1. Developing a Sustainable Solution
for Food Packaging Waste
Motivations:
• Reducing the growing landfill problem
• Why PHB and PLA?
Bio-Based and
Biodegradable or
Compostable
Versatile and
Strong
Catherine Zhang, Shrewsbury High School
Mass Science Fair, May 2013
Used in Variety of
Applications
Safety and Experimental Procedures:
• Why backyard composting?
• Current challenges of composting PLA
• Most ecological and least expensive
degradation process
• Reducing carbon footprint (CO2e)
• Enriching garden soil
Reduce the
landfill problem
with backyard
composting
Preparing Polymers:
Size: 6x6 cm
N-Rich
C-Rich
• Genetically modified
bacteria produce PHB
monomer from corn or
switchgrass
• Direct Condensation
Reaction
Both
made by
bacteria
from
starch
Ingredients
Compost
Plastic Type
Type
Material
Manufacturer
Form
Sandwich
NatureWorks
Bags
PLA+PHB
Shopping
(medium
Bags
crystallinity)
PHB
(medium
crystallinity)
PHB:
• Formation of lactic acid by
fermentation
• Formation of the PLA by
either direct condensation
or ring-opening
polymerization
Control
Metabolix
Standard
Sheets
Metabolix
N-Rich
Formulations (wt.%)
Standard N-Rich
C-Rich
Black Kow
Manure Organic
Compost
100%
40%
50%
Coffee Ground
0%
40%
0%
C-Rich
Tree Leaves
0%
20%
50%
Total Weight (g)
2500
2500
2500
PLA+
PHB
PLA
PLA
PLA+PHB
PHB
PLA @ 0 week
PLA @ 12 weeks
• 3 Composts: Standard (Processed Cow Manure), N-Rich (Coffee
Grounds and Dry Leaves), C-Rich (Dry Leaves)
Material
Standard
PLA + PHB @ 0 week
PLA + PHB @ 12 weeks
Experimental Plan:
PLA
Introduction of PLA and PHB Synthesis:
PLA:
Making Composts:
Degradation Study (TGA):
Samples massed
every week
Mass Change
Surface
after Ultrasonic
Morphology
Clean
No
TGA
PHB
Yes
Only
perform on
Mass at Week 4, the samples
Mass at
Week 12
8, and 12
when mass
Week 0, 1,
on
loss is
2, 4, 6, 8
selected
observed
and 12
samples
• There is no thermal stability change
of the PLA
• Decrease of thermal stability of PHB
(257.3 vs. 227.2oC) indicating that
degradation occurred
• Increase of thermal stability of
PLA+PHB (224.8 vs. 234.8oC)
indicating the degradation may only
occur on the PHB
Degradation Mechanisms:
Molecular
Weight (Da)
Rate of
Mass
MW
Loss
Decrease
Stage I
• Place 3 samples of each type of plastic in each compost: heated
throughout the day
• Massed and then analyzed under SEM
Composts are turned
twice a week, moisture
level is 60%
Results- Mass Loss (Influence of Polymer Type):
PLA
PLA+PHB
PHB
PLA
PLA+PHB
PHB (F)
PLA
PLA+PHB
PHB
PLA
PLA+PHB
PHB
Mass
Change
PHB @ 0 week
PHB @ 12 weeks
100,000 to
200,000
Slow
No
Stage II
< 20,000
Fast
Yes
Stage I
100,000 to
500,000
Fast
Yes
PLA
PHB
Reaction
Degradation
Mechanism
Bulk (chain
scission)
Surface
Enzymatic
Erosion
Surface
Enzymatic
Erosion
Hydrolysis
Duration
weeks to
months
Weeks
Weeks
• PLA:
Results- Mass Loss (Influence of Compost Type):
• 2 Stage Degradation
• Slight mass gain observed may
indicate that the degradation is still in
Stage I
• PHB:
Biopolymer Challenges:
PLA:
PHB:
• Cost: $2-3/kg
• Low Tg and High WVTR
Melting
Molecular Modulus
Point
Weight
(GPa)
(°C)
100k to
130 to
~2
300k
215
Tg
(°C)
55 to
70
WVTR
(g/m2*
day)
325
• PHB copolymer lost 28.6% in
standard compost, 7.5% in
N-Rich, 14.0% in C-Rich
• Standard is most effective,
followed by C-Rich, followed
by N-Rich
1. Standard
2. C-Rich
3. N-Rich
• PHB copolymer is the best in terms
of its bio-degradability. It lost 28.6%
mass at standard, 14.0% in C-Rich,
and 7.5% in N-Rich compost
followed by PLA+PHB.
