IMPACT OF DEGRADATION MECHANISMS ON POLY(3-HYDROXYBUTYRATE-CO-3-HYDROXYVALERATE) DURING COMPOSTING

The individual impact of different degradation mechanisms occurring du ring composting on the degradation of poly(3-hydroxybutyrate-co-6%-3-h ydroxyvalerate) [poly(3HB-co-6%-3HV)] have been assessed in simulated tests. Biotic hydrolysis with Aspergillus fumigatus had the largest im pact on the breakdown of poly(3HB-co-6%-3HV) during composting conditi ons. with small changes in molecular weight and large weight loss. The major degradation products in the biotic environment were 3-hydroxy b utyric acid and 3-hydroxy valeric acid. Abiotic hydrolysis during comp osting conditions (sterile water pH 7 at 60 degrees 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-oxi dation of poly(3HB-co-6%-3HV) showed no degradation at all. The quanti tation of degradation products and copolymer composition analysis by H -1 NMR indicate that the abiotic hydrolysis is not random. Crotonic an d 2-pentenoic acid which is produced at 100 degrees C in air was not p roduced at 60 degrees C during 298 days. We propose that this temperat ure is too low to promote the well-known six-member transition that pr oduces crotonic acid, 2-pentenoic acid and oligomers with crotonyl or pentenoyl end groups.