Criteria for rheological compatibility of polymer blends

Criteria for rheological compatibility of polymer blends are suggested. The criteria suggested make use of plots of first normal stress difference ( N 1 ) against shear stress (σ 12 ), and of storage modulus ( G ′) against loss modulus ( G″ ). Compatible blend systems considered are (1) blends of two different grades of low‐density polyethylene, (2) blends of poly(vinylidene fluoride) and poly(methyl methacrylate), (3) blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide) and polystyrene, and (4) blends of poly(styrene‐co‐acrylonitrile) and poly(styrene‐co‐maleic anhyride). And incompatible blend systems considered are (1) blends of nylon 6 and poly(ethylene‐co‐vinyl acetate) and (2) blends of nylon 6 and an ethylene‐based multifunctional polymer. It has been found that plots of N 1 vs. σ 12 and G ′ vs. G ″ give (a) temperature‐independent correlations for both compatible and incompatible blend systems; (b) composition‐independent correlations for compatible blends; (c) composition‐dependent correlations for incompatible blends.