Effect of Filler Treatment and Crosslinking on Mechanical and Dynamic Mechanical Properties and Electrical Conductivity of Carbon Black-Filled Ethylene–Vinyl Acetate Copolymer Composites N. C. Das, T. K. Chaki, D. Khastgir Rubber Technology Centre, Indian Institute of Technology, Kharagpur-721302, India Received 29 July 2002; accepted 23 January 2003 ABSTRACT: Mechanical, dynamic mechanical, and elec- trical conductivity of conductive carbon black-filled ethyl- ene–vinyl acetate (EVA; 28% VA) composites were investi- gated. The above-mentioned properties were also measured when carbon black was treated with nitric acid before addi- tion to the EVA matrix. It was found that acid-treated carbon black exhibits a higher filler–polymer interaction and this was reflected in the improvement of the mechanical prop- erties and the modification of electrical conductivity of these composites, especially when measured against the temper- ature. The effect of curing of the polymer matrix on the mechanical properties and electrical conductivity was also investigated. It was found that the introduction of crosslinks in the polymer matrix improves its mechanical properties as well as the thermal stability of its electrical conductivity. The electrical conductivity of ethylene propylene diene (EPDM) and an EVA–EPDM (50/50) blend filled with carbon black were also studied for comparison. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2073–2082, 2003 Key words: crosslinking; conductive composite; filler treat- ment; electron beam radiation INTRODUCTION Conductive polymer composites made by incorpora- tion of different volume fractions of conductive fillers like carbon black (CB), carbon fiber, and metal powder into a polymer matrix have found many applications in the field of electronics and in electrical industries such as for electrostatic charge dissipation and elec- tromagnetic interference shielding. 1–3 Positive temper- ature coefficient of resistance (PTC) composites are commonly employed in a wide range of uses, includ- ing in temperature sensors, protection circuitry, mi- croswitches, flow meters, self-regulating heating ele- ments, and self-resetting over current protection ele- ments. However, the range of their technical application is restricted because most of the conduc- tive particulate-filled polymer composites are electri- cally and/or dielectrically unstable with respect to thermal cycling (rise and fall in temperature) in tech- nically useful temperature intervals. Therefore, it is necessary to determine the sources of the instability of the electrical properties filled to minimize this defect. Composite thermistors composed of highly conduct- ing CB-filled polyethylene having room-temperature resistivity in the order of 1–100 ohm cm exhibit a PTC effect of six to eight orders of magnitude (at about 130°C, T m for PE). These materials can easily be fabri- cated and are intrinsically cost-effective. 4–7 Thermal recycling (heating– cooling cycle) of CB- filed polymer composites has been studied extensively because a large number of industrial applications are based on either their electrical properties or mechan- ical properties. It was found that the conductivity, in particular, changes during thermal cycling, and there is a hysteresis-type loop in the conductivity versus temperature plots during the heating– cooling cycle with some electrical set, that is, there is a permanent change in the starting value of the conductivity at room temperature after the heating– cooling cycle. Further, the conductivity versus temperature plot also changes during a repeated heating– cooling cycle. This is due mainly to the breakdown and formation of a conductive network due to CB aggregates present in the insulating rubber materials. The PTC and negative temperature coefficient (NTC) phenomena of filled polymer composites were studied by number of authors. 8 –12 In our previous work, 13 we studied the NTC and PTC effects of ethyl- ene–vinyl acetate (EVA)-based flexible composites filled with conductive CB and carbon fiber. It is pre- dicted that the conductive filler network undergoes two processes during an increase in temperature: One is breakdown and the other is reformation through reagglomeration of a conductive filler, especially par- ticulate fillers. The ultimate PTC/NTC behavior of the Correspondence to: D. Khastgir (khasdi@rtc.iitkgp.ernet.in). Journal of Applied Polymer Science, Vol. 90, 2073–2082 (2003) © 2003 Wiley Periodicals, Inc.