The power’s in the peel

 The power’s in the peel.  A favourite of parents whenever kids don’t want to consume the skin of apples, pears or other fruits, this phrase is getting a whole new meaning when it comes to oranges. Of course orange peels cannot be eaten, as everyone knows. But: they’re suitable for producing excellent plastics – in a process, no less, that binds carbon dioxide from the atmosphere.

At least 50 per cent of the fruit is lost when oranges are processed into orange juice, which according to expert estimates adds up to approximately 20 million tonnes of waste each year. Why not use the leftovers to produce something sensible? That’s what chemist Geoffrey Coates from Cornell University thought when way back in 2006 he became the first scientist to develop a process to produce plastics from orange peels. By now several scientists have managed to replicate his success, enriching the market with bio-based plastics as replacements and/or supplements for petroleum-based products.

German universities researching plastics made from tropical fruits include the Institute for Macromolecular Chemistry at the University of Freiburg headed by Prof. Dr. Rolf Mühlhaupt and the University of Bayreuth’s Macromolecular Chemistry II department under the leadership of Prof. Dr. Andreas Greiner. The latter recently published a report about a new, green all-rounder called “PLimC”. This cryptic term stands for a polycarbonate originating from a synthesis with limonene oxide, i.e., ultimately, from the naturally occurring substance in orange peels known by chemical scientists as limonene. The limonene is oxidised and combined with carbon dioxide in order to create the bio-based plastic, which unlike petroleum-based polycarbonates does not contain the harmful compound bisphenol A. In this way, climate-damaging carbon dioxide can be chemically fixed while producing low-cost, eco-friendly functional materials for a wide range of industrial applications.

The waste product from orange processing comes with a whole series of properties that make it particularly attractive for industrial applications. Hard, extremely heat-resistant and transparent, PLimC is particularly suitable as a material not just for coatings but also for moulded parts for interior and exterior car trims, thermal-insulation foam and adhesives. Valuable product benefits result from the combination with other chemicals. For instance, PLimC-based plastics can prevent the growth of E. coli bacteria in containers. Hence the material is perfectly suited for medical use in hospitals and care facilities. When combined with water-soluble polymers in bottles, bags or other containers, the bio-polycarbonate can help to counteract the dramatic increase in ocean pollution caused by non-soluble plastic particles. Other scientists as well have already demonstrated that first-rate plastic products can be derived from waste. Bio-based plastics can be produced from wood waste, palm leaves, potato skins and much more. The environment benefits in two ways: less waste, on the one hand, and a greater number of products without petroleum-based plastics, on the other.