Effect of fiber mat moisture content on physical properties of polyisocyanate-bonded hardboard

This paper reports on the effects of fiber mat moisture content (MMC) (8%, 15%, and 22%) on the physical properties of hardboard bonded at a 3 percent diphenylmethane-diisocyanate (MDI) adhesive level, and compares them to hardboard bonded at phenol-formaldehyde (PF) levels of 3 and 10 percent and an MMC of 7 percent. The physical properties examined were: water absorption (WA), thickness swell (TS), and linear expansion (LE) after immersion in water for 24 hours; and weight change (WC), TS, and LE after two, four, and six cycles of ASTM D-1037 accelerated-aging treatment (AAT). MMC significantly influenced WA and TS (between the 8% and 15% MMCs) and the LE (between 15% and 22% MMCs) of water-immersed hardboard bonded with MDI. The overall water-immersed properties were optimal at an MMC of 15 percent. MMC had no significant effect on TS and LE of MDI-bonded hardboard exposed to as many as six cycles of AAT. However, MMC did impose some significant effects on WC after exposure to two and four cycles of AAT. No significant differences among MMCs were observed at six cycles of AAT. The MDI-bonded specimens performed better than the PF-bonded specimens (3% and 10% adhesive levels) in water-immersed WA and TS. MDI outperformed PF in TS due to AAT at the 3 percent adhesive level, while MDI was comparable to the 10 percent PF-bonded specimens.

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