Correlation of normal stresses in polystyrene melts and its implications

Abstract

It is found that the principal normal stress difference, N₁, in commercial polystyrene melts is a unique function of shear stress σ₁₂, independent of temperature and molecular weight, An empirical expression representing this relationship is developed. The functional dependence reported does not represent data for narrow molecular weight distribution polystyrenes, generally significantly overpredicting N₁ values. The basis for this behavior is discussed. The implications of the N₁ − σ₁₂ relationship to some rheological and processing problems are described.