Preparation of photoluminescent transparent balsa wood with densifying structure for light-scattering windows based on cross-linking of lignocellulose and poly(vinyl alcohol)

To satisfy the urgent demand to green, renewable and high value-added building and decorative materials, the research field on photoluminescent transparent wood has been developed more and more rapidly. Herein, approximately 84.7 % of lignin in balsa wood was modified to remove the chromogenic groups, and approximately 15.3 % of lignin was removed, thereby exposing more hydroxyl groups and pores of wood. Such pretreated balsa wood was then cross-linked with polyvinyl alcohol to create transparent wood films (TWF). By impregnating the treated wood with polyvinyl alcohol and blue or yellow carbon dots (BCDs or YCDs), blue and yellow photoluminescent TWFs (B-TWF and Y-TWF) were produced. The B-TWF incorporates BCDs throughout the wood following the polyvinyl alcohol (PVA), while Y-TWF has YCDs cross-linked with lignocellulose in the wood cell walls initially and then PVA in wood cell cavities. Both B-TWF and Y-TWF exhibited excellent light scattering and flexibility. Y-TWF had higher UV-blocking rate (92.4 %) and tensile strength (39.5 MPa) but lower visible light transmittance (64.8 %) compared to B-TWF (82.5 %, 22.7 MPa and 65.8 %), as well as good expansibility and water stability, which used to overlay a glass window indoors append additional resistance to UV and light scattering.