What are the methods for surface modification of silica?
Chemical modification has the characteristics of high stability, easy control, and good product performance. It is the main direction of silica
modification research and industrial application at present. It mainly includes: surface grafting modification, coupling agent modification, ionic
liquid modification, macromolecular interface modification and combined modification.
(1) Surface grafting modification
The principle of surface grafting modification is to graft macromolecular polymers with the same properties as the matrix polymer (such as rubber)
on the surface of silica through chemical grafting. On the one hand, it can enhance the interaction between particles and the matrix and change
the polarity of the particle surface. On the other hand, it can also improve the dispersibility of silica itself.
Surface grafting can be divided into "Grafting from" (main chain grafting method) and "Grafting to" (grafting to the main chain method) according
to the different grafting methods. The former can accurately control the molecular weight and grafting density of the grafting, but the steric hindrance
in the later stage is large and the grafted molecular weight is small; the latter can graft molecular chains with higher molecular weight and the steric
hindrance effect is relatively low, but the conditions are more stringent.
(2) Coupling agent modification
The principle of coupling agent modification is to use some functional groups on the coupling agent to react chemically with the hydroxyl groups on
the surface of silica, thereby changing the group structure and distribution on the surface of silica to improve the compatibility with the matrix and its
own dispersibility.
Coupling agent modification has the advantages of good modification effect and high reaction controllability, and is one of the most widely used
modification methods. Currently, the most widely used coupling agents include silane coupling agents, siloxane coupling agents and silazane coupling
agents. In practical applications, the main process of coupling agent modification is divided into four steps: mixing reaction, cooling separation, repeated
washing and precipitation.
(3) Ionic liquid modification
Ionic liquid, also known as room temperature ionic liquid, is a molten salt composed of organic cations and organic or inorganic anions, which is liquid
below 100°C. Ionic liquid modification is to use ionic liquid modifiers instead of traditional organic phase modifiers to modify silica. Compared with
traditional organic phase modifiers, ionic liquids have the advantages of being liquid at room temperature, strong conductivity, high stability and good solubility.
In addition, they are non-volatile and not easy to cause pollution, which is more in line with the requirements of green production.
The ionic liquid modification process is relatively simple. After adding a certain amount of anhydrous ethanol to the mixed system of silica and ionic liquid,
it is placed in a constant temperature water bath for reaction. After the reaction is sufficient, the modified silica is obtained by drying.
(4) Macromolecular interface modification
The modifier used for macromolecular interface modification is a macromolecular polymer containing polar groups. During the modification reaction with
silica particles, the molecular main chain of the macromolecular interface modifier can introduce more polar epoxy groups while maintaining the basic main
chain structure, thereby improving the compatibility between silica particles and the matrix and achieving a better interface modification effect.
Anticorrosion Pigments, Inkjet Receptive Coating, Matting Agent
How to control the dispersion quality of silica matting powder?
* Highly dispersible matting powder has a lot to do with its surface area
Like traditional matting powder, when the surface area of highly dispersible matting powder is higher, the reinforcement
performance is also better. When the surface area is larger, the reinforcement performance is better, but the processing
performance is poor. The reinforcing performance of high-dispersibility matting powder with the same surface area is better
than that of traditional matting powder.
Matting powder with high surface area has a higher concentration of silanol groups. The free silanol groups will interact strongly
with the accelerator, which will lead to a decrease in the vulcanization rate of the rubber compound. When the BET surface area
of the matting powder exceeds 200㎡·g, the vulcanization rate will be too low. Therefore, the BET surface area of high-dispersibility
matting powder generally does not exceed 200㎡·g.
When the structure of the matting powder is higher, the dispersibility is better and the vulcanization rate is also higher. The phenomenon
of better dispersibility when the structure is higher can be explained as follows: matting powder with high structure has more pores,
and the polymer will penetrate into the pores at the beginning of mixing. Then, when the agglomerates are subjected to the mixing
shear force and are broken into aggregates, they will be better dispersed in the polymer. However, traditional matting powder with
low structure is pressed very hard at the beginning of mixing a
SL-715 Silica Matting Agent is synthetic amorphous silica appearing as white powder.
CAS Number(SILICON DIOXID
Anticrrosion Pigments, Inkjet Receptive Coating, Matting Agent
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