Life Cycle Assessment of Supermarket Carrier Bags - Save The ...

average 5.88 items in the conventional HDPE carrier bag and an average 7.96 items intothe heavy duty LDPE carrier bagThe average weight, volume and item capacity for each carrier bag type included in thisstudy was then calculated. The material weights of the HDPE prodegradant and starchpolyesterbags were adjusted pro-rata to match the average volume of the conventionallightweight HDPE bag (19.1 litres carrying 5.88 items). For the paper, LDPE, non-wovenPP and cotton bags, the item capacities were adjusted according to their volumes.These revised bag capacities were then used to calculate the reference flow 14 for eachtype of bag as shown in table 3.1. The initial reference flows shown do not include anyprimary reuse of carrier bags.Table 3.1The assumed volume, weight, items per bag and required referenceflow for each carrier bag (excluding primary reuse).Bag typeConventional high-density polyethylene(HDPE) bagHigh-density polyethylene (HDPE) bagwith a prodegradant additiveVolume perbag (litres)Weight perbag (g)Itemsper bagRefflow –No. bags19.1 8.12 5.88 82.1419.1 8.27 5.88 82.14Starch-polyester blend bag 19.1 16.49 5.88 82.14Paper bag 20.1 55.20 7.43 64.98Low-density polyethylene (LDPE) bag 21.52 34.94 7.96 60.68Non-woven polypropylene (PP) bag 19.75 115.83 7.30 66.13Cotton bag 28.65 183.11 10.59 45.59Supermarket policies and consumer behaviour have changed since the reference period(2006/07) but there is no evidence to suggest the capacities of HDPE and LDPE bagshave changed significantly. However, while data used for starch polyester blend bagswere provided by the manufacturer, since the reference period the weight of some ofthese bags may have been reduced and the effect of this is discussed in section 7.23.3 System boundariesThe study is a ‘cradle to grave’ life cycle assessment. Therefore, the carrier bag systemsinvestigated include all significant life cycle stages from raw material extraction, throughmanufacture, distribution use and reuse to the final management of the carrier bag aswaste. The system boundaries are defined so that all inputs and outputs from the system14 The reference flow is the number of each type of bag required to fulfil the functional unit (483 items ofshopping in one month).18 Environment Agency Life Cycle Assessment of Supermarket Carrier Bags