The Inorganic Coating and Organic Modification of Titanium Dioxide

The Inorganic Coating and Organic Modification of Titanium Dioxide

Titanium dioxide is considered to be the best white pigment in the world due to its high refractive index, whiteness, gloss and non-toxic characteristics. It is widely used in coating, plastic, paper, ink, chemical fiber, rubber, and other industrial fields.

However, due to its semiconductor properties, titanium dioxide has a certain photocatalytic activity and can degrade the organic matter in contact with it in the sun, especially ultraviolet radiation, resulting in the coating yellowing, pulverization, and other phenomena. In addition, titanium dioxide pigment particles are usually submicron particles, its polarity is strong and has a high specific surface area, so it is easy to form aggregates. The formation of aggregates will seriously affect their application performance, such as coloring force, gloss, hiding force, processing performance and so on.

Titanium-Dioxide-Powder
Titanium-Dioxide-Powder

In addition to adjusting and optimizing the early production process of titanium dioxide, it is necessary to master the surface strengthening treatment methods at the end of titanium dioxide production to improve the quality of titanium dioxide products. Optimization of the preliminary process of titanium dioxide can effectively reduce the inherent defects of titanium dioxide products, but it cannot completely eliminate them. Surface treatment processes such as inorganic coating and organic modification can further improve the inherent defects of titanium dioxide, and improve the overall wearability, dispersibility, oil absorption value, hiding power and other application properties of titanium dioxide.

Inorganic coating and organic modification

At present, the general solution to improve the quality of titanium dioxide is to carry out surface inorganic coating and organic modification on titanium dioxide to reduce its photocatalytic activity and improve the weather resistance and dispersion in the application system. Inorganic coating agents are mainly silicon, aluminum, zirconium, phosphorus hydrated oxide or hydroxide, which can not only improve the dispersion of titanium dioxide in the matrix but also improve its weather resistance.

The weatherability of titanium dioxide coated with dense Si-Al was the best (showed in the figure below). In practical application, different inorganic coating combinations are designed according to the requirements of the different application system.

TEM-images-of-single-silicon-(A, B)-and-silicon-aluminum-coated-(C, D)-samples
TEM-images-of-single-silicon-(A, B)-and-silicon-aluminum-coated-(C, D)-samples

The inorganic coating is usually followed by an organic coating to further improve the dispersion and processing performance of titanium dioxide in the matrix. Organic surface treatment agents are usually polyols, organic amines or silicone (silane coupling agents and siloxane). By selecting appropriate inorganic coating and organic modification, the surface properties of titanium dioxide were changed, the photocatalytic activity was reduced and the photocatalytic activity was better compatible with the applied matrix, all of which promoted the full play of its optical properties to adapt to the needs of different application systems.

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