The Effects of Sealing Treatment and Wood Species on Formaldehyde Emission of Plywood

Urea-formaldehyde (UF) resin (F/U: 1.25), melamine-urea-formaldehyde (MUF) resin (F/(U+M): 1.05), and three kinds of wood species including poplar (Populus davidiana Dode), beech (Fagus engleriana Seem.), and eucalyptus (Eucalyptus robusta Smith) were used to produce plywood. The effects of sealing treatment and wood species on the formaldehyde emissions were studied. The anatomical characteristics of different wood species were measured. The results showed that: (1) formaldehyde emission of plywood treated by surface sealing was higher than without treatment; (2) formaldehyde emission of nine-ply poplar plywood bonded by UF resin decreased by 74.4% to 1.98 mg/L after edge sealing treatment; (3) compared with beech and poplar plywood, the formaldehyde emission of five-ply eucalyptus plywood bonded by MUF resin was the lowest obtained, at 0.19 mg/L; (4) formaldehyde emission of poplar plywood from the surface changed slightly in spite of different layers. The contact angle and spreading-penetration coefficient, K, analyses showed that the cell arrangement of eucalyptus was dense. Scanning electron micrographs indicated that the pore sizes of eucalyptus samples were the smallest in contrast to poplar and beech.