The effect of carbon blacks and surface active substances (SAS) on the synthesis and properties of poly(ethylene terephthalate) (PET). Part II. By-products content, molecular weight, and thermal stability of the polymer
Results of studies on the effect of carbon blacks and ionic and nonionic SAS on the resulting PET properties have been presented. Carbon black type (furnace or channel) and specific surface area and SAS type were found to affect the content of carboxyl groups and reaction by-products (i.e., diethylene glycol and oligomers) in PET. For comparison, some reference experiments were performed to study the formation of diethylene glycol from ethylene glycol on heating over 140—195°C in the presence of a carbon black and/or an SAS. Moreover, the effect of carbon black and SAS type on the viscosity-average molecular weight, thermal stability of PET (by derivatography) and the degradation coefficient of molten PET were estimated. This coefficient was evaluated from changes in the melt flow index and Mv observed in PET kept in the rheometer capillary for 65 minutes at 270°C.
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