The demand for lightweight cars continues to grow. How can carbon fiber recycling increase efficiency and reduce costs?

To put it simply, carbon fiber is a material with a carbon content of more than 90% with high strength, light weight, corrosion resistance, and good energy absorption effect. It can replace many traditional materials and has cross-era significance for automobile lightweight. However, the high price has deterred car companies and consumers. In recent years, the cost has been slightly reduced before it can be used for civilian use. The current price of 200-250 yuan per kilogram is still far higher than that of traditional materials, making many auto companies stretched when using carbon fiber.

Current status of carbon fiber use in automotive industry

In other industries, including automobiles, the demand for carbon fiber has grown rapidly in recent years and is expected to grow to 140000 tons per year in 2020. The service life of carbon fiber in the motor vehicle industry is 15 years, and in the aviation field it is 20 to 25 years, and the current aircraft fuselage carbon fiber accounts for 40%, so in the next 10 to 20 years, there will be a large amount of carbon fiber materials in the market. To recycle, China issued the "Leading Action for Circular Development" in April 2017, and the "Industry Key Common Technology Development Guide" in October, it all mentions the recycling of carbon fiber composites.

Nowadays, except BMW I3 carbon fiber composite materials account for 50%, most fuel vehicles still use steel or alloy bodies. New energy vehicles used all-aluminum bodies and carbon fiber bodies before. With the enhancement of power, steel and alloys have also been used in order to reduce costs. For example, Tesla Model S uses all-aluminum bodies. Now the new Model 3 is replaced by steel and aluminum hybrid bodies, and BMW I3 will be replaced by steel, aluminum and carbon hybrid bodies, domestic new energy vehicles are more small cars, mostly using low-cost all-aluminum alloy frames, the overall automotive industry carbon fiber utilization rate is low, it is difficult to achieve the ultimate lightweight, carbon fiber recycling is imperative.

High efficiency recycling still faces technical difficulties

First of all, thermosetting polymers cannot be directly heated to reshape, and recycled materials are often mixed with pollutants, such as metal and plastic debris. If the current recycling technology is to go out of the laboratory and carry out industrial production, the cost problem must be solved. Professor Meng Fanran from Nottingham University brought their experimental results to the 2018 International Forum on Automotive Materials (Xiqing).

At present, the carbon fiber recycling process is mainly divided into three kinds, mechanical method, chemical method and pyrolysis method. The mechanical recycling method is not suitable for the recycling of carbon fiber composite materials for automobiles, and the chemical method recycling is still limited to the laboratory stage, which is far from industrial production. There is still a big gap, so the pyrolysis method is the only carbon fiber composite material recycling technology that realizes industrial production at present.

At present, the carbon fiber recycling process is mainly divided into three kinds, mechanical method, chemical method and pyrolysis method. The mechanical recycling method is not suitable for the recycling of carbon fiber composite materials for automobiles, and the chemical method recycling is still limited to the laboratory stage, which is far from industrial production. There is still a big gap, so the pyrolysis method is the only carbon fiber composite material recycling technology that realizes industrial production at present.

The experiment uses a fluidized bed recovery process in the pyrolysis method. First, the waste is loaded into the fluidized bed. The fluidized bed passes through a high temperature of 500 degrees or more. After the recovered polymer is removed by oxidation, the rest is carbon fiber. The carbon fiber is then collected through the recycling process, and the remaining exhaust gas can be recycled. The entire process can recycle the carbon fiber from the waste, effectively separating pollutants and carbon fiber, including impurities. And the use of exhaust gas circulation to reduce the energy consumption of the entire process, to achieve energy reflux, has a good market prospects.

However, the recycled carbon fiber is different from traditional materials and cannot be directly used in the manufacture of final products. The recycled carbon fiber should be used for intermediate treatment, including fiber distribution, suspension, thermal drying and other processes. Finally, the obtained carbon fiber needs to be arranged. The direction of the fiber can be corrected and unified by rotation. Finally, the adjusted and arranged carbon fiber material is obtained, used to produce high-strength carbon fiber composites.

From the decomposition of recycled materials to the production of subsequent compounds and motor vehicle parts, many variables affect the cost of recycling, including the speed of conveying waste and the quality of waste, and the energy consumption is significantly reduced when feeding faster.

At the same time, from the perspective of the whole life cycle, the fuel economy of the whole vehicle produced by recycled carbon fiber is 20% to 60%. The recycled compound can reduce greenhouse gas emissions and bring higher strength after being arranged. Compared with traditional materials, the performance of recycled carbon fiber still has obvious advantages.