Abstract
Preservative effectiveness of candidate fungicides for glue-line treatment was investigated using 4.0-and 5.6 thick lauan plywoods glued with melamin-urea formaldehyde resin. Non-weathered ply-woods treated with the following three fungicides were able to inhibit effectively the decay by a brown rot fungus Tyromyces palustris Murr. at active ingredient retentions shown in the parentheses : 4-chlorophenyl-3'-iodopropagylformal (0.6kg/m3 ), 3-ethoxycarbonyloxy-1-bromo-1, 2-diiodopro-pene (1.0kg/m3), and mixture of tributyltinphthalate and potassium iodide (0.24kg/m3+0.48kg/m3). Higher retentions of these fungicides were necessary to inhibit the decay by a white rot fungus Coriolus versicolor Quél. The enhancement of preservative effectiveness was recognized oftenly in any fungicide-treated plywoods after 3-month exposure to 60°C, followed by its decent after longer term exposure. Such a enhancement was found more oftenly in case of 90 repetitions of wet (6 hrs water soaking) and dry (60°C for 18 hrs) cycling than in 30 repetitions. It was probable that the amount of fungicides diffusing into veneer wood from resin adhesive was more than that of fungicide losses by liberating or leaching during a limited term exposure to 60°C.
From the results with preservative effectiveness after several weathering treatments, the first and second organic iodo compounds described above are considered to be the most promissing fungicide for glue-line treatment and the third organic tin compound is the next. However, improvement of curing condition should be necessary to enlarge the fungicide distribution into veneer wood of treated plywood.
