Treating wood with water-soluble resins is a well-known and effective method to improve the durability of wood. However, there has been no systematic work to date related to the influence of average molecular size of phenol-formaldehyde (PF) resin on the decay resistance of wood, especially of hardwoods. Therefore, the goal of this study was to investigate the effect of average molecular size of PF resin treatment on the resistance of beech wood against brown- and white-rot fungi. Four different average molecular weights ( M w ) of resol type resin oligomers (297, 421, 655 and 854 g/mol) were examined. Different weight percent gains (WPGs) in European beech ( Fagus sylvatica ) wood blocks (15 × 20 × 50 mm 3 ) were attained through vacuum impregnation using various concentrations of aqueous-PF solutions. Afterwards treated wood blocks passed the leaching and were exposed to brown-rot fungi ( Gloeophyllum trabeum ; Coniophora puteana ) and white-rot fungi ( Trametes versicolor ) for 16 weeks. No effect of oligomer size on the resistance against G. trabeum decay of wood blocks was observed, resulting in resin loadings of 7–8%. The required WPG for resistance to brown-rot decay by C. puteana increased slightly with increasing oligomer molecular size: 6, 7, 10 and 11% for wood treated with 297, 421, 655 and 854 g/mol, respectively. The extent of white-rot fungal decay resistance of treated wood was affected by the molecular size of oligomers. Resin loadings of 8% and of 17% against T. versicolor were required to attain similar durability levels for beech wood treated with M w = 297 and 854 g/mol, respectively.

中文翻译：

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酚醛树脂低聚物粒径对榉木耐腐性能的影响

用水溶性树脂处理木材是提高木材耐久性的一种众所周知的有效方法。然而，迄今为止，还没有关于酚醛 (PF) 树脂平均分子大小对木材，尤其是硬木的耐腐性影响的系统工作。因此，本研究的目的是研究 PF 树脂处理的平均分子大小对山毛榉木材对褐腐和白腐真菌的抗性的影响。检测了四种不同平均分子量 (M w ) 的甲阶酚醛树脂低聚物 (297、421、655 和 854 g/mol)。欧洲山毛榉 (Fagus sylvatica) 木块 (15 × 20 × 50 mm 3 ) 的不同重量百分比增益 (WPG) 是通过使用不同浓度的 PF 水溶液真空浸渍获得的。之后处理过的木块通过浸出并暴露于褐腐真菌（Gloeophyllum trabeum；Coniophora puteana）和白腐真菌（Trametes versicolor）16周。没有观察到低聚物尺寸对木块抗 G. trabeum 腐烂的影响，导致树脂加载量为 7-8%。随着低聚物分子大小的增加，C. puteana 抵抗褐腐腐烂所需的 WPG 略有增加：对于用 297、421、655 和 854 g/mol 处理的木材，分别增加 6、7、10 和 11%。处理过的木材的抗白腐真菌腐烂程度受低聚物分子大小的影响。对于分别用 M w = 297 和 854 g/mol 处理的山毛榉木材，需要 8% 和 17% 的树脂负载量才能达到类似的耐久性水平。