*Article* **Process Chain Optimization for SWCNT**/**Epoxy Nanocomposite Parts with Improved Electrical Properties**

#### **Manuel V. C. Morais, Marco Marcellan, Nadine Sohn, Christof Hübner \* and Frank Henning**

Polymer Engineering Department, Fraunhofer Institut für Chemische Technologie (ICT), Joseph-von-Fraunhofer-Straße 7, 76327 Pfinztal, Germany; manuel.morais@ict.fraunhofer.de (M.V.C.M.); s182212@student.dtu.dk (M.M.); sona1014@hs-karlsruhe.de (N.S.); frank.henning@ict.fraunhofer.de (F.H.) **\*** Correspondence: christof.huebner@ict.fraunhofer.de

Received: 17 July 2020; Accepted: 11 August 2020; Published: 14 August 2020

**Abstract:** Electrically conductive nanocomposites present opportunities to replace metals in several applications. Usually, the electrical properties emerging from conductive particles and the resulting bulk values depend on the micro/nano scale morphology of the particle network formed during processing. The final electrical properties are therefore highly process dependent. In this study, the electrical resistivity of composites made from single-walled carbon nanotubes in epoxy was investigated. Three approaches along the processing chain were investigated to reduce the electrical resistivity of nanocomposites-the dispersion strategy in a three-roll mill, the curing temperature, and the application of electric fields during curing. It was found that a progressive increase in the shear forces during dispersion leads to a more than 50% reduction in the electrical resistivities. Higher curing temperatures of the nanocomposite resin also lead to a decrease of around 50% in resistivity. Furthermore, a scalable resin transfer molding set-up with gold-coated electrodes was developed and tested with different mold release agents. It has been shown that curing the material under electric fields leads to an electrical resistivity approximately an order of magnitude lower, and that the properties of the mold release agen<sup>t</sup> also influence the final resistivity of different samples in the same batch.

**Keywords:** Carbon nanotubes; CNTs; nanocomposites; electrical resistivity; conductivity; electric fields
