Introduction and Classification of Coupling Agents

Oct 15, 2021

In plastic compounding, a plastic additive that improves the interface performance of synthetic resins and inorganic fillers or reinforcing materials. Also known as surface modifier. It can reduce the viscosity of the synthetic resin melt in the plastic processing process, improve the dispersion of the filler to improve the processing performance, and then make the product obtain good surface quality and mechanical, thermal and electrical properties.

The dosage is generally 0.5 to 2% of the filler dosage. Coupling agents generally consist of two parts: one is an inorganic group that can interact with inorganic fillers or reinforcing materials; the other is an organic group that can interact with synthetic resins.
Coupling agent is a kind of substance with two functional groups with different properties. The biggest feature of its molecular structure is that the molecule contains two groups with different chemical properties. One is an inorganic-philic group, which is easy to chemically react with the surface of inorganic substances. ; The other is an organophilic group, which can chemically react with synthetic resins or other polymers or generate hydrogen bonds to dissolve them. Therefore, coupling agents are called "molecular bridges" to improve the interface between inorganics and organics, thereby greatly improving the properties of composite materials, such as physical properties, electrical properties, thermal properties, and optical properties. Coupling agents are used in the rubber industry to improve the wear resistance and aging resistance of tires, rubber sheets, hoses, rubber shoes and other products, and can reduce the amount of NR, thereby reducing costs. The role of the coupling agent in the composite material is that it can react with certain groups on the surface of the reinforcing material and the matrix resin to form an interface layer between the reinforcing material and the resin matrix, and the interface layer can transmit stress. This enhances the bonding strength between the reinforced material and the resin, improves the performance of the composite material, and can also prevent other media from penetrating to the interface and improve the interface state, which is conducive to the aging resistance, stress resistance and electrical insulation properties of the product.

1. Monoalkoxy type;
Monoalkoxy titanate produces a chemical bond at the interface between the inorganic powder and the matrix resin. Its extremely unique property is to form a monomolecular film on the surface of the inorganic powder, but there is no multimolecular film on the interface.
Because it still has the chemical structure of titanate, in the presence of excess coupling agent, the surface energy changes and the viscosity is greatly reduced. In the matrix resin phase, the trifunctional group of the coupling agent and the transesterification reaction can make The titanate molecule is coupled, which facilitates the modification of the titanate molecule and the selection of the filled polymer system.
This type of coupling agent (except the pyrophosphate type) is especially suitable for dry filler systems that do not contain free water, but only contain chemically or physically bonded water, such as calcium carbonate, hydrated alumina, etc.
2. Monoalkoxy pyrophosphate type:
This type of titanate is suitable for filler systems with higher moisture content, such as clay, talc, etc. In these systems, in addition to the monoalkoxy group reacts with the hydroxyl group on the filler surface to form a coupling, the pyrophosphate group It can also be decomposed to form a phosphate group and combine with a part of water.
3. Coordination type:
The side reaction of tetravalent titanate in some systems can be avoided. Such as the transesterification reaction in polyester, the reaction with hydroxyl in epoxy resin, the reaction with polyol or isocyanate in polyurethane, etc. This type of coupling agent is applicable in many filler systems, has a good coupling effect, and its coupling mechanism is similar to that of the monoalkoxy type.
4. Sting type:
This type of coupling agent is suitable for high-humidity fillers and water-containing polymer systems, such as wet-process silica, clay, talc, aluminum silicate, water-treated glass fiber, lamp black, etc. In high-humidity systems, general Monoalkoxy titanate has poor hydrolytic stability and low coupling effect, while this type has good hydrolytic stability. In this state, it shows good coupling effect.