Capillary Rheometry

Capillary rheometry uses a capillary rheometer to measure the viscosity of a polymer. The capillary rheometer melts the polymer inside a small barrel, and then a plunger forces the polymer melt through a small capillary.
The rheometer measures the amount of force required to push the polymer through the capillary. The shear stress on the melt equals the force divided by the surface area of the plunger.
The shear rate is a measure of how fast the material is being tested. The shear rate is determined by the rate of flow through the capillary, and the die geometry. The viscosity of the material is equal to the shear stress divided by the shear rate.
In capillary rheometry, the viscosity is usually determined at different temperatures and shear rates. When the viscosity data is graphed, it provides a good representation of how the material behaves during processing.
If capillary rheometry data can be obtained, it is a good method of comparing the flow characteristics of different resins. When comparing capillary rheometer data, try to compare the data at similar shear rates and temperatures.