New materials is one of the seven strategic emerging industries in China, and it is also an important focus for accelerating the transformation and development of China's petrochemical and chemical industries. It is closely related to industries such as energy, information, equipment manufacturing, energy conservation and environmental protection, and biomedicine. At present, new materials have been included in the planning priorities of the country, local governments at all levels, and production enterprises, and are a hot research area for investors. The "new" and "old" of materials are actually relative, depending on the technical content, performance, and craftsmanship level of the product itself, as well as the social development stage of the country and the scarcity of the regional market.
Especially in the rapidly developing modern society of materials science and production technology, the connotation and varieties of "new materials" are also being updated at an unprecedented speed - some well-known "new materials" have been or are gradually being mass-produced and widely used, while more innovative material products continue to emerge. Therefore, in order to enhance the development level of China's new materials industry, it is necessary to broaden our horizons, closely track the forefront trends of new materials industry development at home and abroad, continuously move towards the top of the material industry pyramid, and make China a leader in the international new materials industry as soon as possible.
Since 2004, more than 2000 papers have been published on the research results of graphene in SCI retrieval journals, and graphene has begun to surpass carbon nanotubes and become the international forefront and hotspot of attention. Graphene based nanocomposites have shown many excellent properties in energy storage, liquid crystal devices, electronic devices, biomaterials, sensor materials and catalyst carriers, and have broad application prospects. At present, graphene composites studied mainly include graphene/polymer composites and graphene/inorganic composites. Their preparation methods mainly include blending, sol-gel, intercalation and in-situ polymerization.
Graphene has attracted much attention for its unique structure, outstanding thermal conductivity, mechanical properties, and electrical properties. Developed countries such as Europe, America, Japan, and South Korea, as well as some multinational corporations, have introduced encouraging policies or raised heavy capital to support the development of the graphene industry, hoping to occupy a favorable position in the market. On November 20, 2015, the "Several Opinions on Accelerating the Innovative Development of Graphene Industry" [1] emphasized the breakthrough of key technologies for large-scale preparation of graphene materials and increased promotion and application. At present, China has become a major producer and consumer of synthetic materials in the world, with expanding application areas and a more complete integrated upstream and downstream industrial chain. Conducting research on the application of graphene in composite materials can quickly and effectively achieve patent breakthroughs in the field of new materials, and apply it to existing industrial chains, forming a large-scale industry. This article provides an overview of graphene preparation technology, domestic graphene research and production status, favorable conditions for conducting graphene industrialization research in China, and proposes the application prospects of graphene in the field of composite materials.
The production methods of graphene are divided into physical and chemical methods. The micro mechanical exfoliation method belongs to the physical method and can obtain high-quality graphene, but its size is small and cannot be produced on a large scale. At present, there are two chemical methods for mass production of graphene: one is chemical vapor deposition, which uses transition metals such as Ni and Ru as substrates, and small molecule carbon containing gases such as methane and ethylene undergo chemical reactions under high temperature and gaseous conditions to grow graphene on the substrate surface. It is mainly used to prepare high-quality graphene films for electronic devices. The morphology and properties of graphene prepared by this method are greatly affected by the substrate, and the substrate material is expensive and the manufacturing cost is high. The second method is chemical reduction, which uses strong acids such as concentrated sulfuric acid and fuming nitric acid to oxidize natural graphite to obtain graphite oxide. After thermodynamic expansion or strong ultrasonic peeling, individual graphite oxide is obtained. Finally, the graphite oxide is reduced using hydrazine hydrate, hydrazine hydrate, etc. The resulting product is mainly used to prepare graphene nanosheets, known as functional graphene, which is low-cost and can be prepared on a large scale. The disadvantage is that the molecular structure of graphene is damaged and prone to agglomeration, resulting in many properties of the product being far from theoretical values; However, due to the presence of certain oxygen-containing functional groups and strong adhesion with polymer matrices such as resins, graphene flakes are suitable for preparing polymer composite materials.
By functionalizing graphene, not only can its solubility be improved, but it can also be endowed with new properties, making it have great application prospects in polymer composites, optoelectronic functional materials and devices, and biomedicine.
Graphene based polymer composites are an important direction for graphene to move towards practical applications. Due to its excellent performance and low cost, functionalized graphene can be processed using conventional methods such as liquid processing, making it highly suitable for developing high-performance polymer composites. Professor Ruoff et al. first prepared graphene polystyrene conductive composite materials, which attracted great attention. They first uniformly dispersed graphene functionalized with phenyl isocyanate into a polystyrene matrix, and then reduced it with dimethylhydrazine, successfully restoring the intrinsic conductivity of graphene with a critical conductivity content of only 0.1%
Professor Brinson et al. systematically studied the properties of functionalized graphene polymer composites and found that the addition of graphene can significantly increase the modulus, strength, glass transition temperature, and thermal decomposition temperature of polymethyl methacrylate, and the effect of graphene is much better than that of single-walled carbon nanotubes and expanded graphite; Adding 1% functionalized graphene can increase the glass transition temperature of polypropylene nitrile by 40 ℃, greatly improving the thermal stability of the polymer.
