Fabrication of thermo- and pH-sensitive cellulose nanofibrils-reinforced hydrogel with biomass nanoparticles.

Cellulose nanofibrils (CNFs) have been widely used as the reinforcing agent. However, there is still a challenge to control the mechanical properties of CNFs-reinforced hydrogels by changing the environmental variables. Here, we demonstrated a thermo- and multi-pH-responsive CNFs-reinforced hydrogel containing lignin nanoparticles as the functional dynamic cross-linkers in the polymeric network. The elastic and viscous modulus of the hydrogel can be tailored: (i) the modulus increases upon increasing pH from 4 to 7, (ii) with pH further increasing from 7 to 9, the modulus decreases. The as prepared hydrogel also responded to the environment temperature, with the gelation at 26.4 °C. The significant differences in CNFs-reinforced hydrogel mechanics at various environment conditions are a direct result of the distinct stress-relaxation dynamics dictated by the dynamic hydrogen bonding and swelling/shrinking of lignin nanoparticles. This work also provides a new approach to design stimuli-responsive hydrogels.