Biologically Produced (R)-3-Hydroxy- Alkanoate Polymers and Copolymers

TLDR: PHB and its copolymers with 3-hydroxypentanoic acid are now available commercially and are being evaluated in numerous potential applications, all genuinely biodegradable in that their rate of chemical hydrolysis is extremely slow.

Abstract: Microorganisms are capable of producing a wide range of polymers and copolymers based on 3-hydroxypropionic acid substituted with various alkyl groups in the 3-position. The most common homopolymer is poly (3-hydroxybutyrate), PHB, which has a 3-methyl substituent, but monomers having C2-C5 alkyl side groups are found in natural copolyesters. The monomers are all optically active in the r absolute configuration. Phb can be produced from carbon substrates as diverse as glucose, ethanol, acetate, methane and even gaseous mixtures of carbon dioxide and hydrogen. The polymer occurs as discrete granules within the cell cytoplasmic space and can represent up to 80% of the dry cell weight. After extraction and purification it behaves as a normal crystalline thermoplastic with a melting point around 180°C and can be processed by conventional extrusion and moulding equipment. PHB and its copolymers with 3-hydroxypentanoic acid are now available commercially and are being evaluated in numerous potential applications. The copolymers are all genuinely biodegradable in that their rate of chemical hydrolysis is extremely slow but microorganisms produce both specific and non-specific esterase enzymes capable of degrading the materials rapidly to non-toxic monomers. Most of the potential uses exploit this property in medical, veterinary, horticultural and general disposable products.