An AFM-IR study on surface properties of nano-TiO2 coated polyethylene (PE) thin film as influenced by photocatalytic aging process

Abstract Most plastic wastes undergo extensive photo-aging in the environment, and the aged plastics exhibit different surface properties from pristine ones. Here, we investigate the surface properties of a nano-TiO2 coated polyethylene (PE) film as influenced by photocatalytic aging process using an atomic force microscopy coupled with infrared spectroscopy (AFM-IR) technique. Results showed that the height range of the as-prepared samples was about 30 nm, and the equivalent diameter of nano-TiO2 was ~70 nm. The photo-induced oxidation of the CH2 bond occurred on the surface of the PE film. Photo-aging mainly affected the thermal properties of PE film in a local area, especially affecting the components surrounding the nano-TiO2 particle. The glass transition temperature of unaged PE film mainly changed in the range of 93.9–96.5 °C, but after aging the temperature gradually increased with the distance to nano-TiO2 increasing from near to far. The plastic film surrounding the nano-TiO2 particle became stiffer after photo-aging, and the photocatalytic reaction had an effect on the stiffness of the film material. The second characteristic peaks with resonance deviations (i.e., 110, 112, and 115 kHz) were used for Lorentz contact resonance (LCR) measurements. The mechanical properties of PE film after photo-aging were closely related to the distance between nano-TiO2 and film surface. These research findings are conducive for us to understand better the photo-induced aging process of functional plastic film.