Predictions and Applicability of the BKZ Type Models in Extensional Flows of Polymer Melts

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Predictions on shear, planar, uniaxial and biaxial extensional flows are obtained from the BKZ type constitutive equations with the assumption of time-strain separability. Using a single relaxation mode, the effects of adjustable parameters on the stress growth coefficients are investigated in detail. A parameter describing the normal stress ratio governs the biaxial extensional flow behavior. It also controls the planar extensional flow behavior in the direction of constant width (perpendicular to the extension direction). Applicability of two representative models with this parameter is investigated for multiple relaxation times by comparing with a set of data for polyisobutylene (literature data) and polystyrene melts. We propose a method to obtain the model parameters from shear, uniaxial and biaxial damping functions. With the introduction of the parameter describing the normal stress ratio, both the PSMLT model (Papanastasiou-Screven-Macosko as modified by Luo-Tanner) and the WDFÖ model (Wagner-Demarmels as modified by Fegel-Öttinger) give good agreements with all the experimental data. It is suggested that the PSMLT model is preferable for engineering purposes, because the model gives non-divergent stresses in almost of all cases investigated.
一般社団法人　日本レオロジー学会の論文
2003-09-15