Motivations:• Reducing the growing landfill problem

• Why PHB and PLA?

• Why backyard composting?• Current challenges of composting PLA

• Most ecological and least expensive

degradation process

• Reducing carbon footprint (CO2e)

• Enriching garden soil

Versatile and

Strong

Bio-Based and

Biodegradable or

Compostable

Used in Variety of

Applications

Reduce the

landfill problem

with backyard

composting

PLA:

• Formation of lactic acid by

fermentation

• Formation of the PLA by

either direct condensation

or ring-opening

polymerization

Introduction of PLA and PHB Synthesis:

PHB:

• Genetically modified

bacteria produce PHB

monomer from corn or

switchgrass

• Direct Condensation

Reaction Both

made by

bacteria

from

starch

PLA:

• Cost: $2-3/kg

• Low Tg and High WVTR

• Can only be degraded in an

industrial composting

facility (hydrolysis)

Biopolymer Challenges:

PHB:

• Cost: $5-7/kg

• Mostly made from corn

(food source)

• Little popularity and

exposure in market

Molecular

Weight

Modulus

(GPa)

Melting

Point

(°C)

Tg

(°C)

WVTR

(g/m2*

day)

100k to

300k~ 2

130 to

215

55 to

70325

Performance

Bio

deg

rad

ab

ilit

y

Objectives and Hypotheses:• Relative Degradability of Plastics

• PHB is biodegradable while PLA is compostable

• Effectiveness of Different Compost Compositions

• Organic material provides necessary

microorganisms for biodegradation

• Proposing an Optimal Backyard Composting Process

1. PHB

Copolymer

2. PHB and

PLA3. PLA

1. N-Rich 2. C-Rich 3. Standard

Propose

optimal

compost

process

Composting:• Surface Area

• C:N Ratio

• Microbes need C as energy source

• Microbes need N to create proteins

• Fast composting: 30:1

• Slow composting: 50:1

Degradation

Su

rface

Are

a

30:1 Ratio

C:N Ratio Formula

Results- Optical Microscope Study:

PHB

PLA

Developing a Sustainable Solution for Food Packaging Waste

Catherine Zhang, Shrewsbury High School

Mass Science Fair, May 2013

Safety and Experimental Procedures:

Making Composts:

Composts are turned

twice a week, moisture

level is 60%

Samples massed

every week

Preparing Polymers:

Experimental Plan:• 3 Composts: Standard (Processed Cow Manure), N-Rich (Coffee

Grounds and Dry Leaves), C-Rich (Dry Leaves)

• Place 3 samples of each type of plastic in each compost: heated

throughout the day

• Massed and then analyzed under SEM

Results- Mass Loss (Influence of Polymer Type): Results- Mass Loss (Influence of Compost Type):

• 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 bio-degradability, only mass gain observed (13.0% at standard compost)

• 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

Results- Surface Morphology Study I – Influence of

Compost Types on the PHB at Week 12 :

Results- Surface Morphology Study II – Influence of Composting Time and Type of Polymers:

PLA+PHB

Copolymer:

Control (Week 0):

PHB

Copolymer:

Week 4 Std. Compost: Week 8 Std. Compost :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

• 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

Standard N-Rich C-Rich

Black Kow

Manure Organic

Compost

100% 40% 50%

Coffee Ground 0% 40% 0%

Tree Leaves 0% 20% 50%

Total Weight (g) 2500 2500 2500

Formulations (wt.%)Ingredients

MaterialMaterial

FormManufacturer

PLASandwich

BagsNatureWorks

PLA+PHB

(medium

crystallinity)

Shopping

BagsMetabolix

PHB

(medium

crystallinity)

Sheets Metabolix

Week 12 Std. Compost :

Standard N-Rich C-Rich

Size: 6x6 cm

1. PHB

2. PHB+PLA

3. PLA

1. Standard

2. C-Rich

3. N-Rich

PHB Copolymer -

0 weeks

PLA+PHB - 12

weeksPHB Copolymer-

12 weeks

PLA+PHB - 0

weeks

Small Holes

in PHB Film

&

Discoloration

PLA - 0 weeks

PLA - 12 weeks

Std. Compost: C-Rich Compost: N-Rich Compost:

Mass Loss: 28.6% Mass Loss: 14.0% Mass Loss: 7.5%

0.0 wt%

24.5 wt%0.0 wt%

6.7 wt%3.3 wt%3.3 wt%

28.6 wt%28.6 wt%

Compost

TypePlastic Type

Mass

Change

Mass Change

after Ultrasonic

Clean

Surface

MorphologyTGA

PLA

PLA+PHB

PHB

PLA

PLA+PHB

PHB (F)

PLA

PLA+PHB

PHB

PLA

PLA+PHB

PHB

Mass at Week 4,

8, and 12

Only

perform on

the samples

when mass

loss is

observed

Yes

Standard

Mass at

Week 0, 1,

2, 4, 6, 8

and 12

Week 12

on

selected

samples

N-Rich

C-Rich

Control No

Degradation Study (TGA):

Degradation Mechanisms:

• PLA:

• 2 Stage Degradation

• Slight mass gain observed may

indicate that the degradation is still in

Stage I

• PHB:

• 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

PLA 2 Stage

Degradation vs.

PHB 1 Stage

Degradation

References: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.

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-plastic-

In-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.

Conclusions:• Biodegradability of Plastics

• 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• PHB: Standard composition is most effective, followed by C-

Rich, followed by N-Rich

• PLA+PHB: Standard composition is most effective, followed by N-Rich, followed by C-Rich

• Possible Errors• Scale is a bit inaccurate (mass readings, 0.01 g)

• Future Work• 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

Most

Successful:

PHB

Copolymer

in Standard

Compost

PLA+

PHB

• 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

PLA @ 0 week

PLA @ 12 weeks

PLA

PLA + PHB @ 0 week

PLA + PHB @ 12 weeks

PLA+PHB

PHB @ 0 week

PHB @ 12 weeks

PHB

Molecular

Weight (Da)

Rate of

MW

Decrease

Mass

LossReaction

Degradation

MechanismDuration

Stage I100,000 to

200,000Slow No Hydrolysis

Bulk (chain

scission)

weeks to

months

Stage II < 20,000 Fast Yes EnzymaticSurface

ErosionWeeks

PHB Stage I100,000 to

500,000Fast Yes Enzymatic

Surface

ErosionWeeks

PLA