Two million tons of expanded polystyrene (styrofoam) are produced worldwide each year, taking up 25 to 30 percent of landfill space. In this project, we attempted to find and refine an efficient, cost-effective styrofoam recycling process.
We found that polystyrene dissolved in D-Limonene produces an adhesive and decided to refine the glue until it became a useful product. During our initial experiments, we mixed the D-Limonene with various amounts of polystyrene and performed tests for adhesive property, drying time, and viscosity to find the ideal proportion of the two elements. Then we added water, as earlier experimentation found that this decreased drying time. However, because polystyrene and D-Limonene are both hydrophobic, the two substances separate from the water over time; we added different emulsifiers to the mixture and tested which was most effective to keep them together. Finally, we tested the finished product for strength, drying time, and viscosity. We found that the ideal proportion for the glue was 2ml of water, 4ml of D-limonene, and 2gm of polystyrene with 0.2gm of emulsifier, which supported our hypothesis that glue could be made from polystyrene. We anticipate that our product can become a viable way to dispose of polystyrene.
In the future, we hope to further refine the formula of the glue to make it stronger and easier to mix. We’ve also found that at certain consistencies the glue dries into a plastic, and we hope to test the ability of this plastic to be recycled.
Question: How can used polystyrene (Styrofoam) be recycled into a functional product?
Hypothesis: If styrofoam is dissolved in D-Limonene, then it will create a product that can be used as glue.
Our FLL Robotics team began researching Styrofoam recycling as part of the First Lego League 2016 “Trash-trek” challenge, which was to find a solution to an existing problem related to trash disposal.
We visited Friendship Village, a retirement community, to find what problems they were having with trash disposal. One of the residents there pointed at a Styrofoam cup and told us that was their biggest disposal problem: Styrofoam was commonly used within the facility, but there was no way for them to dispose of it sustainably.
After that, we visited Waste Management, a local landfill. The plant manager told us that Styrofoam took up too much space in the landfill due to its widespread use and the time it took to decompose.
We set out to find a solution for Styrofoam recycling. At first, we tried to find alternative materials Friendship Village could use instead of Styrofoam, but they were either too expensive for a retirement community to use on a large scale or didn’t insulate as well as Styrofoam did, so we took a different approach, returning to the main issue landfills were having with Styrofoam: the physical space it took up. Upon research, we found that Styrofoam dissolves in a variety of solvents, greatly reducing the amount of space it consumes.
Expanded Polystyrene (EPS, commonly known as Styrofoam) (C8H8) is a petroleum-based plastic polymer composed of styrene monomers, which are made of hydrocarbons.
It’s cheap, easy to manufacture, and lightweight, which makes it an almost ideal insulator. Because of this, over 3 million tons of polystyrene are produced worldwide annually, of which approximately 70% is used for food and beverage containers.
80% of polystyrene ends up in landfills, where it takes 500 years to decompose. The other 20% is recycled. There are three ways to recycle polystyrene. The first method, thermal recycling, burns the polystyrene to produce electricity. However, if the polystyrene is burned below 900 degrees, thermal recycling releases dangerous compounds, such as carbon monoxide and alkyl benzenes, into the atmosphere. The second method is chemical recycling, or breaking down the chemical bonds in styrene monomers using catalysts such as platinum or rhodium, then remaking the styrene monomers. Chemical recycling tends to be costly and inefficient. The third and most common method is traditional material recycling, or compressing the polystyrene, which is inefficient and expensive due to its high air content. Ninety percent of styrofoam, by volume, is made up of air, making it expensive to transport and inefficient to recycle. In addition, the styrofoam is often contaminated with food, causing the recycling process to use more energy than it saves.
Polystyrene’s solubility in solvents such as hydrocarbons, alkyl halides, aromatics, esters, ketones, and petroleum-based solvents has been known since the 1990s; however, our research uncovered only one study attempting to find a dissolution-based solution for polystyrene recycling.
In 1997, the Sony Corporation used evaporation, electrospinning, and precipitation to try to repurpose dissolved polystyrene into new polystyrene, but the project was abandoned. A project presented in the 2016 Google Science Fair also found that heating polystyrene, as in thermal recycling, creates an activated carbon that can be used as a water filter, but this method, which used burning rather than dissolving, releases the same toxic fumes as thermal recycling, as mentioned above.
