Melt Flow Index

Melt flow indexing is the most popular, and yet least accurate way to determine material viscosity. Melt flow index uses a standard testing apparatus with a standard capillary to measure the flow of the material. The melt flow indexer tests the polymeric material at a single shear stress and melt temperature.
The melt flow index is the measure of how many grams of polymer pass through the capillary over 10 minutes. A higher melt flow index indicates a lower material viscosity. This means that a material with a melt flow index of 20 flows easier than a material with a melt flow index of 5.
The value obtained through the melt flow index test is a single data point. The melt flow index only tests the material at one shear stress, and temperature.
Melt flow index information from different materials and material grades may be used for a rough comparison of flow characteristics for different materials. The melt flow index value is given for each material by virtually all material suppliers.