Surface changes of corona-discharge-treated polyethylene films

Morphological and chemical changes of the surface of low-density polyethyle ne (LDPE), linear middle-density polyethylene (L-MDPE), and their 80/20 ble nd were studied by different techniques after corona-discharge treatment in air and subsequent annealing. The surface tension was determined by wettin g; the roughness was measured by atomic force microscope (AFM), and the sur face chemical composition was analyzed by X-ray photoelectron spectroscopy (XPS), whereas the low-molecular-mass fraction washed off by chloroform by FTIR. The surface tension of the films increases with the electrode current . The surface roughness depends primarily on the polymer type and is less a ffected by the corona treatment. At the initial stage of annealing, posttre atment-type oxidation and hydrophobic recovery are competing. The former is more pronounced in L-MDPE, the latter in LDPE. After annealing at 50 degre es C for 160 days, hydrophobic recovery becomes predominant in each film st udied, which is accompanied by significant smoothening of the surface. Acco rding to XPS and FTIR results, this is due to the migration of low-molecula r-mass components (oligomers, oxidized polymer fractions, and additives) to the surface. (C) 2000 John Wiley & Sons, Inc.