High-Frequency and Hot-Platen Curing of Medium-Density Fiberboards

The effects of two curing methods (high-frequency heating and hot-platen heating) on the properties of medium-density fiberboard were studied. Panels were made of a furnish produced by pressurized-refining of a mixture of 50 percent red oak (Quercus falcata var. falcata), 25 percent mockernut hickory (Carya tomentosa) and 25 percent sweetgum (Liquidambar styraciflua) unbarked chips. The boards, made at three densities (38, 44 and 50 lbs/ft3), were bonded with 8 percent urea-formaldehyde resin. Density gradients across the thickness were less pronounced in the low and medium density boards bonded by high-frequency heating than those cured by hot-platen heating, while this property was not affected by curing method at the high density. Modulus of rupture and modulus of elasticity values of the high frequency-cured boards exceeded those of the hot-platen cured boards at the high density level; the two bending properties were similar for the two curing methods at the two lower density levels. Internal bond strengths of the high-frequency cured boards were higher than those of the hot-platen cured boards at all density levels. There were no significant differences attributable to the curing methods in tension parallel to the surface, linear expansion, and thickness swelling.

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