Surface characteristics of low-density polyethylene films modified by oxyfluorination-assisted graft polymerization

In this study, a unique two-step process, i.e., an oxyfluorination-assisted graft polymerization (OAGP), was used to modify the surface properties of low-density polyethylene (LDPE) films. Based on the results of the 1,1-diphenyl-2-picrylhydrazyl (DPPH) method, which was performed to estimate the amount of hydroperoxides generated by oxyfluorination, oxyfluorination conditions that maximize the amount of hydroperoxide groups were selected. Hydroperoxides were generated by oxyfluorination to provide active sites for the OAGP of the different monomers. Depending on the type of monomers used, two different graft polymerization behaviors were observed. Hydrophilic methacrylic acid (MA) monomers were graft polymerized onto the oxyfluorinated LDPE (OFPE) surface in a perpendicular direction, forming a spike-shaped morphology. On the other hand, hydrophobic styrene (ST) monomers were graft polymerized parallel to the OFPE surface, forming a valley-shaped morphology. By changing the type of vinyl monomers, two different surfaces could be prepared using the hydroperoxides generated by oxyfluorination. After OAGP with MA monomers, a hydrophilic surface following the Wenzel model was obtained, whereas after OAGP with ST monomers, a hydrophobic surface following the Cassie–Baxter model was obtained. Therefore, the OAGP process may be an efficient method for preparing two different surfaces by changing the monomer used.