To decrease the formaldehyde emission of poplar plywood, the effect of heat treatment upon the
material of a veneer sheet was investigated. The results showed that when the veneer was heated at a
temperature higher than 150 °C for 1 h, the emission from the poplar plywood decreased. Moreover,
heating at temperatures less than 170 °C did not decrease the strength of the veneer sheet. The water
adsorption properties of the heated veneer were estimated from the adsorption isotherms. When the
poplar veneer was heated at 150 °C and 170 °C, the hydrated water (monomolecular adsorption)
decreased slightly and the dissolved water (polymolecular adsorption) did not change. It is thought that
formaldehyde emission is related to the adsorption properties of the monolayer and that free
formaldehyde from uncured adhesive temporally reacted with the hydroxyl groups of the wood
substance. Heat treatment at temperatures ranging from 150 °C to 170 °C was very useful, because
such treatment can control the emission of formaldehyde from poplar plywood, while having little
influence on its mechanical properties.