The effect of nano-CaCO3 with mean size of 30 nm and CPE on microstructure and properties of PVC blends was investigated．Nanoparticles of CaCO3 were prepared in a novel rotating packed bed reactor and modified by the selected surface modifiers．Then they were mixed with polyvinyl chloride

chlorinated polyethylene and the other reagents in high-speed stirrer and the mixtures were extruded by means of single-screw extrusion．The results showed that the CaCO3 nano particles toughen PVC／CPE blends significantly when the CPE content reached a certain value．The rigidity and the tensile strength of the blends were also increased．The notched impact strength of the PVC blend can reach 81.1 kJ／m2

which is 7.3 times higher than that of the blends without nano-CaCO3．The morphology of the fracture surfaces of blends was observed by SEM．The fracture microstructure of blends implied the mechanism that the toughness of PVC／CPE was remarkably improved by the addition of CaCO3 nano particles．And the microstructure of dispersed calcium carbonate nanoparticles in the matrix was observed by TEM．It was found that CaCO3 nanoparticles were well-dispersed in PVC matrix at nano-scale．It is confirmed that calcium carbonate nanoparticles after properly surface-treated can be used as a new functional material．When they are well-dispersed in PVC matrix

the PVC blend is toughened remarkably．The rheological property of PVC／CPE／nano-CaCO3 blends was also investigated．The final torque of PVC／CPE／nano-CaCO3 blend in Brabender tests was higher than that of the blend without CaCO3 nano particles．