Recycling of carbon fiber composites into thermoformable hybrid laminates
Topic(s) : Manufacturing
Co-authors :
Alice PROIETTI (ITALY), Leandro IORIO , Denise BELLISARIO , Fabrizio QUADRINI (ITALY), Loredana SANTOAbstract :
As new technological challenges are going to be faced, thermosetting carbon fibres-reinforced (CFR) composites are playing a key role in newly designed structures and laminates multi-functionality has become of primary importance. However, the diffusion of the circular economy culture had generated significant concerns regarding the end-of-life of these materials that, traditionally, were not recovered, but dismissed in landfills. This was a valid solution in the past because of the small amount of discarded laminates, but nowadays a new approach is promoted. Specific recycling technologies have been developed with pyrolysis and solvolysis being the most valuable solutions but, unfortunately, only chopped fibres can be obtained.
In this work an innovative recycling technology for thermosetting composite materials is presented, based on thermo-mechanical disassembly of 10 plies CFR composites obtained by compression molding. Thanks to the proposed recycling strategy, a thermosetting CFR material can be disassembled into single cured plies by applying a strong deformation, Figure 1. Since CFR laminates are rigid at room temperature, heating is required to avoid fibres breaking during bending.
In the experimentation, the composite has been heated in oven at 250 °C for 15 min in such a way to minimize the temperature gradient along the laminate thickness; subsequently, mechanical bending has been performed by positioning the material between the rollers of a roll bending machine. This equipment is commonly used to bend small thickness aluminium sheets and permits to gradually curve the plane laminate; for this reason, it is particularly suitable for CFR composites thermo-mechanical disassembly since a gradual increase of the applied deformation permits to minimize fibers damaging. However, the heated plate cooled after some passings since the rollers were not heated and, additional thermal steps were necessary to obtain the full separation of the material.
By thermo-mechanical disassembly long impregnated fibres have been recovered that have been re-assembled with a thermoplastic interlayer of polyamide 6 (PA6). The recycled CFR plies have been stacked by interposing PA6 and a parallel plate hot press has been used for consolidation. In this way, a hybrid composite is obtained with the different materials that can be still recognized after manufacturing. Stereoscopy has been performed to investigate the adhesion among the layers and tensile tests have been used for laminates mechanical characterization. Finally, additional properties of the hybrid composite have been evaluated in terms of thermoformability, Figure 2, and a U-shaped geometry has been obtained.
In this work an innovative recycling technology for thermosetting composite materials is presented, based on thermo-mechanical disassembly of 10 plies CFR composites obtained by compression molding. Thanks to the proposed recycling strategy, a thermosetting CFR material can be disassembled into single cured plies by applying a strong deformation, Figure 1. Since CFR laminates are rigid at room temperature, heating is required to avoid fibres breaking during bending.
In the experimentation, the composite has been heated in oven at 250 °C for 15 min in such a way to minimize the temperature gradient along the laminate thickness; subsequently, mechanical bending has been performed by positioning the material between the rollers of a roll bending machine. This equipment is commonly used to bend small thickness aluminium sheets and permits to gradually curve the plane laminate; for this reason, it is particularly suitable for CFR composites thermo-mechanical disassembly since a gradual increase of the applied deformation permits to minimize fibers damaging. However, the heated plate cooled after some passings since the rollers were not heated and, additional thermal steps were necessary to obtain the full separation of the material.
By thermo-mechanical disassembly long impregnated fibres have been recovered that have been re-assembled with a thermoplastic interlayer of polyamide 6 (PA6). The recycled CFR plies have been stacked by interposing PA6 and a parallel plate hot press has been used for consolidation. In this way, a hybrid composite is obtained with the different materials that can be still recognized after manufacturing. Stereoscopy has been performed to investigate the adhesion among the layers and tensile tests have been used for laminates mechanical characterization. Finally, additional properties of the hybrid composite have been evaluated in terms of thermoformability, Figure 2, and a U-shaped geometry has been obtained.