Rheology of Highly Filled Polymers

T his paper reviews current knowledge about the rheology of highly filled polymers,focusing on hard fillers. Understanding the rheological properties would help forassist the formulation and processing of such polymeric materials. When solid particles areincorporated in a fluid, they affect the rheological behavior of the system via changes in theflow field. Nowadays rheology of suspensions, especially concentrated suspensions, is ofgreat importance due to their wide uses in various fields such as composite, petrochemical,and food industries. The main factors affecting the rheological behavior of these compositessuch as maximum packing fraction, percolation threshold, and the size distribution of thefillers are discussed. The size distribution of the fillers facilitates higher filling levels anddecreases the melt mixture viscosity for a specified content of fillers. The limitations andflow instabilities of highly filled polymers often lead to non-linear rheological behaviorsuch as wall slip, polymer-filler separation, swelling and surface instabilities phenomena.Following, mathematical models predicting the maximum packing fraction, which is oneof the most important rheological parameters of highly filled composites, is presented.The viscosity-containing also discussed as a function of the filler content for monomodal,bimodal, and multimodal highly filled suspensions.