Optimization of lactide synthesis from lactic acid by varying temperature, pressure, and concentration of catalyst ZnCl₂through response surface methodology

The mounting non-biodegradable polymer waste has become one of the primary concerns in the century. One solution to reducing such waste while still providing materials with similar properties is by developing biodegradable polymers, such as polylactic acid (PLA). PLA is more commonly synthesized by the ring-opening polymerization of lactide. In this study, lactide was synthesized by polycondensation of lactic acid, followed by depolymerization of the formed oligomer. The polycondensation was carried out without catalyst, while the lactide formation was catalyzed using ZnCl₂. Optimization of lactide synthesis was performed by varying ZnCl2 concentration and the operating pressure and temperature during the depolymerization step. The experimental design was conducted using Design-Expert software, and optimization was done through Response Surface Methodology. The model generated by the RSM shows good adequacy in predicting the crude lactide yield. The result indicates that catalyst concentration has a more pronounced effect on crude lactide yield, followed by vacuum pressure and temperature. The highest experimental crude lactide yield was 78.95%, obtained using 0.1% wt ZnCl2 at 610 mmHg and 205°C. Whereas the RSM model suggested an optimum crude lactide yield of 79.86% could be achieved with 0.125% wt ZnCl2 at 640.5 mmHg and 211°C.