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- Thermally modified wood exposed to different weathering conditions: a reviewPublication . Godinho, Delfina; Araújo, Solange; Quilhó, Teresa; Cunha Diamantino, Teresa; Gominho, JorgeABSTRACT: Outdoor wood applications are exposed to several different biotic and abiotic factors, and for that reason, they require protection to increase their service life. Several technologies of wood protection are already commercialized. One of these technologies is thermal modification, which refers to the structural, mechanical, and chemical transformations occurring in the lignocellulosic material when gradually heated up to specific temperature ranges. In the past few years, several researchers have undertaken weathering resistance evaluations on different wood species. Some cases have considered natural exposure in different countries with different climatic conditions, while others focused on artificial exposure under UV and xenon radiation tests. Most works evaluated the weathering effects on the chemical, mechanical and physical, and anatomical shifts compared to the original characteristics of the material. This review has established a considerable lack of studies in the bibliography focusing on abiotic factors, such as the industrial and maritime environment, or even isolated climatic factors such as salt spray (simulating maritime environments) or pollutant gases (simulating industrial environments). This lack of information can be an opportunity for future work. It could help to understand if thermally modified wood is or is not sensitive to pollutant gases or salinity, or to a combination of both. By knowing the degradation mechanisms caused by these factors, it will be possible to study other forms of protection.
- The behavior of thermally modified wood after exposure in maritime/industrial and urban environmentsPublication . Godinho, Delfina; Ferreira, Cristina; Lourenço, Ana; Araújo, Solange; Quilhó, Teresa; Cunha Diamantino, Teresa; Gominho, JorgeABSTRACT: Natural and thermally modified Pine, Ash, and Acacia woods were exposed in two different environments: urban and maritime/industrial. The weathering effects were evaluated during 24 months regarding color, chemical, and structural changes. In all wood species, thermal modification induced color, chemical, and structural changes. All woods became darker (Pine Delta L*: -32.01; Ash Delta L*: -36.83; Acacia Delta L*: -27.50), total extractives content increased (Pine: 19 %; Ash: 32 % and Acacia: 18 %), and the samples presented deformation and damaged cells. Total lignin was not significantly changed, although there were detected changes in lignin, namely the reduction of G -units in Pine (approximate to 2 %) and reduction of S/G ratio in Acacia (approximate to 0.04 %). Ash remained almost the same. After weathering, modified woods suffered fewer color changes, indicating that the thermal modification could improve the resistance to color change. Acacia wood, when exposed to maritime/industrial conditions, revealed a higher color change (Delta E: 35.7 at 24 months) when compared with urban conditions (Delta E: 23.5 at 24 months). Delignification, possibly caused by photodegradation, occurred in all wood samples, and the loss of extractive happened, perhaps caused by rain. Modified woods were slightly less resistant to weathering in maritime/ industrial environments. Some structural damage, namely cracked cells, the appearance of molds, blue staining, and particle deposition, was observed. The thermal modification enables color stabilization but does not seem to improve the weathering resistance in all studied wood species. Exposure to the different environments did not lead to significant differences in the morphology and chemical composition of the three natural and modified wood species.
- Thermally modified wood: assessing the impact of weathering on mechanical strength and exposure to subterranean termitesPublication . Godinho, Delfina; Lourenco, Ana; Araújo, Solange; Machado, José Saporiti; Nunes, Lina; Duarte, Marta; Duarte, Sónia; Ferreira, Cristina; Quilhó, Teresa; Cunha Diamantino, Teresa; Gominho, JorgeABSTRACT: The main objective of this study was to evaluate the mechanical properties of three thermal-modified wood species when exposed to weathering in urban and maritime/industrial environments and their durability against subterranean termites. The wood species studied were Maritime pine, ash, and blackwood acacia. All wood samples were exposed to two different environments (urban and maritime/industrial) for 24 months. Then, its physical and mechanical properties were evaluated (modulus of elasticity (MOE), modulus of rupture (MOR), compression strength (CS), and modulus of compression (MOC). Thermally modified woods revealed a lower density, which could explain the loss of MOE and MOR. In compression, no significant changes were verified. The weathered samples showed changes in mechanical properties, mostly verified in MOE and MOR, where some decreases were reported in both locations. Tests were performed to evaluate biodegradation and the resistance of all wood samples to subterranean termites. The grade of attack (approximate to 4) and termite survival rate were similar in all wood species (above 75% and lower than 80%), except for modified acacia (59%), which could indicate that thermal modification increased toxic substances. The cellulose degradation was reflected in FTIR-ATR and Py-GC/MS in natural and thermally modified woods. Py-GC/MS showed a decrease in levoglucosan, while lignin suffered some modifications with slight changes in monomeric composition reflected by the reduction of the S/G ratio. No changes were found between the two environments, and thermal modification did not give extra protection against termites and weathering.