Epoxy-carbon black composite foams with tunable electrical conductivity and mechanical properties: Foaming improves the conductivity

In this study, conductive epoxy foams with different carbon black (CB) contents were fabricated with expandable microspheres as foaming agents. The effect of the CB content, microsphere concentration, precuring time, and foaming temperature on the electrical conductivity and compressive properties of the obtained foams were investigated systematically. The differential scanning calorimeter and rheological tests confirmed that the CB accelerated the curing reaction, increased the onset viscosity of the epoxy blend during foaming, and affected the foaming process. In addition, all of the parameters, including the CB content, microsphere concentration, precuring time, and foaming temperature, were confirmed to change the foam structures and further change the conductivity and mechanical properties. The electrical properties test revealed that the foaming process improved the conductivity of the composites. On the basis of the electrical properties test results and scanning electron microscope images, a flow-induced CB aggregation mechanism is presented, in which the thermally triggered microsphere expansion pushed the resins away, squeezed the CB together, and changed the CB distribution throughout the foams. This made more conductivity paths. The obtained foam could just be used as an antistatic material, but it gave us an example for exploring lightweight and low-cost conductive epoxy foams with other applications, for example, electromagnetic shielding. (C) 2017 Wiley Periodicals, Inc.