Impact of preservative impregnation on wettability, surface free energy, and adhesive bonding of Scots pine CLT

This study examined the impact of preservative treatment and preservative type on the physical, mechanical, and bonding properties of Scots pine cross-laminated timber (CLT). CLT panels were fabricated using copper azole (Cu Azole) and a boron-based formulation (Tar & imath;mBor) at three retention levels. Increasing preservative loading significantly reduced surface free energy (by up to 24%) and shear strength (by up to 26%), while thickness swelling and water absorption increased by 15-28% compared to the untreated control. Moderate Cu Azole retention (Cu Azole A) provided the most balanced performance, maintaining adequate bonding strength and dimensional stability. The observed mechanical losses were closely related to reduced wettability and changes in wood surface chemistry induced by preservative components. These findings demonstrate that optimizing preservative retention is crucial for achieving both biological protection and reliable bonding performance in CLT production, providing practical guidance for the industrial manufacturing of durable structural panels.