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

Abstract

Analytical pyrolysis (Py-GC/MS) was used to fingerprint a polylactic acid (PLA) with polybutylene succinate (PBS) (950 g Kg:50 g Kg) film extruded with variable quantities (0, 20, 50 and 65 g Kg) of a commercial additive (Proallium) prepared from Allium spp. extracts. The carbon isotopic signature(δC) 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 0.997R (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 δC signatures between the polymeric base and the additive.