Biopolyesters

Grafting reactions onto a polymer backbone with a polymeric initiator have recently been reported by Hazer [56-60]. Active polystyrene [56], active polymethyl methacrylate [57], or macroazoinitiator [58,59] was mixed with a biopolyester polyhydroxynonanaate [60] (PHN) or polybutadiene to be carried out by thermal grafting reactions. The grafting reactions of PHN with polymer radicals may proceed by H-abstraction from the tertier carbon atom in the same manner as free radical modification reactions of polypropylene or polyhy-droxybutyratevalerate [61,62]. 

The vast majority of these interesting biopolyesters have been studied and produced only on the laboratory scale. However, there have been several attempts to develop pilot scale processes, and these provide some insight into the production economics of poly(3HAMCL)s other than poly(3HB) and poly(3HB-co-3HV). These processes utilize diverse fermentation strategies to control the monomer composition of the polymer, enabling the tailoring of polymer material properties to some extent. The best studied of these is poly(3-hydroxyoctano-ate) (poly(3HO)), which contains about 90% 3-hydroxyoctanoate. This biopolyester has been produced on the pilot scale and is now being used in several experimental applications. 

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. 

Keywords. Poly(hydroxyalkanoates), Biopolyesters, Properties, Modification, Crosslinking, Bio-... 

The most well known application of PHB and poly(3HB-co-3HV) is as substitute for conventional, non-biodegradable plastics used for packaging purposes and derived products [21, 115, 116]. Single-use bottles for shampoos, cosmetics and biodegradable motor-oil have been manufactured from these biopolyesters by common molding techniques. Containers and cups for food products were developed similarly, and bags have been produced from blown films of the material. 

Fig. 3. Biodegradable flower pot and food container from molded biopolyesters...

Technically, the prospects for PHAs are very promising. If the price of these materials can be further reduced, application of biopolyesters will also become economically very attractive. At the moment, a worldwide effort is being made to produce PHAs from major crop plants, such as corn, potatoes and rape seed [9, 145-148]. This should ultimately provide cheaper technology for PHA production, leading to the implementation of PHA-based products in everyday life. 

In addition to triterpenoids in the bark of Betula spp., suberin (a biopolyester comprising primarily hydroxy, epoxy and dicarboxylic acids) is also present, as... 

Kim, Y. B. and Lenz, R. W., Polyesters from Micro-organisms. In Advances in Biochemical Engineering/Biotechnology, Vol. 71, Biopolyesters, Babel, W. and Steinbiichel, A. (Eds), Springer-Verlag, Berlin, 2001, pp. 52-79. 

Isolation of the Biopolyesters. Cutin was obtained from the skin of limes using published methods (8,9). The final solvent extractions were omitted in studies of cutin-wax interactions. Typically, 20 limes provided 800 mg of powdered polymer. Suberized cell walls were isolated from wound-healing potatoes after seven days of growth (10), with a yield of 4.5 g from 22 kg of potatoes. Chemical depolymerization of both polyesters was accomplished via transesterification with BF3/CH3OH (11). 

Solid-state 13C NMR was employed to characterize intact samples of cutin and suberin biopolyesters. Although a considerable degree of structural heterogeneity was observed for both materials, it was possible nonetheless to resolve and assign many NMR peaks, even when the polyesters were accompanied by waxes or cell walls. Quantitative estimates for the various aliphatic, aromatic, and carbonyl carbon types indicated that cutin was primarily aliphatic in composition, whereas suberin had more aromatic and olefinic moieties. Additional analysis should be facilitated by the biosynthetic incorporation of selectively 13C-enriched precursors (26,27). 

Fig. 3 Metabolic routes towards biopolyester synthesis. Dashed lines represent engineered biosynthesis routes. Triangles depict targets for inhibitors enabling biopolyester synthesis. Enzymes indicated on shaded boxes on solid lines are biopolyester biosynthesis enzymes. With kind permission from Springer Science+Business Media [7]...

PHAs can consist of a diverse set of repeating unit structures and have been studied intensely because the physical properties of these biopolyesters can be similar to petrochemical-derived plastics such as polypropylene (see Table 1). These biologically produced polyesters have already found application as bulk commodity plastics, fishing lines, and for medical use. PHAs have also attracted much attention as biodegradable polymers that can be produced from biorenewable resources. Many excellent reviews on the in vivo or in vitro synthesis of PHAs and their properties and applications exist, underlining the importance of this class of polymers [2, 6, 7, 12, 26-32]. 

Lin TS, Kolattukudy PE (1978) Induction of a biopolyester hydrolase (cutinase) by low levels of cutin monomers in Fusarium solani f sp. pisi. J Bacteriol 133 942-951... 

Grapos, J., Santos, S. (2007). Suberin a biopolyester of plants skins. Macromolecular Bioscience, 7, 128-135. 

Franke, R., Schreiber, L. (2007). Suberin - a biopolyester forming apoplastie plant interfaces. Curr. Opin. Plant... 

Kolattukudy, P. E. (1980). Biopolyester membranes of plants Cutin and suberin. Science 208, 990-1000. 

Figure 9.16 Chemical structure of cutin, a biopolyester mainly composed of interester-ified hydroxy and epoxy-hydroxy fatty acids with a chain length of 16 and/or 18 carbons (Ci6 and C[s class). Also, the chemical strcuture of the aliphatic monomers of suberin, derived from the general fatty acid biosynthetic pathway, namely from palmitic (16 0), stearic (18 0), and oleic acids.

Scholz, C. and Gross, R.A. (Eds.) Polymers from renewable resources Biopolyesters and biocatalysis, ACS Symposium Series 764, 2000. 

Spassky, N. and Simic, V. (2000) Polymerization and copolymerization of lactides and lactones using some lanthanide initiators. American Chemical Society Symposium Series, 764 (Polymers from Renewable Resources Biopolyesters and Biocatalysis) 146-159. 

Sasikala, K., Ramana, Ch.V. (1995). Biotechnological potentials of anoxygenic phototrophic bacteria. II. Biopolyesters, biopesticide, biofuel, and biofertilizer. Adv. Appl. Microbiol. 41, 227-278. 

Hocking PJ, Marchessault RH (1994) Biopolyesters. In Griffin GJL (ed) Chemistry and technology of biodegradable polymers. Blackie Academic and Professional, New York, p 48... 

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