1. Life cycle implications of managing plastic wastes
Ming Xu, Ph.D.
Associate Professor
School for Environment and Sustainability
Department of Civil and Environmental Engineering
University of Michigan, Ann Arbor
@MingXuUMich

2. Agenda What is life cycle assessment (LCA)?
What can LCA offer in managing plastic wastes?
What do we know in the plastics-LCA space?
What are the challenges and possible solutions?

3. 1. What is life cycle assessment (LCA)?

4. LCA in environmental policymaking
Identify key processes contributing to the environmental footprint to guide technology development
Evaluate system-wide environmental impacts of consumption to avoid shifting environmental burdens from one process to another
Inform consumer choices and public policy

5. 2. What can LCA offer in managing plastic wastes?
The war on plastics is not new
Plastic is criticized for its end-of-life impact on ecosystems
A symbol of environmental literacy in the 1970s

6. Paper and plastics from life cycle perspective
Life cycle of paper
Life cycle of plastic

7. Life cycle energy use and air emissions
It depends!
What are included in the life cycle
What environmental impacts are concerned …
Hocking, M. B. Science 1991, 251 (4993),

8. What LCA can offer? Compare environmental impacts of different end-of-life pathways for plastics

9. Characterization factors
How does LCA work?
Hellweg and Milà i Canals (2014)
3. Impact assessment:
Characterization factors
2. Inventory analysis
Unit process data kg
GWP
(kg CO2 eq.)
Damage to ecosystem
(species.yr)
CO2 1
8.73E–06
CH4 28
2.44E–04
N2O
265
2.31E-03 …
Plastic film (kg)
Polyethylene
1.02 kg
Electricity
0.66 kWh
Wastewater
0.027 m3 …

10. 3. What do we know in the plastics-LCA space?
Three main application areas:
Comparison
With bio-based plastics
With other materials
Identifying “hotspots” for improvement
Life cycle cost analysis
Key words = “life cycle assessment” & “plastics” in Scopus

11. Compare bio-based plastics with fossil fuel-based plastics: GHG emissions
Upcycling carbon dioxide into polymers
11-20% reductions in GHG emissions and the depletion of fossil resources
From plants to plastics
20-50% reduction in GHG emissions
Zhu, Y., Romain, C., & Williams, C. K. (2016). Nature, 540 (7633), 354.

12. Compare bio-based plastics with fossil fuel-based plastics: GHG emissions
Global carbon footprint of fossil fuel-based plastics produced in 2015: 1.8 GtCO2e or 3.8% of global emissions
Dominated by resin production (61%) and conversion (30%) stages
For strategies to reduce plastic carbon footprint:
Using renewable energy
Bio-based plastics
Recycling
Reducing demand
Zheng, J., & Suh, S. (2019). Nature Climate Change, 9, 374.

13. Compare bio-based plastics with fossil fuel-based plastics: Other environmental impacts
Main impacts: ozone depletion, acidification, eutrophication, carcinogens, and ecotoxicity
Causes: farming and fertilizer use
Fossil fuel-based
Main impacts: fossil fuel depletion, global warming
Causes: oil refining, chemical process
Tabone, M. D., Cregg, J. J., Beckman, E. J., & Landis, A. E. (2010).  Environmental Science & Technology, 44 (21),

14. Compare plastics with other materials
Conclusion: for identical transportation distances, plastic pots have smaller environmental burdens in almost all impact categories compared to glass jars
Humbert, S., Rossi, V., Margni, M., Jolliet, O., & Loerincik, Y. (2009). 
The International Journal of Life Cycle Assessment, 14 (2),

15. Identify “hotspots” for improvement
Lean manufacturing opportunities are identified in plastic injection moulding process guided by LCA
Lean manufacturing improvements can reduce the life cycle environmental impacts by approximately 40% in climate change, human toxicity, photochemical oxidant formation, acidification, and eco-toxicity.
Cheung, W. M., Leong, J. T., & Vichare, P. (2017). Journal of Cleaner Production, 167,

