The aging effects of repeated oxygen plasma treatment on the surface rearrangement and adhesion of LDPE to aluminum

The effects of aging temperature and time on the adhesion properties of oxy gen plasma-treated low-density polyethylene (LDPE) were investigated. As th e aging temperature and time increased, surface rearrangement and the migra tion of molecules containing polar functional groups into the bulk were acc elerated to the surface to form a hydrophobic surface. The adhesion strengt h of oxygen plasma-treated LDPE/aluminum joints was measured using a 90 deg rees peel test by varying the plasma treatment time and aging temperature. The adhesion strength was constant, regardless of the plasma treatment time . As the aging temperature increased, the adhesion strength of the LDPE/alu minum joints decreased and the locus of failure changed from cohesive to in terfacial failure. It was also found that the polar functional groups burie d in the bulk could be reoriented to the surface in a polar environment. Th is study also investigated whether repeated oxygen plasma treatment would i ncrease the concentration of polar functional groups at the surface and red uce the surface rearrangement and the migration of molecules containing pol ar functional groups during aging. Contact angle measurements and X-ray pho toelectron spectroscopy (XPS) showed that repeated oxygen plasma treatments increased the concentration of polar functional groups at the surface. How ever, the aging time between plasma treatments had a negligible effect on t he concentration of polar functional groups at the surface.