While it is true that many polystyrene solvents are not environmentally friendly, D-Limonene (C10H16), made from two molecules of isoprene (C5H8) bound together, is a natural, environmentally friendly solvent of polystyrene extracted from citrus fruits. It reduces the volume of polystyrene to 1/20th of its original size.
Due to the lack of polystyrene recycling solutions involving dissolution, we decided to explore the solubility of polystyrene in D-Limonene to try to find a way to convert waste polystyrene into an environmentally sustainable product.
Summary of Experimental Timeline
Phase 1: Mixing polystyrene and D-Limonene Only
Will mixing D-Limonene and polystyrene produce an adhesive?
How does adding different concentrations of polystyrene affect the composition of the glue?
D-Limonene amount kept constant at 4ml
Polystyrene Amounts: 2g, 2.5g, 3g
Quantitative Tests: drying time, viscosity
Qualitative Tests: Which materials the glue is effective on, ease of use
Phase 2: Adding Water to the Polystyrene-D-Limonene Solution
In what way will adding water affect the composition of the glue?
Can water be added to the solution without the aid of an emulsifier?
D-Limonene kept constant at 4ml; polystyrene kept constant at 2.5g
Water amounts: 0ml, 2ml, 4ml
Quantitative Tests: drying time, viscosity, separation time of water
Qualitative Test: ease of use
Phase 3: Adding Emulsifier to Solution
What is the ideal emulsifier?
What is the ideal proportion of polystyrene, water, emulsifier, and D-Limonene?
An emulsifier is a substance that can help an oil-like and water-like substance to mix. Research online revealed that adding an emulsifier to a solution changes the way the parts of the solution interact, invalidating much of our earlier experimentation.
Emulsifiers Tested: polysorbate 40, polysorbate 60, polysorbate 80, polyvinyl alcohol, lecithin
Phase 4: Testing the Final Product
Will the product be comparable to commercially available adhesives?
On what materials can the glue be used?
Final Concentration: 4 drops of emulsifier Lecithin, 2ml of water,
4ml of D-Limonene and 2g of Polystyrene
Quantitative Tests: drying time (note: different amount of glue tested due to lack of materials), viscosity, peel strength
Qualitative Tests: ease of use, ease of mixing, what it can glue
Materials: different product variations, paper, timer, identical bottles, identical spheres, popsicle sticks, weights, cup
Viscosity = (d^2(b-i)gt)/(18L)
Phase 1 Results
Polystyrene & D-Limonene
Increasing polystyrene increases viscosity
Decreasing polystyrene increases drying time
Increased polystyrene increases strength of glue
Increased polystyrene increases stringiness
Phase 2 Results
4ml water didn’t stay mixed long enough for testing
D-Limonene and water must be mixed before adding polystyrene
Without polystyrene, water and D-Limonene separate immediately, so during polystyrene dissolving, the solution must be mixed repeatedly
No matter how carefully the solution is created, the water separates from the D-Limonene and polystyrene in 12 to 48 hours
Water increases viscosity by 259 %
Water decreases drying time by 31 minutes
Phase 3 Results
Adding Emulsifier to Solution
D-Limonene and water can’t mix because D-Limonene is a nonpolar substance and water is a polar substance. The Hydrophile-Lipophile Balance (HLB) System assigns a number to a substance or group of substances that can be emulsified, then matches them to an emulsifier or group of emulsifiers with the same number. During this phase, we mixed different emulsifiers, each closer to the necessary HLB number, with the solution until one kept the product together. At first, we mistakenly used oil-in-water rather than water-in-oil emulsion procedures and picked emulsifiers based on safety rather than effectiveness, leading to the failed emulsification shown below, but eventually we learned about HLB numbers and switched procedures with the correct emulsifiers.
The HLB number range for water-in-oil emulsions is 4-6.
|Emulsifier||HLB#||Did it mix?|
Phase 4 Results
Testing the Final Product
Properties of Stryofoam Glue Prepared
|Final Concentrations||4ml D-Limonene, 2ml water, 2 gm styrofoam, 0.2g lecithin|
|What it Glues||Wood, Acrylic, Fabric, pipe cleaner, Metal, Paper, Plastic, Wax,|
|Cost to make 30 ml glue||62 cents|
How to Create Glue
The goal of this experiment was to find a way to recycle polystyrene. We realized that dissolving polystyrene in D-Limonene created a glue and began refining this glue.
