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The Basics of Mixing Polymers

Jan 16

Mixing Polymers with EvenMix is a key industrial process in the production of polymeric materials. It helps to reduce costs by allowing manufacturers to combine different polymer materials to create new products without developing an entirely new material from scratch. It is also used to improve processing efficiency and achieve desired physical properties of the final product. There are a wide variety of mixing techniques and chemistry methods that can be used to optimize a blend's performance.

The morphology of an immiscible polymer blend develops through mechanical and thermodynamics interactions during flow. The morphology is controlled by the interfacial tension between the two phases, which in turn depends on the size of the particles and the viscosity of the two phases. In general, higher molecular weight materials have lower viscosities than low molecular weight materials and therefore produce a lower interfacial tension. Nonetheless, the morphology of an immiscible blend may vary significantly between different conditions. For example, the morphology that emerges during extrusion will differ from that which is moulded using injection.

In order to mix an immiscible polymer blend, mechanical energy must be introduced to the system. The energy must be sufficient to overcome the interfacial tension between the two different phases. This can be done either by shear or agitation. Both methods have their advantages and disadvantages. Shear mixing is effective for achieving rapid and complete mixing, but it can result in particle breakup and shear deformation. On the other hand, agitation results in more gradual mixing and is suitable for preserving particles size and shape.

However, both shear and agitation can lead to the development of phase-separated mixtures. In addition, these types of mixtures are highly unstable thermodynamically. For example, the thermodynamics of a phase-separated blend of poly(ethylene terephthalate) and poly(vinyl alcohol) can be described using a phase diagram (see Figure 1). Both the binodal and spinodal regions are shown.

The thermodynamics of a blend depend on the composition, molecular weight and temperature. Using these variables, a simple model can be used to predict the free energy of mixing (DGm) for binary and partially miscible systems.

A chemistry method that has been used to enhance mixing of immiscible polymer blends is the use of compatibilizers. These compounds are added to the polymers and decrease their interaction with each other by increasing their surface area. This allows the major and minor components of a mixture to minimize contact, which increases their overall stability. The spheres of the minor component are made larger, as well, so they are less likely to come into contact with those of the major component and disperse. The result is a more stable immiscible polymer blend.