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Relationship in polypropylene melt between its linear viscoelasticity and its steady capillary flow properties

1972; Wiley; Volume: 16; Issue: 2 Linguagem: Inglês

10.1002/app.1972.070160202

1097-4628

Mitsuyoshi Fujiyama, Hiroshi Awaya,

Polymer Foaming and Composites

Abstract It is the object of the present study to obtain clear knowledge of the relations in the polypropylene melt between its linear viscoelasticity and its nonlinear steady capillary flow, paying particular attention to the elastic properties in its capillary flow. By representing the linear viscoelasticity numerically with zero‐shear viscosity, η 0 , and steady‐state compliance, J , evaluation has been made of the properties concerning the elasticity of polymer melt in the capillary flow, such as non‐Newtonianity, the entrance pressure loss, the end correction, the Barus effect, and the melt fracture. The steady flow viscosity η, the entrance pressure loss P 0 , the critical shear stress, τ c , and the critical shear rate $\dot \gamma _c$ at which melt fracture begins to occur are subject to η 0 as follows: From the well‐known relationship between η and the weight‐average molecular weight M̄ w , these quantities are governed by M̄ w . Meanwhile, for such quantities as structural viscosity index N , end correction coefficient ν, and elastic pressure loss ratio P 0 / P , following correlations hold: As η 0 and J are respectively determined mainly by M̄ w and the molecular weight distribution MWD, these quantities are governed by both M̄ w and MWD. Physical meanings of η 0 · J and η 0 2 · J are, respectively, mean relaxation time and a measure of stored energy in steady flow. The Barus effect has a positive correlation to J , ν, and P 0 / P . (The symbol ∝ employed here means positive correlation.)