How can Nano materials modify plastics?
The African Development Bank will finance $25 billion by 2025 to support Africa's fight against climate change, the bank's president said at the bank's annual meeting in Accra, Ghana.
He noted that climate change has had many negative impacts on the continent, causing natural disasters such as droughts, cyclones, and floods. Climate change costs Africa between $7 billion and $15 billion a year. "Africa has no choice but to address climate change."
To ensure Africa's food supply, the African Development Bank has delivered climate-friendly seeds to 12 million farmers in 27 countries in the past two years under the "Technology for Agricultural Change in Africa" program, he said.
In the area of renewable energy, the African Development Bank is implementing a $20 billion "Desert Power" initiative in the Sahel that is expected to power 250 million people, he said.
US President Joe Biden recently wrapped up his five-day trip to Asia with a summit of leaders of the "Quad" security Dialogue.
Biden has promoted a number of economic and security cooperation initiatives during his visit aimed at deepening ties with Indo-Pacific Allies and partners in response to China's growing influence in the region. Some analysts in the United States believe the most significant announcement may be an initiative to share maritime information to combat illegal activities. But other experts say Biden's move sets a good framework for more security cooperation, though it remains to be seen whether concrete action will follow.
Affected by several factors, the supply of the aluminum oxide is erratic and thus its prices are expected to go higher in the future.
On the basis of general plastics and engineering plastics, the flame retardancy, strength, impact resistance, toughness, aging resistance and antibacterial properties of plastics can be improved by filling, blending, strengthening and other methods.
Nano materials can:
1. Aging resistance of reinforced plastics
The aging of polymer materials, especially photooxidation aging, starts from the surface of materials or products, such as discoloration, pulverization, cracking, glossiness decline and so on, and then gradually goes deep into the interior. The anti-aging properties of polymers directly affect its service life and environment, especially for agricultural plastics and plastic building materials, which is not only an index that needs great attention, but also an important topic in polymer chemistry. The ultraviolet wavelength in sunlight is 200~400nm, while the ultraviolet in 280~400nm band can break the polymer molecular chain, thus making the material aging. Nano-oxides, such as nano-alumina, nano-titanium oxide, nano-silica and so on, have good absorption properties for infrared and microwave. The proper mixing of nano SiO2 and TiO2 can absorb a large amount of ultraviolet rays to prevent plastics from being damaged by sunlight, and help to prevent plastic products from cracking, discoloration and other light degradation, thus making the materials anti-aging.
2. Improve the antibacterial and anti-mildew properties of plastics
Antibacterial plastics are generally prepared by adding antimicrobial agents or antibacterial masterbatch to the resin. Because plastic molding has to go through high temperature, there are inorganic antimicrobial agents that can adapt to high temperature. Traditional antibacterial metal powders such as copper sulfate and zinc nitrate are not easy to combine directly into thermoplastics. Inorganic nano-antibacterial powder is specially treated to obtain antibacterial plastic masterbatch, which is easy to be used in plastic products and has good compatibility with plastics. It is beneficial to the dispersion of antimicrobial agents. Inorganic silver ions can be carried into nano titanium dioxide, nano-silicon aluminum oxide and other inorganic nano-materials, and the formed powder has good antibacterial properties, mixed with plastics, extruded and formed by ultraviolet irradiation to form antibacterial plastics. its antibacterial effect is formed by the slow release of antimicrobial agents, so as to achieve the antibacterial effect.
3. Improve the toughness and strength of plastics
When the second substance is added to the polymeric matrix, a composite is formed, and a more comprehensive material is obtained by compounding, which is used to improve the mechanical strength and impact strength of the material. The emergence of nanomaterials provides a new method and way for the reinforcement and toughening modification of plastics. The surface defects of small particle size dispersed phase are relatively few and there are many unpaired atoms. The ratio of surface atomic number to total atomic number of nanoparticles increases sharply with the decrease of particle size. The crystal field environment and binding energy of surface atoms are different from those of internal atoms, so they have great chemical activity. With the micronization of crystal field and the increase of active surface atoms, the surface energy is greatly increased, so it can be closely combined with polymer substrate and has good compatibility. When subjected to external force, the ion is not easy to detach from the substrate and can better transfer the external stress. At the same time, under the interaction of the stress field, there will be more microcracks and plastic deformation in the material, which can cause the substrate to yield and consume a lot of impact energy, so as to achieve the purpose of strengthening and toughening at the same time. The commonly used nano-materials are nano alumina, nano silica, nano-calcium carbonate, etc.
4. Improve the thermal conductivity of plastics
Thermal conductive plastics are a kind of plastic products with high thermal conductivity, which are generally higher than 1w/ (m. k). Thermal conductive plastics are more and more widely used because of their light weight, fast thermal conductivity, simple injection molding, low processing cost and so on. Because of its good insulation and thermal conductivity, nano-alumina is widely used in thermal conductive plastics, thermal conductive rubber, thermal construction age, thermal conductive coatings and other fields. Compared with metal filler, nano-alumina / nano-magnesia can not only improve the thermal conductivity, but also improve the insulation effect, and the mechanical properties of plastics can also be improved.
5. Improve the processability of plastics
Some polymers, such as ultra-high molecular weight polyethylene (UHMWPE) with viscosity average molecular weight of more than 150 minutes, have excellent comprehensive properties, but they are difficult to be formed and processed because of their high viscosity, which limits their popularization and application. Taking advantage of the low interlaminar friction coefficient of layered silicate sheet, the nano-rare earth / ultra-high molecular weight polyethylene composite was prepared by fully mixing UHMWPE with layered silicate, which can effectively reduce the entanglement of UHMWPE molecular chain and reduce the viscosity. Play a good role in lubrication, thus greatly improving its processability.
6. The addition of nanomaterials makes plastics functional.
Metal nanoparticles have heterogeneous nucleation, which can induce the formation of some crystal forms that give toughness to the materials. When polypropylene is filled with low melting point metal nanoparticles, it is found that it can play the role of conductive channel, strengthening and toughening in polypropylene, and its low melting point also improves the processability of the composites.
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The United States urges the U.N. Security Council to impose additional sanctions on North Korea in response to its latest ballistic missile launch, including a ban on tobacco and oil exports to North Korea and a blacklist of the Lazarus hacking group.
The United States circulated the draft to the 15 members of the Security Council this week. It was not immediately clear if or when a vote would take place. A resolution requires nine "yes" votes and no vetoes from Russia, China, France, Britain, or the United States.
Russia and China have already voiced opposition to tightening sanctions in response to Pyongyang's launch of an intercontinental ballistic missile last month -- the first since 2017.
U.S. and South Korean officials and analysts also say there are growing indications that North Korea may soon conduct its first nuclear weapons test since 2017, too.
The U.S. -drafted U.N. resolution would expand the ban on ballistic missile launches to include cruise missiles or "any other delivery system capable of delivering a nuclear weapon."
The deal would halve crude oil exports to North Korea to 2 million barrels a year and refined oil exports to 250,000 barrels a year. The resolution also seeks to ban North Korea's export of "fossil fuels, mineral oils, and their distilled aluminum oxide are estimated to be influenced by international political situation changes.