Optimizing synthesis of PET oligomers end capped with phthalic/maleic anhydride via recycling of off grade PET using design of experiments

Abstract

Poly(ethylene terephthalate) (PET) from off grades of industrial manufacturer was partially and thoroughly depolymerized using excess glycol to synthesize PET oligomers and bis(hydroxyethyl) terephthalate (BHET), respectively. Design of experiments and analysis of variance were applied for optimization of samples. Effects of reaction time, volume of glycol, catalyst concentrations and particle size of off grade PET on the yield of products were investigated based on the design of experiments. Thermal analysis of glycolyzed products is performed by differential scanning calorimetry. The optimum samples were also well characterized by Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy (proton nuclear magnetic resonance spectroscopy and carbon nuclear magnetic resonance spectroscopy). The optimal conditions to synthesize PET oligomers were glycol/PET molar ratio of 2 with no catalyst using granule-shape PET for a 120-min glycolysis reaction time. Desired oligomer repeating units were 3–8. On the other hand, a reaction time of 180 min, weight ratio (catalyst to PET) of 0.25 wt% and glycol/PET molar ratio of 5 were obtained as the suitable conditions of BHET production. Then, end capped PET oligomers, as a compatiblizer for preparing PET nanocomposites, were produced via reaction between maleic anhydride and phthalic anhydride (MA/PhA) composition. The combination of reaction time of 106 min and PhA/MA molar ratio of 0.85 produced the best results based on d-spacing and peak intensity of nanocomposite samples. Moreover, the reaction of MA and BHET from glycolyzation of PET was successfully performed at 160°C and 190°C for 8 h.