First, the characteristics of nano materials
Nano is a unit of length measurement, 1 nanometer is a billionth of a meter (10-9m). Nanomaterials refer to additives with particle sizes ranging from 1 to 100 nm. This particle size range is in the transition region between the cluster and the macroscopic object. It is a typical mesoscopic system. When the particle size of the material enters the nanometer range, it has special properties that are not found in ordinary particle sizes. This is because the size of the nanoparticles is equivalent to many characteristic lengths of the material, such as the electron Deblow wavelength, superconducting coherence length, ferromagnetic critical size, etc., resulting in the physical and chemical properties of the nanomaterial being different from the microstructure. Atoms, molecules, and objects of macrostructure are also in between.
(1) The combined effect of nanoparticles
The structure of a nanoparticle is an atomic group or a group of molecules composed of a small number of atoms or molecules. The surface atoms are amorphous layers with neither long-range order nor short-range order; while inside the particles, there are well-crystallized, periodically arranged atoms. It is this special type of structure of nanoparticles that leads to the following special properties.
1, volume effect
The volume effect is also known as the small size effect. When the size of the nanoparticles is as small as or smaller than the characteristic wavelengths such as the wavelength of the light wave, the wavelength of Deblow, the coherence length or the transmission depth of the superconducting, the periodic boundary conditions of the crystal will be destroyed, and the atoms near the surface amorphous are destroyed. The density is reduced, resulting in great changes in the acoustic, optical, electrical, magnetic, thermal, and catalytic properties of the material compared to ordinary materials.
2, surface effects
Surface effect, also known as interface effect, means that the ratio of the atomic to total atomic number of the nanoparticle increases sharply with the decrease of the particle size, and there are various defects in the same nanocrystal (such as twin boundaries, Stacking faults, dislocations, etc.), and even different metastable phases coexist, this special structure leads to a change in performance, and thus derives many special properties that traditional solids do not have.
3. Quantum tunneling effect
The ability of microscopic particles to have a penetrating barrier is called quantum tunneling. The magnetization of nanoparticles and the like also have quantum tunneling effects, which can be changed by the barrier of the macroscopic system. This is due to a decrease in particle size and a decrease in atoms within the particle.
(2) Characteristics of nanoparticles
The properties of nanoparticles can be analyzed in two ways: surface properties and intrinsic properties.
Many of the good properties of nanoparticles are related to surface properties such as low density, low flow rate, high adsorption, high mixing and weak compression properties. Physically speaking, it is due to its large specific surface area: many properties of nanoparticles are related to their large specific surface area. Due to their special surface structure, atomic surface layers are formed on the surface of nanoparticles, and the smaller the particles, the surface layer of atoms. The greater the thickness. The atomic surface layer is not a "gas-like" free structural layer, but a highly symmetrical, low-density, unstable structural layer associated with the particle size and preparation method. In terms of physicochemical properties, the surface energy is high, the adsorption is strong, and it is difficult to uniformly disperse. Especially for nanoparticles prepared by physical methods, mechanical energy can be easily converted into surface energy to cause aggregation between particles.
The intrinsic properties of nanoparticles are mainly manifested in the following aspects: increased reactivity, high catalytic performance, reduced melting point, increased electrical resistance, magnetic enhancement, strong light absorption, strong light emission, excellent photoelectric performance, hardness and plasticity. And high specific heat, high thermal expansion and high diffusivity.
Second, commonly used nano materials
In theory, any material can be a nano-material, and industrialized nano-materials are mostly chemical synthesis methods. Currently, only physical methods are graphene.
(1) Nano inorganic filler
1. Nanoclay
Clay is a general term for a class of silicate materials, including montmorillonite (MMT), attapulgite clay (TA), illite, sepiolite, hydromica and opal, among which montmorillonite is most commonly used.
(1) Montmorillonite (MMT)
Montmorillonite is a natural mineral material with a main component of SiO2 (content 72%) and (Al2O3 content 14%), which can be used for barrier modification of plastics. Montmorillonite has hydrophilic and oleophobic properties, and has poor compatibility with most resins. To form a good composite with resin, it should first be hydrophobically and oleophilic modified to improve compatibility with the resin. Sex. Utilizing the good intercalation properties of montmorillonite, the intercalation of long-chain organic compounds can be carried out, and the compatibility with various resins can be greatly improved, and various nano-plastic filler materials can be manufactured, and the tensile strength and bending strength of the composite materials can be improved. , flexural modulus and impact strength, which is the focus of current research on nanomaterials. At present, composite materials such as PA6/montmorillonite, PET/montmorillonite, PMMA/montmorillonite, PI/montmorillonite, EP/montmorillonite, PS/montmorillonite have been successfully developed.
