SiO_x layer as functional barrier in polyethylene terephthalate (PET) bottles against potential contaminants from post-consumer recycled PET

Abstract

The barrier effect of a silicon oxide (SiO _x ) coating on the inner surface of PET bottles, in terms of the ability to reduce the migration of post-consumer compounds from the PET bottle wall into food simulants (3% acetic acid and 10% ethanol), was investigated. The barrier effect was examined by artificially introducing model substances (surrogates) into the PET bottle wall to represent a worst-case scenario. Test bottles with three different spiking levels up to ∼1000 mg kg⁻¹ per surrogate were blown and coated on the inner surface. The SiO _x -coated bottles and the non-coated reference bottles were filled with food simulants. From the specific migration of the surrogates with different bottles wall concentrations, the maximum surrogate concentrations in the bottle wall corresponding to migration of 10 µg l⁻¹ were determined. It was shown that the SiO _x coating layer is an efficient barrier to post-consumer compounds. The maximum bottle wall concentrations of the surrogates corresponding to migration of 10 µg l⁻¹ were in the range of 200 mg kg⁻¹ for toluene and ∼900 mg kg⁻¹ for benzophenone. Consequently, the SiO _x coating allows use of conventionally recycled post-consumer PET flakes (without a super-clean recycling process) for packaging aqueous and low alcoholic foodstuffs (under cold-fill conditions) and protects food from migration of unwanted contaminants from post-consumer PET.

Keywords:

• functional barrier
• PET recycling
• SiO _x coating
• challenge test
• food packaging
• migration

Acknowledgement

The authors would like to thank SIG Corpoplast for SiO _x coating of the bottles. Special thanks are due to Erik Lüpke (SIG), Hermann Neugebauer (Rexam), Silvia Demiani, Hans Ewender, Alexandra Mauer and Sonja Smolic (Fraunhofer IVV) for experimental contributions and fruitful discussions.