Adhesion of plasma-deposited silicon oxide barrier layers on PDMS containing polypropylene

The adhesion of SiOx coatings deposited by plasma-enhanced chemical vapor deposition onto injection-molded polypropylene (PP) was investigated as function of polypropylene surface Si enrichment. The PP was either used in its original state or was modified by a by-mixture with small amounts of polydimethylsiloxane (PDMS) in the extrusion process. The substrates where characterized by X-ray photoelectron spectroscopy, attenuated infrared reflection and time of flight spectroscopy; it was seen that the PP/PDMS substrates showed a Si-enriched top layer about 1 nm thick. The adhesion of the SiOx coatings to the PP/PDMS substrates was greatly enhanced with respect to the non-functionalized PP, which shows that adhesion of plasma-deposited SiOx layers to polymer substrates can be improved without the need to deposit intermediate adhesion layers, and without the need to include a plasma pre-treatment step into the process.