Â«Non-NanoÂ» Zinc Oxide - Kobo Products Inc.

«Non-Nano» 

Zinc Oxide 

Pascal Delrieu, Yun Shao, and David Schlossman 

Kobo Products, Inc. 

SCC - Annual Scientific Meeting - December 2009 

www.koboproducts.com

Introduction 

• In the past years, arguments have been made by consumer 

groups and environmental organizations about safety of 

nanoparticles. 

• Accordingly, international regulatory agencies continue to 

move towards global «nano» regulation (ex : Amended 

European Union Cosmetic Directive in March 2009). 

• The control of TiO 2 and ZnO particle size has been known 

since the 1980’s to be a key element in obtaining optimum UV 

attenuation and a transparency acceptable for cosmetic use ; 

because it has a lower refractive index than titanium dioxide, 

zinc oxide was considered a more suitable choice as a nonnano 

sunscreen pigment. 


EU Directive - Nanoparticle Definition 

An insoluble or bio-resistant and intentionally manufactured 

material with one or more external dimensions, or an internal 

structure, on the scale from 1 to 100 nm 

Definition of Nanomaterials - Amended European Union Cosmetic Directive - 

March 2009 

The purpose of this study was : 

• to understand particle size measurement methods and the 

significance of their results 

• to apply these results to the development of non-nano ZnO 

sunscreen pigments 


Particle Size 

• The primary particle size (pps) is the size 

of the crystals obtained during the 

production process. 

• However, when supplied as a powder, 

particles are agglomerated (agglomerates 

typically in excess of 1 micron). 

Agglomerate 

PPS 

• To be used as a sunscreen, the size of these 

agglomerates have to be reduced : the size 

of the resulting aggregates affects the UV 

attenuation and transparency. 

Size 

reduction 

Aggregates 

Internal structure 


Significance of Size Measurement 

Mean / Median Particle Size 

Attenuation of a specific 

UV light range 

Tail/small sizes 

Nanomaterial regulations 

Tail/large sizes 

Contribute to 

skin whitening 


Size Measurement Methods 

• Electron Microscopy (SEM or TEM) + Image Analysis 

• Measure a global characteristics of a suspension (Light 

scattering, Brownian movement, sound attenuation, …) + 

Convertion to size and distribution 

• Results can be averaged using different methods : Length (or 

Number Mean) or Volume Mean ; Volume mean is generally 

preferred : AAPS Journal 2004:6(3) article 20 

d i 

Number mean = D[1,0] = 

n 

d i 

4 

Volume mean = D[4,3] = 

d i 

3 


Electron Microscopy & Image Analysis 

Transmission electron microscopy (TEM) 

Length / width of each visible 

particle is measured (manual / 

computer). 

Measures Primary Particle Size 

Scanning electron microscopy (SEM) 

Limitations and biases : 

• Sampling : reliable description of the 

size distribution implies a large 

number of particles (ISO 13322-1). 

• Geometry : analysis of 3-dimensional 

objects on a 2-dimensions image. 

• Ease of use : not a technique that can 

be routinely used for size 

measurements. 


Laser Diffraction 

• Laser Diffraction / Light Scattering 

instruments analyze the light scattering 

properties of a suspension of particles and 

convert it into particle size/distribution. 

• Gives a reliable description of the size 

distribution 

• Measures the size of aggregates in a solvent : cannot be used for 

measuring Primary Particle Size 

• Quick, easy to use & repeatable method 

• Depending on their polarity, some solvents can disperse inorganic 

UV filters efficiently, when others will promote agglomeration : 

size measurements need to be made in different solvents (IPA & 

Hexane) 


Possible Answers to Nano Regulations 

• Use current «nano» inorganic filters and mention “contains 

nanotechnology” on the label 

• Interpret the EU definition narrowly as Primary Particle Size 

(Electron Microscopy & Image Analysis) 

• Interpret the EU definition broadly as Aggregate Particle Size 

(Laser Diffraction) 

• Other possibilities (complex particles) 


Non-nano ZnO 

(Primary Particle Size greater than 100 nm) 


Large Size ZnO (USP3) 

Size = (long axis + short axis)/ 2 

Mean size : 170 nm 

% below 100 nm : 20 % 

Size = short axis 

Mean size : 126 nm 

% below 100 nm : 42 % 

205 particles measured 

200 nm 


ZnO-C - Non-Nano Zinc Oxide 

100 nm 

Data Courtesy of Sumitomo Osaka Cement 


ZnO-C - Particle size distribution (1) 

Frequency(%) 

Total(%) 

Measurement made on 5 SEM pictures 

representing about 600 particles 

Distribution calculated for 2-axis 

mean diameter 


ZnO-C - Particle size distribution (2) 

Measurement 

Cumulative Diameter 

D10% 

(nm) 

D50% 

(nm) 

D90% 

(nm) 

< 100nm 

(%) 

Mean Diameter 

(nm) 

Long-axis 189 343 651 0.3 396 

Short-axis 131 201 312 2.2 214 

Equivalent circular diameter* 150 232 365 0.9 249 

2-axis mean diameter 166 260 444 0.4 297 

Calculated using Mac-View (Particle Size Distribution Analysis Software) on 606 particles 

