The mechanical behaviour (strength and stiffness) of natural fibre reinforced thermoplastics is investigated on the example of an injection moulded sisal-polypropylene system. An analytical model based on the rule of mixtures is developed to predict the mechanical behaviour of such composites. Considering interfacial characteristics this model accounts for the different modes of load transfer between matrix and fibre and their changeover. Close agreement between model and experimental results was achieved at low fibre contents (below 20 wt.%) as well as at higher contents (exceeding 40 wt.%). The model was finally verified against the experimental data and against available literature results.
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