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Bonding Performance of Adhesive Systems for Cross-Laminated Timber Treated with Micronized Copper Azole Type C
Expanding the use of cross-laminated timber (CLT) to outdoor applications is “one sticky problem.” Research must examine compatibility between adhesive and wood preservative, evaluate bond strength and wood failure under applied forces, and test bond durability to withstand accelerated weathering without delamination.
Durability and Wood Protection Research
Parameters for three adhesive systems (melamine formaldehyde, resorcinol formaldehyde, and one component polyurethane) were described for manufacturing 3-ply CLT from 35 mm thick boards that were untreated or treated with two retentions of the wood preservative MCA-C (micronized copper azole – type C). All adhesive and preservative retention combinations met the minimum standard requirements for wood failure percentage. The low preservative retention (1.0 kg/m3 for above ground use), however, reduced block shear strength regardless of adhesive, while the high retention (2.4 kg/m3 for ground contact use) did not affect block shear strength when the adhesive was resorcinol formaldehyde or polyurethane. In the accelerated weathering test, only the polyurethane resin provided satisfactory bonding performance for all treatment levels. These combined results indicate that under these test conditions best bonding performance was obtained with the one component polyurethane system.
Hyungsuk Lim and Sachin Tripathi - Mississippi State University