Production of PHBV

The fermentation results directly in polymer with no need for further polymerization as opposed to, for example, PLA. Nevertheless, the polyester needs to be extracted from the bacteria (often using chloroform or enzymes) and purified, and this is again a high contributor to the cost of PHA. Tianan also reports a patented commercial production of PHBV using a water-based extraction technology [67]. 

The description of present or past processes for the commercial production of PHAs have been the subject of recent reviews [75, 135, 227, 228]. Current industrial PHBV production utilizes a glucose-assimilating strain of R. eutropha in fed-batch regime with phosphate limitation as the triggering factor for biopolymer accumulation and propionic acid as 3HV precursor [227]. For convenience, this R. eutropha cdihohydsdiid propionate combination in fed-batch mode will be referred to here as a conventional strategy for production of PHBVs. 

Ten-liter-scale fed-batch fermentations (fermentations with addition of different substrates during the experiment) were used by Braunegg and co-workers [187] for the production of PHBV with A. latus growing on glucose and propionate, and P(3HB-cc -4HB) with R. eutropha on glucose and y-butyrolactone. In the first case, 6.6 g (72% of the CDM) of a copolymer containing 28 mol% 3HV were obtained per liter in only 33.75 h. With R. eutropha, 7.2 g P(3HB-co-7.9-mol% 4HB) L was produced in 83 h. 

Previously, Yu et al (2005) studied the increase of a co-biopolymer of PHBV by Ralstonia eutropha in a continuous stirred tank reactor. It was found that the productivity rate increased when sodium propionate was used as the carbon source. Later, Yezza et al (2007) investigated the use of maple sap as a carbon for PHB production by A. latus. The productivity of PHB reached 2.6 gH h-i. 

The alkaline hydrolysis products of PHB and PHBV have been detected by LC [141,143]. Monomers, oligomers, and derivatives, produced by dehydration at the OH-terminus were identified after the hydrolysis. According to these studies CZE showed that the accelerated hydrolysis of PHB led to the formation of hy-droxyacid oligomers and a series of peaks formed by a side-reaction leading to the C=C bond at the non-carboxylic acid end [135]. 

Other approaches to improve the properties of PHB is the production of derivatives based on PHB via the biosynthesis of copolyesters containing PHB units with other 3-hydroxyalkanoates units [19], such as poly [3-hydroxybutyrate-co-hydroxyvalerate] [PHBV] [20] or poly [3-hydroxybutyrate-co-3-hydroxyhexanoate] [21], with different molar ratios of hydroxycarboxylic acids. This approach has been investigated extensively [22] because it can... 

For the bacterial production of PHAs by wild-type strains, the Ralstonia eutropha (formerly called Alcaligenes eutrophus, Wautersia eutropha, or Cupri-avidus necator) has been the most commonly used wild-type strain for the industrial production of PHB, P3HB4HB, and PHBV. 

Commercial production of PHB and PHBV is carried out in batch systems as large as 200,000 L in capacity. The medium used in the fermenter in the production stage contains glucose, a desired amount of phosphate to produce the required amoimt of biomass, and an excess of all other nutrients. The culture is then inoculated with microorganisms, which reproduce until phosphate is depleted, and then begin to store... 

PHA technology goes back to the 1970s and 1980s, when Imperial Chemical Industries (ICI) developed Biopol PHA and was the first company achieving commercial production of namely PHBV. Chemie Linz AG also produced small amount of PHB for application exploitation. Later, Monsanto based on the ICI patents tried to produce PHA industrially but failed as the PHA produced in this ways were not competitive compared with petrochemical-based materials. 

FIGURE 1.12 Overview of PHA synthesis schematic depiction of (a) chain polymerization catalyzed by enzymes, (b) a PHA granule with granule-associated proteins, (c) different forms of the PHB polymer chain, and (d) semicrystaUine polymer structure, (e) AFM image of PHBV film (f) final plastic products. Reproduced with permission from Ref. [55]. 2013 Elsevier. (See insert for color representation of the figure.)... 

Several studies are being conducted in order to improve PHBV mechanical properties and/or decrease its cost and enabling its industrial application. Among many studies it is possible to find addition of plasticizers (Choi and Park 2004), production of blends, including blends with natural polymers such as polycapro-lactone, poly(L-lactic acid), starch, and cellulose (El-Hadi et al. 2002 Ferreira et al. 2002) and also with synthetic polymers such as polyvynyl phenol (Fei et al. 2004), oxidized polyethylene, and polypropylene (Avella et al. 2002), blends with natural rubber (Han et al. 2004), among others. 

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