Meaning
Duration required for a polymer chain to escape its initial tube of surrounding entanglements. Disengagement time determines the elastic memory of a melt, influencing how quickly a part stabilizes after exiting a die. It is a fundamental parameter for understanding the relaxation of stress in a flowing polymer.
Molecules Behavior
Long chains take more time to navigate the obstacles created by their neighbors. This delay in movement causes the material to behave like a solid on short timescales and a liquid on long timescales. Heat helps.
Increasing the temperature of the melt reduces the disengagement time by providing more thermal energy for the molecules to move.
Polymer Processing
Extrusion lines must operate at speeds that account for how the molecules relax as they leave the die. If the line speed is too high relative to the disengagement time, the part will suffer from high internal stresses and shrinkage. Gravity pulls.
In blow moulding, this parameter determines how much a parison will sag before the mould closes. Thickening the material by using a higher molecular weight grade increases this time and improves the stability of the melt during the shaping phase.
Rapid Cooling
Rapid cooling often locks these stresses into the final geometry.
