Effect of compression on the liquid absorption of Chinese fir wood with different heartwood-to-sapwood ratios

Abstract

In this study, the Chinese fir (Cunninghamia lanceolata Hook.) specimens with different ratios of heartwood thickness to sapwood thickness (HS) were radially compressed at different compression speeds, and then absorbed amine copper quat-type D (ACQ-D) preservative solution under the negative-pressure produced by the recovery of compression deformation. The liquid uptake (A _l), the recovery rate of compression deformation (R _s) and the chemical absorption (A _c) of samples were determined, as well as the overall distribution of density and effective component of ACQ-D (i.e., copper in wood), the mechanical properties such as surface hardness were also measured. The A _l, R _s, A _c values of compressed samples including the whole heartwood ones were higher than those of uncompressed samples, showing that radial compression had an obvious positive effect on improving the liquid absorption of heartwood. Higher compression speed of 3 mm·min⁻¹ is preferable since the samples with that speed could reach the highest A _l and A _c; in addition, more deformation fixation has been produced possibly because of the faster heat and moisture transmission at the higher compressed speed, and more bonds of hydrophobic nature were formed, leading to the higher surface hardness and density. A consistent tendency of the density distribution and the copper retentions along the thickness direction could be explained that the layers with higher density have smaller volumes of void areas, and more chemicals were absorbed and fixed, resulting in the higher copper retentions.