Application of Silane Coupling Agent
Silane coupling agent was first developed as a glass fiber treatment agent for glass fiber reinforced plastics. As silane coupling agent improves the adhesion between glass fibers and resins, the mechanical properties of reinforced plastics are significantly improved. With the rapid development of composite materials, silane coupling agents have developed rapidly in variety and yield. In recent years, introducing specific functional groups into some materials by silane coupling agents can improve the surface properties of materials, and obtain antistatic, antimildew, odor, anticoagulation and physiological inertia, which become the beginning of new uses of silane coupling agents. Because of the development of many important applications, silane coupling agents have become an important branch of organosilicon.


Silane coupling agent is obtained by alcoholysis of silicone chloroform (HSiCl3) and unsaturated olefins with reactive groups catalyzed by platinum chloric acid. Silane coupling agent is essentially a kind of silane with organic functional groups, in which there are both chemical bonding reaction groups with inorganic materials (such as glass, silica sand, metal, etc.) and chemical bonding reaction groups with organic materials (synthetic resins, etc.). The general formula Y(CH2)nSiX3 can be used to express that, here, n=0-3; X-hydrolyzable group; Y-organic functional group, can react with resin. X is usually chloro, methoxy, ethoxy, methoxyethoxy, acetoxy and so on. When these groups are hydrolyzed, they form silicone alcohol (Si (OH) 3), which binds with inorganic substances to form siloxane. Y is vinyl, amino, epoxy, methacryloxy, mercapto or urea. These reaction groups can react with organic substances and bind.


Therefore, through the use of silane coupling agent, a "molecular bridge" can be built between the interface of inorganic and organic substances, and two materials with different properties can be joined together to improve the properties of composite materials and increase the bonding strength. This property of silane coupling agent was first applied to glass fiber reinforced plastics (FRP) as surface treatment agent of FRP, which greatly improved the mechanical, electrical and anti-aging properties of FRP. The importance of silane coupling agent in FRP industry has been recognized for a long time.


At present, the use of silane coupling agent has expanded from FRP to FRTP, inorganic filler and sealant, resin concrete, water-crosslinked polyethylene, resin packaging material, shell moulding, tire. Belts, coatings, adhesives, abrasive materials (grinding stones) and other surface treatment agents.


Among the two groups of silane coupling agents with different properties, Y group is the most important one, which has a great influence on the properties of products and plays a decisive role in determining the properties of coupling agents. Only when the Y group reacts with the corresponding resin can the strength of the composite be improved. The Y group is generally required to be compatible with the resin and to react with it. Therefore, silane coupling agent with appropriate Y group should be selected for certain resins. When Y is a non-reactive alkyl or aryl group, it does not work on polar resins, but can be used in bonding of non-polar resins such as silicone rubber, polystyrene, etc. When Y contains reactive functional groups, attention should be paid to its reactivity and compatibility with the resin used. When Y contains amino group, it is catalytic. It can be used as catalyst in the polymerization of phenolic aldehyde, urea aldehyde and melamine formaldehyde, and also as curing agent for epoxy and polyurethane resins. At this time, the coupling agent is fully involved in the reaction and forms new bonds. Aminosilane coupling agents belong to the general type, and can almost interact with various resins, except polyester resins. The type of X group had no effect on the coupling effect.

Therefore, according to the types of reaction groups in Y group, silane coupling agents are also called vinyl silane, aminosilane, epoxy silane, mercapto silane and methacryloxy silane, which are the most commonly used silane coupling agents.