From yogurt cups to building blocks
Students worked with nonprofit Reimagined Recycling to provide recommendations on pressing and processing of discarded plastics to transform them into durable home goods and building materials.
While polypropylene plastics are commonly found in everyday single use items from takeout food containers to yogurt cups, it is increasingly difficult to find municipalities that accept these items through their recycling programs. Reimagined Recycling, a Pittsburgh based non-profit, has set out to address the issue of these items ending up in landfills through their collection program that transforms the discarded plastics into durable home goods and architectural building materials.
The organization recently acquired a plastic sheet press that enabled them to collect and process more plastics, creating sheets that they could sell as building materials for items such as outdoor furniture. However, they were facing issues related to the quality and durability of the sheets, so they established a partnership with a team of students from the Materials Science and Engineering Department at Carnegie Mellon University to address challenges and provide recommendations as part of the senior capstone project.
The students who took on this project, Audrey Lambert, Ellie Lowe, Aleena Siddiqui, and Eliana Szabo, were drawn in by the opportunity to connect their materials science coursework with solving a real-world problem related to plastics recycling.
As engineers, we have a responsibility to think about resilience and sustainability in all of the problems we aim to solve.
Aleen Siddiqui, Undergraduate student, Materials Science and Engineering
“As engineers, we have a responsibility to think about resilience and sustainability in all of the problems we aim to solve,” said Siddiqui, who is also majoring in environmental and sustainability studies. “I am interested in how this is realized in materials science, and how we can design systems to reduce waste and extend their life.”
Throughout the project, the team members characterized recycled polypropylene sheets in order to determine if they could be used for architectural or building applications. Using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) characterization methods, they were able to determine the melting temperature of the recycled material and confirm that the sheets were purely composed of polypropylene without contamination from improperly sorted plastics.
They conducted chemical resistance testing using common household cleaners to evaluate how the recycled polypropylene would respond to environmental stressors. They attempted tensile testing, but due to defects in the sheets, such as air bubbles and large voids, most of the samples fractured prematurely, so they were forced to rethink their testing approach. Additionally, they performed mechanical testing, including Charpy impact, Rockwell hardness, and 3-point bend tests, then comparing results to virgin polypropylene, as well as other commonly used polymers in order to establish a baseline for the recycled material.
The group had the opportunity to visit the Reimagined Recycling facility, where they observed the entire production process firsthand.
“The visit helped us to gain a better understanding of how the processing conditions impacted the quality of the sheets and informed our recommendations for optimizing the sheet pressing procedure and final material properties,” said group member Audrey Lambert.
Through this iterative process, the team members went beyond collecting and analyzing data as they adapted to unexpected outcomes and managed timelines and the expectations of their partner organization.
“The project provided opportunities to develop our project management skills, and more importantly, our ability to adapt when things didn’t go as planned,” said Lambert. “Outside of learning about different mechanical tests and material characterization processes, we gained experience working as a team and collaborating with our organization company sponsor to meet their goals.”
The findings of the group ultimately found that the recycled polypropylene material properties were generally similar to the virgin material, but that mechanical properties were sacrificed.
They provided Reimagined Recycling with specific recommendations to optimize their sheet pressing procedure through processing changes that could improve the mechanical properties.
“Working with this group was the highlight of our year,” said Ashley McFarland, executive director of Reimagined Recycling. “They were not only enthusiastic and knowledgeable about the tests that could be performed on our materials, they also brought a professionalism to the project in their reports and findings.”
McFarland said that thanks to the group’s contributions, the organization is now creating stronger sheets with less structural and visual defects. Additionally, they have a larger database of material parameters to pull from when marketing and selling these sheets to artists, makers, and designers.