• PLA is the worst in terms of its biodegradability, only mass gain
observed (13.0% at standard
1. PHB
compost)
• Cost: $5-7/kg
• Mostly made from corn
(food source)
• Little popularity and
exposure in market
• Can only be degraded in an
industrial composting
facility (hydrolysis)
Biodegradability
2. PHB+PLA
3. PLA
Results- Surface Morphology Study I – Influence of
Compost Types on the PHB at Week 12 :
Results- Optical Microscope Study:
PLA - 0 weeks
PHB Copolymer 0 weeks
PLA+PHB - 0
weeks
Std. Compost:
C-Rich Compost:
• 1 Stage Degradation, and non-uniform
• Curve fitting revealed PHB degradation
rate at the standard compost: y =
0.4844x-0.178 (x: composting time) @ R²
= 0.9791
Conclusions:
• Biodegradability of Plastics
•
•
•
N-Rich Compost:
Performance
Composting:
•
PLA+PHB - 12
weeks
•
PHB Copolymer12 weeks
•
30:1 Ratio
•
• PLA has become more brittle and wrinkled causing
discoloration and cracks formed.
• PHB-PLA has widespread discoloration
• PHB has small holes and cracks most likely from
degradation
Small Holes
in PHB Film
&
Discoloration
Use unprocessed cow manure for compost to take
advantage of the exothermic nature of the composting
process to degrade PLA
Research needs to focus on creating a new polymer, which
is made of non-food renewable sources, and that can be
degraded truly naturally
Mass Loss: 28.6%
Mass Loss: 14.0%
Mass Loss: 7.5%
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.
Endres, H., & Siebert-Raths, A. (2011, March). Basics of PHA. Bioplastics, 6, 42-45.
Control (Week 0):
• Relative Degradability of Plastics
2. PHB and
PLA
3. PLA
Week 4 Std. Compost:
Week 8 Std. Compost :
0.0 wt%
Objectives and Hypotheses:
3.3 wt%
3.3 wt%
Week 12 Std. Compost :
6.7 wt%
PLA+PHB
Copolymer:
• PHB is biodegradable while PLA is compostable
• Effectiveness of Different Compost Compositions
2. C-Rich
Most
Successful:
PHB
Copolymer
in Standard
Compost
References:
Results- Surface Morphology Study II – Influence of Composting Time and Type of Polymers:
1. N-Rich
Scale is a bit inaccurate (mass readings, 0.01 g)
• Future Work
C:N Ratio Formula
• C:N Ratio Degradation
• Microbes need C as energy source
• Microbes need N to create proteins
• Fast composting: 30:1
• Slow composting: 50:1
1. PHB
Copolymer
PHB: Standard composition is most effective, followed by CRich, followed by N-Rich
PLA+PHB: Standard composition is most effective, followed
by N-Rich, followed by C-Rich
• Possible Errors
Surface
Area
• Surface Area
PHB Copolymer degrades most rapidly (28.6%), followed by
PLA + PHB Copolymer (6.7%), followed by PLA
The degradation mechanisms of PHB and PLA+PHB are
through the surface erosion
OM observation showed cracks on the PLA, which may
indicate its degradation is still at stage I - absorbed water
(weight gain @ 13.0%)
• Effectiveness of Composts
•
PLA - 12 weeks
PLA 2 Stage
Degradation vs.
PHB 1 Stage
Degradation
0.0 wt%
3. Standard
• Organic material provides necessary
microorganisms for biodegradation
Propose
optimal
compost
process
• Proposing an Optimal Backyard Composting Process
PHB
Copolymer:
24.5 wt%
28.6 wt%
28.6 wt%
Observations:
• Very little change in
PLA+PHB (mass loss:
6.7% at 12 weeks)
• Significant change in
PHB (mass loss:
28.6% at 12 weeks)
• Surface Erosion
Occurred
• Initiated from
Amorphous Region
Surface
Erosion in
PHB
Copolymer
Fraser, A. (2012). Describe why food spoils. Retrieved from
http://www.foodsafetysite.com/educators/competencies/general/spoilage/spg1.html.
Greentech GmbH & Cie KG. (2010). Bioplastics: Bioplastics: Economic opportunity or
temporary phenomenon. Ostfalia: Widdeck, H., Otten, A., Marek, A. & Apelt, S.
Stevens, E. S. (2002, December). How green are green plastics? Biocycle, 42-45.
Washam, G. (2010, April). Plastics go green. ChemMatters, 10-12.
Wool, R. P., & Sun, X. S. (2005). Bio-based Polymers and Composites. Amsterdam: Elsevier
Academic Press.
Zhang, C., & Carter, J. (2012, March). Effectiveness of biodegradable plastic in preventing
food spoilage. Journal of Emerging Investigators. Retrieved from
http://emerginginvestigators.org/articles/2012/03/effectiveness-of- biodegradable-plasticIn-preventing-food-spoilage.
Acknowledgements:
I would like to thank Professor HJ Sue from Texas A&M University for his
guidance. I would especially like to thank Dr. Olly Peoples from Metabolix for
both his advice and help in attaining plastic samples. Thanks also to Dr. Raj
Krishnaswamy from Metabolix and Mr. Allen King from NatureWorks for donating
PLA samples. Thanks to Mr. Bob Lituri from Bose for experimental assistance. I
would also like to thank my parents for both allowing me to run my experiment at
home and for their encouragement throughout this project.