Nanomaterials

Nanotechnology term

Nanotechnology derives from the Greek word nãnnos, meaning dwarf, and refers to a heterogeneous field of technology that deals with structures on the nanometre scale (one nanometre equals one billionth of a metre or 10-9 m). At this dimension, materials exhibit novel properties that often cause uncertainty.

A thorough investigation of the effects of nanomaterials and open communication are essential.

Definition of nanomaterials

According to definitions by the International Organisation for Standardisation (ISO), the term ‘nanoscale’ refers to matter in the size range from 1 nm to 100 nm [ISO/TS 27687:2008].

Figure 2.1: Overview of the definitions in the field of nanotechnology (the terms already defined by ISO/TS 27687:2008 are highlighted in grey).

Further ISO standards for nanotechnology are currently being developed, including ISO/TS 12901, which contains definitions for nanostructured materials, and ISO/TS 11751, which defines carbon nanomaterials.

Agglomerates and aggregates

Agglomerates or aggregates are formed when nanoparticles combine to form larger composite systems. An agglomerate refers to a collection of weakly bound particles. The surface area of the agglomerates is comparable to the sum of the surface areas of the individual particles. The term aggregate, on the other hand, refers to particles that are strongly bound to each other. Surface area of the aggregate can be significantly smaller than the sum of the surface areas of the individual components. The nanostructures involved in the aggregation are referred to as primary particles, while aggregates, like agglomerates, are classified as secondary particles and belong to nanostructured matter.

Occurrence of nanomaterials

The natural occurrence of nanoparticles is largely due to volcanic eruptions and forest fires. Nanoparticles are unintentionally released through combustion processes in transport or energy conversion, mechanical wear and tear, and numerous industrial processes. The combustion of diesel produces complex mixtures of soot, sulphates, lubricants, unburned fuel residues and polycyclic aromatic hydrocarbons (PAHs) with an average particle diameter of 5–20 nm. During welding, the high temperatures mainly produce metal oxides, including the oxides of metals such as aluminium, cadmium and copper. Nanoparticles produced industrially, mostly on a large scale, include carbon black and metal oxides such as silicon, aluminium or titanium dioxide, metals such as gold and silver, and semiconductors such as gallium arsenide.

Nanoscale metal oxides

Due to their mechanical, optical and electrical properties, nanoscale metal oxides are of great importance for both industry and science and are widely used in the consumer goods sector. The best known and most systematically characterised metal oxides in nanostructured form include titanium dioxide, silicon dioxide, aluminium oxide, zinc oxide and iron oxide. These inorganic nanoparticles are used as UV protection in cosmetics and textiles, as photocatalysts with antibacterial properties or as additives in food and food contact materials.

In cosmetics, they are mostly found in sunscreen products, where consumers can recognise these substances by the addition of (nano) in the INCI declaration.

The most commonly used metal oxide is nanoscale titanium dioxide. This semiconductor is characterised above all by its efficient absorption and scattering of UV light and is therefore used in sunscreen creams or on textiles. Particles with a diameter of 20–40 nm are usually used for this purpose, as this is the optimal particle size range according to Rayleigh scattering theory. Due to its photocatalytic properties and the resulting potential generation of superoxide and hydroxyl radicals, it is now only used coated and in the rutile form with a maximum of 5% anastase structure in cosmetics.

Increased reactivity of nanomaterials

Matter of the same chemical composition in the micrometer range has comparable physical properties, regardless of its actual size. Reducing the size of the material to the nanometer range results in new properties.

The properties also differ from those of the material in atomic or molecular form. Nanomaterials thus occupy a transitional state between atomic/molecular and coarse-structured matter.

One possible explanation is that the surface area increases exponentially in relation to the volume as the particle diameter decreases. This also increases the proportion of surface atoms: at a diameter of 10 nm, nanoparticles have 20% of the approximately 30,000 atoms of the entire particle on their surface, while nanoparticles with a diameter of 2 nm already have 80% of the atoms on the surface.

