Chemical oxidation of high‐density polyethylene: Surface energy, functionality, and adhesion to liquid epoxy

Abstract The application of polyolefins has increased significantly over the past few decades. However, their chemical inertness and low surface energy limits their application in many industries where high adhesion to polar materials is required, such as for composites and protective coatings. Herein, six different acids are used to create polar functional groups on High‐Density Polyethylene's (HDPE) surface and to increase its adhesion to liquid epoxy (LE). Contact angle measurements, Fourier Transform Infrared Spectroscopy (FTIR), X‐ray Photoelectron Spectroscopy (XPS), and pull‐off strength measurements are used to analyze the surface energy and functionality of HDPE and to measure its adhesion to LE. The results show that each acid increases both the polar and disperse surface energies of HDPE to a different extent, but that this is not necessarily a function of acid strength. Chlorosulfonic acid and chromic acid increase the oxygen to carbon ratio by a factor of 8 and increase HDPE's adhesion to LE by more than 400%. Furthermore, a comparison between predicted work of adhesion values from the OWRK model and experimental results shows that the latter are significantly higher than what is predicted, especially with increasing surface polarity.