Coupling agents refer to a class of compounds that can generate active groups under specific conditions and chemically combine with the adhesives on both sides of the bonding interface, thereby increasing the strength. It is an important treatment agent with an increasingly wide range of applications. It is mainly used as an additive for polymer composite materials. The biggest feature of the molecular structure of the coupling agent is that the molecule contains two groups with different chemical properties. One is an inorganic-friendly group, which is easy to react chemically with the surface of inorganic substances; the other is an organic-philic group, which can react with the inorganic substance. Synthetic resins or their polymers undergo chemical reactions or form hydrogen bonds to dissolve in them. Coupling agents are called “molecular bridges” and are used to improve the interface between inorganic substances and organic substances, thereby greatly improving the properties of composite materials, such as physical properties, electrical properties, thermal properties, optical properties, etc.
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 higher fatty acids, alcohols, and esters. In recent years, there are also rare earth coupling agents and composite coupling agents. At present, the most widely used are silane coupling agents and titanate coupling agents.
01. Silane coupling agent
The general formula of alkane coupling agent is RnSiX4-n, where R is a non-hydrolyzable organic functional group that can be combined with polymers. Among them, R is an organic group, which is an active group that can form chemical bonds with synthesis. X is a group that is easily hydrolyzable and can interact with the glass surface after hydrolysis. n is 1, 2, 3, and most silane treatment agents have n=1.
According to the different properties of the polymer, R should have strong affinity or reactivity with the polymer molecules, such as methyl, vinyl, amino, epoxy, mercapto, acryloyloxypropyl, etc. X is a hydrolyzable group, which can cause decomposition when exposed to aqueous solution, moisture in the air or moisture adsorbed on the surface of inorganic substances, and has good reactivity with the surface of inorganic substances. Typical X groups include alkoxy, aryloxy, acyl, chlorine, etc.; the most commonly used are methoxy and ethoxy, which generate methanol and ethanol by-products respectively during the coupling reaction. Since chlorosilanes generate corrosive by-product hydrogen chloride during the coupling reaction, they should be used with caution.
The coupling agent structure and its applicability to the resin matrix are listed below
The product is Wolan, the chemical name is chromium methacrylate chloride, suitable for polyester, epoxy, phenolic, PE, PP, PMMA;
The product is A-151, the chemical name is vinyl triethoxysilane, suitable for polyester, 1,2-polybutadiene, thermosetting butyl styrene, PE, PP, PVC;
The product is A-172, Z-6075, the chemical name is vinyl tris (β-methoxyethoxy) silane, suitable for unsaturated polyester, PP, PE;
The products are A-174, KH-570, E-6030, the chemical name is γ-propyl methacrylate trimethoxysilane, suitable for saturated polyester, PP, PE;
The product is A-1100, KH-550, the chemical name is γ-aminopropyltriethoxysilane, suitable for epoxy, phenolic, melamine, polyimide, PVC;
The products are A-1120, KH-843, Z-6020, the chemical name is aminoethylaminopropyltrimethoxysilane, suitable for epoxy, phenolic, polyimide, PVC;
The product is KH-580, the chemical name is γ-mercaptopropyltriethoxysilane, suitable for epoxy, phenolic, PVC, polyurethane, PS;
The products are A-189, KH-590, Z-6060, the chemical name is γ-mercaptopropyltrimethoxysilane, suitable for epoxy, phenolic, PS, PVC, polyurethane, synthetic rubber;
The product is B-201, A-5162, the chemical name is γ-diethylenetriaminopropyltriethylsilane, suitable for epoxy, phenolic, and nylon;
The product is B-202, the chemical name is γ-ethylenediaminepropyltriethoxysilane, suitable for epoxy, phenolic, and nylon;
The product is Nanda-24 (ND-24), the chemical name is hexamethylenediaminemethyltriethoxysilane, which is suitable for epoxy and phenolic;
The product is A-111, Y-2967, the chemical name is bis(β-hydroxyethyl)γ-aminopropyltriethoxysilane, suitable for epoxy, PA, polysulfone, PC, PVC, PP
In recent years, silane coupling agents with larger relative molecular weights and special functional groups have been developed rapidly, such as octenyl, dodecyl, as well as peroxy, urea, carbonyloxy and cationic hydrocarbon groups. Silane coupling agent, etc.
The commonly used coupling agents currently produced in China include Wolan, A-151, KH-151, KH-550, KH-560, KH-570, KH-590, ND-42, B-201, B -202 etc.
The silane coupling agent has a significant effect on glass, silica, clay, silicate, silicon carbide, etc.; it is slightly less effective on talc, clay, wollastonite, aluminum hydroxide, and iron powder; it is less effective on asbestos and titanium It has little effect on white powder and iron red; it has even less effect on calcium carbonate, barium sulfate and carbon black.
02.Titanate coupling agent
According to the molecular structure of titanate coupling agents, they are divided into 4 basic types: (1) Monoalkoxy type. This type of coupling agent is suitable for a variety of resin-based composite material systems, especially suitable for systems that do not contain free water. , a filling system containing only chemically bonded water or physical water; (2) Monoalkoxy pyrophosphate type, this type of coupling agent is suitable for various resin-based composite material systems, especially suitable for filler systems with high moisture content ; (3) Chelated type, this type of coupling agent is suitable for various resin-based composite material systems. Because they have very good hydrolytic stability, this type of coupling agent is especially suitable for water-containing polymer systems.Compound system; (4) Coordination type. This type of coupling agent has good coupling effect when used in a variety of resin-based or rubber-based composite material systems. It overcomes the effect of general titanic acid coupling agents on resins. Disadvantages of matrix composite systems.
Titanate coupling agent has better effect on titanium dioxide, calcium carbonate, calcium sulfate, aluminum hydroxide, magnesium hydroxide, metal powder, mica, titanium dioxide, iron red, etc.
03.Aluminate coupling agent
Aluminate coupling agent is a new coupling agent developed by Fujian Normal University. Its structure is similar to titanate coupling agent. Its molecular structure is as shown below.
Aluminate coupling agent is comparable to titanate coupling agent in improving the impact strength and heat distortion temperature of products; its cost is lower, the price is only half of that of titanate coupling agent, and It has the characteristics of light color, non-toxic, easy to use, etc., and its thermal stability is better than that of titanate coupling agent.
