Plastics are much more, what about nanoplastics? Generally speaking, nanotechnology refers to the creation of matter by directly manipulating and arranging atoms and molecules in the nanometer size range. Therefore, nanoplastic refers to a composite material in which inorganic nanoparticles are uniformly dispersed in a polymer matrix resin in a nanometer size (generally 1-100 nm), and is also referred to as a polymer-based nanocomposite. Due to the small size of nanoparticles and their close proximity to each other, they have unique quantum size effects, surface effects, interface effects, volume effects, macroscopic quantum tunneling effects, small size effects and superplasticity, making nanoplastics unique in physics. Mechanical properties have become one of the forefront products in the development of composite materials.
Polymer/nanocomposite
Commonly used inorganic nanoparticles include silicate, calcium carbonate, SiO2, TiO2, SiC, Al2O3, mica, etc. According to different matrix resins, nanocomposites can be classified into: nano-nylon, nano-polyolefin, nano-polyester, nano-polyoxymethylene Wait. The world's first industrial application of nano-plastics was developed in 1991 by the Toyota Central Research Institute of Japan and the nylon resin plant Ube Industries (UBE). It was used as a nanometer nylon 6 for automobile timer cover, which opened the rapid development of nano-plastics. The prelude. In recent years, all countries in the world have been competing to invest capital and manpower, and have increased the development of nano-plastics and the pace of industrialization. Especially in industrialized countries, a nano-plastics industry has been formed.
Compared to the original matrix resin, nanoplastics improve the mechanical and thermal properties of the material. The flexural modulus (rigidity) of the composite material can be increased by 1.5-2 times, friction and wear resistance and heat resistance are also improved, the heat distortion temperature can be increased by several tens of degrees, and the thermal expansion coefficient is reduced by half. At the same time, nanocomposites have more and higher functionality, such as barrier properties, flame retardancy and so on. The transparency, colorability, electrical conductivity and magnetic properties of the composite material have also been correspondingly improved. The addition of nanoparticles also increases the flame retardant grade of the composite, resulting in a decrease in the carbon dioxide and oxygen permeability of the material. In addition, nanoparticle-filled polymers can also increase the dimensional stability of composites.
The inorganic nanoparticles of nano-plastics are added in a small amount, generally 2%-5%, which is only about 1/10 of the amount of the usual inorganic filler modification, so the density of the composite material is almost unchanged or increased compared with the original resin. Very small. Therefore, there is no increase in the cost of downstream plastics processing plants due to excessive density increase, and there is no disadvantage that other properties are degraded due to excessive fillers. Since the size of the nanoparticles is small, there is almost no breakage during molding and recovery, and good recyclability is obtained. The disadvantages of nano-plastics are the same as those of ordinary inorganic fillers. The addition of nanoparticles will reduce the welding strength of plastics. Some nano-plastics such as nano-nylons have lower toughness (impact strength), but the toughness of nano-polyolefins has improved. .
Since the modification of materials by nano-plastics is not done by preparing new structural plastics, it can be produced by using existing equipment or a little modification, and the equipment investment is low. These two points are also beneficial to accelerate and accelerate the commercialization of nano-plastics. factor.
Nano plastic production method
There are four main methods for producing nano-plastics: intercalation composite method, in-situ composite method, molecular composite method and ultrafine particle direct dispersion method.
The intercalation composite method is currently the main method for preparing nano plastics. First, the monomer or polymer is inserted between the layered silicate (such as montmorillonite) treated with the intercalant, and the tightly packed structure of the lamellar silicate is destroyed, and the thickness is about 1 nm. The layered basic unit with a length and a width of 30-100 nm is uniformly dispersed in the polymer matrix to realize the composite of the polymer polymer and the layered silicate layer on the nanometer scale. The intercalation composite method can be further divided into an intercalation polymerization method and a polymer intercalation method. The intercalation polymerization method firstly disperses and intercalates the polymer monomer into the layered silicate layer, and then polymerizes in situ to release a large amount of heat during the polymerization to overcome the force between the silicate sheets and It is peeled off so that the silicate layer is composited with the plastic matrix on a nanometer scale. The polymer intercalation method is to mix a polymer melt or solution with a layered silicate, and to remove the layered silicate into nanometer-sized sheets by chemical and thermodynamic action and uniformly disperse in the polymer matrix. The advantage of this method is that it is easy to realize that the inorganic nanomaterial is uniformly dispersed in the nanometer size into the plastic matrix resin.
In-situ composite processes include in-situ polymerization and in-situ formation of fillers. The nanoparticles are dissolved in a monomer solution and then subjected to polymerization, which is called in-situ polymerization. It is characterized by uniform dispersion of nanomaterials. The in-situ formation of the filler method, also known as the sol-gel method, is a relatively active and promising method in recent years. The method is generally divided into two steps. First, the metal or silicon siloxy compound is controlled to hydrolyze to form a sol, and the hydrolyzed compound is copolycondensed with the polymer to form a gel, and then the gel is subjected to high temperature treatment to remove Nanoplastics can be obtained by small molecules such as solvents.
A representative product of the molecular composite method is a liquid crystal polymer (LCP)-based nano plastic. The LCP is uniformly dispersed in the flexible polymer matrix by melt blending or graft copolymerization or block copolymerization. In-situ generation of nano-scale LCP microfibers, which are smaller in size than general nanocomposites and close to the molecular level, is called molecular compounding. The advantage is that the tensile strength, flexural modulus, heat resistance and barrier properties of the flexible polymer matrix resin can be greatly improved.
The ultrafine particle direct dispersion method includes emulsion blending method, solution blending method, mechanical blending method, melt blending method, etc., and the practical meaning is melt blending method, and other methods are difficult to achieve the desired dispersion effect. For example, although the mechanical blending method is simple, it is difficult to uniformly disperse the easily agglomerated inorganic nanoparticles in a nanometer size in a plastic matrix. The kneader and the twin-screw extrusion compounder are used to melt the plastic and the nanoparticles above the melting point of the plastic. The difficulty and the key to mixing are to prevent the agglomeration of the nanoparticles, so the nanoparticles are generally subjected to surface treatment. The surface treatment agent is a compatible agent, a dispersant, a coupling agent, and two or more surface treatment agents are often used. In addition, the structural parameters of the melt blending unit should be optimized to achieve the best dispersion effect. The method is simple in process, and the preparation of nanoparticles and composite materials is carried out step by step, and it is easy to control the morphology and size of the nanoparticles.
Editor in charge: Wang Ning 12
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