Polyurethane from Orange Oil
Researchers at the Institute of Macromolecular Chemistry at the University of Freiburg have developed a process with which bio-based polyurethanes can be derived from the naturally occurring substance limonene through reaction with oxygen and carbon dioxide. Limonene is the primary component of orange oil and is collected in large quantities as a by-product in the course of producing orange juice.
According to reports, limonene oxide has for the first time successfully undergone reaction with carbon dioxide without the need for a solvent. The reaction yields limonene dicarbonate, a compound that can be cast and cured (hardened) with amines. The researchers also used citric acid amidoamine as the curing agent for the first time; it too is derived from citrus fruits. The curing reaction produces polyurethanes as the product. The materials obtained from limonene can, for instance, be used for molded parts in the automobile industry and thermal insulation as well as coating systems and adhesives.
In contrast to conventional polyurethanes, no toxic intermediates are required. Furthermore, there is no competition with food production, since large quantities of orange oil are collected as a by-product during production of orange juice. About 70 million tons of oranges are harvested worldwide annually. The largest producers are Brazil and the USA. It is estimated that worldwide production of orange oil is about 30,000 tons per year.
Production of polymers from orange oil is not completely new, however - in 2005 scientists at Cornell University in Ithaca/USA developed a process for producing plastics from limonene and carbon dioxide. In this case, the resulting plastics had properties similar to those of polystyrene.