Effect of polyisocyanate level on physical properties of wood fiber composite materials

This study examined the effects of using higher diphenylmethane diisocyanate (MDI) levels (3%, 10%, 20%, and 30%) on physical properties of wood fiber composites and contrasts them with wood fiber composites consolidated with a phenol-formaldehyde (PF) resin. The physical properties examined were water absorption (WA), thickness swell (TS), and linear expansion (LE) after immersion in water for 24 hours (wet); and weight change (WC), TS, and LE after exposure to six cycles of ASTM D 1037 accelerated-aging treatment (AAT). The most efficient resin level was defined as that level at which a further increase does not result in a statistically significant improvement in the property being examined. Wet-WA did not significantly improve with MDI levels higher than a level near 20 percent, while wet-TS and wet-LE were minimized efficiently 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 similar to the 10 percent PF, and the 10 percent MDI level was statistically similar to the 20 and 30 percent PF levels. There was little difference in resin efficiency 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 PF in AAT-TS at the 3 percent level. Also, MDI specimens at the 10 percent level were statistically lower in AAT-TS than those consolidated at the 3, 10, and 20 percent PF levels. The PF-consolidated specimens had significantly less change in AAT-LE than the MDI-consolidated specimens at the 10, 20, and 30 percent levels.

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