Rheological Characterizations of Segmented Hydrophilic Polyurethanes
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The rheological characterizations of L-Tyrosine based segmented hydrophilic polyurethanes were analyzed. These hydrophilic polyurethanes form aqueous dispersions and are capable of forming gels by sedimentation under gravity as well as shear-induced sedimentation. Steady-state shear measurements and oscillatory measurements were carried out to investigate the rheological behavior of the dispersions and gels as a function of solid content and ionic strength. The viscosity measurements show an increase in viscosity with increase in solid content. The oscillatory measurements show that the loss modulus (G") dominated the storage modulus (G') which indicates the viscous like behavior of the polyurethane gels and dispersions. The time dependent behavior of the polyurethanes is analyzed by performing the non-linear dynamic response measurements which show that the gels and dispersions have the capacity to reverse back from liquid to solid state upon the removal of stress. The creep and creep recovery behavior and the multiple stress creep recovery (MSCR) tests showed that the polyurethanes exhibited a viscoelastic liquid like behavior with limited reformation behavior.