Investigation of catalytic glycolysis of polyethylene terephthalate by differential scanning calorimetry

The glycolysis of polyethylene terephthalate resin with excess amount of ethylene glycol, using metal acetates as catalysts, was examined by differential scanning calorimetry (DSC). The experiments were carried out under a nitrogen atmosphere of 600 psi. The efficiency of glycolysis was measured from the peak temperature associated with reaction endotherm. Among all the catalysts studied zinc acetate was confirmed to be the most effective for glycolysis. The glycolyzed products were mainly composed of small oligomers of bis-hydroxyethyl terephthalate in the presence of zinc acetate. Two isoconversion methods of kinetic analysis were applied for estimating the activation energy of glycolysis. The activation energy was lowered either by adding zinc acetate or by decreasing resin size. The results suggest that the depolymerization or the removal of polymer molecules from solid matrix should be the rate-limiting step of polyethylene terephthalate (PET) glycolysis, and that zinc acetate might facilitate the bond scission of polymer chains. (C) 1997 Elsevier Science B.V.