Only 9% of the world’s plastic generated every year is recycled, and thus there is a need to develop new processes for end-of-life plastics. One possibility is the chemical recycling of a polymer chain, such as the depolymerization of polyethylene terephthalate (PET), one of the most widely used commercial plastics, 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 aims to determine the evolution of chain structure in the depolymerization of PET in a heterogeneous reaction as a function of catalysts and reaction temperatures. 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 (Mn) and intrinsic viscosity (Mv), offering a measure of chain length and dispersity of the chain length (i.e. Mv/Mn) with reaction time. The depolymerization process entails 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 PET in ethylene glycol. Comparison of the two catalysts shows that the ZnAc forms EG soluble oligomers more quickly than the TBD:MSA. Initial results show 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 available products from the depolymerization reaction over the course of the reaction.

Evolution of chain structure in the glycolysis of poly(ethylene terephthalate)

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