Renewable Long-Chain Fatty Acids for Production of Biodegradable Medium-Chain-Length Polyhydroxyalkanoates (mcl-PHAs) at Laboratory and Pilot Plant Scales

Abstract

Several types of mcl-PHAs were produced by Pseudomonas putida KT2442 at pilot and laboratory scales from renewable long-chain fatty acids (LCFAs) and octanoic acid. These and other mcl-PHAs are now available in sufficient amounts to carry out application and processing studies. We have isolated and purified these polymers in preparative amounts of 10−500 g by solvent recovery and selective enzymolysis. The molecular weights of mcl-PHA copolymers produced from LCFAs were generally similar to those found for octanoic acid based material, but the polydispersity was higher and the degree of polymerization was lower. The polymers showed thermal properties common for amorphous or semicrystalline thermoplastic elastomers above their Tg, which decreased with increasing average pendant chain length. PHAs derived from LCFAs, which contained 3−12 new hydroxyacid comonomers compared to PHA produced from oleic acid, were amorphous, did not crystallize, and showed liquid properties at room temperature. As the number of comonomers and thus the degree of disorder increased in these PHAs, the polymers became more viscous and tacky. PHAs derived from octanoic acid and oleic acid were not affected by the production scale in terms of composition and physical properties. Although different production process control strategies used at lab and pilot scale did influence the process productivity, the substrate yield was not affected by the process control type applied and was always close to the theoretical PHA yield to be expected for fatty acid utilization through the β-oxidation pathway. Isolation and GC−MS analysis of the methanolyzed trimethylsilyl- (TMSI-) derivatives allowed the identification of a large number of previously unknown 3-hydroxy acid PHA components. All purified polymers were subjected to in vitro aerobic biodegradation using a compost isolate. The extent of mineralization varied from 15 to 60% of the theoretical biochemical oxygen demand (ThBOD). The polymer weight loss after 32 days ranged from 40 to 90% for the different mcl-PHAs.