macroscopic, insoluble mate- rial [1]. The yields of scission and crosslinking, or more precisely the mutual ratio of these two pa- rameters, determine the outcome. To achieve the desired aim, irradiation of polymeric material can be conducted under special conditions. Particu- larly, the state of material under processing is of a great significance. Thus, an elevated temperature, the polymer is in molten state, is often use [2]. Dose rate can be the variable; irradiation with EB * Corresponding author. Present address: Nuclear Engineer- ing Research Laboratory, The University of Tokyo, 2-22 Shirakata-Shirane, Tokai-mura, 319-1188 Ibaraki-ken, Japan. Tel.: +81-29-287-8984; fax: +81-29-287-8488. E-mail address: rawach@utnl.jp (R.A. Wach). 0168-583X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0168-583X(03)01513-1 Nuclear Instruments and Methods in Physics Research B 211 (2003) 533–544 www.elsevier.com/locate/nimb