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

Abstract

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.

Epoxy composite foams with excellent electromagnetic interference shielding and heat‐resistance performance

“…Relationship between content of NiCFs and EMI SE was depicted in Figure 7(b). Its efficient EMI SE is in range of 26.4 to 36.3 dB cm 3 g 21 mm 21 . This can be ascribed to the possibility of entanglements among NiCFs increase with an excessive content of NiCFs which caused defects in polymer matrix.…”

“…Bisphenol-A epoxy resin (NPEL-128, EEW 187 g equiv 21 ) was purchased from NanYa Plastics Group Co., Ltd. (Taiwan). The curing agent, a viscous alicyclic amine (Baxxodur EC331, AHEW 61) was provided by BASF SE (Germany).…”

“…An epoxy composite foam sample 0.5NiCF10-2CNT-2micro85 with T g at 178.3 8C and EMI SE of 32.7-45.0 dB over X band was successfully fabricated in this work. Its efficient EMI SE is in range of 26.4 to 36.3 dB cm 3 g 21 mm 21 . As a result of synergistic effect between MWCNTs and NiCFs, foams developed in this work have great EMI shielding performance at low filler loadings.…”

“…[19][20][21] These microspheres were prepared by low-boiling blowing agent encapsulated in a copolymer shell. Previously, an untraditional foaming method using expandable microspheres (Expancel) was adopted by our group to efficiently decrease the density of target composites.…”

“…Previously, an untraditional foaming method using expandable microspheres (Expancel) was adopted by our group to efficiently decrease the density of target composites. [19][20][21] These microspheres were prepared by low-boiling blowing agent encapsulated in a copolymer shell. 22 When heated, they can swell many times than its original volume according to the foaming temperature and then make the foaming process easily controlled.…”