Renewable long-chain fatty acids for production of biodegradable medium-chain-length polyhydroxyalkanoates (mcl-PHAs) at laboratory and pilot plant scales
Mb. Kellerhals et al., Renewable long-chain fatty acids for production of biodegradable medium-chain-length polyhydroxyalkanoates (mcl-PHAs) at laboratory and pilot plant scales, MACROMOLEC, 33(13), 2000, pp. 4690-4698
Several types of mcl-PHAs were produced by Pseudomonas putida KT2442 at pil
ot and laboratory scales from renewable long-chain fatty acids (LCFAs) and
octanoic acid. These and other mcl-PHAs are now available in sufficient amo
unts to carry out application and processing studies. We have isolated and
purified these polymers in preparative amounts of 10-500 g by solvent recov
ery 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 polyme
rization was lower. The polymers showed thermal properties common for amorp
hous or semicrystalline thermoplastic elastomers above their T-g, which dec
reased with increasing average pendant chain length. PHAs derived from LCFA
s, which contained 3-12 new hydroxyacid comonomers compared to PHA produced
from oleic acid, were amorphous, did not crystallize, and showed liquid pr
operties at room temperature. As the number of comonomers and thus the degr
ee of disorder increased in these PHAs, the polymers became more viscous an
d tacky. PHAs derived from octanoic acid and oleic acid were not affected b
y the production scale in terms of composition and physical properties. Alt
hough 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 th
eoretical PHA yield to be expected for fatty acid utilization through the b
eta-oxidation pathway. Isolation and GC-MS analysis of the methanolyzed tri
methylsilyl- (TMSI-) derivatives allowed the identification of a large numb
er of previously unknown 3-hydroxy acid PHA components. All purified polyme
rs were subjected to in vitro aerobic biodegradation using a compost isolat
e. The extent of mineralization varied from 15 to 60% of the theoretical bi
ochemical oxygen demand (ThBOD). The polymer weight loss after 32 days rang
ed from 40 to 90% for the different mcl-PHAs.