Influência do tratamento térmico nas propriedades químicas, físicas e mecânicas de madeiras de reflorestamento
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Data
2020-02-20
Autores
Oliveira, Carolina Aparecida Barros
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O tratamento térmico é um processo realizado com madeiras para aumentar a durabilidade e mudar a aparência. Nesse processo vários fatores devem ser observados para um melhor aproveitamento do potencial mecânico da madeira, dentre eles: tempo, temperatura e velocidade de aquecimento. Observa-se que na maioria dos estudos já realizados sobre esse tema algumas espécies de madeira ainda não tiveram todas as suas propriedades mecânicas analisadas. Além disso, a maior parte dos estudos desenvolvido no Brasil considera o aquecimento da madeira em estufa com ambiente controlado. O objetivo desse trabalho consistiu em avaliar a influência do tratamento térmico realizado industrialmente para as temperaturas 155, 165, 175 e 185 ºC nas propriedades químicas, físicas e mecânicas de madeiras de Eucalipto grandis (Eucalyptus grandis), Pinus taeda (Pinus taeda L.), Cedro indiano (Acrocarpus fraxinifolius) e Cedro australiano (Toona ciliata var. australis), em relação às respectivas propriedades das madeiras in natura. O tratamento térmico das madeiras foi realizado em autoclave com controle de temperatura e de pressão com ingestão de vapor saturado. Após o tratamento térmico a análise química identificou, para as quatro espécies estudadas, um aumento nos teores de extrativos e redução nos teores de holocelulose; o teor de lignina aumento para o Pinus taeda e o Cedro australiano e não apresentou modificações estatisticamente significantes para o Eucalipto grandis e Cedro indiano. A densidade aparente apresentou redução para as madeiras Pinus taeda e Cedro australiano e aumento para o Cedro indiano, para o Eucalipto grandis não houve mudanças significativas. De uma maneira geral, as propriedades mecânicas de resistência (à compressão, tração, flexão estática, ao cisalhamento e impacto na flexão paralela às fibras e de dureza Janka paralela e normal às fibras) e de rigidez (à compressão, tração e flexão estática paralela às fibras) reduziram para as quatro espécies estudadas. O tratamento térmico proporcionou alterações nas propriedades químicas, físicas e mecânicas das madeiras, sendo que, de maneira geral, a elevação da temperatura de tratamento não apresentou influência significativa nessas propriedades.
Heat treatment is a wood treatment process to increase durability and change appearance. In this process, several factors must be observed for better use of the mechanical potential of the wood, including time, temperature and heating speed. It’s observed that in most studies already done on this topic some wood species have not yet had all their mechanical properties analyzed. Also, most studies conducted in Brazil consider the heating of wood in a controlled environment greenhouse. The objective of this paper was to evaluate the influence of the heat treatment performed out industrially at temperatures 155, 165, 175 and 185 ºC on the chemical, physical and mechanical properties of Eucalyptus grandis, Pinus taeda, Indian cedar (Acrocarpus fraxinifolius) and Australian cedar (Toona ciliata var. australis), in relation to their properties of in natura woods. Heat treatment of the woods was performed in an autoclave with temperature and pressure control with saturated steam intake. In the chemical analysis, after the heat treatments, it was identified an increase in the extractives content and a reduction in the holocellulose contents for the four species; lignin content increased for Pinus taeda and Australian Cedar and showed no statistically significant changes for Eucalyptus grandis and Indian Cedar. The apparent density decreased for Pinus taeda and Australian Cedar and increased for Indian Cedar, for Eucalyptus grandis there were no significant changes. In general, the mechanical properties of resistance (to compression, tensile, static bending, shear and flexural impact strength parallel to the fibers and Janka hardness parallel and normal to the fibers) and stiffness (to compression, tensile and static bending parallel to the fibers) decreased for the four species studied. The thermal treatment provided changes in the chemical, physical and mechanical properties of the wood, and, in general, the elevation of the treatment temperature did not show any significant influence on these properties
Heat treatment is a wood treatment process to increase durability and change appearance. In this process, several factors must be observed for better use of the mechanical potential of the wood, including time, temperature and heating speed. It’s observed that in most studies already done on this topic some wood species have not yet had all their mechanical properties analyzed. Also, most studies conducted in Brazil consider the heating of wood in a controlled environment greenhouse. The objective of this paper was to evaluate the influence of the heat treatment performed out industrially at temperatures 155, 165, 175 and 185 ºC on the chemical, physical and mechanical properties of Eucalyptus grandis, Pinus taeda, Indian cedar (Acrocarpus fraxinifolius) and Australian cedar (Toona ciliata var. australis), in relation to their properties of in natura woods. Heat treatment of the woods was performed in an autoclave with temperature and pressure control with saturated steam intake. In the chemical analysis, after the heat treatments, it was identified an increase in the extractives content and a reduction in the holocellulose contents for the four species; lignin content increased for Pinus taeda and Australian Cedar and showed no statistically significant changes for Eucalyptus grandis and Indian Cedar. The apparent density decreased for Pinus taeda and Australian Cedar and increased for Indian Cedar, for Eucalyptus grandis there were no significant changes. In general, the mechanical properties of resistance (to compression, tensile, static bending, shear and flexural impact strength parallel to the fibers and Janka hardness parallel and normal to the fibers) and stiffness (to compression, tensile and static bending parallel to the fibers) decreased for the four species studied. The thermal treatment provided changes in the chemical, physical and mechanical properties of the wood, and, in general, the elevation of the treatment temperature did not show any significant influence on these properties
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Palavras-chave
Tratamento térmico, Termorretificação, Propriedades da madeira, Madeira de rápido crescimento, Heat treatment, Thermorectification, Wood properties, Fast-growing wood, Madeira - Tratamento térmico, Reflorestamento