Experimental investigation and theoretical prediction of extrudate swell using conformational rheological models

In this study the extrudate swell of polymer solutions is estimated using the microstructure of polymer molecules. When a flexible polymer chain goes through a narrow die shear stress exerting on the chain will cause the polymer chain to be stretched along the flow direction. After emerging from die all external stresses vanish immediately and the chains tend to recover their previous state due to elastic recovery. This phenomenon will results in a gradual increase in extrudate diameter and this is used as the key idea for estimating swell ratio. A Giesekus based conformational model was used in order to predict polymer chains microstructure everywhere in the domain. The resulting PDE set including, continuity, momentum, and conformational theological model were solved using a finite volume method with the OpenFOAM software. Numerical results were compared with experimental data which were obtained for aqueous solutions of Carboxymethylcellulose. It was found that model predictions are in good agreement with experimental data. The results were also compared to results which were obtained by the Tanner relation which underestimates experimental data.