Potential Use of Limonene as an Alternative Solvent for Extraction of Gutta-Percha from Eucommia ulmoides

Limonene was used as an extraction solvent to obtain gutta-percha from leaves, samara, and bark of Eucommia ulmoides. The extraction conditions for the gutta-percha of E. ulmoides were optimized using a set of optimization processes. The optimized conditions were a liquid–solid ratio (L/S ratio) of 19.7 mL/g, extraction temperature of 134 °C, and extraction time of 1.8 h for the bark; an extraction temperature of 128 °C, extraction time of 1.7 h, and L/S ratio of 14 mL/g for the samara; and an extraction time of 1.4 h, L/S ratio of 15 mL/g, and reaction temperature of 138 °C for the leaves. Under these optimized extraction conditions, the actual extraction yields of gutta-percha were 55.32 ± 2.53 mg/g (bark), 81.14 ± 3.84 mg/g (samara), and 22.15 ± 1.08 mg/g (leaves). The gutta-percha obtained by limonene extraction was evaluated by thermogravimetric and differential thermogravimetric tests, gel permeation chromatography, differential scanning calorimetry, and Fourier transform infrared spectroscopy. Limonene has promising potential to replace traditional petroleum-based solvents to isolate gutta-percha from E. ulmoides.