Preparation of optically transparent Eucalyptus spp. wood as a substrate for new electrochromic materials

• Autor(a) principal: Valente, Vasco António Marinho
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/33438
• topic: Transparent wood; Eucalyptus spp. wood; Photovoltaic devices; Bio-based materials

Transparent wood has recently emerged as a new bio-based material that combines the mechanical rigidity of wood with high optical transparency. The high transmittance of this material allows its use in various applications such as building materials or photovoltaic devices. However, it is necessary to study the feasibility of using different species of wood as well as the development of more sustainable approaches for their preparation. In this context, this work aimed to prepare a new transparent wood (TW) substrate and evaluate its potential as an electrochromic material (after incorporation of a luminescent material). Thus, for the first time Eucalyptus spp. wood was used, which after delignification, was infiltrated with two different monomers (methyl methacrylate (MMA) and butyl methacrylate (BMA)) and promoted its polymerization, in order to obtain Eucalyptus transparent wood. Initially, the delignification method was optimized by evaluating the effect of the concentration (1, 2, and 3 wt%) of sodium chlorite (NaClO2) and reaction temperature (25, 50, and 80 ºC). Delignified wood (DW) samples were characterized by visual analysis, UV-Vis spectroscopy, color coordinates determination, gravimetry, attenuated total reflection- Fourier transform infrared spectroscopy (FTIR-ATR), and scanning electron microscopy (SEM), in order to determine the ideal conditions for wood delignification, having been verified that these were a concentration of NaClO2 of 3 wt%, temperature of 80 ºC and delignification time of 6 h. Then, two TW samples were prepared by incorporation of poly(methyl methacrylate) (TW PMMA) and poly(butyl methacrylate) (TW PBMA) through infiltration and polymerization of the respective monomers in the delignified wood structure. The presence of the polymers was confirmed by FTIR and SEM. Optical properties (transmittance and haze) were evaluated by UV-Vis spectroscopy. TW PMMA and TW PBMA exhibited high transparency, with relative transmittances of 78 and 75%, respectively, while the haze was approximately 80% for TW PMMA and 60% for TW PBMA. Both TW presented good mechanical performance, with Young's modulus values of 9.8 and 10.3 GPa, tensile strength at break of 95.1 and 120.9 MPa, and elongation at break of 1.50 and 2.26%, respectively, for TW PMMA and TW PBMA. Dynamic-mechanical analysis (DMA) showed that the glass transition temperature of these materials was 83 ºC and 75 ºC, respectively, for TW PMMA and TW PBMA. Finally, fluorescent TW substrates were prepared by incorporating rhodamine 6G (Rh6G) before impregnation and polymerization of pre-polymerized solutions MMA or BMA in the delignified wood. The fluorescence of the samples was confirmed by exposure to UV light (365 nm), as well as by analyzing their fluorescence spectra. It should be noted that these samples maintained their transparency and haze. Thus, it was possible to conclude that both TWs prepared in this work have excellent optical and mechanical properties, as well as functionalization capacity, clearly demonstrating their potential as substrates for the preparation of electrochromic materials.