Flow-Induced Warpage of Injection-Molded TLCP Fiber- Reinforced Polypropylene Composites


The most common belief is that warpage in injectionmolded fiber-reinforced thermoplastics is primarily attributed to residual thermal stresses associated with shrinkage and thermal contraction of the parts. Therefore, it is assumed that flow-induced stresses generated during mold filling do not play a significant role. Injection-molded plaques of polypropylene (PP) reinforced with pregenerated thermotropic liquid crystalline polymer (TLCP) microfibrils were generated in order to investigate the role of residual flow-induced stresses relative to that of thermal stresses on the warpage. In an effort to relate the material parameters to warpage, the rheological behavior of these fiber-filled systems was investigated. The shrinkage and the thermal expansion of the TLCP/PP composites, and hence, the thermally induced stresses decreased with an increase in fiber loading while the flow-induced stresses increased. The increase in the flow-induced stresses was attributed to increased relaxation times (this is not the only cause, but is a significant factor) with an increase in fiber loading. Therefore, it was found that in order to accurately predict the warpage of fiber-reinforced thermoplastics, the flow-induced residual stresses must be accounted for. It is expected that the results reported here can be extended to glass-reinforced PP composites as well. POLYM. COMPOS., 27:239–248, 2006. © 2006 Society of Plastics Engineers

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@inproceedings{DePolo2006FlowInducedWO, title={Flow-Induced Warpage of Injection-Molded TLCP Fiber- Reinforced Polypropylene Composites}, author={W . S . DePolo and Donald G. Baird}, year={2006} }