The Rheology of Polymer Alloys and Blends

Rheology is part of continuum mechanics. Thus, the basic principles of continuity, homogeneity and isotropy are incorporated into the basic rheological relations. The continuity principle requires that there is no discontinuity of material properties from one mathematical point to another homogeneity demands that there is no concentration gradient, and isotropy imphes that the flow does not impose orientation on the flow elements. In multiphase systems that comprise polymer alloys and blends, these three principles are seldom obeyed [Utracki, 1995]. 

Another aspect of the multiphase rheometry is related to the interrelations between the flow field and system morphology. In this text the term morphology will refer to the overall physical form or shape of the physical structure of a material, usually described as either a dispersed phase (particles or domains), co-continuous lamellae, fibrils or spherulites. Furthermore, morphology considers distribution and orientation of the phases, the interfacial area, the volume of the interphase, etc. However, the term must be distinguished from micro-morphology, which describes structures of the crystalline phase. Flow may induce two modifications of morphology that may complicate interpretation of data the concentra- 

Three types of flow are mainly used in the rheological measurements steady state shearing, dynamic shearing, and elongation. The three can be classified according to the strain, y, vorticity, as well as uniformity of stress, a, and strain within the measuring space (see Table 7.1). 

The flow characteristics listed in Table 7.1 indicate that the steady-state flows strongly affect the morphology, whereas the dynamic flows have less influence. The extensional flows are characterized by uniform deformation and lack of vorticity, thus they are the most effective in changing the morphology and orientation of the system. 

In multiphase systems, there are many possible configurations of the interacting phases. Following the concepts of statistical mechanics, the rheological functions must be volume-averaged [Hashin, 1964]. The averaged quantities are sometimes known as bulk quantities. For example, the bulk rate of strain tensor, (y ), is expressed as  

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This topic has been already presented in Chapter 7, The Rheology of Polymer Alloys and Blends. In the following text only the aspects pertinent to mixing will be summarized [Utracki, 1991, 1995]. 

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