Imaging of Trapped Contents in Plastic Seals via Optical Coherence Tomography

Abstract

Food contents such as coffee powder, sugar, flour, cheese particles etc. trapped in plastic seals of packaged products can eventually result in air leak and potential contamination of contents due to entry of air or bacteria. This is an ongoing industry-wide problem for which no straightforward inspection solution has been identified. Backscattered light is used by optical coherence tomography (OCT) to provide cross-sectional images of micro-layers of tissues and other samples. OCT is akin to “optical ultrasound” in its utilising light waves instead of sound waves for image acquisition. As a relatively new NDT technique for non-biomedical applications, OCT might be suitable for assessment of seal integrity by revealing the presence of contents trapped within the laminates of the seal structure. This experimental study uses an OCT system (Lumedica OQ Labscope) using broadband light of 840 nm centre wavelength and capable of attaining depth resolution of 7 µm and lateral resolution of 15 µm. Our imaging results indicate that OCT can clearly show the presence of trapped powder and food particles in transparent and translucent plastic seals. Attempts to image trapped contents in opaque metallized plastic seals are largely unsuccessful. However, distortion of geometrical profile in the opaque seals can be observed by OCT and might serve as an indirect indicator of the defect.