Polyhydroxyalkanoates materials

Steinbuchel A (1991) Polyhydroxyalkanoic acid. In Byrom D (ed) Biomaterials. Novel materials from biological sources. Macmillan, Basingstoke, p 123... 

Polyhydroxyalkanoate (PHA) is a biodegradable and biocompatible thermoplastic that can be synthesized in many microoiganisms from almost all genera of the microbial kingdom. Many microoiganisms synthesize polyhydroxyalkanoates (PHAs) as intracellular carbon and energy reserve materials [1]. These microbial polyesters materials are thermoplastics with biodegradable properties [2]. PHAs are usually accumulated... 

Roller, M., Bona, R., Braunegg, G., Hermann, C., Horvat, P., Kroutil, M., Martinz, J., Neto, J., Pereira, L. and Varila, P. 2005. Production of Polyhydroxyalkanoates from Agricultural Waste and Surplus Materials. Biomacromol., 6, 561-565. 

Various procaryotic microorganisms can produce polyhydroxyalkanoates using regenerable carbon sources. This polymer is a storage material and can make up to 90 % of the dried cell weight. The most widely researched material in this group up till now is the poly-D(-)-3-hydroxybutyric acid (PHB). 

Metabolix Inc., is a private firm based in Cambridge, Massachusetts, USA, that was spun out of the Massachusetts Institute of Technology in 1992 and acquired biopolymer technology from Monsanto Inc. in 2001. Metabolix began its first commercial production of organic polyhydroxyalkanoate (PHA) resin, based on corn sugar in 2005 at an undisclosed location in the Midwest. The plant was expected to produce around 100 tonnes of material in 2005 and close to 1000 tonnes in 2006. 

Polyester is a general term referring to any polymer where the monomers are linked by ester bonds and includes the biodegradable microbially derived polyhydroxyalkanoates, which, as they are naturally produced, are beyond the scope of this article (for a review see Kim Rhee, 2003). Most synthetic polyesters in large-scale use are the aromatic poly(ethylene tetraphthalate) or poly(butylene tetraphthalate) polyesters as they have excellent material properties and are used in a wide range of applications including plastic containers, fibres for synthetic fabrics, films... 

Special types of purpose-built polymers can also be made with the intention of enabling more rapid direct microbiological attack and decomposition of these materials. Classes of both condensation and addition polymers among the polyesters, vinylic polymers, and polyhydroxyalkanoates typify current candidate materials being tested in these applications (e.g., Eq. 23.9), but as yet high costs have discouraged large scale exploitation. 

Within this context, the search for a material that is durable while in use and degradable after its disposal has led to the emergence of biodegradable plastic— materials that decompose into carbon dioxide and water as the final result of the action of microorganisms such as bacteria and fungi [5]. Polyhydroxyalkanoates (PHAs) constitute examples of such materials. 

The synthesis of bacterial storage compounds is reviewed in Chapter 10, focusing on two systems, namely polyhydroxyalkanoic acids and cyanophycin. Bacterial storage compounds are very interesting biopolymers having attractive material properties, sometimes similar to those of the petrochemical-based polymers. 

Koller, M. R. Bona G. Braunegg C. Hermann P. Horvat M. Kroutil J. Martinz J. Neto L. Pereira P. Varila. Production of polyhydroxyalkanoates from agricultural waste and surplus materials. Biomacromolecules 2005, 6, 561—565. 

Polymers derived from renewable resources (biopolymers) are broadly classified according to the method of production (1) Polymers directly extracted/ removed from natural materials (mainly plants) (e.g. polysaccharides such as starch and cellulose and proteins such as casein and wheat gluten), (2) polymers produced by "classical" chemical synthesis from renewable bio-derived monomers [e.g. poly(lactic acid), poly(glycolic acid) and their biopolyesters polymerized from lactic/glycolic acid monomers, which are produced by fermentation of carbohydrate feedstock] and (3) polymers produced by microorganisms or genetically transformed bacteria [e.g. the polyhydroxyalkanoates, mainly poly(hydroxybutyrates) and copolymers of hydroxybutyrate (HB) and hydroxyvalerate (HV)] [4]. 

The bacterial polyhydroxyalkanoates (PHAs) and their principal representative poly(3-R-hydroxybutyrate) (PHB) create a competitive option to conventional synthetic polymers such as polypropylene, polyethylene, polyesters et al. These polymers are nontoxic and renewable. Their biotechnology output does not depend on hydrocarbon production as well as their biodegradation intermediates and resulting products (water and carbon dioxide) do not provoke the adverse actions in environmental media or living systems [1-3]. Being enviromnent friendly [4], the PHB and its derivatives are used as the alternative packaging materials, which are biodegradable in the soil or different humid media [5, 6]. 

The language used to describe these new (or sometimes old ) materials can be confusing, and too often is misused. One particularly problematic term is bioplastics. One common definition for bioplastics is plastics that are either biodegradable or made from renewable sources a clear recipe for confusion. We will not use this term. Rather, we will use the term biobased plastics to refer to plastics made from biological sources (typically plants). The plastics may be made directly by biological organisms (e.g., polyhydroxyalkanoates) or by chemical polymerization of monomers made from such sources (e.g., polylactide). Plastics may also be partially biobased (such as the CocaCola PlantBottle made from PET that is partially biobased). 

An important development of orthopaedic implants has been the development of artificial composites, which when combined with biomolecules will induce osteogenesis. The properties of hydroxyapatite (HA) materials have been studied over the years with a view to increasing elasticity. Because biocompatibility has been a problem when HA has been combined with various polyethylenes and polysulphones, polyhydroxyalkanoates (PHAs) and its chemical composites, a polymer of hydroxybutyric acid (PHB), copolymers of hydroxybutyric acid and... 

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