Multilayer cellulose hybrid films with tunable UV selectivity and mechanical performance.

Self-standing films that combine low thickness with robust mechanical performance and selective UV shielding are increasingly needed for lightweight protective materials based on renewable polymers. Regenerated microcrystalline cellulose (MCC) provides a sustainable and scalable carbohydrate-polymer platform for such films; however, conventional cellulose formulations face a trade-off between mechanical integrity and optical selectivity when UV-active additives are incorporated. Here, an interface-engineered multilayer design is introduced to overcome this limitation by modular stacking of regenerated cellulose (RC) layers, which densifies interlayers and enhances stress transfer across hydroxyl-rich cellulose interfaces. Increasing the number of stacked layers systematically improves tensile compliance, achieving an elongation at break of approximately 7.5%, consistent with cohesive coupling between adjacent cellulose films. Sepiolite acts as a rheology-active nano-reinforcement that restructures the cellulose casting suspension into a viscoelastic cluster network, yielding tensile strengths up to approximately 9.4 MPa while preserving cellulose crystallinity. In contrast, SiO₂ enables sharp and tunable UV-C attenuation, with an absorption edge adjustable within approximately 2 nm and transmittance below 10% up to 280 nm. In this approach, multilayer stacking is treated as a modular design variable that allows mechanical and optical functions to be independently assigned to different cellulose-based layers, enabling programmable UV-edge tuning without re-optimizing the bulk composition.