Chen et al. prepared composite materials of graphene functionalized with sulfonic acid and isocyanate groups and thermoplastic polyurethane (TPU), and studied their application in infrared triggered driving devices
Applied in actuators. They found that adding only 1 wt% graphene can increase the strength and modulus of TPU composite materials by 75% and 120%, respectively Further research has shown that graphene composites functionalized with sulfonic acid groups exhibit excellent infrared light responsiveness. After being irradiated with infrared light, the composite film can rapidly shrink, lifting a 21.6g object by 3.1 cm. Moreover, after repeated stretching and shrinking 10 times, the film maintains a high recovery rate and energy density, indicating that the optical drive device based on this graphene composite material exhibits good driving performance and cycling stability, and has great application prospects.
Due to its single atomic layer structure, graphene has a large specific surface area and is highly suitable for use as a drug carrier. Dai et al. first prepared polyethylene glycol functionalized graphene with biocompatibility, which made graphene highly water-soluble and able to maintain stable dispersion in physiological environments such as plasma; Then, utilizing the π - π interaction, the anti-tumor drug camptothecin derivative (SN38) was successfully loaded onto graphene for the first time, opening up research on the application of graphene in biomedicine.
By utilizing hydrogen bonding, soluble graphene was used as a drug carrier to achieve efficient loading of anti-tumor drug DXR onto graphene. Due to the high specific surface area of graphene, the loading capacity of DXR can reach 2.35 mg/mg, which is much higher than that of other traditional drug carriers (such as polymer micelles, hydrogel microparticles and liposomes, the loading capacity is generally less than 1 mg/mg). In addition, controllable loading and release were achieved by adjusting the pH value to alter the hydrogen bonding between graphene and the load. Research has found that DXR has the highest loading under neutral conditions, followed by alkaline conditions, and the lowest under acidic conditions. Its release process can also be controlled by pH value. They also used graphene functionalized with iron oxide as a drug carrier and studied its targeting behavior. The loading capacity of DXR on graphene functionalized with iron oxide can reach 1.08 mg/mg, which is higher than that of traditional drug carriers. The load can undergo aggregation and sedimentation under acidic conditions, and can move directionally under the action of a magnetic field. It can also dissolve again under alkaline conditions. The above research indicates that functionalized graphene materials are expected to be used as drug carriers for controlled release and targeted control, and have good application prospects in fields such as biomedicine and biological diagnostics.
Scientific research institutions and universities represented by Shenyang Institute of Metals, Chinese Academy of Sciences, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Tsinghua University, Peking University, Fudan University, Zhejiang University, etc. have carried out a large number of basic research and application research and development on graphene, and a large number of related enterprises have emerged. In July 2013, the China Graphene Industry Technology Innovation Strategic Alliance was established. Jiangsu, Zhejiang, Shenzhen, Shanghai, Shandong, Fujian, Liaoning, Chongqing, Heilongjiang and the Chinese Academy of Sciences have established industrial technology alliances in various forms, and established four industrial innovation bases in Wuxi, Qingdao, Shenzhen and Ningbo. As of 2014, a total of 5047 patents have been applied for, of which composite materials account for 37%, preparation technology accounts for 29%, electronic devices account for 17%, and the battery field accounts for 17%.
At present, there are more than 50 enterprises in China engaged in graphene preparation and related application development, mainly focusing on large-scale preparation technology and downstream commercial application docking. They have initially mastered the international mainstream preparation methods, and their product indicators meet the needs of low-end applications. Representative companies engaged in the industrialization of graphene films include Changzhou 2D Carbon Technology Co., Ltd., Wuxi Gefei Electronic Film Technology Co., Ltd., Chongqing Moxi Technology Co., Ltd., etc. They mainly use natural gas as raw material and prepare products using chemical vapor deposition method, with thin films as the main product.
