Bifunctional Ni-TiO2 catalyst for the efficient glycolysis of polylactic acid: a selective route to obtain 2-hydroxyethyl lactate

Abstract

While plastic offers exceptional properties and economic efficiencies, its indiscriminate disposal presents a significant threat to humans and the environment. Recycling plays a significant role in shifting from a linear to a circular economy. Among various methods, chemical depolymerization of plastic wastes enables the recovery of high-value monomers, offering an effective solution to resource recovery and environmental remediation. Although polylactic acid (PLA) is a biodegradable polymer, its extensive use in various applications has resulted in significant waste accumulation. Therefore, developing efficient chemical depolymerization strategies is essential to reduce environmental pollution caused by PLA and promote its circular economy. In this work, Ni-TiO₂ catalyst was employed for the glycolysis of PLA, yielding 2-hydroxyethyl lactate as a selective depolymerization product. The reaction was performed under relatively mild conditions, and the parameters were optimized to obtain good selectivity and product yield. The best yield (98%) was obtained at 190 °C for a reaction time of 8 h. A gram-scale-experiment was also performed to demonstrate the large-scale implementation of this reaction. Additionally, green metric parameters were analyzed to assess the sustainability of the designed reaction protocol. The Ni-TiO₂ catalyst also demonstrated excellent recyclability, maintaining consistent product yield over five consecutive cycles without any loss in activity. This study presents a sustainable and environmentally benign approach for the catalyst-assisted chemical depolymerization of PLA to a selective monomer in high yields.