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

Abstract

Rationale A combination of stable carbon ( δ 13 C) and hydrogen ( δ 2 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. Methods Petroleum‐ and bio‐based precursor materials and in‐market plastics were analysed and their δ 13 C, δ 2 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. 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 δ 13 C which was well correlated (R 2 = 0.98) to 14 C. It was not possible to establish a C3‐petroleum isotope mixing model due to δ 13 C isotopic overlap with petroleum plastics; however, the addition of δ 2 H 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 s table 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.

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