Formaldehyde Dynamic Air Contamination By Hardwood Plywood: Effects of Several Variables and Board Treatments

Small, edge-sealed specimens of an unfinished lauan plywood were subjected to dynamic (air ventilated) tests at a variety of board loadings (L) (m2 of board area per m3 of chamber volume) and ventilation rates (N) (air exchanges per hour). For low ventilation rates and/or short times (days to a few weeks), the apparent steady state air concentrations (Cs) (ppm) of formaldehyde followed the two-parameter Hoetjer equation in their dependence upon N/L. At high ventilation rates and/or longer times, the concentrations decreased due to depletion of readily available formaldehyde in the specimens. Within certain limits, therefore, the Hoetjer equation can be employed to evaluate the acceptability of formaldehyde-emitting plywood over a range of loading and ventilation rate situations. Dynamic tests were employed to evaluate the effects of aging, of exposure to ammonia, and of a coating upon the formaldehyde emission by this same plywood. One and two aging periods of 30 days at 75?C and 50 percent relative humidity (RH) reduced the apparent Cs values for the untreated board from an initial value of 3 ppm to 0.3 ppm and then to <0.01 ppm. Exposure to ammonia reduced Cs to about 0.01 ppm; this increased to about 0.05 ppm after one and two aging periods. A urea-containing coating reduced Cs to 0.3 ppm and this was further reduced to 0.04 ppm after one aging period. Both treatments, therefore, are highly effective over long ambient periods. The Hoetjer equation was extended to a mixture of two formaldehyde-emitting boards. The steady state concentration from the mixture can be expressed as an additive function of the two separately measured concentrations. However, the value of the mixed board concentration cannot be calculated from only the Hoetjer parameters for the two separate boards.

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