Effect of resin variability on the treatability of radiata pine heartwood with copper azole preservative

The effect of resin variability on the preservative treatability of radiata pine heartwood was investigated. The results showed that the tangential permeability of low-resin radiata pine heartwood (LRH) was predominantly governed by its radial permeability, with the radial permeability being 55 times that of the transverse permeability. During transverse impregnation, the copper azole preservative preferentially entered the LRH interior through unblocked radial resin canals, then penetrated into surrounding cells via the interconnected resin canal network, ultimately achieving complete penetration. In contrast, high-resin radiata pine heartwood (HRH) displayed substantial resin accumulation in the latewood, where the resin nearly completely blocked radial resin canals and ray-cell lumina, significantly decreasing latewood porosity and pore size to form penetration barriers. This latewood occlusion drastically diminished HRH's radial permeability, thereby making HRH extremely difficult to treat. Furthermore, in LRH, latewood exhibited superior treatability compared to earlywood due to its higher radial resin canal density. However, although HRH latewood also had a higher radial resin canal density than HRH earlywood, its treatability was severely compromised by resin occlusion.