(2) attapulgite clay (AT or ATP)
The attapulgite clay is a species of nanoclay and is a non-metallic mineral of hydrated magnesium aluminosilicate. The attapulgite is a crystal chain layer structure, but it is obviously different from the layered structure of montmorillonite. The attapulgite is a water-rich magnesium aluminosilicate with a natural fibrous crystal structure. The typical molecular formula is Si8Mg5O20. [Al](OH)2(OH2)4.4H2O. Since the nano-sized ingots are easy to aggregate, the mixing of the attapulgite with the polymer can only be a micron-scale mixing, which serves as an incremental filling. A large amount of silanol groups on the surface of the attapulgite are poorly compatible with the non-polar polymer, and are subjected to surface treatment before filling. At present, the application of attapulgite in plastics mainly focuses on PET and PA nucleating agents and thermal insulation materials.
(3) Illite
Illite is a clay mineral containing potassium aluminosilicate mica, also known as "water muscovite", and its chemical structure is KAl2[(Al,Si)Si3O10](OH)2.nH2O. The composition of illite is complex, and its specific composition varies within a certain range, so its application is limited.
Illite powder as a sheet-like reinforcing filler has both the effect of increment and modification. Taking the filling in PVC as an example, when the amount is about 3 parts, the tensile strength and the impact strength are all at a maximum, and the bending strength, the flexural modulus, and the heat distortion temperature are gradually increased before 10 parts. While reinforced and toughened, illite improves the dimensional stability, creep resistance, gas barrier properties, insulation and warpage resistance of plastics.
(4) sepiolite
Sepiolite is an aqueous magnesium silicate with a transitional structure of chain and layered fibers and belongs to a 2:1 chain structure clay. The structural formula is (Si12)(Mg8)O30(OH)4(OH2)4.8H2O, which is composed of a silicon oxytetrahedron and a magnesia octahedron. Sepiolite as a needle-like reinforcing filler has both the effect of increment and modification, which is similar to illite. Taking the filling in PVC as an example, when the amount is about 3 parts, the tensile strength and the impact strength reach the maximum value, the bending strength decreases, and the flexural modulus and the heat distortion temperature increase slowly before 10 parts, especially the bending. The modulus increases faster.
(5) Opal
Opal, also known as proteinaceous soil, is an aqueous, non-crystalline or colloidal active silica whose chemical composition is SiO2nH2O. The appearance of the opal is a dense glassy block. The color is white, gray and light blue porous, and the relative density is 2.07. It is a relatively light inorganic filler.
The opal is filled with polyethylene with obvious toughness modification. For example, the 3000 mesh opal treated by the titanate coupling agent is added to the HDPE by 30%, the tensile strength is substantially flat, and the impact strength is increased by 160%. The addition of ABS also significantly improves the impact strength.
2, nano zinc oxide
Nano-ZnO (ZnO) with a particle size between 1 and 100 nm is a new type of high-performance fine inorganic product for the 21st century. It exhibits many special properties such as non-migration, fluorescence, piezoelectricity, absorption and Scattering of ultraviolet light, etc., using its wonderful properties in light, electricity, magnetism, sensitivity, etc., can produce gas sensors, phosphors, varistors, image recording materials, piezoelectric materials, varistors, high-efficiency catalysts, magnetic materials and plastics. Film and the like. Nano zinc oxide can be used as an insulating and heat conductive material, and is used in combination with high-priced metal nitrides and carbides. Nano-zinc oxide is also a good antibacterial material, and the antibacterial efficiency can reach more than 98%. Nano zinc oxide is also a good UV shielding material.
3, hydroxyapatite
The hydroxyapatite (HA) composition is a calcium phosphate hydroxide compound having the formula Ca10(PO4)6(OH)2. Hydroxyapatite is the main component of vertebrate bones and teeth. The content of hydroxyapatite in human enamel is above 96%. Hydroxyapatite has excellent biocompatibility and is a major component of human bone tissue, and is widely used for bone tissue repair. When the plastic is used to produce the bone-like material, an appropriate amount of hydroxyapatite is added: the mechanical properties of the composite material can be improved to match the human bone; the physiological compatibility of the composite material with the human body can be improved, and even the human body can be organically combined.
