In this paper, nano-CaCO3 was added into short carbon fibre/polypropylene composites in order to improve foamability. According to differential scanning calorimetry results, there were slight influences on the melting point and crystallinity with the addition of nano-CaCO3. The increase in melt strength with nano-CaCO3 content could be qualitatively certified by torque rheology curves. The dispersion of nano-CaCO3 was determined by scanning electron micrograph. Depressurisation foaming method was used to foam the composites using supercritical CO2. Characterisation of the cell morphology was conducted to investigate the effects of the nano-CaCO3 content and processing conditions. Concerning the effect of nano-CaCO3 content, it is found that the mean cell diameter first decreased and then increased, whereas the cell density showed the opposite trend. Moreover, increasing saturation pressure or decreasing foaming temperature made the cell size smaller and the cell density larger.
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