THE EFFECT OF SURFACE FLUORINATION ON THE WETTABILITY OF HIGH-DENSITY POLYETHYLENE

High-density polyethylene (HDPE) samples have been fluorinated and oxyfluorinated for different times. Dynamic contact angle analysis was used to determine the effect of fluorine gas mixtures on the surface of HDPE. The total surface tension of HDPE increased drastically with the length of oxyfluorination treatment, but levelled off after longer treatments. Fluorination resulted in a marked decrease in the total surface tension of HDPE. During fluorination, the dispersive component of the surface tension decreased progressively with fluorination time, while the polar component increased initially but decreased again with longer fluorination treatments. This indicates that short fluorination times lead to increased wettability by polar liquids, while longer fluorination times have the opposite effect. Fluorinated and oxyfluorinated surfaces were exposed to elevated temperatures. Whereas it was found that fluorinated surfaces changed measurably, oxyfluorinated surfaces changed dramatically upon heating at 100 degrees C. Photoacoustic FT-IR spectroscopy indicated that this was probably due to migration of surface polar groups into the bulk of the polymer, rather than chemical change.