After a slow start, composite material manufacturers began to take advantage of the unique properties of graphene.
In 2004, researchers at the University of Manchester in the UK developed graphene, which is the world's first two-dimensional man-made material. In the next few years, graphene has been hailed as a magical material for its many extraordinary properties. Although graphene is very light and one million times thinner than human hair, it is the strongest material in the world-the tensile strength is 200 times that of steel. It has high electrical and thermal conductivity, is almost transparent, and is impermeable, very flexible and stretchable. However, what is truly unique about graphene is that it can provide all these properties at the same time.
Like many other high-tech discoveries, graphene did not initially achieve the effect of publicity. Early attempts to use its investment failed. There are several reasons for these failures. Early users were also confused by the abnormal behavior of graphene. For example, when composite material manufacturers want to improve the performance of a material, they are used to adding more substances to the composite material. But graphene has the opposite effect. Reducing the amount of graphene can usually improve the performance of graphene reinforced composites. For example, people initially added 1% by weight of graphene to the composite material, but it was found that graphene with 0.5% by weight achieved better results.
Through continuous research and experiments, researchers have a better understanding of the behavior of graphene, and finally recognized its benefits. This nanomaterial proves to be a valuable asset in the composites industry because it can be used for thermosetting and thermoplastic composites, can be used for glass, carbon and basalt fibers, and is used with various resins.
At present, more than 45 different graphene vertical markets have been identified, and composite materials are obviously the main application market, followed by coatings.
Graphene shell aircraft
Graphene production
The purest graphene is a layer of carbon atoms with a thickness of one atom, arranged in a dense hexagonal lattice. Although scientists have known graphene in theory for several years, it is difficult to produce. Researchers at the University of Manchester used tape to separate flakes from a piece of graphite, and then continued to split the flakes with more tape until they formed monoatomic flakes.
Although the development of manufacturing methods has now far exceeded the level of tape, the production of single-layer graphene is still difficult and expensive. However, the researchers found that graphene does not have to be in this pure form to be effectively used.
Few layers of graphene (FLG), usually less than 10 layers, still exhibit many unique characteristics of graphene. The general assumption is that the fewer the layers of graphene material, the better the quality, but this really depends on the specific application. Composite material manufacturers usually use multi-layer graphene (MLG), which is composed of 11 to 20 carbon atoms.
Today's graphene can be produced in many ways. Chemical vapor deposition (CVD) produces the purest form, which consists of one to two layers of carbon atoms. A 25-micron thin-foil copper sheet heated to 1000 ° C in a vacuum container, and bathed with a mixture of argon, helium, and methane. Graphene sheets gather on the surface of copper, and then copper is digested by chemicals such as hydrochloric acid, leaving graphene.
CVD is a very expensive method. The cost of producing graphene is as high as $ 500,000 per gram. Even a continuous CVD production line cannot provide the output required for mass production. Therefore, manufacturers have developed mass production methods that use physical, mechanical, chemical, and thermal exfoliation of graphite raw materials to obtain FLG and MLG.
In one technique, a stone crusher and a ball mill decompose graphite into fine powder, and then put it into a solvent such as ethanol or methylpyrrolidone, and are hit by ultrasonic vibration to further decompose the graphene layer. The longer the processing time, the fewer the number of graphene layers. In the form of powder or solution, the pure graphene or FLG of this graphene is priced from US $ 100 to US $ 500 per gram, while the price of MLG is only US $ 50 per gram.
Some researchers are using filters to remove graphene from biochar, which is a residue from biofuel production. Others are experimenting with a detonation method that introduces hydrocarbon gas and oxygen into the combustion chamber and then uses a spark plug to detonate. After the gas burns, carbon residues containing graphene are left behind. There are currently many other graphene manufacturing methods that are being explored or converted to commercial-scale production.
Graphene comes in many forms, including flakes, nanosheets, flake powder, and graphene dissolved in solution. Each form has different properties and characteristics, including lateral dimensions, which makes it suitable for specific applications. Graphene can also be functionalized with other materials to impart certain properties. For example, graphene functionalized with boron nitride is a better insulator than molecular conductors. Since graphene oxide is easier to disperse than other forms of graphene, and is compatible with many organic systems and polymers, it is widely used. R & D personnel can adjust the properties of graphene to match the matrix of the material to achieve the desired effect.
Market opportunities and application barriers
When adding graphene to composite materials, one of the biggest obstacles manufacturers face is overcoming their tendency to agglomerate.
Generally speaking, due to the hydrophobicity and chemical inertness of graphene, compared with graphene oxide, its dispersion performance is relatively low. Therefore, the phenomenon of graphene agglomeration in the matrix has also attracted more and more attention from researchers. People have tried a variety of methods to overcome the problem of graphene agglomeration.
The uniform dispersion method of graphene in the matrix mainly includes two major categories of physical dispersion and chemical dispersion.
The in-situ polymerization method is to first uniformly disperse the nanoparticles in the monomer, and then use the initiator to initiate the polymerization, so that the nanoparticles or molecules are uniformly dispersed on the polymer matrix and form an in-situ molecular polymerization material. In-situ multiphase polymerization not only maintains the nano-characteristics of the particles, but also achieves uniform dispersion of the filled particles, and can form core-shell nano-shaped particles with an elastic coating layer. Because the outer layer is an organic polymer, it can increase the affinity of the material with the organic phase.
