Thermally modified hybrid aspen : adding value to fast growing broadleaved species in Northern Europe

Abstract: This thesis is focused on thermal modification of hybrid aspen (Populus tremula L. x Populus tremuloides Michx.), its mechanical properties, wood defects and potential use in construction. In the recent years, wood as a building material has become increasingly popular. It is preferred because of its aesthetic appeal; it is renewable and substitutes fossil-based energy consuming materials. However, greater use of wooden products can also put more pressure on our natural forests. The main problems discussed in this paper were: mechanical characteristics after intense thermal modification and overall quality characteristics of thermally modified hybrid aspen. The present thesis conducts an empirical research of harvesting model trees, band sawing them into boards and kiln-drying, in order to prepare samples for thermal modification. Specimens were prepared for compressive strength, bending strength and wood density testing. Mechanical tests were carried out following the standards of ISO 13061-17, ISO 13061-3 and ISO 13061-2, accordingly. Furthermore, thermally treated sample boards from hybrid aspen (Populus tremula L. x Populus tremuloides Michx.), were evaluated according to 14 predetermined quality characteristics. Thermally modified hybrid aspen showed lower wood density and lower bending strength, but higher compressive strength in comparison with untreated hybrid aspen material. Wood quality evaluation showed that hybrid aspen had almost two times more wood defects compared to European aspen. Thermal modification process had statistically insignificant effect on measured wood quality. As a result, it can be said, that despite the decrease of some mechanical properties, thermally modified hybrid aspen still has a potential in areas where load bearing abilities are not so important, for example sauna interiors and interior panelling.