Rheological behavior of two‐ and three‐phase fiber suspensions

Abstract The rheology of two polyamide 6.6 systems filled with long glass fibers, as well as at of a three‐phase polyamide 6.6‐glass fiber‐gas bubble system, was studied using capillary rheometry, To investigate the influence of fiber concentration, the shear and extensional viscosities were determined for both 30 and 40 vol% fiber filled suspensions as well as for the base polymer. Comparison revealed a modest increase in both the shear and extensional viscosities with increased fiber fraction. The shear viscosities, η_s, of both suspensions are shown to be close to one order of magnitude greater than the base matrix fluid viscosity, η. However, the extensional viscosities, η_E, of the suspensions are determined to be approximately four orders of magnitude greater than the shear viscosity of the matrix fluid for strain rates from 10⁰ s⁻¹ to 10² s⁻¹. The addition of a gas bubble phase to the neat polymer and polymer‐fiber suspensions was accomplished through the decomposition of various percentages of an azodicarbonamide blowing agent. The presence gas bubbles resulted in reduced shear and extensional viscosities for both the neat and fiber‐filled polyamide with greater reductions observed for the neat polyamide. Greater viscosity reductions were observed as the blowing agent centration was increased.