Biodegradation of aliphatic–aromatic copolyesters: evaluation of the final biodegradability and ecotoxicological impact of degradation intermediates

The biological degradation behaviour of the aliphatic–aromatic copolyester Ecoflex® was investigated with regard to the degree of degradation and the intermediates formed during the degradation process. The individual thermophilic strain Thermomonospora fusca, isolated from compost material, was used for the degradation experiments in a defined synthetic medium at 55°C. After 22 days of degradation more than 99.9% of the polymer had depolymerized and with regard to the degradation of the diacid and diol components of Ecoflex® only the monomers of the copolyesters (1,4-butanediol, terephthalate and adipate) could be detected by gas chromatography/mass spectroscopy (GC–MS) measurements in the medium. In interrupted degradation experiments predominantly the monoesters of adipic acid and terephthalic acid with 1,4-butanediol were observed in addition to the monomers. In toxicological tests with Daphnia magna and Photobacterium phosphoreum no significant toxicological effect was observed, neither for the monomeric intermediates nor for the oligomeric intermediates. From a risk assessment it can be concluded that there is no indication for an environmental risk when aliphatic–aromatic copolyesters of the Ecoflex-type are introduced into composting processes.