Effect of Alkali and Enzymatic Pretreatments of Eucommia ulmoides Leaves and Barks on the Extraction of Gutta Percha

Abstract

This paper exploited a novel method of single solvent recycling plus enzymatic pretreatment. Petroleum ether (60-90 degrees C) was an ideal solvent to extract Eucommia gum at high temperature (approximately 80 degrees C) and to precipitate the gum (flocculent) as the temperature of the solution fell to below 40 degrees C. The gutta percha was almost completely precipitated from solution as the temperature cooled down to below 0 degree C. After filtration and recovery of the precipitated gum, the filtrate, petroleum ether, was applied to an activated carbon column to remove dissolved impurities and reused for next gutta percha extraction. Because impurities were kept in solution, the precipitated gutta percha was highly pure. In an experiment of enzyme hydrolyzing the plant cell wall, cuticle layers on the surfaces of leaves prevented cellulase from approaching to and hydrolyzing the cellulose of the cell wall. NaOH (1%) at 70 degrees C efficiently degraded the cuticle layer, which greatly improved the enzymatic hydrolysis of cellulose within eucommia leaves. Gutta percha that was extracted from the alkali- and cellulase-treated leaves had a degree of polymerization as high as in the leaves, and the yield increased from 2.5% of milled leaves up to over 3.2%. The tensile strength of obtained gutta percha increased from 0.02 MPa of milled Eucommia leaves to 60.5 MPa, the breakage extensibility ranged from about 0 to 24%, and the tearing strength ranged from 0.5 to 36 kN/m.