Melt Residence Time, Thermal History & IV Loss Risk

The formula

This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.

How the result is derived

Step by step, from the values you type to the figure on screen.

1. The 9 inputs are read from the form on every keystroke: Set Melt Temperature, Shear Heating Above Set Point, Melt Residence Time, Reference Temperature, Activation Energy, Thermal IV Loss Rate at Reference, Moisture Entering the Extruder, Hydrolysis Coefficient and Allowable IV Loss.
2. Each value is checked against the accepted range in the input table below. A value outside its range stops the calculation rather than producing a misleading figure — the results blank out and a message appears.
3. The validated values are substituted into the expression above, which resolves Predicted IV Loss together with every supporting figure in one pass — no value is carried over from a previous entry.
4. The supporting outputs — Thermal Component, Hydrolytic Component, Hydrolytic Share of the Loss, Equivalent Time at Reference, Rate Ratio vs Reference, Effective Melt Temperature and Residence Time the Budget Allows — come from the same pass, so they always describe the same case as the headline figure.
5. Results are rounded for display only. The full-precision value is used throughout the chain, so reading a rounded intermediate figure back into the tool by hand can shift the last digit.

What each input means

Where to read each value on the floor, the unit it must be in, and the range the tool accepts.

What the tool returns

The headline figure and every supporting value it is built from.

Worked example

Substituting

Eight degrees of shear heating nobody measured is doing most of the damage: it alone raises the rate by 82% over the reference, and the eight-minute residence the machine was designed around is already 36% over the budget.

How to use it

1. Work through the input groups in order — Thermal History and Kinetics & Moisture. The defaults are a realistic case, so you can change one value at a time and watch what moves.
2. There is no calculate button. Every figure recalculates as you type or drag, which is what makes this usable for a what-if sweep rather than a single answer.
3. Read Predicted IV Loss in the dark results panel — that is the headline figure, expressed in dL/g.
4. Check the supporting rows underneath (Thermal Component, Hydrolytic Component, Hydrolytic Share of the Loss, Equivalent Time at Reference, Rate Ratio vs Reference, Effective Melt Temperature and Residence Time the Budget Allows) before acting on the headline — they are where an implausible input usually shows itself first.
5. Reset to defaults returns every field to the reference case, which is the quickest way to check whether a surprising result came from the tool or from an input you had changed earlier.

Where this is used

• Process planning — establishing Predicted IV Loss before a trial is booked, so machine time and material in Polymer Rheology & Synthetic Extrusion are committed against a calculated figure rather than an estimate.
• Costing and quotation — Predicted IV Loss is an input to the cost sheet, and quoting from a worked number rather than a remembered one is what keeps a margin intact.
• Troubleshooting — when the floor result drifts from plan, entering the measured values (starting with Set Melt Temperature) shows how much of the gap in Predicted IV Loss each variable explains.
• Teaching and study — the accepted ranges bracket normal Polymer Rheology & Synthetic Extrusion practice, so moving one variable at a time shows the shape of the relationship rather than a single answer.

Reading the result

Typical bands and what each one is telling you.

Assumptions and limits

• 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.
• Every input is bounded to the range normal practice occupies (Set Melt Temperature 200 to 340 deg C, Shear Heating Above Set Point 0 to 40 deg C and Melt Residence Time 0.5 to 60 min, and so on for the rest). Those bounds are guard rails against typing errors, not a claim that the formula fails one unit outside them.
• The calculation is deterministic: the same inputs always give the same result. It carries no allowance for machine condition, operator skill, ambient conditions or lot-to-lot material variation unless an input above explicitly represents one.
• Nothing is sent anywhere. The maths runs in your browser, so the numbers you type never leave the page.

Standards and further reading

• ASTM D4603 - Inherent Viscosity of PET by Glass Capillary Viscometer, the measurement this predicts a change in.
• ISO 1628-5 - Determination of viscosity number of thermoplastic polyester.
• ISO 15512 - Determination of water content in plastics, for the moisture input.
• ASTM D3418 - Transition temperatures by DSC, used to establish the safe melt window.

Questions people ask