Infrared radiative properties of thin polyethylene coating pigmented with titanium dioxide particles

The infrared (IR) radiative properties of TiO₂ pigment particles must be known to perform thermal analysis of a TiO₂ pigmented coating. Resins generally used in making pigmented coatings are absorbing at IR wavelengths, which means that the conventional Mie solution (MS) may not be adequate in this domain. There are two approaches to evaluating radiative properties in an absorbing medium: far field approximation (FFA) and near field approximation (NFA). In this study, after reviewing these two approaches, we evaluated the radiative properties of TiO₂ particles in polyethylene resin as an absorbing matrix in the wavelength range of 1.7-15 μm based on the MS, FFA, and NFA. We then calculated the effective scattering and absorption coefficients for different models. To investigate the effect of the particle size and volume concentration on the transmittance of IR wavelengths, we made a nongray radiative heat transfer in an anisotropic scattering monodisperse pigmented layer, with independent scattering using the radiation element method by the ray emission model. The results showed that all three approaches predicted similar results in the particle size domain and volume fraction range utilized in pigmented coatings.