In the first phase of our experiments, we tested which proportion of polystyrene and D-Limonene created the most functional glue. We discovered that more polystyrene increased the glue’s viscosity and decreased its drying time.
In the second phase, we added water to the solution to dilute the solution, which we found increased viscosity and decreased drying time. We tested different proportions of D-Limonene and water; the ideal proportion turned out to be half as much water as D-Limonene. Any more water than this increased the polystyrene’s dissolving time by a significant amount.
In the third phase, we added an emulsifier to thoroughly mix the water with the polystyrene and D-Limonene solution. After a few mishaps, we figured out the proper emulsifier for the solution, then added as much polystyrene into the solution as possible. Our final glue consisted of 2g polystyrene, 2ml water, 0.2g lecithin, and 4ml D-Limonene.
If this experiment were to be repeated, we would change little. We would add a strength test in every phase so we could find what each component does to the stickiness of the overall glue and modify the water tests so we could use three data points instead of just two. We would also research more about emulsifiers earlier on, as we had to abruptly change how we made our glue before phase 3, and test our glue against existing commercial products and under different weather conditions.
Overall, this project was a success. We found a way to produce glue out of polystyrene, supporting our hypothesis.
In the future, we hope to figure out the further industrial applications of the glue. We also wish to test if the combination of D-Limonene and polystyrene can produce any other solutions to reuse or recycle polystyrene. For example, midway through testing, we found that if a large portion of glue dries at certain concentrations, it produces a plastic, which could be used for other purposes.
Sindhu Bala (15): My interest in science developed as I watched documentaries, attended lectures, and read books when I was young. I took part in the St. Louis Science Fair every year in elementary school and competed in First Robotics from 3rd grade through middle school. I have also been part of Science Olympiad, Science Bowl, and H20/TED, a program about Missouri wildlife and conservation. In 2017, I attended Ecology Project International, a project in Yellowstone National Park where I studied wildlife behavior, and in college, I hope to study environmental science or biotechnology.
Winning the science fair could give our project more visibility and attract the attention of the scientific community to make this a real, sustainable solution for polystyrene recycling.
Christina Yepez (16): By joining FIRST, For Inspiration and Recognition of Science and Technology, at a young age, I found that I enjoyed learning how different things were made and why. It teaches kids how to solve problems and work as a team. I am inspired by Dean Kamen founder of FIRST and Sylvia Acevedo Girl Scout CEO.
For college, I want to go to Duke or MIT nanoscience to learn how I can cure diseases. My goal is to research to find a cure for cancer since 3 of my grandparents have had cancer. Winning any prize would give me a hands-on feel for developing and presenting a project that is not just an idea but a solution.
Our experiments were conducted at Sindhu's house. We were very cautious throughout experimentation and while using the various chemicals, including the emulifiers and D-Limonene.
Before using any emulsifiers, we checked the safety guidelines, then adjusted experimentation methods to accommodate any hazards.
The D-Limonene was kept closed at all times to avoid deep inhalation.
Any solutions or emulsifiers were carefully labelled to avoid mishaps.
Contact Details of Adult Mentor
Name: Bharathi Raju
Cellphone Number: 636 236 5820
Home Phone Number: 636 527 5024
Email Address: email@example.com
Charles E. Frazier, Ph.D, Thomas M. Brooks Professor of Sustainable Biomaterials, Director of Wood-Based Composites Center, Virginia Tech
Dr. Frazier helped us understand how a research project should be conducted, and told us the importance of negative results. He also taught us some of the chemistry behind adhesives.
Marcus Foston, Ph.D, Assistant Professor, Department of Energy, Environmental & Chemical Engineering, Washington University in St.Louis.
Dr. Foston, a polymer chemists, gave us access to relevant articles from the Washington University Library. He also provided valuable feedback for our project.
Sindhu’s mom aided us in some of the experimentation, acting as another pair of hands in the lab. She also provided supervision to ensure the research remained safe and provided the materials for the various experiments.
Daniel Dougherty, Physical Science and Chemistry Teacher at Lindbergh High School
Mr. Dougherty provided certain materials for the experiment.