As the particle diameter decreases and the proportion of surface atoms increases, the proportion of surface energy in the total energy also increases. This results in increased reactivity, and the properties of the nanoparticles are primarily determined by the atoms on their surface and no longer by the atoms inside the particle, as is the case with extended solids.

Toxicological considerations of nanomaterials

Nanostructured substances could potentially be absorbed through the skin. The increasing use of synthetic nanomaterials in cosmetics, e.g. shampoos, sun creams, etc., could increase this risk. In addition, airborne NPs can be deposited on the skin.

However, compared to the lungs or the digestive tract, the skin offers a relatively small surface area of approximately 2 m² (lungs: 140 m², intestines: 400 – 500 m²). Healthy and undamaged skin forms an effective barrier against external influences thanks to its dense cell layers.

In vitro penetration studies of cosmetic products containing nanoparticulate ZnO or TiO2 did not find any penetration of the skin.

Our conclusion

Ultimately, the extent to which nanomaterials are used in cosmetics depends on communication, the brand and the product concept. It is certainly wrong to demonise nanomaterials per se, as these materials are present in large quantities in our civilisation. In the field of sun protection, physical, nanostructured UV filters such as titanium dioxide offer proven added value.

However, Cosmacon refrains from using nano-compounds per se, unless our customers expressly request them. Please feel free to contact us for advice.

Literature

Paschen H, Coenen C, Fleischer T, Grünwald R, Oertel D, Revermann C, 2004. Nanotechnology, Springer-Verlag, Berlin 1st edition

Biological effects of selected nanostructures in cells of the gastrointestinal tract; Dissertation; Joanna Pelko, 2010

Som C, Nowack B, Wick P, Krug H. 2010. Nanomaterials in textiles: environmental, health and safety aspects. EMPA Materials Science & Technology

Höpker K, Wurster U, Kunigkeit G, Ott G, 2007. Application of nanoparticles. LUBW, State Agency for the Environment, Measurements and Nature Conservation Baden-Württemberg: 13

Donaldson K, Aitken R, Tran L, Stone V, Dun R, Forrest G, Alexander A. 2006. Carbon nanotubes: a review of their properties in relation to pulmonary toxicology and workplace safety. Toxicol Sci 92(1): 5 22.

Donaldson K, Tran L, Jimenez LA, Du‑n R, Newby DE, Mills N, MacNee W, Stone V. 2005. Combustion-derived nanoparticles: a review of their toxicology following inhalation exposure. Part Fibre Toxico 2(10).

Burniston N, Bygott C, Stratton J. 2004. Nano Technology Meets Titanium Dioxide. Surface Coatings International Part A: 179-814

Niederberger M. 2004. Metal oxides – nanoparticles with special properties. http://www.laborpraxis.vogel.de/articles/106377/, 11 July 2010

Meili C, Widmer M, Husmann F, Gehr P, Blank F, Riediker M, Schmid K, Stark W, Limbach L. 2007. Synthetic nanomaterials. Risk assessment and risk management. Basic report on the action plan. Environmental Knowledge No. 721, Federal Office for the Environment (FOEN) and Federal Office of Public Health (FOPH), Bern, www.umwelt-schweiz.ch/uw0721-d.

Pflücker F, Wendel V, Hohenberg H, Gärtner E, Will T, Pfeiffer S, Wepf R, Gers-Barlag H., 2001. The human stratum corneum layer: An effective barrier against dermal uptake of different forms topically applied micronised titanium dioxide. Skin Pharmacol Appl Skin Physiol 14: 92-97

Lademann J, Weigmann H, Rickmeyer C, Barthelmes H, Schaefer H, Mueller G, Sterry W. 1999. Penetration of titanium dioxide microparticles in a sunscreen formulation into the horny layer and the follicular orifice. Skin Pharmacol Appl Skin Physiol 12(5): 247-256.