Rationale
A combination of stable carbon (δ13C) and hydrogen (δ2H) isotope ratios and carbon content (% C) was evaluated as a rapid, low‐cost analytical approach to authenticate bioplastics, complementing existing radiocarbon (14C) and Fourier transform‐infrared (FTIR) analytical methods.
Methods
Petroleum‐ and bio‐based precursor materials and in‐market plastics were analysed and their δ13C, δ2H and % C values were used to establish isotope criteria to evaluate plastic claims, and the source and biocontent of the samples.
14C was used to confirm the findings of the isotope approach and FTIR 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 δ13C which was well‐correlated (R2=0.98) to 14C.
It was not possible to establish a C3‐petroleum isotope mixing model due to δ13C isotopic overlap with petroleum plastics; however, the additon of δ2H 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.
Eighteen out of thirty seven in‐market products labelled as bioplastic were found to contain varying amounts of petroleum‐based plastic and did not meet their bio‐based claims.