Thermal stability of polyethylene terephthalate

Abstract

The kinetics of thermal and thermal‐oxidative degradation of polyethylene terephthalate (PET) have been investigated as a function of melt temperature, melt residence time, melt environment, and drying environment. Rates of thermal and thermal‐oxidative degradation were measured in terms of: weight loss of volatile degradation products, decreasing inherent viscosity, and increasing carboxyl end group concentration. Thermal‐oxidative degradation was also investigated by Differential Scanning Calorimetry. Calorimetric results show that thermal‐oxidative degradation of PET is an exothermic reaction, with an apparent activation energy of 117 kJ/mol. Melt temperature, melt residence time, melt environment, and drying environment have all been found to affect the degradation of PET. Analysis of inherent‐viscosity kinetic data has been carried out, utilizing existing theories based on a random chain scission mechanism. Activation energies of 117 and 159 kJ/mol have been calculated for air‐dried and vacuum dried samples respectively.

Processing characteristics of PET/PEN blends, part 2: Rheology and degradation kinetics

“…The activation energy for thermal degradation of PET was determined to be 187 kJ/mol (44.7 kcal/mol) and that for thermal-oxidative degradation was determined as 116 kJ/mol (27.7 kcal/mol). Jabarin and Lofgren 6 have reported activation energies of 159 and 117 kJ/mol respectively for the thermal and thermaloxidative degradation of PET. Zimmerman and Kim 14 have reported activation energies for PET in the range of 121-172 kJ/mol (29-41 kcal/mol).…”

“…The enthalpy or the heat evolved during the oxidative degradation has been used to monitor this process. 6,7,11 The time required for the enthalpy to reach 50% of the maximum value (half-time) has been related to the rate constant for thermal-oxidative degradation. The process of degradation leads to a reduction in the melt viscosity with time.…”

Effect of moisture on the crystallization behavior of PET from the quenched amorphous phase

“…This, in particular, could be a possible reason for the large differences in the T, values for dry PET samples between the present study and Ref. 1. Some DSC scans of samples subjected to the above-described drying procedures are reported in Figure 4.…”

Numerical modeling of multilayer film coextrusion with experimental validation

“…At identical temperatures the primary PET polymer is more viscous than the co-PET resin, but the red-PET resin, as used in the final film sample, is the most viscous. It is common practice within DTF to process PET at temperatures approaching 300 C. Within the total melt system residence time of 127 s for the polymers and hardware used in this study, thermal degradation is only observed at temperatures exceeding 300 C [60]. Differential scanning calorimetry was used to determine that the melting temperatures of PET and red-PET was 255 C and that of co-PET 220 C. Furthermore, the glass transition temperature of PET and red-PET was found to be 78 C and that of co-PET 76 C. Three film samples at different processing conditions (temperatures) were manufactured.…”