Waferboard/oriented strandboard (OSB) has been traditionally manufactured almost exclusively with trembling aspen in Canada. With the declining availability of aspen wood resource, OSB mills have begun to use alternative species in their production, usually other hardwood species. Meanwhile the mills have also begun experiencing some constraints in the use of phenol-formaldehyde (PF) resins for bonding these species, such as poor resin distribution and low retention on the surfaces of strands, particularly for a powdered form. The change of binder systems for bonding dense hardwoods can be extremely costly to OSB producers. The objective of this study is to determine the optimum adhesive and process requirements for manufacturing OSB from high-density hardwood furnish.
Study in 1997-1999 has shown that a dense wood is more difficult to bind than a less dense wood with a powder phenolic resin due to the poor resin distribution and retention. A liquid resin appears to produce stronger panels compared to a powder resin. The powder resin blending and bonding efficiency could be apparently improved by different resin application methods: (1) enhancing the wax distribution; (2) separately applying wax and resin to individual species strands and then mixing them up; (3) spraying a small amount of liquid additives after resin application; and (4) finally using small particle-size powders. A series of strandboards were constructed with aspen, birch, southern yellow pine, and sweetgum, using powder PF resins in the face and powder PF, liquid PF or diphenylmethane diisocyanate (MDI) in the core. An overall comparison showed that the aspen panels performed best followed by the southern yellow pine panel while the birch and sweetgum panels performed similarly with regard to both physical and mechanical properties.
Work in 1999-2000 focused on some fundamental studies on wood chemical and physical properties. Seven wood species were characterised for pH, base and buffering capacities, bound and soluble acids, and water and ethanol-toluene solubility. The wood species included aspen, white birch, yellow birch, red maple, sugar maple, southern yellow pine, and sweetgum. The study was also extended to the mixed wood species, included white/yellow birch, aspen/birch, southern yellow pine/sweetgum, aspen/red maple, aspen/sugar maple, and aspen/red maple/birch. This work indicated that there were significant differences in the chemical characteristics between the species investigated. These wood species were also characterised for surface roughness using a surface roughness tester. It was found that aspen strands showed significantly rougher surfaces than did southern yellow pine, sweetgum, and sugar maple. Strand surface characteristics seem to be related to the wood anatomical structure. A species (like aspen) having low density appears to yield a rougher surface than does one having high density (like sweetgum).
In the coming year, the efforts will focus on characterisation of wood/resin interaction, modification of phenolic resin, and optimization of panel manufacturing process parameters in order to more efficiently utilise various high-density hardwood furnishes for OSB production based on the information obtained in the previous studies of this project. The detailed information on project plan and milestone is illustrated in Appendixes 1 and 2.