Surface studies by attenuated total reflection spectroscopy. I. Corona treatment of polypropylene

The chemical changes produced by brief corona treatments of polypropylene films have been studied by attenuated total reflection (a.t.r.) infrared spectroscopy. Surface layers of different thicknesses were investigated by varying the reflection conditions. Changes in the surface spectra were quantitatively compared by the use of an internal correction method which compensated for irreproducible experimental conditions. Corona treatment in a nitrogen atmosphere produced thin surface layers (less than 500 Å) of C—C unsaturation. Nitrogen derivatives were not detected in the surface. Corona treatment in oxygen caused surface changes which depended markedly on the corona conditions owing to the generation of ozone in the discharge zone. At low ozone concentrations, both unsaturation and oxidation were found in surface layers of under 500 Å thickness. At higher ozone concentrations, extensive oxidation occurred at appreciable depths into the polymer (several microns). An oxygen corona appears to result in essentially the same surface changes as does a nitrogen corona treatment, followed by exposure to ozone.