Rheological properties of blends: facts and challenges

Three forces will continue to provide incentive for the industry to produce new polymer blends: the ability to tailor product properties to a particular performance cost balance; fast entry into new markets; and it is easier to develop products for small or niche markets than by synthesizing new polymers. The utilization of polymer blends in commerce represents some 16% of all plastics and the sector is growing at a rate of approximately 10% per year. We expect that polymer blends will grow at a much faster pace in the next decade. The most important class of blends from the commercial viewpoint are the so-called immiscible blends, where the presence of a distinct minor phase may be observed. The minor phase in an immiscible polymer blend is deformable and a wide range of sizes and shapes can thus be obtained for this dispersed phase during processing [1]. Both the size and the shape of the minor phase can influence a multiplicity of physical properties. At present the processing/ morphology/ property relationships in immiscible and partly miscible blends remain poorly understood and a given processing strategy may result in high value added blends. Rheological methods are powerful tools to elucidate such relationships. The morphology of blends is strongly dependent on the rheological properties of the components and rheological properties are needed to understand the processing of blends and changes occurring during processing. Conversely, the blends’ morphology affects the rheological properties.