Megan Roegner, Gifted Resource and English Teacher at Lindbergh High School
Mrs. Roegner supervised the experimentation we did at school and provided feedback for the english side of the project.
“What Is Expanded Polystyrene (EPS) Foam? The Possibilities Are Endless!” What Is Expanded Polystyrene (EPS) Foam?, Insulation Corporation of America, insulationcorp.com/eps/
Environmental Impacts of Styrofoam
Advancing Sustainable Materials Management: 2015 Tables and Figures , EPA, July 2018, www.epa.gov/sites/production/files/2018-07/documents/smm_2015_tables_and_figures_07252018_fnl_508_0.pdf
Derrick, Sean. Polystyrene Recycling. Green Manufacturing Initiative, 14 Sept. 2010,wmich.edu/mfe/mrc/greenmanufacturing/pdf/Polystyrene%20Recycling.pdf
“CDC - POLYSTYRENE - International Chemical Safety Cards - NIOSH.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 2001, www.cdc.gov/niosh/ipcsneng/neng1043.html
“Say Goodbye to Styrofoam.” State of the Planet, Columbia University: Earth Institute, 11 Mar. 2015, blogs.ei.columbia.edu/2015/03/11/say-goodbye-to-styrofoam/
“The Environmental Impacts of Styrofoam.” Impacts-of-Styrofoam, GEC Student Union, sustainability.wustl.edu/wp-content/uploads/2013/02/Impacts-of-Styrofoam.pdf
“The Facts on Styrofoam: Reduce and Recycle.” The Facts On Styrofoam: Reduce and Reuse | Collier County, FL, Collier County, www.colliercountyfl.gov/your-government/divisions-s-z/solid-hazardous-waste-management/keeping-green-helpful-information-page/the-facts-on-styrofoam-reduce-and-reuse
Styrofoam and Solvents
Firdaus, Maulidan, et al. “Terpene-Based Renewable Monomers and Polymers and Polymers via Thol-Ene Additions.” Macromolecules, vol. 44, no. 18, 2011, pp. 7253–7262
Hattori, Kazuyuki. Recycling of Expanded Polystyrene Using Natural Solvents. IntechOpen, 15 July 2015, www.intechopen.com/books/recycling-materials-based-on-environmentally-friendly-techniques/recycling-of-expanded-polystyrene-using-natural-solvents
Helmenstine, Anne Marie Marie. Dissolve Styrofoam in Acetone for a Great Chemistry Demonstration. ThoughtCo, 31 Jan. 2018, www.thoughtco.com/dissolving-styrofoam-in-acetone-608924
Kazuyuki, Hattori, et al. “Solubilization of Polystyrene into Monoterpenes.” Advances in Polymer Technology, vol. 27, no. 1, 2008, pp. 35–39
D-Limonene Compound Summary
“D-LIMONENE.” CAS - 5989-27-5 (02155234) - MP Biomedicals, Mpbio, www.mpbio.com/product.php?pid=02155234&country=223
“Limonene, (+)-.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, pubchem.ncbi.nlm.nih.gov/compound/___-Limonene#section=Top
“Hermann Staudinger " Discoverer of Ketenes & Staudinger Reaction.” Worldofchemicals.com, World of Chemicals', 20 Mar. 2013, www.worldofchemicals.com/215/chemistry-articles/hermann-staudinger-discoverer-of-ketenes-staudinger-reaction.html
Mohsen, Riham Abdel Aziz Abdel. CiteSeerX, Jan. 2014, citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.845.197&rep=rep1&type=pdf
“Polymers.” Polymers, Penn State University, courses.chem.psu.edu/chem112/materials/polymers.html
University of Wisconsin Oshkosh, www.uwosh.edu/faculty_staff/mihalick/materials/Chapter5.pdf
Aminudin, Eeydzah, et al. “A Review on Recycled Expanded Polystyrene Waste as Potential Thermal Reduction in Building Materials.” International Conference on Environment and Industrial Innovation , vol. 12, 2011, pp. 113–118
