Melt Viscosity and Apparent Melt Viscosity - ASTM D3835

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Melt Viscosity

The ratio of shear stress to shear rate at a given shear stress or shear rate.

Apparent Viscosity

The melt viscosity of a material exhibiting non-Newtonian behavior (ratio of shear stress to shear rate is not constant at a specified temperature and pressure). Apparent viscosity values can be corrected for comparison with melt viscosity values.

Capillary Rheometer

Testing is performed using a capillary rheometer. A plastic charge is heated in the rheometer barrel and is forced through a die with a plunger. The plunger is pushed either by a constant force or at constant rate depending on the equipment. Measurements are taken once the system has reached steady-state operation.

Melt viscosity is sensitive to molecular weight, melt stability, fillers, and additives.