Recycling materials

Professor Mike Ashby gave the Kelly lecture as part of the Armour and Braziers Cambridge materials forum. The topic of the lecture was ‘environmentally informed materials selection’. Professor Ashby talked about strategies for engineering design to account for the environmental impact over the lifetime of a product. This is driven by the desire to reduce environmental impact, or to meet design directives introduced to do this.

Metals are more easily recycled than polymers, this is due largely to the use of polymer blends. Separation of the different polymers can be aided by proper labeling.

Fraction of various materials recycled today.

Material	Fraction Recycled
Lead	0.78
Steel	0.41
Aluminum	0.39
Copper	0.35
Zinc	0.2
PET	0.18
HDPE	0.1
PP	0.05
PS	0.02
PVC	0.1

It was proposed that the total energy use is the most meaningful indicator, due to the relative ease of assessing this, and the fact that CO2 production is the major concern today, and this is closely related to the energy.

During the life of a product, one phase of the product life is usually has a dominant effect on the total energy. The phases are; The Materials, Manufacturing, Use, Disposal. A container to carry a liquid would have it’s energy use determined mainly by the energy used in the materials. In contrast the energy usage of an aeroengine is completely dominated by use, so it makes sense to try and optimise the operation as much as possible to reduce the lifetime energy use/environmental impact.

Energy content in bottles/cans.
The energy used in the lifetime of a bottle or can is dominated by the energy content of the materials.

Material	Energy Content
	MJ/litre
Glass bottle	8.2
PE	3.2
PET	5.4
Aluminum	9.0
Steel	2.4