Carbohydrate Polymers 87 (2012) 2582–2588 Contents lists available at SciVerse ScienceDirect Carbohydrate Polymers j ourna l ho me pag e: www.elsevier.com/locate/carbpol Biodegradable superabsorbent hydrogels derived from cellulose by esterification crosslinking with 1,2,3,4-butanetetracarboxylic dianhydride Hiroyuki Kono ∗ , Sayaka Fujita Department of Science and Engineering for Materials, Tomakomai National College of Technology, Nishikioka 443, Tomakomai, Hokkaido 059 1275, Japan a r t i c l e i n f o Article history: Received 19 October 2011 Received in revised form 10 November 2011 Accepted 10 November 2011 Available online 22 November 2011 Keywords: Superabsorbent hydrogel Cellulose Butanetetracarboxylic dianhydride Esterification crosslinking a b s t r a c t Superabsorbent hydrogels were prepared from native celluloses dissolved in lithium chloride and N-methyl-2-pyrrolidinone (LiCl/NMP) by esterification crosslinking with 1,2,3,4-butanetetracarboxylic dianhydride (BTCA). Subsequent conversion of the unreacted carboxyl groups to sodium carboxylates by the addition of aqueous NaOH was performed to enhance the water affinity of the gels. The absorbency of the products was strongly dependent on the amount of BTCA that was esterified to cellulose, and the highest absorbency was observed for the hydrogel composed of approximately 0.25 molecules of BTCA per anhydroglucose unit (AGU) of cellulose. Furthermore, it was confirmed that the absorbency was enhanced as the average degree of polymerization (DP) of the starting cellulose increased. The use of cotton cellulose with a high DP of about 2400 produced a hydrogel with an absorbency of 720 times its dry weight, which exceeded the absorbency of commercial crosslinked sodium polyacrylate superab- sorbent hydrogel (SPA). The hydrogels exhibited good biodegradability, with a maximum degradation of 95% within 7 days using cellulase. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Superabsorbent hydrogels are crosslinked hydrophilic polymers that are capable of absorbing large amounts of water, as much as 100–500 times their own weight. These crosslinked polymers are widely used in many applications such as paper diapers, sani- tary napkins, and as soil additives in agriculture (Buchholz, 1998; Buchholz & Peppas, 1994). The most widely used commercially available superabsorbent hydrogel is crosslinked sodium polyacry- late (SPA), which is synthesized by the copolymerization of acrylic acid with various monomers. A major drawback of SPA is that it is non-biodegradable (Buchholz, 1998). Because many of the applications of SPA fall within the category of disposable goods, widespread use of this polymer may lead to environmental pollu- tion. The development of biodegradable superabsorbent polymers as substitutes for SPA is thus necessary. Because of the increasing focus on environmental problems associated with synthetic polymers, there is an emerging ten- dency toward the use of naturally occurring polymers instead of synthetic ones. Among these natural polymers, cellulose, which is composed of -(1→4)-d-glucopyranose repeating units and forms fibrous structures with high crystallinity (Updegraff, 1969), is a prime candidate as a starting material for biodegradable ∗ Corresponding author. Tel.: +81 144 67 8036; fax: +81 144 67 8036. E-mail address: kono@sem.tomakomai-ct.ac.jp (H. Kono). superabsorbent polymers because it is the most abundant biopolymer on earth. Among the biodegradable cellulose deriva- tives, sodium carboxymethylcellulose (CMC) is a representative water-soluble polymer in which sodium carboxylate groups are substituted onto the AGU of the cellulose chain via an ether link- age. The biodegradation speed of CMC can be easily regulated by controlling the degree of substitution (DS), because the biodegrad- ability of CMC generally decreases as its DS increases (Hamacher & Sahm, 1985; Sieger, Kroon, Batelaan, & van Ginkel, 1995; Wirick, 1968). Therefore, a vast number of reports on methods of preparing biodegradable superabsorbent hydrogels from CMC have emerged (Matsumoto & Zenkoh, 1992; Qiu et al., 2007; Reza & Nicoll, 2010; Wach, Mitomo, Nagasawa, & Yoshii, 2003). However, most of these methods have never been put to practical use because of associ- ated issues regarding cost, scaling up for production and ecological safety of the products, among other concerns. Recently, biodegradable superabsorbent hydrogels have been prepared from unmodified cellulose by the reaction with succinic anhydride in the presence of 4-dimethylaminopyridine (DMAP), as an esterification catalyst, in a mixture of either LiCl/NMP or tetra- butylammonium fluoride/dimethylsulfoxide (Yoshimura, Matsuo, & Fujioka, 2006). In this reaction, succinic anhydride serves to initi- ate both the crosslinking of cellulose by the formation of the diester as well as the formation of succinylated cellulose by grafting. Fol- lowing neutralization with NaOH, the carboxyl group generated by the graft reaction is converted to sodium carboxylate, which enhances the affinity to water, and consequently, the product is 0144-8617/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2011.11.045