Investigation of crystallinity effects on the surface of oxygen plasma treated low density polyethylene using X-ray photoelectron spectroscopy

Plasma treated polymer surface shows rapid hydrophobic recovery after plasma treatment. Surface rearrangement and the hydrophilicity change of low density polyethylene (LDPE) films with different degrees of crystallinity after oxygen plasma treatment were investigated using X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Since the mobility of polymer chain was restricted in the crystalline region, the chain movement of high crystalline polymer would be reduced. Water contact angles of quenched and annealed LDPE just after plasma treatment were almost same and oxygen contents of quenched LDPE was slightly higher than that of annealed LDPE. However, annealed LDPE showed slower contact angle raise and kept higher oxygen concentration than quenched LDPE with increasing aging time. By deconvolution of carbon XPS spectra, it was observed that major group contributed to decrease of oxygen contents was the hydroxyl groups and hydroxyl groups of quenched LDPE decayed faster than annealed LDPE while other oxygen species kept constant or decreased slightly. Increasing crystallinity reduce the surface rearrangement of polymer chain after plasma treatment.