Finger jointing is complex and requires numerous efforts in order to evaluate the various parameters that influence the process and to optimize product performance. Some of the key parameters are related to the conditions of the lumber material such as moisture content (MC) and temperature. Attempts are made by the finger jointing industry to control the lumber conditions prior to finger jointing; however, the process has proved to be difficult. There is a need to evaluate the impact of MC and temperature of lumber and the interaction between the two, on the end product performance, especially with new adhesives systems.
Black spruce (Picea mariana (Mill) B.S.P.) 2x3 blocks in green and at different MCs (12, 16 and 20%) were condi-tioned at various temperatures (-5, 5, 12 and 20oC) prior to finger jointing. Two types of adhesives were used in this study: Polymer Emulsion Polyurethane (PEP) and a new fast curing formulation of Phenol Resorcinol Formaldehyde (PRF). All specimens were tested in tension after 24h of curing at room temperature to determine their ultimate tensile strength (UTS). Microscopic analysis of the adhesive bond was performed to evaluate the glue penetration into the wood following conditioning. Results have shown that the operating envelop for PEP adhesive is between 12 and 16% MC and between 5 and 20oC, while optimum MC for PRF adhesive was found to be around 16%. It was found that PRF adhesive performed better at high moisture content. High wood failure and uniform glue penetration profiles were associated with dry lumber. Failure in the glue and irregular glue penetration profiles were generally associated with green wood.