Abstract
Abstract Effects of processing variables on the structural gradients developed in the injection molding of thermotropic wholly aromatic copolyester parts were investigated using optical macro and microscopy combined with image analysis techniques at various sections of the molded LCP parts. The studies indicate the existence of a multi-layer structure from skin to core of the parts. These include: a skin layer, a transition zone composed of a sub-skin layer, a shear layer and a core region. The effects of processing conditions including injection speed, mold temperature, and mold size on the structural features were evaluated. An interesting buckling phenomenon resembling features observed in jetting at core regions near the end of the cavity after the divergence section was observed for the samples molded at the lowest injection speed and mold temperature. Digital image analysis of the images of the sectioned parts revealed that there are more layers than one observes macroscopically. In certain instances as many as 15 layers were detected. Orientation behavior and the positional light reflection intensity appear to correlate with each other particularly away from the skin regions. This may be the manifestation of high visible light absorption anisotropy exhibited by these aromatic polymers.
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