The influence of precipitated calcium carbonate particles on the toughening behaviour of aliphatic polyketone has been studied. The calcium carbonate particles had a particle size of 0.7 mu m and a stearic acid coating (1%). Composites of 0-31.5 vol% CaCO3 content have been compounded and injection moulded. Studied are the morphology of the composites, the modulus, yield strength, the notch Izod impact strength and the temperature development in the deformation zone by infrared thermography. The thermal properties of the matrix remained unchanged upon addition of CaCO3. With increasing particle content the modulus increased and the yield strength decreased. This decrease in yield strength is due to the debonding of the particles and was similar as with rubber particles. With increasing particle content the notched impact resistance increased strongly. The notched impact energy at room temperature was increased from 10 to 80 kJ/m(2) and the brittle-to-ductile transition temperature was lowered to 80 degrees C. At calcium carbonate contents higher that 16 vol% no further impact improvement was observed. The calcium carbonate particles seemed to debond quite well despite the expected thermal contraction of the matrix polymer. The temperature development in the deformation zone was strong, as strong as with rubber particles. The toughening mechanism with these rigid particles is discussed. (c) 2006 Elsevier Ltd. All rights reserved.