Nano-sized oxide powders for UV applications Nano-sized oxide powders for UV applications
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
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Some properties change dramatically with sizeSome examples (where Umicore is active) :
! Optical: from colored to transparent
UV protection
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(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?
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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
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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
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2. Umicore UV absorbers
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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%
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Umicore UV absorbers1) Nano Mn-doped TiO2 (Optisol®)
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r rat
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Optisol TM sunscreenCommercial sunscreen ACommercial sunscreen BCommercial sunscreen CCommercial sunscreen D
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No star
UVA Star Rating System (Boots)
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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
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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
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Umicore UV absorbers2) Nano ZnO (Zano®)
• Typical physical properties:SSA (BET): 30 m2/g - 35 nm
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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
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2
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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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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