Chemical Conversion of Polylactic Acid into Methyl Lactate by Methanolysis Using Copper-Supported Ceria as an Efficient and Reusable Catalyst

Chemical recycling of plastic waste has attracted attention from all around the world, because it offers a sustainable solution to the problem of plastic waste accumulation and helps create a circular plastic economy. One of the sustainable methods of conserving resources and protecting the environment is chemical depolymerization or recycling of commercial plastics. In this regard, polylactic acid (PLA) is a widely used plastic material for three-dimensional (3D) printing of objects and for various other purposes ranging from agricultural films to food packaging. In this work, the chemical depolymerization of PLA was investigated using Cu-CeO2 as a catalyst, yielding methyl lactate (ML) as a selective product under mild reaction conditions. This environmentally friendly and cost-effective approach aims to achieve closed-loop chemical recycling of PLA waste. The reaction conditions were optimized to attain good catalytic activity and product selectivity. The PLA was completely depolymerized in the presence of the Cu-CeO2 catalyst at 140 °C in 8 h. The specific rate of the reaction was found to be 0.0189 mol m–3 s–1 based on the amount of ML formed in the reaction. 1H NMR spectroscopy was used to support the detailed depolymerization mechanism. Experiments on a gram scale were also carried out to demonstrate the utility of the developed reaction protocol. The effectiveness and sustainability of the designed protocols were investigated by the evaluation of the green metric parameters, including environmental factor (E), energy economy coefficient (ε), and environment energy impact factor (ξ). This study offers a sustainable, low chemical input, and environmentally friendly method for chemical recycling of waste PLA materials.