Authenticating bioplastics using carbon and hydrogen stable isotopes - An alternative analytical approach.

Abstract

A combination of stable carbon (δ13 C) and hydrogen (δ2 H) isotope ratios and carbon content (% C) was evaluated as a rapid, low-cost analytical approach to authenticate bioplastics, complementing existing radiocarbon (14 C) and Fourier transform infrared (FTIR) analytical methods. Petroleum- and bio-based precursor materials and in-market plastics were analysed and their δ13 C, δ2 H and % C values were used to establish isotope criteria to evaluate plastic claims, and the source and biocontent of the samples. 14 C 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. 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 δ13 C which was well correlated (R2 = 0.98) to 14 C. It was not possible to establish a C3-petroleum isotope mixing model due to δ13 C isotopic overlap with petroleum plastics; however, the addition of δ2 H and % C was useful to evaluate if petroleum-bioplastic mixes contained C3 bioplastics, and PLS-DA modelling reliably clustered each plastic type. 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.