Do you know the modifiers for powder surface modification?

The powder surface modification is primarily achieved through surface modifiers acting on their surfaces. Therefore, the modifier formula (types, dosage, usage) critically impacts modification effectiveness and final product performance. Surface modifier formulas are highly targeted (“a specific key for a specific lock”), involving type selection, dosage determination, and application methods.

Screening of surface modifiers

Properties of powder raw materials

The properties of powder materials mainly include acidity, alkalinity, surface structure, functional groups, adsorption, and chemical reaction characteristics.
It is best to choose surface modifiers that can chemically react or adsorb to the powder particles. Physical adsorption may desorb easily under strong stirring or compression during later applications.

For example, the acidic silicate minerals like quartz, feldspar, mica, and kaolin can bond with silane coupling agents, forming strong chemical adsorption. Titanates and aluminates coupling agents can chemically adsorb onto carbonate-based alkaline minerals under certain conditions and to some extent.

Product Usage

The product’s application is the most important factor when choosing surface modifiers, along with the compatibility and compatibility with the components of the application system. For example:

• ou can choose organic surface modification to enhance the compatibility and dispersion of inorganic powders in organic polymers, improving material strength and overall performance.
• You can choose intercalation modification to obtain new mineral intercalation compounds, such as clay or graphite intercalation compounds.
• You can choose surface-coated silica to replace silica and complement its deficiencies in certain properties.
• You can choose surface-coated titanium dioxide to replace titanium dioxide or reduce its usage.
• You can select surface-coated metal particles to improve certain special properties of rubber products.
• You can select surface-coated metal oxides such as titanium oxide, chromium oxide, or iron oxide to improve optical benefits and visual effects of products.

Modification process

The modification process is also an important consideration when choosing surface modifiers, such as temperature, pressure, and environmental factors. All organic surface modifiers will decompose at certain temperatures. For example, the boiling point of silane coupling agents varies between 100–310°C depending on the type. Therefore, the chosen surface modifier’s decomposition temperature or boiling point should preferably be higher than the processing temperature during application.

For wet processes, the water solubility of surface modifiers must be considered. Only water-soluble modifiers can fully interact with powder particles in wet environments.
For example, adding stearic acid directly to calcium carbonate in a wet process fails to achieve the desired effect. This results in low efficiency, severe modifier loss after filtration, and excessive organic discharge in the filtrate. Therefore, you must saponify, ammoniate, or emulsify modifiers that cannot dissolve in water to ensure dispersion in aqueous solutions.

Price and environmental factors

It is important to meet application performance requirements or optimize them.
Under this premise, it is preferable to choose more affordable surface modifiers.
This helps reduce the cost of surface modification. At the same time, it is important to select surface modifiers that do not cause environmental pollution.

Dosage of surface modifier

Theoretically, the optimal amount of surface modifier is the quantity required for monolayer adsorption. This adsorption occurs on the particle surface. This amount is related to the specific surface area of the powder material and the molecular cross-sectional area of the surface modifier. However, this amount is not necessarily the amount required for 100% surface coverage.
It may not achieve full coverage.

. For inorganic surface coating modification, different coating rates and membrane thicknesses may exhibit different characteristics, such as color and gloss. Therefore, the actual optimal amount should be determined through modification and application performance tests. This is because the amount of surface modifier not only depends on the dispersion and uniformity of coating during modification but also on the specific requirements of the application system for the powder’s surface properties and technical indicators.

For wet modification, the actual coating amount of the surface modifier on the powder surface is not necessarily equal to the amount used. This is because a portion of the surface modifier does not react with the powder particles and is lost during filtration. Therefore, the actual amount used must be greater than the amount required to achieve monolayer adsorption.

How to use surface modifiers

The application method of surface modifiers is an important part of the surface modifier formulation. It has a significant impact on the surface modification effect of the powder.

A good application method can improve the dispersion of the surface modifier and enhance its surface modification effect. On the other hand, improper application can lead to increased modifier usage and failure to achieve the desired modification effect. The application methods of surface modifiers include preparation, dispersion, and addition techniques, as well as the sequence of adding multiple modifiers when used together.

Preparation

The preparation method of surface modifiers depends on the type, modification process, and equipment. Different surface modifiers require different preparation methods. For silane coupling agents, the silanol group reacts with the powder surface. Therefore, you should perform hydrolysis before use.

For other organic modifiers like titanates, aluminates, and stearic acid, dilute or dissolve them with appropriate organic solvents. Use solvents like anhydrous ethanol, toluene, ether, or acetone for dilution and dissolution.
For modifiers like stearic acid, titanates, and aluminates, which cannot dissolve in water, pre-saponify, ammoniate, or emulsify them to make them water-soluble.

Add method

The best method for adding surface modifiers is to ensure uniform and thorough contact with the powder, achieving high dispersion and even coating on the particle surface. Therefore, you should use a continuous spraying or dripping (adding) method linked to the powder feeding rate. Only continuous powder surface modification machines can achieve continuous addition of surface modifiers.
The preparation method for inorganic surface modifiers is more specific and requires consideration of factors like pH, concentration, temperature, and additives.For example, when coating muscovite with titanium dioxide, you should pre-hydrolyze titanium sulfate or titanium tetrachloride.

Dosing order

When using more than one surface modifier to treat powder, the order of addition affects the final surface modification effect. First, analyze the role of each surface modifier and its interaction with the powder surface. Determine whether physical adsorption or chemical adsorption is the primary interaction. Generally, add the modifier with the primary effect and chemical adsorption first. Add the modifier with secondary effects and physical adsorption afterward.
For example, when mixing a coupling agent and stearic acid, add the coupling agent first. The main purpose of adding stearic acid is to enhance hydrophobicity and reduce coupling agent usage, lowering modification costs.

For example, when mixing a coupling agent and stearic acid, you should generally add the coupling agent first, followed by stearic acid. The main purpose of adding stearic acid is to enhance the powder’s hydrophobicity and reduce the amount of coupling agent, lowering modification costs.

Conclusion

In powder surface modification, selecting the right modifier, controlling dosage, and using proper application methods are crucial. These factors directly affect the modification effect and final product performance. Therefore, they must be designed and adjusted based on specific needs and process conditions.

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