The secret of making inorganic filler closer to polymer matrix~
It is widely seen in industry that such application scenarios can add / fill inorganic powder materials into organic material matrix, or reduce costs, or enhance the original "constitution" of organic materials, or give organic materials new skills
1 example of packing application scenario
For example, alumina and boron nitride can be used as plastic fillers to make plastics have good thermal conductivity and electrical insulation at the same time; talcum powder can be used as plastic fillers to improve the electrical insulation, acid resistance and fire resistance of plastic products; mica can be used as plastic reinforcement fillers to improve the bending modulus and tensile modulus of elasticity of plastic products; kaolin has excellent electrical insulation It can be used as the coating of PVC and other polyolefin insulated wires with certain flame retardancy; quartz has a high reinforcing effect on thermoplastic resin and thermosetting resin, and can improve the rigidity and hardness of products, and also can play a certain role in improving the electrical insulation of plastic products; rutile titanium dioxide, as a plastic filler, can increase the reflectivity of light and play a role of light shielding agent Red mud and fly ash are plastic fillers, which can not only eliminate pollution, but also reduce the cost of plastic products
The application of fillers makes wires and cables safer and more reliable
2. The consequence of poor compatibility is very serious
However, inorganic powder materials are generally polar or highly polar hydrophilic minerals, which have poor compatibility with the organic polymer matrix with non-polar hydrophobic surface. If the two materials are mixed directly, the interface between the matrix and the filler is easy to break away and form a ring gap or gap in the subsequent molding process because the cooling shrinkage of the matrix is greater than that of the inorganic filler. As a result, inorganic fillers not only have no reinforcement effect, but also have poor mechanical properties due to the formation of micropores inside the materials. The interface strength between the filler and the base material can be enhanced by proper surface treatment of the filler, and the greatest advantage of the composite material can be exerted. There are many kinds of surface treatment agents, such as coupling agents, surfactants, organic polymers, etc. in this paper, we will briefly introduce the most used coupling agents in the filling system.
What are the common types of coupling agents? Coupling agent is a kind of substance with amphoteric structure. One part of its molecular groups can react with the chemical groups on the surface of inorganic materials to form chemical bond; the other part of the group has the property of being organic friendly, which can react with organic molecules or produce strong interaction between molecules, so that two materials with different properties can be firmly combined. Because most of the coupling agents can have chemical effect on the surface treatment of fillers, the effect is very good, which can effectively improve the dispersion state of inorganic fillers in the polymer matrix, improve the mechanical properties and service properties of the filled polymer materials.
Coupling agent can be divided into silane coupling agent, titanate coupling agent, aluminate coupling agent, zirconate ester coupling agent, bimetal coupling agent (aluminum zirconate ester, aluminum titanium composite coupling agent), rare earth coupling agent, phosphorus coupling agent, boron coupling agent, etc. Among them, silane coupling agent is the first coupling agent researched and applied by people. Titanate coupling agent first appeared at the end of the 20th century. It has good coupling effect on many dry powders. The coupling agent often used in production and its application will be briefly introduced in the following.
1. Silane coupling agent
Silane coupling agent is so called because its central atom is silicon (SI). Its molecular structure is: r-si-x3, where R is a hydrophobic group, such as vinyl, epoxy, amino, methacrylate, sulfuric acid group, etc.; X is a hydrolyzable inorganic group, such as alkoxy, methoxy, ethoxy, chlorine, etc. The amount of filler is about 1%.
Filler. Silane coupling agent can be used in many inorganic fillers, among them, in the glass fiber with more silicic acid components; quartz powder is the best for spreading black seeds, followed by clay and hydrated alumina, and not good for calcium carbonate without free water.
Matrix. For example, amino group can react with epoxy resin, phenolic resin, nylon, vinyl polymer or some thermosetting elastomers. However, most silane coupling agents have many reaction groups in the structure, more reaction points with the surface of the filler, and less carbon atoms and short chains in the organic hydrophobic group at the other end, so they are thermoplastic In the filling plastics with plastics as matrix resin, the use of silane coupling agent often brings adverse effects on the processing flow performance of the filling system. In addition, silane coupling agent is much more expensive than other coupling agents, so the amount of silane coupling agent in polyethylene is not much, and it is mainly used in thermosetting plastics such as epoxy or unsaturated polyester.
2. Titanate coupling agent
According to the different structure of titanate coupling agent, it can be roughly divided into four types: monoalkoxy type, monoalkoxypyrophosphate type, integrated type and coordination type. The amount of titanate is usually 0.5% of the amount of filler.
Matrix. Titanate coupling agent has a wide range of applications, and has good coupling effect in the filler systems of thermoplastic, thermosetting plastic and rubber.
Filler. Titanate coupling agent can be used to deal with various inorganic fillers, such as calcium carbonate, talc, barium sulfate and aluminum hydroxide.
3. Aluminate coupling agent
Aluminate coupling agent has the characteristics of light color, non-toxic and convenient application. Its thermal stability is better than that of titanate coupling agent, and its price is only half of that of titanate coupling agent. Aluminate coupling agent, like titanate coupling agent, is beneficial to increase the filling amount of the system. It can effectively reduce the viscosity of the filling system and improve the processing performance of the resin.
Generally, the dosage of aluminate coupling agent is 0.3 ~ 1.0% of the filler mass used in the filling system. For the injection or extrusion of polyethylene hard products, the dosage is about 1.0% of the filler. For other process products, soft products and foaming products, 0.3-0.5% of the filler is used. 1.0% - 1.3% can be used for fillers with high specific surface, such as aluminum hydroxide, magnesium hydroxide, white carbon black, etc.
4. Other coupling agents
Zirconium coupling agent. This kind of coupling agent can not only promote the combination of inorganic and organic matters, but also improve the performance of the filler system. Its characteristics are that it can significantly reduce the viscosity of the filler system, inhibit the interaction between filler particles, so as to improve the dispersion of filler in the system and increase the filling amount. It has good modification effect on the filling system of calcium carbonate, silica, alumina, titanium oxide and ceramsite. It is mainly used in polyolefin, polyester, epoxy resin, synthetic rubber and other different polymer filling systems.
Organic chromium coupling agent. It is a kind of mature coupling agent. It is a kind of valence metal complex formed by unsaturated organic acid and trivalent chromium atom. It has a good application effect in glass fiber reinforced plastics. The use cost of organic chromium coupling agent is low, but the variety is monotonous, the use range and coupling effect are not as good as that of silane coupling agent and titanate coupling agent, and the more important heavy chromium ion (heavy element with significant biological toxicity) toxicity will bring environmental pollution, so the amount of it is decreasing.
5. Compound coupling agent
Aluminum titanium composite coupling agent. Aluminum replaced some of the central atoms of the coupling agent, which reduced the content of titanium with high coupling agent price and reduced the cost. It has the characteristics of titanium and aluminum coupling agents, and the coupling effect is better than single titanate, aluminate and their simple mixture.
Aluminate coupling agent. This kind of coupling agent is the oligomer of organic complex containing aluminum and zirconium elements. Aluminum zirconate lipid coupling agent has the characteristics of low price (about half of silane coupling agent), good application effect (good hydrolysis stability), good thermal stability (heat resistance to 300 ℃).
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