Particle size reduction of poly(ethylene terephthalate) increases the rate of enzymatic depolymerization but does not increase overall conversion extent

Richard K. Brizendine, Erika Erickson, Stefan J. Haugen, Kelsey Ramirez, Joel Miscall, Davinia Salvachúa, Andrew Pickford, Margaret J. Sobkowicz, John McGeehan*, Gregg T. Beckham*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

Enzymatic depolymerization of poly(ethylene terephthalate) (PET) has emerged as a potential method for PET recycling, but extensive thermomechanical preprocessing to reduce both the crystallinity and particle size of PET is often conducted, which is costly and energy-intensive. In the current work, we use high-crystallinity PET (HC-PET) and low-crystallinity cryomilled PET (CM-PET) with three distinct particle size distributions to investigate the effect of PET particle size and crystallinity on the performance of a variant of the leaf compost-cutinase enzyme (LCC-ICCG). We show that LCC-ICCG hydrolyzes PET, resulting in the accumulation of terephthalic acid and, interestingly, also releases significant amount of mono(2-hydroxyethyl)terephthalate. Particle size reduction of PET increased the maximum rate of reaction for HC-PET, while the maximum hydrolysis rate for CM-PET was not significantly different across particle sizes. For both substrates, however, we show that particle size reduction has little effect on the overall conversion extent. Specifically, the CM-PET film was converted to 99 ± 0.2% mass loss within 48 h, while the HC-PET powder reached only 23.5 ± 0.0% conversion in 144 h. Overall, these results suggest that amorphization of PET is a necessary pretreatment step for enzymatic PET recycling using the LCC-ICCG enzyme but that particle size reduction may not be required.
Original languageEnglish
JournalACS Sustainable Chemistry and Engineering
Early online date7 Jul 2022
DOIs
Publication statusEarly online - 7 Jul 2022

Keywords

  • plastic recycling
  • cutinas
  • interfacial biocatalysis
  • kinetics
  • crystallinity
  • particle size

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