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AdNano Zinc Oxide Properties, Applications, Manufacturing and Product Availability, Supplier Data By Degussa

Topics Covered

Background

Applications

AdNano® Zinc Oxide as a mineral UV Filter

Heterogeneous Catalysis

Biological Action

Product Properties

UV Filter Effect

Dispersing Properties

Purity, Solubility, Morphology

Packaging and Storage

Manufacturing of AdNano® Zinc Oxide

Background

AdNano® zinc oxide has the potential to improve products by providing valuable additional functions in a wide variety of applications. Examples include transparent cosmetic UV protection and transparent UV-protected coating or polymer systems. The high chemically accessible surface area of AdNano® zinc oxide additionally provides an array of potential uses in areas such as crosslinking, chemical catalysis, biostatics, and corrosion protection. In some instances, it is also possible to reduce the quantity of zinc oxide used when substituting conventional grades of zinc oxide.

In addition, Degussa offers significant expertise in adjusting the material to different systems. Through the availability of surface modification and sample dispersions, the rapid qualification of AdNano® zinc oxide can be facilitated in the most demanding applications.

AdNano® zinc oxide is available in the following grades:

•        VP AdNano® ZnO 20 hydrophilic version

•        VP AdNano® Z 805 silanized hydrophobic version

•        TEGO® SUN Z 500 hydrophilic version: high purity cosmetic grade

•        TEGO® SUN Z 800 silanized hydrophobic version: high purity cosmetic grade

•        Sample dispersions of VP AdNano® ZnO 20 or VP AdNano® Z 805 according to request

Applications

AdNano® Zinc Oxide as a mineral UV Filter

Surfaces exposed to direct sunlight often require effective, long-lasting UV protection. Mineral UV filters distinguish themselves from most conventional UV absorbers by their high stability and long life. Degussa’s extensive formulation know how and expertise in both cosmetic and coating or polymer applications provide for the effective use of mineral filters. High-purity TEGO® SUN Z 500 and TEGO® SUN Z 800 are offered for personal care applications.

As one example (shown in Figure 1), the UV-protective action of VP AdNano® ZnO 20 and VP AdNano® Z 805 in coatings is exhibited in aqueous acrylic/polyurethane clear coatings. AdNano® zinc oxide is formulated at 2% and applied to metal sheets with the white priming coat. With effective dispersion of the zinc oxide in the formulations, the samples containing VP AdNano® ZnO 20 show distinctly better 60° gloss values after a QUV test in comparison to the sample with an organic UV filter (benzotriazole,2.6%).

AZoNano - The A to Z of Nanotechnology - High Gloss Retention

Figure 1. High gloss retention.

The advantage of reduced yellowing (Figure 2) after weathering of another pure PU water-based coating formulated with VP AdNano® ZnO 20 has also been demonstrated. The suitability of AdNano® zinc oxide for UV protection has to be confirmed using weathering tests for each polymeric or coating system in which it is intended for use.

AZoNano - The A to Z of Nanotechnology - Less yellowing

Figure 2. Less yellowing.

Heterogeneous Catalysis

The high yield provided by copper/zinc oxide catalysts in methanol synthesis is attributable essentially to zinc oxide. Using nanostructured systems has the potential to contribute to improved technical processes. The high accessible surface area of AdNano® zinc oxide minimizes diffusion-limited processes during catalysis.

Biological Action

Zinc is an essential trace element necessary for human and vertebrate nutrition. It does not accumulate in the human organism. The Federal Drug Administration (FDA) in the USA has classified zinc oxide as “generally regarded as safe”, meaning that zinc oxide can be used as a food additive. Zinc oxide is used particularly in vitamin/mineral preparations.

The solubility of zinc oxide and the action of zinc ions on algae and bacteria is one reason for classifying zinc oxide as “very toxic to aquatic organisms” and “environmentally hazardous.”

During storage, transport, use and disposal, the appropriate instructions must be followed and the safety data sheets which are provided must be consulted. AdNano® zinc oxide does not differ in this aspect from conventional pigmentary zinc oxide.

Product Properties

UV Filter Effect

AdNano® zinc oxide is an effective UV-A filter. High transparency in the visible wavelength range (400-800 nm), combined with a strong filter action in the intensive UV-A spectrum of sunlight is a special feature of this product. These desirable optical properties are achieved only through proper dispersing, using equipment with high shear forces (e.g. rotor-stator equipment, bead mills or a 3-roll mill).

