مطالعه آزمايشگاهي تجزيه پلي‌اتيلن‌ترفتالات (PET) از ضايعات (بطري پلاستيكي) با استفاده از حلال‌هاي يوتكتيك عميق (DESs)

In this experimental study, the depolymerization of polyethylene terephthalate (PET) derived from waste plastic bottles was investigated using deep eutectic solvents (DESs). In the first stage, various DES systems based on choline chloride combined with organic acids, as well as systems containing catalytic metal ions, were comparatively eva‎luated to identify the most effective solvent for PET depolymerization. The performance criterion was defined as the percentage of PET degradation. The results showed that the choline chloride–gallic acid system, without the addition of a metal salt, achieved only about 30% degradation, whereas the addition of zinc chloride increased the degradation yield to 100%. Furthermore, the system based on oxalic acid an‎d ferric chloride hexahydrate (FeCl₃•6H₂O) was able to achieve complete polymer degradation under optimized conditions. To investigate the structural, physical, an‎d chemical properties of the synthesized solvents, Fourier-transform infrared spectroscopy (FTIR) an‎d differential scanning calorimetry (DSC) analyses were performed. The results confirmed the formation of deep eutectic systems an‎d the presence of hydrogen-bonding interactions among the solvent components. Following the screening stage, the selec‎ted solvent system was optimized using the Box–Behnken experimental design method. The effects of temperature, reaction time, an‎d polymer-to-solvent ratio were eva‎luated. The results indicated that complete PET degradation (100%) was achieved under the optimal conditions of 110 °C, a reaction time of 60 minutes, an‎d a polymer-to-solvent ratio of 0.125. In the recovery stage, terephthalic acid (TPA) was separated from the reaction medium as a precipitate after the addition of water an‎d the application of an electrical potential of 6.6 V with a current of 0.32 A. The solvent was subsequently regenerated using HCl an‎d H₂O₂. The results demonstrated that the recovered solvent retained its reusability an‎d exhibited satisfactory performance in subsequent cycles. Overall, this study demonstrated that the use of suitable deep eutectic solvents, particularly systems based on ferric chloride hexahydrate, provides an effective an‎d recyclable approach for the chemical recycling of polyethylene terephthalate. The proposed method shows significant potential for practical application in sustainable plastic waste management.

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