Characterisation of a bio-based packaging containing a natural additive from Allium spp. using analytical pyrolysis and carbon stable isotopes

• A biopolymer with an additive was analysed by pyrolysis and carbon stable isotopes.
• Propyl sulphide was found of diagnostic to trace the additive in the biopolymer.
• There was a differential isotopic signature between polymer and additive.
• Isotopic signature was useful to estimate the amount additive in the biopolymer.

Analytical pyrolysis (Py-GC/MS) was used to fingerprint a polylactic acid (PLA) with polybutylene succinate (PBS) (950 g Kg−1:50 g Kg−1) film extruded with variable quantities (0, 20, 50 and 65 g Kg−1) of a commercial additive (Proallium®) prepared from Allium spp. extracts. The carbon isotopic signature(δ13C) was used to estimate the amount of additive to be incorporated into the casting of the active biopolymer. The main PLA:PBS pyrolysis products were lactide enantiomers and monomer units, in addition to structures from the PBS fraction. The pyrolysis of the plant extract additive, apart from a number of organosulphur compounds derived from the active ingredients, released oligomers of polyethylene glycol, alkyl ethers and a conspicuous peak of oleic acid, 3-hydroxypropyl ester compatible with a polyoxyethylene sorbitan monooleate surfactant. The sulphur compound, propyl sulphide, was a diagnostic peak with which to trace the additive in the polymer. In fact, a correlation coefficient of value 0.997R2 (p < 0.001) was found between the chromatographic area of this peak and the amount of additive in the bioplastic. The real amount of additive incorporated in the bioplastic was estimated through a mass-balance equation, taking advantage of the differential δ13C signatures between the polymeric base and the additive.