Relaxation Ratio
Viscoelastic behavior in polymer melts is quantified by comparing the material relaxation time to the duration of the deformation process. The deborah number represents this dimensionless ratio, showing whether the polymer behaves like a viscous liquid or an elastic solid during spinning. A high value indicates that elastic forces dominate, meaning the polymer remembers its shape and resists continuous flow.
Extrusion Behavior
Melt spinning operations depend heavily on this value to predict flow stability at the spinneret. When the deborah number is low, the polymer flows smoothly and behaves like a liquid, allowing stable extrusion of fine filaments. If the value becomes too high, the melt behaves like an elastic solid, which causes melt fracture and uneven fiber diameters.
Spinning Limit
Draw resonance arises when the deformation occurs too quickly for polymer chain rearrangement. At these high draw speeds, the deborah number exceeds the critical threshold, leading to periodic variations in yarn thickness.
Deformation Rate
Process engineers adjust the extrusion speed and cooling rate to keep the parameter within acceptable limits. By changing the temperature of the melt, the molecular relaxation time changes, directly altering the deborah number during drawing. Higher temperatures shorten the relaxation time, which shifts the behavior toward viscous flow and stabilizes the drawing process.
