Silane coupling agent is obtained by the addition of silicon chloroform (HSiCl3) and unsaturated olefins with reactive groups catalyzed by platinum chloric acid, followed by alcoholysis. Silane coupling agents are essentially a type of silane with organic functional groups, which have both reactive groups in their molecules that can chemically bond with inorganic materials (such as glass, silica sand, metals, etc.) and reactive groups that can chemically bond with organic materials (synthetic resins, etc.). It can be represented by the general formula Y (CH2) nSiX3, where n=0-3; X - a hydrolyzable group; Y is an organic functional group that can react with resins. X is usually a chlorine group, methoxy group, ethoxy group, methoxyethoxy group, acetoxy group, etc. These groups hydrolyze to form silanol (Si (OH) 3), which combines with inorganic substances to form siloxane. Y is vinyl, amino, epoxy, methacryloyloxy, mercapto, or urea. These reactive groups can react with organic substances and combine.
Therefore, by using silane coupling agents, a "molecular bridge" can be built between the interface of inorganic and organic substances, connecting two materials with vastly different properties together, thereby improving the performance of composite materials and increasing adhesive strength. This characteristic of silane coupling agent was first applied to glass fiber reinforced plastics (GRP) as a surface treatment agent for glass fiber, which greatly improved the mechanical properties, electrical properties and anti-aging properties of GRP. Its importance in the GRP industry has long been recognized.
At present, the use of silane coupling agents has expanded from glass fiber reinforced plastics (FRP) to glass fiber surface treatment agents for glass fiber reinforced thermoplastic plastics (FRTP), surface treatment agents for inorganic fillers, sealants, resin concrete, water crosslinked polyethylene, resin encapsulation materials, shell molding, tires, belts, coatings, adhesives, grinding materials (grindstones), and other surface treatment agents.
Among the two types of functional groups with different properties in silane coupling agents, the Y group is the most important and has a significant impact on the performance of the product, playing a decisive role in determining the performance of the coupling agent. Only when the Y group can react with the corresponding resin can the strength of the composite material be improved. Generally, it is required that the Y group be compatible with the resin and capable of coupling reaction. So, certain resins need to choose silane coupling agents containing appropriate Y groups. When Y is a non reactive alkyl or aryl group, it does not work on polar resins, but can be used in the 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 groups, it belongs to catalytic properties and can act as a catalyst in the polymerization of phenolic, urea formaldehyde, melamine formaldehyde, as well as a curing agent for epoxy and polyurethane resins. At this time, the coupling agent fully participates in the reaction and forms new bonds. Aminosilane coupling agents are universal and can almost couple with various resins, except for polyester resins. The type of X group has no effect on the coupling effect.
Therefore, based on the types of reactive groups in the Y group, silane coupling agents are also referred to as vinyl silane, amino silane, epoxy silane, mercapto silane, and methacryloyloxy silane, among others. These organic functional silanes are the most commonly used silane coupling agents.
