Coupling agent is a widely used additive in industrial fields such as plastics, rubber, and coatings, mainly used to improve the interfacial properties between inorganic and organic substances and enhance the overall performance of composite materials. The following is a detailed introduction about coupling agents:
1、 Definition and Structure
Coupling agent is a type of organic silicon compound with a special structure, which contains two groups with different chemical properties in its molecule: one group that is hydrophilic to inorganic substances and can react chemically with the surface of inorganic substances (such as glass, cement, metals, etc.); Another organic group that can react chemically or form hydrogen bonds with synthetic resins or other polymers and dissolve in them. Therefore, coupling agents are vividly referred to as "molecular bridges", used to improve the interfacial interaction between inorganic and organic substances.
2、 Classification
According to the chemical structure and composition of coupling agents, they can be divided into the following categories:
Silane coupling agent: The general formula is RSiX3 (where R represents organic functional groups such as amino and thiol groups, and X is a group that is easily hydrolyzed, such as alkoxy and aryloxy groups), mainly used to improve the interfacial properties between inorganic fillers and synthetic resins.
Titanium ester coupling agent: has similar functions to silane coupling agent, but has different chemical structures and reaction mechanisms.
Aluminum ester coupling agent: suitable for coupling aluminum and its alloy surfaces with organic polymer materials.
Chromium complex coupling agent: developed in the early 1950s, a metal chromium complex formed by unsaturated organic acids and trivalent chromium ions.
Other coupling agents: including bimetallic coupling agents, phosphate coupling agents, borate coupling agents, etc.
3、 Mechanism of action
The mechanism of action of coupling agents mainly includes the following aspects:
Coupling modification: Chemical coupling reactions occur on the surface of particles, resulting in good compatibility between the particle surface and organic compounds.
Improving dispersibility: Coupling agents can improve the dispersibility of inorganic fillers in synthetic resins and avoid agglomeration.
Enhancing adhesion: Coupling agents can enhance the adhesive strength between inorganic fillers and synthetic resins, improving the overall performance of composite materials.
4、 Application Fields
Coupling agents are widely used in the following fields:
Rubber industry: Improve the wear resistance and aging resistance of products such as tires, rubber sheets, rubber hoses, and rubber shoes.
Plastic industry: Improve the interfacial properties between synthetic resins and inorganic fillers or reinforcing materials, enhance the surface quality and mechanical, thermal, and electrical properties of plastic products.
Coating industry: Enhance the adhesion between coatings and substrates, and improve the durability of coatings.
In the fields of glass, ceramics, metal anti-corrosion, etc.: improve the wettability and reactivity of inorganic material surfaces, enhance the adhesion and corrosion resistance of coatings.
5、 Dosage and selection
The amount of coupling agent is generally 0.5-2% of the amount of filler, and the specific amount needs to be adjusted according to product requirements, raw material properties, processing conditions, and other factors. When selecting coupling agents, factors such as their chemical structure, reactivity, stability, and compatibility with raw materials should be fully considered.
In summary, coupling agents, as an important industrial additive, play a crucial role in improving the performance of composite materials and enhancing the interfacial interaction between inorganic and organic substances. With the continuous advancement of technology and the development of industry, the application fields of coupling agents will be further expanded, and their varieties and properties will also be continuously improved.
