Low formaldehyde emission particleboard bonded by UF-MDI mixture adhesive

Chinese wood-based composite manufacturers are plagued with serious formaldehyde emission (F-emission) problems. Most products release formaldehyde between 35 and 60 mg per 100 g board. In this study, a particleboard with an emulsifiable diphenylmethane-4, 4′-diisocyanate (MDI) ? urea-formaldehyde (UF) mixture adhesive was investigated in order to decrease F-emission to below 9 mg per 100 g board. Comparison of physical and mechanical properties of particleboard showed that the acidic agent NH4Cl did not improve the UF-MDI system curing, and it also affected the adhesive application method. When the two adhesives were mixed first, without adding NH4Cl, and then sprayed onto particles, properties were improved. Hot-press conditions that would optimize particleboard mechanical properties and ensure that F-emissions met E1 grade requirements were determined; hot-pressing at 175?C for 4.5 minutes might lower F-emissions to below 9 mg per 100 g particleboard.

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