Investigation of variables affecting hot-press formaldehyde and methanol emissions during laboratory production of urea-formaldehyde-bonded particleboard

Abstract

An extensive research project has been undertaken to investigate variables that affect hot-press formaldehyde and methanol emissions from particleboard bonded with urea-formaldehyde resin. A system has been developed to collect hot-press emissions from particleboard made in the laboratory (1). The system consists of an aluminum caul plate that is sealed when the press is closed, but has an inlet and outlet to allow air to be drawn through the air space immediately surrounding the board during pressing. The emissions are trapped with a series of liquid-filled scrubbers in an ice bath. The scrubber contents are then analyzed for formaldehyde using the chromotropic acid method. Some of the samples were analyzed for methanol using gas chromatography. The results from a number of studies demonstrate that several variables affect hot-press formaldehyde and methanol emissions. Formaldehyde emissions increased with increasing press time, platen temperature, moisture content, resin level, and formaldehyde-to-urea (F/U) mole ratio. Formaldehyde emissions decreased with increasing board thickness, but were not affected by wood particle size and degas time. Formaldehyde emissions were also affected by the type of chemically bound formaldehyde present, i.e., methylol groups emitted much more formaldehyde than methylene groups. Methanol emissions increased with increasing press time, moisture content, and decreasing wood particle size. Degas time did not affect the methanol emissions. There was a close relationship between the emissions and the moisture movement out of the panel.