nano-sized oxide powders for uv applications · nano-sized oxide powders for uv applications...

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Nano-sized oxide powders for UV applications

Nano-sized oxide powders for UV applications

1. Introduction

2. Umicore UV absorbers

3. The importance of stable dispersions

4. Conclusions

Presentation outline

1. Introduction

Innovation for Sustainable Production (I-SUP2008) Bruges 22-25 April 2008

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Some properties change dramatically with sizeSome examples (where Umicore is active) :

! Optical: from colored to transparent

UV protection

0,0

0,5

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250 300 350 400 450 500Wavelength (nm)

Abs

orba

nce

(A)

Standard ZnO Zano

! Chemical : from inert to active

catalysis (Precious metals , oxides)

! Thermal: from stable to low temperature sintering

printed electronics (nano Ag)

Nano: Hype or future?


Inorganic UV absorbers

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! Some inorganic powders (as TiO2, CeO2, ZnO):• are broadband UV-absorbers• guarantee long-term protection• don�t migrate out of or in the coating (environmentally friendly)• are heat resistant

! Inorganic pigments have relatively high refractive index, therefore: • Particle size distribution should be well below 100 nm• Particles should be well dispersed in application to maintain transparancy


Inorganic UV absorbers

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! Umicore has a portfolio of UV-absorbing nanomaterials: • Nano TiO2 (Optisol®)• Nano ZnO (ZANO®) and • NanoGrain® CeO2

! Potential markets : • Coatings• Plastics• Cosmetics• Textiles

! Such UV-absorbers often have other synergistic properties


2. Umicore UV absorbers


Umicore UV absorbers

ConventionalTiO2

Optisol®Mn-doped TiO2

OH

OH�OH

OH

OH

OH

OH

Ultraviolet Ultraviolet

Free radicalsformed

Mn

OH�

1) Nano Mn-doped TiO2 (Optisol®) for cosmetic applications

! Special modified TiO2 powder:• Specific surface area: 20 m²/g (70nm)• 100% rutile crystal phase structure• Doped with manganese: 0.65-0.69wt%


Umicore UV absorbers1) Nano Mn-doped TiO2 (Optisol®)

Time / min0 20 40 60 80 100 120

Sta

r rat

ing

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Optisol TM sunscreenCommercial sunscreen ACommercial sunscreen BCommercial sunscreen CCommercial sunscreen D

*****

****

***

**

*

No star

UVA Star Rating System (Boots)


Umicore UV absorbers1) Nano Mn-doped TiO2 (Optisol®)Performance:

• Most sunscreens mainly protect UVB (sunburn), only slightly UVA (skin ageing, skin cancer)

→ Increased UVA protection (50% increase)

• Most sunscreens only protect the skin formaximum a few hours

→ Up to 6 hours protection

• High Skin Protection Factors (SPF) result in a white-coloured sunscreen which can be hardlyspread out

→ Transparent sunscreen can be easily spread out


Nano-ZnO (Zano) for personal care applications

� 2 available products:� Zano 10: uncoated zinc oxide� Zano 10 Plus: coated zinc oxide

�Coating on Zano 10 Plus will enhance dispersion and compatibility of Zano in oil phases of emulsions

�Advantage of Zano as UV absorber in personal care applications:

� Long-term protection� Broad band protection (UVA and UVB)� Non-whitening on the skin


Umicore UV absorbers2) Nano ZnO (Zano®)

• Typical physical properties:SSA (BET): 30 m2/g - 35 nm


Umicore UV absorbers3) Nano CeO2 (NanoGrain® CeO2)

• Typical physical properties:BET: 60 m2/g - 15 nm


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Nano ZnO and CeO2: excellent transparent UV absorbers

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nano ZnOnano CeO2

UV/vis absorbanceUVB UVAUVC

�ZnO is a broad-band UV absorber

�CeO2 is most efficient in UVB


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Why nano?

•Transparency, determined by:• Size of particles in a coating• Refractive index:

ZnO: 2.0, CeO2: 2.2, (TiO2: 2.6)

• Particle concentration in the system/film

• Scattering determined by particle size to power 6 → nano particles to ensure transparency

62

2

24

2

2

0 2212

2)cos1(

+−

+= d

RII

ηη

λπθ

Raleigh scattering


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Why nano?

•Transparency of wood coating with nano and pigment grade ZnO

� Pigment grade ZnO: 150-300 nm

� Nano ZnO: ~35 nm

nano ZnOpigment ZnOno ZnO

3. Importance of stable dispersions


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Dispersion and stabilization

• Agglomerates of nano particles will behave as micron sized particles and needs to be prevented at all times → development steps:

Powder development and synthesis

Applicationcompatibility

Dispersionand

stabilisation

• De-agglomeration of particles:• Overcome the Van der Waals interactive forces


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Dispersing nano particles

•De-agglomeration of particles:• Apply the right amount of energy to obtain desired results

Low

�Used to prepare pre-mixes�De-agglomeration not optimal

�Examples: �dissolver

Intermediate

�Low solids loading�De-agglomeration

�Examples:�ultrasone�rotor-stator

High

�High solids loading�De-agglomeration and milling

�Examples:�bead mills�ball mills


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Importance of dispersion stability

•UV/vis spectrum upon dispersion instability

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Stable dispersionInstable dispersion

�Increased absorbance in visible light region → decreased transparency

�Decreased absorbance in UV region

abso

rban

ce


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Example: Water based Zano® 30 dispersion

•Solids content 50 wt%•Mean particle size ~35 nm•Introduced into water-based PU wood coating

nano ZnO in 25µm (dry) water-based PU coating

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Wavelength (nm)

Tran

smitt

ance

(%)

Ref. (no ZnO)

1w% ZnO

2w% ZnO

5w% ZnO

UV/vis transmission

PSD measured via XDC


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Degradation of ZnO versus organic UV absorbers

•degradation overviewPerformance of UV absorbers during QUV-A exposure

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QUV test duration (hours)

perf

orm

ance

(%)

Benzophenone-12

Cyanoacrylate

hydroxyphenyl-benzotriazole

ZANO (s-b alkyd)

ZANO (w-b PU)

4. Conclusions


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Conclusions

� All TiO2, ZnO and CeO2 are efficient UV absorbers:� TiO2 (Optisol®) used in cosmetic sunscreen formulations� ZnO is a true broad band UV absorber� CeO2 is most effective in UV-B

� Optisol Mn:TiO2 offers:� Increased UVA protection (50% increase)� Up to 6 hours skin protection� Transparent sunscreen xhich can easily spread out


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Conclusions

� Stable dispersions and full compatibility with coating system are important to ensure:� Transparency of the clear coating� Most efficient protection against UV radiation

� Inorganic UV absorbers truly provide long-term protection:� After 1300 hours QUV ZnO still provides more than 90-95% effectiveness� Most of the commonly used organic UV absorbers degrade fast over time

� Recommended level: 2-3w% of ZnO or CeO2 relative to the dry coating film

nano-sized oxide powders for uv applications · nano-sized oxide powders for uv applications...

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