Improving Surface Functionality, Hydrophilicity, and Interfacial Adhesion Properties of High-Density Polyethylene with Activated Peroxides

Polyolefins have had limited application in advanced technologies due to their low surface energy, hydrophobicity, and weak interfacial adhesion with polar coatings. Herein, we propose the use of transition metals at their lowest oxidation state and inorganic peroxides to improve the functionality, surface free energy, hydrophilicity, and adhesion properties of high-density polyethylene (HDPE). Among the nine combinations of transition metals and peroxides used in this study, the combination of Co(II) and peroxymonosulfate (PMS) peroxide was the most effective for surface modification of HDPE, followed closely by the combination of Ru(III) and PMS. After chemical treatment, HDPE's surface functionality, composition, and energy were analyzed via Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and contact angle measurements. Hydroxyl, carbonyl, and carboxylic acid functional groups were detected on the surface, which explained the improved hydrophilicity of the modified HDPE surface; the contact angle of HDPE with DI water decreased from 94.31 to 51.95° after surface treatment. To investigate the effect of HDPE's surface functionality on its interfacial properties, its adhesion to a commercial epoxy coating was measured via pull-off strength test according to ASTM D54541. After only 20 min of surface treatment with Co(II)/PMS solution, the adhesion strength at the interface of HDPE and the epoxy coating increased by 193%, confirming the importance of polyolefins' surface functionality on their interfacial adhesion properties. The method outlined herein can improve HDPE's surface functionality by introducing sulfate radicals. It improves HDPE's hydrophilicity and adhesion properties without requiring strong acids or time-consuming pre- or post-treatment processes. This process has the potential to increase the use of polyolefins in various industries, such as for protective coatings, high performance lithium-ion battery separators, and acoustic sensors.