16. Life cycle cost assessment of plastic waste
Three scenarios:
simple mechanical recycling
advanced mechanical recycling
feedstock recycling
Conclusion: all scenarios achieved net financial revenues in case of market substitution factor above 0.7 (price of recycled material = 70% of price of virgin material)
sMR: simple mechanical recycling
aMR: advanced mechanical recycling
FR: feedstock recycling
Faraca, G., Martinez-Sanchez, V., & Astrup, T. F. (2019). Resources, Conservation and Recycling, 143,

17. Case study: life cycle assessment of end-of-life treatments for plastic film waste
landfill
Incineration
Recycling
Requires a large amount of space
One of the major sources of CH4 emissions
Reduce the need for landfill
Recover energy from combustion of waste
Hazard air pollutants
Make new products
Collection and transportation consume energy
Hou, P., Xu, Y., Taiebat, M., Lastoskie, C., Miller, S. A., & Xu, M. (2018). Life cycle assessment of end-of-life treatments for plastic film waste. Journal of Cleaner Production, 201,

18. Goal and scope definition
Functional unit: Film waste in 1 metric ton of either recyclable or mixed waste
Recyclable: 0.6% by weight
Mixed: 2%
Collection scenarios
Urban, mixed or recyclable
Rural, mixed or recyclable
Consumer drop-off, recyclable
End-of-life scenarios
Landfill in mixed stream
Incineration in mixed stream
Recycling in mixed stream
Recycling in recyclable stream
Weights from NIST Building for Environmental and Economic Sustainability (BEES) used for relative importance of each impact category

19. Life cycle environmental impacts of different end-of-life scenarios based on the same collection scenario (rural, mixed)
avoidance of virgin material production
Mixed > recyclable: larger mass fraction of film waste

20. End-of-life stage dominates

21. decrease by 72% if using solar energy instead of US average grid
Sensitivity analysis
Parameters change by 1%
LCA result changes
Collection distance
0.02%
Electricity and diesel fuel consumption at MRF
0.01%
Recycling rate at MRF
1.22%
Utilization rate of recycled plastic films
Waste-to-energy conversion rate at incinerators
0.81%
Mass fraction of films in the waste
1.99%
Type of electricity replaced at incinerators
decrease by 72% if using solar energy instead of US average grid
Strategies for reducing environmental impacts of plastic:
Improve recycling rate at MRF  technology innovations
Improve utilization rate of recycled plastic films  incentives
Increase mass fraction of films in waste stream  source separation
Low-carbon electricity  energy system transition

22. Data challenges in plastics-LCA, and LCA in general
Laboratory test
Onsite investigation
Literature review
Questionnaires, surveys
Expensive
& Time
Consuming
More
Efficient
Methods

23. Data science helps fill data gap in LCA
datanami.com

24. Life cycle inventory (unit process) data is a network
Paper (g)
Pulp
2.3 g
Water
1 L … ?
Waste-water
0.8 L ? ?
Estimate missing data in a unit process database
Predict missing links in a network =

25. Use online shopping recommendation system to estimate missing data in life cycle inventory?
We can estimate missing data in ecoinvent database with very high accuracy (<5% error) if missing less than 10% of data
Hou, P., Cai, J., Qu, S., & Xu, M. (2018). Estimating missing unit process data in life cycle assessment using a similarity-based approach. Environmental Science & Technology, 52(9),

26. Summary
LCA offers a holistic and system-based evaluation of the environmental impacts of the plastic system:
Identify environmental hotspots for improvement
Avoid shifting environmental burdens to different processes
Inform consumers
Data gaps are large; Data science can help with “generating” data from data

27. Resources, Conservation & Recycling
Special issue on Sustainable Cycles and Management of Plastics Deadline: May 15,
Guaranteed social media coverage
@RCRjournal
WeChat