Lactide synthesis via thermal catalytic depolymerization of poly lactic acid oligomer using ZnO nanoparticle dispersion

Abstract

Abstract Owing to its capacity to synthesize high molecular weight of Poly Lactic Acid (PLA), polymerization via Ring Opening Polymerization (ROP) has gotten the attention of researchers. Accordingly, since the ROP technique utilizes lactide as a potential monomer for PLA synthesis, the production of lactide is indispensable. Currently, in order to solve the problem associated with commonly used homogeneous tin-based catalyst, looking for alternative catalysts for lactide synthesis are becoming more attractive. In the present study, the optimum reaction conditions for lactide synthesis via thermal catalytic depolymerization by using ZnO nanoparticle dispersion were investigated. The effects of three major factors including reaction temperature (190 °C, 210 °C, and 230 °C), reaction time (1 h, 2 h, and 10 h), and catalyst concentration (0.3%w/w, 0.65%w/w, 1.0%w/w) on the yield of lactide were studied. The oligomer PLA was produced from an aqueous solution of Lactic acid (50 mL, 88%) via polycondensation reaction at 150 °C for 4 h. The suspension of Zno Nps was prepared by dissolving Zno Nps powder in distilled water with a ratio of 1:4. The produced oligomer of PLA was depolymerized via thermal catalytic depolymerization using 20% w/w of the prepared Zno NPs dispersion. The optimization of lactide yield and depolymerization reaction parameters was done via response surface methodology with a Box-Behnken design. Based on the analysis, the optimum conditions were found to be a reaction temperature of 215.73 °C, a reaction time of 7.32 h, and a catalyst concentration of 0.72%w/w along with the maximum lactide yield of 80.4%. Generally, the outcome of the study reveals that the utilization of ZnO nanoparticle dispersions as a catalyst for lactide synthesis from oligomer PLA via thermal catalytic depolymerization is worthful.