In recent years, thermoplastic structural composites have attracted increasing interest due to their combination of high mechanical performance, processability, and recyclability. However, their susceptibility to damage, particularly under cyclic loading and impact conditions, still represents a critical limitation. In this context, the integration of intrinsic self-healing functionalities into thermoplastic matrices emerges as a promising strategy to enhance durability and reduce maintenance costs [1]. This contribution summarizes a comprehensive research pathway aimed at the development of self-healing thermoplastic composites based on polyamide 6 (PA6) matrices modified with cyclic olefin copolymers (COC) and compatibilized with ethylene glycidyl methacrylate (E-GMA). In a first step, the PA6/COC/E-GMA matrix formulation was optimized through a systematic investigation of the effects of compatibilizer content and healing temperature on rheological, microstructural, and mechanical properties. The optimal formulation (PA6/30 wt% COC/5 wt% E-GMA) exhibited significantly improved COC dispersion and interfacial adhesion, enabling high healing efficiencies, up to 82% under impact conditions at 160 °C [2]. Subsequently, this optimized matrix was employed in the development of short carbon fiber-reinforced composites processed via extrusion and injection molding. In these systems, the addition of COC led to a moderate reduction in quasi-static mechanical properties, accompanied by a significant improvement in impact resistance and self-healing capability. In particular, healing efficiencies up to 80% were achieved in impact tests, and fatigue life was extended by up to 77%, demonstrating the ability of the system to repair microdamage induced by cyclic loading. Microstructural analysis further highlighted the key role of phase morphology and COC mobility in governing the healing mechanisms [3]. Finally, the approach was extended to continuous carbon fiber-reinforced laminates manufactured via film stacking and hot pressing. Despite the additional complexity associated with continuous reinforcement and laminate architecture, the self-healing composites exhibited competitive mechanical properties compared to reference systems and, most importantly, outstanding healing performance. In short-beam shear tests, PA6/COC/E-GMA laminates demonstrated complete recovery of interlaminar shear strength (healing efficiency ~100%), whereas negligible recovery was observed for non-healable laminates. These results were attributed to the ability of the COC phase to effectively flow and fill matrix cracks and delaminated regions during thermal mending [4]. Overall, the results demonstrate that a multiscale design approach, combining matrix formulation and composite architecture, enables the development of structural thermoplastic composites with effective and repeatable self-healing capability. This strategy opens new perspectives for the design of damage-tolerant composites, particularly suitable for applications involving cyclic loading and harsh service conditions.

References

1- Z.P. Zhang, M.Z. Rong, M.Q. Zhang Prog Polym Sci 2023, 144, 101724.

2- D. Perin, L. Botta, D. Rigotti, A. Dorigato, G. Fredi, A. Pegoretti Polymers 2025, 17, 280.

3- M. Coser, D. Perin, G. Fredi, L. Aliotta, V. Gigante, A. Lazzeri, A. Dorigato, A. Pegoretti Compos Sci Technol 2025, 268, 111213.

4- D. Perin, G. Fredi, P. Russo, A. Pegoretti, A. Dorigato Compos Part A - Appl S 2026, 201, 109393.

Acknowledgments

This research was funded by the European Union - Next Generation EU - PNRR, Mission 4 Component 2, Investment 1.3 - PE MICS Spoke 5 - LOLIMAR Project (PE00000004, CUP D43C22003120001.