Effect of UV Treatment on the Degradation of Biodegradable Polylactic Acid

Catherine Zhang!Catherine Zhang!

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!


Outline!

  Motivations and Introduction!  Objectives!  Hypotheses!  Experimental Approaches!  Results!  Conclusions and Future Work!  Acknowledgements!


Motivations!

•  Reducing the Growing Landfill Problem!•  Why polylactic acid (PLA)?!

•  Why photodegradation?!  Hydrolysis is well-studied, both energy and time-consuming!  Photodegradation can break bonds of polymers!  UVC Light: Highest Energy Photon!

Versatile and Strong!

Bio-Based and Biodegradable!

Used in Variety of Applications!


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)!

Performance!

Natural Biodegradability!


Objectives!

 Effectiveness of the UVC treatment!

 Effectiveness of mechanical chopping!

 Proposing an economic alternative composting process!


Hypotheses!

•  UVC Treated vs. Untreated!

  UVC Light oxidizes and breaks bonds between monomers!•  Chopped vs. Unchopped!

  Chopping may help breaking polymer chains!

Longer Treatment Time!

Accelerated Degradation!

Accelerated Degradation!

Mechanical Chopping!


Experimental Approaches!

•  Experimental Plan:!

PLA Bag

Unchopped 6x6 cm

Chopped

UVC Chamber

Digital Balance

GPC


Results – Visual Observations!

a)!

0 Minutes!

b)!

30 Minutes!

c)!

60 Minutes!

d)!

90 Minutes!

Increasing levels of discoloration and brittleness over UV treatment time was observed!


Results – Mass Loss!

Chopped: Mass loss increased as UV treatment time increased!

Unchopped: Mass loss increased as UV treatment time increased!

Unchopped lost ~ twice amount of mass as the chopped!


Results – Molecular Weight (GPC)!

Increased treatment time results in decreased molecular weight except 90 minute !

Unchopped PLA Film:

Increased treatment time results in decreased molecular weight!

Chopped PLA Pieces:


Results - Molecular Weight (GPC)!

Molecular Weight Decreased Dramatically After UV Treatment!


PLA Degradation!

•  PLA degradation:!•  Photo degradation: photooxidation leading to formation of

hydroperoxide derivatives, then degraded to compounds containing carboxylic acid and unstable diketones!


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%!


4-Step Alternative Composting Process!

Proposed Industrial Scale of Composting Process!

PLA Waste!Mechanical Chopping!

UV Treatment Conveyor Belt

Oven!

Water Soaking Bath !Composting!


•  Conclusions:!•  UVC Light can rapidly degrade PLA, but not mechanical chopping!

  Level of discoloration and brittleness increased as treatment time increased!

  Mass loss decreased linearly as treatment time increased!  Unchopped film lost twice as much mass as chopped!

  Clear molecular weight reduction was observed (113.5k vs. < 24k)!  Inconsistency of the GPC results need to be investigated further!

•  Possible degradation process: Photooxidation!•  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)!

In order to see any positive environmental effects, two things must occur:!1.  Consumers must be educated about how to correctly

dispose of their biodegradable plastics.!2.  Scientists need to continuously innovate more effective and

economic composting processes.!

Conclusions and Future Work!


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.!


Thank You! Questions?!


References!

Beaucage, G. (2005). Determination of molecular weight. Retrieved from http://www.eng.uc.edu/~gbeaucag/Classes/!!Characterization/MolecularWeighthtml/MolecularWeight.html!

Brenndorfer, B. (n.d.). Photodegradation of plastics. Retrieved from http://www.fao.org/docrep/X5018EX501.!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 http://www.time.com/time/

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.!

Effect of UV Treatment on the Degradation of Biodegradable Polylactic Acid

Technology

uv treatment time increased

pla degradation

uvc treatment

results mass loss

step composting process

longer treatment time

step process

results molecular weight