Highly Active Calcium-based Heterogeneous Catalysts Prepared Together with Biomass and Biochar Modifiers for the Methanolysis of Poly(lactic Acid)

Abstract

The growing demand for sustainable solutions to plastic waste has intensified interest in efficient chemical recycling methods for biodegradable polymers such as polylactic acid (PLA). This study explores the catalytic depolymerization of polylactic acid (PLA) via methanolysis by using calcium-based catalysts prepared in the presence of different biomass and biochars modifiers, including rice husk (RH), cocoa pod husk (CPH), and palm kernel shell (PKS). Catalysts synthesized with CPH and PKS biochar (calcined for 14 h) exhibited remarkable catalytic performance, achieving up to 100% compared to the almost negligible conversion of the thermal reaction (T = 100 ^oC, time: 30 min, 0.5 Wt% of catalyst). CPH biochar was identified as the most effective surface modifier, likely due to its ability to promote phase changes from calcium carbonate to the more reactive calcium hydroxide phase, confirmed through FTIR and XRD analyses. The Ca-CPHB-14 catalyst demonstrated complete PLA conversion at 100 °C with 0.5 wt% catalyst, indicating a promising approach for chemical recycling. The reaction mechanism was analyzed, with findings suggesting that the enhanced performance is linked to specific phase transformations and surface hydroxyl groups on calcium hydroxide, facilitating base-catalyzed depolymerization. These findings demonstrate that incorporating biomass-derived additives during catalyst synthesis is an effective strategy to improve performance in polymer recycling. The work offers a promising, low-temperature route for PLA depolymerization and contributes to the development of sustainable, biomass-enhanced catalysts for plastic waste valorization.