Rheological behavior of polymer blends

Abstract

Abstract Steady and oscillatory shearing flow properties of compatible and incompatible polymer blend systems were measured, using a cone‐and‐plate rheometer. The compatible blend systems investigated are blends of two low‐density polyethylenes (LDPE) having different values of molecular weight and blends of poly(methyl methacrylate) (PMMA) with poly(vinylidene fluoride) (PVDF). The incompatible blend system investigated is a blend of poly(methyl methacrylate) (PMMA) with polystyrene (PS). It was found that (1) plots of first normal stress difference (τ 11 – τ 22 ) vs. shear stress (τ 12 ) and plots of storage modulus ( G ′) vs. loss modulus ( G ″) for the LDPE blends become independent of temperature and blend composition; (2) plots of τ 11 – τ 22 vs. τ 12 , and G ′ vs. G ″ for the PMMA/PVDF blends become independent of temperature but dependent upon blend composition. It was found further that, for the incompatible PMMA/PS blends, the dependence of τ 11 – τ 22 on blend composition, when plotted against τ 12 , is different from the dependence of G ′ on blend composition, when plotted against G ″. However, in both compatible and incompatible blend systems, plots of τ 11 – τ 22 vs. τ 12 and plots of G ′ versus G ″ are independent of temperature. The seemingly complicated composition‐dependent rheological behavior of the incompatible blend system is explained with the aid of photomicrographs describing the state of dispersion.