Surface modification of food-grade PVC monitored by angle-resolved XPS

In this work the covalent functionalization of polyvinyl chloride (PVC) with (3-mercaptopropyl)trimethoxysilane (MPTMS) by nucleophilic substitution was investigated by X-ray photoelectron spectroscopy (XPS). The surface of food-grade PVC was characterized before and after treatment with ethanol and with 5% and 10% MPTMS solutions in ethanol. Special attention was paid to the determination of the chemistry, composition and thickness of the functionalized polymer surface by angle-resolved XPS (ARXPS). XPS analysis in standard mode and ARXPS spectra showed the presence of sulphur, silicon and oxygen from the MPTMS molecule. The quantitative analysis was in good agreement with the stoichiometry of the molecule. A small amount of chlorine, detected also at grazing angles, supported the formation of a layer, which resulted to be 2.2(0.2) nm thick including the hydrocarbon contamination usually detected by XPS on samples in contact with solutions. It is here demonstrated that XPS and ARXPS allow monitoring the surface functionalization and tune the conditions for achieving a good reproducibility during the functionalization of food-grade PVC by MPTMS. This is the starting point for further functionalization to obtain active food packaging with antimicrobial properties.