Background and overview[1][2]
Coupling agents are also called surface treatment agents. A substance that promotes or establishes a stronger bond at the interface between the resin matrix and the reinforcing material. According to the chemical composition, there are three main categories: chromium complex, silane, and titanate. There are reactive functional groups with different properties at both ends of its molecules, which can be combined with the surface of synthetic resins and reinforced materials respectively to form “bridge bonds” through physical or chemical effects, so that the resin and fibers can be firmly combined into a whole, improving the strength and weather resistance of composite materials. , water resistance, chemical resistance and electrical properties, etc. Different coupling agents should be used for different resins. Coupling agents are a type of additive that can improve the interface properties between polymer materials and fillers.
There are two groups with different properties in its molecular structure. One group can react chemically with polymer materials or have good compatibility, and the other group can form chemical bonds with inorganic materials or fillers. It can improve the interfacial adhesion of two materials and significantly improve the performance of filled or reinforced polymer materials. Varieties include silane coupling agents such as trichlorovinylsilane, triethoxyvinylsilane, γ-aminopropyltriethoxysilane, trichloropropenylsilane, etc., titanate coupling agents such as tetrabutyl titanate , isopropyl triisostearyl titanate, isopropyl triisostearyl titanate, ethyl diisostearyl titanate, etc., organic chromium coupling agents such as methacryloyl chromium complex, zirconium aluminate coupling agents and polymer coupling agents, etc.
Mainly used in polymer reinforced materials as reinforcing agent and surface treatment for glass fiber. Silane coupling agents are also used for cross-linking polyolefins and directly for plastic and rubber blend modification or tackification.
Category[3][5]
There are many types of coupling agents, mainly including silane coupling agents, titanate coupling agents, aluminate coupling agents, bimetal coupling agents, phosphate coupling agents, borate coupling agents, Coupling agents for chromium complexes and other high-grade fatty acids, alcohols, and esters. Currently, the most widely used are silane coupling agents and titanate coupling agents.
1. Silane coupling agent: Silane coupling agent is the earliest studied and applied coupling agent. Due to its unique properties and the continuous emergence of new products, its application fields have gradually expanded and it has become an important branch of the silicone industry.
In recent decades, the development of glass fiber reinforced plastics has promoted the research and development of various coupling agents. The synthesis and application of modified aminosilane coupling agents, peroxysilane coupling agents and azidosilane coupling agents were the main achievements of this period.
2. Titanate coupling agent: Titanate coupling agent first appeared in the 1970s. In December 1974, Kenrich Petrochemical Company of the United States reported a new type of coupling agent, which has good coupling effects on many dry powders. Since then, inorganic-filled polyolefin composites with titanate coupling agents have been introduced.
At present, titanate coupling agent has become one of the indispensable raw materials for composite materials. Titanate coupling agents can be divided into 4 categories according to their chemical structures: monoalkoxy fatty acid type, phosphate ester type, chelate type and ligand type. The molecular formula of titanate coupling agent is:
3. Aluminate coupling agent: Aluminate coupling agent is a new coupling agent developed by Fujian Normal University. Its structure is similar to titanate coupling agent. There are two types of active groups in the molecule. Groups, one type can interact with the surface of inorganic fillers; the other type can be entangled with resin molecules, thereby producing a coupling effect between the inorganic fillers and the matrix resin.
Aluminate coupling agent is comparable to titanate coupling agent in improving the physical properties of products, such as increasing impact strength and heat distortion temperature; its cost is lower, and the price is only that of titanate coupling agent. Half of the agent, and has the characteristics of light color, non-toxic, easy to use, etc., and its thermal stability is better than that of titanate coupling agent.
4. Bimetallic coupling agent: The characteristic of bimetallic coupling agent is the introduction of organic functional groups on two inorganic skeletons, so it has properties that other coupling agents do not have: low processing temperature, room temperature and room temperature. Can interact with fillers; coupling reaction speed is fast; good dispersion, can make the modified inorganic fillers and polymers easy to mix, can increase the filling amount of inorganic fillers in the polymer; low price, about silane coupling half of the combined dose.
5. Lignin coupling agent Lignin is a macromolecular organic matter containing active groups such as hydroxyl, carboxyl, methoxy and other active groups. It is the main component of industrial papermaking wastewater. The development and application of lignin can not only reduce industrial pollution, but also increase its use value.
6. Tin coupling agent: In the industrial production of solution-polymerized styrene-butadiene rubber (SSBR), tin tetrachloride is often used to couple active SBR, and the resulting SSBR is called tin-coupled SSBR. Its characteristic is that the carbon-tin bond is easily broken by shear and heat during the mixing process, resulting in a decrease in relative molecular mass, thereby improving the processing performance of the rubber compound; the tin atoms at the end of the chain are highly active, which can enhance carbon black The interaction with the rubber material improves the strength and wear resistance of the rubber material, which is beneficial to reducing rolling resistance and hysteresis loss. Due to its unique properties, tin coupling agents have attracted more and more attention.
Main coupling agent applications[3][4]
1. Silane coupling agent
When using silane coupling agents, in order to obtain better results, it is necessary to conduct pre-selection tests for each specific application.. The silane coupling agents for different materials summarized based on general rules and experimental experience are shown.
Silane coupling agents are widely used, mainly in the following aspects: (1) used as surface treatment agents to improve the adhesion properties of room temperature curing silicone rubber and metal; (2) used when filling plastics with inorganic fillers , can improve its dispersion and adhesion; (3) used as a tackifier to improve the adhesion between cement and epoxy resin in hydropower station projects (4) used as a sealant, with water resistance, high temperature resistance, and weather resistance and other properties, used for bonding and sealing between fluorine rubber and metal.
2. Titanate coupling agent
(1) When used in latex systems, first add the titanate coupling agent into the water phase. Some titanate coupling agents are insoluble in water and require quaternary alkali reaction, emulsification reaction, mechanical dispersion and other methods. Make it soluble in water.
(2) The dosage of titanate is usually 0.15% of the filler dosage, or 0.125% of the solid resin dosage. The optimal dosage is ultimately determined by performance. The dosage of titanate coupling agent is generally 0.125% to 2% of the inorganic filler.
(3) Most titanate coupling agents, especially non-coordinating titanate coupling agents, can undergo transesterification reactions with ester plasticizers and polyacyl resins to varying degrees. Therefore, plasticizers need It can be added after coupling.
(4) The chelating titanate coupling agent has the best modification effect on wet fillers or polymer aqueous solution systems.
Main reference materials
[1] Concise Dictionary of Fine Chemicals
[2] Stomatological Dictionary
[3] Guo Yunliang, Zhang Shurong, Li Liping. Types, characteristics and applications of coupling agents[D]. 2003.
[4] Plueddemann E P. Silane and titanate coupling agents[J]. 1987.
[5] Zhang Dianrong, Zhao Yongyun, Yang Qingzhi, et al. The role of lignin as coupling agent in rubber [J]. Special Rubber Products, 2001, 22(6): 22-23.
