PHB-PHV copolymer

The readiness of the industry to use PHB in the range of low price materials has failed dimng the last years because of the costs of PHB. Production of PHB or the PHB/PHV-copolymer under the trade name Biopol for technical use was abandoned, while in the last years efforts to use PHB for the medical sphere and niche products have continued. 

Chen, L., Wang, M. Production and evaluation of biodegradable composites based on PHB-PHV copolymer. Biomaterials 23, 2631-2639 (2002)... 

PHB has many physical properties in common with poly(propylene), and a PHB-PHV copolymer (BIOPOL) has recently been used to manufacture plastic shampoo bottles. PHB-PHV is of special interest because it is biodegradable. Since it is a naturally occurring polymer, it is easily degraded by enzymes produced by soil microorganisms and therefore does not persist in the environment after disposal. Other biodegradable polymers, such as polyesters derived from e-caprolactone and lactic acid, are also known and have been commercialized. Although it remains to be seen how widespread the use of biodegradable plastics will become, research and development of these materials is sure to continue as we try to deal with contemporary environmental issues. ... 

Table 12. Tensile properties of blends of PCL with PHB-PHV copolymers containing 12% and 20% PHV data taken from [115]...

The degradation dynamics of polyhydroxyalkanoates of different compositions (a PHB homopolymer and a PHB/PHV copolymer with 14mol% of hydroxyvalerate) have been studied in a eutrophic storage reservoir for two seasons. It has been shown that the biodegradation of polymers under natural conditions depends not only on their structure and physicochemical properties but also, to a great extent, on a complex of weather-climatic conditions affecting the state of the reservoir ecosystem. 

J.C. Knowles and G.W. Hastings, "In vitro degradation of a PHB/PHV copolymer and a new technique for monitoring early surface changes". Biomaterials, 12, 210-214,... 

Olher studies have investigated PHB-PHV composite, bioactive ceramics containing HA and tricalcium phosphate. This yields biodegradable copolymers and has potential for medical applications [175]. 

We now have the capacity to produce PHAs containing various blocks such as PHB-/)-PHV or PHB-/)-PHBV, and PHB-f)-PHA. These block PHAs have been found to show new properties. More PHB block copolymers are under development and they have the potential to generate more unique applications. 

The PHAs, PHB is the most extensively characterized polymer, mainly because it was the first to be discovered. The diversity of bacterial PHAs has changed dramatically. Until 1970 s, 3HB was considered as the only constituent of PHAs. hi 1980 s, PHAs having other monomers besides 3HB were shown to be accumulated by many bacteria with addition of certain precursors in the production medium. Figure 2 shows widely studied polyhydroxyalkanoates, which are PHB, PHV, and copolymer of PHB-co-PHV Today more than 150 different monomers of PHAs are synthesized by different microorganisms which include the following ... 

Fig. 1.10). In the family of aliphatic polyesters are found polymers of natural origin (PHA, PHB, PHV, PHH), mineral origin (PBS, PBSA, PCL) or those which originate from both (PLA and PGA). In the family of aromatic polyesters, those coming from PET or from PBT (PBST, PBAT, PTMAT) and copolymers are separately classified. 

The copolymer poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-co-PHV) produced by A eutrophus has generated more interest than poly-(R)-3-hydroxybutyrate (PHB) homopolymer. Since these bacterial polyesters are biodegradable thermoplastics, their mechanical and physical properties have received much attention. PHB is a relatively stiff and brittle material because of its high crystallinity. However, the physiochemi-cal and mechanical properties of [P(HB-HV)] vary widely and depend on the molar percentage of 3-hydroxyvalerate (HV) in the copolymer (4,5) as shown inTable 1. Propionic acid is converted by a synthetase to propionyl-CoA, and the biosynthetic P-ketothiolase catalyzes the condensation of propionyl-CoA with acetyl-CoA to 3-ketovaleryl-CoA by the acetoacetyl-CoA reductase. The hydroxyvaleryl moiety is finally covalently linked to the polyester by the PHA synthase (6). 

ICI has developed a fermentation process for PHB having various levels of polyhy-droxyvalerate (PHV) as a copolymer. This polymer is marketed under the product name BIOPOL. The material is extrudable and can be used as bottles for packaging cosmetics. Because of the high migration rate of the triacetine plasticiser used (see Chapter 4) it is not suitable for food use. Currently efforts are being made to manufacture this material as a film. 

Polyhydroxybutyrate (PHB) and polyhydroxyvalerate (PHV) are also being researched for use in medical devices. The PHB homopolymer is crystalline and brittle, whereas the copolymers of PHB with PHV are less crystalline, more flexible, and easier to process. These polymers typically require... 

Synthetic or man-made, e.g., PVAl, CA, polylactams e.g., polycaprolactam), polyglycols (e.g., polyethylene glycol), poly(aspartic acid), poly(butylene succinate-co-adipate), as well as poly(3-hydroxy butyrate) or PHB, poly(P-hydroxybutyric acid) or PHBA, poly(hydroxy-valerate) or PHV, poly(lactic acid) or PLA, polyCglycolic acid), polyglycolides, polybu-tyric acid, their copolymers and mixtures. 

Higher molecular weight PHB and its copolymers with poly(3-hydroxy-valerate) (PHV) can be synthesized from racemic P-butyrolactone and P Valerolactone, using an oligomeric alumoxane catalyst. These polyesters, with only partial stereoregularity, are less susceptible to enzymatic degradation than the bacterial ones. Polyhydroxy-butyrate-valerate (PHBV) is produced by Monsanto as Biopol . 

PHB-co-PHV [54] is obtained from Azotobacter chroococcum [58, 63). The biodegradation is slower for the copolymers than poly-3-hydroxybutyrate. 3-hydroxy-n-phenylalkanoic acids and 3-hydroxyaliphatic acids are obtained from Pseudomonas putida [59]. Poly (3-hydroxyoctanoic acid) and poly (6-hydroxyhexanoic acid) and poly (3-hydroxyoctanoic acid) [64], Poly-(R)-3-hydroxybutyrate/polyphosphate (PHB/polyP) complexes are isolated from the plasma membranes of bacteria [65,66]. Polyhydroxyoctanoate is produced by feeding octanoic acid to Pseudomonas oleovorans [67]. 

Besides the common polyhydroxybutyrate (PHB), other polymers of this class are produced by a variety of organisms such as poly-4-hydroxybutyrate, PHV, and polyhy-droxyhexanoate. PHV is a naturally occurring bacterial polyester, which was first isolated by Wallen and coworkers [172,173]. Also, PHV/PHB copolymers have been studied to make a wide range of thermally processable polyesters, which exhibit the necessary long-term degradation profile required for a degradable fracture fixation device [174]. 

The major commercial microial polyesters are polyhydroxyalkanoates (PHAs) (see Poly(3-HYDROXYALKANOATES)) Poly(3-hydroxybutyrate) (PHB) (8) is brittle, but as the number of carbon atoms in the side chains of PHAs increases, eg, poly(3-hydrox5Tvalerate) (PHV) (9), the properties tend from polypropylene-like to elastomeric. Copolymers, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), have a range of properties depending on composition (Table 1). 

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