Among natural polymers polyhydroxyalkanoates (PHAs) are a very particular polymer
class. Chemically they can be described as linear aliphatic polyesters and due to their
thermoplastic behaviour (ability to be melted and shaped) they can in principle be used
directly as plastics without modification. Polyhydroxybutyrate (PHB), the first discovered
polymer from this group, occurs naturally in low amounts in the cells of some
microorganisms and serves them as energy reserve material. In the 20th century scientists
succeeded to obtain PHB in high yields in the cells of microorganisms through fermentation.
It was also found out that by varying the type of carbon source, "digested" by
microorganisms, different types of PHAs (with different chemical structures) can be
synthesized. Production of PHAs consists of two steps:
1) Fermentation, i.e. bio-chemical synthesis of PHAs in the cells of microorganisms
using different carbon sources such as sugars, vegetable oils, fatty acids, etc) and
2) 2) extraction of the synthesized polymers from the cells. Several types of PHAs and
their blends are available on the market.
They posess a variety of properties making them amenable for production of different
types of final products: films, sheets, moulded articles, fibres, etc. PHAs are
biodegradable. Because PHAs are biocompatible and bio-resorbable polymers they can
be used in medicine, as well.