SURFACE CHARACTERIZATION OF EVA COPOLYMERS AND BLENDS USING XPS AND TOF-SIMS

The surface chemistries of semi-crystalline copolymers of ethylene (CH2=CH2) and vinyl acetate (CH2=CHCO2CH3) (EVAs) and blends of these copolymers with low-density polyethylene (LDPE) have been examined critically for the first time using angle-resolved XPS and time-of-flight SIMS (ToF-SIMS) analyses. Specimens were fabricated using a variety of methods (commercial extrusion, spin coating and thermal compression) to determine the influence of processing conditions on EVA surface chemistry. The XPS and ToF-SIMS analysis of these specimens has provided techniques for identifying surface EVA (also thermal oxidation), has provided both XPS and ToF-SIMS methods for quantitative EVA analysis and has revealed the details of EVA surface chemistry. The XPS core-level spectra indicate the presence of the ester (VA) and ether (surface oxidation) species, but do not provide positive EVA identification. The ToF-SIMS spectra show features specific to both the ethylene and vinyl acetate portions of the polymer. Both XPS and ToF-SIMS analyses have been calibrated to provide quantitative VA (error < 2 wt.% VA) and oxygen (error < 1.0 at.% oxygen) analyses. Surface VA content was found to increase linearly with bulk VA content, and was not influenced by the type of fabrication method used. The EVA surfaces appear to consist of two layers. The near-surface region (> 20 Angstrom depth) is dominated by a VA-poor (ethylene-rich) layer. This region is covered by a thin (less than or equal to 20 Angstrom thick) VA-enriched layer.