Nanomaterials: Properties, Preparation and Applications - Environmental and Human Health Impacts of Nanotechnology - page 66

Other (5%)

Friction Products
(29%)

Roofing materials
(48%)

Gaskets (17%)

Paper (1%)

Figure 2.20 The relative use of asbestos in commercial and industrial applications in the
United States in 1997. (Adapted from Spengler et al. , 2001.)

market for asbestos and its dark history currently serves as a warning for future
manufactures of nanomaterials and probably is currently serving as a break on the
rate of commercialisation of nanotechnology in the west. This history of asbestos
clearly shows not only the need to understand the toxic effects of nanomaterials,
but also how a material with exceptional properties can rapidly fi nd uses in a very
wide range of products and applications.

2.6.1.2 Carbon Black

Carbon black containing rubbers have excellent wear properties and the neat mate-
rial also unrivalled optical properties. In 1995 its world wide production was 7200
tonnes per annum (Gardiner, 1995). Its use as an ink, as already discussed, predates
industrial production by thousands of years. However, as a source of black pigment
it still has excellent properties. This is because the carbon particles absorb light over
a wide range of the optical spectrum with little bleaching of the colour with time.
Generally, an ink will actually comprise of a suspension of carbon black in a suit-
able carrier liquid; in ancient times this might have been an oil or water. To date,
the use of carbon black in tyres accounts for the largest use of the material. The
incorporation of carbon black into the rubber has a signifi cant impact in increasing
the wear properties of the rubber and thereby increasing tyre life. Several studies
have been conducted on the effects of carbon black on human and animal health
and there are some excellent reviews on the subject. Gardiner (1995) generally
found that the carbon black itself has little adverse effect on organisms. However,
recently particular concern has been placed on aerial exposures and carbon black
particles containing signifi cant levels of PAHs. It is suffi cient to say that the effects
of carbon black on human health are not considered to be as signifi cant as those
relating to asbestos. However, the history of carbon black give a good demonstra-
tion of how the complexity of a nanomaterial, in this case a chemically simple one,
can cause diffi culties in assessing their effects on human health.

2.6.2 The Present and Near Future

The use of asbestos and carbon black date back more than fi ve decades. In this section
present applications of nanomaterials (

< 30 years) are discussed. It will particularly