by Hannah Kannenberg & Theresa Voigt
– white, opaque and quite brittle
– 175 °C melting point
– not resistant to heat above 185 °C for more than 3 minutes
– isotactic & linear which results in a thin liquid melt
melt is suitable for fine structures, thin walls and micro parts
– 1.3 % shrinkage
– must be heated to at least 90 °C for sufficient crystallisation
– microwave safe
– insoluble in water & waterproof with hot liquids up to 120 °C
– non-toxic, therefore suitable for medical applications
– can be processed with conventional plastics machines
Description of the material
Polyhydroxybutyric acid (PHB, poly- 3 – hydroxybutyric acid) is a completely biodegradable bioplastic that is formed by bacteria in a fermentative process and can then be optimised for further industrial processing.
Motivation for the development of the material / technology
Unlike many other biodegradable bioplastics, PHB is hydrophobic and thus water-repellent. This property makes PHB suitable as a packaging material in the food sector. Another aspect that speaks for this application is the complete degradability after 6-12 months.
Polyhydroxybutyric acid is a polyester and belongs to the group of polyhydroxyalkanoates (PHA). Chemically it is divided into Poly-3-hydroxybutyric acid, Poly-4-hydroxybutyric acid and Poly-3,4-hydroxybutyric acid. With each structural change, different properties arise. For example, 4 PHB is more elastic than 3 PHB.
PHB is a bioplastic that you could theoretically simply decompose in one‘ s garden. However, the decomposition of the plastic would take place over a longer period of time. For this reason, recycling under controlled conditions in a composting facility is in some ways preferable to disposing of it on one‘ s own compost. PHB is not harmful and is an absolutely natural material.
Due to its complex production, the material is not yet industrially produced in larger scales. Since it has not yet found many application in economic areas, there are also no cycles in which the material is returned separately. Currently, the focus is more on the biodegradability of the material.
Regional importance of the material
Currently, PHB has a rather low regional significance, as it is not integrated into any real cycle or is not yet in circulation. If PHB could be extracted from a waste stream, for example, the material could be embedded in a regional cycle. But this scenario is still very unlikely at the moment.
Advantages and disadvantages
One advantage of PHB is that it is not based on fossil resources, because the material is produced by bacteria. Yet, the bacteria are feed with sugars and other plant based materials and is therefore in competition with the food industry. PHB is more dimensionally stable at higher temperatures compared to conventional plastics.
However, PHB is still very cost-intensive to produce. Thus, the bioplastic is hardly able to compete with conventional plastics at the moment. This is one of the reasons why the material has not yet found much use.
Possibilities / obstacles of recycling
Technically, the material can circulate in up to three cycles before the PHB loses quality. This means that infinite circulation without downcycling is not possible. The material can be completely biodegraded with the formation of CO₂ and water by destruents in a composting plant.
Biodegradability definitely addresses a positive aspect of the material. However, since the production of PHB is very complex and cost-intensive still, the question arises whether technical recycling would not be more sustainable –not just from an ecological perspective.
PHB is produced by bacteria. In a fermentative process, the bacterium breaks down carbon-containing nutrients and stores PHB in its own body in the form of granules. Up to 80 % of the bacterium can consist of these granules. Through a downstream process and using e.g. chloroform, the cell membrane is broken up and separated from the PHB. The PHB obtained can be adapted by adding further additives so that it is suitable for industrial production.
The material is currently only used in a few areas, which is due to the fact that it is not yet industrially produced in larger quantities. As a result, it is still too expensive for many applications. However, since PHB is hardly used for creative areas, it offers a multitude of possibilities to establish innovative design approaches that can go beyond packaging design.PHB is mainly processed by injection moulding, extrusion and film extrusion. PHB is mainly processed by injection moulding, extrusion and film extrusion. What are the next steps here? What other processes are there? How can the material gain attention in order to rerate to production on a tonne scale?
Currently envisaged areas of application
The possible applications of PHB are manifold. The bioplastic is similar to conventional polypropylene (PP) and has roughly the same properties and can be used for the same applications. By means of the injection moulding process, very precise moulded parts can be moulded, including packaging. PHB is also used to make films. As the material is non-toxic and biocompatible, it is also used in medical applications such as wound dressings and suture material. PHB is also used as hard rubber and adhesives.
Possible areas of application, potentials
Since the material behaves similarly to PP, it is exciting to see for which processes this actually applies. For example, thermoplastics can be shaped by blow moulding (special injection moulding process). How does PHB behave in such a process? Future potentials of the material can only really be thought of with the question: What if the material is cheaper and thus more accessible for many markets? Can PHB possibly be thought of as far as furniture design, thus overcoming the stigma of the ideal packaging material?