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The research presented in this paper offers insight into the availability of intermediates in the depolymerization of polyethylene terephthalate (PET) to be used as feedstock to create value‐added products. Monitoring the dispersity, molecular weight, end groups, and crystallinity of reaction intermediates during the heterogeneous depolymerization of PET offers insight into the mechanism by which the polymer chains evolve during the reaction. Our results show dispersity decreases and crystallinity increases while the yield of insoluble PET remains high early in the reaction. Our interpretation of this data depicts a mechanism where chain scission targets amorphous tie chains between crystalline phases. Targeting the tie‐chains lowers the Mnof the polymer without changing the amount of recovered polymer flake. Chain scission of tie‐chains and isolating highly crystalline PET lowers the dispersity (Đ) of the polymer chains, as the size of the crystalline lamellae guides the molecular weight of the depolymerized oligomers. When sufficient end groups of PET chains are converted to alcohol groups, the PET flakes break apart into highly crystalline and less disperse polymer. Our results also demonstrate that the oligomeric depolymerization intermediates are readily repolymerized, offering new opportunities to chemically recycle PET more effectively and efficiently, from both an energy and purification standpoint.
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The structural evolution of poly(ethylene terephthalate) oligomers produced via glycolysis depolymerization
Polymeric materials have become an integral part of our society, and their high demand has created a large quantity of polymers that end up in the waste stream. For instance, poly(ethylene terephthalate) (PET) is widely used in a broad range of applications, where the chemical recycling of PET is of growing interest. Most methods focus on the complete depolymerization of PET to the monomer, however pushing the equilibrium reaction to the monomer is time- and energy-intensive. We hypothesize that by intercepting intermediates in the depolymerization, telechelic oligomers can be captured that can also be used as reactants to produce value-added goods. To this end, the effect of reaction type, catalyst loading, reaction time, and temperature on the evolution of the product chain structure and yield of the glycolysis depolymerization of PET is studied. For a heterogeneous reaction at lower temperatures (165 °C), the rate of depolymerization is sufficiently slow to offer access to a broad range of molecular weight products (3000–10 000 Daltons) at a high yield (nearly 100%). At higher heterogeneous reaction temperatures (175 and 185 °C), the reaction rate increases, producing oligomers of a narrower molecular weight range (2000–5000 Daltons) with significant loss of the original PET, up to 40%, as water soluble products. In the heterogeneous reaction, little change was observed when altering the catalyst loading at higher temperatures, but lower temperatures and decreased catalyst loading produce accessible higher molecular weight oligomers. Homogeneous catalysis of the glycolysis reactions increases the rate of depolymerization, such that it is difficult to isolate oligomers with M n > 1000 Daltons. The oligomers from heterogeneous reactions were used as reactants to form block copolymers with ethylene glycol, exemplifying their use as precursors in the production of value-added materials. These experiments, therefore, offer crucial insight into how reaction conditions can be readily tuned to produce target telechelic oligomers of PET.
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- Award ID(s):
- 2104982
- PAR ID:
- 10435024
- Date Published:
- Journal Name:
- Journal of Materials Chemistry A
- Volume:
- 11
- Issue:
- 9
- ISSN:
- 2050-7488
- Page Range / eLocation ID:
- 4679 to 4690
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2TA07467B
