Humidity and Temperature Effects on MOR and MOE of Hard Maple-Veneered Medium Density Fiberboard

There is a lack of information on the effect of various environments on the bending properties of hardwood-veneered medium density fiberboard (MDF) composite because MDF is a relatively new wood-base material. This study was to determine the effects of relative humidity (RH), temperature (TP), and hard maple veneer thickness or shelling ratio (SR) on modulus of rupture (MOR) and modulus of elasticity (MOE) of hard maple-veneered MDF panels for the purpose of developing a hardwood composite. This composite would be used as a substitute for conventional softwood plywood and lumber. Bending properties (MOR and MOE) of 5/8-inch-thick, 9- by 23-inch hard maple-veneered MDF composites were evaluated at all combinations of 50, 64, 78, and 92 percent RH, and at 50, 75, and 100?F (10?C, 23.9?C, and 37.8?C) conditions. For comparison purposes, 5/8-inch hard maple lumber and Douglas-fir plywood were also tested. Hard maple veneer thickness (SR), RH and TP affected MOR and MOE of all panels tested. Reliable regression models were developed to predict two bending properties of all panels. Both MOR and MOE were improved at high SR and reduced at higher RH and TP. The effects of RH and SR were greater than the effect of TP on MOR and MOE. Certain combinations of hard maple veneers and MDF were found to possess MOR and MOE properties approaching those of the hard maple lumber and Douglas-fir plywood. The lower MOR and MOE of veneered MDF panels at high RH were attributed to a lower density or thickness swelling. The effects of high TP on MOR and MOE were greater at high RH than those at lower RH levels.

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