The world is hurtling rapidly towards a developed future, and carbon fiber-reinforced polymers (CFRPs) play a key role in enabling technological and industrial progress. These composite materials are lightweight and highly strong, making them desirable for applications in various fields, including aviation, aerospace, automotive, wind power generation, and sports equipment.
However, recycling CFRPs presents a significant challenge, with waste management being a pressing issue. Conventional recycling methods require high-temperature heating or chemical treatments, which result in high environmental impact and elevated costs. Moreover, it has been a challenge to recover high-quality carbon fibers. In this regard, electrohydraulic fragmentation has been proposed as a promising option. In this technique, intensive shockwave impulses generated by high-voltage discharge plasmas are applied along the interfaces of different materials to separate the various components.
While this method is lucrative, can we do better? Answering this question, a team of researchers from Waseda University, led by Professor Chiharu Tokoro from the Department of Creative Science and Engineering, and including Keita Sato, Manabu Inutsuka, and Taketoshi Koita, has come up with a novel direct discharge electrical pulse method for efficiently recycling CFRPs. Their findings have been published in the journal Scientific Reports on November 30, 2024.
Tokoro talks about the motivation behind their present work, stating: "In our previous studies, we had already established research expertise in generating shock waves in water using electrical pulse phenomena to efficiently fragment difficult-to-process materials. However, in applications such as lithium-ion batteries, we discovered that direct discharge, which utilizes Joule heating and vapor expansion of the material itself, is more effective for high-efficiency separation than relying on shock waves. We now apply this approach to CFRP, hypothesizing that it could achieve more efficient separation compared to current methods."
The direct discharge electrical pulse technique leverages Joule heat generation, thermal stress generation, and expansion force due to plasma generation, foregoing the need for heating or chemicals. The researchers compared this method with electrohydraulic fragmentation by examining the corresponding physical properties of the recovered carbon fibers, including length, tensile strength, resin adhesion, and structural degradation, as well as the energy efficiency in terms of fiber separation. They found that their new technique is more effective for carbon fiber recovery. It preserves relatively longer fibers with higher strength and also precisely separates CFRPs into individual fibers without retaining any residual resin on the surface.
Furthermore, the direct discharge approach improves energy efficiency by a factor of at least 10 compared to traditional alternatives, while reducing environmental impact and promoting resource utilization.
Therefore, this technology is anticipated to accelerate CFRP recycling, contributing significantly to the development of a sustainable society. According to Tokoro, "Our research findings have numerous applications, pertaining to the recycling of CFRPs from spent aircraft components, automotive waste, and wind turbine blades. Thus, the present innovation supports sustainability across industries by enabling efficient resource recovery and reducing environmental impact."
Overall, this work is expected to further the United Nations Sustainable Development Goals of Industry, Innovation and Infrastructure (SDG 9) and Responsible Consumption and Production (SDG 12).
