Thermo-vacuum process for wood thermal modification: results for some European softwood and hardwood species treated at different conditions

Three softwoods (Picea abies Karst., Abies alba Mill. and Larix decidua Mill.) and five hardwoods (Quercus petraea Liebl., Fraxinus excelsior L., Fagus sylvatica L., Prunus avium L. and Robinia pseudoacacia L.) were treated at high temperature in vacuum conditions with TERMOVUOTO® technology. The laboratory prototype used for the tests is a one cubic meter unit, with an oil heating system and high efficiency fans, which allow the heat transfer through convection even under partial vacuum conditions. All the wood species were treated at different temperatures (from 160 to 220°C), different time (from 45 minutes to 5 hours) and under different pressure conditions (160, 210, and 330 mbar). The treated material was physically characterized in terms of mass loss, color changes and equilibrium moisture content. Results show dissimilar behavior of various wood species and their different sensitivity to treatment schedules. Consequently, the series of tests performed allowed detailed characterization of the TERMOVUOTO® process and its effect on product quality.