MSc.Thesis Defense:Serra Kori
CHEMICAL RECYCLING OF POLY(ETHYLENE TEREPHTHALATE) AND INVESTIGATION OF CONDITIONS FOR EFFECTIVE RESYNTHESIS
Serra Kori
Materials Science and Nano Engineering MSc. Thesis, 2024
Thesis Jury
Assist. Prof. Serkan Ünal (Thesis Advisor), Assoc. Prof. Nuray Kızıldağ (Thesis Co-Advisor), Assoc. Prof. Bekir Dizman, Prof. Engin Burgaz
Date & Time: 23th July, 2024 – 2:00 PM
Place: FENS 2019
Keywords : Bis(2-hydroxyethyl) terephthalate, chemical recycling, poly(ethylene terephthalate), repolymerization, solid state polymerization
Abstract
The increase in plastic production leads to formation of more and more plastic waste, which causes the destruction of the natural environment. Poly(ethylene terephthalate) (PET) has become one of the most investigated polymers because of its high consumption. The high consumption of PET products means huge quantities of PET waste, which causes significant environmental pollution. Therefore, recycling of PET waste is an important issue to be addressed.
Accordingly, the PET materials were chemically recycled in the first part of the thesis. Different types of PET materials such as transparent PET beverage bottles and PET yarns were depolymerized by glycolysis method. (Zn(OAc)2), 1,3-Dimethylurea/Zn(OAc)2 deep eutectic solvent (1,3-DMU/Zn(OAc)2 DES) and Butyl-3-methylimidazolium bromine ([Bmim]Br) were used as catalysts in depolymerization reactions. The obtained Bis(2-hydroxyethyl) terephthalate (BHET) was characterized with regards to its chemical structure and thermal properties and compared to commercially available BHET. Additionally, the yields of different applied glycolysis processes were evaluated.
In the second part of the thesis, experiments were conducted to resynthesize PET from recycled BHET and increase its molecular weight by solid state polymerization (SSP). The effects of different reaction conditions were investigated for an optimum synthesis reaction. The influence of the reaction time of the repolymerization and the applied vacuum time on the chemical structure, physical and thermal properties of the PET product was investigated. Moreover, ethylene glycol (EG) in various concentrations and phosphoric acid were added to the repolymerization reactions and their effects on the PET formed were evaluated. The catalyst concentrations were changed to determine the best catalyst concentration that leads to the formation of PET with the desired properties. Finally, a polymerization reaction was carried out with untreated BHET to evaluate the differences in the properties of PET obtained from recycled BHET. During the SSP, different reaction conditions such as different reaction times and reaction temperatures were applied to the synthesized PET products. Besides, the effect of BHET particle size on the PET properties was investigated. The obtained recycled PET was characterized with regard to its chemical structure as well as its physical and thermal properties.