Toughened PP /CaCO3 composites were obtained by designed interface of composite[1]. Resistance curve method has been used to detendne the Jc values of polypropylene (PP) and the toughened polypropylene /CaCO3 composites. The addition o f CaCO3 gives rise to substantial increases in both the Young’s modulus (E) and notched Izod impact strength (SI)

a slight increases in Jc and a sharp rise in the crack propagation resistance dJ/ d(△a). The results show that the incorporation of filler leads to both stiffening and toughening effects for pp

the elastic component JE of the J is larger than the plastic component Jp(=hysteresis component Jh).As the filler content increases

Jc changes slightly but Jh rises sharply

indicating large dissipation of energy.Scanning electron microscope(SEM) observation reveals that the microscopic damage process responsible for energy dissipation are cavitation and plastic deformation.It is proposed that the criterion for toughening in a particulate-filled polymer is that the composite has a higher Jh value than the polymer.