A comparison of melt flow index to rheology in the injection molding process

摘要

High shear rheology in coordination with injection molding process simulation, is the most accurate tool to assist in understanding the optimal process conditions and highlight potential concerns. Although melt flow index may be used in the general comparison of plastic products, the test method (ASTM D- 1238) does not introduce the high shear condition in the polymer seen during the molding process. Typically, melt flow index is used as a measure to compare flow lengths of materials. The concern in using the melt flow index is that the experiment is performed at conditions that do not replicate the actual molding environment. Specifically, under conditions in which the temperature does not approach the recommended melt temperature of the material. Also shear rates in the molding process are much higher. When comparing materials, rheological data (ASTM D-3835) offers a more precise comparison of how materials will perform under actual molding conditions.