Factors Affecting the Dispersibility of Titanium Dioxide
1、Electrical resistivity
It is usually difficult to avoid the introduction of a large number of impurity ions during our surface treatment of rutile titanium dioxide, of which anions such as SO42+, Cl- and cations such as Na+ are common. Although the production process conditions vary from manufacturer to manufacturer, they all have an adverse effect on the dispersibility of the final product.
For this reason, it is necessary to remove impurities from the product after surface treatment, and this indicator is often expressed in terms of resistivity.
2、The PH value of the system
During the preparation of titanium dioxide, the PH value itself varies considerably. Understanding the influence of this indicator on the dispersibility will help us to control the PH value of the titanium dioxide within a more effective range and to improve the dispersion of the titanium dioxide in the aqueous system as much as possible.
The PH value of the system will also be an important factor affecting the dispersion of rutile titanium dioxide in aqueous systems close to the ideal state, and the main mechanism of its influence may still be attributed to the double electric layer.
3. Surface chemical properties
In practice, in water-based coating systems, the ξ potential increases rapidly with the increase in the unit adsorption of titanium dioxide, but when the ξ potential rises to a certain level, the increase becomes progressively slower. This indicates that the titanium dioxide particles must reach a certain adsorption capacity in order to have a certain charge stability, which has far-reaching implications for the actual formulation of waterborne coatings.
As the particles of titanium dioxide become finer, the proportion of surface atoms increases. At different pH values, the surface chemical properties of the powder dispersed in water are determined by the H+ and OH- particles adsorbed onto the particle surface.
4、Influence of water-based coating dispersant on the properties of titanium dioxide powder
Under the condition that the content of titanium dioxide remains unchanged, the amount of adsorption per unit is directly proportional to the content of the dispersant. According to the DLVO theory of colloidal stability, there is a van der Waals attraction between the colloidal masses, and the masses are close to each other due to the overlap of the double electric layer and the repulsion, the stability of the colloid depends on the relative size of the attraction and repulsion between the masses. In the preparation of slurry, in order to obtain a highly dispersed and stable slurry, some polymer electrolytes are usually used to improve its suspension properties.
The introduction of dispersant increases the absolute value of ξ potential on the particle surface, which is due to the addition of dispersant, negatively charged anionic groups of dispersant adsorbed on the surface of titanium dioxide particles, making the negative charge on the particle surface higher, the highest charge density on the particle surface, and the maximum electrostatic repulsion between particles, so the slurry has the best dispersion. Therefore, the preparation of high solids titanium dioxide slurry selection of the best pH value should be in 8 ~ 9.
5、Influence of water-based coating dispersant on the rheological properties of titanium dioxide slurry
The rheological properties of the suspension are determined by the solid content of the slurry and the interaction between the particles. Titanium dioxide powder in the water medium is prone to agglomeration or flocculation, affecting the stability and uniformity of the slurry. The addition of dispersant not only improves the surface characteristics of the powder, but also has a greater impact on the rheological behaviour of the titanium dioxide suspension, by adding dispersant method can obtain low viscosity, high stability and good uniformity of the coating slurry.
But too much dispersant, excess dispersant molecules bridge each other to form a network structure, limiting the movement between the particles, making the rheology poor.
