Coupling agent: a "molecular bridge" connecting inorganic and organic
In the modern chemical industry, coupling agents, as a unique additive, are playing an increasingly
important role. They are like a bridge, connecting the gap between inorganic and organic
substances, greatly improving the performance of composite materials.
1. What is a coupling agent?
A coupling agent, as the name implies, is a chemical agent that can couple (connect) two substances of
different properties. Its molecular structure is unique. One end is an inorganic-philic
group that can react chemically with the surface of inorganic substances; the other end is an organic-philic
group that can react chemically with synthetic resins or polymers or dissolve in
them through hydrogen bonds. Therefore, coupling agents are known as "molecular bridges" to strengthen
the interfacial interaction between inorganic and organic substances.
2. Working principle of coupling agents
The reason why coupling agents can play their unique coupling role is due to the two types of chemical groups
that are simultaneously present in their molecules. They can react with
hydroxyl groups in inorganic substances and combine with long molecular chains in organic substances,
thus playing a bridging role. Its mechanism of action can be summarized into the
following three steps:
Hydrolysis reaction: The hydrolyzable groups (such as alkoxy) in the coupling agent molecules decompose
and convert into hydroxyl groups when encountering aqueous solution or moisture
in the air.
Coupling reaction: These hydroxyl groups combine with the hydroxyl groups on the surface of inorganic
substances by generating hydrogen bonds or dehydrating to ether bonds to form
chemical bonds.
Organic reaction: The other end of the coupling agent molecule (organophilic group) reacts or interacts with
organic matter, thereby firmly connecting inorganic and organic substances
together.
3. Types of coupling agents
There are many types of coupling agents, which are classified by chemical structure, mainly including silanes,
titanates, aluminates, organic chromium complexes, borides, phosphates,
zirconates, stannates, etc. Among them, silane coupling agents and titanate coupling agents are highly respected
for their superior performance and have the widest application range.
Silane coupling agent: Silane coupling agent is a chemical substance with a long history of research and application,
and its application field continues to expand with the continuous
emergence of new products. The general structural formula of silane coupling agent is RNSIX(4-N), where R
represents a non-hydrolyzable organic functional group that can combine with
high molecular polymers; X is a hydrolyzable group.
Titanate coupling agent: Titanate coupling agent has shown its unique coupling effect since its advent in the
1970s. Its molecular formula is R—O—TI—O—X—R′—Y)N, which has multiple
functional areas and can undergo multiple chemical reactions with inorganic fillers and polymers, thereby
significantly improving the performance of the material.
4. Application fields of coupling agents
Coupling agents play an important role in many industrial fields, mainly including:
Plastic industry: Coupling agents, as plastic additives, can improve the interface properties between synthetic resins
and inorganic fillers or reinforcing materials, reduce the viscosity of
synthetic resin melts, and improve the dispersion and processing properties of fillers, thereby enabling products to obtain
good surface quality and mechanical, thermal and electrical
properties.
Rubber industry: The application of coupling agents in the rubber industry is particularly significant. It can improve
the wear resistance and aging resistance of products such as tires, rubber
sheets, rubber hoses and rubber shoes, while reducing the use of natural rubber (NR), thereby achieving the purpose
of reducing costs.
Glass fiber reinforced plastics: Coupling agents are important additives for glass fiber reinforced plastics. They can
improve the bonding strength between glass fiber and resin and improve
the overall performance of composite materials.
Other fields: In addition, coupling agents are also widely used in metals, ceramics, adhesives, coatings, sealants and other
fields to improve the bonding strength, weather resistance, corrosion
resistance and other properties of materials.
5. Conclusion
As a "molecular bridge" connecting inorganic and organic, coupling agents play a vital role in the modern chemical industry.
With the rapid development of high-performance and
high-functional materials, the application fields of coupling agents will continue to expand, and their advantages in improving
the performance of composite materials, reducing costs,
and improving production efficiency will become more significant.
