Analytical pyrolysis of the bioplastic PBAT poly(butylene adipate-co-terephthalate)

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PBAT (poly(butylene adipate-co-terephthalate) is an important player in the field of bioplastics for its biodegradability performance and good mechanical properties. Awareness of the forecasted increased use of PBAT has prompted researchers to develop methods for its analysis in a variety of samples. Py-GC-MS, conventional or with derivatising agents, is a technique of excellence for the analysis of polymers that relies on a detailed structural knowledge of the evolved products. This study presents a comprehensive investigation on the chemical composition of the pyrolysate of PBAT evolved at 600 °C alone and in the presence of various reagents (hexamethyldisilazane, HMDS; acetic anhydride, Ac2O, tetramethylammonium hydroxide, TMAH). Identification of relevant pyrolysis products was confirmed through the analysis of pure standards and associated reagents/byproducts. A GC-MS data set of about 50 compounds was compiled, including open chain fragments of the polymer and their derivatives as well as single and mixed subunit cyclic dimers. A compound distinctive of PBAT (but-3-en-1-yl (4-((6-(but-3-en-1-yloxy)-6-oxohexanoyl)oxy)butyl) terephthalate) containing the adipic, terephthalic and butylene units was tentatively identified by its mass spectrum. Pyrolysis products with active hydrogens (alcoholic and carboxylic) were efficiently silylated by HMDS. Two pyrolysis products containing the hydroxybutyl moiety could be acetylated by pyrolysis with Ac2O. Thermally assisted hydrolysis and methylation with TMAH caused important transmethylation of the ester groups of the polymer chain with the formation of dimethyl adipate and dimethyl terephthalate. The importance of the results for the analysis of PBAT in commercial bioplastics and environmental samples was discussed.