Poly( N -isopropylacrylamide)-Grafted Macroporous Cellulose Hydrogels for Thermoresponsive Oil Uptake and Release

Abstract

Achieving controllable adsorption and desorption remains an important challenge in separation processes, particularly for oil–water systems that require both efficient uptake and reliable release. In this study, we develop a thermoresponsive cellulose-based macroporous hydrogel capable of efficient and repeated oil–water separation. The hydrogel is fabricated by grafting poly(N-isopropylacrylamide) (PNIPAAm) onto a macroporous skeleton based on itaconic acid-modified cellulose nanofibers via free-radical polymerization. The macroporous structure is constructed through a freeze–thaw process followed by Ca2+-induced ionic cross-linking, providing a mechanically robust and interconnected framework. The resulting hydrogels exhibited sponge-like compressibility with a Young’s modulus of 0.10 MPa at 20 °C and maintained mechanical durability under cyclic compression, showing a recovery ratio of 89% after 20 cycles. Owing to the incorporation of thermoresponsive PNIPAAm, the hydrogels demonstrated temperature-dependent adsorption–desorption behavior, absorbing hydrophobic solvents at 50 °C and releasing them at 20 °C. This reversible behavior was repeated for at least 10 cycles, with the separation efficiency maintained at 84%. These results indicate that the developed hydrogels provide a promising platform for reusable and efficient oil–water separation.