Volatile organic compound emissions during hot-pressing of southern pine particleboard : panel size effects and trade-off between press time and temperature

In previous research, it was shown that decreasing either press temperature or press time generally resulted in decreased volatile organic compound (VOC) emissions during the hot-pressing of southern pine particleboard. However, because it is impossible to reduce both pressing time and temperature while maintaining panel physical and mechanical properties, this study evaluated two sets of conditions to determine whether it might be more advantageous, from an emissions perspective, to hot-press at a lower temperature for a longer pressing time or at a higher temperature for a shorter pressing time. An enclosed caul plate was used to collect VOC emissions during the pressing of panels manufactured using each of the three major wood adhesives: urea-formaldehyde, phenol-formaldehyde (PF), and polymeric methylene diisocyanate . Each of the resins was pressed under two different temperature/time conditions that yielded panels with equivalent internal bond strengths. It was generally found that panels pressed at a high temperature for shorter press times emitted more formaldehyde, pinenes, and higher molecular weight VOCs (defined as VOCs with boiling points higher than 40°C). Increases at the higher temperature condition ranged from 10 to 204 percent. The one exception to the increases in VOCs at the higher temperature and shorter pressing times was formaldehyde emissions from panels bonded with PF resin. This may be an anomaly that results from an additive in the PF resin that serves as a formaldehyde scavenger.This study also evaluated the effects of increasing panel size on emissions from pressing of panels. Small panels (305 by 305 mm) and larger panels (610 by 610 mm) were manufactured using each resin under press conditions appropriate for the resin. In all cases, emissions from the larger panels were lower on a per weight basis compared to the smaller panels. The decreased edge area relative to panel area clearly has a significant effect on the release of the emissions from the panels during manufacture.