Bioinspired selective cell lumen densification for high-loading transparent cellulosic fiber composites with controlled light scattering.

Traditional cell lumens in cellulose fibers induce severe light scattering. Though polymer impregnation boosts transparency, it drastically lowers fiber content and composite sustainability. Herein, we propose a chameleon skin-inspired selective cell lumen densification strategy that converts intrinsic scattering defects into a tunable optical asset. By mechanically closing the lumens, selectively reopening inter-fiber gaps via alkaline swelling, and infiltrating a refractive-index-matched polymer, we fabricate cellulosic fiber-reinforced composites (CFRC) that can achieve ultrahigh fiber content of 91% and optical transmittance of up to 89.7%. The material delivers a tensile strength of 71.8 MPa, superior to most plastics and glass. We establish quantitative relationships between scattering/transmission behavior and lumen width (0-20 nm) by combining optical measurements with COMSOL simulations, revealing a transition from Rayleigh- to Mie-type scattering as the dominant mechanism. The developed CFRC possesses outstanding thermal insulation, favorable water resistance and low environmental footprint validated by life-cycle assessment. We verify its practical potential as light-diffusing greenhouse screens for shade-sensitive plants and laser-scattering windows to eliminate laser hazards. This biomimetic structural regulation provides a facile strategy for high-performance sustainable polysaccharide optical composites.