The following is a table of major national aluminum ingot standard grades
In recent years, major fires caused by the ignition of polymer materials have been on the rise, and the flame retardancy of polymer materials has attracted more and more attention. However, at present, most flame-retardant polymers are mainly achieved by adding halogen-containing flame retardants, which will produce a large amount of smoke and toxic, harmful and corrosive gases when burning, causing "secondary disasters". Therefore, the study of low-smoke and halogen-free flame retardancy of polymer materials is of great significance for reducing the occurrence of fires and reducing the loss of life and property caused by fires. Among them, the use of clean and efficient inorganic flame retardants is an important way to improve the flame retardant properties of materials.
Sb2O3 is an additive flame retardant, mainly used for flame retardancy of plastic products (polyvinyl chloride, polyolefin, polyester) and textile fabrics. It can also be used as a flame retardant for canvas, paper, paint, coatings, etc. and a catalyst for petrochemicals, synthetic fibers, etc. It can also be used as a flame retardant for rubber and art materials, a covering agent for the enamel industry, and electronic industrial materials. As a flame retardant additive, Sb2O3 has a great influence on the performance and flame retardant effect of synthetic materials due to its particle size and morphology. Particle size is an important indicator of Sb2O3 products. Flame retardant treatment of synthetic chemical fibers and textile products often requires that the particle size of Sb2O3 is in the nanometer range. The finer the particle size, the less Sb2O3 is used to achieve the same flame retardant effect, and it will not block the spinneret hole, which is the key to flame retardant of textiles. However, the inorganic flame retardant particles currently used are generally above the micron level, with a large amount of flame retardant filling and low flame retardant efficiency, which causes serious problems in processing technology and product performance. Nano flame retardants are blocks, films, multilayer films and fibers formed by the agglomeration of ultrafine flame retardant particles with a particle size of 1-100nm. By ultra-finely transforming traditional inorganic flame retardant materials, using the quantum size effect, small size effect and surface effect of nanoparticles themselves to enhance the interface effect, improve the compatibility of inorganic substances and polymer matrices, and achieve the purpose of reducing dosage and improving flame retardancy. The application of nanotechnology in traditional flame retardant materials has opened up a new field for flame retardant technology. Nano inorganic flame retardant composite materials provide a new way to develop flame retardant polymer materials. Its emergence will lead to a historic change in the inorganic flame retardant industry.
1. Synthesis method of nano inorganic flame retardant
The currently developed nano inorganic flame retardants include: nano antimony trioxide flame retardant, nano aluminum hydroxide flame retardant, nano magnesium hydroxide flame retardant, nano layered double hydroxide flame retardant, nano antimony pentoxide flame retardant, nano calcium carbonate, nano titanium dioxide, nano zinc oxide, etc. However, nano calcium carbonate, nano titanium dioxide, nano zinc oxide, etc. have low flame retardant properties and are generally only used as fillers. Nano antimony pentoxide flame retardant is less used, mainly ultra-fine antimony trioxide, nano aluminum hydroxide, nano magnesium hydroxide and nano layered compounds.
1. Nano antimony trioxide
The particles of nano Sb2O3 are mostly oblong rectangular bodies, which can produce synergistic effects when used with other flame retardants and smoke suppressants. Its synthesis methods are as follows: (1) Precipitation method: SbCl3 powder crystals are precipitated in concentrated hydrochloric acid to form nanoparticles; (2) Low-pressure evaporation: Sb2O3 powder is placed in a sealed heating container and compacted, and then evacuated to maintain the vacuum degree at 30Pa and the temperature is raised to 610-630 ℃ to obtain Sb2O3 ultrafine powder. This method is used to synthesize nano antimony trioxide with a particle size of 43.3nm; (3) Pyrometallurgical production process: refined antimony is melted into antimony liquid under high temperature conditions. The antimony liquid comes into contact with oxygen in the air, and antimony is oxidized to Sb2O3 and volatilizes. By controlling the crystallization and cooling conditions, Sb2O3 white powder of different particle sizes can be obtained. This method can be used to synthesize nanoparticles with controllable particle size; (4) Arc method Arc discharge is generated by electric energy between antimony metal electrode and carbon electrode, Sb2O3 vapor can be generated at high temperature, and then the vapor is condensed into fine particles, and then captured to obtain colloidal fine powder below 0.01um, but it is difficult to synthesize nano-scale products by this method; (5) The plasma method uses antimony ore to react in a high-frequency plasma reactor, which can effectively inhibit the formation of metal oxides such as lead, and can also make the gasified antimony trioxide excited and ionized by plasma, thereby forming a large number of active groups, reducing the content of high-valent antimony, and thus obtaining high-purity Sb2O3; co-precipitation method can also be used to generate nano Sb2O3-SiO2 composite flame retardant.
