[ Dr. Sascha Peters ] Polyhydroxybutyrates (PHB) reinforced by nano particles

As a result of diminishing resources and rising prices the age of oil is drawing to a close. Accordingly there is increasing interest in renewable raw materials as alternative sources of energy and as a basis for the production of plastics. These new bio materials are above all useful for packaging, because they are naturally degradable and break down into their original components. The best future potential is shown by the biopolymers polylactid (PLA) and polyhydroxy butanoic acid (PHB). While PLA has similar properties to the PET which is familiar from plastic bottles, the properties of PHB are similar to those of the widely used plastic polypropylene PP. So far, however, the widespread use of these materials has been restricted by high production costs and some less than ideal characteristics, such as the tendency on the part of PHB to crack, which has limited its applications. But now US researchers have developed a process for reinforcing PHB with nano particles, which will bring the large-scale use of this biopolymer much closer.

Polyhydroxy butanoic acid (PHB) is regarded as the most promising of the biopolymers. It was discovered in France as early as 1925, is a member of the polyester group and can be produced by a range of micro-organisms. PHB's resilience values, in particular, are similar to those of PP. This thermo-plastic organic plastic melts in a range of between 170-180 °C, which means that it can be processed with the standard production processes which are used in the plastic industry. However it must be taken into account that molten PHB sticks to the skin. In the moulding process a reduction in material of approx. 1.3% has to be expected.
The material is stable in a temperature range of between –30 and +120°C. Because of its high crystalline content polyhydroxy butanoic acid does not dissolve in water or solvents, although it is less resistant to lye or acid. A further disadvantage is a greater tendency to crack and break than is displayed by polypropylene. In order to improve its properties PHB is therefore mixed with other components such as cellulose acetate, cork or inorganic materials to form PHB blends.