This article reviews the recent progress and challenges of using silane coupling agents in composite materials. It focuses on their effects on the interfacial properties, mechanical performance, and environmental durability of the composites.
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Research on the application of silane coupling agents in composite materials

Silane coupling agents are synthetic hybrid inorganic-organic compounds that can improve the adhesion between dissimilar materials, such as organic polymers and inorganic fillers. They have been widely used in various applications, such as polymer composites, coatings, water treatment, and surface modification.

In this article, we will review the recent progress and challenges of using silane coupling agents in composite materials, focusing on their effects on the interfacial properties, mechanical performance, and environmental durability of the composites.

Interfacial properties of silane coupling agents

The interfacial properties of silane coupling agents depend on their molecular structure, which consists of two functional groups: an alkoxy group that can hydrolyze and form a covalent bond with the inorganic surface, and an organic group that can interact with the polymer matrix.

The alkoxy group can be either mono-, di-, or tri-methoxy, which affects the hydrolysis rate and the stability of the silanol group. The organic group can be either amino, epoxy, vinyl, or methacryloxy, which affects the compatibility and reactivity with the polymer matrix.

The interfacial properties of silane coupling agents also depend on the surface characteristics of the inorganic fillers, such as their chemical composition, morphology, and surface energy. The silane coupling agents can modify the surface properties of the fillers by forming a thin layer of siloxane network, which can increase the surface roughness, hydrophobicity, and chemical bonding with the polymer matrix.

Mechanical performance of silane coupling agent-modified composites

The mechanical performance of silane coupling agent-modified composites depends on the type and amount of silane coupling agent used, as well as the processing conditions and the testing methods. Generally speaking, silane coupling agents can improve the mechanical performance of composites by enhancing the interfacial adhesion, reducing the interfacial defects, and increasing the stress transfer between the polymer matrix and the inorganic fillers.

For example, a recent study showed that KH570-modified rubber-cement-based composites had significantly improved mechanical properties compared with composites treated with PR550, PR560, and PR151. The PR570 molecules could effectively bond the elastic rubber to the hard cement matrix by forming a mechanical occlusion and a chemical bonding at the interface. This resulted in improved frictional resistance and deformation properties of the composites under stress.

However, there are also some challenges and limitations of using silane coupling agents to improve the mechanical performance of composites. For instance, some factors such as humidity, temperature, aging, and UV radiation can affect the stability and durability of the silane coupling agent layer on the filler surface. Moreover, some silane coupling agents may have negative effects on the thermal stability, flame retardancy, or biodegradability of the composites.

Future perspectives and conclusions

Silane coupling agents are promising modifiers for composite materials due to their ability to improve the interfacial properties and mechanical performance of composites. However, there are still some challenges and opportunities for further research and development.

Some possible directions for future research include:

– Developing new types of silane coupling agents with novel functional groups or structures that can enhance the compatibility and reactivity with different types of polymers and fillers.
– Optimizing the processing conditions and methods for applying silane coupling agents to achieve uniform and stable coating on filler surfaces.
– Investigating the effects of silane coupling agents on other properties of composites such as thermal stability, flame retardancy, biodegradability, electrical conductivity, optical transparency, etc.
– Exploring new applications of silane coupling agent-modified composites in various fields such as biomedical engineering, energy storage and conversion, environmental engineering, etc.

In conclusion, silane coupling agents are effective modifiers for composite materials that can improve their interfacial properties and mechanical performance. However, more research is needed to overcome some challenges and to expand their applications in various fields.

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