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

Abstract

AbstractThe 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.