Poly Hydroxyalkanoates PHAs

Poly(hydroxyalkanoates) (PHAs), of which poly(hydroxybutyrate) (PHB) is the most common, can be accumulated by a large number of bacteria as energy and carbon reserve. Due to their bio degradability and bio compatibility these optically active biopolyesters may find industrial applications. A general overview of the physical and material properties of PHAs, alongside with accomplished applications and new developments in this field is presented in this chapter. 

Since poly(hydroxybutyrate), a naturally abundant poly(hydroxyalkanoate) (PHA, Fig. 1), was first isolated and characterized by Lemoigne in 1925, PHAs have been studied extensively by biochemists who referred to them as lipids [1, 2]. Further research on PHAs however, made it clear that these materials are in fact water-insoluble polyesters, which are synthesized and accumulated intra-cellularly as storage compounds by many different bacteria. Using various types of substrates, an almost infinite variety of PHAs can be synthesized [3-9]. 

Poly-(3-hydroxybutanoic acid) (PHB), belongs to the large family of poly-(hydroxyalkanoates) (PHAs), high molecular weight natural polymers produced by various microorganisms and stored in cell cytoplasm (200). Low molecular weight PHB, also present in bacteria and are primarily involved in transport of ions and DNA across inner bacterial membrane (201). PHB could be developed as a valuable biocompatible material with possible applications in gene delivery after cytotoxic, safety, and efficacy evaluations. 

On the other hand, photosynthetic bcteria can produce poly-hydroxyalkanoate (PHA) intracellularly under nitrogen source deficient condition (Brandi et ah, 1991 Suzuki et ah,... 

As a raw material for the production of biopolymers such as poly-hydroxyalkanoates (PHA), produced directly from starch by fermentative 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. 

Chakravaity P, Mhaisalkar V, Chakrabarti T (2010) Study on poly-hydroxyalkanoate (PHA) production in pilot scale continuous mode wastewater treatment system. Bioresour Technol 101 2896-2899... 

Figure 21.9 The biodegradable polyester family poly(hydroxyalkanoates) (PHA), poly(hydroxybulyrate) (PHB), poly(hydro3qdiexanoate) (PHH), poly(hydrox3rvalerate] (PHV), polyflactic acid) (PLA), poly(caprolactone) fPCL), poly(butylene succinate) (PBS), poly(butylene succinate adipate) (PBSA), aliphatic-aromatic copolyesters (AAC), poly(ethylene terephthalate) (PET), poly(butylene adipate/terephthalate) (PBAT), poly(methylene adipate/terephthalate) (PTMAT). Adapted from [103].

Organisms produce a number of biological polymers, such as polynucleotides, polypeptides, polysaccharides, polyphosphates, and polyesters. Many scientists have made efforts to elucidate their physiological role and function. The microbial poly(hydroxyalkanoates) (PHAs), a femily of polyesters, are synthesized, and accumulated within the cells of a wide variety of microorganisms [1,2]. Poly(3-hydro butyrate)... 

Braunegg G., in Sustainable Poly(hydroxyalkanoate) (PHA) Production Degradable Polymers Principles and Application, Ed. Scott G., 2nd Edition, Kluwer Academic Pubhsher, Dordrecht/Boston/London, 2002, Chapter 8. 

Poly(Hydroxyalkanoates) Unlike bio-based PE, PET, and PEA, the poly(hydroxyalkanoates) (PHA) are bioplastics synthesized by bacteria. It was the first bacterial polymer to be harvested commercially. PHAs are deposited within the bacterial cells of many species as a lipoic material (Bnrdon, 1946). It is also unusual in that PHAs though hydrophobic still rapidly biodegrade in the environment. All bacterial polymers are not necessarily biodegradable (Steinbuchel, 2005) PHAs biodegradability is attributed to its saturated polyester chemical structure. 

Braunegg G (2002) Sustainable poly(hydroxyalkanoate) (PHA) production. In Scott G, editor. Degradable polymers - principles and applications. Dordrecht/Boston/London Kluwer Academic Publishers, pp. 235-293. 

Figure 16.7 Open, continuous, energy, and water-saving processes for production of bioplastics poly-hydroxyalkanoates (PHA) and biofuels.

Microbial biocatalysis is often employed for polymer synthesis. A successful application area is the poly(hydroxyalkanoate) (PHA). Thus, Noda et al (22) reported the development of Nodax family of copolymers, which were shown to have versatile physical properties. Srienc et al (23) engineered yeast to produce PHAs comprising 6-13 carbon monomers. Henderson (5) included whole-cell approaches and metabolic engineering in the biomass conversion program. 

With the increasing concern of human society to environmental and energy problems, the family of microbial synthesized polymers poly(hydroxyalkanoates) (PHA) have been attracting more and more attention in both academic and industrial fields due to their complete biodegradability and the renewable carbon resources used to produce them (Doi, 1990 Muller, 1993). 

Polyhydroxybntyrate/valerate (PHBV), one of the truly biodegradable non-cellulose based plastics, is a bacterially grown polyester with properties similar to PP. It was sold nnder the name Biopol. PHPB is one member of family of poly hydroxyalkanoates (PHAs) prodnced by microbes from sugars or other biobased materials. Metabohx PHAs are reported to be better water vapor barriers than most biodegradable plastics. 

Poly[(i )-3-hydroxybutylate] (PHB) is accumulated within the cells of a wide variety of bacteria as an intracellular energy and carbon storage material [125,126]. Poly(hydroxyalkanoate) (PHA)s are commercially produced as biodegradable plastics. In the biosynthetic pathways of PHA, the last step is the chain growth polymerization of hydroxyalkanoate CoA esters catalyzed... 

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