Analysis of the inhibition of thermal degradation of molten polycarbonate at tool steel interfaces by thin TiAlN coatings

The inhibition of the thermal degradation of molten polycarbonate at tool steel interfaces by magnetron sputtered TiAlN coatings was studied on fundamental level by means of in-situ and ex-situ spectroscopic and microscopic techniques. As reference systems, which enable the application of in-situ analytical techniques, oxide covered iron films were compared with atmosphere exposed Ti0.52Al0.48N1.14 hard coatings. Moreover, SiO2 terminated silicon and glass substrates as prototypical insulating and inert materials were studied. Interface and interphase analysis of the inorganic substrates and the polymer were performed using confocal fluorescence spectroscopy as well as FTIR, UV/VIS and X-ray photoelectron spectroscopy (XPS). The degradation of polycarbonate at the Fe-oxide interface as revealed by FTIR and UV/VIS spectroscopy indicated the formation of aromatic esters, cyclic anhydrides and discoloring products including char. Simultaneous cross-linking could be verified by strong broadening of the polycarbonates Young's modulus at the Fe-oxide interface as measured by AFM. XPS results indicate that the Fe(III)-states in the Fe-oxide were reduced to Fe(II) states which are likely to act as catalytic sites for PC degradation. In contrast, the surface oxidized Ti0.52Al0.48N1.14 coatings effectively inhibited the thermal degradation but however induced slight restructuring of polycarbonate in comparison to the completely inert SiO2 surface.

123