| Volatile organic compound (VOC) emissions arising during the manufacture of wood-based products became an issue of particular concern after the Clean Air Act Amendment of 1990. This research was intended to investigate the VOC press emissions as a function of press variables and minimize VOC press emissions under typical particleboard manufacturing conditions. VOC emissions from hot pressing were generated utilizing a laboratory-scale press equipped with a sealed caul plate system. The VOCs trapped in a collection system were extracted with methylene chloride and analyzed by gas chromatography/mass spectrometry. Three adhesives, urea formaldehyde resin (UF), phenol formaldehyde resin (PF), and polymeric methylene bis(phenyl isocyanate) (pMDI), were used in this investigation. A statistical experimental design, 25-1 fractional factorial design, was employed to examine the effect of press variables. The press variables investigated were press temperature, press time, mat resin content, mat moisture content, and board density. The VOC press emissions detected in GC/MS included terpenes and their derivatives, lower molecular weight aldehydes, ketones, and some high boiling point linear alkanes. The results showed that the high molecular weight VOCs (HMwVOCs), not including methanol, formaldehyde, and acetic acid, emitted from hot-pressing accounted for about 20 percent of the volatile compounds contained in the wood extractives. Differences in the HMwVOCs emitted from boards with or without UF resin were insignificant. Formaldehyde emissions were significantly affected by press temperature and press time for all three adhesives and by mat moisture content for UF and PF resins. Increasing press temperature significantly increased formaldehyde emissions from panels bonded with UF and pMDI and decreased emissions from panels bonded with PF. However, mat resin content and board density did not significantly influence formaldehyde emissions. HMwVOC emissions significantly increased with press temperature for all three adhesive types, press time for the UF and PF resin, and mat moisture content for pMDI. While UF and PF resin did not significantly affect HMwVOC emissions, application of pMDI caused a statistically significant decrease in HMwVOC emissions. Changes in pinene emissions with press conditions were similar to the changes seen in HMwVOC emissions. When the panel size (length and width) doubled, HMwVOC emissions were significantly decreased by 34.3% and 29.4% for UF- and pMDI-bonded particleboard, respectively, but remained unchanged for PF bonded particleboard. The formaldehyde emissions were significantly decreased by 53.6% and 3 8.8% for PF and pMDI-bonded particleboard, respectively, but remained unchanged for UF-bonded particleboard. The optimum press conditions that minimize VOC press emissions was found by studying the trade-off between press temperature and time without compromising particleboard properties (internal bond strength). VOC press emissions can be minimized by selecting lower press temperatures and longer press times. This research provided valuable information for the wood industry to understand VOC press emissions as a function of press variables and adjust the manufacturing variables to minimize the VOC press emissions. |
