Dissolution of polystyrene into cyclic monoterpenes present in tree essential oils

We examined dissolution of polystyrene (PS) into cyclic monoterpenes present in tree essential oils, in order to develop an environmentally friendly shrinking agent for expanded polystyrene. The relationship between the chemical structure of the monoterpenes and their dissolution power for PS was studied through the solubility parameter (δ) and apparent activation energy (E _a) for dissolution. (R)-Limonene and its structural isomers on a C=C bond have high solvent power for PS. This favorable solubility was explained by their solubility parameters. The occurrence of hydroxyl group in a solvent molecule, such as in terpinen-4-ol, reduced affinity for PS. Bicyclic monoterpenes and 1,8-cineole, which have sterically bulky structure, showed limited dissolution power even though they have solubility parameters similar to that of (R)-limonene. Their bulky structures would interfere with permeation of solvent into the PS matrix. Cyclic monoterpenes and PS were recovered almost quantitatively by simple steam distillation of the PS solution.