Coupling agent

Definition and Classification of Coupling Agents Coupling agents are a class of additives that improve the interfacial properties between polymeric materials and fillers. There are two different groups in the molecular structure. One group may chemically react with the polymer material or have good compatibility, and the other group may form a chemical bond with the inorganic material or the filler. It improves the interfacial adhesion of the two materials and significantly improves the performance of the filled or reinforced polymer material. Varieties include silane coupling agents (trichlorovinylsilane, triethoxyvinylsilane, γ-aminopropyltriethoxysilane, trichloropropenylsilane, etc.), titanate coupling agent (tetrabutyl titanate) Ester, isopropyl triisostearyl titanate, isopropyl trititanate, diisostearyl acyl decanoate, etc., organic chromium coupling agent (methacryloyl chromium complex), aluminate Zirconium coupling agent, polymer coupling agent, and the like. It is mainly used in polymer reinforcement materials as surface treatment for reinforcing agents and glass fibers. Silane coupling agents are also used as polyolefin crosslinks and are used directly in plastics, rubber blending or tackifying. Titanate coupling agent Titanate coupling agent is a new type of coupling agent developed by Kenrich Petrochemical Company in the United States in 1975. It has a unique structure for thermoplastic polymers and dry fillers. Good coupling efficiency. According to the molecular structure and the coupling mechanism with the surface of the filler, titanate coupling agents can be classified into four basic types: (1) monoalkoxy type (2) monoalkoxy pyrophosphate type (3) Chelating type (4) Ligand type. Figure 1 is a ligand-type titanate coupling agent titanate coupling agent should be avoided as much as possible with surface-active additives, they will interfere with the coupling reaction of titanate at the interface, if not used When not possible, the filler, coupling agent and polymer should be added after they are thoroughly mixed. Most of the titanates undergo transesterification with ester plasticizers to varying degrees. Therefore, the addition of the ester plasticizer should also be carried out after the filler, the coupling agent and the polymer are thoroughly mixed to form a coupling. The titanate coupling agent and the silane coupling agent can be used in combination to produce a synergistic effect, for example, the treatment of the glass fiber treated with the silane coupling agent with the chelating type titanate, and the coupling efficiency is greatly improved. The silane coupling agent silane coupling agent is the earliest and most widely used coupling agent. It has been developed by UCC for the development of glass fiber reinforced plastics for more than 30 years. A silicone monomer having two or more different reactive groups in a molecule, which can be chemically bonded (coupled) with an organic material and an inorganic material. The chemical formula of the silane coupling agent is: RSiX3. X represents a hydrolyzable functional group which can undergo a coupling reaction with a methoxy group, an ethoxy group, a cellosolve, and an inorganic material (glass, metal, SiO2). R represents an organic functional group which can be coupled with an organic group such as a vinyl group, an ethoxy group, a methacryl group, an amino group or a fluorenyl group, and an inorganic material, various synthetic resins, and rubber. Figure 2 shows the physicochemical properties of several commonly used representative silane coupling agents. According to the reaction mechanism of the silane coupling agent, the hydrolyzable functional group X forms silicon alcohol in contact with water. In the case of an inorganic material such as glass, the coupling agent and the silanol on the surface of the glass undergo a condensation reaction to form a covalent bond between the glass and the silane coupling agent. Using this feature, silane coupling agents can be used to treat glass fibers (reinforced plastics), improve the performance of coatings and adhesives, and the surface used to treat inorganic fillers. For glass fiber reinforced unsaturated polyesters, Methacryloxysilane is preferred; for epoxy laminates, epoxidized silanes and aminosilanes are preferred. A new use of the silane coupling agent is as a polyethylene crosslinking agent, graft copolymerization of polyethylene and vinyltrimethoxysilane, or crosslinking by condensation of polyethylene with silane. Treated polyethylene can be used as a cable and as a complex shaped material. In order to adapt to the development of functional polymer composites, some new silane coupling agents have been developed, such as γ-ureidopropyl-trimethoxysilane, γ-glycidylpropyl-methyl-diethoxysilane. And N-phenyl-γ-aminopropyl-dimethoxysilane. Application of Coupling Agents in Glass Fiber Reinforced Polyester Resins A key technology in glass fiber reinforced polyester resins is to solve the problem of bonding between glass fiber and resin interfaces. This combination may be physical or chemical bonding, and only chemical bonding will result in the strongest bond between the glass fiber and the resin. Chemical bonding can be achieved using a coupling agent. There are two main types of coupling agents: one is an organosilicon compound; the other is an organic chromium complex. The structure of the silicone coupling agent is generally R4-nSiXn, wherein R is an organic group, X is an easily hydrolyzable group such as OR', Cl, R", and R', R" is a hydrocarbon group, n = 1, 2, 3, most n=3. The organic group R can react chemically with the unsaturated polyester, and the easily hydrolyzable group is hydrolyzed, condensed, and interacts with the glass surface, and may have the following results: Figure 3 is the result of the interaction between the silicone coupling agent and the glass surface. As a result of the action on the surface of the glass, a strong covalent bond is formed, thereby changing the original properties of the glass surface to impart hydrophobicity, an organic solvent and a pro-resin, thereby improving the mechanical properties of the composite. The organic chromium complex coupling agent mainly has chromium chloride methacrylate, which can be used in an unsaturated polyester resin to improve the bonding condition of the interface between the glass fiber and the resin. Chromium chloride methacrylate can be bonded to the surface of the glass by the hydroxyl group and silanol contained in the self-hydrolysis, and the methacrylic group is extended outward to chemically bond with the resin. The process is as follows: Results of interaction between organic chromium complex coupling agent and glass surface