Lipase-catalyzed degradation of poly(ε-caprolactone)

Abstract

The lipase-catalyzed degradation of poly(ε-caprolactone) (PCL) is described in the present work. The enzymatic degradation of PCL, having number-averaged molecular weight ( M n) of about 87,000 g/mol and molecular weight dispersion ( M w/ M n) of 1.51, was carried out in organic solvent (toluene) and the effects of medium composition, temperature and source of lipase were evaluated and quantified. Three fungal lipases of Candida rugosa, Mucor miehei and Rhizopus delemar were tested to select the best biocatalyst for PCL degradation. The retention of catalytic activity of M. miehei lipase was determined in organic solvent at different temperatures by pH-stat titration, using olive oil as substrate. The experimental data of the activity coefficient versus time were then used to calculate, for each temperature, the corresponding value of the first-order denaturation constant ( k d) and to estimate the main thermodynamic parameters of the enzyme thermal denaturation. The results of the degradation reaction, followed by size exclusion chromatography (SEC), showed that M. miehei lipase was able to catalyze the degradation of PCL with a maximum conversion degree of about 70% only after 1 h, within the temperature range of 40–60 °C. The catalytic activity of this biocatalyst demonstrated to be nearly stable at 40 °C, whereas the enzyme half-life was less than 2 h at 60 °C.