Bacterial thermoplastic

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. 

Barham PJ, Keller A, Otun EL, Holmes PA. Crystallization and morphology of a bacterial thermoplastic poly-3-hydro xybutyrate. J Mater Sci 1984 19 2781. 

Poly(3-hydroxybutyrate) (1.8) is a bacterial polyester that behaves as an acceptable thermoplastic, yet can be produced from renewable agricultural feedstocks and is biodegradable. It is typically produced not in the pure state. 

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). 

Poly(3-hydroxybutyrate) (1.8) is a bacterial polyester that behaves as an acceptable thermoplastic, yet can be prodticed from renewable agricultural feedstocks and is biodegradable. It is tyjiically produced not in the pure state, but formed alongside minor amounts of poly(3-hydroxyv alerate). The ratio of these two polymers in a given sample is determined by the ratio of glucose and propionic acid in the medium in which the bacteria live and carry out their metabolic processes. 

Poly(hydroxyalkanoates) (PHAs) are a very common class of bacterial reserve materials, that have attracted considerable industrial attention (Anderson and Dawes, 1990). These polyesters are biodegradable and biocompatible thermoplastics with physical and mechanical properties dependent on their monomeric composition. The production of PHAs is a typical biotechnological process whose development requires the involvement of several scientific disciplines, i.e. genetics, biochemistry, microbiology, bioprocess engineering, polymer chemistry, and polymer engineering. 

Botana et al. [50] have prepared polymer nanocomposites, based on a bacterial biodegradable thermoplastic polyester, PHB and two commercial montmorillonites [MMT], unmodified and modified by melt-blending technique at 165°C. PHB/Na and PHB/ C30B were characterized by differential scanning calorimetry [DSC], polarized optical microscopy [POM], X-ray diffraction [XRD], transmission electron microscopy [TEM], mechanical properties, and burning behavior. Intercalation/exfoliation observed by TEM and XRD was more pronounced for PHB30B than PHB/Na,... 

Cellulose, like the polysaccharides above, has certain drawbacks. These include poor solubility in common solvents, poor crease resistance, poor dimensional stability, lack of thermoplasticity, high hydrophilicity, and lack of antimicrobial properties. To overcome such drawbacks, the controlled physical and/or chemical modification of the cellulose structure is essential [160]. Introduction of functional groups into cellulose can alleviate these problems while maintaining the desirable intrinsic properties of cellulose. Apart from the conventional plant source, cellulose is also obtained from bacteria, termed bacterial cellulose. 

In 1958, an article was published detailing the development of a thermoplastic biopolymer material, through a fermentation process [13]. The article described how the polymer developed as submicron granules in and was later extracted from bacterial cells. Marchessault and coworkers published a paper in the late 1980s discussing the characteristics of... 

Recently, bacterial cellulose, produced by Acetobacter Xylinum, was used as reinforcement in composite materials with a starch thermoplastic matrix [230]. The composites prepared with bacterial cellulose displayed better mechanical properties than those with vegetable cellulose fibers. 

In the case of 5C/-PHAs, the monomers consist of three to five carbon atoms, and mainly constitute R-configured chiral 3-hydroxyalkanoates. jcZ-PHAs mainly feature properties of classical thermoplasts hence, on the market, they compete with poly(ethylene) (PE) or poly(propylene) (PP), and, to a certain extent, also with bio-based poly(Z,-lactic acid). The strain Cupriavidus necator, a member of the Burkholderiaceae family, can be regarded as the best investigated bacterial jcZ-PHA producer. 

PHB is the most widespread and thoroughly characterized PHA found in bacteria. Despite its relative poor physical properties as a thermoplastic, PHB was initially targeted for production in plants. This is because the first bacterial PHA biosynthetic... 

Poly(hydroxyalkanoate)s are semicrystalline, thermoplastic polyester compounds that can either be produced by synthetic methods or by a variety of microorganisms, such as bacteria and algae. Traditionally known bacterial poly (hydroxyalkanoate)s include poly(3-hydroxybutyrate), poly(hydroxybutyric acid), and poly(3-hydroxy-butyrate-co-valerate) (4). 

Poly(j3-hydroxy butyric acid) is a thermoplastic polyester that is useful as a biodegradable plastics material. It is accumulated by many bacteria as an energy reserve material in the form of granules within the bacterial cells (6). 

Synthesis PL A is a thermoplastic aliphatic polyester which is formed by condensation polymerization of lactic acid, as mentioned in the preceding. Lactic acid is isolated from tapioca, corn and other plant root starches, sugarcanes, or other resources. Bacterial fermentation is normally used to produce lactic acid... 

Extensive studies in the molecular biology and physiology of the bacterial biopolyester synthesis has been made in the last decade. Previous research activities were mainly aimed at the biotechnological production of the extracted and semicrystalline thermoplastic polyester materials. Recently, however, it has been recognized that the intracellular polyester inclusions or those derived from in vitro synthesis can be considered as natural bionanoparticles. 

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