Mark Dadmun1,Shelby Watson-Sanders1,Joshua Moncada1
University of Tennessee1
Mark Dadmun1,Shelby Watson-Sanders1,Joshua Moncada1
University of Tennessee1
There is a need to develop new processes for end-of-life plastics to limit waste accumulating and contaminating our environment. One possibility is the chemical recycling of polymer, such as the depolymerization of polyethylene terephthalate (PET). PET is one of the most widely used commercial plastics, which can be depolymerized via glycolysis. In order to broaden the available products from the depolymerization process, we are interested in understanding the evolution of chain structure during chemical recycling. This study therefore monitors the evolution of chain structure in the depolymerization of PET in a heterogeneous reaction as a function of catalyst and reaction temperature. PET, sourced from Coke bottles, is depolymerized by glycolysis catalyzed with the salt of Triazabicyclodecene (TBD) and methanesulfonic acid (MSA) (1:1) or Zinc Acetate (ZnAc) in heterogenous reactions with ethylene glycol (EG). PET was depolymerized with TBD:MSA at 180 C, and with ZnAc at 165 C, 175 C and 185 C. Products of each depolymerization reaction were taken at predetermined intervals to monitor the evolution of chain structure. The chain size as a function of reaction time was determined by NMR (M<sub>n</sub>) and intrinsic viscosity (M<sub>v</sub>), offering a measure of chain length and dispersity of the chain length (i.e. M<sub>v</sub>/M<sub>n</sub>) with reaction time.<br/>The depolymerization process entails the interfacial reaction of the EG and insoluble PET, where progress of the reaction forms smaller PET chains that become soluble in EG. This analysis follows the decrease in chain length, and solubility of depolymerized PET in ethylene glycol. Comparison of the two catalysts shows that the decrease in chain length occurs more quickly in the ZnAc catalyzed reaction than the TBD:MSA, where increasing temperature increases the rate of depolymerization. Correlation of reaction rate to change in solubility is underway. Monitoring the dispersity of the PET in the reaction vessel shows that the polymer chain size distribution becomes narrower with depolymerization. These results will therefore provide insight into the mechanism that controls the chain depolymerization and available products from the depolymerization reaction over the course of the reaction.