Poly-P-hydroxybutyrate, PHB

This is a new bacterial thermoplastic and is an ideal model substance for crystalhzation studies. Burham, Keller, Otun, and Holmes found that the crystals always thicken logarithmically with time when heated above original crystallization temperature, but synchrotron radiation has shown that is does not thicken in situ during isothermal crystallization from the melt. This is true even at temperatures where one can observe thickening of lamellae which had previously been crystallized at lower temperatures. 

2 Small Angle Scattering During Annealing Above the Crystallization Temperature 

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Poly-P-hydroxybutyrate (PHB) is a biodegradable thermoplastic that is produced by several microorganism. The PHB synthesis has been characterized eutrophus and the operon iavolved ia PHB productioa has beea cloaed. Recombiaant E. coli straias that can produce high levels of... 

PolyCy-benzyl L-glutamate) (PBLG), 15 109 Poly(y-ketosulfide)s, optically active, 23 711 Poly(P-alanine), 1 292 Poly-P-hydroxybutyrate (PHB), 12 482 Polybetaines, 20 479-482 applications of, 20 482 preparation of, 20 480-481 solution properties of, 20 481-482 synthesis of, 20 479-481 Polyborates, 4 256-258 Polyborosiloxanes, in silicon carbide manufacture and processing, 22 533 Polybrominated diphenyl ethers (PBDEs), 13 142-143 20 56... 

Another example where metabolic pathway engineering has made a dramatic impact is in the biodegradable polymer field. One of the most widely studied polymers in this family is poly-P-hydroxybutyrate (PHB) (64). A related member of the poly-P-hydroxyalkanoate (PHA) family commercialized by Imperial Chemical Industries (ICI), which later became Zeneca Bio Products,... 

Poly-P-hydroxybutyrate (PHB) crystallizes in a low temperature modification (LTM), which is transformed into a high temperature modification (HTM) when heated above 320 °C. Both modifications exhibit distinct WAXS patterns, thus a quantitative determination of the two fractions is possible. However, measurements at the HTM are only feasible with S.R., since the molecules quickly decompose at the high temperatures. Figure 23 shows the fraction of the HTM during heating the PHB sample from 280 °C to 340 °C at a rate of 2 °C/min and subsequent cooling to 280 °C at the same rate [49], A reversible transformation is observed. But the transition from the LTM to the HTM occurs at a temperature, which lies about 20 °C higher than the transition in the opposite direction. This indicates, that each modification is formed by its own nucleation process. 

The enzymatic hydrolysis of poly-p-hydroxybutyrate, PHB, by several different bacteria, which are known to secrete active esterases, has been studied in some detail by several research groups [7, 8]. As with the polysaccharides, the final products of these degradation reactions are the monomers, dimers and trimers, which are removed by hydrolysis only from hydroxyl-end of the polymer chain, as follows ... 

Free living S. meliloti 41 accumulates up to 50% of its weight as poly- p-hydroxybutyrate (PHB) in yeast salts medium with mannitol as carbon source. When other carbon sources are used, S. meliloti 41 still produces high amounts of PHB under the same growth conditions (Table 1). This strain can also accumulate a copolymer when propionate or n-valerate were supplied to the culture (data not shown). 

Tombolini R., Povolo S., Buson A., Squartini A., Nuti M.P., 1995, Poly-P-hydroxybutyrate (PHB) biosynthetic genes in Rhizobium meliloti 41. Microbiol. 141 2553-2559. 

The wide spread use of biosynthetic poly(P-hydroxybutyrate) (PHB) appears yet limited by the relatively high price when compared with synthetic polyolefins displaying comparable physical properties. Whereas the cost-bound features could be very much mitigated by economy of scale. 

Yilmaz M, Soran H, Beyatli Y (2005) Determination of poly-P-hydroxybutyrate (PHB) production by some Bacillus spp. World J Microbiol Biotechnol 21 565-566 Zhao HY, Li HM, Qin LF, Wang HH, Chen G-Q (2007) Disruption of the polyhydroxyalkanoate synthase gene in Aeromonas hydrophila reduces its survival ability under stress conditions. FEMS Microbiol Lett 276 34-41... 

Unlike animal or plant cells, there is no endoplasmic reticulum to which ribosomes are bound. Bacteria contain storage deposits of certain building blocks. The volutin granules serve as a reserve source of phosphate and are themselves composed of polyphosphates. Poly-p-hydroxybutyrate (PHB) a Upid-Iike material, serves as a carbon and energy source. 

Figure 9.10 Poly-p-hydroxybutyrate (PHB), the biodegradable bacterial polyester, n =...

Poly-P-hydroxybutyrate (PHB) A Biodegradable Polymer of Microbial Origin... 

The aliphatic biopolyesters are mainly polyhydroxyalkanoates (PHAs) like the poly-P-hydroxybutyrate (PHB), polyhydroxyvalerate (PHV), and polyhydroxyhexanoate (PHH). It not only resembles conventional petrochemical mass plastics (like PE or PP) in its characteristics, but it can also be processed easily on standard equipment that already exists for the production of conventional plastics. 

Md Din, M. F., Ujang, Z., van Loosdrecht, M. C. M., Razak, R., Wee, A., and Yunus, S. M. (2004). Accumulation of Sunflower Oil (SO) under Slowly Biosynthesis for Better Enhancement the Poly-P-hydroxybutyrate (PHB) Production Using Mixed Cultures Approach. Faculty of Civil Engineering (FKA), Universiti Teknologi Malaysia (UTM). 

A homopolymer of (R)-3-hydroxybutyrate (PHB) is the most common type of PHA that bacteria accumulate in nature and has been studied and characterized extensively by many researchers. Poly (P-hydroxybutyrate) (PHB) has a number of interesting characteristics and can be used in various ways similar to maity conventional synthetic plastics now in use. The properties of polyhydroxyalkanoates viz. PHB, PHV and comparison with synthetic polymer polypropylene (PP) have been described by Sasikala and Ramana (1996). 

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