Factors affecting volatile organic compound emissions during hot-pressing of southern pine particleboard

Three types of adhesives, urea-formaldehyde (UF) resin, phenol-formaldehyde (PF) resin, and polymeric methylene bis(phenyl isocyanate) (pMDI) were used to bond particleboard during the investigation of the effect of hot-pressing variables on volatile organic compound (VOC) emissions. The variables examined included press temperature, press time, mat moisture content, resin content, and panel density. The VOCs emitted during particleboard hot-pressing with southern pine furnish were collected with two chilled scrubbers filled with water and methylene chloride, respectively. The solution in the aqueous scrubber was analyzed for formaldehyde using a colorimetric method. The other VOCs contained in the scrubbers were extracted with methylene chloride and characterized and quantified by gas chromatography/mass spectrometry (GC/MS). Formaldehyde emissions were significantly affected by press temperature and press time for panels pressed with all three adhesives. For panels pressed with both UF and PF resins, mat moisture content significantly affected formaldehyde emission, but mat resin content and panel density did not have a significant effect on formaldehyde emissions. Formaldehyde emissions correlated well with the amount of water vapor collected for panels pressed with UF and pMDI, but not for panels pressed with PF resin. An additive in the PF resin decreased formaldehyde emissions during pressing of panels with PF, so that pressing panels with the PF resin yielded lower formaldehyde emissions than pressing with pMDI resin. Other compounds emitted during pressing were terpenes and their derivatives, lower molecular weight aldehydes, ketones, and some high boiling point linear alkanes. The emissions of high molecular weight VOCs (HMwVOC [defined as compounds with boiling points greater than 40?C]) were significantly affected by press temperature for all three adhesive types, and by press time for the UF and PF resins. Moisture content also significantly increased HMwVOC emissions for pMDI. While application of UF and PF to the wood furnish did not significantly affect HMwVOC emissions, application of pMDI caused a significant decrease in HMwVOC emissions. Changes in pinene emissions with press conditions were similar to the changes seen in HMwVOC emissions.

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