Dynamic visualisation of a solvent-borne preservative in wood using confocal laser scanning microscopy

Abstract Recently, a rapid method of protecting mass timber has been developed involving a combination of incising and spraying the incised wood with a solvent-borne preservative. The preservative penetrates the wood longitudinally from incisions and a deep protective envelope is achieved in the species tested to-date. However, many questions remain about the mechanism involved in creating this protective envelope. For example, how long does it take for the envelope to be created? How does wood’s microstructure affect preservative penetration? To answer these questions, we developed a novel confocal laser scanning microscopy (CLSM) system that permits the dynamic visualisation of rate and penetration patterns of a fluorescent solvent-borne preservative into wood. We demonstrate the value of this system by investigating the speed and penetration pathways of the preservative into sugi sapwood. We found that initial axial through-penetration of the preservative to a depth of 10 mm occurs rapidly (< 60 s) via tracheids in the early-to-latewood transition zone and then spreads to adjacent earlywood areas. Complete penetration throughout wood’s microstructure occurred within the holding time for commercial treatment (10 days). In conclusion our CLSM system provides valuable information on the effect of wood’s microstructure on the dynamic longitudinal penetration of a solvent-borne preservative in wood, and it could potentially be used to optimise the treatment of different wood species and mass timber using the newly developed incising/spraying treatment method.