DEVELOPMENT OF THERMOPLASTIC POLYMER BLENDS FOR STRUCTURAL COMPOSITES WITH SELF-HEALING CAPABILITY
Topic(s) : Multifunctional and smart composites
Co-authors :
Andrea DORIGATO (ITALY), Davide PERIN (ITALY), Alessandro PEGORETTI (ITALY)Abstract :
The development of materials with self-healing properties is primarily attempting to mimic the healing mechanisms developed by nature. However, self-healing materials are generally characterized by a limited technological readiness level [1-3]. In this work, the investigation of intrinsic self-healing polymer blends, composed of a polyamide 6 (PA6) matrix and a cyclic olefinic copolymer (COC), was performed. The produced compatibilized blends could be potentially used as matrices for multifunctional structural composites with self-healing capability.
The PA6 used in this work was a Radilon S 24E 100 NAT, provided by Radici Group SpA, while the COC selected as healing agent was Topas COC 9506F-500, supplied by TOPAS GmbH. The compatibilizer was a poly(ethylene-co-glycidyl methacrylate) (E-GMA). PA6 and COC were melt compounded in an internal mixer at 230 °C for 6 min, and then compression moulded in a hot-plate press at 235 °C for 8 min. A comprehensive rheological, microstructural, and thermo-mechanical characterization was performed. The healing efficiency of the system was determined through plane-strain fracture toughness tests, both in quasi-static and impact mode. The tested samples were then thermally healed for 1 h at 120, 140, 160, and 180 °C, under a pressure of 0.5 MPa.
Without the compatibilizer, the healing efficiency after a mending process at 160 °C was 12 % in quasi-static mode and 57 % in impact mode. Thanks to the addition of the E-GMA compatibilizer, COC domains were homogeneously distributed within the PA6 matrix, and the healing efficiency values increased up to 38 % in quasi-static mode and 82 % in impact mode, after a mending process at 160 °C. From FESEM images of the fracture surfaces it was possible to notice that compatibilized samples tested in quasi-static mode reported severe plasticization, while the same blends tested in impact mode reported a brittle behavior. Therefore, in quasi-static mode the corrugated morphology hindered the flow of the healing agent, while in impact conditions the healing agent could flow and fill the cracks much more efficiently. In conclusion, the addition of a suitable compatibilizer significantly improved the healing efficiency, significantly enabling these matrices to be used in structural thermoplastic composites.
The PA6 used in this work was a Radilon S 24E 100 NAT, provided by Radici Group SpA, while the COC selected as healing agent was Topas COC 9506F-500, supplied by TOPAS GmbH. The compatibilizer was a poly(ethylene-co-glycidyl methacrylate) (E-GMA). PA6 and COC were melt compounded in an internal mixer at 230 °C for 6 min, and then compression moulded in a hot-plate press at 235 °C for 8 min. A comprehensive rheological, microstructural, and thermo-mechanical characterization was performed. The healing efficiency of the system was determined through plane-strain fracture toughness tests, both in quasi-static and impact mode. The tested samples were then thermally healed for 1 h at 120, 140, 160, and 180 °C, under a pressure of 0.5 MPa.
Without the compatibilizer, the healing efficiency after a mending process at 160 °C was 12 % in quasi-static mode and 57 % in impact mode. Thanks to the addition of the E-GMA compatibilizer, COC domains were homogeneously distributed within the PA6 matrix, and the healing efficiency values increased up to 38 % in quasi-static mode and 82 % in impact mode, after a mending process at 160 °C. From FESEM images of the fracture surfaces it was possible to notice that compatibilized samples tested in quasi-static mode reported severe plasticization, while the same blends tested in impact mode reported a brittle behavior. Therefore, in quasi-static mode the corrugated morphology hindered the flow of the healing agent, while in impact conditions the healing agent could flow and fill the cracks much more efficiently. In conclusion, the addition of a suitable compatibilizer significantly improved the healing efficiency, significantly enabling these matrices to be used in structural thermoplastic composites.