How To Choose Surface Modifiers
Surface modifiers are the key to powder surface modification to achieve the desired purpose, but there are various types and strong pertinence. Considering the interaction between surface modifier molecules and the surface of inorganic powder, it should be selected as much as possible. Surface modifiers that undergo chemical reactions or chemical adsorption on the surface of powder particles are easily desorbed under the action of strong stirring or extrusion during subsequent application due to physical adsorption.
1. Selection principle of surface modifier
In the actual selection, in addition to considering the type of adsorption, other factors must also be considered, such as product use, product quality standards or requirements, modification process, cost, environmental protection, etc.
(1) Purpose of the product
This is the most important consideration for selecting surface modifier varieties, because different application fields have different technical requirements for powder application properties, such as surface wettability, dispersibility, pH value, electrical properties, weather resistance, gloss, Antimicrobial properties, etc., which is one of the reasons for choosing a variety of surface modifiers depending on the application.
For example: Inorganic powders (fillers or pigments) used in various plastics, rubber, adhesives, oily or solvent-based coatings require good lipophilicity on the surface, that is, good affinity with organic polymer substrates or Compatibility, which requires the selection of surface modifiers that make the surface of inorganic powder hydrophobic and lipophilic;
When choosing calcined kaolin for coating cable insulation fillers, the influence of surface modifiers on dielectric properties and volume resistivity should also be considered;
For the inorganic pigments used in ceramic blanks, it is not only required to have good dispersibility in a dry state, but also to have good affinity with inorganic blanks and be able to disperse evenly in the blanks;
Surface modifiers for inorganic powders (fillers or pigments) used in water-based paints or coatings require the modified powders to have good dispersion, sedimentation stability and compatibility in the water phase.
At the same time, the components of different application systems are also different. When selecting a surface modifier, compatibility and compatibility with the components of the application system must also be considered to avoid failure of other components in the system due to the surface modifier.
(2) Modification process
Modification process is also one of the important considerations in selecting surface modifier varieties. The current surface modification process mainly adopts dry method and wet method.
For the dry process, there is no need to consider its water solubility, but for the wet process, the water solubility of the surface modifier must be considered, because only when it is soluble in water can it fully contact and react with the powder particles in a wet environment.
For example, stearic acid can be used for dry surface modification of calcium carbonate powder (either directly or after being dissolved in an organic solvent), but in wet surface modification, such as directly adding stearic acid, it is not only difficult to achieve The expected surface modification effect (mainly physical adsorption), and the utilization rate is low, the loss of surface modifier after filtration is serious, and the discharge of organic matter in the filtrate exceeds the standard.
A similar situation holds true for other types of organic surface modifiers. Therefore, for surface modifiers that cannot be directly water-soluble but must be used in a wet environment, they must be saponified, ammonized or emulsified in advance so that they can be dissolved and dispersed in an aqueous solution.
In addition, process factors such as temperature, pressure and environmental factors should also be considered when selecting surface modifiers. All organic surface modifiers will decompose at a certain temperature. For example, the boiling point of silane coupling agent varies between 100-310°C depending on the species. Therefore, the selected surface modifier preferably has a decomposition temperature or boiling point higher than the processing temperature of the application.
(3) Price and environmental factors
Finally, the price and environmental factors should also be considered in the selection of surface modifiers. Under the premise of meeting application performance requirements or optimizing application performance, try to use cheaper surface modifiers to reduce the cost of surface modification. At the same time, attention should be paid to the selection of surface modifiers that do not pollute the environment.