Authors Gorenflo, V. ; Schmack, G. ; Vogel, R. ; Steinbüchel, A.
Title Development of a Process for the Biotechnological Large-Scale Production of 4-Hydroxyvalerate-Containing Polyesters and Characterization of Their Physical and Mechanical Properties
Date 14.05.2001
Number 8706
Abstract A process for the large-scale production of 4-hydroxyvalerate (4HV)-containing biopolyesters with a newmonomer composition was developed by means of high-cell-density cultivation applying recombinant strainsof <I>Pseudomonas putida</I> and <I>Ralstonia eutropha</I>, harboring the PHA-biosynthesis genes <I>phaC</I> and <I>phaE</I> of<I>Thiocapsa </I><I>pfennigii. </I>Cell densities of about 20 g/L revealing a PHA content of 52% (w/w) and a molarfraction of 4HV of up to 15.4 mol % were obtained by a two-stage fed-batch cultivation process at a 25-Lscale using octanoic acid during the growth phase and levulinic acid for the accumulation of 4HV-containingpolyesters. Besides 4HV the polyester contained significant amounts of both 3-hydroxybutyric acid (3HB)and 3-hydroxyvaleric acid (3HV) and traces of 3-hydroxyhexanoic acid (3HHx) and 3-hydroxyoctanoicacid (3HO). With glucose or gluconic acid as the growth substrate, the components of the polyester couldbe reduced to mainly 3HV and 4HV with only a negligible fraction of 3HB, resulting in a polyester witha new composition. Scale-up of the cultivation process to a 500-L scale was successfully performed, resultingin the production of these polyesters at a pilot plant scale. Short-term shifts in temperature and pH resultedin the formation of cell agglomerates of about 50-100 <IMG SRC="/images/entities/mgr.gif">m by which the effectiveness of the semicontinuouscentrifugation process was drastically increased. Washing of the fre<br />eze-dried cells with boiling methanolsignificantly shortened the extraction process and resulted in a polyester of higher purity. The physical andmechanical properties of these copolyesters were characterized by means of size exclusion chromatography,dynamic mechanical analysis, differential scanning calorimetry, stress-strain measurements, and measurements of the viscosity of the solution. The copolyesters were cast into films, spun to fibers, or processedinto test bars by melt spinning and injection molding, respectively. They revealed an almost entirely amorphousstructure and consequently were sticky and lacked strength. However they showed high thermal stabilityand an unusually high elongation at break of about 200%; the molecular weights (<I>M</I><SUB>w</SUB>) were between 2.0 &#215;10<SUP>5</SUP> and 3.3 &#215; 10<SUP>5</SUP> g/mol. It was shown that 4HV-containing polyesters belong to the class of thermoplasticelastomeres.
Publisher Biomacromolecules
Citation Biomacromolecules 2 (2001) 45-57

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