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

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 (HiPPTA, eta(inh) = 7.15 dL/g) to ordinary PPTA (Ord-PPTA, eta(inh) = 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 N-1 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 N-1 minimum and increase in the corresponding shear rate (gamma) over dot(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. (C) 2015 Elsevier Ltd. All rights reserved.