BIOPOLYMERS - Polyhydroxybutyrate
________________________________________ Polyhydroxybutyrate (PHB) Name of biopolymer: Polyhydroxybutyrate (PHB) Name of enzyme used to synthesise PHB: Alcaligenes Eutrophus The biopolymer PHB is produced by placing bacteria, such as Alcaligenes Eutrophus, in a suitable growth medium e. g. molasses from agricultural waste and fed high levels of nutrients such as glucose, causing it to multiply rapidly. Nitrogen is then restricted from the nutrient supply, making the bacteria unable to reproduce further. The bacteria store their excess energy in the biopolymer PHB, much as humans do with fatty tissue. The levels of PHB extracted can reach a maximum of 80% of the bacteria’s dry body weight, with the organism being harvested and the polymer separated out. Properties of PHB: Water insoluble and relatively resistant to hydrolytic degradation; Good ultra-violet resistance but poor resistance to acids and bases; Soluble in chloroform and other chlorinated hydrocarbons; Biocompatible and hence is suitable for medical applications; Sinks in water, facilitating its anaerobic biodegradation in sediments; Nontoxic; Thermoplastic. Stiff and brittle; High melting point. Use or Potential use of PHB: The biodegradability of PHB has given it extraordinary appeal as a potential replacement for the widely used polymers derived from petrochemicals. These petrochemical products, such as polypropylene and polyethylene, are often used for packaging, but are a hazard to the environment because of the fact that when discarded they do not decompose and can cause injury to plants and animals.