PLASTIC PRODUCTS - Plastics and Environmental Sustainability - page 142

crude oil is used for transportation (in engines that waste 2/3 of the energy
as heat!), 8 which is also a highly polluting application. Indispensability of
reliable transportation in modern life has allowed this energy cost to be
accommodated. The 8-9% investment in fossil fuels provides an incredibly
wide range of useful items that we simply cannot avoid coming into contact
with in our daily lives. Plastics in some instances (such as in residential
insulation or aircraft construction) save energy and in applications such as
wind turbines even help generate green energy. The reader is invited to
review some of these benefits in Chapter 5 .
Embodied energy (EE) in a material or product is all the energy directly or
indirectly used in the creation of a unit mass (for instance, a metric ton)
of it. This would include the energy used in extraction of raw materials,
their transportation to a plant, processing in the plant, and maintenance
energy for dedicated plant. 9 The metric therefore depends on the boundary
conditions used in the definition and the mix of energy used (therefore
the location of manufacture). When it is taken to mean all energy from
extraction of raw materials until the product leaves the manufacturer's
location, it is called “cradle-to-gate” energy or the “front-end” energy
investment in producing the material. It does not include the energy cost
of using and disposal of the material or product. The values of EE reported
vary because of how the quantity is calculated;
One criterion in sustainable material selection is to select one with the least
EE that also meets the performance requirements for a given application.
When the raw material itself is an energetic material (such as oil, coal, or
gas) with fuel value, EE also includes the raw-material energy in addition to
the energy expended in manufacturing and transportation. The EE referred
to here is that associated with converting feedstock materials into plastic
resin pellets and not that associated with manufacturing a product. In a
subsequent step where the resin pellets are converted into a product such as
a bottle or a bag, additional energy has to be expended. This latter energy
will be referred to as “process energy,” for clarity.
Although minimizing the EE is a sustainable strategy, at least two other
factors must be taken into consideration: (1) the complete service life of the
material and (2) energy cost per functional unit of the material. There are