Influence of climate oscillations on moisture content profiles of beech timber during initial stages of drying

Abstract

This study aimed to determine the influence of equilibrium moisture content (EMC) oscillations on MC profiles of beech timber (38 x 120 x 500 mm) during drying in the climatic chamber. Two test runs with EMC oscillations (along with constant temperature) were followed by the equivalent test runs in constant climate: altogether, 4 drying runs were carried out. The amplitudes of EMC oscillations were ca. +/- 1.5% (absolute value) compared to the value in constant climate test, while the temperature in all cases was 35 degrees C. Among others, MC profile across thickness was periodically determined by slicing five lamellae and using the oven-dry method to determine their MC. Drying curves produced during constant and oscillation climate drying were similar and no statistical difference was found between average MC determined on the same day during constant and oscillation drying. In all cases it was found that MC difference between core and surface is lower (or at least not higher) in oscillating compared to constant climate conditions. This indicates that, if the positive influence of additional mechanosorptive creep (caused by EMC oscillations) on stresses in wood is taken into account, lower stresses in surface layers can be expected during oscillation drying. Further tests will be done to reveal the exact MC changes within surface layers of the boards. It is demonstrated that the climatic chamber is very stable in reaching and maintenance of air parameters during oscillation drying; it has practically no uncontrolled oscillations and will be used in further testing, along with the tests in semi-industrial and industrial kilns.