4, aerogel
Aerogel is a solid material form. It is currently the world's smallest known man-made substance. Its solid relative density can be as low as 0.003. It is known as the "solid smoke". Aerogel is a new type of lightweight nano-multi-hollow solid material. It is considered to be the lightest and most insulative solid new material, and it is a transparent insulating material. In addition to excellent thermal insulation properties, it also has sound insulation and shock absorption properties, and has unmatched performance of other insulation materials for use in optical devices, super capacitors and other fields. The aerogel insulation contains three heat transfer mechanisms, namely heat radiation, heat convection and heat transfer, which are a wide range of insulation materials.
5, nano calcium carbonate
Nano-calcium carbonate is a kind of light calcium carbonate which is obtained by controlling the carbonization process conditions and adding a crystallizing agent during the process of producing light calcium carbonate carbonization. The use of different shapes of nanometer calcium carbonate is different. The needle-like and chain-like nano-calcium carbonate can achieve the purpose of reinforcement. The spherical nano-calcium carbonate can achieve the purpose of toughening. The hollow-core spherical nano-calcium carbonate can achieve the purpose of lightweight filling. Nano-calcium carbonate can improve the barrier properties of composite materials, and can also replace some titanium dioxide with its high hiding power.
6, nano-silica
Nano-silica is fumed silica, which is one of the most important high-tech ultra-fine inorganic new materials. Due to its small particle size, it has large specific surface area, strong surface adsorption, large surface energy, high chemical purity and dispersion. It has excellent performance and excellent performance in terms of thermal resistance and electrical resistance. With its superior stability, reinforcement, thickening and thixotropy, it has unique characteristics in many disciplines and fields and has an irreplaceable role. In plastics, silica is a reinforcing agent that is second only to carbon black. It is often used to form composite plastics with plastics. The addition amount is 3%~5%, and the performance of composite plastics can be improved. In particular, silica gel is filled with silica, which is a typical reinforced composite. In the PP/silica composite system, the impact strength can reach 3.7 kJ/m2. Micro-foaming with PP/silica composite material, the impact strength can reach 45.7kJ/m2.
(2) Nano carbon materials
1, graphene
Graphene is a new allotrope of carbon. The different isomers of various carbon materials that have been developed so far are shown in Table 1.
Table 1 Introduction of different carbon materials
Graphene is a new material of a single-layer sheet structure composed of carbon atoms. It is a planar film composed of a carbon atom and a sp2 hybrid orbital composed of a hexagonal honeycomb lattice, and has a two-dimensional material having a carbon atom thickness. The graphene produced by the conventional mechanical peeling method and the redox method is separated from graphite. At present, a variety of methods for producing graphene without using graphite as a raw material have been developed, mainly including mechanical stripping method, redox method, chemical vapor deposition method, solvent method, solution method, etc., and most of them have begun commercial production.
Based on its chemical structure, graphene has many unique physical and chemical properties, such as high specific surface area, high electrical conductivity, high thermal conductivity, high barrier properties, high thermal stability, high magnetic properties, high mechanical strength, excellent light transmission, and Easy to modify and mass production. At present, the biggest bottleneck restricting the application of graphene is dispersibility. For example, to improve its dispersibility in polymers, the following methods are often used: mixed addition, sheet/spheric composite mixing to facilitate dispersion; surface treatment (surface graft treatment, surface) Plasma treatment, surfactant treatment, surface silane coupling agent treatment); adding a compatibilizer, adding a functional functional group dielectric polymer material such as maleic anhydride, can effectively improve the compatibility with the resin.
At present, there are two pain points that restrict the development of graphene: one is the problem of dispersion, and currently only the problem of dispersion in liquid is basically solved, while the progress in solids is slow, only to see the laboratory report as mentioned above; the other is the price problem, currently graphite The price of olefins is very high and the application is unbearable in ordinary plastic modification.
2. Carbon nanotubes
The English name of carbon nanotubes is Carbon nantube, abbreviated as CNTs, which is a coaxial hollow tubular structural material formed by a large number of carbon atoms agglomerating under certain conditions. The radial size is nanometer and the axial dimension is micron. Although carbon nanotubes are also members of the allotrope in the carbon material family, they are excellent in mechanical, electrical, and chemical properties because they are a one-dimensional quantum material that is perfectly connected by a hexagonal structure. According to different structures, carbon nanotubes can be divided into two types: single-wall and multi-wall. Currently, single-walled carbon nanotubes are mainly used.
