In Germany, University of Freiburg researchers have produced polyurethanes using limonene, oxygen and carbon dioxide. In a solvent free process, limonene oxide was processed with CO2 to produce limonene bicarbonate, which can then be molded and hardened with amines. Citric acid amidoamine was successfully used as a hardener, further greening the process. Limonene can be sourced from orange juice production byproducts.
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