Colegio Técnico Profesional de San Isidro

To check the results of this study we compared the impact assessment to other LCA studies of carrier bags, some of which are described in annex A. It is difficult to make detailed comparisons between the studies due to differences in system boundaries, functional unit and impact assessment methods. However, a common feature in all the studies is the inclusion of GWP as an impact category and therefore a basic data comparison can be made by dividing the global warming potential of each bag by its reference flow weight. This should remove any difference due to bag capacities and reuse and highlight any disparities in the data used. Figure 7.1 shows the results of this and three other studies based on the weight of CO2 equivalents generated per kg of each bag. The results for each study are relative to the baseline of the HDPE carrier bag in that study which is set at 100 per cent.

0% 20% 40% 60% 80% 100% 120% 140% 160%

Current study ExcelPlas Australia et al. 2003 Ecobilian PwC 2004 Murphy et al. 2008

Pe rc e n ta g e (%)

HDPE bag HDPE bag with a prodegradent additive

Starch polyester blend bag Paper bag

LDPE bag PP bag

Figure 7.1 A comparison of the global warming potential of each bag type in

each report based on the kg CO2 eq. produced per kg of bag weight.

Each report provides only a limited amount of information regarding the assumptions made and there are differences in material content, production, transport and end-of-life processing, so it is difficult to identify the sources of difference between each study. Generally, other studies have found that the impact of HDPE bags with prodegradant have a lower global warming potential when compared to conventional HDPE bags. This may be due to differences in the material content of the bags. Murphy et al (2008)

assumed that the HDPE bag was produced using only HDPE, whilst the HDPE prodegradant bag contained 96 per cent HDPE and 4 per cent catalyst. The

prodegradant additive was modelled as an organic chemical with a lower GWP impact than HDPE from the ETH database. This study used a more complex combination of materials, including chalk and titanium oxide, and used a surrogate for the prodegradant additive (90% stearic acid, 10% cobalt) which had a larger impact when compared to HDPE.

The global warming potential of the paper bag was lower than the HDPE bag in three of the four studies when compared by material weight. The LDPE reusable bag had a higher global warming potential than the baseline HDPE bag in the three studies. The results of this study generally lie between the results of the other studies for these formats.

The impact of the starch polyester blend varies considerably between studies. Both ExcelPlas Australia et al. (2003) and Murphy et al. (2008) show a lower gram for gram impact of the starch polyester bag than HDPE. However, the Ecobilian PwC (2004) and this study both show a higher impact by weight from the starch polyester bag. This is partially due to the impact of the material in landfill at the end-of-life

Figure 7.2 compares the grams of material used per litre for each bag type relative to the HDPE bag which was set at 1 for each study.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Current study ExcelPlas Australia et al. 2004 Ecobilian PwC 2005 Murphy et al. 2009

Ratio

HDPE bag HDPE bag with a prodegradent additive

Starch polyester blend bag Paper bag

LDPE bag PP bag

Figure 7.2 A comparison of the grams of material used per litre in each report

The ratios of material per litre capacity for the HDPE prodegradant bag, the paper bag and the LDPE bag relative to the HDPE bag in each report are comparable. However, there are differences between the grams per litre used for starch-polyester blend bags. Murphy et al. (2008) is the only study which assumes that both the prodegradant bag and the starch-polyester bag require less material per unit volume than the HDPE bag. The difference is almost certainly linked to the different samples used to generate the weight and capacity data. Although the data used here was supplied by manufacturers the results of this report only represent the reference period, 2007. There is evidence that biopolymer materials have improved since that period and weights have been reduced21_{. The current products on the market are based on new polyesters with much} higher perfromace at lower grade.

All the reports agree that the extraction and production of raw materials has the greatest effect on the environmental performance of the carrier bags studied. Ecobilan PwC (2004) found that improvements were seen when secondary reuse was considered for conventional HDPE bags and that reducing weight and reuse were the best options for improving the environmental performance of the carrier bags. The level of reuse required for LDPE bag to be superior to the conventional HDPE bag was also found to be similar to this study. Nolan-ITU (2003) reported that reusable bags had a lower environmental impact, although they assumed reuse was significantly higher than the other studies at 10 uses for the LDPE bag. Nolan-ITU also found that degradable bags have a similar environmental impact to conventional lightweight HDPE bags and that starch-polyester blend bags have higher eutrophication and acidification impacts. Like this study, Murphy et al. (2008) reported that the recycling of HDPE bag reduces both abiotic depletion and global warming potential and the composting of starch-polyester bags increases the impact in those categories. However, this study shows that recycling greater effects on both eutrophication and acidification. This is probably due to the transport of recyclates to China included in this report which increases the impact in these categories.