Extensional flow of a model long-discontinuous-fiber filled thermoplastic melt

A computer-controlled elongational rheometer revealed the transient elongational behavior of a polyethylene (PE) melt filled with highly-aligned long-discontinuous-fibers. Nylon monofilament of 0.50 mm diameter was the filler at 60 % volume fraction. A modified weaving process produced preform plys with controlled fiber length and fiber overlap distribution. Two fiber length-to-diameter ratios (L/D) of 25 and 100 afforded significantly different levels of viscosity increase. Extension rates from 0.001 to 0.1 s-1 at 140 C established the response of each L/D ratio to increasing strain rate. Cone-and-plate and capillary rheometers characterized the neat PE shear viscosity at 140 C. A shear cell model suggests that highly aligned, high fiber volume fraction melts react to global extensional deformation with a local shear flow of greater magnitude. The elongational viscosity of the filled melt combined with the micromechanics of the model yielded values of matrix shear viscosity with a strong correlation to the PE Carreau behavior.

Extensional flow of a model long-discontinuous-fiber filled thermoplastic melt Conference Paper