Surface tension of polyethylene used in thermal coating

Abstract

In this work the surface tension of a polyethylene used in thermal coating, identified as a mixture of low density polyethylene (LDPE) and stearic acid, was measured as a function of temperature for temperatures ranging from 120°C to 150°C using a pendant drop apparatus. The values were compared to the surface tension of the pure components (low density polyethylene and stearic acid). It was shown that the surface tension of the mixture is higher than the surface tension of the pure components (more than 25%). Surface analysis by Electron Spectroscopy for Chemical Analysis (E.S.C.A.) of the polyethylene used in thermal coating before and after surface tension measurement was conducted; the experimental results showed that the oxygen and the carbon present at the surface of both the powder and the drop were involved in COH and COOH bonds (for oxygen) and in CC and CO bonds (for carbon). It was shown that there is an increase of COOH and a decrease of COH bonds at the surface when the polymer is heated. It was also shown that there is an increase of C bounded to O at the surface of the drop and consequently a decrease of CC bonds. The decrease of COH was attributed to the drying of the polymer during heating and the decrease of CC was attributed to the coalescence of the polymer particles during pendant drop fomation.