This study relates to technology for tailor-making PF resin with molecular weight and size distributions beyond those now available for commercial processing. Consequently, adhesive mobility and cure speed can be adjusted through use of a two-component resin system comprised of continuous and dispersed phases. Current studies specifically concern two-component alkaline plywood formulations suitable for bonding veneer at 12 plus or minus 2% m.c.
The objectives of this study were to produce and modify phenolic dispersion based adhesives using technology recently developed at Forintek and to further characterize the physical properties and bonding properties of these systems for veneer and composite board applications with emphasis on faster cure speed potential. Data developed in this study indicate opportunities to improve waferboard and plywood PF adhesives in terms of color, cure rate and application properties. Further research work is recommended to improve techniques for producing and characterizing appropriate powder disperson-like formulations for wood bonding.
Further data on flow, viscosity-solids and veneer bonding at dry and 11 plus or minus 2% wood m.c. conditions are provided for heated PF powder systems. This information is intended to supplement the main report issued in March 1987.
A series of dispersion-resin plywood formulations were prepared in the laboratory and their bond performance assessed on incised spruce veneer at 10% m.c. Excellent bond quality results were achieved in these laboratory experiments as indicated by high average % wood failure values of over 90%. To further develop the plywood dispersion resin, a pilot plant trial at a gluing company was conducted and again excellent bond quality results were achieved. A large quantity of the plywood dispersion resin was prepared and a successful mill trial at Cantree Plywood was carried out. This trial demonstrated that more dimensionally stable panels can be prepared from high m.c. veneer. The waferboard dispersion technology developed in this study helped facilitate a mill trial using high moisture content face wafers.
Wood failure evaluation is the key criterion for predicting the long-term durability of plywood. At present, the conventional visual method for plywood wood failure evaluation is slow and subjective. Evaluations can be influenced by factors such as: room lighting, wood species, sample treatment, and readings from prior samples. An automated wood failure evaluation system using image analysis techniques could potentially be programmed to consider all the variables and respond with consistent wood failure values regardless of the machine operator's experience level. This report describes the results of a six-month study in which a system for automated plywood wood failure determination was compared with conventional visual wood failure evaluation. It was built upon research undertaken in the 1996/97 year in which the feasibility of the approach was initially established. In the research reported previously, a colour optical imaging system was assembled and suitable wood failure algorithms were compiled with promising results. The imaging system was 100 % effective in reproducing sample values. The data were discussed with the project liaisons and a three-month comparison with Canply readings was suggested. In this study, machine evaluation of 4,150 samples was compared with readings of monthly plywood mill quality control samples. The sampling was designed to include all British Columbia plywood mills and all categories of commercial plywood production. The differences in average values for wood failure between human and machine evaluation were found to be less than plus or minus 5% in the majority of cases. In addition, 93 % of ‘set average' readings fell in the plus or minus 10% range of deviation expected of human wood failure readers. Agreement on readings of individual samples within each set was not quite as good with 72% falling in the plus or minus 15% range.
Wood failure evaluation is the key criterion for predicting the long-term durability of plywood. At present, the conventional visual method for plywood wood failure evaluation is slow and subjective. Even experienced evaluators can show significant differences in their evaluations on the same plywood specimen and an individual evaluator can make different wood failure estimates on the same specimen at different times. Differences among evaluators can be as high as 50% for some samples. Evaluations can be influenced by room lighting, the wood species, sample treatment, and readings from prior samples. An automatic wood failure evaluation system using image analysis techniques could potentially be programmed to consider all the variables and respond with consistent wood failure values regardless of the experience level of the machine operator. This report describes the results of a one-year project in which a system for automatic plywood wood failure determination was investigated. A color optical imaging system was assembled and the preliminary work of compiling suitable algorithms was completed with promising results. The imaging system was 100% effective in reproducing individual sample values. Samples were sorted according to plywood type and test method to develop appropriate program algorithms for each category. The wood failure program was then further developed to automatically detect wood species and test method, thus avoiding the need for specimen separation prior to evaluation. Based on nearly 1200 samples in four categories, the differences in average values of wood failure between human evaluation and machine vision were found to be less than plus or minus 5%. In addition, a minimum of 85% of individual machine readings fell in the plus or minus 15% range of deviation expected of human wood failure readers. The imaging system was more accurate for light-colored specimens (i.e., Canadian Softwood Plywood) than darker-colored specimens (i.e., Douglas fir ) and for specimens where resin had been applied by spray. In order to make the imaging system more reliable and robust, the algorithm parameters now need to be fine-tuned based on a larger sample database.
The new technologies, incising, moisture tolerant phenolic adhesives and steam pressing were evaluated for the manufacture of laminated veneer lumber (LVL). Both 8- and 13-ply incised spruce LVL panels were prepared using these new technologies. The results showed that both steam pressing and self-generated steam from wet face and back veneers accelerated temperature rise in the innermost glueline of 13-ply incised spruce LVL panels. This would help facilitate faster production rates for LVL manufacture. Bond quality and edge bending values were determined for the steam-pressed 8-ply and 13-ply incised spruce LVL panels. In all cases the average % wood failure was above 90% indicating excellent adhesion between the moisture tolerant adhesive and wood. The modulus of rupture and modulus of elasticity values measured for the steam-pressed incised spruce LVL samples compared very favourably with those for a commercial Norway spruce 15-ply LVL product.
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.
A series of plywood and laminated veneer lumber (LVL) panels were prepared using incised veneers in the second phase of this two year project. The primary purpose of the work was to evaluate the effects of steam injection on the pressing times. A secondary objective was to expand the study of warpage in three-ply and four-ply plywood which was begun in phase one. Thirteen-ply 40 mm (1 5/8 inch) thick panels were evaluated for press times and thin 9.5 mm (3/8 inch) and 12.5 mm (1/2 inch) panels were evaluated for cupping and bowing. Press temperatures of 150 degrees C, 175 degrees C and 204 degrees C were used with a commercial adhesive mix for the LVL study while normal plywood pressing conditions were used for the plywood. For the plywood warpage study, the effect of lathe check orientation and species mix were evaluated. The lathe check orientation had little effect while the surface veneer species had a pronounced effect on the warpage in the plywood. Steam used for injection was heated to 260 degrees C at 450 KPa (65 psi) with a super-heater. All panels were made with incised 3.2 mm (1/8 inch) SPF veneers. The project demonstrated that steam injection can shorten press times by fifty percent if incised veneers are used.