Coating of organosilicon thin films protecting polypropylene against photodegradation

Photodegradation of polymers limits the options for its use outdoor and reduces its useful life. Deposition of thin films of organosilicon by plasma on polymers can increase their resistance to photodegradation without interfering in aspects such as color and brightness due to the transparency and nanometric dimension of these films. Polypropylene (PP) films were pre-treated with oxygen plasma (5 minutes - 7,5.10-2 Torr - 50W), and treated with a plasma of 1:1 oxygen and hexamethyldisiloxane (15, 30, 45, 60 minutes - 2,3.10-2 Torr - 80 W) (Seufitellis, 2015). Homogeneous and continuous films were obtained, with a thickness between 50 and 550 nm and roughness between 26 and 52 nm. Scanning Electron Microscopy was used to follow the surface cracking as a function of photodegradation time (Figure 1). After 196 hours of UV-C photodegradation we had mainly two findings: 1) PP samples without coating showed less, but deeper and broader crackings than the PP coated with organosilicon thin films, and 2) In all coated samples the crackings followed the same pattern of deposition. Despite the visual modification of the coating after 196 hours of UV-C photodegradation, there was no observable detachment of the coatings from the PP substrate. These findings showed a role of the organosilicon thin film in the evolution of cracking as a function of photodegradation time. Additionally, we have observed, using FTIR, lower carbonyl and vinyl formation for the coated samples than the found for the PP without coating.