Drying and thermal modification of wood - studies on influence of sample size, batch size, and climate on wood response

Abstract: Research on wood drying and wood modification is primarily done in laboratories, using clear wood specimens treated under well-defined conditions in laboratory cabinets. Laboratory tests differ from industrial treatment both regarding the size and homogeneity of the material treated, and the size of the batch and kiln used.Knowledge about how the size of the material treated and the size of the batch or kiln influence the results is limited, which makes it difficult to utilize results from laboratory research in development of industrial processes. A better understanding of the influence of size can also improve the possibilities to design laboratory studies so that the results are easier to implement industrially.The studies presented in this thesis focus on how the size of the batches treated and the size of the individual wood samples treated influence the process and resulting properties of the wood. The aim of the studies, the so called researchquestion in the context of a PhD-thesis, is to help transfer knowledge gained from testing small wooden samples in laboratories to industrial treatment of full size timber.This thesis describes studies on vacuum drying, high temperature (HT) drying, and thermal modification of wood according to the Thermowood© process. Drying and thermal modification of wood have been studied under industrial andlaboratory conditions. Kiln climates and wood response have been determined during vacuum drying, conventional drying, high temperature drying, and thermal modification.The results show that both the size of the material treated and the size of the kiln or batch strongly influence the processes and the resulting wood properties.The results show that the sample size influences different material properties in different ways. Equilibrium moisture content is reduced less during thermal treatment of small clear wood specimens than during treatment of dimensionaltimber. Mass loss on the other hand is higher in small samples. Reduction in impact bending strength, mass loss, and reduction in EMC after thermal treatment of dimensional timber do not seem to be correlated.Laboratory treatment of small clear wood specimens show considerably stronger influence on the wood properties than treatment of similar samples together with industrial production.