Environmental Engineering Reference
In-Depth Information
well, plastics are used for retort packaging and microwavable cookware.
The inherent low thermal conductivity can be improved further by
making the plastic into a closed-cell foam that traps air or other gas to
make it an excellent insulation material. Again, where needed, a desired
level of thermal conductivity can be imparted into the plastics using a
conductive filler.
From sustainability considerations, all materials are not created equal. A
distinction needs to be made between materials derived from:
1. fossil fuel;
2. other limited resources such as critical metal and oxide ores;
3. raw materials available in abundant or renewable supply (e.g., wood,
sand, sodium chloride); and
4. waste or residues from the use or consumption of the three other
categories earlier.
Wagner and Wellmer (2009) have formalized this classification into a
hierarchy, suggesting that substituting for materials placed higher in the
hierarchy with those at a lower level constitutes a sustainable change. This
included recycling a material or reusing within its own class within the
hierarchy. The hierarchy is based on the valuation of the materials alone
and lacks the dimension of environmental and human safety that should
also be important considerations in material selection and use. The use of
a material or a product that contains a potentially toxic residue/leachate or
does not have a means of recovery is certainly not a sustainable practice.
1.3 ENVIRONMENTAL POLLUTION
Emissions that pollute the environment, particularly the air and water
resources, are inextricably linked with the life cycle of a generic product
especially where the raw material has to be extracted from the earth's crust
as shown in the generalized diagram in
Figure 1.10
.
Each step involves the
use of energy and some emissions into the environment and generates a
residue that invariably needs to be disposed of. These costs are neither
immediately evident or are fully accounted for in the cost of the product or
reflectedinassessingtheGDPoftheproducernations.Itisthisshortcoming
of GDP as a measure of development that helped the popularity of the
