An even distribution of preservatives is favoured as non-impregnated parts of wood will lead to a less durable material. Plenty of factors could be the reasons for the observed uneven distribution of preservatives, such as wood products dimension, moisture content, drying process, wood extractives and structure.
In this study, the influence of drying conditions, extractives and wood structure to uneven distribution of preservatives was studied. 294 Scots pine (Pinus Sylvestris) boards were treatment with copper based preservatives. The boards were kiln dried under two different drying temperatures (dry temperature was 60 and 80 °C, respectively) to three different target MC (10-12, 18 and 24%). Before drying and impregnation, green and dried test samples (2×400 mm) from these boards were taken and stored in freezer at -24°C, respectively. The total failure ratio (boards which have failure/total boards) was 31%. The highest failure ratio occurred in group whose drying temperature was 80oC and MC was 13.8%, and the minimum failure ratio occurred group whose drying temperature was 80oC and MC was 20.2%. Quantitative analysis of extractives on matched impregnated and umimpregnated areas of dried and green samples were done by GC-FID. The microstructure of wood on the areas with impregnation failures was also studied by SEM. The results showed that fatty acids, resin acids and fats could play an important role in explaining uneven distribution of preservatives. The areas with impregnation failures contained more fatty acids, resin acids and fats than impregnated areas on dried samples. Those extractives could block resin canal (resin acids) as well as parenchyma cells (fats and fatty acids) which will hinder liquid penetration. Also, the drying process (drying temperature and MC) has an influence to presence of fatty acids, resin acids and fats, which could well explain the impregnation failure ratio of the whole batch. In addition, the influence of reconditioning to uneven distribution of preservatives was investigated with the help of CT-scanner. However, the results showed that the influence of reconditioning to impregnation results was not obvious.
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