Broadwith, Phillip. Polystyrene Depolymerisation: New Recycling Option. Chemistry World, 1 Oct. 2012, www.chemistryworld.com/news/polystyrene-depolymerisation-new-recycling-option/5489.article
Chandra, Satish, et al. “ASC Sustainable Chem. Eng.” ASC Sustainable Chem. Eng., vol. 4, no. 11, 2016, pp. 6095–6100
Gutiérrez, Cristina, et al. “Recycling of Extruded Polystyrene Wastes by Dissolution and Supercritical CO2 Technology.” Journal of Material Cycles and Waste Management, no. 4, 2012, doi:10.1007/s10163-012-0074-9
Hearon, K. “A High-Performance Recycling Solution for Polystyrene Achieved by the Synthesis of Renewable Poly(Thioether) Networks Derived from D-Limonene.” Adv Mater, vol. 26, no. 10, 12 Mar. 2014, pp. 1552–1558
Mwasha, Abrahams, et al. “Management of Polystyrene Wastes Using a Supercritical Solvent.” The Journal of the Association of Professional Engineers of Trinidad and Tobago, vol. 41, no. 1, 2013, pp. 23–28
Mwasha, Abrahams. “Dissolved EPS Wastes as Wood Adhesive”. Adv Recycling Waste Manag 1: 105, 2016
Noguchi, Tsutomi, et al. “A New Recycling System for Expanded Polystyrene Using a Natural Solvent. Part 1. A New Recycling Technique” Packaging Technology and Science, vol. 11, no. 1, Feb. 1998, pp. 19–27
Shin, Changyun, and George G. Chase. “Nanofibers from Recycle Waste Expanded Polystyrene Using Natural Solvent.” Springer Link, Sept. 2005, link.springer.com/article/10.1007/s00289-005-0421-2
Life Cycle Assessment of Polystyrene
“Life Cycle Assessment of the Industrial Use of Expanded Polystyrene Packaging in Europe .” PRICEWATERHOUSECOOPERS, www.anape.es/pdf/gabinete_oi.pdf.
Cassiday, Laura. Emulsions: Making Oil and Water Mix. Apr. 2014, www.aocs.org/stay-informed/read-inform/featured-articles/emulsions-making-oil-and-water-mix-april-2014
“Commonly Used Emulsifiers and Their HLB Values.” The Pharmaceutics and Compounding Laboratory, pharmlabs.unc.edu/labs/emulsions/hlb.htm
D'Limonene Emulsifiers ~ Formulations & Procedures ~ DeForest Enterprises, Inc. DeForest Enterprises, Inc., deforest.net/deforest-specialty-surfactants/dlimonene-emulsifiers/
Dow Surfactants Reference Chart, Dow, Mar. 2014, msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_09b0/0901b803809b0065.pdf?filepath=surfactants/pdfs/noreg//119-01491.pdf&fromPage=GetDoc
“Required HLB Values of Emulsifiers.” Saffire Blue Inc, www.saffireblue.ca/blog/hlb-values-of-emulsifiers.htm.
“What Is HLB? How Is It Applied to Formulate Emulsions?” Dow Answer Center, 27 Mar. 2018, dowac.custhelp.com/app/answers/detail/a_id/327
Solvent Comparison. Eastman, www.eastman.com/Literature_Center/S/SOLOM3026.pdf
“The HLB System.” 75_Book_HLB_ICI.Pdf, ICI Americas Inc, www.firp.ula.ve/archivos/historicos/76_Book_HLB_ICI.pdf
Oxiteno. What Is Polysorbate? | Polysorbate 20 vs. 60 vs. 80 Uses. Oxiteno, 12 June 2018, www.oxiteno.us/what-is-polysorbate-20-vs-60-vs-80-uses/
Polysorbates (Polysorbates 20, 60, 65, and 80). Food Safety Commission, June 2007, www.fsc.go.jp/english/evaluationreports/foodadditive/polysorbate_report.pdf
Lecithin Food Label
“Fearn Liquid Lecithin -- 32 Fl Oz.” Vitacost, www.vitacost.com/fearn-liquid-lecithin-32-fl-oz
Lecithin-Bleached. United States Department of Agriculture National Organic Program, 6 Aug. 2006, www.ams.usda.gov/sites/default/files/media/Lecithin%20bleached%20TR%202009.pdf
Measuring Fluid Viscosity by Ball Drop. Brown University Physics Department, wiki.brown.edu/confluence/download/attachments/1162150/Tang_Balldrop.pdf?version=1&modificationDate=1466695891000&api=v2.