Extraction of polylactic acid degradation products with supercritical carbon dioxide

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2022-11-25

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Koçak Bütüner, Sümeyye

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Polylactic acid (PLA) is a bio-based polyester derived from starch feedstocks such as sugar cane, sugar beet, or corn. PLA is used in industries like the medical sector, fibers and textiles, packaging, and agriculture. Since the PLA usage area is increasing, its recyclability has gained importance. Currently, chemical recycling for PLA has been conducted by pyrolysis, alcoholysis, or hydrolysis. In this research, an environmentally benign separation method was developed to recover the PLA depolymerization products. PLA degradation was realized using supercritical carbon dioxide (SCCO2). Subsequently, degradation products were extracted by SCCO2. The effects of extraction parameters such as temperature, pressure, and static extraction time on the extracted product distribution and extraction yield were studied. The effect of temperature was investigated at three different temperatures. Results showed that as extraction temperature increased, extraction yield enhanced since the solubility of decomposition products in SCCO2 increased. High temperature also decreased the viscosity of the reaction products, facilitating the mass transfer of the extractable products into the SCCO2 phase. The influence of static extraction time was investigated by extending the time. Results revealed extraction yield increased at longer static extraction time since more products could be dissolved in SCCO2. The effect of pressure was studied at two different pressures. A slight increase in extraction yield was observed, indicating that increasing the pressure was inadequate to accelerate the mass transfer of the products. The extracted product composition consisted of D, L lactide, meso lactide, lactic acid, and some unknown products. The highest extraction yield of 89% was obtained at 80 °C, 310 bar for 2 hours of static extraction time. The product obtained in a condenser under these conditions comprised of 53% D, L lactide, 30% meso lactide, 9% lactic acid, and 8% unknown products.

Subject Keywords

Polymer degradation, Pla, Supercritical carbon dioxide, Extraction

URI

https://hdl.handle.net/11511/101215

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

S. Koçak Bütüner, “Extraction of polylactic acid degradation products with supercritical carbon dioxide,” M.S. - Master of Science, Middle East Technical University, 2022.