RHEOLOGY MORPHOLOGY/FLOW CONDITIONS RELATIONSHIPS FOR POLYMETHYLMETHACRYLATE/RUBBER BLEND/

Viscoelastic behavior, phase morphology and flow conditions relationsh ips in polymer/rubber blends have been investigated. The importance of such correlations is illustrated on polymethylmethacrylate (PMMA)/rub ber blends subjected to different flow conditions both under small and large deformations. In small-amplitude oscillatory shear (the morphol ogy does not change during the flow) the elastic modulus G' of the con centrated blends shows a secondary plateau, G'(p), in the low frequenc y region. This solid-like behavior appears for rubber particle content s beyond the percolation threshold concentration (15%). Morphological observations revealed that for concentrations higher than 15%, the par ticles are dispersed in a three-dimensional network-type structure. In capillary flow it was found that the network-type structure was destr oyed and replaced by an alignment of particles in the flow direction. This morphological modification resulted in a decrease in both viscosi ty and post-extrusion swell of the blends. Morphological observations revealed that the ordered structure in the flow direction was concentr ated only in the skin region of the extrudate, where the shear stress is higher than the secondary plateau, G'(p). A simple kinetic mechanis m is proposed to explain the observed morphology. Similarly, steady sh ear measurements performed in the cone-and-plate geometry revealed ali gnment of particles in the flow direction for shear stress values high er than G'(p).