EFFECT OF STEAM PRESSURE REFINING AND RESIN LEVELS ON THE PROPERTIES OF UF-BONDED RED MAPLE MDF

A study was undertaken to determine the influence of steam-pressure-re fining levels on red maple (Acer rubrum L.) wood chips fabricated into medium density fiberboard (MDF) test boards using four urea-formaldeh yde resin levels. Red maple chips were fiberized using a pressurized, double-disk refiner operating at six refining pressures (50, 60, 70, 8 0, 90, and 100 psi). MDF test boards were produced using the six group s of refined fibers at four urea-formaldehyde resin contents. Static b ending (MOE and MOR), internal bond (IB), water absorption, and thickn ess swell properties were measured. An increase in refining pressure d id not significantly affect MDF strength or dimensional stability prop erties. In contrast, the resin content of the boards had a significant effect on all board properties. An increase in resin content from 6 t o 12 percent resulted in a 174 percent increase in internal bond stren gth, a 68 percent increase in the modulus of rupture, and a 40 percent increase in the modulus of elasticity, whereas thickness swell and wa ter absorption properties decreased by 113 and 60 percent, respectivel y. Preliminary data indicate that the most significant factor, other t han resin content, influencing both fiber and board properties was the wood chip moisture content during refining. Nearly all fiber and MDF properties were affected by the addition of moisture to the wood chip prior to refining. Further investigations concentrating on wood chip m oisture content during refining and refiner plate design should be con ducted in order to more clearly understand the relationship between re finer variables and red maple MDF board properties.