Principle, Influencing Factors and Process of Modification of Quartz Powder by Silane Coupling Agents

Quartz powder, silica micro powder, and other forms of silica powder used for plastics, rubber, and other resins must be surface-treated to improve their compatibility with high polymer materials, thereby enhancing the comprehensive performance and processability of filling materials.

Principle of Quartz Powder Modification with Silane Coupling Agents

The surface chemical modification of quartz powder, silica micro powder, or other silica powder mainly uses silane coupling agents, including various silane coupling agents such as amino, epoxy, methyl acrylate, trimethyl, methyl, and vinyl groups.

The principle of quartz powder modification with silane coupling agents: the -RO functional group of the silane coupling agents can hydrolyze in water (including free water adsorbed on the surface of the filler) to produce a silanol group. This group can chemically combine with SiO2 or combine with the surface's original siloxy and alcohol groups, becoming a homogeneous system. In this way, the water on the surface of SiO2 is removed, and a silicone-covered surface with organic functional groups - R' having good affinity with high polymer material is formed on the surface of quartz or silica particles, forming a reactive coating.

The organic functional group - R' has good affinity with high polymer materials such as epoxy resin, which can reduce the surface energy of quartz or silica powder, improve the wettability with high polymer materials, and improve the compatibility between the powder and high polymer materials. In addition, the formation of this new interface layer can improve the rheological properties of the filling composite system.

Factors Affecting the Surface Modification of Quartz Powder Modified with Silane Coupling Agents

The main factors that affect the surface treatment effect of quartz powder and other silica powders are the silane coupling agent's variety, dosage, usage method and treatment time, temperature, pH value, etc.

Because the organic functional group - R' of the silane has selectivity for high polymers or resins, the type of resin to be filled with quartz powder should be considered when selecting the silane coupling agent. The dosage of the silane coupling agent scan be determined based on the specific surface area of quartz or silica powder or through experiments to determine the optimal dosage.

Surface Modification Process of Quartz Powder Modified with Silane Coupling Agents

The wet process is to mix the silane coupling agents with an appropriate diluent and an auxiliary agent to prepare a treatment solution. The quartz powder or silica powder is then heated or soaked in a stirred reaction kettle or reaction tank and then dehydrated.

When preparing amorphous silica powder using the chemical precipitation method, the wet surface treatment process is often used.

The dry process is to add a small amount of diluent to the silane to prepare a treatment agent. Under the conditions of high-speed stirring and heating, the quartz powder is dispersed, and the mist is sprayed into the prepared silane treatment agent. After a certain reaction time, the material is discharged. This method does not require dehydration and drying, and the process is simple.

The dry-wet combined process is to first mix the acidified water (deionized water is used when the electrical performance requirements are high) with a suitable amount of coupling agent in a strong stirring device to prepare a treatment solution with a certain concentration, then add 8%-10% of the treatment solution to the quartz powder by weight, and then mix and grind in a small ball mill with corundum balls or silicon stone balls for 1 hour, dry at 110°C, and finally sieve and grade.

In the treatment process, the amount of water and the mixing time have a significant effect on the treatment effect. If the amount of water is too large, the powder is prone to agglomerate, and the mixing time needs to be longer, which will increase the re-grinding of the powder and introduce impurities. If the amount of water is too small, it is not conducive to the full dispersion of the coupling agent and its uniform effect on quartz powder. At the same time, the acidity or alkalinity of the solution directly controls the hydrolysis degree of the coupling agent. Quartz powder modified by this method has been tested in resin mortar, resin anticorrosive coating, resin powder coating, and PVC artificial leather with good results.