A number of researchers have reported an anomalous lowering of viscosity in immiscible polymer blends. Slip at the interfaces between the polymers has been proposed to explain these observations. Because of the complex morphology developed in melt blends it is difficult to test the slip hypothesis. However, using layer multiplication dies in coextrusion, two or more polymers can be alternatively combined into hundreds or even thousands of continuous layers generating a large amount of well-defined interfacial area. Polypropylene (PP) and polystyrene (PS) with closely matched viscosity were blended in a twin screw extruder and also coextruded into 2, 32, 128 alternating layers. The steady shear and dynamic shear viscosity of the blends was measured in a capillary rheometer and a rotational shear rheometer using parallel plates geometry. While the steady shear viscosity of the blends was lower than that of both homopolymers, the dynamic shear viscosity of the blends was the same as that of the homopolymers. The pressure drop of the coextruded multilayer melts through a slit die was lower than that of both homopolymers and decreased with an increase in the number of layers. From these results interfacial slip viscosity and velocity were estimated. Addition of diblock copolymer was able to suppress interfacial slip.
|Original language||English (US)|
|Journal||Materials Research Society Symposium - Proceedings|
|State||Published - 2000|
|Event||Interfaces, Adhesion and Processing in Polymer Systems - San Francisco, CA, United States|
Duration: Apr 24 2000 → Apr 27 2000
Bibliographical noteFunding Information:
The authors are grateful to T. D. Jones for synthesizing the block copolymer, P. J. Cole for assistance with the multilayer coextrusion and Dr. David Giles for assistance with rheology measurement. The financial support of this project is provided by the National Science Foundation under Grant CTS9527940 and the Army Research Office under Grant DA/DAAD19-99-1-0337.