Effect of natural variability of European Oak wood on heat treatment process and potential implication on wood durability

IRG/WP 15-40693

J Hamada, A Pétrissans, F Mothe, M Pétrissans, P Gérardin

Environmental pressures appeared in France and in most European countries during the last decade has led to the development of more environmentally acceptable preservation methods. In this context, wood heat treatment has been one of the most investigated alternative method during the last years. Treated at temperatures ranging between 180 and 220°C, wood components undergo more or less important chemical modifications conferring to the material new properties like increased decay resistance or higher dimensional stability. However, even if industrial heat treatment processes are relatively well controlled, the main difficulties remaining today are to obtain final products with constant qualities (durability, dimensional stability, colour). These difficulties may be due to the heat treatment processes themselves or the inter- or intra-specific wood heterogeneity. The aim of this study is to assess the effect of the variability of the initial intrinsic wood quality depending on different silvicultural systems, on the level of thermo-degradation recorded for similar curing conditions and consequently on conferred properties to the final end products. Oak wood (Quercus petraea Liebl) boards with different densities were selected from different positions in the same tree and/or from trees from different forests. Samples density was determined by X-ray computed tomography and micro densitometry before and after heat treatment. X-ray tomography observations did not allowed establishing a clear relationship between initial oak density and its susceptibility to thermo-degradation. However, it was noticed an influence of the position in the board and of the nature of the wood (heartwood versus sapwood) on the levels of thermo-degradation. Thermo-gravimetric analysis (TGA) performed on earlywood and latewood sampled within a same board indicated a strong influence of the intra ring heterogeneity, earlywood tending to be more sensitive to thermo-degradation than latewood. Wood quality, often characterized by its density resulting from forests management, appears therefore as an influencing parameter to consider during wood thermo modification.


Keywords: density, earlywood, heat treatment, latewood, oak, ring, thermo-gravimetric analysis, variability, X-Ray CT

Conference: 15-05-10/14 Vina del Mar, Chile


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