The Effect of Fiber Concentration on Fiber Orientation in Injection Molded Film Gated Rectangular Plates

Fiber orientation in film gated injection-molded rectangular
plates was characterized using micro computed
tomography. Polyamide 12 materials with 15, 30, and
50 wt% glass fibers were used in this study. For all
three materials, the typical core-shell layer structure of
fiber orientation was observed, but several features of
the fiber orientation were highly dependent on the fiber
content. Increasing fiber content resulted in increasing
core layer thickness and a higher degree of orientation
in the shell layer. These effects may be associated
with plug flow induced by extra stress from the fibers,
which changes the melt rheology compared to nonfilled
material. The Dinh–Armstrong model for the fiberinduced
extra stress could not explain the fiber content
dependencies. This appears to be attributed to
the uncertainty in determining the particle number Np
for the high fiber concentrations present in the samples.
Analyses of fiber orientation as a function of fiber
length revealed a dependence on fiber length in qualitative
agreement with Jeffery’s model for fiber dynamics.