# Presentation: 062945

## Perspectives on Supplying Attenuation Grades of Titanium Dioxide and Zinc Oxide for Sunscreen ApplicationsDavid Schlossman, Yun Shao, Ph.D., Pascal Delrieu, Ph.D., Kobo Products Inc.

**Perspectives on Supplying Attenuation Grades ****of Titanium Dioxide and Zinc Oxide ****for Sunscreen Applications****David Schlossman, Yun Shao, Ph.D., **_**Pascal Delrieu**_**, Ph.D., ****Kobo Products Inc.**

## Inorganic UV Filters 

- Titanium dioxide (TiO2) and zinc oxide (ZnO) pigments are commonly used in personal care products to provide protection against UVA and UV B
- They attenuate UV light by absorption and scattering
- They are usually surface coated to minimize photo-catalytic activity.
- They are typically produced as finer crystals from the same feed stocks and with similar processes as pigmentary grades.

## Manufacturing Process

- Attenuation grades

- Pigmentary grades

- 10nm 			          200nm

**Manufacturing Process**

- The production of TiO2 and ZnO is a two step process :
- 1. Purification of the raw material
- 2. Growing of crystals (primary particles) of the desired size
- They are two different processes for TiO2, known as sulfate and chloride, and three for ZnO, known as American, French and Wet.
- Crystals are grown at high temperatures to the required sizes : 200 nm and above (pigmentary grades) and finer than 200 nm (attenuation grades).

## Surface Treatment of Inorganic UV Filters

**Surface Treatment of Inorganic UV Filters**

*M. Kobayashi and al., Cosm & Toil., Vol. 112, No. 6, p83, 1997*
** Rate constant of the first order reaction of oxydation of acetalydehyde*
- It is common industry practice to use surface treated inorganic UV filters when formulating sunscreens.

## Optical Properties - TiO2 and ZnO

- TiO2 :	420 nm (rutile) / 390 nm (anatase)
-  ZnO :	380 nm (3.24 eV)

- _Scattering_
- Refractive Index :
- TiO2: 	2.76 ( Rutile) / 2.52 (Anatase)
- ZnO: 	1.99

- Wavelength

- Particle size

**Optical Properties - TiO2 and ZnO**

- Attenuation of UV light is influenced by particle size.
- Scattering of visible light (whitening effect) is influenced by particle size and the difference between the refractive index of the pigment and the surrounding media.
- Maximum scattering occurs when size equals 1/2 the wavelength and particles are uniformly dispersed (Mie theory).

## Particle Size and Light Scattering

**UV**

**Visible**

**Size reduction**

**Whitening**

**Transparent**

**Typical existing form supplied >1 ********m**

**Particle Size and Light Scattering**

## Dispersions of Attenuation Grade TiO2

**15 nm TiO****2**

**35 nm TiO****2**

**Dispersion    vs    Powder**

**Freeze Fracture TEM (40,000X)*

**Dispersion    vs    Powder**

- Comparison of Dispersions and Powders

- Smaller primary particles are more difficult to disperse :
- 11/1 ratio of dispersion size to primary particle size for 10 nm TiO2).

**Dispersions of Attenuation Grade TiO2**

## TiO2 Dispersions in Cyclopentasiloxane

- 	195	60	35	15	10	nm

- 	195	60	35	15	10	nm

- 	195	60	35	15	10	nm

- 	195	60	35	15	10	nm

**TiO2 Dispersions in Cyclopentasiloxane**

**10nm TiO2 (110 nm dispersion particle size) makes transparent dispersions for all skin types.**
*All dispersions diluted in Cyclopentasiloxane (to 20% TiO2)*

## Particle Size and UV attenuation

**Particle Size and UV attenuation**

*308/360 extinction ratio : indication of UVB/UVA balance*
* **308/524 extinction ratio : indication of transparency*

## Inorganic Sunscreen Formulations  

** Tests were performed by Consumer Product Testing Co.  - All testing on 3 people*
*** FDA method*
**** JCIA PPD method  (Rating 2-4: +; 4 - 8: ++; 8 - 12: +++).*

**Inorganic Sunscreen Formulations****  **

- Effect of Particle Size on Attenuation

## Conclusions

**Conclusions**

- Attenuation grade Titanium Dioxide and Zinc Oxide are produced using the same processes as larger pigmentary grades. They are usually surface coated to minimize their photo-catalytic activity.
- TiO**2 **and ZnO attenuate UV light according to their particle size :
- Small primary particle sizes (10 - 15 nm) are necessary to produce dispersions (100 - 150 nm) transparent to visible light and efficient against UVB.
- ZnO and larger TiO2 (35 - 150 nm) are more efficient against UVA.
- The particle size of pigmentary grades are appropriate to scatter visible light, but they are not efficient at attenuating UV light or effective as sunscreens.