Oriented strandboard (OSB) manufacturing technology has been advancing steadily during the past few years. Today, the industry can produce higher quality OSB at lower costs than ever before in the product's history. Research results have shown that drying costs can be reduced and strand quality can be improved through proper wood yard management, and that the production efficiency can be improved through various ways of optimizing the pressing and processing operations. OSB quality has been improved and board density has been reduced by using long and thin strands in panel face layers and relatively short and thick strands in the panel core. The press times have been reduced by using higher press temperatures and higher mat face-layer moisture contents. The degree of strand alignment has been improved by controlling the falling distance from the alignment heads to the top of mat being formed. Strands alignment has been further enhanced by arranging the alignment disc gaps in such a way so that narrower strands can be aligned through narrower gaps and directed towards core while wider strands can be aligned through wider gaps and directed towards the panel surfaces. Based on these technical advancements, OSB can be produced faster and at a lower density without sacrificing quality. Consequently, the OSB industry is in the position to improve panel quality without resorting to costly options such as increasing resin content and press time.
In this project, a comprehensive experiment studied the impact of wax type, wax content, wax heating temperature and wax molecular weight on OSB panel performance. It shows that to allow tall oil, hydrogenated soybean wax, linseed oil, and low density polyethylene (LDPE) to be used for OSB, further work is needed. We need to add wax in the OSB process; otherwise panel dimensional stability will be ruined. There is an optimal wax content of around 1% in OSB production. The wax content in OSB panel did not need to be higher than 1%. With the waxes tested, wax heating temperature should be higher than 90°C. At a fixed wax heating temperature, optimal wax molecular weight is 520 Daltons for OSB application. Applying high molecular weight wax (600 Daltons) on panel surface may help to improve panel bending strength.
The experiment shows that partial substitution of slack wax with LDPE at the OSB panel surface layer may be feasible.
Experimental results also show that using contact angle and surface tension tests may help us to screen waxes for OSB panel application.
Based on the experimental data, one should handle different waxes in different ways. By engineering wax application parameters one can develop a cost effective way to produce composite panels to meet dimensional stability requirement. Further testing on the feasibility of using contact angle and surface tension to differentiate wax should be conducted. Emulsifying low density polyethylene should be further investigated. Further research is also needed to verify how wax operational parameters affect panel strength.
The objectives of this study were to characterize OSB panel permeability in comparison with plywood and low density fiberboard; to determine the effect of panel characteristics on the speed of moisture movement through the thickness of the OSB panels; to create a finite element model of the permeability of OSB; to suggest improvements of the OSB panel structure in function of permeability.
The introduction of current report presents extracts of the theory of moisture transfer in wood materials and introduces the concept of water potential and the instantaneous profile method as adapted to OSB to be used for the determination of the diffusion coefficient (D).
The experimental part is divided into three stages. In the first stage the permeance of the OSB panels, plywood and low density fiberboard is compared according to the dry cup method. The experiments showed that the low-density fiberboard panels’ permeance is more than twice as high as compared with the permeance of the OSB panel; the Western Red Cedar has an approximately equal permeance with the OSB panel, which is in turn higher as compared with the permeance of the Aspen plywood. The Aspen plywood produced with parallel plies shows approximately 30 % higher permeance as compared to the regular plywood.
In the second stage, the effects of density, strand geometry and orientation level, panel density and moisture content on the permeance and on the diffusion coefficient are determined. The experiment is organized based on an experimental design. For the permeability (permeance and diffusion coefficient), the lower the strand thickness, the lower the permeability; the lower the level of strand orientation, the higher the permeability; the larger the strand width and length (surface area), the lower the permeability, the higher the permeability.
During the third stage, the dynamics of moisture movement in the panel is modeled with a finite element model based on an unsteady-state moisture transfer equation and the results from simulations are compared to experimental results in order to validate the model. Ten cases of adsorption and two cases of desorption are considered. Seven of the cases are duplicated with experimental results to serve for validation of the model. The closeness of the experimental and simulation results allow concluding the validity of the finite element model, which can be used to optimize the OSB panel structure by selecting practical layer characteristics leading to desired moisture permeability.
Under current ASTM D-3501 procedures, the only practical method of obtaining compressive properties of wood based panels is to glue two or more plies of the specimen together to provide a compact column cpapble of resisting buckling. It is thought, however, that this method may not provide representative compression strength and stiffness data due to load sharing.
The optimum moisture content of the raw logs used in the manufacturing of oriented strand board (OSB) may be defined by a minimum requirement for fibre conversion and a maximum that will limit the cost of drying the flakes. This criterion could become the mainstay of an effective raw-log purchasing and inventory management program. However, OSB manufacturers have lacked the technology for monitoring whole-log moisture content. FERIC tested several technologies and identified time domain reflectometry (TDR) as an effective means of sampling the moisture content in a large number of logs.
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.
