Study of glycolysis of poly(ethylene terephthalate) recycled from postconsumer soft-drink bottles. III. Further investigation

A modified glycolysis reaction of recycled poly(ethylene terephthalate) (PET) bottles by ethylene glycol (EG) was investigated. Influences of the glycolysis temperature, the glycolysis time, and the amount of catalysts (per kg of recycled PET) were illustrated in this study. The manganese acetate was used as a glycolysis catalyst in this study. Bis-2-hydroxyethyl terephthalate (BHET) and its dimer were predominately glycolysis products. It was found the optimum glycolysis temperature is 190°C. And the best glycolysis condition is 190°C of glycolysis temperature, 1.5 h of glycolysis time, and 0.025 moles of manganese acetate based on per kg of recycled PET. If the best glycolysis condition is conducted, the glycolysis conversion may be as high as 100%. For a given reaction time (1.0 h), the ln(% glycolysis conversion) is linear to 1/T (K−1) and the activation energy (E) of glycolysis reaction is around 92.175 kJ/(g mole). The glycolysis conversion rate increases significantly with increasing the glycolysis temperature, the glycolysis time, or the amount of manganese acetate (glycolysis catalyst). Thermal analyses of glycolysis products were examined by a differential scanning calorimetry (DSC) and a thermogravimetric analysis (TGA). According to the definition of a 23 factorial experimental design, the sequence of the main effects on the glycolysis conversion of the recycled PET, in ascending order, is the glycolysis time (0.18) < the amount of catalyst per kg of the recycled PET (0.34) < the glycolysis temperature (0.40). Meanwhile, the prediction equation of glycolysis conversion from the result of a 23 factorial experimental design is Ŷ = 0.259+0.20X1+0.09X2+0.17X3+0.06X1X2+0.145X1X3+0.05X2X3+0.035X1X2X3. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2004–2010, 2003