Abstract:
An increasing number of companies are exploring ways to improve their environmental footprint. Some environmental benefits are offered by bio-based plastic packaging; however, this approach requires trade-offs. For example, plastic bottles made with polylactic acid (PLA), a bio-based plastic resin, lack the impact strength offered by plastic bottles made with polyethylene terephthalate (PET). Other trade-offs include diminished shelf life capabilities, increased cost, and recycling infrastructure. In particular, displacement of recyclable plastic packaging with plastics made from renewable resources has created controversy among environmental advocates. Despite its performance, cost, and recycling shortcomings, PLA offers an attractive choice to some because it represents the transition towards use of renewable resources.
In an attempt to address trade-offs, I developed an analytical framework with assistance from key stakeholders. After identifying the fundamental objective of the best choice of resin for the manufacture of plastic bottles, I surveyed stakeholders to create a list of essential packaging criteria, with the three major criteria being performance as a bottle material, cost, and environmental impact. I relied on private interviews with industry experts and conference presentations to gather bottle data for four resins: PLA, PET, high density polyethylene (HDPE) and polypropylene (PP). The framework for comparison was Multiattribute Utility Theory (MAUT), a methodology designed to address trade-offs among multiple objectives to achieve an overall objective.
Based on the survey results and best available data as input for MAUT, PET was the best choice of resin for the beverage bottle. This non-bio-based plastic emerged as the top choice largely due to its superior performance on criteria such as strength and shelf life. Further analysis of the characteristics of the four plastics showed that even if all environmental and cost characteristics of the bio-based plastic, PLA, were as favorable as any of the other plastics I analyzed, PLA still would not come to the top. Only if PLA’s performance as a bottle material (strength, etc.) increased several fold would PLA become the top choice among the four I analyzed. Similarly, analysis of the weighting of the criteria showed that increasing the weights on environmental criteria, compared to performance and cost criteria, cannot elevate PLA to the top choice, mainly because HDPE has desirable environmental characteristics such as recyclability. Only increasing the weight on environmental criteria such as greenhouse gas emissions while decreasing the weight on all other environmental criteria would allow PLA to become the top choice among the four bottle materials I analyzed.
