Life cycle assessment of single use thermoform boxes made from polystyrene (PS), polylactic acid, (PLA), and PLA/starch: cradle to consumer gate

Currently, the bio-based plastics have been drawing considerable attention from the packaging industry as a sustainable solution for replacing petroleum-based plastics in order to reduce the accumulation of plastic waste in the environment. This work has benchmarked the environmental impact of bio-based against petroleum-based plastics for single use boxes. In this paper, the cradle to consumer gate environmental impact data of these boxes was calculated and reported as part 1. End-of-life options of both bio- and petroleum-based boxes are an important subject which will be further studied for part 2. The energy sources in this work were taken from the Thailand energy database namely: Thai electricity grid mix (TEGM), Thai coal electricity (TCE), Thai natural gas combine cycle (TNGCC), and Thai coal integrated gasification combine cycle (TIGCC).

The materials studied were polystyrene (PS) derived from petroleum, polylactic acid (PLA) derived from corn, and PLA/cassava starch blend (PLA/starch). The tray with lid (herein after called box) was processed in a plastic manufacturing in Thailand using cast sheet extrusion and then thermoforming techniques. The functional unit is specified as 10,000 units of 8.0 × 10.0 × 2.5 cm of PS, PLA, and PLA/starch boxes which weigh 447.60, 597.60, and 549.56 kg, respectively. Three impact categories; namely global warming potential including direct greenhouse gas, and indirect land use change (LUC) emissions, acidification, and photochemical ozone formation are investigated. Finally, the normalization results including and excluding LUC consideration were compared and reported.

The results from this study have shown that the total environmental impact including LUC emission of bio-based boxes were different when the various energy sources were supplied throughout the life cycle production stage. It can be seen that the PS box has lower environmental impact than PLA and PLA/starch boxes when TEGM, TCE, TNGCC, and TIGCC were used as energy supplied. LUC of renewable feedstocks, such as corn and cassava, were considered as the biggest impact of absolute scores of PLA and PLA/starch boxes. These results are consistent with Piemonte and Gironi (2010).

PLA and PLA/starch boxes give a slightly higher environmental impact than the PS box by 1.59 and 1.09 times, respectively, when LUC was not accounted in the absolute scores and clean energy TIGCC was used throughout the life cycle.