Abstract:

Chinese wood based composite manufactures are plagued with serious formaldehyde emissions (F-emission). This study investigated using a diphenylmethane-4, 4′-diisocyanate (MDI)-urea formaldehyde (UF) adhesive mixture in particleboard manufacture in order to decrease F-emission below 9mg·(100g)^-1. In this article, we paid more attention to the effect of NH₄Cl on UF-MDI curing and the method of adhesive application using differential scanning calorimetric (DSC) analysis and mechanical properties. The ratio of UF to MDI was 6 (based on dry particle mass, UF content was 6%, and MDI was 1%). Hot press temperature was 175? ℃, cycle time 6?min, and pressure 3?Mpa. We pressed the particleboard on with or without NH₄Cl, separately spray or mix UF/MDI then spray. Further, we analyzed the process of UF-MDI curing by DSC. Both results proved acidic NH 4Cl hinder MDI-UF curing. We hold that when UF∶MDI=6∶1, spray mixed adhesives without NH₄Cl was the best combination for improving mechanical properties and simultaneously decreasing F-emission to below 9mg·(100g)^-1. Ranking all the properties, adhesive application method should be: mix UF/MDI then spray without NH 4Cl>spray separately with NH₄Cl>spray separately without NH₄Cl=mix UF/MDI then spray with NH₄Cl.

Key words: UF-MDI adhesive mixture, formaldehyde emission, particleboard, curing agent, separately application, mixing application