Determination of oligomers in virgin and recycled polyethylene terephthalate (PET) samples by UPLC-MS-QTOF

Abstract

An oligomer is a molecule that consists of a few monomer units. It can be formed during polymer manufacturing and also due to polymer degradation processes or even during use conditions. Since oligomers are not included in chemical databases, its identification is a complex process. In this work, the oligomers present in 20 different PET pellets samples have been determined. Two different sample treatment procedures, solvent extraction and total dissolution, were applied in order to select the most efficient one. The analyses were carried out by UPLC-MS-QTOF. The use of high resolution mass spectrometry allowed the structural elucidation of these compounds and its correct identification.The main oligomers identified were cyclic as well as lineal from the first, second and third series. All of them were composed by terephthalic acid (TPA), diethylene glycol (DEG) and ethylene glycol (EG). Quantitative values were very different in both procedures. In total dissolution of PET samples, the concentration of oligomers was always, at least, 10 times higher than in solvent extraction, being some of the compounds only detected when total dissolution was used. Results showed that the oligomers with the highest concentration values were dimers and trimers, cyclic as well as lineal, from the first and second series. The oligomer with the maximum concentration value was TPA2-EG-DEG, that was found in all the samples in a concentration range from 2493 to 19290 ng/g PET. No differences between virgin and recycled PET were found. Migration experiments were performed in 2 PET bottles, results showed the transference of most of these oligomers to a fat food simulant (ethanol 95%).

Analysis of PBT and PET cyclic oligomers in extracts of coffee capsules and food simulants by a HPLC-UV/FLD method

“… Oligomers FCMs Matrix Analytical technique Ref. PET cyclic oligomers Microwavable PET Migration solutions HPLC-FLD Begley et al, 1990 PET cyclic and linear oligomers Ovenable PET bags and trays Migration solutions HPLC-UV De Freire, Damant, Castle, & Reyes, 1999 PES linear and cyclic oligomers Several PES items Extraction solutions after hydrolysis HPLC-UV and GC–MS LC-ESI-MS Brenz et al, 2017 PES cyclic oligomers FCM multilayers Migration solutions UPLC-MS-qTOF Ubeda, 2017 PET linear and cyclic oligomers Virgin and recycled PET food-grade pellets Extraction and migration solutions UPLC-MS-qTOF Ubeda, Aznar, & Nerin, 2018 PBT linear and cyclic oligomers Several PBT items Extraction solutions HPLC-UV and LC-ESI-MS Brenz et al, 2018 PET and PBT cyclic dimers and trimers PET bottles Migration solutions HPLC-UV Tsochatzis et al, 2019a ; Dehouck et al, 2018 PBT cyclic dimer to pentamer PBT beverage cups Migration and extraction solutions HPLC-UV Tsochatzis et al, 2019b PET trimer and PBT dimer and trimer PET and PBT food-grade pellets Extraction solutions HPLC-UV Eckardt et al, 2019 PES cyclic oligomers PLA pellets and films Migration and total dissolution solutions UPLC-qTOF-MS Ubeda, 2019 PET cyclic and linear oligomers PET tea bags Migration solutions UHPLC-qTOF-MS Tsochatzis et al, 2020 PES cyclic...…”

Isolation, Characterization and Structural Elucidation of Polybutylene Terephthalate Cyclic Oligomers and Purity Assessment Using a 1H qNMR Method

“…When no standards of known purity are commercially available, the two most commonly used approaches are either to synthetize or isolate them from a known matrix. Some examples exist already in the literature related with FCM oligomers [6,7,8]. However, to the best of the author’s knowledge, no analytical standards for the individual PBT cyclic oligomers are yet commercially available.…”

Strategic Possibility Routes of Recycled PET

“…The analyses were carried out by UPLC-MS-QTOF. The use of high-resolution mass spectrometry allowed the structural elucidation of these compounds and their correct identification [ 1 ]. Some material is too complex or high impurity to separate PET.…”

“…The most significant application of polymers in the last two decades is polyethylene terephthalate (PET), which is of excellent chemical and physical properties for many implementations, for instance, characteristic of the gas barrier, low diffusivity, excellent mechanical and thermo mechanical properties, highly inert material, clearness and fine process operation [ 1 , 2 , 3 , 4 ]. On the other hand, PET waste is already highlighting for humans and the environment.…”