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Effects of Biological and Chemical Degradation on the Properties of Scots Pine Wood—Part I: Chemical Composition and Microstructure of the Cell Wall
Research on new conservation treatment for archaeological wood requires large amounts of wooden material. For this purpose, artificial wood degradation (biological—using brown-rot fungus Coniophora puteana, and chemical—using NaOH solution) under laboratory conditions was conducted to obtain an abundance of similar samples that mimic naturally degraded wood and can serve for comparative studies. However, knowledge about its properties is necessary to use this material for further study. In this study, the chemical composition and microstructure of degraded cell walls were investigated using FT-IR, XRD, helium pycnometry and nitrogen absorption methods. The results show that biological degradation caused the loss of hemicelluloses and celluloses, including the reduction in cellulose crystallinity, and led to lignin modification, while chemical degradation mainly depleted the amount of hemicelluloses and lignin, but also affected crystalline cellulose. These changes affected the cell wall microstructure, increasing both surface area and total pore volume. However, the chemical degradation produced a greater number of mesopores of smaller size compared to fungal decomposition. Both degradation processes weakened the cell wall’s mechanical strength, resulting in high shrinkage of degraded wood during air-drying. The results of the study suggest that degraded wood obtained under laboratory conditions can be a useful material for studies on new consolidants for archaeological wood.
How thermal treatment affects the chemical composition and the physical, mechanical and swelling properties of Scots pine juvenile and mature wood
AbstractHigh variations in juvenile wood properties in the radial direction and its worse performance than mature wood make it less suitable for some applications and often treated as waste material. This study aimed to assess how thermal modification affects the chemical composition and the physical, mechanical and swelling properties of Scots pine juvenile and mature wood. An additional goal was to evaluate if the modification can equalise the differences in selected properties of juvenile wood to those of mature wood so that from waste material, juvenile wood can become a fully-fledged raw material for various industrial applications. Thermal treatment at 220 °C influenced wood chemical composition, degrading mainly hemicelluloses but also affecting cellulose and lignin, which resulted in a reduction of hydroxyls and carbonyl/carboxyl groups. These changes were more pronounced for mature than juvenile wood. It reduced mass loss and swelling rate, and increased swelling pressure in the tangential and radial directions to a higher degree for juvenile than mature wood. Changes in mechanical properties in compression were statistically significant only for mature wood, while wood hardness remained unaffected. Although the applied heat treatment improved the performance of juvenile wood by reducing its swelling rate, it did not equalise the examined properties between juvenile and mature wood. Since higher juvenile wood proportion is expected in the wood supply from the future intensively managed forests, there is still a need to find suitable modification methods or better processing techniques so that instead of being thrown away as waste, it could be used broadly in various industrial applications.