Polysaccharide-Based Superabsorbents: Synthesis, Properties, and Applications

Abstract

Traditional absorbent hydrogels are based on the copolymerization of petroleum-based synthetic vinyl monomers such as acrylic acid, methacrylic acid, and acrylamide derivatives. Nevertheless, these materials are usually expensive, poorly degradable, and non-environmentally friendly. On the contrary, natural polysaccharides display significant advantages such as availability, low production cost, nontoxicity, biocompatibility, and biodegradability. Accordingly, polysaccharides emerge as an interesting sustainable alternative to traditionally employed polymers. In addition, polysaccharides can easily form hydrogels by chemical or physical crosslinking (including hydrogen bonding and ionic interactions) or a combination of both, which makes the crosslinking of natural polysaccharides a versatile and promising approach for superabsorbent hydrogel (SAH) production. Therefore, in the last years, numerous polysaccharides including starch, cellulose, alginate, chitosan, and guar gum, among others, have been employed in SAH fabrication. Polysaccharide-based SAHs have been used in agriculture, hygiene products, waste treatment, crack mitigation in building applications, tissue engineering, and controlled release, for biomedical and soil conditioning applications. Despite of the evident commercial and environmental advantages of polysaccharide-based SAHs, they also display some drawbacks that make them continue appearing as a challenge research field. In this sense, although the biodegradability of polysaccharide-based hydrogels is a key characteristic for some applications because it avoids pollution-related issues and enables enhanced controlled release, at the same time, it could delay the development of longtime sustained release systems. Moreover, polysaccharide crosslinking leads to hydrogels with poor mechanical stability which is another associated disadvantage of these types of materials that needs to be overcome. Therefore an increasing amount of investigations about new synthetic approaches to improve the properties of polysaccharide-based hydrogels have been reported in the last years. In this chapter, the recent progress of this type of hydrogels is reviewed. The synthetic methods employed to obtain SAHs from the most common polysaccharides and the main properties of these materials with a special emphasis on swelling and mechanical properties are studied. Furthermore, the applications of SAHs have been summarized highlighting the most outstanding and promising uses.