EFFECT OF RESIN TYPE ON PROPERTIES OF STEAM-PRESS-CURED FLAKEBOARDS

Six potentially important wood adhesives for gluing southern pine and white oak flakeboards were evaluated for their performances in steam-i njection pressing and conventional platen pressing. Of the six resins tested, polyisocyanate resin performed well in both steam injection an d conventional platen pressings. Phenol-formaldehyde (PF) and melamine urea-formaldehyde (MUF) resins performed poorly in steam-injection pr essing. However, adding a small amount of polyisocyanate improved perf ormance considerably. Bending strengths were consistently higher with conventional platen pressing than with steam-injection pressing. The l ower density face in steam-injection pressing would result in lower be nding properties. In PF and MUF resin systems, steam-injection pressin g resulted in low bond strength and high dimensional stability, wherea s conventional platen pressing resulted in high bond strength and low dimensional stability. The pairing of low strength with high stability suggested that bonding strength could not be the cause of improvement in dimensional stability. Most probably, steam pressing reduced inter nal stresses and stabilized the flakes, which in turn resulted in an i mprovement in dimensional stability. The improvement in dimensional st ability may also be related to less strength loss of the board in stea m-injection pressing when exposed to high relative humidity treatment.