DIE SWELL IN SEMIRIGID POLYMER-SOLUTIONS

This paper reports on an experimental study of jets of xanthan solutio ns. Die swell of this semi-rigid polymer is similar to that which is o bserved with flexible polymer solutions or fiber suspensions. At low s hear rates, we relate the variation of the swell ratio to the shear th inning properties of the solutions. At high shear, stable delayed die swell is observed above a critical shear rate. Using the jet shape and the dependence on the shear rate of the distance from the nozzle to t he station where the swelling is maximum, we show that delayed die swe ll can be either smooth or discontinuous depending on the polymer conc entration.