Scrap and end-of-life composite structures are part of the waste stream and have risen in tandem with the demand for carbon fiber. To be considered sustainable, a material’s environmental impact must be taken into account over its entire life cycle, including reuse and recycling. As a result, businesses in Germany, Japan, and the United States are using pyrolysis to recycle carbon fiber composites. Pyrolysis produces a combustible gas and oil that can be used as fuel, or chemical feedstock, and carbon fibers by heating carbon-fiber composites at high temperatures (400 to 500 degrees Celsius) in the absence of oxygen.
Carbon fiber is one of the mightiest and lightweight materials that has ever been discovered. To create a composite material, high-strength carbon fibers are incorporated in a polymeric matrix, such as an epoxy resin. Carbon-fiber composites show more significant demand in aerospace, wind-turbine, automotive, industrial, and sporting-goods applications due to their lightweight and high strength. Carbon-fibersheets have largely replaced aluminium in aircraft as a way of reducing fuel consumption (distance travelled per volume of fuel). Carbon-fiber wind turbine blades are also lighter than glass-fiber blades, allowing for the manufacture of longer blades with higher energy output for the same weight.
However, one of the significant reason carbon fiber is now preferred over other materials is its ability to be recycled. Yes, you heard it right! Recycling carbon-fiber composites has two main advantages: it decreases the amount of material that ends up in landfills and saves producers 30 percent on fresh carbon fiber. While recycled carbon fibers sheets from aerospace applications cannot be used in aircraft, they retain 90 of their original properties and are considered to be of superlative quality than industrial grade fibers used in the automotive industry.
It is a complex argument to make for recycled CNC carbon fiber parts. The industry is based on the drive to solve issues, such as keeping carbon fiber waste out of landfills and filling a possible carbon fiber supply and demand gap. It is generally believed that about 30% of carbon fiber produced ends up as waste. Meanwhile, most experts predict that useful materials will end up in landfills. The majority of analysts believe that annual demand for the commodity will exceed the current annual production capacity in the coming years. According to Brett Schneider’s figures, global carbon fiber demand is around 65,000-85,000 metric tonnes per year, with a worldwide nameplate capacity (which is more than actual capacity) of around 150,000 metric tonnes. Although commercial suppliers of recycled carbon fibre (rCF) point to reused and repurposed content as a possible solution to the supply-demand gap, the rCF industry faces its own set of challenges.
While the technology to recycle carbon fiber composites has been around for a while and is capable of producing a product with mechanical properties that are quite close to those of virgin content, the composites recycling industry is still in its infancy, with markets for the products it manufactures from recyclate still being developed. Despite the fact that the mechanical recycling process can recycle both CFRP (carbonfiber reinforced plastic)and GFRP(glass fiber reinforced plastic), the majority of research is focused on GFRP. The key reasons for such research variance may be discontinuous recyclates and their re-incorporation with low-value applications like fillers or reinforcements. Furthermore, CFs are on expensive than GFs. Mechanical recycling can cause economic and fiber property loss by disrupting their physical integrity. Even though studies like Mou et al. showed increased flexural strength of concrete after the addition of GF recyclates as filler materials, significant drawbacks have been present since the process’s inception. However, according to studies like Pickering’s, the use of GF recyclates as fillers is not economically viable due to the availability of cheaper virgin fillers like calcium carbonate or silica. As people become more confident in the quality of fiber provided by recyclers, concerns about cost and availability have arisen. Concerns around supply chain protection are becoming the industry’s most significant problem. Furthermore, Carbon fiber materials are notoriously challenging to decompose or recycle. To retrieve the carbon fiber, it is possible to grind or break them down with extremely high temperatures or chemicals. However, the carbon fiber can be damaged during the process, and the matrix resin materials in the composites can be lost.
In the current scenario, total fiber recovery (direct structural recycling) is thought to be helpful to the composites industry. Because of the low use of natural resources, energy, and labour power, as well as the near-virgin fiber quality, recycled fibers from this method have a higher market value. Since solution selection is dependent on the form of material to be recycled and the application in which it will be reused, numerous methods, particularly mechanical, thermal, and chemical-based recycling approaches, have been studied and developed thus far. It is also tough to choose one traditional recycling system from a plethora of options.
There are two types of recycling of carbon fibers sheets and composites: Mechanical and Thermal recycling. Mechanical recycling, in general, is a method for reducing the size of scrap composites into smaller recyclates. Slow-speed cutting or crushing mills are usually used to minimize material size to 50–100 mm, but where scrap composites are homogeneous and free of metal parts, high-speed milling can reduce the size 50–10 mm. There is coarse recyclates (higher fibre content) fiercely and fine recyclates (higher resin content) using cyclones and sieves. Particle size determines the effectiveness of recyclates. In the current situation, the past has aided us in many ways. This has been used as a pre-recycling process for various reasons. In a thermal recycling process, heat is used to break down the scrap composite. Due to a higher operating temperature (450–700 °C), the insignificant volatile materials are likely burnt, leaving the valuable fibers behind. Usually, the process temperature depends on the type of resin utilized in the scrap composite. Improper temperature can either leave char on the fiber surface (undercooked) or result in reducing the diameter of the recovered fibers (overcooked).
The primary aim is to define different recycling strategies for CFRP and GFRP waste and prioritize sustainable recycling approaches focused on economic and environmental principles. Process parameters, process results, mechanical properties, ease of reuse, environmental effects, and cost-effectiveness were all used to make a precise comparison. In addition, their benefits and drawbacks were briefly addressed. LCA research comparing the environmental and economic aspects of recycling methods was also included to affirm the credibility of these techniques. Overall, this report calls for a circular economic approach to recycling CF and GF composite wastes into remanufactured composites.
All in all, carbon fiber composites are used in various industries like Koenigsegg supersport car chassis, drones, industrial machines, and aircraft, and many more. And the good news is that it can be recycled, which makes it superior to other materials, in terms of reduced cost over the years and more eco-friendly. Resultantly, we have seen an exponential rise in their usage.