Water-induced shape memory cellulose nanofiber-based nanocomposite membrane containing lignin with quick water response and excellent wet mechanical property

Cellulose-based water-responsive shape memory materials have received widespread attention due to their wide range of sources, high response rate, and environmental friendliness. However, fast responsive shape memory polymers (SMPs) tend to lose wet strength due to excessive hydration. Thus, it greatly limits the application range of cellulose-based water-responsive shape memory materials. To address this issue, in this work, a cellulose nanofiber (CNF) nanocomposite membrane with high water-induced shape memory properties was successfully prepared containing polyvinyl alcohol (PVA) and lignin (LIG). Citric acid (CA) was used as the cross-linking agents. Changes in the content ratio of CNF to PVA and the amount of LIG added will change the crosslinked network structure of the CA/LIG/PVA/CNF membrane, leading to changes in the microstructure, water responsiveness and mechanical properties of the membrane. With the addition of LIG, the fracture surface of the microstructure will orient along longitudinal direction and form a densely packed layered structure. The increase content ratio of CNF to PVA can improve the compatibility of each component. The water-induced shape memory recovery rate of the nanocomposite can reach 100% within 4 s. In the dry state, the maximum tensile strength of the film can reach 138.0 MPa, and the maximum tensile modulus of the film can reach 9.0 GPa. After wet swelling, the highest tensile strength and tensile modulus are up to 60 MPa and 0.7 GPa, respectively. The CNF nanocomposite film has excellent performance in blocking ultraviolet and the transmittance value of the membrane is below 8% in the ultraviolet region of 200-400 nm. Hence, the resultant CA/LIG/PVA/CNF membrane will have potential applications in smart science and the provide a framework for developing a cellulose-based shape memory polymer.