Recyclable conductive epoxy composites with segregated filler network structure for EMI shielding and strain sensing
Compared to intrinsically conducting polymers, electrically polymer composites exhibit superior processing and tunable electrical properties desirable for numerous applications. Among the available preparation methods, forming a segregated filler structure at the interfaces of the polymer particles, provides an efficient and cost-effective approach for fabricating polymer composites with low filler content and enhanced properties. Nevertheless, this strategy is not applicable to thermoset based polymers that do not undergo melt processing. Due to the increasing demand and engineering applications of thermoset epoxies, carbon nanofillers have been widely used to reinforce their mechanical and electrical properties. However, available conventional fabrication methods for epoxy composites with good mechanical and electrical properties entail uniform dispersion of conductive fillers which is more than often difficult to achieve.
Vitrimers are a new class of chemically crosslinked polymers, in which thermally stimulated exchange reactions permit the change of the network topology allowing them to be processed or reprocessed as thermoplastic materials at elevated temperature. The main challenge, however, is achieving mechanical and thermal stability properties comparable to those of classic thermosets. To overcome these limitations, scientists at Case Western Reserve University led by Professor Ica Manas-Zloczower: Dr. Dian Yuan, Haochen Guo, Dr Kai Ke (currently an associate Professor at Sichuan University) presented a new facile strategy for fabricating a segregated filler network at thermoset epoxy particles interface to enable recycling of the epoxy waste based on the vitrimer chemistry while at the same time enhancing system properties at low carbon filler content. Their research work is currently published in the journal Composites Part A.
In their approach, the research team first converted the permanent network in the epoxy waste into a dynamic network via catalysts infusion. Based on the interface design strategy, branched carbon nanotubes were introduced into the recycled epoxy system to form a segregated network structure of fillers via compression molding. The properties of the resultant composites were examined and compared to those of conventional thermoset composites.
Results showed that the resultant composites exhibited remarkable mechanical properties and good electrical conductivity at low filler content. For instance, a composite with 0.25 wt% branched carbon nanotubes reported an improvement in the tensile strength and modulus of up to 252% and 1757%, respectively. Moreover, the system achieved an electrical percolation threshold as low as 0.01 wt% with significantly enhanced electrical conductivity at low filler content. Furthermore, the researchers noted that the high-performance composites could be reprocessed by only adding a small amount of catalyst. On a positive note, the results compared well with conventional thermosets, thus confirming the feasibility of the presented approach.
In summary, the study by Case Western Reserve University researchers is the first to develop a facile and effective strategy for converting epoxy waste into useful materials at low carbon filler content. The presented approach enabled the fabrication of recyclable conductive epoxy composites with a segregated filler network structure and good mechanical and electrical properties. In a statement to Advances in Engineering, the authors highlighted that the resultant composites would enable potential electromagnetic interface (EMI) shielding and strain sensing applications.
Yuan, D., Guo, H., Ke, K., & Manas-Zloczower, I. (2020). Recyclable conductive epoxy composites with segregated filler network structure for EMI shielding and strain sensing. Composites Part A: Applied Science and Manufacturing, 132, 105837.