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Hardboard is closely tied to the building industry and 60 percent of all hardboard is used directly in construction. Hardboard siding is probably the least expensive wall cladding available. Its share of the construction market has been increasing and this trend is expected to continue.
In the hardboard manufacturing process, shorter fibers eliminate high density spots because of uneven fiber distribution in the wet manufacturing process (11). Generally, hardwoods having short fibers make better wet process hardboard. Hardwoods also require less energy as compared to softwoods (11). Hardwoods such as black locust, oak, beech, and sweetgum are extensively available in the eastern United States, but have not been filly utilized (5,14). This is especially true for black locust, which is a fast-growing species that could be cultivated on marginal land as an energy and fiber crop. Its high decay resistance due to its high extractive content is one of the major advantages of this species (7,10). Woody materials with high extractives content are known for their low fiber-saturation point and their good dimensional stability (4,12).
Production of naturally decay-resistant hardboard would be desirable and may expand the use of black locust in the manufacture of hardboard. Therefore, the purpose of this study was to evaluate some of the physical and mechanical properties of hardboard made of black locust furnish. Static bending properties, internal bond strength, tension strength, thickness swelling, surface roughness properties, and decay resistance of laboratory manufactured hardboards were investigated based on three standards: American National Standards Institute A135.4-1982, American Society for Testing and Materials (ASTM) D-1037, and American Wood Preservers' Association (AWPA)
MATERIALS AND METHODS
Twenty-year-old black locust (Robinia pseudoacacia) logs with diameters ranging from 20 to 30 inches were harvested from Kellogg Experimental Forest located at Augusta, Mich. Logs were debarked with a ring debarker then reduced into chips by means of an Eager Beaver chipper, model 200 from Morbark, Inc. Chips were impregnated with sodium hydroxide and sodium sulfite in a Sprout-Bauer 560-GS impressafiner at a 4 to 1 compressive ratio. Impregnated chips were then cooked in a rapid-cycle digester for 30 minutes at 150degC. Finally, a 36-inch double-disk refiner, model 401 Sprout-Bauer, was used to defiberize cooked chips using different specific energies.
Pulp samples were analyzed according to standard TAPPI...