Latex paint as a delivery vehicle for diethylphthalate and di-n-butylphthalate: Predictable boundary layer concentrations and emission rates

The description of emission processes of volatile and semi-volatile organic compounds (VOCs and SVOCs) from building products requires a detailed understanding of the material and the air flow conditions at the surface boundary. The mass flux between the surface of the material and air depends on the mass transfer coefficient (h_m) through the boundary layer, the gas phase concentration of the target compound immediately adjacent to the material (y₀), and the gas-phase concentration in bulk air (y(t)). In the present study emission experiments were performed in two chambers of quite different sizes (0.25 m3 and 55 m3), and, in the larger chamber, at two different temperatures (23 °C and 30 °C). The emitting material was latex wall paint that had been doped with two plasticizers, diethylphthalate (DEP) and di-n-butylphthalate (DnBP). The phthalate content in the paint was varied in the small chamber experiment to evaluate the impact of the initial concentration in the bulk material (C₀) on the emission rate. Boundary layer theory was applied to calculate h_m for the specific phthalates from the Sherwood number (Sh) and the diffusion coefficient (D_air). Then y₀ was determined based on the bulk gas-phase concentration at steady state(y). For both, DEP and DnBP, the y₀ obtained was lower than the respective saturation vapor pressure (P_s). Furthermore, for both phthalates in latex paint, the material/air partition coefficient (C0/y0) was close in value to the octanol/air partition coefficient (K_OA). This study provides a basis for designing phthalate emitting reference materials that mimic the emission behavior of common building materials.