EFFECT OF POLYISOCYANATE LEVEL ON STRENGTH PROPERTIES OF WOOD FIBER-COMPOSITE MATERIALS

The development of strong, durable, and hydrophobic wood composite mat erials that can be manufactured in a technically simple and efficient operation have been sought by wood scientists and industry for decades . Polyisocyanate resins possess unique characteristics that may enable the manufacture of performance-driven and hybrid wood composites for partially fulfilling the desired attributes. The objectives of this st udy were to examine the effectiveness of using increasing levels of di phenylmethane diisocyanate (MDI) resin (3%, 10%, 20%, and 30%) for imp roving strength properties of wood fiber composites. The strength prop erties of MDI-consolidated fiber composites are compared with those co nsolidated with phenol-formaldehyde (PF) resin at comparable resin lev els. Strength properties evaluated were modulus of elasticity (MOE), m odulus of rupture (MOR), and internal bond (IB) of specimens subjected to dry, water-immersion (wet), and ASTM D-1037 accelerated-aging trea tments (AAT). Results indicate that an MDI level near 20 percent may b e the most efficient in maximizing strength properties of MDI-consolid ated wood fiber composites. Dry-MOE and dry-MOR were maximized at MDI resin levels near 10 and 20 percent, respectively, while dry-IB was ma ximized at the 20 percent level. Resin level had no effect on AAT-MOE. AAT-MOR and AAT-IB were maximized at the 10 percent and 20 percent le vels, respectively. Wet-MOE and wet-MOR were most efficiently maximize d at the 30 and 20 percent levels, respectively. There were practicall y no differences between MDI- and PF-consolidated wood fiber composite s in MOEs under the dry, water-immersed, and AAT conditions at each of the four resin levels. However, there were significant differences be tween MDI and PF in MOR and IB under all test conditions; the MDI-cons olidated composites were far superior to the PF-consolidated composite s.