Impact of degradation mechanisms on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) during composting

The individual impact of different degradation mechanisms occurring during composting on the degradation of poly(3-hydroxybutyrate-co-6%-3-hydroxyvalerate) [poly(3HB-co-6%-3HV)] have been assessed in simulated tests. Biotic hydrolysis with Aspergillus fumigatus had the largest impact on the breakdown of poly(3HB-co-6%-3HV) during composting conditions, with small changes in molecular weight and large weight loss. The major degradation products in the biotic environment were 3-hydroxy butyric acid and 3-hydroxy valeric acid. Abiotic hydrolysis during composting conditions (sterile water pH 7 at 60°C) has minor or no effect during such short times as 21 days. During abiotic hydrolysis both monomers and dimers were idientified while the abiotic thermo-oxidation of poly(3HB-co-6%-3HV) showed no degradation at all. The quantitation of degradation products and copolymer composition analysis by ¹H NMR indicate that the abiotic hydrolysis is not random. Crotonic and 2-pentenoic acid which is produced at 100°C in air was not produced at 60°C during 298 days. We propose that this temperature is too low to promote the well-known six-member transition that produces crotonic acid, 2-pentenoic acid and oligomers with crotonyl or pentenoyl end groups.