Polyhydroxyalkanoates or PHA

Polyhydroxyalkanoates or PHAs are linear polyesters produced in nature by bacterial fermentation of sugar or lipids.

They are produced by the bacteria to store carbon and energy. More than 150 different monomers can be combined within this family to give materials with extremely different properties.

These plastics are biodegradeable and are used in the production of bioplastics. They can be either thermoplastic or elastomeric materials, with melting points ranging from 40 to 180 °C.

The mechanical and biocompatibility of PHA can also be changed by blending, modifying the surface or combining PHA with other polymers, enzymes and inorganic materials, making it possible for a wider range of applications.

Production

PHA are produced by bacteria and micro-organisms. It’s more appropriate to refer to it as biosynthesis than production.

To make PHA, a culture of a micro-organism are fed with nutrients so that they multiply rapidly. Once the population has reached a certain level, the nutrient composition is changed to force the micro-organism to synthesize PHA.

PHA is be stored by the micro-organisms. The PHA can weight as much as 80 % of the organism’s dry weight

The biosynthesis of PHA is usually caused by certain deficient conditions such as the lack of macro elements (phosphorus, nitrogen, trace elements, oxygen) and the excess supply of carbon sources.

Properties

PHA polymers are thermoplastic; they become liquid at their melting point.

They are UV stable and have a low permeation of water.

Processability, impact strength and flexibility can be imporved with a higher percentage of valerate in the material.

PHAs are soluble in halogenated solvents such chloroform, dichloromethane or dichloroethane.

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