Water-based coatings require coalescing aids to achieve properties equivalent to solvent-borne paints. A common coalescing aid in latex paints is 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (TMPD-MIB). The relatively large quantity of TMPD-MIB used in latex paints has raised concerns regarding its emissions to both indoor and outdoor atmospheres. In this study, a one-dimensional dual (paint and material) layer diffusion model was developed to estimate emissions of TMPD-MIB from two latex paints applied to gypsum board. The paints contained different pigment volume concentrations (PVC) and different amounts of TMPD-MIB. Different modeling approaches were used depending on the PVC of the paint. The proposed model for paint drying and TMPD-MIB emissions was tested with data from previous chamber experiments. Experimental data were first used for purposes of parameter estimation, and the model was then compared against an independent experimental dataset. The diffusion coefficient of the paint layer was adjusted as a function of the water content remaining in the wet paint film. The effective diffusion coefficient of TMPD-MIB in the paint layer was found to be dependent on the PVC and water content of the paint. Nomenclature j A Rate of mass transfer per unit area (mg m À2 h À1 ) c A Concentration of TMPD-MIB in paint film or gypsum board (g m À3 ) z Space coordinate measured normal to the section (m) D AL1 Diffusion coefficient for TMPD-MIB in paint film (m 2 h À1 ) D AL2 Diffusion coefficient for TMPD-MIB in gypsum board (m 2 h À1 ) R A Kinetic retardation factor for transport in paint film or gypsum board c L1 Concentration of TMPD-MIB in layer 1 (paint) (mg m À3 ) c L2Concentration of TMPD-MIB in layer 2 (material) (mg m À3 ) D eff1Effective diffusion coefficient of TMPD-MIB in layer 1 (m 2 h À1 ) D eff2Effective diffusion coefficient of TMPD-MIB in layer 2 (m 2 h À1 ) R 1 Kinetic retardation factor for transport of TMPD-MIB in layer 1 R 2 Kinetic retardation factor for transport of TMPD-MIB in layer 2 k a TMPD-MIB mass transfer coefficient (m h À1 ) k c Water mass transfer coefficient (m h À1 ) aMaterial thickness (m) bLocation of the paint-air boundary (m) M T Initial mass of TMPD-MIB applied to gypsum board (mg) f T Fraction of TMPD-MIB present in the paint Dz 1 Distance between nodes in layer 1 (m) A Area over which the paint is applied (m 2 ) 291 DdVariation of the paint thickness (m) C w Saturation vapor density of the water (kg m À3 ) qDensity of water (kg m À3 ) RH Relative humidity (%) t evap Time for water to completely evaporate from the film (h)
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