Polyester polyhydroxyalkanoate

Biodegradable polymers can be mainly classified as agro-polymers (starch, protein, etc.) and biodegradable polyesters (polyhydroxyalkanoates, poly(lactic acid), etc.). These latter, also called biopolyesters, can be synthesized from fossil resources but main productions can be obtained from renewable resources (Bordes et al. 2009). However for certain applications, biopolyesters cannot be fully competitive with conventional thermoplastics since some of their properties are too weak. Therefore, to extend their applications, these biopolymers have been formulated and associated with nano-sized fillers, which could bring a large range of improved properties (stiffness, permeability, crystallinity, thermal stability). The resulting nano-biocomposites have been the subject of many recent publications. Bordes etal. (2009) analyzed this novel class of materials based on clays, which are nowadays the main nanoflllers used in nanocomposite systems. 

Naturally occurring organic polymers (biopolymers) are produced by all living organisms and play an essential role for life [83]. They include polysaccharides (cellulose, starch), hydrocarbons (rubber), polyesters (polyhydroxyalkanoates, poly(glutamic acid)), and proteins (collagen, gelatin, wool, silk, hair) - all of which... 

Genetic modifications are being used to produce polymers in plants. Similar polyesters polyhydroxyalkanoates, are produced in bacteria, as are poly(amino acid)s. 

Other blends such as polyhydroxyalkanoates (PHA) with cellulose acetate (208), PHA with polycaprolactone (209), poly(lactic acid) with poly(ethylene glycol) (210), chitosan and cellulose (211), poly(lactic acid) with inorganic fillers (212), and PHA and aUphatic polyesters with inorganics (213) are receiving attention. The different blending compositions seem to be limited only by the number of polymers available and the compatibiUty of the components. The latter blends, with all natural or biodegradable components, appear to afford the best approach for future research as property balance and biodegradabihty is attempted. Starch and additives have been evaluated ia detail from the perspective of stmcture and compatibiUty with starch (214). 

Keywords. Polyhydroxyalkanoic acids, Microbial polyesters, PHA, PHA synthase, Metabolic engineering, PHA granules, Ralstonia eutropha, Pseudomonas aeruginosa... 

Many bacteria are able to synthesize polyesters of hydroxyalkanoic acids and to accumulate these water insoluble polyhydroxyalkanoic acids (PHA) in the cytoplasm as inclusions and as storage compounds for energy and carbon these in-... 

Keywords. Polyhydroxyalkanoates, Polyhydroxybutyrate, Polyester, Transgenic plants, Metabolic engineering... 

Polyesters offer multiple options to meet the complex world of degradable polymers. All polyesters degrade eventually, with hydrolysis being the dominant mechanism. Degradation rates range from weeks for aliphatic polyesters (e.g. polyhydroxyalkanoates) to decades for aromatic polyesters (e.g. PET). Specific local environmental factors such as humidity, pH and temperature significantly influence the rate of degradation. 

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... 

Polyhydroxyalkanoates (PHAs) are biological polyesters that are produced by a wide variety of bacteria as osmotically inert carbon- and energy-storage compounds that accumulate in the form of granules (see Fig. 1). 

Polyhydroxyalkanoate (PHA) is a polyester of hydroxyalkanoates synthesized by numerous bacteria as an intracellular carbon and energy storage compound and accumulated as granules in the cytoplasm of cells... 

Polyhydroxyalkanoates (PHAs) are polyesters that were first isolated and characterized in 1925 by French microbiologist Maurice Lemoigne. They are produced by microorganisms (e.g. Alcaligenes eutrophus mdBacillus megaterium) in response... 

Polysacharides such as starch are the most prevalent naturally biodegradable polymer in commercial use. Aliphatic polyesters such as polyhydroxyalkanoates (PHA) are also a family of easily biodegradable polymers found in nature that are beginning to find commercial use. 

Polyhydroxyalkanoates Linear aliphatic polyesters produced in nature by bacterial fermentation... 

Biodegradable polymers that are based on renewable resources include polyesters such as polylactic acid (PLA) and polyhydroxyalkanoate (PHA). Biodegradable polymers can also be made from extracts from plants and vegetables such as corn, maize, palm oil, soya and potatoes. 

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... 

These environmentally degradable polyolefins, because of their cost/ performance profiles are very competitive for the growing markets for such plastics. They will be strong competition for the polyester types such as poly(lactic acid) and polyhydroxyalkanoates so frequently publicized as the innovative solution to plastic waste management. 

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. 

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