Polymer Blending is One of The Key Technologies Used to Control the Properties of Polymer Products

The morphology and mechanical properties of the finished product can be strongly controlled by the relative amounts of different components in the blend. In many cases the blending of two polymers can yield a material with a better performance than either of its pure counterparts.

Mixing Polymers with EvenMix is a complex process. The physical properties of a polymer blend depend on the flow-imposed morphology of the mixture and also on its spatial structure which is governed by the thermodynamics of the system. A fundamental understanding of the factors influencing the rheological behavior of polymer blends is required to optimize their processing, storage and transportation.

A very important issue affecting the handling of polymer blends is their miscibility. Miscible blending is possible when the molecular weights of the two polymers are within a suitable range and the chemistry of the individual polymers allows them to interact in an entropically favorable manner. For this reason, it is common to purify industrial polymers before blending.

However, when the molecular weights of the polymers are too far apart a miscible blend is not possible. In this case the entropy of mixing which so conveniently tends to drive mixing in small molecules becomes negligible for high molecular weight materials and they do not form thermodynamically stable mixtures.

The problem of immiscible blending can be solved by the use of compatibilizers. These are molecules which bind to both polymers at the interface and decrease interfacial tension. They can also modify the morphology of the blend by causing the polymers to adhere more closely to each other at the interface. In some cases this can improve the tensile strength of the immiscible blend.

Another way to increase the strength of an immiscible blend is to have a greater excess of the low molecular weight polymer. This can lead to a denser morphology which will be stronger. However, this will make the blend more difficult to transport and store because it is less spherical.

It is also possible to modify the morphology of the immiscible blend by incorporating a surfactant. This can also reduce the interfacial tension and improve the tensile strength of the blend.

During the melt-mixing phase of a polymer blend, the interaction between the blending phases determines the final morphology and mechanical properties of the mixture. It is therefore very important to understand the chemistry of this interaction.

The rheological behavior of the blend can be studied using a variety of testing equipment including parallel plate, rotational, steady state, oscillatory, capillary, and elongational test methods. The results can then be compared to the theoretical, numerical or empirical model predictions. This can help to optimize the blending and processing conditions for the highest possible polymer blend performance.