Synthesis of poly(L-) lactide under simultaneous cooling and microwave heating by using immobilised candida antarctica lipase B

Abstract

Heavy metals based catalysts and time taking conduction heating mode is a challenge in poly(l-) lactide (PLLA) synthesis. In this study PLLA has been synthesised under simultaneous cooling and microwave heating using biocatalyst. Effect of immobilised lipase concentrations, polymerisation times and simultaneous cooling application was investigated in PLLA synthesis. Combination of techniques; intrinsic viscosity, proton nuclear magnetic resonance (HNMR), Fourier Transform Infrared Spectroscopy (FTIR) and Differential scanning calorimetry (DSC) was used to characterise PLLA. 8 % w/w biocatalyst relative to monomer was found an optimum concentration for ring opening l-lactide polymerisation. By the application of simultaneous cooling molar mass of PLLA was increased due to increased penetration of microwaves irradiations. PLLA of molar mass (Mη) 56,125 g/mol with 50.3 % crystallinity having specific rotation of 145 deg.dm-1 g-1 cm3 was obtained in 8 h. Maximum 98 % monomer conversion was achieved in 8 h that is significantly short polymerisation time than several days of conventional heating. In toluene, 90 °C was found as optimum temperature for polymerisation at microwave power level of 200 W. Biocatalyst was recovered completely by centrifugation. Polymerisation reaction was faster due to rapid microwave energy transfer and increased stability of biocatalyst under simultaneous cooling.