Six impregnating phenol formaldehyde (PF) resins having low to moderate molecular weight were synthesized and evaluated for their wood veneer penetration and curing properties. Based on the results from the penetration and curing properties studies, a PF resin designated as B-2 was used to impregnate subalpine fir, white spruce and lodgepole pine veneer. LVL panels, 12 x 12 inch, were prepared with these veneers. Both modulus of rupture (MOR) and modulus of elasticity (MOE) were increased by 10 to 15% for the resin-impregnated LVL made from each of the SPF species. Edgewise bending results for specimens cut from 2 x 4 foot white spruce LVL panels showed an increase of 15% both for MOR and MOE for the resin impregnated specimens. As well, the dimensional properties (% edge swelling and % water uptake) of the SPF LVL panels were improved by 50% using the patented Forintek resin impregnation method.
A series of plywood and laminated veneer lumber (LVL) panels were prepared using veneers with higher than normal moisture contents in face and back layers. The purpose of the work was to evaluate the effects of self-generated steam on the pressing times and panel warpage. Panels made with 6% and 10% m.c. faces and backs were compared with control panels made with all dry veneer. Thirteen- ply 40 mm (1 5/8 inch) thick panels were evaluated for press times and thin 9.5 mm (3/8 inch) panels were evaluated for cupping and bowing. Normal plywood press temperatures and adhesives were used. All panels were made with incised 3.2 mm (1/8 inch) SPF veneers. The project demonstrated that substantially shorter press times and more dimensionally stable panels can potentially be made using higher moisture content outside veneers.
Steam press drying of green SPF veneers was evaluated on a 4 x 8 foot prototype steam press set up at a local plywood mill. A used industrial press has been modified into a single opening oil heated hot press with grooves machined into the upper platen. Standard green nominal 4 x 8 foot 3.2 mm (1/8 inch) thick mill veneer was dried with super-heated steam injected through 6 mm (1/4 inch) holes in the bottom platen. All veneers were incised with Forintek's patented veneer incisor. The project demonstrated that steam injection can dry green veneers three to four times faster than conventional veneer driers. From the results of this project, a study on the press drying of redry veneer was initiated and showed good potential for industrial implementation.
The purpose of this study was to determine if press-drying of redry veneer is a practical option for the plywood industry. Two press-drying schedules were tested - one minute and two minutes at 340 degrees F with 10 psi press pressure. Drying two redry sheets per opening for two minutes gave the best results. Moisture pockets in the veneer were reduced to an acceptable level and moisture equalization occurred between the two sheets in the press and during the veneer load cool-down time. Press drying redry veneer may provide a relative low cost processing option for mills to complement more capital-intensive alternatives such as radio-frequency (RF) drying.