Sustainable transparent wood composites from alternative biomass sources and polyvinyl alcohol for optical applications

The increasing demand for sustainable high-performance materials has necessitated the development of alternatives to conventional glass- and petroleum-based plastics, particularly for transparent and mechanically robust applications. Transparent wood composites (TWCs) have gained attention as eco-friendly structural materials. However, existing studies have primarily focused on stem wood (SW) and epoxy-based polymers, which limit material flexibility, environmental sustainability, and diversified biomass utilization. To address this limitation, this study introduces a novel approach utilizing delignified biomass from branch (BH) and bark (BK) along with SW in combination with polyvinyl alcohol (PVA), a biodegradable and eco-friendly polymer matrix. The delignification process effectively removed the lignin, leading to enhanced cellulose crystallinity, increased optical transmittance, and improved polymer infiltration. Fourier-transform infrared spectroscopy (FTIR) confirmed substantial lignin removal, whereas X-ray diffraction (XRD) revealed differences in crystallinity across the biomass sources, with SW exhibiting the highest structural order. Optical analyses demonstrated that transparent composites made from branches with a smaller particle size (< 200 μm) and a wood powder ratio of 40% (TBH < 200 − 40) achieved the highest transmittance (85% at 600 nm) and superior light diffusion, making them suitable for optical and photonic applications. In contrast, transparent composites made from stem wood (TSWs) exhibited the highest mechanical strength, which was attributed to their densely packed fiber structure and high cellulose content, making them more suitable for load-bearing applications. BK-based composites demonstrated inferior mechanical and optical performance due to poor polymer adhesion and residual lignin content. These findings highlight the potential of alternative biomass sources for the development of high-performance TWCs, thereby enhancing their applicability in sustainable architecture, advanced optics, and flexible electronics.