Definitive screening design for the development of alkali resistant PECVD coatings for returnable PET bottles

Abstract

Definitive screening design is put to test for the development of plasma polymeric silicon organic coatings as protective coatings for polyethylene terephthalate (PET) against the influence of strong NaOH alkaline solutions (c = 0.5 mol/L). To evaluate the protection performance of the coatings, oxygen transmission rate measurements are employed after washing experiments under application-oriented conditions. Parameter influences on the maintained OTR values after exposure to NaOH solution are derived by statistical correlation and used for optimization. Significant optimization is achieved for two coatings, that are subjected to long term performance evaluation and characterized in regard to their topography as well as atomic and chemical composition in dripping tests. Long term stability of two optimized coatings was lost after 50 minutes of exposure. Optimization was shown to be primarily achieved by an increase of the microwave pulse length. Both coatings showed similar atomic compositions and functional groups. Coatings System B showed chemical integrity of its functional groups up to 120 min of exposure to NaOH. Therefore, a denser structure with few pinholes was attributed, that was reinforced by lower roughness values. Defect and pin hole free coating structure as well as a high carbon content could be identified as beneficial properties.