Polyhydroxybutyrate

• Polyhydroxybutyrate
• Poly- (R) -3-hydroxybutyrate ( P3HB )
• Polyhydroxybutansäure

Biopolymer

Fixed

Approximately 175 ° C

• Chloroform 42 g · l-1
• Dichloromethane 40 g · l-1
• 1,2-dichloroethane, 4.5 g · l-1
• Aniline, 4 g · l-1

Values ​​each at 30 ° C.

The biopolymer poly ( other names: polyhydroxybutyrate, PHB, poly - (R )-3- hydroxybutyrate, P ( 3HB ) ) is a polyhydroxyalkanoate (PHA ) and belongs to the group of thermoplastic polyester. It was first isolated and characterized in 1925 by French microbiologist Maurice Lemoigne. PHB is accumulated in a plurality of microorganisms as storage substances, such as Cupriavidus necator, and Bacillus megaterium.

Biogenic production

PHB is mainly synthesized during the assimilation of carbon in the form of glucose and starch as an energy storage and metabolized in the absence of other sources of energy again. The biosynthesis of PHB by bacteria generally proceeds in three stages, which are catalyzed by three enzymes: two molecules of acetyl -CoA condense in a Claisen condensation by catalysis of β -ketothiolase to acetoacetyl- CoA, which in a stereospecific reaction by the NAD (P) H-dependent acetoacetyl-CoA reductase is reduced to R-3- hydroxybutyryl -CoA. This PHB synthase serves as a substrate for the polymerization to PHB. The poly -3- hydroxybutyrate ( P3HB ) form of PHB is probably the most common form of polyhydroxyalkanoates. A number of other polymers of this class are produced by a variety of organisms: including poly-4- hydroxybutyrate ( P4HB ), polyhydroxyvalerates ( PHV ), Polyhydroxyhexanoate ( PHH ), Polyhydroxyoctanoate (PHO ) and their copolymers. The polymers can be extracted from the cell material in granules of the bacteria.

A special strain of the bacterium Acidovorax is capable of degrading PHB by means of the enzyme D- beta-hydroxybutyrate dehydrogenase.

Properties

• Melting point of about 175 ° C
• Tensile strength of 20-31 MPa (like polypropylene)
• Glass transition temperature 15 ° C
• Insoluble in water and relatively stable to hydrolysis (in contrast to most other biopolymers )
• Permeable to oxygen
• Resistant to ultraviolet rays
• Little resistant to acids and alkalis
• Soluble in chloroform and dichloromethane, moderately in 1,2-dichloroethane and aniline
• Non-toxic and biocompatible and thus suitable for medical applications
• Biodegradable

Industrial use

PHB can be processed thermoplastically according to the isolation from bacterial cells. It is a from renewable resources by fermentation producible polyester, with properties similar to those of petrochemical-derived plastic polypropylene (PP). The fermentative synthesis can be carried out based on sugar and starch, but also from other nutrients such as glycerin and palm oil possible.

PHB is considered a " sleeping giant " in the bioplastics. Problematic are currently still relatively high production costs, which are still higher than those of petro chemically synthesized plastics and material properties ( brittleness ) of PHB. There are various approaches to reduce the production cost. Already in the 1980's, the three genes that are responsible for PHB production, transferred from Alcaligenes eutrophus by genetic engineering into the lighter manipulated E. coli. Furthermore, were transferred to Michigan State University PHB genes of garden cress. The transgenic plants produced up to 14% PHB in the dry matter of the leaves.

Worldwide announce numerous companies to enter the PHB production or expand production as intended along with some medium-sized manufacturers now the South African sugar industry, the production of PHB on an industrial scale to realize prices below 5 € / kg.

PHB is also mixed with other ingredients as PHB blend used. This particular material properties can be achieved for example by the addition of cellulose acetates. The range of properties of PHB blends extends from adhesives to hard rubber. Instead of cellulose, starch, cork and inorganic materials as additives are conceivable. The mixing with cheap additives ( cellulose acetate is an inexpensive waste product from the cigarette filter production ) has a favorable effect on the production cost of PHB blends of. The medium can be, according to many researchers thus the production costs up to the area of oil -based plastic materials lower.