Towards recycling of waste carbon fiber: Strength, morphology and structural features of recovered carbon fibers

• Published in: Waste management (Elmsford) 2023-06, Vol.165, p.59-69
• Main Authors: Salas, A., Berrio, M.E., Martel, S., Díaz-Gómez, A., Palacio, Daniel A., Tuninetti, V., Medina, C., Meléndrez, M.F.
• Format: Article
• Language: English
• Subjects: Carbon Fiber; Carbon fibers; Chemical analysis; Pyrolysis; Recycling; Strength; Surface analysis; Tensile Strength
• ISSN: 0956-053X; 1879-2456
• DOI: 10.1016/j.wasman.2023.04.017

[Display omitted] •Carbon fibers are recycled by two-step pyrolysis (TSP) and microwave-assisted thermolysis (MAT).•TSP limits fiber damage and quasi-preserves its original mechanical properties.•Significant surface changes and 60% reduction in strength of MAT-recovered fibers.•MAT yields surface activation and onset of –OH, –CO and –CH functional groups.•MAT recycling process 70% faster than TSP. Carbon fiber is one of the most widely used materials in high demand applications due to its high specific properties, however, its post-recycling properties limit its use to low performance applications. In this research, the carbon fiber recovering is examined using two methods: two-step pyrolysis and microwave-assisted thermolysis. The results indicate that the fibers recovered by pyrolysis show reduced surface and structural damage, maintaining the original mechanical properties of the fiber with losses below 5%. The fibers recovered by microwaves undergo significant surface changes that reduce their tensile strength by up to 60% and changes in their graphitic structure, increasing their degree of crystallinity by Raman index ID/IG from 1.98 to 2.86 and their amorphous degree by ID”/IG ratio from 0.411 to 1.599. Recovering fibers from microwave technique is 70% faster compared to two step pyrolysis, and provides recycled fibers with superior surface activation with the presence of polar functional groups –OH, –CO, and –CH that react with the epoxy matrix. The thermal, morphological, structural and mechanical characterizations of the recovered fibers detailed in this work provide valuable findings to evaluate their direct reuse in new composite materials.