Repurposing Waste Sulfur for the Ionic Vulcanization of Nanocellulose Hydrogels

Large quantities of sulfur amass annually as waste material produced in the desulfurization of crude oil. Commonly applied in rubber vulcanization, sulfur can covalently crosslink polymer chains to improve the material properties. Herein, the concept of ionic vulcanization is introduced - ionotropic gelation of sodium polysulfides with alcohol moieties and bridging calcium ions, exemplified using cellulose nanocrystals, introduces ionic sulfur crosslinked areas of hydrophobicity to a bio-based hydrogel. These crosslinks can be broken at will in an aqueous environment. It is demonstrated that ionic vulcanization increases the storage modulus of the calcium gelled CNC by up to 888%, and the swelling percentage by 235%. This swelling ratio increase translates to improved moisture sorption, with 98 wt.% water captured from the atmosphere, proving the potential application of ionically vulcanized materials for water harvesting. Ionic vulcanization is therefore proposed as a method to reversibly generate functional gel materials with improved properties that utilize waste and bio-based components.