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Effect of UV Treatment on the Degradation of Biodegradable Polylactic Acid


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In this study, an alternative composting method of biodegradable polylactic acid was proposed, capable of reducing the molecular weight by over 80% in 90 minutes.

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Effect of UV Treatment on the Degradation of Biodegradable Polylactic Acid

  1. 1. Effect of UV Treatment on the Degradation of Biodegradable Polylactic Acid (PLA)! Catherine Zhang! Grade 11, Shrewsbury High School! Presented at National AJAS Conference, Boston, Feb. 2013! Catherine Zhang!
  2. 2. Outline!               Motivations and Introduction! Objectives! Hypotheses! Experimental Approaches! Results! Conclusions and Future Work! Acknowledgements! Catherine Zhang!
  3. 3. Motivations! •  Reducing the Growing Landfill Problem! •  Why polylactic acid (PLA)?! Bio-Based and Biodegradable! Versatile and Strong! Used in Variety of Applications! •  Why photodegradation?!   Hydrolysis is well-studied, both energy and time-consuming!   Photodegradation can break bonds of polymers!   UVC Light: Highest Energy Photon! Catherine Zhang!
  4. 4. Introduction of PLA Synthesis and Challenges! •  Synthesis (2-step process):! •  Formation of lactic acid by fermentation! •  Formation of the PLA by either direct condensation or ring-opening polymerization! •  Challenges:! •  20% more expensive! •  Low Tg and high WVTR! •  Can only be degraded in an industrial composting facility (hydrolysis)! Natural Biodegradability! Performance! Catherine Zhang!
  5. 5. Objectives!  Effectiveness of the UVC treatment!  Effectiveness of mechanical chopping!  Proposing an economic alternative composting process! Catherine Zhang!
  6. 6. Hypotheses! •  UVC Treated vs. Untreated! Longer Treatment Time! Accelerated Degradation!   UVC Light oxidizes and breaks bonds between monomers! •  Chopped vs. Unchopped! Mechanical Chopping! Accelerated Degradation!   Chopping may help breaking polymer chains! Catherine Zhang!
  7. 7. Experimental Approaches! •  Experimental Plan:! PLA Bag Unchopped 6x6 cm Chopped UVC Chamber Digital Balance GPC Catherine Zhang!
  8. 8. Results – Visual Observations! 0 Minutes! 30 Minutes! a)! b)! 60 Minutes! 90 Minutes! c)! d)! Increasing levels of discoloration and brittleness over UV treatment time was observed! Catherine Zhang!
  9. 9. Results – Mass Loss! Unchopped: Mass loss increased as UV treatment time increased! Chopped: Mass loss increased as UV treatment time increased! Unchopped lost ~ twice amount of mass as the chopped! Catherine Zhang!
  10. 10. Results – Molecular Weight (GPC)! Unchopped PLA Film:   Chopped PLA Pieces:   Increased treatment time results in decreased molecular weight except 90 minute ! Increased treatment time results in decreased molecular weight! Catherine Zhang!
  11. 11. Results - Molecular Weight (GPC)! Molecular Weight Decreased Dramatically After UV Treatment! Catherine Zhang!
  12. 12. PLA Degradation! •  PLA degradation:! •  Photo degradation: photooxidation leading to formation of hydroperoxide derivatives, then degraded to compounds containing carboxylic acid and unstable diketones! Catherine Zhang!
  13. 13. Results – Mass Loss! 15 Minute Water Soaking of the 60 minute UV treated sample can further increase mass loss from 2.5% to 31.6%! Catherine Zhang!
  14. 14. 4-Step Alternative Composting Process! Proposed Industrial Scale of Composting Process! PLA Waste! Composting! Mechanical Chopping! UV Treatment Conveyor Belt Oven! Water Soaking Bath ! Catherine Zhang!
  15. 15. Conclusions and Future Work! •  Conclusions:! •  UVC Light can rapidly degrade PLA, but not mechanical chopping!   Level of discoloration and brittleness increased as treatment time increased! In order Mass loss decreased linearly as treatment effects, two things   to see any positive environmental time increased! must occur:!   Unchopped film lost twice as much mass as chopped! 1.  Consumers must be educated aboutobserved correctly < 24k)!   Clear molecular weight reduction was how to (113.5k vs. dispose of their biodegradable plastics.! investigated further!   Inconsistency of the GPC results need to be 2.  •  Scientistsdegradation process: Photooxidation! effective and Possible need to continuously innovate more economic composting processes.! •  A 4-Step alternative composting process was proposed! •  Future Work:! •  Process development of 4-Step composting process! •  Detailed process comparison analysis (hydrolysis vs. 4-Step)! Catherine Zhang!
  16. 16. Acknowledgements! I would like to thank Professors Julie Goddard and Shaw Hsu from UMass, as well as Fang Tian, for their guidance. I would especially like to thank Mr. Sahas Rathi for conducting the GPC testing, and Professor Goddard for allowing me to use her lab. I would like to thank Professor Sakai from Kyoto Institute of Technology for his advice. I would also like to thank Mr. Allen King from NatureWorks® for donating PLA samples. Thanks also go to Ms. Constantine and Mr. Collins from Shrewsbury High School.! Catherine Zhang!
  17. 17. Thank You! Questions?! Catherine Zhang!
  18. 18. References! Beaucage, G. (2005). Determination of molecular weight. Retrieved from Classes/! !Characterization/MolecularWeighthtml/MolecularWeight.html! Brenndorfer, B. (n.d.). Photodegradation of plastics. Retrieved from! Copernicus Institute for Sustainable Development and Innovation. (2009). Product Overview and Market Projection of Emerging Bio-Based Plastics. Utrecht, The Netherlands: Shen, L., Haufe, J. & Patel, M.K.! Dell, K. (2010, May 3). The promise and pitfalls of bioplastic. Retrieved from magazine/article/0,9171,1983894,00.html! Groot, W., Krieken, J.V., Sliekersl, O., & Vos, S. (2010). Production and purification of lactic acid and lactide. In R. Auras, L. Lim, S. E. M. Selke, & H. Tsuji (Eds.), Poly (lactic acid): synthesis, structures, properties, processing, and applications (pp. 3-26). Hoboken, NJ: John Wiley & Sons Inc.! Pandey, J. K., Reddy, K. R., Kumar, A. P. & Singh, R. P. (2005). An overview on the degradability of polymer nanocomposites. Polymer Degradation and Stability, 88, 234-255.! Sakai, W., & Tsutsumi, N. (2010). Photodegradation and radiation degradation. In R. Auras, L. Lim, S. E. M. Selke, & H. Tsuji (Eds.), Poly (lactic acid): synthesis, structures, properties, processing, and applications (pp. 413-421). Hoboken, NJ: John Wiley & Sons Inc.! Selke, S. E. M. (1990). Packaging and the environment. Lancaster, PA: Technomic Publishing Company Inc.! Wiles, D. M., & Scott, G. (2005). Polyolefins with controlled environmental degradability. Polymer Degradation and Stability, 91, 1581-1592.! Wool, R. P., & Sun, X. S. (2005). Bio-based polymers and composites. Amsterdam: Elsevier Academic Press.! Catherine Zhang!