Silice, also known as silicon dioxide, is an important inorganic chimique raw material. Due to its unique surface structure and particle morphology, silica exhibits excellent stability, reinforcing capability, thickening behavior, and thixotropy. These properties make it a crucial inorganic filler in many fields such as rubber, coatings, and plastics. However, to fully unlock its potential and enhance compatibility with various organic matrices, the modification de la surface of silica is often employed. This process is key to tailoring its properties for specific applications.
Modification de surface of Silica
The internal polysiloxane structure and surface-active silanol groups make precipitated silica highly hydrophilic, resulting in poor wettability and dispersibility in organic phases. The hydroxyl groups on the surface contribute to a high surface energy, causing agglomeration that affects product performance. During production, this leads to aggregation, hydrophilicity, high costs, low efficiency, and heavy energy consumption. Under increasing environmental pressures, reducing costs, improving efficiency, and enhancing surface hydrophobicity have become especially important.
There are three types of hydroxyl groups on the silica surface:
- Isolated hydroxyl groups, which are free and unaffected;
- Geminal hydroxyl groups, where two hydroxyls are bonded to the same silicon atom;
- Associated hydroxyl groups, which are hydrogen-bonded to each other.
Surface modification of silica involves using a modifier that reacts chemically with these surface hydroxyl groups to remove or reduce silanol groups, thereby altering the surface properties.
Surface Modification Processes
Based on the nature of the modifier, surface modification can be classified into organic et inorganic modifications. Among them, organic modification is the most widely used. The key technology for organic modification is organosilane treatment, where organic functional groups replace hydroxyl groups on the silica surface.
Organic modification methods are generally divided into dry, wet, and pressurized heat methods. Currently, developed countries mainly use the dry method for modifying fumed silica.
Advantages of the Dry Method:
- Simple process with fewer post-treatment steps.
- Easy integration with the fumed silica production process.
- Suitable for large-scale industrial production.
Disadvantages of the Dry Method:
- High consumption of modifier.
- Requires high equipment standards and strict operating conditions.
- Relatively high production cost.
Le wet modification method is also commonly used and mainly includes two approaches:
Advantages of the Wet Method:
- Lower modifier consumption.
- Simple process and fewer equipment requirements.
- Lower production cost and better quality control.
Disadvantages of the Wet Method:
- Complex post-treatment process.
- Environmental pollution issues.
- Difficult to scale up for industrial mass production.
Another wet modification approach involves in-situ modification during the precipitation process of silica, which can enhance efficiency and integration.
Common Modifiers and Modification Principles
Common modifiers include organic halogenated silanes, silane coupling agents, silylamines, siloxanes, and alcohol compounds. These reagents chemically bond to or replace the surface hydroxyl groups on silica, thus improving hydrophobicity, dispersibility, and compatibility with organic materials.
Applications of Modified Silica
Modified silica is an important reinforcing agent in rubber products, filling the gap where noir carbone cannot be used in light-colored materials. In tire manufacturing, adding modified silica improves the mechanical strength of rubber, reduces hysteresis loss, lowers rolling resistance, and maintains excellent wet skid resistance.
In sealants and adhesives, modified silica enhances dispersibility, compatibility, and product durability. In coatings, silica serves as a common matting agent; the use of modified silica improves its dispersion and reduces aggregation or sedimentation issues.
Compared with ordinary silica, modified silica demonstrates better overall performance and a broader application range.
Conclusion
Modified silica not only retains the excellent properties of regular silica but also features enhanced hydrophobicity and improved surface characteristics. This greatly expand the application potential. With the continuous development of economy, the market demand for modified silica continues to grow. Developing environmentally friendly, cost-effective, and large-scale production technologies for modified silica has become a key direction for silica manufacturers in the future.