The highlights of a co-operative research program developed by the U.S. Forest Products Laboratory (FPL) and Forintek Canada Corp. to provide detailed creep-rupture and some creep information for composite panel products are summarized here. Support for this program has been provided by the American Plywood Association, The Waferboard Association (now the Structural Board Association), as well as the U.S. and Canadian Forest Services. Commercially produced plywood, oriented strandboard (OSB), and waferboard were tested to identify three mills that produced panels with high, low and median flexural creep performance. These three plywood, three OSB, and three waferboard products were then extensively tested to provide information on their duration of load and creep performance.
The bending properties of aspen waferboard can be improved by increasing the resin content and/or board density. These options, however have limited effect and are very costly. On the other hand, panels produced with longer, oriented stands have demonstrated significant improvements in bending strength and stiffness. The panel industry has recently used wafers or strands up to approximately 102mm (4in), however, the utilization of much longer material is practical. In addition to more efficient use of the wood resource, structural panels with improved properties can penetrate more demanding applications, particularly as future engineering materials, and overcome some problems experienced with traditional wood composites such as creep. The overall objective of the study was to demonstrate that by using long strands, coupled with appropriate strand alignment, strand thickness, and face-to-core layer ratio, a structural panel can be produced with superior strength and stiffness in the aligned direction while maintaining adequate properties in the cross direction. The specific objective for this year's work was to establish the improved performance using panels produced in structural sizes and under conditions that parallel those of the industry more closely. Manufacturers of oriented strandboard and waferboard can use the information to produce high performance OSB panel products with minimal effects on production parameters and costs.
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.
This study was undertaken in response to the many troubleshooting enquiries received from manufacturers and users of overlaid panel products as demand for and production of these products increase. In the past, Canada was without an independent laboratory for conducting overlay tests in accordance with Canadian and United States standards. During the past three years, Forintek staff have acquired the expertise and the testing equipment needed to effectively evaluate overlays in accordance with standard test procedures. Information on the various types of decorative overlays and coatings used to finish wood-based panels was summarized in terms of properties, adhesives used, and typical applications. A computer and a hard copy file database was developed from information gathered from the literature, from visits to mills and other facilities, and from discussions with industry representatives and other colleagues. A dedicated Overlay Testing Laboratory was established at Forintek with all the necessary test equipment and with displays of the reference standards and overlay and edgebanding materials. Three particleboard manufacturers provided Forintek with samples overlaid with melamine-impregnated paper for evaluation in accordance with standard test procedures. Two common problems with which Forintek has been successful in providing guidance to the industry are described.
Trembling aspen and ponderosa pine sapwood treated with sulphonated wattle tannins or cashew not shell liquid and with or without copper chloride using either the single of double treatment were evaluated for durability against a white- and brown-rot fungi using the standard soil block method.
