Liquid penetration of precompressed wood .5. Effects of cyclic loading, type of impregnated chemicals and annual ring angles on the uptake of water or oily solvents

For the development of pre-compression treatments to accelerate liquid penetration into refractory wood, the effects of cyclic loading, the types of the liquids and the annual-ring angles of the specimens on the liquid uptakes were evaluated. When three-cycle loading with a constant strain up to 50% was applied to wood specimens, the stresses of the second and third cycles remarkably decreased to less than that of the first one. In the case of three-cycle loading with rising strains up to 30, 40 and 50%, the stresses of the second and third cycles increased exceeding over the prior one. Improvement of liquid penetration virtually was recognized after the pre-compressed woods were impregnated with water-born preservatives under pressure. The largest retention of liquid was detected for wood. specimens which had been treated under three-cycle loadings at constant strains up to 50%. No significant difference of liquid retention was detected among the three types were water-born preservatives of CCA, copper naphthenate and zinc versanate. Pre-compressed wood also took up a considerable amount of hydrophobic oil-based solution when the fixed strain was released in the liquid. In this case, the liquid uptake was affected largely by the moisture contents of the specimens when compressed, and the amounts decreased at more than 25%. The visible damages hardly were detected for the specimens with annual ring angles smaller than 45 degrees, however, the amount of liquid uptake gradually decreased with increases of annual ring angles. This was suggested to be caused by the reduction of liquid pass-ways and the incomplete recoveries of compression strains, which originated from the decreases of cell-wall fractures around pits and the occurrences of separations along the middle layer, respectively.