Quantitative Results and Discussion: Mass Loss

Mass loss of both unchopped and chopped PLA increases linearly with increasing the UV exposure time Greater mass loss in unchopped PLA film than chopped PLA pieces at same UV treating conditions

GPC (Gel Permeation Chromatography)

From Highest Molecular Weight To Least (less degradation to more): a) Unchopped: 0 min, 30 min, 90 min, 60 min b) Chopped: 0 min, 30 min, 60 min, 90 min c) 30 Minute UV Treated: Unchopped, Chopped d) 90 Minute UV Treated: Chopped, Unchopped

UV treatment reduced the molecular weight significantly even after only 30 minutes UV exposure time (decreased about 80%) Further UV treatment can further reduce the molecular weight Chopping only accelerated PLA degradation at 30 minutes

Effect of UV Treatment on Degradation of Biodegradable PLA

Introduction: Though many biodegradable plastics have recently entered the market in aims of reducing the growing landfill problem, only a minority of these plastics ends up in an industrial composting facility and fulfills its primary purpose of degrading quickly. Hence, there is a need to develop a new alternative composting method to accelerate degradation of biodegradable polymers. Polylactic acid (PLA) was selected for this study due to its potential in packaging, textiling, and medical applications to replace non-bio and non-biodegradable plastics, such as polyethylene.

Develop an alternative composting method to accelerate degradation

Environmental Issues: Packaging containers made up 31% of total solid waste (after recycling) in 2005, and this percentage is increasing annually (Dell, 2010). Increasing need for a more efficient as well as economically viable method of plastic waste treatment

PLA Synthesis and Properties: Synthesis

Created in a 2-step process 1) Production of lactic acid: Extracting sugar from corn, which is then fermented by microorganisms 2) Production of PLA from lactic acid by direct condensation of the lactic acid or ring-opening polymerization of cyclic lactide dimer.

PLA is both bio-based (made from feedstock), as well as biodegradable (Shen et al., 2009, p. 60).

Advantages

PLA can be shaped into transparent films, fibers, bottles, and containers. Its properties can be improved by fillers or layering it with silicate nano-composites (Pandey et al., 2005). PLA will degrade in a industrial compositing facility by hydrolysis method and its by-products are non-toxic.

Disadvantages At temperatures above Tg, it loses its stiffness significantly. PLA is 20% more expensive compared

with traditional plastics, and there could be a potential shortage of feedstock (Groot et al., 2010) Applications:

PLA is also used in many food packaging applications such as in cups, bottles, food bags, etc. Coca-Cola®

used in clothing applications

Though PLA is both bio-based

and biodegradable, there are

challenges in expanding its

usage

Goals: The aims of this study were: 1) to evaluate the effectiveness of UV treatment on the degradation of PLA; 2) to examine the influence of mechanical chopping on the degradation of PLA consequently to propose an alternative composting method to accelerate the degradation of PLA.

1. UV Treatment 2. Mechanical

Chopping

Polymer Degradation: When a polymer degrades, it becomes brittle, limiting its lifespan Photodegradation: Process in which UV light oxidizes polymeric structure, causing mechanical and molecular breakage into small pieces (Brenndorfer, n.d.)

UVC Light has an energy per photon of 4.43 to 12.4 eV Exposure to UV light causes the breakage of bonds in polymers leading to photo-oxidation

Hydrolysis: Chemical process in which a water molecule is added to a polymer resulting in the break down of that polymer

GPC (Gel Permeation Chromatography) An analytic technique that measures relative molecular weight, consisting of passing a dilute polymer solution through a column filled with polymeric gel beads During GPC, a sample of the solution with the PLA and without it is injected into the chromatograph (column) Difference in molecular weight results measured in a difference in the time it takes the polymer to pass through the column (Beaucage, 2005)

UVA: 315-400 nm UVB: 280-315 nm UVC: 100-280 nm

Polymers can be degraded through photodegradation

and hydrolysis

GPC can be used to measure relative molecular weights

of polymers

PLA has been used in

multiple packaging

applications

Increasing plastic waste

in landfills

Experimental Design: During experimentation, the PLA bag was cut into ten 6 cm by 6 cm squares. Half of the PLA cut films was chopped into small pieces (mechanical degradation) and half was left whole. The PLA (chopped and unchopped) was treated for 30, 60, and 90 minutes in the UV Chamber at the UMass Food Science Department. At 30 minute intervals, the PLA was taken out to be massed and observed visually. At the end of the total treatment time, the treated PLA was sent to the UMass Polymer Science Department for GPC testing.

