Monitoring the thermal oxidation of thin polymer films by means of acoustic resonant spectroscopy

This paper describes the use of acoustic resonant spectroscopy to monitor the thermal oxidation of a thin polymer film. The samples were linear low-density polyethylene films with thicknesses of 11.6 μm. These were heat treated at temperatures ranging from 80 to 100 °C in a furnace with an air ambient for a maximum of 10 h. Although no obvious difference between the optical microscope images of the films with and without heating were found, the sound velocity and density, which were measured using acoustic resonant spectroscopy, clearly changed depending on the heat treatment temperature and time. These changes in the acoustic properties were confirmed to be due to thermal oxidation of the films and to correlate with the growth of the oxide which depends on the temperature and time of the heat treatment.