Thermal History Where the melt has been and for how long

Set Melt Temperature deg C

Shear Heating Above Set Point deg C

Melt Residence Time min

Reference Temperature deg C

The temperature the equivalent time is expressed at

Kinetics & Moisture Rate constants for the polymer and the water it carried in

Activation Energy kJ/mol

PET main-chain scission is typically 100-140

Thermal IV Loss Rate at Reference dL/g/min

Moisture Entering the Extruder ppm

Hydrolysis Coefficient dL/g/ppm/min

Allowable IV Loss dL/g

Predicted IV Loss

— dL/g

Thermal and hydrolytic scission combined

Rate, Split & Time Budget

Thermal Component: — dL/g
Hydrolytic Component: — dL/g
Hydrolytic Share of the Loss: — %
Equivalent Time at Reference: — min
Rate Ratio vs Reference: — x
Effective Melt Temperature: — deg C
Residence Time the Budget Allows: — min

Both mechanisms are treated as first order and independent, which is a simplification: hydrolysis is autocatalytic through the carboxyl end groups it generates, so a badly dried melt degrades faster as it goes and this will read low for high moisture. The single residence time is a mean, and the damage in a real machine is dominated by the tail of the distribution rather than the mean, so a machine with dead volume will lose more IV than this predicts while appearing correct on paper. The rate constants are grade-specific and must be calibrated against a measured chip-to-yarn IV pair before absolute predictions are trusted; the rate ratio and the equivalent time are far more transferable and are the outputs to rely on when comparing conditions. Thermo-oxidative degradation from air ingress at the hopper throat is not modelled and can dominate everything here if it is present.

Melt Residence Time, Thermal History & IV Loss Risk — free, with the formula and a worked example, at Textile School.