Fluoropolymer Processing Aid Dosing Economics under High Shear Profile Tooling
Optimize fluoropolymer dosing between 400 and 800 ppm to balance wall slip against startup induction scrap and avoid masterbatch working capital drag.
Apparent Shear Viscosity
Meaning
Fluid dynamics measurements define the resistance of a polymer melt to flow under specific deformation conditions. Calculating apparent shear viscosity allows engineers to model how a material behaves inside an extruder barrel where the rate of shear is not uniform. It differs from true viscosity because it does not account for the pressure drops at the entrance and exit of the die.
Flow Resistance
Molten polymers typically show a decrease in thickness as the speed of processing increases. Because of this shear thinning behavior, apparent shear viscosity remains a necessary variable when moving from a low speed lab trial to a high volume production run.
Process Stability
Maintaining a constant temperature is necessary to prevent fluctuations in the material thickness. If the apparent shear viscosity varies during a run, the resulting dimensions of the extruded part will drift outside of the specified tolerances. Frequent audits of the melt flow index provide a proxy for these changes.
Production Scaling
Selecting a pump or screw design based on a supplier forecast rather than a demonstrated rate can lead to overheating. High apparent shear viscosity at low speeds might suggest a material is easy to handle, yet it can cause excessive backpressure at production speeds. This mismatch results in wasted energy and degradation of the polymer chains.
To solve this, the operator must verify the pump curve against the actual melt behavior at the target throughput.