Rapid carbothermal shock processing converts shredded wind turbine blade waste into high-purity silicon carbide and graphene, achieving tunable structures, strong performance, and major environmental and cost savings.
(Nanowerk Spotlight) Global wind power expansion has created a new industrial waste stream that is difficult to manage. Wind turbine blades, built from glass fiber or carbon fiber reinforced polymers with tough epoxy and polyvinyl chloride foam cores, are designed to withstand decades of weather and mechanical stress.
Their durability becomes a liability at the end of service. Their retired mass is projected to rise from about 6,000 tons in 2025 to 653,000 tons by 2040. Most are sent to landfills or incinerated because their composite structure resists mechanical shredding and chemical breakdown.
Current recycling methods such as pyrolysis or solvolysis can recover some fibers but usually yield degraded materials or low-value fillers, while consuming large amounts of energy and producing harmful by-products.
At the same time, demand is rising for high-performance ceramics and carbon materials such as silicon carbide and graphene, used in electronics, sensors, and advanced composites. Producing these materials from raw minerals requires pure feedstocks and long, high-temperature processing that fixes stable crystal structures but limits control over microstructure. Past efforts to convert mixed waste into such products have largely failed because heterogeneous feedstocks behave unpredictably when heated slowly.
CTS is a millisecond Joule-heating process carried out inside a graphite tube that serves as both reactor and heating element. When a high electrical current passes through the tube, it rapidly raises the internal temperature to about 3 000 kelvin in a few seconds. This direct, fast heating creates strong temperature gradients that drive chemical reactions away from equilibrium.
As the researchers show, these conditions can transform unsorted wind turbine blade fragments into valuable silicon carbide or graphene simply by adjusting the peak temperature and the duration of heating.
Schematic illustration summarizing the temperature- and time-modulated non-equilibrium phase engineering pathways for SiC polytypes (3C, 6H) and graphene architectures (turbostratic, hybrid AB-turbostratic) obtained via CTS from GFRP/PVC waste. (Image: Adapted with permission from Wiley-VCH Verlag) (click on image to enlarge)
The authors describe CTS as a nonequilibrium manufacturing platform. Because the temperature changes so quickly, it can trap metastable atomic structures—arrangements that would normally revert to lower-energy forms during slower heating. Using shredded blade waste composed of glass fiber reinforced polymer and polyvinyl chloride, the team demonstrates temperature-dependent synthesis.
At around 2 400 °C, CTS produces cubic silicon carbide (the 3C polytype), formed when silicon from the glass reacts with carbon from the polymer. Raising the temperature to about 2 700 °C instead breaks down silicon carbide and yields turbostratic graphene, a form of graphene where layers are slightly misaligned and loosely stacked. The difference arises because silicon’s vapor pressure increases much faster than carbon’s at high temperature, driving silicon loss and shifting the balance toward carbon formation.
Time control adds further versatility. Holding the temperature at about 1 500 °C for tens of seconds produces hexagonal 6H silicon carbide, a metastable variant containing more silicon vacancies—missing atoms that affect electrical behavior—than the cubic form. Holding at about 2 000 °C for 30 seconds produces a hybrid graphene containing both ordered AB-stacked regions, similar to graphite, and disordered turbostratic zones.
Molecular dynamics simulations support these findings and show that the hybrid structure results from local temperature variations inside the reactor that cause some regions to partially reorder while others remain amorphous.
The chemical mechanism follows known thermodynamics of the silicon–carbon–oxygen system. Silicon carbide remains stable up to about 2 400 °C but decomposes above that as silicon vaporizes. Density-functional calculations show that defective carbon surfaces bind silicon dioxide strongly and help reduce it, while silicon monoxide interacts more readily with pristine graphene, promoting silicon carbide growth.
Together these reactions explain how surface chemistry and rapid heating determine whether the product becomes silicon carbide or graphene.
Material performance reflects the structural control achieved. After purification by acid and oxidation, the cubic 3C silicon carbide reaches over 99 percent phase purity. Particle size decreases from about 250 nanometers to 20–50 nanometers as synthesis temperature rises, increasing surface area to 66 square meters per gram—useful for catalysis or adsorption.
Compacted powders show electrical conductivity of 148 siemens per meter under 4 megapascals of pressure for 3C material, higher than the 6H form, while 6H shows greater thermal conductivity.
The carbon products show complementary traits. Turbostratic graphene has a large specific surface area of about 136 square meters per gram and a porous texture. The hybrid graphene couples conductivity with stable dispersion. Its ordered nanodomains form efficient electron paths, and the disordered regions keep sheets from restacking.
Compressed hybrid graphene conducts at about 1 800 siemens per meter under 4 megapascals and has thermal conductivity near 0.29 watts per meter kelvin. When added to epoxy at 5 percent by weight, it increases tensile strength by about 22 percent and improves flexibility compared with pure epoxy.
CTS also works with other wastes. The team synthesizes 3C silicon carbide from silica and carbon black, or from recycled photovoltaic silicon mixed with carbon black, and produces graphene from carbon black or crushed polyvinyl chloride alone. The simple graphite-tube reactor, powered by a capacitor bank, allows continuous flashing between 900 °C and 2 700 °C with heating rates of 2–4 seconds and controlled hold times.
Environmental and cost analyses indicate large advantages. A life-cycle assessment estimates a global-warming potential of 2.08 kilograms of carbon-dioxide equivalent per kilogram of blade processed—86 percent lower than pyrolysis and 27 percent lower than solvolysis.
Modeled operating costs are about $0.11 per kilogram, compared with $11.18 for pyrolysis and $0.42 for solvolysis. If scaled globally, CTS could prevent millions of tons of carbon-dioxide emissions annually by 2040 as blade retirement accelerates.
This study demonstrates that rapid, electrically driven heating can turn complex waste into high-value materials with controllable structure. By adjusting only temperature and time, carbothermal shock produces cubic or hexagonal silicon carbide, turbostratic graphene, or a hybrid graphene that combines conductivity and processability.
The method avoids sorting, supports continuous operation, and offers major gains in efficiency and cost. If adopted industrially, it could transform the growing stockpile of discarded turbine blades from a waste burden into a source of advanced functional materials.
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