Another method is to add graphene to the liquid resin. The graphene material is dispersed in the monomer and then introduced into the polymer. Functionalizing graphene to change its surface chemistry and surface energy also helps dispersion. The functionalization of graphene has developed into the preparation of materials with special properties or to solve the shortcomings of certain aspects of graphene.
The functionalized graphene not only maintains the original performance of graphene, but also shows the reactivity of the modified group, which provides the possibility for the dispersion and reaction of graphene, further increasing the application range of graphene.
Although graphene may not be a magical material, its many properties should bring a wide range of new opportunities to the composite industry. Graphene can make the function of composite materials better. Due to the increased strength brought by nanomaterials, graphene composites may now be able to compete directly with metals. Adding graphene to thermoplastics increases the heat distortion temperature, so it can now be applied to temperature ranges that were previously unavailable.
Sneakers made of graphene
As the prices of graphene and graphene-related materials decrease, and methods for preparing graphene on a large scale are improved, more and more graphene composite materials should start to be seen on the market. The incredible properties that graphene materials can bring means a huge motivation to achieve this goal.
Earlier, the famous British off-road brand cooperated with the University of Manchester to develop new shoes and launched their new achievements, the world's first pair of sports shoes made of graphene. Experts at the Graphene Institute at the University of Manchester have recommended a rubber sole reinforced with graphene, which is particularly suitable for running and fitness. In the current test, sports shoes made with this kind of sole show better wear resistance in 1000 miles, which is 1.5 times higher than that of ordinary running shoes.
Graphene imparts bio-erosion and corrosion resistance to coatings and may have an impact on the global economy. Marine corrosion is one of the main reasons leading to the failure of offshore equipment, and it is also a problem of global anti-corrosion. The installation of biofuels on the hull shells of commercial vessels creates an additional $ 36 billion in diesel cost for the shipping industry every year because it causes resistance in the water. Globally, the damage caused by the corrosion of bridges, steel bars and automobiles is about US $ 2.4 trillion.
The discovery of two-dimensional materials, especially graphene, provides new ideas for the development of new anticorrosive coatings for marine equipment. Graphene has a monoatomic layer structure and molecular impermeability, and is considered to be the thinnest protective material. However, the artificially prepared graphene is easy to re-agglomerate, and it cannot fully exert the excellent characteristics of the graphene monolayer.
Integrating graphene into automotive components can provide a variety of more sensitive sensors that consume less power.
Last summer, the graphene load was successfully reduced to 0.05%, and the performance of the parts was even better. Ford may one day use graphene polyurethane foam for hoods, headgear and door panels in car cabins.
Market applications that are gradually expanding
Composite materials containing graphene are now widely used in the manufacture of various products from golf balls, sports rackets and training shoes to fireproof coatings and building materials.
One company introduced a prepreg specifically for lightning protection last year, which uses functionalized nanomaterials to improve electrical conductivity. This will eliminate the use of copper mesh or silver nanowire mesh to protect the aircraft. The same technology can also be used for unmanned aerial vehicles and offshore wind turbine blades.
GEIC is working with industrial customers in the field of building materials to add graphene to concrete and asphalt mixtures. Adding a very small amount of graphene powder to the concrete mixture can significantly increase the compressive strength of the concrete and reduce the amount required by the builder by 30%. Since the concrete production process emits a large amount of carbon dioxide into the atmosphere, the use of graphene is beneficial to the environment.
Adding graphene to polymers, foams and textiles can improve its flame retardancy. Several industries that focus on fire protection in the aerospace field have achieved some very positive results in the fields of thermoplastics and textile materials. This flame retardancy is usually just one of the many beneficial properties graphene provides for these applications.
Because graphene is a very flexible material, it can be used as a sensor for composite products. Emergency helmets and sports helmets can be designed to measure the impact of balls or other objects; if someone is hit in the head, it is easier to determine whether they have a concussion and need further medical care.
Graphene, which has excellent physical properties and electrical properties, has broad application prospects and has great application potential in many fields. At present, the application of graphene is more as a reinforcement to prepare composite materials to improve the performance of the matrix material.
In recent years, semiconductor particles, metal and metal oxide graphene functional composites have appeared, and have shown good application prospects, and can be widely used in catalysis, electrochemistry, biomedicine, and energetic materials.
In addition to applications in photoelectric conversion, graphene also has important applications in battery materials. Because graphene has good mass transfer characteristics and a relatively large open surface, graphene is generally used as a carrier for supporting precious metal catalytic materials in fuel cells.
In addition, graphene composite materials have a wide range of applications in the fields of solar cells, sensors, nanoelectronics, high-performance nanoelectronic devices, composite materials, field emission materials, gas sensors, and energy storage.
At present, China is one of the most active countries in graphene research and application development. According to 2018 data from the International Graphene Product Certification Center, China has become one of the most active countries in graphene research and application development, and 58% of global graphene patents come from China.