Towards making polymer food packaging suitable for the circular economy: Cleanliness is next to godliness

Single use plastic packaging and its environmental impacts have received much attention over the last few years from governments, businesses and consumers. One option to reduce plastic packaging waste and its associated environmental impacts is to shift towards circular business models, supplying reusable packaging options that are used many times before being recycled. One technical barrier to the implementation of plastic food packaging reuse is the need to effectively clean the packs and provide cleaning assurance to prevent the possibility of product crossover. This research investigated the feasibility of using Ultraviolet Fluorescence imaging to optically detect residual food fouling and thus assuring cleanliness in the case example of margarine spread tubs. Processing of obtained images was carried out using MATLAB® applying Otsu’s thresholding method. It was established that for the current setup the minimum detectable quantity of fouling was of the order 10^-4 g/mm2. The assessment process was correlated against that of Adenosine Triphosphate assay, an industry-standard process for assessing the cleanliness of food contact surfaces. The implications of the investigated technique overcome one barrier to plastic food packaging reuse on an industrial scale. Fast and reliable fouling evaluation of every pack will underpin business and consumer trust in such a circular material flow. The established technique has the potential to form part of the wider reuse system for polymer packaging. Implications on optical detection optimization, packaging design, and suitability for automation are discussed alongside wider food supply chain considerations.