Title: Treatment of tropical hardwoods by using environmentally friendly alkaline copper quaternary (ACQ) for cross laminated timber

Abstract

Alkaline Copper Quaternary (ACQ) wood preservatives are composed of copper oxide and a quaternary ammonia compound which are extensively used as substitutes for chromate copper arsenate (CCA) in wood preservation. ACQ is less toxic owing to the absence of arsenic or chromium. Preservative treatments change both the physical and chemical properties of wood, consequently affecting the bond integrity of glued products. This study evaluates the influence of ACQ preservative relative to the bonding strength and surface wettability of four tropical hardwoods that are used for making cross laminated timber (CLT). The lumbers were impregnated with 2% ACQ solutions by applying a full cell process treatment. The treated lumbers were evaluated for chemical retention, density increment, wood surface roughness and wettability. Three-layered CLT were fabricated at different parameters i.e., species combination, glue spread rates and clamping pressures, and phenol resorcinol formaldehyde (PRF) as binder. The bonding performance of the CLT was examined through block shear and delamination tests. The ACQ treatment resulted in increased in density, noteably for lower density wood such as batai (15.8%). Higher density wood experienced much less increment: kedondong (0.88%), rubberwood (2.2%) and sesendok (2.4%). Both the chemical retention and cu content followed the same trend. Treated wood of higher density has much rougher surfaces which evidently found to reduce the wettability of wood surface. Generally, ACQ did not significantly affect the bonding properties of CLT produced irrespective of parameters used. Among the wood species, rubberwood shows superior bonding ability either in single or in combination with other species. None of the CLT delaminated after being subjected to vacuum pressure soaking and oven drying.