Véronique Michaud is currently Associate Professor and head of the Laboratory for Processing of Advanced Composites, and Associate Dean of Engineering for Education, at the Ecole Polytechnique Fédérale de Lausanne, in Switzerland. She graduated in 1987 from Ecole des Mines in Paris with an engineering degree, in 1991 from MIT with a PhD in Materials Engineering, and obtained a Research Habilitation from INPG in France in 1994. After a post-doctoral research stay at MIT, she spent 3 years at Ecole Centrale in Paris for teaching and research in the Laboratory for Materials, Structures and Soils Mechanics, before joining EPFL in 1997. Her fields of research are fundamentals of composite materials processing, as well as smart materials and structures including self-healing, shape and vibration control and tailored damping.

Title

Composites for a more sustainable future…tough, healable, recyclable?

Abstract

Fiber reinforced thermoset composites (FRP) are found in many applications, including mobility, energy generation, or sport equipment. However, the brittleness of the thermoset matrix results in high sensitivity to small damage events through early matrix cracking. A commercially available approach to limit damage growth is to toughen the matrix by dispersing small rubbery or thermoplastic particles in the thermoset; however this tends to impact production processes, does not prevent costly repair operations, and these materials remain difficult to recycle. Thermoplastic based composites, on the other hand, gain market shares as they are more easily recyclable, but remain costly, or suffer from a lack of stiffness at moderate temperatures. A compromise can arise from the use of thermoplastic/thermoset blends, which, if the microstructure is well engineered, can lead to tough and damage tolerant materials, which can also be easily repaired and recycled, thus enhancing their potential for increased sustainability.

We recently showed that healing matrices based on thermoset-thermoplastic (more specifically epoxy and polycaprolactone) phase-separated blends demonstrated a large potential for heat-assisted repair [1-5]. The thermoplastic phase expands upon melting at moderate temperature, filling (repeatedly) small cracks. When integrated to FRPs (through conventional liquid composite molding process), the developed healing matrix led to composites with similar stiffness and bending strength to that of pure epoxy composites, but also to full recovery of compression after impact strength for low damage extent (impacts of 8.5 J), however the toughness of the material was quite reduced. By playing on the composition of the blend and the reaction kinetics of the thermoset phase, a wide range of promising materials were found, that lead to good structural properties at room temperature and improved initial toughness. If needed, these materials can also accommodate SMA stitches, which improve crack closure and provide even higher initial toughness to the material. We are now able to propose a structural FRP that (i) is tougher than benchmark epoxy-based composites, (ii) can repeatedly heal matrix microcracks (iii) has a manufacturing route compatible with large scale industrial processes (iv) shows better recyclability than benchmark epoxy alternatives. We will present this new composite material combination, as well as its static, fatigue and impact healing properties.

References

[1] A. Cohades, C. Branfoot, S. Rae, I. Bond, V. Michaud, Progress in Self-healing Fiber reinforced Polymer Composites, Progress report, Advanced Materials Interfaces, 2018, DOI: 10.1002/admi.201800177.

[2] A. Cohades, N.Hostettler, M. Pauchard, C.J.G Plummer, V. Michaud, Stitched shape memory alloy wires enhance damage recovery in self-healing fiber reinforced polymer composites, Composite Science and Technology, Volume 161, 16 June 2018, Pages 22-31.

[3] A. Cohades, E. Manfredi, C. J.G. Plummer, V. Michaud, Thermal Mending in phase-separated Epoxy -polycaprolactone blends, European Polymer Journal, Volume 81, August 2016, Pages 114–128.

[4] A. Cohades, V. Michaud, Damage recovery after impact in E-glass reinforced Poly(ε-caprolactone)/epoxy blends, Composite Structures 180 (2017) 439–447.

[5] A. Cohades, V. Michaud, "Thermal mending in E-glass reinforced Poly(ε-caprolactone)/epoxy blends", Composites Part A, Volume 99, August 2017, Pages 129–138.