Graphene with different layers and shapes has different specific application fields, and the corresponding industrialization progress in each field is also different. Using natural gas as raw material, graphene films produced by chemical precipitation method were used to mass produce graphene touch screens with a size of about 14 cm, suitable for mobile phone screens. Jiangnan Design Institute has a production capacity of about 100000 pieces per year. In March 2015, Chongqing Moxi Technology Co., Ltd. released 30000 mass-produced graphene phones, but the cost was 1000 yuan more expensive than phones with the same performance, and the cost-effectiveness and market still need to be verified. Graphene nanosheets produced using natural graphite as raw material and chemical reduction method are mainly used in battery materials, functional coatings, conductive inks, and heat dissipation films. Due to the fact that most of the products are a mixture of few or multiple layers of graphene, although multiple hundred ton production lines have been built, there are problems such as small scale, low technical content, and low product added value, making it difficult to form effective economic impetus.
The development of graphene preparation and application levels are complementary, and composite materials, microelectronic materials, display screen film materials, and electronic components cannot be industrialized in a short period of time. The research and development entities are mainly universities and research institutions, with a focus on basic science rather than practical technology. The high-end production processes are not yet mature and cannot achieve low costs, while downstream application entities lack enthusiasm and are difficult to form large-scale industries.
From the perspective of development level, it is expected that the application of electronic products such as mobile phones will mainly need to overcome the difficulties of preparation technology, which is also a hot research direction. There will be breakthroughs in the next 1-2 years. Graphene composite materials and graphene energy products have certain requirements for the quality and application technology of graphene, and breakthroughs will be made within 3-5 years. The application of graphene in the field of electronic components has the highest quality and technical requirements, and it is also the most difficult to achieve. Industrial application is expected to take about 10 years. It is expected that by 2020, the global market value of graphene will reach over 1 trillion US dollars, with a compound annual growth rate of 44% from 2014 to 2020.
On October 30, 2015, the overall goal of the "Made in China 2025" key area technology roadmap (2015 version) was to "form a billion yuan industrial scale by 2020 and exceed 100 billion yuan in overall industrial scale by 2025".
Usually, the surface resistivity of polymer materials is greater than 1012 Ω· cm, and anti-static packaging materials require a surface resistivity of 107-1011 Ω· cm. Carbon black is usually used as an anti-static agent, with a filling mass fraction of up to 15%, which has a deteriorating effect on the mechanical properties and surface smoothness of plastic products. In addition, carbon black is prone to precipitate from the substrate, causing problems such as short circuits in electronic devices. Therefore, the industry has been trying to use nano carbon materials with higher conductivity (such as carbon nanotubes) as anti-static agents, and graphene anti-static plastic masterbatch can be used as a research and development direction.
With the improvement of national power transmission and distribution levels, especially the rapid development of electric vehicles, the stability of power grid currents has decreased, and the problems of heat release and partial discharge of peroxides in cables have become increasingly prominent. Graphene has good conductivity, thermal conductivity, and high specific surface area. It is recommended that research institutions focus on studying the addition ratio and uniform dispersion of graphene in cable shielding resins. Utilize R&D and production institutions to focus on solving processing and molding problems, quickly form patents, and promote their application in cable processing and production enterprises.
Vorbeck Materials, a company based in the United States, has developed a "Vor-x" graphene conductive additive by adding a mass fraction of 4% "Vor-x" graphene to rubber, achieving a conductivity of 0.3 S/m. Meanwhile, graphene has extremely high hardness, and adding an appropriate proportion of graphene to rubber can effectively improve tire wear resistance and reduce rolling resistance.
There are many applications of graphene as an additive in resins, such as polypropylene masterbatch/graphene, polypropylene sheet/graphene, ultra-high molecular weight polyethylene fiber/graphene, etc. The project leader of Nano Masterd in Europe stated that adding 5% graphene by mass can double the performance of thermoplastic polyolefins and polypropylene. Mixing 1% graphene with polymethyl methacrylate can increase the tensile modulus of the composite material by 80%. Graphene reinforced thermoplastic composite materials and color masterbatch can adapt to existing production, endowing new characteristics for mass production of parts through injection molding, extrusion, and blown film. Ovation Polymers in the United States has launched graphene thermoplastic masterbatch and composite masterbatch. In addition, Xiamen Kaina Graphene Technology Co., Ltd. has developed conductive graphene flakes, and adding graphene flakes with a mass fraction of 10% to polycarbonate can achieve conductivity level; Equivalent in performance to adding 10% superconducting carbon black (priced at over 200000 yuan/t). XG Science Corporation in the United States also provides conductive graphene nanosheets products.
China has made certain achievements in graphene mechanism and preparation technology, but its industrial layout is still in the research and development stage. With the deepening of application research, the theoretical basis for the combination and compatibility of graphene and polymer materials in composite materials continues to break through, improving and perfecting various performance indicators. The application fields are gradually expanding, and preliminary application research has shown excellent performance and unique advantages. Combining low-cost and high-quality production technology, it showcases rich imagination space for downstream industrial chains. Therefore, further in-depth application research should be carried out.
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