Analytical screening and development of an analytical method for quality assurance checking of market usual PET flakes

Due to the increasing market share of soft drink bottles made from poly(eth ylene terephthalate) (PET), the recycling of PET for new food packaging app lications is gaining more and more economic interest. However, in order to meet the challenging food regulatory requirements, a rapid and efficient an alytical quality assurance is necessary to recognize any foreign and unwant ed compounds in the PET material. Moreover it is required to have knowledge about real life contaminants concentrations in market PET recyclates in or der to allow an assessment whether such PET recyclates can be further proce ssed to obtain purified recyclate products of virgin material like quality suitable for direct food contact packaging applications. The aim of this study was to determine the current status quo of market-usu al PET flakes with respect to their migration relevant foreign compound pot ential. The establishment of an analytical method suitable for quality assu rance checking was another aim. For this purpose approx. 150 PET samples or iginating from 14 European PET recyclers and recyclate converters have been investigated, from each of the PET samples an analytical GC fingerprint wa s made which was qualitatively evaluated, In addition, acetaldehyde and lim onene were specifically quantified. As a result, it was shown that the inve stigated "post-consumer" PET samples as obtained from conventional recyclin g processes are not as such already suitable for direct food contact. The t hreshold concentration in the PET material as proposed by US-FDA was found to be exceeded in numerous cases for several substances. On the other hand, these substances were identified in the major cases to be aroma constituen ts of soft drinks of no toxicological concern. Limonene, as an example, was found to occur in a concentration range from 1.5 to 11 ppm in the PET flak es. The investigated PET samples were of good and very homogenous quality, thus being promising candidate materials for inclusion in a sandwich struct ure behind a functional barrier. In any case, however, the observed materia l qualities can serve or be used as input material for further purification processes, Given sufficient cleansing efficiency of such a process, in thi s way "post-consumer" PET recyclate qualities can be obtained which should be suitable for new direct food contact packaging applications. The same ho lds true and even more clearly for the investigated industrial scrab sample s which are almost comparable to virgin PET quality. The acetaldehyde conce ntrations were, however, found to be significantly higher in scrab samples. In opposite, PET samples obtained from the German DSD recollection system turned out as not suitable for food packaging. The reasons can be seen in t he low polymer type purity and the relatively high fractions of foreign com pounds resulting from former technical bottle contents, Concerning the analytical methodology the established headspace GC procedur e has been proven to be the most suitable approach to solve the problem. Th e low limits of detection achieved with this methodology do allow an evalua tion and certification of PET recyclates for this highly challenging and se nsitive re-application in food packaging.