Page 364 - Materials Chemistry, Second Edition

348 5 Life Cycle Interpretation, Reporting and Critical Review

as admissible by the authors of the study for assessment comparisons of
scenarios where system boundaries only comprise a single product system
with a comparatively small complexity.
In the case of the present study, possible developments of PET systems
for the period from 2006 to 2010 are included. In view of the prospective
character of these estimations, the significance threshold value was increased
to 20% for the examination of the results for all compared scenarios.
This approach is by no means transferable as standard to all LCAs. It should
be noted that the beverage packaging LCAs of the Federal Environmental
Agency 39) did not apply discrete significance thresholds at all.

For a critical analysis of the comparison on the level of impact categories, the
results in Table 5.1 are discussed on the basis of a fixed significance threshold.

For a comparison of relative differences in computation (Table 5.1) regarding
a significance threshold of 20%, the following are the advantages and
disadvantages: advantages of the beverage carton under the categories fossil
resource demand, greenhouse effect, acidification, terrestrial eutrophication
and aquatic eutrophication, and disadvantages under summer smog and
land use - forest area. The differences in terms of fossil resource demand,
greenhouse effect and land use - forest area are particularly large.
No significant changes occur if sensitivity analyses targeting an increased
sorting depth of used PET bottles as well as the use of recycled PET
amounting to 25% of the bottle production are considered.

5.6.6
Sensitivity Analyses

In the example study, the key parameters of the assessment were varied in order
to examine their relevance on the result. The following two types of sensitivity
analyses that have been accomplished are presented as examples:

• Result relevance of technical improvements of PET bottles
• Result relevance of system allocation.

In Table 5.2, the results of two sensitivity scenarios are presented, assuming
technical improvements of the PET bottle considered in the system modelling: for one
scenario an input of recycling material of 25% PET (R-PET; open-loop material),
for the other scenario, an assortment optimisation of the collected light-packaging
stream was assumed.
Compared with Table 5.1, the result of the computation of the PET-bottle-based
scenario, the study states as follows:

39) Umweltbundesamt (UBA) Germany.