Sustainable materials: focus on bioplastics

Bioplastics offer a promising alternative to conventional plastics, as they are made from renewable raw materials and can be biodegradable. They help to reduce CO2 emissions and promote the circular economy. Some of these materials can even have mechanical properties comparable to synthetic polymers. However, bioplastics face challenges such as limited stability, high production costs and a lack of market acceptance. Despite these hurdles, they offer great potential for a sustainable future, particularly through their use in medicine and the packaging industry.

What is the difference between bioplastics and are they all biodegradable?

Bioplastics include both bio-based and biodegradable plastics, including biocomposites such as natural fiber-reinforced plastics and wood-plastic composites. These compounds combine the benefits of natural fibers with synthetic polymers to achieve improved mechanical properties, weight savings and reduced environmental impact.

The main natural polymer compounds used in bioplastics include cellulose, lignin, inulin, latex, chitin and starch. However, chemical derivatives such as cellulose acetate and polymerizable biomolecules, e.g. terpenes, which can be obtained from industrial waste streams from the paper and beverage industry, for example, are also used [1]. This approach promotes the circular economy by converting waste into valuable resources.

In addition to natural polymer compounds, there are also a number of synthetic polymers that are considered "bio" plastics due to modifications or as derivatives. Figure 1 provides an overview of these. The use of "bio" often leads to the misunderstanding that the term automatically means bio-based or implies biodegradability. In fact, most conventional plastics and a number of biodegradable plastics are derived from fossil raw materials, such as poly(butylene adipate-co-terephthalate) (PBAT) or polycaprolactone (PCL). PBAT is a copolymer of polyester (PE) and can be processed using typical processing techniques such as extrusion and injection molding. It is comparable to polypropylene (PP) in terms of its mechanical properties, but is biodegradable with the help of microorganisms and enzymes. Due to these properties, it is often used for packaging, in agriculture and in the food industry. PCL is a polyester that melts at a low temperature and is degraded by microorganisms in the absence of oxygen. It is also often used in medical technology.

The chemical structure of the material is the most decisive factor in biodegradability, which is mainly based on bacteria or fungi. This also determines which physico-chemical processes are required to break down the structures. These include, for example, high temperatures, UV radiation, high humidity and alkaline or acidic environments. These boundary conditions must be maintained so that the bacteria or fungi can absorb the material into their metabolism and use it as an energy source, so that only CO2, salt, water and biomass remain. Due to this complex degradation process, biodegradable plastics cannot simply be disposed of in the environment. It is therefore advisable to dispose of these materials either in specialized industrial composting plants or in domestic compost to ensure optimal decomposition and to fully exploit the eco-logical benefits of bioplastics.