The effect of shear-induced migration of conductive fillers on conductivity of injection molded articles

摘要

Conductive filler particles tend to migrate in non-uniform shear fields such as during mold filling from the regions of high shear stress to low shear stress leading to the loss of conductivity in polymeric articles. In this work, the effect of conductive filler migration on surface and volume conductivity was investigated in conductive compounds of polystyrene and polypropylene and carbon black. Injection molded articles with mean particle concentration of φ_c and 3.5φ_c where φ_c is the percolation threshold, showed volume conductivity values of respectively 10~(-18) and 10~(-4) S-cm, while compression molded specimens with same composition offered volume conductivity of 10~(-4) S-cm. Removal of surface layers from injection molded specimens by excimer laser ablation technique restored the conductivity to 10~(-4) S-cm. The extent of migration was evaluated in terms of the thickness of polymer layers removed from the surface, which depended on the type of polymer used.