Formaldehyde Sorption and Desorption Characteristics of Gypsum Wallboard

The sorption and subsequent desorption of formaldehyde (CH₂0) vapor from unpainted gypsum wallboard have been investigated in environmental chamber experiments conducted at 23 °C, 50% relative humidity, an air exchange to board loading ratio of 0.43 m/h, and CH₂0 concentrations ranging from 0 to 0.50 mg/m₃. Both CH₂0 sorption and CH₂0 desorption processes are described by a three-parameter, single-exponential model with an exponential lifetime of 2.9 ± 0.1 days. The storage capacity of gypsum board for CH₂0 vapor results in a time-dependent buffer to changes in CH₂0 vapor concentration surrounding the board but appears to cause only a weak, permanent loss mechanism for CH₂0 vapor. Prior to significant depletion of sorbed CH₂O₁ desorption rates from CH₂0-exposed gypsum board exhibit a linear dependence with negative slope on CH₂0 vapor concentration. Analogous CH₂0 emissions properties have been observed for pressed-wood products bonded with urea-formaldehyde resins.