Titanium Dioxide (Tio2) is the most important white pigment used in the plastics industry.

The other white pigments used additionaly are Zinc Sulphide, Aluminium Silicate (Kaolin) and Barium Sulphate (Barytes), Magnesium Silicate (Talc), Calcium Silicate (Wollastonite). These provide some other properties such as electrical resistance by Kaolin, nucleation to semicrystalline polymers like PP and PA by Talc, reinforcement of plastics by Wollastonite and sound dampening or x-ray capacity by Barytes can and also provide white pigmentation.

TiO2 however offers much higher tint strength compared to all other alternatives. Zinc Sulphide, is the second best alternative, providing almost 75% of the whiteness offered by TiO2.

There are two different crystal structures of TiO2 : Anatase and Rutile.
The Rutile form has higher Opacity and better tinting strength compared to the Anatase form. The Rutile is also more weather resistant because it is less photocatalytically active. Due to its higher refractive index, the Rutile grade offers more scattering of light compared to the Anatase grade.

The typical comparative properties of TiO2 are summarised below :

T o prevent or restrict Photocatalytic activity ,TiO2 particle is required to be surface treated. The Rutile grade readily accepts Surface Treatments compared to the Anatase grade and therefore demonstrates better weather resistance and light fastness. Reduction in gloss as well as chaulking also takes place due to surface treatment. The surface treatment mainly creates a physical barrier between surface of TiO2 and polymer matrix. This barrier blocks the active sites as well as minimises degradation. There are several types of Inorganic and Organic surface treatments such as Alumina, combination of Alumina and Silica, Siloxanc or Polyols. Alumina and Silica tend to improve weathering while Siloxanes and Polyols provide better wettability.

Most of the TiO2 used are usually surface treated . Different surface treatments provide different attributes to the grades. It is therefore necessary to understand the characteristics of each grade before it is considered for an application.
The manufacturing process employed for TiO2 also influences the weathering characterstics. The Chloride Process is considered to be better for imparting weathering resistance.
The Particle size of TiO2 plays another important role in control of opacity. The particle size range between 0.2-0.4 micron provides opacity while higher particle could provide better durability. The smaller particle size also provides blues undertones while the coarser particles provide reddish undertones.
Rutile TiO2 provides high tinting strength and good weathering. On the other hand, the Anatase grade is lesser abrasive than Rutile grades and provide bluer colour tones.

Also Read
	Styrenics Business Scenario in India - 2002
	Superstrong UHMWPE fibers are gaining importance as antiballistic product material