The combined effects of temperature and compression on the microstructure of solid-wood panels produced by Aspen (Populus tremula) wood were evaluated. Thermal compression was applied on aspen wood to increase the density for improving its physical and mechanical properties. The solid wood panels with dimensions of 100 mm by 500 mm by 25 mm were hot-pressed by using a laboratory hot press at a temperature of either 150 °C or 170 °C and pressure of either 1MPa or 2 MPa, respectively, for 45 min. Changes in the microstructure were detected by using a light microscope. The microscopic investigations revealed that the wood exhibited much defects in the process conditions of 170 ºC / 2 MPa, and the distribution of defects were not uniform in the growth rings of the wood specimens in the two treatment groups. All defects in cell structure were quite distinct in the beginning and the last parts of the growth rings and the largest damages occurred in the fibers and vessels for the two process conditions. The results indicate that growth ring structure, vessel porosity, and cell wall thickness have a strong effect on wood behavior in various process conditions.

This study evaluates the microscopic changes of paulownia solid wood panels subjected to thermal compression via characterizing the changes in wood microstructure. The panels, with dimensions of 500 mm × 100 mm × 20 mm, were hot-pressed in a tangential direction by using a laboratorytype hot press at a temperature of either 150 °C or 170 °C and a pressure of 2 MPa for 45 min. Microscopic investigations conducted by light microscopy showed that slightly more damage occurred in the samples compressed at 170 °C and 2 MPa than at 150 °C and 2 MPa, and that the distribution of deformation in the panels was not uniform in the growth rings of the two treatment groups. The cell collapse was not observed in the microstructure of paulownia wood after the thermal compression. Cell shapes and their arrangement in the growth ring alongside loading direction were interpreted as effective factors governing the non-uniform distribution of damage and the lack of cell collapse in the microstructure.

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For many product and applications, the penetration of preservatives or modification substances into wood species should be deep and homogeneous. Caucasian spruce and European larch are resistant to impregnation. This study compared how different incising pre-processes increased the retention of impregnation materials and the depth of their penetration into the structures of these refractory wood species. Mechanical, biological, and laser incising pretreatments were applied to increase the permeability of sapwood samples before the impregnation. To compare the uptake of the wood preservatives transverse and longitudinal to the axial tracheids in the samples, the cross-sections of some of the samples that had been subjected to different incising pretreatments were covered with a polyurethane-based paint. All wood samples were impregnated using a vacuum method with Celcure C4 new generation preservatives. The study compared the possible effects of these different incising pretreatments on the uptake of preservatives into the tracheids in the spruce and larch woods in both longitudinal and transverse directions. The results showed that the copper (Cu) uptake levels increased in these refractory wood species, especially in the transverse direction, after the different incising pretreatments. Moreover, the results showed it is very important to choose the most suitable pretreatment method for the refractory tree species before impregnation.

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