Bio-based isobornyl polymer matrices for transparent wood: optical, thermal, and mechanical trade-offs

Transparent wood was prepared by infiltrating delignified balsa templates with bio-based isobornyl acrylate (IBOA) and isobornyl methacrylate (IBOMA) matrices, including the corresponding homopolymers and three copolymer compositions. The formulations were compared in terms of refractive index, optical transmittance, haze, thermal conductivity, bending response, and ultrasonic stiffness components. All samples showed high visible transmittance at 550 nm, ranging from 69 to 80 %, while haze remained substantial due to scattering within the anisotropic wood structure. Copolymerization improved the optical balance relative to the homopolymers: the three copolymer compositions showed comparable transmittance, whereas the 0.25/0.75 (IBOA/ IBOMA) and 0.75/0.25 compositions exhibited lower haze than the 0.50/0.50 composition. Thermal conductivity varied only slightly (between 0.15 and 0.18 W⋅m-1⋅K-1), indicating that heat transport was mainly controlled by the wood-polymer architecture. Bending tests showed that IBOA-rich systems provided the most favorable mechanical response. An exploratory optical-mechanical desirability comparison indicated that the 0.75/0.25 copolymer offered the most balanced optical and mechanical profile within the investigated set.