Page 73 - Materials Chemistry, Second Edition

LIFE CYCLE INVENTORY MODELING IN PRACTICE 55

material is not available, energy for the baking process should be included
because of its contribution to energy impacts.
Sometimes additional research can uncover options for inclusion of compo-
nents for which data do not initially seem to be available. Take the example of a
molded plastic product that has inputs of a large quantity of resin and a much
smaller quantity of a material identified as a color compound. Because the color
compound represents a small percentage of the total mass of inputs, and data
on production of pigments are generally not available, the first inclination may
be to exclude the color compound. However, manufacturer literature for the
compound indicates that the compound consists of a small amount of pigment
blended into the same resin used as the main input to the process. In this situa-
tion, the amount of resin in the color compound can be included in the modeling,
increasing the total mass of inputs covered in the analysis. Only the very small
amount of pigment in the color compound would still be excluded. Information
in manufacturer literature and material safety data sheets (MSDS) can often help
identify constituents of specialty materials so that at least some of the content of
these products can be included or suitable surrogate data can be selected.
Another cut-off decision is the decision whether or not to include capital
goods and infrastructure, i.e., the buildings and equipment used to manufac-
ture the product, or the vehicles used to transport products. In the past, sample
calculations suggested that the contributions of infrastructure tend to be small
when allocated over the total amount of output over the lifetime of the infra-
structure. However, more recent analyses have indicated that infrastructure
contributions may be significant for certain industry sectors, e.g., non-fossil
electricity generation [3]. Constructing infrastructure models can be very com-
plex and time-consuming on a study-specific basis; however, LCA databases
such as ecoinvent contain general modules for commonly used infrastructure
such as chemical plants, metalworking equipment, vehicles, etc. that can be
used to estimate the contribution of infrastructure [4].

3.4 Methodology Issues

In this section, several important methodological issues are discussed, includ-
ing areas where different methodological choices can be made depending on
the specific systems being studied, as well as methodological issues that are the
focus of increasing interest in the environmental community, such as water use
and carbon tracking. In cases where the choice of methodology has a strong
influence on the study results and conclusions, the practitioner should justify
the reasons for the methodology chosen, and a sensitivity analysis should be
conducted to see if an alternative methodological choice produces similar or
different results and conclusions.

3.4,1 Feedstock Energy
For a complete energy accounting, an LCA must include not only the energy
that is expended during the process and transportation steps over the life cycle