Viscosity is the index of the resistance of a fluid to flow. The viscosity of simple fluids, like water or oil, is usually a constant value at a constant temperature. The viscosity of plastic, however, is more complicated and depends on its chemical structure, composition, and processing conditions. Furthermore, within a chemical structure and formulation, viscosity is dependent on temperature, shear rate, and pressure.
This lesson covers the difference in viscosity of plastic materials between Newtonian and non-Newtonian fluids, how to compare viscosity of different materials within a group using single point MFR (melt flow rate) values, interpreting material viscosity curves, and how pressure, fill speed, and shear rate affect viscosity and temperature inside a molded part.