Abstract: Thermally conductive and clectroinsulating polypropylene(PP)composites were prepared with a twin-screw extruder using different mesh of talc as filler. The effect of particle size, which varied between 3 .6 μm and 50μm, on the thermal conductivity, volume resistivity, mechanical properties,and crystallization behavior of the PP/talc (70/30) composites was investigated.As the talc particle size became smaller, the tensile and flexural strength of the composites increased firstly and then decreased，while the thermal conductivity decreased firstly and then increased.The composite containing 12μm talc exhibited the maximum tensile and flexural strengths, 29.92MPa and S2.S8 MPa, which arc 5.5%and 12.8%higher than those of neat PP, respectively. The composite filled with 50μm talc gave rise to the maximum thermal conductivity, 0.3237W/(m*K)，which is 32.7%higher than that
of neat PP. When a mixture of 12μm and 30μm talc(1/1)was used，the thermal conductivity of the composite was 0 .3184W/(m*K)，which is higher than that of the composites when either single talc was used .In addition，all the volume resistivitics of the PP/talc composites were higher than10^8Ω*cm

Key words: polypropylene, talc, thermal conductivity, electrical insulation