Melt Flow Testing for Production Efficiency

Melt flow testing is arguably one of the most useful tests in the plastics and polymer industry. It primarily helps measure the melt flow rate (MFR) of thermoplastic materials by determining the ease with which plastics and polymers can be melted and processed under specified conditions. Understanding how a material behaves during processing and manufacturing provides valuable insights into how it will respond in practical applications. (Figure 1)

A lineup of bottles representing the various types of plastics and polymers used in manufacturing plastic bottles.
Figure 1. Knowing how a plastic or polymer reacts during processing and manufacture is a key indicator of the overall integrity of a finished product.

There are several ways that the melt flow index (MFI) contributes to the production and manufacture of plastics and polymer-based products, including:

  • Evaluating quality and consistency
  • Improving production efficiency
  • Meeting regulatory requirements
  • Enhancing customer satisfaction

Why is Material Behavior Important

MFR indicates how easily the polymer or plastic flows when melted. The flow depends on the material’s viscosity—think of viscosity as resistance. The thicker a material, the higher the viscosity and the slower it will flow, resulting in a lower MFI. Similarly, a plastic composition that flows easily has a higher MFI and a lower viscosity.

The length of the molecular chain of the resin, called molecular weight, is also related to flow. Shorter polymer chains with simple geometry and thinner consistency offer less flow resistance. Fiber spinning, film blowing and thin-walled injection molding are typical production methods for this type of material.

Longer chains with a high molecular weight and more complex structure will have greater resistance as well as a thicker consistency. This material is used for blow molding, extrusion, and thick-walled injection molding, for example.

A melt flow index tester is the most popular device in the plastic industry to determine a polymer’s MFI value. It measures material viscosities and enables validation for batch-to-batch flow consistency that helps prevent defects in processing and ensures a reliable final product.

Understanding MFI is a notable aspect in plastics production, since some applications, such as thin film, precision parts and fiber and filaments, require a polymer with a higher MFI, so it flows easier. Other applications requiring more durable parts that withstand warping or shrinkage, for example, need a lower MFI polymer, so the final product will maintain its strength. These include containers, pipes, industrial housings, and automotive parts.

When choosing materials for a specific product or switching between suppliers, knowing the MFI provides a standardized way to compare different plastics or grades of the same polymer. Product quality remains consistent throughout the manufacturing process.

Plastics During Processing

During melt flow testing, a constant load is applied to a standardized sample of material, while measuring the rate of protrusion through a specific opening to get the MFR.

For test environments where load, viscosity, composition, and temperatures are constantly changing, such as research labs, universities or third-party testing facilities, an MFI with a load cell is a practical choice. These digital-based systems enable push-button calibration and load setting to quickly move from one test set up to the next, accounting for all the application variables.

Traditional machines using a manual or automatic dead weight loading system are sufficient when testing the same mixture consistently under the same load, as found throughout manufacturing, but production efficiency and plant modernization may still warrant a load cell test system in many of today’s manufacturing environments. (Figure 2)

Tinius Olsen melt flow testers come with manual or motorized dead weights for static test applications or with digital load cells, where greater precision and flexibility is needed.
Figure 2. Melt flow testers come with manual or motorized dead weights (L: MP1200M motorized) for static test applications or with digital load cells (R: MP1500), where greater precision and flexibility is needed.

Consistent Quality Through Industry Standards

The melt flow rate helps to define the needed parameters, such as temperature, pressure, and screw speed, for a material during each specific manufacturing process.

Without this insight into how that material may react during manufacture, the polymer may be processed incorrectly, leading to quality or safety concerns, such as poor surface finish, voids, or incomplete filling of molds.

ASTM D1238 and ISO1133, the most common industry standards for melt flow testing, are also an integral part of melt flow indexing, as they further ensure the quality and consistency across different manufacturing environments and polymer applications.

  • ASTM notes that ASTM 1238D-23a is a “standard test method for melt flow rates of thermoplastics by extrusion plastometer.”
  • Per ISO, ISO1133-1:2022 is for the “determination of the melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics.”

Each provides testing parameters for a manual method – (Procedure A; Method A) as well as for an automatic timed flow measurement (Procedure B; Method B).

Impact of Material Quality on Manufacturing

With global shifts in the overall supply chain, from raw material to final products, manufacturers need reliable methods to evaluate production at every stage of product development. Having a good understanding of the manufacturing process and identifying any possible defects that could appear in the final product is on the forefront of the minds of plant engineers, product developers, and CEOs, alike. (Figure 3)

Physical properties of raw materials, especially, are under scrutiny to ensure that the correct material or material formulation is selected for the right application, and that the material being used is suitable for the end product. Melt flow testing is one such test that helps companies ensure the plastics and polymers being used are consistent in quality and are appropriate for the intended end use.
Figure 3. From raw material (L) to finished product (R), melt flow index testing ensures consistency across the manufacturing process to ensure quality results.
Figure 3. From raw material (L) to finished product (R), melt flow index testing ensures consistency across the manufacturing process to ensure quality results.

Physical properties of raw materials, especially, are under scrutiny to ensure that the correct material or material formulation is selected for the right application, and that the material being used is suitable for the end product. Melt flow testing is one such test that helps companies ensure the plastics and polymers being used are consistent in quality and are appropriate for the intended end use.

Check out our Melt Flow Index Testing playlist on YouTube to learn more.