ABSTRACT

Eucalyptus grandis presents low durability, and due to its anatomical characteristics, impregnation with chemicals is not an effective alternative to increase it. This work analyses the effect that thermal modification carried out in an oxygen depleted atmosphere has on mass, density, hygroscopicity, chemical composition of the cell wall and decay resistance against locally collected wild strains of wood destroying Basidiomycetes, Trametes versicolor and Pycnoporus sanguineus. E. grandis boards were modified in a vacuum environment (P = –100 kPa) at 160°C, 180°C and 200°C for 1, 2 and 3 h. Hygroscopicity was determined by a sorption isotherm over saturated saline solutions at 25°C. The cell wall composition was characterized by the content of structural carbohydrates, lignin and total extractives. A mini-block fungal test was performed by exposing treated wood samples to mycelia, using Populus sp. as reference. The results showed that the thermal treatment caused mass and density reduction. Modified samples showed a reduction in xylose content while lignin content increased, and cellulose content remained constant. Treated samples presented lower hygroscopicity, especially the ones modified at higher temperatures. The analysis by the Hailwood-Horrobin model showed that the main effect occurred at the monomolecular level, causing a reduction of the sorption capacity of the treated wood. The fungi test evidenced that the modification increased the decay resistance of E. grandis against T. versicolor and P. sanguineus. Both fungi were capable of degrading modified wood, but had limited activity, explained by a reduction of moisture content and a change in the chemical composition of the wood.

摘要

巨桉树耐久性低，由于其解剖学特征，用化学品浸渍并不是增加耐久性的有效替代方法。这项工作分析了在贫氧大气中进行的热改性对细胞壁的质量、密度、吸湿性、化学成分以及对当地收集的破坏担子菌、云芝栓菌和血红孔菌的野生木材菌株的抗腐烂性的影响。E. grandis板在真空环境中进行了修改（P = –100 kPa) 在 160°C、180°C 和 200°C 下保持 1、2 和 3 小时。吸湿性通过 25°C 下饱和盐水溶液的吸附等温线确定。细胞壁组成的特征在于结构碳水化合物、木质素和总提取物的含量。使用Populus将处理过的木材样品暴露于菌丝体中，进行小块真菌测试sp。作为参考。结果表明，热处理导致质量和密度降低。改性样品显示木糖含量降低，而木质素含量增加，而纤维素含量保持不变。处理过的样品表现出较低的吸湿性，尤其是在较高温度下改性的样品。Hailwood-Horrobin 模型的分析表明，主要影响发生在单分子水平，导致处理过的木材的吸附能力降低。真菌测试证明，该修饰增加了E. grandis对T. versicolor和P. sanguineus的抗腐烂性. 两种真菌都能够降解改性木材，但活性有限，原因是水分含量降低和木材化学成分发生变化。