Identification of unknown compounds in PE and PP for food contact materials

Packaging materials are complex mixtures and can contain unknown compounds due to unexpected reactions or degradation of substances present in the materials used for their manufacture. Polyethylene (PE) and polypropylene (PP) are polymers widely used for packaging applications, which may undergo changes during their manufacture. One of the challenges in the food packaging field is the identification of unknown compounds present in the final material and that could be originated during its processing. In the present work a non-targeted analysis for the identification of unknown compounds was applied. Different PE and PP were analyzed. Samples consisted of raw materials as well as the additives used in its manufacture. Each sample was analyzed by gas chromatography coupled to mass spectrometry (GC-MS) after solvent extraction to detect semi-volatile compounds and GC-MS coupled to Purge and Trap (GC-MS-P&T) in case of volatile compounds. To be analyzed by GC-MS, samples were previously extracted with hexane at 70ºC for 4 hours and with a mixture of Hexane: Ethanol (3:1 v/v) at 20ºC for 8 hours. Likewise, each sample was directly subjected to a slight heating (Purge) during which the volatiles present were dynamically dragged through a stream of Helium being retained in a trap. Subsequently the trap was subjected to rapid heating and the retained compounds were eluted to the chromatograph where they were analyzed. The presence of alkanes as more abundant components was confirmed by both techniques, as well as the presence of 2,4-di-tertbutylphenol as can be seen in Figure 1. This compound is a product of degradation of the antioxidants used in the processing of this material.

The study was financially supported by the “Ministerio de Economía y Competitividad”, "Fondo Europeo de Desarrollo Regional (FEDER) and by "Agencia Estatal de Investigación" ref. RTC-2017-6553-2. “NAPA” (MINECO/FEDER, UE).

Author(s): Patricia Vázquez Loureiro

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