Polyethylene terephthalate thermal degradation

This comprehensive article supplies details of a new catalytic process for the degradation of municipal waste plastics in a glass reactor. The degradation of plastics was carried out at atmospheric pressure and 410 degrees C in batch and continuous feed operation. The waste plastics and simulated mixed plastics are composed of polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile butadiene styrene, and polyethylene terephthalate. In the study, the degradation rate and yield of fuel oil recovery promoted by the use of silica alumina catalysts are compared with the non-catalytic thermal degradation. 9 refs. lAPAN... 

Schaaf, E. and Zimmermann, H., Thermogravimetric investigation on the thermal and thermooxydative degradation of polyethylene terephthalate, Faserforschung Textiltechnik, 25, 434-440 (1974). 

The thermal degradation of PE mixed with polyethylene terephthalate (PET) and PE only degradation were compared. The presence of small amounts of PET is quite possible with the mixture of PE, PP, and PS, which is generally considered as municipal waste plastics. The yields of product gases, liquids and residues from the degradation of PET and the mixtures of PET and PE in ratios of 1 9 and 2 8 are shown in Table 18.4. Unlike PE or PVC, no liquid products could be obtained from the degradation of PET. The decomposition of PET proceeds with the production of a large amount of pale yellow... 

Y. Sakata, M. A. Uddin, K. Koiznmi, and K. Mnrata, Thermal degradation of polyethylene mixed with poly(vinyl chloride) and poly(ethylene terephthalate), Polym. Degr. Stab., 53, 111-117 (1996). 

K. Stoeffler, P. G. Lafleur, and J. Denault, Thermal decomposition of various alkyl onium organoclays Effect on polyethylene terephthalate nanocomposites properties. Polymer Degradation and Stability, 93 (2008), 1332-50. 

Some general known relationship between flammability and polymer structure are reviewed. Our studies on relating polymer end groups and molecular weights to flammability indicated that the known thermal degradation mechanisms for nylon 6 and polyethylene terephthalate (PET) are, in part, related to their flammability behavior. 

Other polymers that have been examined by EGA include polyvinylchloride (PVC) [17-19], polystyrene [20-23], styrene-acrylonitrile copolymers [24-26], PE and PP [27-32], polyacrylates and their copolymers [33-36], and polyethylene terephthalate, polyphenylenes, and polyphenylene oxides and sulfides [36-41]. Studies involving the use of chromatography include the thermal degradation of PVC [42], vinyl plastics [43] and polysulfone [44],... 

When polyesters are processed, thermal degradation is caused by ester bond cleavage here, polyethylene terephthalate is more stable than polybutylene ter-ephthalate. Ester cleavage is influenced to various degrees by different trans-esterification and polycondensation catalysts. This is less significant in the thermai degradation of polybutylene terephthalate compared to polyethylene terephthalate. 

Thermal-oxidative degradation proceeds in a similar way as in polyolefins via peroxy radicals. Fig. 4.64. Thermal oxidation of PET begins in a temperature range from 180 to 220 °C. The exact temperature depends on the catalyst used, s. Section 5.4.3.7.2. At very high temperatures, polyethylene terephthalate can also crosslink under oxidative conditions [20]. 

Figure 4.64 Thermal-oxidative degradation of polyethylene terephthalate [20]...

Polyethylene terephthalate is prone to hydrolytic degradation. During processing, hydrolytic degradation requires decidedly more careful attention than thermal and thermal-oxidative degradation. 

Thermal degradation in polyethylene terephthalate can be described as a hetero-lytic chain cleavage process. First, vinyl ester and carboxyl end groups are formed that undergo further complex reactions. Thermal degradation is characterized by a loss of relative solution viscosity and an increase in carboxyl end groups. 

The reaction mechanism of thermal degradation during the manufacture of polyethylene terephthalate can be subdivided into the following characteristic steps ... 

Figure 5.202 Thermal degradation of polyethylene terephthalate of different manufacturing routes at various temperatures DMT dimethyl terephthalate, EG ethylene glycol, TPA terephthalic acid...

Figure 5.203 Increase in number of carboxyl groups during thermal-oxidative degradation of polyethylene terephthalate (2 mm thick) with various diethylene glycol contents and catalysts at 160 °C in air DMT dimethyl terephthalate, DEG diethylene glycol, TPPat triphenyl phosphate...

Hydrolysis in polyethylene terephthalate at temperatures of 100 to 120 °C and a relative humidity of 100% takes place approx. 10,000 times faster than thermal degradation, and 5,000 times faster than oxidation in air in the same temperature range. Just 0.01 wt.-% content of effectively acting water at elevated temperatures (100 C) causes a noticeable decrease in molecular mass and viscosity as well as in mechanical properties because of hydrolytic cleavage. This is important in particular for the manufacturing of PET with high molecular masses by solid-phase condensation [774]. 

Goodings, E. R Thermal Degradation of Polyethylene Terephthalate, Soc. Chem. Ind. Monograph No. 13 (1961)... 

Pearce, E. M. et al. Fourier Transform IR Spectroscopy for the Study of Polymer Degradation, Thermal and Thermooxidative Degradation of Polyethylene Terephthalate, American Chemical Society (1983)... 

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