Properties of Populus genus veneers thermally modified by two modification methods: wood treatment technology and vacuum-thermal treatment
¹Latvia University of Life Sciences and Technologies, Forest Faculty, Department of Wood Processing, Liela street 2, LV3001 Jelgava, Latvia
²Latvia State Institute of Wood Chemistry, Laboratory of Wood Biodegradation and Protection, Dzerbenes street 27, LV1006 Riga, Latvia
Due to environmental concerns the use of wood materials is becoming more extensive and is causing wood supply shortage, therefore the use of Populus genus wood species with a short rotation period is vital. Populus genus species wood has several shortcomings – it is not durable, has low density and is hygroscopic. Thermal modification is a technology that can be used to improve the situation. In this study aspen (Populus tremula L.) was thermally treated using the Wood Treatment Technology (WTT) device for 50 min at 160 °C (50–160 WTT) and poplar (Populus x canadensis Moench) was vacuum-treated (VT) 120 min at 204 °C (120–204 VT), 120 min/ 214 °C (120–214 VT), 180 min 217 °C (180–217 VT) and 30 min 218 °C (30–218 VT). Mass loss (ML), colour change, density, tensile strength along the fibres, moisture exclusion efficiency and weight loss (WL) after brown rot fungus Coniophora puteana were determined and also light microscopy images were taken. Aspen veneers showed a ML of 5.3% between 120–214 VT (6.2%) and 30–218 VT (4.6%) treatment that coincided with the same mass loss in aspen boards cited in the literature. The highest ML was 8.7% calculated from 180–217 VT, while the lowest ML was 2.9% computed from 120–204 VT. The total colour change ΔE was 44, where lightness parameter L provided the greatest impact that was reduced twice after modification. Tensile strength reduced by 47% in the WTT process and had ~29% reduction in the VT process. The WL after fungus C. puteana was 33% at 50–160 WTT. After VT treatment, WL was 0–2.4%. 120–214 VT and 180–217 VT poplar veneers were the most suitable for plywood production.