Chemically programmed timing for nanocellulose colloidal gelation

Cellulose nanofibrils (CNF) have generated great research interest due to their biocompatibility, sustainability and potential to build functional materials and devices with better mechanical properties. This work involves a chemically programmed timing method to form CNF hydrogels from aqueous colloidal suspensions by making use of slow hydrolysis reaction of glucono-delta-lactone(GdL) to gluconic acid. Fourier transform infrared spectroscopy and UV-Vis spectroscopy using cationic dye toluidine blue (TB) suggests that the gelation is driven by the supracolloidal crosslinking of the CNF nanofibrils by hydrogen bondings mediated by carboxylic acid dimerization. This results from the transition of the sodium carboxylate groups in the TEMPO oxidized CNF fibrils to carboxylic acids. Rheological experiments revealed that the concentration of GdL used to form hydrogels allows tuning of the gelation times from minutes to days. In addition, the storage modulus of the gels can be tuned by the amount of added GdL. Thus we envision that the chemically programmed timing concept allows the programming of processing window before the elastic gels are formed. The method also allowed a controlled introduction of redox active tetra(aniline) (TANI) onto the CNF hydrogels. The method is suggested to open up new possibilities for functional hydrogels, e.g. incorporating conductivity or electrochromic properties and making mechanically tough double gels