Theory 028/Materials Processing
Die Swell Is a Time Ratio
The claim
Polymer extrudate swell is set by the ratio of relaxation time to residence time in the die, not by shear rate alone.
01The mechanism
Recoverable strain stored in the melt relaxes before exit if the residence time is long, reducing swell.
02Predictions
- P1Swell should collapse onto the ratio.
- P2Longer dies should reduce swell at fixed rate.
03Refutation
Swell tracking shear rate alone would remove the relaxation term.