Table 2 Comparison of properties of different high strength materials
The carbon nanotubes are black odorless powder with a relative density of 2.1 and a melting point of 3652-3687 ° C. The main characteristics are as follows:
(1) High strength
Carbon nanotubes are an ideal one-dimensional model material with a large aspect ratio that gives them carbon fiber-like properties, namely high strength and high modulus. Its weight is 1/6 of steel, the strength is 100 times that of steel, and the specific strength is 600 times that of steel. See Table 2 for details.
(2) High conductivity
The P electrons of the carbon atoms on the carbon nanotubes form a wide range of delocalized π bonds. Since the conjugation effect is remarkable, the carbon nanotubes have good electrical properties, and their volume resistivity is 0.09 Ω·cm. The theory predicts that its electrical conductivity depends on its diameter and the helix angle of the tube wall. When the diameter of the CNTs is larger than 6 nm, the electrical conductivity is degraded; when the diameter is less than 6 nm, the CNTs can be regarded as a one-dimensional quantum wire having good electrical conductivity. It has been reported that Huang calculated that the carbon nanotubes with a diameter of 0.7 nm are superconducting, although the superconducting transition temperature is only 1.5×10-4K, which indicates the application prospect of carbon nanotubes in the field of superconductivity.
(3) High thermal conductivity
Carbon nanotubes have good heat transfer performance, and CNTs have a very large aspect ratio, so their heat exchange performance along the length direction is high, and the relative heat exchange performance in the vertical direction is low. Nanotubes can synthesize highly anisotropic heat conductive materials. In addition, the carbon nanotubes have a high thermal conductivity. As long as a small amount of carbon nanotubes are doped in the composite material, the thermal conductivity of the composite material may be greatly improved. See Table 3.
Table 3 Conductive and thermal conductivity of carbon nanotubes
(4) Other performance
Carbon nanotubes also have other good properties such as optics and hydrogen storage. It is these excellent properties that make carbon nanotubes considered to be ideal reinforcement materials for polymer composites, especially in hydrogen fuel cell vehicles.
For many years, carbon nano-development has not been solved due to the dispersibility of polymers. In recent years, the problem of dispersibility of carbon nanotubes has been solved, and the processing has dropped to a level of one hundred yuan per kilogram, making its application such as blowout breakthrough. For example, 4% carbon nanotubes (modified with PVDF surface) were added to PMMA by solution blending ultrasonic dispersion method, the electrical conductivity was 0.01 S/cm, the tensile strength was 80 MPa, and the impact strength was 24.2 kJ/m 2 .
Third, nano metal materials
In recent years, advanced nano silver and nano copper fibers have been developed, which are widely used in the manufacture of flexible transparent conductive polymer films and become an indispensable positive electrode material in OLEDs.
1, nano silver wire
The nanosilver wire is a metallic silver one-dimensional fiber having a diameter in the nanometer range (generally between 20 and 100 nanometers) and an unlimited length. The nano silver wire has a small volume, a large specific surface area, good chemical and catalytic properties, electrical conductivity, antibacterial property and physiological compatibility, as shown in Table 4. The production methods of nano silver wire include template assist, polyol, light wave radiation, soft chemical solvothermal, etc. The polyol method has become the current mainstream production method due to simple operation, high production efficiency and low cost, and the disadvantage is that the product concentration is low. For example, the nano silver wire can produce a transparent soft plastic conductive film, the specific structure is a PET film, the coating layer is a nano silver wire dispersion, and the surface layer is an acrylic protective coating. The substrate is a support layer, and the intermediate layer is a transparent conductive layer. The protective layer protects the silver from oxidation and reduces the conductivity, and mainly replaces the transparent conductive film of ITO and metal mesh.
Table 4 Comparison of performance of three transparent conductive films
2, nano copper wire
The dimensions are 150 ± 50 nm in diameter and 10 μm in length. With high electrical conductivity, friction reduction, transparent addition, wear resistance, etc., for transparent touch screen film, conductive and antistatic coatings, adhesives and inks, self-lubricating polymer reinforced composites.
Conclusion
With the rapid development of materials and physics, nanoparticle addition has become an excellent method for plastic modification. However, the development of plastics has a long way to go. It is necessary for industry colleagues to continue their efforts to enhance the performance of modified plastics by using nanoparticles. Plastics develop more new applications.
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