Dear Johan Sanchez!

Thank you very much for such a clear and meaningful answer. The polyethylene I would like to mention here is the eye-drop LDPE bottles with thickness more than 1mm, not extruded film. They have a quite opaque appearance, do you know that people use TiO2 in these bottles?

Following your words, I regconized that TiO2 is not only used as white pigment but also UV absorber providing protection to the polymer. However, I found in the literature that TiO2/UV is widely used as an advanced oxidation technology to oxidize many chemical pollutants. So how do you think as per this issue: TiO2 serves as a protector or catalyst for oxidation of LDPE bottle under UV light? I absolutely feel confused as per this point of view.

Best regards,

hi all

TiO2 is a white pigment.

It contributes to opacify PE and decrease UV absorption thus increasing the photostability of the polymer.

However, its surface chemistry makes possible the so called photocatalytic effect: small amount of moisture undergoes a photocatalyzed reaction which gives some very reactive free radicals: H2O -> HO° + H°

this negative effect can be avoided by using a surface treated TiO2 (coated with Al2O3).

last, some stabilizers (antioxidants, UV absorbers) can be adsorbed by TiO2 particles at the detriment of overall photoxidative stability.

to make short a long story: some positive (opacification) and negative (photocatalytic effect, stabilizer trapping) effect

and a very specific effect depending on granumoletry, surface treatment, polymer thickness and stabilizer package

I hope it can help

ps: some literature paper to browse:

Eldar B. Zeynalov, Norman S. Allen. An influence of micron and nano-particle titanium dioxides on the efficiency of antioxidant Irganox 1010 in a model oxidative reaction. Polymer Degradation and Stability, Volume 86, Issue 1, October 2004, Pages 115-120

Peter P. Klemchuk. Influence of pigments on the light stability of polymers: A critical review. Polymer Photochemistry, Volume 3, Issue 1, January 1983, Pages 1-27

Dear Emmanuel Richaud!

Thank you very much for your answer. It's helpful for me!

Best regards,