Waste to high-value products: The performance and potential of carboxymethylcellulose hydrogels via the circular economy

Hydrogels are a class of materials that have found many applications across society. Petrochemicals are a dominant, but unsustainable feedstock of crosslinked polymer networks that underpin functional hydrogels. Therefore an urgent need exists for sustainable biopolymer replacements, where agricultural by products, such as cellulose prove an ideal source of green hydrogels. These polymers are cheap and environmentally friendly, have excellent water absorption capacity and the products are inherently biodegradable and, most importantly for technical applications, can be easily functionalised. For example, 3-D cross linked hydrogel structures can be optimised by modifying the hydroxy groups of the parent structure into ether and ester derivatives that include additional functional groups. In this regard, carboxymethylcellulose (CMC) has emerged as a promising cellulose derivative as it possesses readily available carboxylic groups along the polymer chain. This property both imparts good water solubility and high chemical reactivity making it an ideal candidate for hydrogel synthesis. This review highlights recent developments in both the preparation and application of CMC based hydrogels. We discuss how the various physical and chemical properties of a range of CMC based hydrogels impinge on key parameters such as water absorption, mechanical strength and biodegradability. Finally, we will discuss key applications and the future potential of CMC hydrogels in various fields. Graphical abstract