Polymer Blending and Polymer Alloys
Polymers are a very large class of materials that have been developed for a vast number of applications in a wide variety of industries. Mixing Polymers with EvenMix process allows manufacturers to create new materials with unique properties without the time and expense associated with developing a whole new material from scratch. But mixing these complex materials presents some very specific challenges.
The physical characteristics of a polymer depend on the molecular size, distribution and concentration of different components. When combining multiple different types of polymers, there are many opportunities to alter these properties by varying the relative amounts of each component. This technique is known as polymer blending or polymer alloying and it can be used to greatly enhance the performance of many different industrial processes.
The mixing of polymer mixtures can be a challenging task for several reasons, including the fact that these mixes are often highly viscous and have high vapor pressures. This makes achieving good mixing conditions difficult, and even with the use of high speed mixers it is often impossible to achieve uniformity in the product. In addition, the mixing process itself often leads to stringers and fisheyes in the product, making it more difficult to bring the material back to spec.
In addition to the difficulties associated with the rheological properties of polymer blends, there are also thermodynamic considerations that make them inherently unstable. The entropy of mixing that drives the mixing of small molecules becomes a very small contributor when dealing with high molecular weight materials, and as such, these systems tend to be very sensitive to temperature changes. The critical solution temperature of a polymer blend is often a function of its composition and is often much lower than that of the pure polymers, creating an unfavorable mixing condition.
This imbalance in entropy often results in the formation of phase-separated polymer blends. These blends are usually very difficult to process and can lead to poor moulding or extrusion results. To stabilize these mixtures, mixing rules must be developed to control the morphology of the blends and limit their interaction at the interface, which is accomplished by using compatibilizers.
Increasing the amount of polymer in a blend generally increases its viscosity, but this may not always be an option. Many manufacturers will blend in additives to reduce the overall viscosity of the system and improve the rheological properties of the blend. In order to do this, it is necessary to understand the rheological properties of the blend and determine how the additive can be introduced to the system in order to minimize its impact on the rheological behavior. This is usually done by measuring the rheological properties of the mixture with both static and dynamic test methods. These tests will help to identify the optimal mixing conditions for the system. This information is then used to develop a blending strategy for the system that will be optimized for its intended application.