Converting thermoset waste into high-performance composites

Recyclable conductive epoxy composites with segregated filler network structure for EMI shielding and strain sensing

Significance 

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.

Converting thermoset waste into high-performance composites: Recyclable conductive epoxy composites with segregated filler network structure for EMI shielding and strain sensing  - Advances in Engineering

About the author

Dr. Kai Ke is currently an associate professor in College of Polymer Science and Engineering at Sichuan University. He received his PhD in Polymer Materials from Dresden University of Technology in 2016. From 2016 to 2017, he worked at University of Connecticut as a postdoctoral fellow in the department of Mechanical Engineering, and from 2017 to 2019 worked at Case Western Reserve University as a research associate in the department of Macromolecular Science and Engineering. His research interests focus on polymer nanomaterials for flexible electronics, sensors and actuators.

About the author

Dian Yuan obtained her Master degree in 2015 and PhD degree in 2019 in polymer science in the department of Macromolecular Science and Engineering at Case Western Reserve university under the supervision of Prof. Ica Manas-Zloczower. Her research interests include polymer composites, self-healing polymers and thermosets recycling.

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About the author

Professor Ica Manas-Zloczower is the Thomas W. and Nancy P. Seitz Professor of Advanced Materials and Energy in the Department of Macromolecular Science and Engineering and the Distinguished University Professor at Case Western Reserve University. She received BS and MS degrees in Chemical Engineering from Polytechnic Institute Jassy, Romania and a Doctor of Science in Chemical Engineering from the Technion-Israel Institute of Technology. She was a post-doctoral fellow at the University of Minnesota. Professor Manas-Zloczower has more than 200 publications in peer-reviewed journals, more than 100 published conference proceedings, and a number of book chapters and patents.

Her research accomplishments have been recognized through more than 90 plenary, keynote and invited lectures at national and international conferences and more than 100 invited seminars at various companies and universities worldwide. Her research interests are in the areas of structure and micromechanics of fine particle clusters, interfacial engineering strategies for advanced materials processing, mixing mechanisms and modeling, polymer based nanotechnology, polymer recycling technologies.

Reference

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.

Go To Composites Part A: Applied Science and Manufacturing

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