Lifetime improvement of poly(ethylene naphthalate) by ZnO adhesive coatings

Zinc oxide (ZnO) coatings were deposited by RF magnetron sputtering on the surface of poly(ethylene naphthalate) (PEN) films to protect the polymer against ultraviolet (UV) radiation. To increase the adhesion of the coating, PEN films were submitted to cold plasma treatments before deposition. Wettability measurements showed that the adhesion strength of the coatings was increased by a CO2 plasma treatment of PEN and varied with the oxygen partial pressure in the sputtering gas. The photodegradation of the ceramic/polymer assemblies, in conditions of artificial accelerated ageing, was monitored by infra-red and UV-vis spectroscopies. Results showed that photoprotection increases with ZnO thickness up to 200 nm. In addition, the sputtering parameters, which act on the composition, the structure and the optical properties of ZnO, were optimised to obtain the best coating in terms of UV and oxygen barrier.