Page 56 - Materials Chemistry, Second Edition

40 2 Goal and Scope Definition

Example

Often several variants can be assumed for the definition of the functional unit
The definition of the fU has substantial influence on the result of the study. A
comparison of different diapers serves as a descriptive example from consumer
products. There are multiple comparative LCAs on disposable and fabric diapers;
the former represents a relevant domestic waste fraction.
Results of LCAs occasionally differ relevantly, depending on the commissioner.
Sometimes disposable diapers, then again the fabric diapers, are environmen-
tally more compatible. There are many possible reasons for a mismatch of the
results in different studies. One reason could be the choice of different fUs.
What functions do diapers have? At first, the answer seems to be simple. The
child is to be kept dry. This thought may result in comparing one cellulose diaper
with one fabric one. However, the fabric diaper is used several times such as 200
times. Washing of the diaper (individual or diaper service) must be considered
for each circulation. The production of the diaper is, however, only considered
by 1/200.
The comparison may look different as soon as the function of a diaper is
defined to hold the child dry for 1 day. It can be argued that per day more
fabric than cellulose diapers are needed, because the child in fabric diapers feels
uncomfortable more quickly. Under this consideration it can be reasonable to
compare, for example, 1.2 fabric diapers with one cellulose diaper. The result will
certainly be different from the 1 : 1 comparison.
Further variants can be thought of to define the function of diapers, for example,
it is the function of diapers to keep a child dry for life. Under this aspect, it
is thinkable that, during the entire swaddling time of the child, more cellulose
diapers than fabric diapers are needed because in the first case the child needs
to be swaddled until it gets older. Fabric diapers are less comfortable, and the
child starts going on the potty earlier.
This example of quite a simple product shows that the definition of the fU is by
no means trivial.

2.2.5.2 Impairment Factors on Comparison – Negligible Added Value
On the rarest occasions, two products have exactly the same performance, even if
they have, technically speaking, the same function. The reason often lies within
aesthetic side benefit, in varying fulfillment of comfort, owner’s pride, and so on.
Such subtle differences, as important as they may be in marketing, are difficult
to capture in LCA, if these cannot be related to measurable parameters, such as,
for example, use time, weight or fuel consumption of cars. At any rate, however,
they can and should be verbally described and be verbally considered in the
Interpretation phase (Chapter 5).
It gets more difficult when the technical functions differ. So, in the example of
floor coverings, the highly varying variants, for example, parquet versus tile, can be
applied alternatively in certain areas (vestibule) but in others such as in the bath