Treated Unchopped and

Chopped PLA for 30, 60, 90

minutes: Massed samples and sent

for GPC

Qualitative Results and Discussion: Darkening and brittleness of the PLA were observed on both unchopped and chopped PLA after UV treatment. There is increased discoloration over time. This phenomenon signifies further oxidation and degradation. Chopped PLA pieces were stacked in a small pile, which may lead to non-uniform UV exposure.

a) b) c) d)

0 Minutes 30 Minutes 60 Minutes 90 Minutes Chopped PLA at Different Stages of UV Treatment: a) b) c) d)

0 Minutes 30 Minutes 60 Minutes 90 Minutes

Unchopped PLA at Different Stages of UV Treatment:

Increased discoloration

and brittleness over time: Sign

of oxidation and

degradation

Mass Loss of PLA Over Time in UV Chamber

a) b) c) d)

Conclusion: UVC light can rapidly degrade PLA due to the correlation between increased treatment time and decreased molecular weight. However, the results of mechanical degradation (chopping) were inconclusive.

Increased discoloration and brittleness seen over time, signifying oxidation and degradation The mass decreased as treatment time increased. The unchopped film lost twice as much mass as the chopped pieces. Molecular weight decreased as treatment time increased with the exception of the 60 minute unchopped Results of unchopped vs. chopped are inconclusive due to:

Only 3 to 5 mg of the PLA were taken from UV treated samples for GPC Location of the PLA could have been altered some of the chopped PLA used for GPC received more direct UV treatment than others (such as: on the top of pile vs. the bottom) due to the shielding effect of the pile

UV light can introduce different groups with oxygen (carboxylic acid) in them into the PLA, leading to a drop in pH UV light can degrade PLA to an extent where it becomes water soluble

Proposed Alternative Composting Process Flow Chart: Combine all steps of experiment to create a process to accelerate PLA degradation

As treatment time increased,

mass decreased, and unchopped lost more mass than

chopped

As treatment time increased,

molecular weight

decreased, inconsistent

comparison of chopped and unchopped

PLA Waste Mechanical Chopping

UV Treatment Conveyor Belt

Oven (60 min)

Water Soaking Bath Composting

UVC light can significantly and rapidly

degrade PLA, results of

chopping vs. unchopping

are inconclusive

Proposed Alternative Process:

Combination of Chopping, UV

Treatment, Water Bath

By Catherine Zhang, Shrewsbury High School, Shrewsbury, MA, USA

Additional Experimental Results: Hypothesis: If the UV treated PLA is soaked in water, it will result in further mass reduction and the pH of water solution will drop (more acidic) because the water solution will dissolve low molecular weight oligomers. Independent Variables: 15 min ultrasonic soaking time in 25 mL de-ionized water of 0.2648 g 60 minute treated chopped PLA Dependent Variables: pH values of de-ionized water solution and masses of the UV treated PLA pieces before and after 15 min ultrasonic water soaking. Results: Mass of 60 Minute UV Treated Chopped PLA: 0.2648 g, Mass Loss: 0.0066 g pH of Untreated Chopped PLA in Water: 7.71 Mass of 60 Minute Treated Chopped PLA After 15 Min. Soaking: 0.1812 g, Mass Loss: 0.0836 g pH of 60 Minute Treated Chopped PLA in Water: 3.87

Acknowledgements: I would like to thank Professor Julie Goddard, Professor Shaw Ling Hsu, Sahas Rathi, and Fang Tian for their guidance and suggestions throughout the study. I would especially like to thank Sahas Rathi for conducting the GPC testing, as well as Professor Julie Goddard for allowing me to use her lab for my study. I would also like to thank Allen King from NatureWorks for donating the PLA samples used in this study. I would also like to thank Ms. Constantine and Mr. Collins for their guidance throughout the study.

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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.

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Soaking in water leads to additional mass loss of 31.6% and decrease in pH