Rheological behavior of compatible polymer blends. I. Blends of poly(styrene‐ Co ‐acrylonitrile) and poly(ε‐caprolactone)

The rheological behavior of blends of poly(styrene‐ co ‐acrylonitrile) (SAN) and poly(ε‐caprolactone) (PCL) was investigated, using a cone‐and‐plate rheometer. For the study, blends of various compositions were prepared by melt blending using a twin‐screw compounding machine. The rheological properties measured were shear stress (σ 12 ), viscosity (η), and first normal stress difference ( N 1 ) as functions of shear rate (γ) in steady shearing flow, and dynamic storage modulus ( G ′) and loss modulus ( G ″) as functions of angular frequency (ω) in oscillatory shearing flow, at various temperatures. It has been found that logarithmic plots of N 1 versus σ 12 , and logarithmic plots of G ′ versus G ″, become virtually independent of temperature but vary regularly with blend composition, and that the zero‐shear viscosity of the blends, (η o ) blend , follows the relationship, 1/log(η o ) blend = w A /log η 0 A + w B /log η 0 B , where η 0 A and η 0B are the zero‐shear viscosities of components A and B , respectively, and w A and w B are the weight fractions of components A and B , respectively. The physical implications of the relationship found are discussed.