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The strain dependence of the dynamic moduli of short fiber reinforced thermoplastic blends

Malchev Plamen G., Norder Ben, Picken Stephen J., Gotsis Alexandros

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Summary

In the present work we relate the microstructure of a distinct type of short fiber reinforced blends (SFRBs) to their melt rheology. These systems consist of polyamide-6 (PA6) and short glass fiber (GF) reinforcement dispersed in a polyethylene (PE) matrix. An appropriate choice of the components, their interfacial characteristics, and the processing route led to the formation of a continuous network, percolating throughout the matrix. The network consisted of fibers (GF) “welded” together by bridges of the dispersed phase material (PA6). A strong strain softening of the melts of the SFRBs was observed at strain amplitudes below 3%, which was absent for their binary equivalents with the same fiber loading and no second thermoplastic component. Based on the specific microstructure of the blends, a model is proposed that accounts for their strain softening behavior. The model considers the “capillary” forces acting between the fibers participating in the network. These capillary forces arise from the deformation of the PA6 bridges “welding” the fibers together. We propose that the macroscopic deformation process produces points of locally concentrated and magnified deformation. The deformation at these points is sufficient to produce the strain softening of the system. The three parameters that appear in the model have a clear physical meaning. The theoretical results are in good qualitative agreement with the experiments.

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