The effect of reprocessing on the EMI shielding effectiveness of conductive fibre reinforced ABS composites

In this investigation, the acrylonitrile-butadiene-styrene copolymer (ABS) was used as the matrix. Ni-coated conductive carbon fibre (NCF) and conductive carbon fibre (CF) were used as the Conductive fillers. For processing, a Twin-Screw Extruder (TSE) and the Brabender Plasti-Corder were used here for compounding composites. The fibre length of composites which were compounded by the twin screw extruder were below the critical length, 200 mu m. Thus, the tensile strength and modulus were not increased by adding fibres. At the same time, the conductive fibre cannot form a conductive network. In this case, the shielding effectiveness (SE) value of composites was 0 decibel (dB). But,when the composites were compounded by the Brabender, the fibre length was above critical length, 200 mu m, even after three processings. The maximum SE value of conductive composites was 47 dB. The SE values of composites decreased with increasing the number of processing cycles. The viscosity of composites decreased with increasing the number of processing cycles. In addition to the polymer chain being scissored, the short fibre length was another reason. SEM shows that the interfacial adhesion between NCF and ABS was not so good. The interfacial adhesion between ABS and CF was better than that of between ABS and NCF. (C) 1997 Elsevier Science Ltd.