Farwa Khalid (Insitute of physical chemistry, Polish Academy of Sciences, Poland)
Abstract: PET (polyethylene terephthalate) is commonly used in bottles, fabrics, and packaging due to its transparency, durability, and mechanical properties. Its extensive use, combined with its natural degradation under sunlight and UV rays, slowly and uncontrollably contributes to environmental pollution [1]. Efforts to address waste PET face challenges in achieving energy-efficient and selective depolymerization through physical sorting or existing chemical methods[2]. The depolymerization of PET in m-cresol under UV light is key to breaking it down into valuable monomers[3].
This study investigates UV-induced depolymerization of PET in m-cresol, focusing on real-time monitoring with Benchtop NMR. A flow-based experimental setup ensures continuous UV light exposure, while Diffusion NMR provides insights into diffusion properties and molecular size distribution during the process. Real-time diffusion data reveals the depolymerization kinetics, transitioning from high-molecular-weight polymer chains to low-molecular-weight monomers. This method offers valuable insights into the mechanistic pathway of PET depolymerization, potentially improving sustainable plastic waste management.
References
[1] F. Cao, L. Wang, R. Zheng, L. Guo, Y. Chen, and X. Qian, “Research and progress of chemical depolymerization of waste PET and high-value application of its depolymerization products,” Nov. 03, 2022, Royal Society of Chemistry. doi: 10.1039/d2ra06499e.
[2] S. Zhang et al., “Selective depolymerization of PET to monomers from its waste blends and composites at ambient temperature,” Chemical Engineering Journal, vol. 470, Aug. 2023, doi: 10.1016/j.cej.2023.144032.
[3] S. S. Karim et al., “Model analysis on effect of temperature on the solubility of recycling of Polyethylene Terephthalate (PET) plastic,” Chemosphere, vol. 307, Nov. 2022, doi: 10.1016/j.chemosphere.2022.136050.
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Hi Farwa, I have a question regarding the interpretation of DOSY experiments. In case of signal overlap, under which conditions is it possible to distinguish the two overlapping components? Would a signal display mono or biexponential decay? Thank you.
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I have used a PGSTE-WET to suppress the solvent signals interfering with the PET peaks. Selecting a gradient strength value where the interfering signal is attenuated and only the desired signal appears. This way, I filter out the solvent peaks in the DOSY spectrum.Also, we are using Tailored fitting Normalization to get the polydispersity index.
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Hi Farwa, great presentation. How does the wavelength of UV light influence the results you see?
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Hi,
The wavelength of the UV light greatly affects the photodegradation. I even tried the experiment with 270nm wavelength, but I didn’t see the degradation efficiently, even though this one has high energy, because PET shows maximum absorption closer to 300-320nm due to the aromatic ring and ester group. In 270 nm, I did not see the degradation product (Monomer) peak in the region around 9ppm, as it is shown in 365nm proton NMR spectra in my presentation and also I have calculated the peak area of the polymer peak its almost constant in 270nm.
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