In the testing of polymers, the specific way that a known or unknown sample responds to heat by its flow pattern is important in identification. The use of melt flow analysis can be instrumental in identifying unknown samples or to determine the purity or presence of contaminants or other materials in a known sample.
When polymers are melted, and the flow rate is measured in specialized equipment the mass-flow rate or MFR, which is sometimes called the melt volume flow rate or MVR, can be determined. This is done by the precise heating of a very small amount of the sample that is either flaked or granules. In the past, these measurements were made by technicians, but new systems allow for the equipment to complete the entire test.
This material is heated in a cylinder or barrel until it has the ability to flow. The specific viscosity of the melted polymer can vary. Pressure on the sample is produced by the piston. This acts on the melted polymer in the barrel to allow it to move through die to determine the shear rate at that specific point in time.
The weight of the extruded amount over the time, usually 10 minutes, with the known of die size, temperature, and mass to create the process allows for the calculation of MFR.
Most commonly, melt flow analysis is used to ensure the quality of a polymer during production or in verification of the quality of materials from vendors. It is also done as part of process control and in comparing the properties of different batches or even between different suppliers.
The use of melt flow analysis goes beyond quality control. It can also be a useful tool in determining how a specific type of polymer will be impacted during processing or in use as material for a given application.