Carbon footprint analysis in plastics manufacturing

This paper describes an investigation of the carbon footprint associated with plastic trays, used as packaging for foodstuffs (e.g., mushrooms). In recent years there has been an increase in both consumer and legislative pressure on the packaging sector to reduce the environmental impact of its products, which are often only single use items. Using data from a plastics manufacturer, a cradle-to-grave study was conducted for trays produced from recycled polyethylene terephthalate, calculating their product carbon footprint and analysing how various parameters affect the carbon footprint. A model based on a spreadsheet analysis was developed, which allows the product carbon footprint to be determined using production batch data. It was found that the cradle-to-grave carbon footprint of 1 kg of recycled polyethylene terephthalate trays containing 85% recycled content was 1.538 kg CO2e. The raw material, manufacturing, secondary packaging, transport and end-of-life stages each contributed 45%, 38%, 5%, 3% and 9% of the total life cycle greenhouse gases respectively. The recycled content of raw material was found to have a significant effect on product carbon footprint: a 24% decrease in tray carbon footprint could be obtained by manufacturing trays from 100% recycled content, compared to the current recycled content level of 85%. A reduction in tray weight was found to give almost an equivalent proportionate reduction in carbon footprint, with 20% and 30% tray weight reductions resulting in product carbon footprint reductions of 18.7% and 28% respectively. Transport was found to only contribute a minor amount of the greenhouse gases (3%) and hence improving transport efficiency had very little effect on the carbon footprint. The effect of end-of-life treatment was also found to be relatively small. The worst case scenario of no recycling taking place in the end-of-life stage results in the carbon footprint of the trays increasing by 2.7%, while increasing the recycling rate from 23.7% to 32% and 50%, results in the carbon footprint decreasing by 1% and 3% respectively. In both the extrusion and thermoforming processes, the specific manufacturing carbon footprints arising from consumption of electricity, chilled water energy and compressed air were found to decrease logarithmically with production speed. The greatest reductions in the carbon footprint of recycled polyethylene terephthalate trays can be achieved in the raw material and manufacturing life cycle stages. The proportion of recycled raw material should be maximised while extrusion and thermoforming process speeds should be optimised as significant manufacturing energy reductions can be attained when the speeds of both processes are increased. Tray light-weighting should be implemented to as great an extent as possible without compromising tray structural integrity while high recycling rates in the end-of-life stage should continue to be targeted.