SYNOPSISPolyester melts exhibit two discrete degradation rates depending on the moisture content in the solid state. The initial fast rate is very sensitive to the moisture content while the later slow rate is not sensitive to the moisture content. The former is attributed to hydrolysis and the latter is attributed to thermo-oxidative degradation. A combined kinetic equation which represents both hydrolysis and thermo-oxidative degration of the polyester melt is proposed. The model equation agrees well with the experimental data. A method to determine hydrolytic and thermal degradation rate constants, moisture content, molecular weight for polyesters by means of a melt viscometry is discussed.

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