Thermoplastics viscosities are described as having a pseudo-plastic non-Newtonian behavior. This type of behavior means that as you push the material at a faster rate, the polymer exhibits a reduction in viscosity. There are two critical factors that affect the viscosity of plastics: temperature and shear rate.
In our material characterization lab we measure viscosity utilizing two primary, capillary based systems: Autodesk Moldflow Injection Molding Rheometer (IMR) and Capillary Rheometer. (We will touch on Therma-flo™ separately in a later article.) Each piece of equipment and associated test method has its own benefits and drawbacks, but the IMR remains the preferred method for material characterization to simulate the injection molding process.