Obvious viscoelastic behaviour appears during die extrusion flow of viscoelastic fluids. such as die-swell. end pressure losses, and unsteady flow or melt fracture. The first normal stress difference (N-1). die-swell ratio (B) and exit pressure drop (DeltaP(ex)) are very important parameters for characterization of the elastic behavior for viscoelastic fluids in die flow. There should be. therefore, some interior correlation between them. In the present paper. the relationship between the first normal stress difference, die-swell ratio and exit pressure drop is discussed. On the basis of previous work. some expressions for describing the relationship of B and N-1, B and DeltaP(ex), and DeltaP(ex), and N-1 during long circular die flow of viscoelastic fluids are proposed. The predictions of N-1 by using the measured data for DeltaP(ex) were compared with the calculations from the die-swell ratio data and the measured N-1 during capillary die extrusion of a high-density polyethylene (HDPE) melt and two low-density polyethylene melts (LDPE) published in the literature. Good agreement was shown among these theoretical calculations of N-1 at high shear stress level, and was consistent with the predictions by using the Bagley-Duffey equation. (C) 2002 Elsevier Science Ltd. All rights reserved. [References: 17]
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