Effects of alumina hollow microspheres on the properties of water-borne polyurethane films

Water-based polyurethane/alumina hollow microsphere (WPU-hAl₂O₃) composite films were prepared via a facile spin coating method. The pristine WPU, as the matrix of the composite films, was tailor-made by hAl₂O₃ with the diameter of 2-5 μm to improve the mechanical and physical properties of the films. The hardness, surface morphology, infrared emissivity, wettability, and light transmittance of the WPU-hAl₂O₃ films with different hAl₂O₃ contents were investigated. The results indicate that the Vickers hardness, coefficient of friction, infrared emissivity at the wavelength of 2-22 μm, and wetting angle of the WPU-hAl₂O₃ films (30 wt%) increased by 53.6%, 51.7%, 21.1%, and 19.0%, respectively, compared with the pristine WPU films. Meanwhile, with the rising of hAl₂O₃ content, the light transmittance decreased by 75.3% at the wavelength of 400-800 nm. This work not only designs a kind of lightweight multifunctional composite film but also provides an effective route for extending further applications of hAl₂O₃ in the field of composite films.