* projected area diameter 


Surface Treated ZnO-C - Distribution (1) 

Triethoxy Caprylylsilane - treated ZnO-C 

Frequency(%) 

Total(%) 

Measurement made on 7 SEM pictures 

representing about 600 particles 

Distribution calculated for 2-axis 

mean diameter 


Surface Treated ZnO-C - Distribution (2) 

Triethoxy Caprylylsilane - treated ZnO-C 

Measurement 


D10% 

(nm) 

D50% 

(nm) 

D90% 

(nm) 

< 100nm 

(%) 

Mean Diameter 

(nm) 

Long-axis 138 223 383 0 404 

Short-axis 110 150 236 0 239 

Equivalent circular diameter* 127 182 281 0 266 

2-axis mean diameter 135 196 311 0 317 

Calculated using Mac-View (Particle Size Distribution Analysis Software) on 678 particles 

* projected area diameter 


ZnO-C - Efficacy (W/O emulsion) 

In Vivo 

ZnO-C 

Ultrafine 

ZnO* 

SPF 12.1 ~15 - 20 

PFA 5.52 ~ 7.5 - 8 

In Vitro 

SPF 5.68 NA 

UVA ratio 0.88 ~ 0.6 -0.85 

Critical wavelength 

(nm) 

381 ~ 370 - 375 

• In-vivo test made with 3 panelists 

• 15 % ZnO 

* typical range 


ZnO-C - Transparency 

2 mg/cm 2 on tanned skin 

Ultrafine ZnO 

(60nm primary particle size) 

Non nano ZnO-C 


Non-nano ZnO 

(Particle Size in Dispersion greater than 100 nm) 


Surface Treatments Promoting Large Aggregates 

• ZnO are often surface treated to be hydrophobic for good wetting 

in a formula and pleasant skin feel. 

• We have evaluated several hydrophobic treatments for their 

capacity to promote larger aggregates 

• Jojoba ester treatment is able to cause the primary particles to 

form aggregates and meet the non-nano criteria 

Coating process 

Aggregates harder to dissociate 


Effect of Jojoba Esters Coating on Size 

ZnO (20nm Primary Particle Size) coated with 5% Jojoba Ester 

Powder dispersed in solvents 

IPA 

Hexane 

Percent of particles < 100nm 

• in IPA : 0% 

• in Hexane : 0% 


Performance of Non-Nano ZnO 

Formula Z-1 Z-2 

ZnO 20 nm Non-nano 

PS in disp. (nm) some < 100 nm all > 100 

SPF 17.4 22.4 

SPF/Active% 1.16 1.49 

PFA 8.17 8.67 

PFA/Active% 0.54 0.57 

• 15% ZnO in W/O sun lotion 

• in-vivo test, 3 panelists 


Jojoba Ester-coated ZnO - Transparency 

2 mg/cm 2 on tanned skin 

Nano ZnO 

Non nano ZnO 


Non-nano ZnO 

(Complex Particle : Small ZnO Particles trapped 

within a Large Polymer Bead) 


Complex ZnO-PMMA Particle 

• Small (20nm PPS) ZnO particles entrapped within 

a large (650nm) PMMA bead 

• 50% ZnO content 

ZnO 

20nm PPS 

PMMA Particle 


Particle Size Distribution 

Image Analysis of 2 SEM 

Pictures (171 particles) 

frequency(%) 

total(%) 

Size Measurement of 

D5 Dispersion 

(Laser Diffraction) 


Particle Size 

Measurement 


D10% 

(nm) 

D50% 

(nm) 

D90% 

(nm) 

< 100nm 

(%) 

Mean Diameter 

(nm) 

Long-axis 422 653 858 0.02 649 

Short-axis 402 628 837 0.17 617 

Equivalent circular diameter* 411 634 832 0.14 624 

2-axis mean diameter 426 661 898 0.12 664 

Dispersion (LD) 476 639 831 0 647 


Summary - Size Measurement 

• Concerns over safety of nano materials and changes in 

regulations have led to the need of inorganic UV filters for 

which a 'Non-Nano' label claim can be made. 

• Electron Microscopy coupled with Image Analysis is suitable for 

measurement of Primary Particle Size. 

• Laser Diffraction is suitable for the measurement of the 

particle size of aggregates in suspension. 

• Each techniques has limitations and biases, including 

calculation methods and sample preparation. 


Summary - Non Nano ZnO 

• ZnO-C, because of its relatively narrow distribution, can be 

used in sunscreens with great benefits (UVA). The percentage 

of primary particles bellow 100nm is very limited. 

• A Jojoba Esters treatment can be used to make large, 'Non- 

Nano' aggregates of nanoparticles, when measured with Laser 

Diffraction. 

• A submicron PMMA bead, containing nano ZnO particles, can 

also be used. 

• All the above products may meet the definition of non nano, 

depending on the interpretation of the new regulations. 


Acknowledgement 

• Sumitomo Osaka Cement 

• Neringa Kontrimiene 

• Carl Orr 

• Ed Bartholomey

Â«Non-NanoÂ» Zinc Oxide - Kobo Products Inc.

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