Rheology of Phase Separated Blends

For phase separated polymer blends, several common mixing rules can be employed  

A number of other models and theories have been proposed for evaluating viscosity data. Two models that are referred to as emulsion models predict the complex modulus or viscosity of an immiscible blend with spherical inclusions of one phase in a continuous phase (Oldroyd [263] and Paherne [264] models). The emulsion models can predict a positive deviation as noted in Fig. 6.21. Application of the Palierne model showed good agreement for viscosity data for EVAc/PE blends [265,266]. Another emulsion model proposed by Choi and Schowalter [267] is based on a cell model composed of a viscous matrix with viscous dispersed spheres (droplets). The viscosity of these models in the limit of zero shear viscosity can be expressed by the following equations. 

Liquid crystalline polymers (LCPs) added to high Tg polymers can often significantly reduce the viscosity of the high Tg polymer at very low LCP addition levels [269-272]. An example of this is shown in Fig. 6.22 for polyamide/liquid crystalline polymer blends. The significant negative deviation behavior was observed with a minor amount of LCP addition. 

The addition of specific fluoropolymers to polyolefins allows for improved processability, including elimination of melt fracture (sharkskin), reduced die build-up, lowered processing viscosity, reduced die pressure and abihty to increase extrusion rates [278-282]. The fluoropolymers are generally added at levels of 100-1000 ppm. Vinylidene fluoride-hexafluoro-propylene fluorocarbon elastomers are often mentioned in the patent examples, such as the commercial systems carrying the tradename Viton duPont. 

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