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 fiber-induced extra stress could not explain the fiber content dependencies. This appears to be attributed to the uncertainty in determining the particle number N-p 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. POLYM. COMPOS., 40:615-629, 2019. (c) 2017 Society of Plastics Engineers