The effect of felling time of year on CCA fixation rate and quality of selected hardwoods

IRG/WP 98-40116

Y T Ung, A Taylor, P A Cooper, D P Kamdem

White birch (Betula papyrifera), poplar (Populus sp.) and red maple (Acer rubrum) trees were harvested in winter, in spring, before the leaves flushed, after leaf flush and later in the summer. Sapwood discs were cut from the freshly felled trees, dried and cut into 25 mm and 19 mm cubes. The cubes were pressure impregnated with CCA-C and fixed under high relative humidity and at 50°C or at room temperature (21°C) conditions. Fixation rate was measured by expressing cubes periodically and analysing the expressate for CrVI content using a diphenyl carbazide indicator. The expressate was also examined for chromium, copper and arsenic using ASOMA X-ray fluorescence spectroscopy. Red maple wood harvested in spring fixed more slowly than wood cut in either the winter or the summer. This is thought to be related to the sugar, starch and other nutrient content of the wood at different times of the year. The time of year of felling had no consistent effect on the speed of fixation in white birch and poplar sapwood. Fixation quality was evaluated by leaching studies on 19 mm cubes using AWPA standard E 11-87. As has been observed elsewhere with red maple and other species, rapid fixation rate is accompanied by poor quality of fixation of CCA components, and especially of arsenic. We conclude that the season during which red maple is harvested can have a great effect of CCA performance in this species, which helps explain variable fixation rates and quality of fixation observed previously with this species.


Conference: 98-06-14/19 Maastricht, The Low Countries

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