CHAPTER ONE

1.0 INTRODUCTION

Polyhydroxybutyrate (PHB) is one of the polyhydroxyalkanoates (PHAs) which has biodegradable and biocompatible properties. They are adopted in the biomed filed, in for example, medical in plants and drug delivery carriers (Keshavarz and Roy, (2010).

Polyhydroxybutyrate was discovered and identified as a granular component in bacterial cells. PHB can grow in a wide variety of natural environmental and is the reserve polymer (intracellular granules) forum in many types of bacteria in nature e.g. in soil, sea water, sewage sludge or compost.Polyhydroxybutyrate (PHAs) can be classified into two groups depending on the numbe3r of carbon atoms in the monomer unit: short-chain-length. (Scl-PHA) 3-5 carbon atom containing monomer and medium chain-length (MclPHAs) 6-14 carbon atom containing monomers (Steribuchel and Valentin, 1995).

The discovery if a polyester by Smet et al, (1983) was the first report of accumulation of medium-chain-length (MCl-PHAs), i constituents of 6-14 carbon atoms in axenic culture (Smet et al., 1983).

Currently, more than 140 hydroxyalkanoic acid have been identified as constituent of polyhydroxyalkanoates (PHAs) representing a versatile class of microbial polymer (Sterinbuchel and Valentin, 1995). Besides linear and branched 3-40,5- ad 6-hydroxyalkaniates, various functionalized PHAs constituents such as polyhydroxyalkanoates (PHAs) containing halogenated or aromatic side chains have been described (Abe eta l., 1990).

The physical properties of the homopolymer of hydroxybutyrate (PHB) are similar to those of poly propylene, for example regarding melting point, crystrallinity, glass transition temperature etc, and represent a stiff and brittle material (itocking and Marchessault,1994). The properties are improved in copolymers containing up to 25 mol% 3-hydroxy valerate (3HV), where toughness and flexibility are increased and the decrease in crystrallinity and melting point advance the melt-processing of the polymer without being degraded(Marchessault and 4u,2002)

Therefore, the poly (3HB-CO-3HV) copolymer gained industrial interest and in the late 1980s, commercialization under the trade name Biopol was initiated (Holmer etal., 1984). Biopol can be processed to useful materials by various processes such, as extrusion, injection molding, fiber spinning, coating or foaming. Because of the versatile applications as themoplastie biopolymers, polyhydroxy allcanoates (PHAs) can also be used for natural fiber composites or as binder in paints and for various application in medicide and pharmary such as tissue engineering (Kessler et al., 1999)

Polyhydroxylbutyrate(PHB) is a commonly found substance and readily biodegradable are robically and anaerobically. Microbes can use polyhydroxylbutyrate (PHB) exists in the cytoplasmic fluid in the from of crystalline granule about 0.5 Hm in diamete. Beta-hydroxybutyrate is connected by ester linkage and from polyhydroxybutyrate (Andreson and Dawes, 1990). This can be extracted from the cells as native granule or by solvent extraction (Doi and lee, 1990) and processed in the way as polypropylene. S

These biopolymers were also found to increase the resistance of bacteria (Tombolini and Nuti, 1989). Lemoigne, Grelet and croson (1958) draw attention to the different amount of poly-beta – hydroxybutyrate obtain by Bacterim Megaterium on different media and maraca and Wilkinson (1958) showed that more of the substance was formed as the glucose concentration of the growth medium was increased; the subsequest depletion of the product during the later stage of growth suggested a storage function. They also showed that organism rich. In poly-beta-hydroxyrate had a slower rate of autolysis than organisms poor in poly-beta-hydroxybutrate. It is probable; therefore, that poly-beta-hydroxybutyrate act as a reserve carbon and energy source – Tinelli(1955) found that the major part of the material was metabolized at sporulation and deduced that the two processes were intimately connected (Kato et al.,1992)