One-Pot Depolymerization and Polycondensation of PET Based Random Oligo- and Polyesters

Abstract

The glycolysis of PET is a promising well-developed technique that could be utilized in a wide range of processes. Due to its equilibrial nature, the high ratio of reagents and the purification steps it is an expensive process. In this study our goal was to modify the standard glycolysis to an easily modulateable method (acido-alcoholysis) suited for one-pot oligoester, polyester synthesis. Adipic acid was added to the depolymerization reaction to connect low molecular weighed components into oligoesters. PET depolymerization reaction series were carried out with ethylene-glycol/adipic acid and butane-1,4-diol/ adipic acid to demonstrate the tuneability of these systems. The reaction products were thoroughly characterized with NMR, FTIR, TGA, DSC and functional group analysis. One-pot depolymerization-polycondensation reactions were engineered to produce unsaturated and saturated polyesters. The unsaturated polyesters were dissolved in styrene, cross-linked and moulded to be characterized with DMA. A decreasing tendency of the glass transition temperature and cross-link density were found in the function of the ratio of adipic acid used during the depolymerization step. Acido-alcoholysis proved to be a versatile technique that could be used to engineer oligoesters and polyesters. The reagent use can be minimalized, and the raw reaction products can be directly applied as mid-products.

Why is Recycling of Postconsumer Plastics so Challenging?

“…Pushing equilibrium toward the monomer is possible with condensation polymers through the use of solvents (water, alcohols, glycols, amines) that can potentially be products of polymerization . However, as these are equilibrium processes, the products tend to be a mixture of monomers and oligomers plus the excess solvent required to shift equilibrium toward monomers . The recovery of monomers to complete the circular economy is thus typically limited by the ability to effectively purify the products from the equilibrium depolymerization.…”

“…169 However, as these are equilibrium processes, the products tend to be a mixture of monomers and oligomers plus the excess solvent required to shift equilibrium toward monomers. 172 The recovery of monomers to complete the circular economy is thus typically limited by the ability to effectively purify the products from the equilibrium depolymerization.…”

Plastic Recycling of Polyethylene Terephthalate (PET) and Polyhydroxybutyrate (PHB)—a Comprehensive Review

“…DMT efficiency of 97% and 97.7% can be achieved at 300 °C and 310 °C, respectively. The most efficient reaction occurs at a temperature range of 259.85 °C to 270.85 °C, pressure range of 9 to 11 MPa, weight ratio of PET to methanol of 8:6 and duration of 40 to 60 min (Kárpáti et al 2019).…”

Valorisation of plastic waste via metal-catalysed depolymerisation

“…Postconsumer PET was depolymerised in the melt (at 250 °C) using DEG and Ca/Zn stearate as catalyst, and the product mixture was used in situ in conjunction with bis(2-ethylhexyl)phthalate and the same metal promoter for the production of flexible poly(vinyl chloride) compounds [ 243 ]. One-pot depolymerisation–polycondensation reactions were developed to produce random copolyesters poly(ethylene terephthalate- co -adipate) from PET in the presence of EG and adipic acid [ 244 ]. The depolymerisation step was carried out using a zinc acetate catalyst (1 wt %), with no need of excess of chemicals.…”