Degradation of pet copolyesters under real and laboratory composting conditions

The present work is aimed on the study of degradation of poly(ethylene terephthalate- co -lactate) copolyesters, prepared by chemical modification of PET waste beverage bottles using l -lactic acid, under laboratory (bioreactor) and natural (Central Composting Plant in Brno, Czech Republic) composting conditions. The structure of solid residues after degradation was analyzed by IR, NMR, thermogravimetric (TGA) methods, and size exclusion chromatography in chloroform and the residues rich on aromatic units were analyzed in CHCl 3 /HFIP solutions. Sample with 57 mol% of aliphatic units showed the highest degree of degradation with mass loss of about 90% independently of composting conditions. The samples with 57 and 60 mol% of aromatic units reached 68 and 51% degradation in the compost pile and only 39 and 5% in laboratory bioreactor. Gravimetric analysis along with molar mass distribution measurement showed that laboratory-level composting study provides more consistent and defined results. However, it should be accompanied with tests performed under real conditions for the purpose of biodegradability evaluation of polymeric materials with varying composition.