High molecular weight effects on steady and transient rheology of lyotropic poly(p-phenylene terephthamide) solution

- High molecular weight PPTA (Hi-PPTA) component is found to affect the rheological properties.
- The Hi-PPTA component shows effect to reduce the viscosity of the solutions.
- The negative first normal stress difference is enhanced with the Hi-PPTA component.
- Strain recovery and evolution of dynamic moduli are affected by Hi-PPTA.

This study investigated some special effects of high molecular weight poly(p-phenylene terephthamide) (PPTA) on steady-state and transient rheology of lyotropic PPTA/H2SO4 solutions. The solutions with the same concentration were prepared to possess different ratios of the high molecular weight PPTA (Hi-PPTA, ηinh = 7.15 dL/g) to ordinary PPTA (Ord-PPTA, ηinh = 5.43 dL/g). With increased Hi-PPTA amount in the solutions, viscosity of the solutions was reduced in the “Newtonian” plateau of the flow curve. The first normal stress difference N1 in the high shear rate range was strongly affected by Hi-PPTA. Increasing the Hi-PPTA amount, the PPTA/H2SO4 solutions showed a significant decrease in the negative N1 minimum and increase in the corresponding shear rate γ˙min. After cessation of steady-state shearing, the recoverable strain obviously increased for the solutions with the increasing Hi-PPTA amount. Accordingly, the dynamic modulus (G″) maximum and time corresponding to the G″ maximum became smaller for the relaxation process.