Hygromorphic nanocomposites elaborated by filtration and ultraviolet curing of cellulose nanocrystal suspensions

Recent developments in the processing of cellulose nanocrystals (CNCs) and polyethylene glycol diacrylate (PEGDA) suspensions into nanocomposites opened new avenues for producing biosourced materials with attractive functional properties. In this work, a new processing method using frontal filtration, followed or not by a transmembrane pressure relaxation step, and finalized by UV crosslinking, enabled the development of nanocomposite films with tunable anisotropic textures, ranging from the nano- to the micrometric scale. For samples developed by filtration without the relaxation step and after UV crosslinking, an original highly cohesive bilayer structure composed of oriented CNCs with very different concentration levels between the two layers exhibited original hygromorphic properties. Combined SAXS, WAXD, and SEM characterization on these nanocomposites revealed a highly organized structure of CNCs oriented parallel to the membrane surface with the presence of an interparticle distance gradient evidenced by SAXS. A more continuous concentration gradient was developed in the nanocomposite films prepared with a relaxation time of 24 and 66 hours before UV crosslinking, with cholesteric organizations revealed by WAXD and SEM. This more continuous structuring reduced the hygromorphism but increased the tensile mechanical properties. This new processing method can be exploited to develop biobased, humidity-responsive actuators for emerging technological applications.