Zinc oxide has distinctly lower photocatalytic activity than, for example, titanium dioxide, enabling it to be used as a UV filter in various coating and polymer systems, even without protective coating with SiO2 or other systems.

Dispersing Properties

Additives can improve the degree of zinc oxide dispersion in a given medium and prevent reagglomeration of the aggregates. A 1-3% addition (in reference to zinc oxide) of polyacrylic acid (sodium salt; MW 2100) performs well for dispersion stabilization in most aqueous systems. Dispersion samples in water or solvents are available on request.

Table 1. Flexibility of VP AdNano in different solvent systems

VP AdNano® Additive (Conc. ref. ZnO)

ZnO 20
none

ZnO 20
A (10-25%)

Z 805
B (10-20%)

Toluene

 

Dowanol PM

 

Dowanol PPh

 

Ethanol

 

Ethyleneglycole

 

Methoxypropylacetate

 

DBE

 

n-Butylacetat

 

Ethylmethylketon

 

Table 1 provides a good impression of the flexibility of VP AdNano® ZnO 20 and VP AdNano® Z 805 in different solvent systems. Dispersion was carried out using an ultrasound finger. All d50 values (PCS) are in the range of 100-170 nm.

Purity, Solubility, Morphology

Utilizing pure feedstocks and a non-contaminating synthesis process, the product is obtained in high purity (zinc oxide content >99.5%). The requirements of USP 27/zinc oxide are met. Like other zinc oxides, VP AdNano® ZnO 20 is amphoteric. It completely dissolves at room temperature in 10% acetic acid and with heating in 2 M NaOH solution. A 4% VP AdNano® ZnO 20 dispersion in water has a pH of 7.6. Under these conditions, 5.4 ppm of zinc ions are in solution. In neutral medium (pH 7.0), the solubility of VP AdNano® ZnO 20 is about 0.023%, or comparable to pigmentary zinc oxide.

AdNano® zinc oxide is a crystalline solid exhibiting the hexagonal wurtzite lattice just as the naturally occurring mineral zincite. The zinc atom is surrounded tetrahedrally by four oxygen atoms.

The smallest units of the compound, visible only with the electron microscope, are the primary particles. Based on this high degree of particle fineness, 1 gram of VP AdNano® ZnO 20 can provide an active surface of 20-25m2.

TEM pictures show that the primary particles are practically never isolated. They are typically joined to each other to form aggregates. The effective particle size, which is present – for example in a dispersion – is therefore in the range of 100 nm.

In AdNano® zinc oxide powder, the loose agglomerates can have sizes of up to one millimeter.

The aggregates can contact each other at points, e.g. via hydrogen bridge bonds, thereby forming a loose agglomerate structure. Accordingly, the tapped density of AdNano® zinc oxide is only ca. 200 g/L. The general dust limit of 5 mg/m3 is maintained with proper handling. Pneumatic conveying of the product can be performed in a trouble-free manner.

Most applications require the reduction of the agglomerates down to the aggregate size by way of intensive shear forces. Typically, this is required in order for the full performance potential of the nanostructured material be utilized.

Packaging and Storage

The standard container size for VP AdNano® ZnO 20 is 10 kg paper bags certificated for dangerous goods. The product is shipped on CP3 pallets with 28 bags each (=280 kg) for larger quantities. VP AdNano® Z 805 is available in 25 kg paper bags, certificated for dangerous goods and is also shipped on CP3 pallets with 28 bags each for larger quantities.

It is recommended to store the product dry in sealed containers protected from volatile substances and to process it within two years after production. Samples of AdNano® zinc oxide are shipped in plastic containers containing 200 grams each.

Manufacturing of AdNano® Zinc Oxide

High purity feedstocks are used to manufacture AdNano® zinc oxide. The conversion to zinc oxide is accomplished in the gas phase. After cooling, the solid zinc oxide is separated from the gas stream and fed into a silo. The hydrophobic VP AdNano® Z 805 is manufactured from VP AdNano® ZnO 20 in a continuous post-treatment process by silanization. This reaction results in elevated compatibility in high-grade coating systems.

 

For more information on this source please visit Degussa.

 

Date Added: Jul 1, 2006 | Updated: Jun 11, 2013
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