Materials in “Green” Technologies - Thanatia: The Destiny of the Earth's Mineral Resources - page 519

high amount of energy needed to produce primary aluminium from alumina will
impose an increase in the use of secondary aluminium as was seen in Chap. 8.
After aluminium, rubber for tyres and other minor parts like engine mounts,
seals, hoses and belts, is the next most commonly used material in vehicle manu-
facture. Indeed around 75% of the world's rubber production is used for vehicle
tyres, and they are so integral to vehicle function and performance that about 20%
of a car's fuel consumption corresponds to them directly 10 . Rubber consumption
within the automobile industry utilises approximately 79% new rubber. Of the new
rubber some 57% is synthetic and a smaller proportion is natural. Natural rub-
ber is obtained from latex whilst artificial rubber comes from the polymerisation
of monomers such as 1-3 butadyene. Both need to be vulcanised to create a more
durable material. This is done with chemical additives like sulphur that cross-link
the individual polymer chains with sulphur atoms. Such rubber is however not
easily recoverable or recyclable (Kumar and Nijasure, 1997).
According to the tyre manufacturer Continental (Continental, 1999) the vulcan-
isation process leaves about 4 g of zinc oxide, 2.3 mg of cadmium oxide and 11 mg
of lead oxide per tyre, that later become dissipated either in its use and/or disposal.
Considering that scrap tyre generation accounts for some 3.2 thousand tonnes per
annum solely in Europe, this is by no means a negligible amount (Reschner, 2008).
And contrary to most metals, rubber cannot be recycled to produce new rubber
with down-cycling the only alternative to date. This means that tyre production
levies an important pressure on natural resources.
Glass is the fifth most used material in vehicles 11 . The world's demand of flat
glass in 2007 was estimated at around 44 Mt. On average, the world consumes 6
kg of glass per person per annum with China, Europe and United States presently
covering around 80% of the worldwide demand 12 . Its production thus entails large
levels of energy consumption, important GHG emissions and the use of key ma-
terials 13 Remelting recycled glass represents a 25% energy saving with respect to
producing glass from raw materials 14 .
For safety and security reasons, road vehicle manufacture requires special lami-
nated glass in windscreens, which involves the placing of a polymeric material be-
tween two or more glass layers. Cerium (IV) oxide is an important component that
absorbs UV radiation whilst remaining transparent to visible light. Consequently
Ce, supplied predominately in China, is a component of the windows and mirrors
of new vehicles. It is also used in catalytic converters to reduce vehicle emissions.
10 See http://www.industrialrubbergoods.com/rubber-tire.html, Accessed, Aug. 2012
11 After the construction industry, the automotive industry represents the largest demand, ac-
counting for 15-20% of the market.
12 See http : ==www:agc flatglass:com=AGC Flat Glass=English=About us=Glass
market=page:aspx=1372. Accessed Aug. 2012.
13 As an example, Glass for Europe obtained a primary energy demand of 17.22.2 MJ per kg
of float glass, and a global warming potential of 1.250.03 kg of CO 2 equivalent. See http :
==www:glassforeurope:com=en=issues=lifecycleanalysis:php#4. Accessed Aug. 2012.
14 See http : ==www:britglass:org:uk=industry. Accessed Aug. 2012.