Preparation of crosslinked lignin-polyacrylamide hydrogel with high resistance to temperature and salinity

In this study, we innovatively prepared a multifunctional lignin crosslinked polyacrylamide (L-cPAM) hydrogel by a sequential two-step strategy of crosslinking of lignin and crosslinked polyacrylamide (cPAM) followed by the polymerization of cPAM. The hydrogen bonding and crosslinking between the molecular chains of lignin and PAM established a rigid and porous network structure, which provided the L-cPAM hydrogel with excellent mechanical strength, thermal stability, and salinity resistance. A series of lignin dosages (0 to 30 %) were investigated during the crosslinking of lignin and PAM. The results showed that the mechanical strength of the obtained L-cPAM hydrogel could be increased by 53.6 % to 180.71 kPa at a lignin dosage of 15 %. Moreover, the recovery coefficient of the L-cPAM hydrogel after 20 compressions could be maintained at 85.28 %, indicating a strong shape recovery ability. After crosslinking cPAM with a lignin dosage of 15 %, the initial thermal degradation temperature was substantially increased from 150 °C to 181 °C and the shape of the L-cPAM hydrogel could also be maintained for over 60 days in 21× 10⁴ mg L^-1 brine at 150 °C. The results suggested that this work provides a new method to construct high-temperature and high-salinity resistant hydrogels using lignin and polyacrylamide.