Microwave-assisted laminated veneer lumber (LVL): Investigation on the effect of preheating time and moisture content on resin penetration and bonding quality

This research presents the effect of microwave preheating and moisture content on phenol-formaldehyde resin penetration and bonding quality of poplar laminated veneer lumber (LVL). Effective penetration and maximum penetration factors were measured individually in the surface and core layer to investigate the bonding characteristics. The bonding quality of the LVL is also measured through shear strength (parallel to grain direction) and the ratio of delamination. The results showed that by increasing moisture content, from 3 to 8%, the shear strength of the LVLs decreased while the ratio of delamination was raised. On the other hand, microwave preheating improved the bonding properties and the core temperature of the preheated LVL reached 100 °C in a shorter time. Results revealed the correlation of penetration parameters on the LVLs shear strength and the ratio of delamination. LVL made from layers with 3% moisture content and 180 s preheating had minimum resin penetration. The highest effective and maximum penetration were observed in samples made with 8% moisture and without preheating which then indicated the weakest shear strength and the highest ratio of delamination. The positive effect of microwave preheating on bonding quality was much more tangible for the billet with higher moisture content.