Authenticating Bioplastics Using Carbon And Hydrogen Stable Isotopes - An Alternative Analytical Approach

Rationale: A combination of stable carbon (delta C-13) and hydrogen (delta H-2) isotope ratios and carbon content (% C) was evaluated as a rapid, low-cost analytical approach to authenticate bioplastics, complementing existing radiocarbon (C-14) and Fourier transform infrared (FTIR) analytical methods.Methods: Petroleum- and bio-based precursor materials and in-market plastics were analysed and their delta C-13, delta H-2 and % C values were used to establish isotope criteria to evaluate plastic claims, and the source and biocontent of the samples. C-14 was used to confirm the findings of the isotope approach and FTIR analysis was used to vertify the plastic type of the in-market plastics.Results: Distinctive carbon and hydrogen stable isotope ratios were found for authentic bio-based and petroleum-based precursor plastics, and it was possible to classify in-market plastics according to their source materials (petroleum, C3, C4, and mixed sources). An estimation of C4 biocontent was possible from a C4-petroleum isotope mixing model using delta C-13 which was well correlated (R-2 = 0.98) to C-14. It was not possible to establish a C3-petroleum isotope mixing model due to delta C-13 isotopic overlap with petroleum plastics; however, the addition of delta H-2 and % C was useful to evaluate if petroleum-bioplastic mixes contained C3 bioplastics, and PLS-DA modelling reliably clustered each plastic type.Conclusions: A combined dual stable isotope and carbon content approach was found to rapidly and accurately identify C3 and C4 bio-based products from their petroleum counterparts, and identify instances of petroleum and bio-based mixes frequently found in mislabelled bioplastics. Out of 37 in-market products labelled as bioplastic, 19 were found to contain varying amounts of petroleum-based plastic and did not meet their bio-based claims.