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

This study examined the effects of using higher diphenylmethane diisoc yanate (MDI) levels (3%, 10%, 20%, and 30%) on physical properties of wood fiber composites and contrasts them with wood fiber composites co nsolidated with a phenol-formaldehyde (PF) resin. The physical propert ies examined were water absorption (WA), thickness swell (TS), and lin ear expansion (LE) after immersion in water for 24 hours (wet); and we ight change (WC), TS, and LE after exposure to six cycles of ASTM D 10 37 accelerated-aging treatment (AAT). The most efficient resin level w as defined as that level at which a further increase does not result i n a statistically significant improvement in the property being examin ed. Wet-WA did not significantly improve with MDI levels higher than a level near 20 percent, while wet-TS and wet-LE were minimized efficie ntly at a level near 10 percent. An MDI level of 3 percent efficiently minimized AAT-WC and AAT-LE, respectively, while the 10 percent level minimized AAT-TS. MDI was more efficient than PF in wet-WA and wet-TS , as the 3 percent MDI level was statistically similiar to the 10 perc ent PF, and the 10 percent MDI level was statistically similar to the 20 and 30 percent PF levels. There was little difference in resin effi ciency between MDI and PF in wet-LE. There was no difference in AAT-WC between MDI and PF among all four resin levels. MDI was better than P F in AAT-TS at the 3 percent level. Also, MDI specimens at the 10 perc ent level were statistically lower in AAT-TS than those consolidated a t the 3, 10, and 20 percent PF levels. The PF-consolidated specimens h ad significantly less change in AAT-LE than the MDI-consolidated speci mens at the 10, 20, and 30 percent levels.