Page 81 - Materials Chemistry, Second Edition

Life Cycle Assessment: Principles, Practice and Prospects
68
The function of the study was defined as the use of shopping bags to carry groceries and
goods from store to home. The number of single-use bags required and the number of reusable
bags required to carry goods home per person per year were calculated. The functional unit
was defined as a household carrying home about 70 grocery items from a supermarket each
week for 52 weeks (Table 6.7).
In order to understand how degradable plastics degrade in aerobic and anaerobic environ-
ments, four different end-of-life waste management treatment technologies were modelled for
all the different bags (Table 6.8):
s landfill (anaerobic environment) – modelled on Victorian landfills
s source-separated green and food MBT (mechanical biological treatment) composting
s municipal solid waste MBT composting
s municipal solid waste anaerobic digestion.

As the littering of HDPE bags results in aesthetic issues and endangers aquatic and marine
life through entanglement and ingestion, the following two litter scenarios were developed,
and each bag was modelled against them (Table 6.9 ):
s litter aesthetics (calculated based on the time the bag would be litter (metre squared per
2
year (m y))
s litter’s effects on marine biodiversity (calculated based on whether the polymer floats
and how long it floats, or whether it sinks and how long it takes to sink).

Figure 6.11 illustrates the greenhouse gas emission profile for the six degradable polymers
compared with six alternative materials: two single-use materials (i.e. HDPE and Kraft paper)
and four reusable materials (i.e. calico, PP fibre ‘green bag’, woven HDPE ‘swag bag’ and LDPE

Figure 6.11 Breakdown of greenhouse gas emissions for all bags. CO , carbon dioxide; N O,
2 2
nitrous oxide. PBS/A, starch polybutylene succinate/adipate; PBAT, starch with polybutylene
adipate terephthalate; PE, polyethylene; PLA, polylactic acid; HDPE, high density polyethylene; PP,
polypropylene; LDPE, low density polyethylene.

100804•Life Cycle Assessment 5pp.indd 68 17/02/09 12:46:18 PM