2. Application of nano inorganic flame retardants
Nano inorganic flame retardant composite materials refer to materials in which one or more inorganic flame retardant components are uniformly dispersed in the matrix of another component at the nanometer size or molecular level. Due to their ultra-fine size, the properties of various types of nano inorganic flame retardant composite materials are greatly improved compared with their corresponding macroscopic or micrometer-level composite materials. Compared with the original parent polymer, the performance of nano inorganic flame retardant composite materials has been improved and enhanced in the following aspects: First, the mechanical and thermal properties are improved, the bending modulus (rigidity) is increased by 1.5-2 times, the friction and wear resistance are improved, the heat resistance is greatly improved, the heat deformation temperature is increased by dozens of degrees, and the thermal expansion coefficient is reduced to half of the original; second, the composite material is given functionality, so that the material has barrier and flame retardancy, and the transparency, pigment coloring, conductivity and magnetic properties of the material are improved; in addition, the dimensional stability of the material can be improved. In particular, polymer/flame retardant nanomaterials will become a new generation of flame retardant polymer materials. Nano flame retardant polymers combine the advantages of good flexibility, low density, and easy processing of organic polymers with the strength and hardness of inorganic fillers, high heat resistance, and non-deformation, showing strong vitality. The main preparation methods are: direct dispersion of ultrafine particles, including emulsion blending, solution blending, mechanical blending, melt blending, etc.; molecular composite method; "template" synthesis method; intercalation composite method, including monomer embedding polymerization, polymer solution embedding and polymer direct melt embedding; in-situ composite method, including in-situ polymerization and in-situ filler formation. At present, the synthesized nanocomposite flame retardant materials are mainly the following.
1. Polymer/antimony trioxide nanocomposite
Mix polyethylene resin, flame retardant and other raw materials according to the ratio (90 parts of flame retardant LDPE, 12 parts of decabromodiphenyl ether, 6 parts of nano Sb2O3), and process them at the corresponding processing temperature to obtain nano Sb2O3/PE flame retardant polymer with an oxygen index of 24.1. Adding 5% nano-Sb2O3 to ABS plastic can produce Sb2O3/ABS nano flame retardant polymer with an oxygen index of 19.3; adding 10% nano-Sb2O3 can produce Sb2O3/ABS nano flame retardant polymer with an oxygen index of 20.9. Mixing 90 parts of flame retardant ABS resin, 10 parts of decabromodiphenyl ether, and 5 parts of nano-Sb2O3, and processing them at the corresponding processing temperature, can produce Sb2O3/ABS nano flame retardant polymer with an oxygen index of 25.5. Cunnionl et al. used nano-antimony trioxide to flame retardant acrylonitrile-butadiene-styrene copolymer (ABS). The impact strength of the obtained material does not change, and the small-sized nanoparticles have a very small refractive index, and light propagation is almost unaffected. Mix 100 parts of PVC, 50 parts of DOP, 8 parts of chlorinated paraffin, 1.2 parts of lead stearate, 1.5 parts of barium stearate, 3 parts of nano Sb2O3 flame retardant and other raw materials according to the ratio to obtain nano Sb2O3/PVC flame retardant polymer with an oxygen index of 30. In addition, Sb2O3 can have a good synergistic flame retardant effect with ZnO, TiO2, etc.
2. Polymer/aluminum hydroxide nanocomposite materials
Generally speaking, since the effective use temperature range of aluminum hydroxide is relatively low, it is suitable for resins with low processing temperatures, such as PP, PVC, polyurethane soft foam, epoxy resin, unsaturated polyester, acrylic resin, etc. In 2001, the application effect of aluminum hydroxide composite flame retardant on PVC cable materials discussed the influence of flame retardant content on the flame retardant and mechanical properties of the material, and pointed out that by adding aluminum hydroxide flame retardant, its flame retardant properties can reach the V-0 level of flame retardant materials, and its mechanical properties are basically not reduced. But so far, the use of ultrafine aluminum hydroxide to flame retard EPDM can make the OI value of the system reach more than 38, and the mechanical properties are improved. The single-component precipitation method, alcohol salt hydrolysis method and co-precipitation method can be used to prepare the synergistic flame retardant of nano Sb2O3-Al(OH)3 composite flame retardant. Sb2O3 and Al(OH)3 can complement each other: the advantage of Sb2O3 is that it has a small amount and little effect on the physical and mechanical properties of the resin itself, but it will produce black smoke when burning and is relatively expensive; Al(OH)3 has the advantages of not producing corrosive gases, low smoke production, and relatively cheap prices. Its disadvantage is that the amount added is large, which has a greater impact on the mechanical properties of the product. However, they both have a flame retardant effect in the gas phase and the solid phase, so the two have a real synergistic effect.
