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• What Is EFM
• The Benefits of EFM
• The Principles of EFM
• How EFM is Designed (CAE Flow Simulation)

WHAT IS EXTENSIONAL FLOW MIXER (EFM^TM)?

The EFM^TM is a device in which plastics is mixed by flowing through flow channels where extensional flow is intentionally promoted so that very efficient dispersive and distributive mixing can be achieved. The EFM^TM can be attached to any machine capable of pumping molten plastic, such as single-screw (SSE) and twin-screw extruders (TSE), for injection molding, blow molding, extrusion, and compounding.

Mixing is one of the most important phenomena in any polymer processing, in which it is common to blend different polymers, additives and fillers to achieve certain features of the processing and products. Even a single-phase polymer has a molecular weight distribution or a small amount of cross-linked polymer due to poor production quality. The high molecular weight fraction can also generate "unmelt" or gel particles during processing, for example, during film production.

SSE is widely used to produce films, sheets, pipes, or profiles. It is also a part of injection and blow molding. Due to the high viscosity, the polymer melt mixing is laminar, composed of distributive and dispersive mixing. SSE can usually do a good job of distributive mixing by utilizing shear deformation. However, SSE with either static or dynamic mixers based on shear flow can neither offer good dispersive mixing, nor break droplets of the minor phase in a polymeric matrix when the viscosity ratio of them is above a limiting value.

In an EFM^TM, minor phase polymer with very high viscosity can be broken into smaller droplets and eventually fully dispersed into the major phase polymer. Comprehensive laboratory and industrial tests have indicated that in some applications the mixing in a SSE with an EFM^TM can outperform that of a TSE. The EFM^TM can eliminate gel particles, change microscopic morphology and enhance mechanical strength of products.

EFM Inc. obtained license for the original EFM technology from the National Research Council of Canada (NRC) from 1998 to 2003. EFM Inc. has been continuing development of EFM technology and products. For NRC's EFM technology, please contact NRC for details.

The Benefits of EFM

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THE PRINCIPLES AND ADVANTAGES OF EFM^TM

The principles of EFM^TM are different from conventional static and dynamic mixers, where molten plastic is subjected to basically shear flow. In an EFM^TM, molten plastic is exposed to extensional flows so that

1. Distributive mixing is more efficient since interfacial area is much higher than that in shear flow.

2. Dispersive mixing is much higher than that in shear, since the drop deformability in elongation is several times higher than in shear. This is especially good for multiphase plastic systems, such as plastic alloys and blends of immisible plastics, master batches, recycled plastics.

3. Energy per unit volume consumed in the EFM^TM is much lower (orders of magnitude) than in shearing type mixers.

Please read "Polymer Blends Handbook" for detailed theory, which is written by Dr. L. A. Utracki, a well known and respected expert on polymer blends and alloys. [Kluwer Academic Publishers, Dordrecht (1999)]

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How EFM Is Designed?

The design of the flow channel inside an EFM determines whether the equipment can enhance better mixing or not. The channel has to generate enough extensional flow to initiate the mixing. However, excessive stretching is not desirable. For example, high pressure drop through EFM can reduce output of the system, and induce the thermo-mechanical degradation.

Modern computer aided engineering (CAE) tools have been used to design the flow channel. With the knowledge of plastics, processing conditions, system integration, and extensive expertise in rheology, optimal flow channels have been designed to achieve the best mixing and maximum output of the system.

The CAE simulations gives all the details about the flow inside an EFM, including velocity, pressure, and temperature distributions, shear rate, extensional flow rate, shear and extensional stresses.

CAE simulations also confirm the principles of EFM, such as increasing intensity of extensional flow rate along the passage of an EFM (see image below). This enables the designers to fine tune the channel design.