Influence of fluorination temperatures on the properties and hydrophilicity of polyethylene terephthalate films

In this study, polyethylene terephthalate (PET) films were directly fluorinated for 30 minutes at temperatures of 55, 75, and 95 °C using a mixture of F2/N2 gases. The chemical composition, surface morphology, and thermal properties of the films were assessed using attenuated total reflection Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and thermogravimetry–differential thermal analysis. The surface free energy was determined by measuring the contact angle of different liquids on the films at different fluorination temperatures. Direct fluorination significantly altered the surface chemical composition and structure of the surface, resulting in progressive changes in surface morphology as the fluorination temperature increased. Fluorinated PET films exhibited significantly higher surface hydrophilicity than non-fluorinated films, with hydrophilicity increasing in parallel with increasing fluorination temperatures. This was due to substantial reductions in water contact angles and significant increases in surface energy. The main reason for the increase in hydrophilicity over time was identified as an increase in polar groups. In addition, the study found that surface fluorination slightly decreased the thermal stability of PET films, most likely due to chain scission.