PROPERTIES OF MEDIUM DENSITY FIBERBOARDS PRODUCED FROM THERMOPLASTICIZED WOOD FIBERS BY ALLYLATION WITHOUT ADHESIVES

Medium density fiberboards (MDF) were produced from thermoplasticized wood fibers by allylation under liquid and vapor phase methods without using adhesives. The internal bond (IB) of the fiberboard with a dens ity of more than 0.6 g/cm(3) was equal to or larger than that of the c ontrol (phenol resin bonded fiberboard) when allylation temperatures w ere more than 80 degrees C in the liquid phase method or 100 degrees C in the vapor phase method. The corresponding modulus of rupture (MOR) was much smaller compared with that of the control. The thickness swe lling (TS) was smaller than that of the control when allylation temper atures more than 80 and 90 degrees C were used in the liquid and vapor phase methods, respectively. This is considered to be caused by the s ubstitution of the hydroxyl groups in wood by hydrophobic allyl groups . To reduce the amount of allylated wood fibers included in the fiberb oards, the untreated or acetylated wood fibers were blended with allyl ated wood fibers. The blending of both fibers decreased the IBs of the fiberboards, but it did not change the MORs. The TS was increased by the blending. However, when the acetylated wood fibers were used, the TS was less than 10% at the blending ratio of less than 20%. This is c onsidered to be due to the great dimensional stability of acetylated f ibers.