Determination of solar optical properties of transparent polymer films using UV/vis spectroscopy

In this paper, 4- and 5-flux models were implemented and used for the determination of absorption and scattering coefficients of transparent polymer films by UV/vis/NIR spectroscopy. The models were applied for a systematic characterization of polar ethylene copolymer films in the solar radiation range. The investigated ethylene copolymer films were highly transparent in the solar range of radiation, with hemispheric transmittance values above 91% and hemispheric reflectance values of about 8%. Both models revealed a significant forward scattering behavior of the films. The 4-flux model fitted hemispheric and diffuse transmittance far better than the 5-flux model. Hemispheric reflectance values were overestimated by both models. Similar absorption coefficient values ranging from 0.4 to 0.6 cm−1 were obtained for all investigated films. While ethylene(acrylic acid/butylacrylate) terpolymer showed the lowest scattering coefficient (10.9 (5-flux) and 6.8 cm−1 (4-flux)), the highest scattering coefficient (26.2 (5-flux) and 35.2 cm−1 (4-flux)) was found for ethylene(butylacrylate) copolymer.