Building a Better Future for Recycled Plastic

Project Team

Each year, the Energy & Environment: Design and Innovation team engages students in the exploration of energy challenges that result in prototypes of new energy technologies, systems or approaches.

This subteam examined plastic waste recycling, which endangers ecosystems and organisms around the world. Recycling plastic often requires large machinery and extensive labor to break down, making it a costlier option for manufacturers. In 2018, the recycling rate of plastics was 8.7 percent.

To tackle this challenge, team members designed an accessible plastic recycling system that uses scraps of plastics #1, 2, 4 and 5 to create building bricks. They found that bricks containing a combination of these plastics were able to support more than 5000 newtons of compression force and had an ultimate tensile strength up to about 37 megapascals. The high structural strength and relative inexpensiveness of these recycled plastic bricks make them an attractive building block option for a variety of small-scale projects.

Check out their team profile and poster below and see what other subteams developed, including an energy-harvesting speed bump, a low-cost wind turbine that can fit into a backpack, new green roof technology, and new heat capture systems for solar cells.


Team profile by Leonora Lee, Filip Bartel, Katherine Li, Jack Patterson and Chang Yan

“It’s all going to the landfill anyway.” Everyone has probably heard (or said) this before, a common excuse for not putting in the effort to properly dispose of recyclable waste. In reality, it’s not completely false – in 2018, only 8.7% of plastic waste was actually recycled, while the majority was landfilled.

Meanwhile, as plastic waste pollutes land, rivers and oceans, microplastics (tiny bits of broken-down plastic) have been bioaccumulating through organisms and even reaching humans (through seafood, drinking from plastic containers, etc.). Microplastics have been detected in human blood for the first time this year in almost 80% of people tested.

As the overproduction and pollution of plastic waste becomes a larger and larger threat to the environment and to human health, our team worked to understand why plastic wastes are largely not recycled, and how we could help to increase the rate of recycling in order to reduce plastic pollution in the environment. 

Graph of plastic pollution.
Plastics waste management from 1960 to 2018, Plastics: Material-Specific Data | US EPA

We found that the problem was fairly simple: Recycling is not economically profitable. Virgin plastic is incredibly cheap and easy to use (due to fossil fuel subsidies, for example), which contributes to a lack of demand for recycled goods. Additionally, due to high levels of contamination in recyclable waste (unseparated and mixed with organic waste, nonrecyclable goods, different types of plastic, etc.), the recycling process becomes even more expensive, as special machines or expensive labor are required to sort and clean the waste.

Shredding plastic.
The credit card shredder which was used for hard flat plastics (left); a plastic bag tangled in the shredder (right)

While this problem requires global government action and attention, our team searched for a solution that we could implement on campus or in our local area. We started exploring a possible solution to melt multiple types of plastic together into a compact recycled plastic brick. This would reduce some pressure from sorting the different plastics, recycle large amounts of plastic at once, extend the life cycle of plastics, create demand for recycled plastics and create incentives to sort and recycle. 

Shredded plastic being melted.
The low-fidelity process of melting plastics on a hot plate with an aluminum foil takeout container and parchment paper

We started researching and testing the melting behaviors of different plastics. We figured out which plastics could be melted together (#1, 2, 4, 5) and which plastics could not (#3, 6, 7). We then began testing different methods for each step of the brick making process: shredding, melting and molding.

Molding plastic.
Our final prototype of using two stacked bread pans (lined with parchment paper) as a mold for the melted plastic

We started off using a tin can or an aluminum foil takeout container lined with parchment paper on a hotplate as a low-fidelity prototype for melting and molding the plastic. For shredding, we started off just using scissors, but found that the process was very time-consuming and inefficient. We tested multiple shredding mechanisms: a manual food processor, a blender and a credit card shredder. We found that the most effective and efficient shredding process was to use scissors to open up bottles and other containers, a credit card shredder for harder flat pieces of plastic and a guillotine paper cutter for plastic bags (which would otherwise get caught in the credit card shredder’s blades).

We then tested and found that a toaster oven (that could heat up to 450°F) was very effective at melting the plastic. For our mold, we found that two bread pans could be stacked to hold and compress the plastic as it melts. The materials needed for our final process (credit card shredder, paper cutter, toaster, bread pans) cost a total of $248.84. In comparison, the Precious Plastic Project kit for creating recycled plastic bricks costs about $10,200. While more expensive kits can create bricks faster and more efficiently, our process could be used by anyone using materials that can be found in a local grocery store or electronics store. 

Through this process, we created four different recycled plastic bricks, containing different combinations of the four recyclable plastics (#1, 2, 4, 5). We used these four bricks to conduct strength tests: a compression test and a three-point-bend test. We found that our bricks could support more than 5000 newtons of compressive force (5000 newtons was the maximum limit of our machine) and an ultimate tensile strength of up to 37 megapascals. To compare, concrete bricks have a flexural strength of about 3-4 megapascals. 

Four recycled bricks.
Our four completed recycled plastic bricks bent after conducting the three-point-bend test

Recycled plastic bricks have been found to have incredible insulating properties and great flexibility that can absorb abrupt shock loads (which would be especially beneficial in earthquake zones). With sustainable government initiatives creating incentives and support for recycled plastic, along with the environmental and structural benefits, recycled plastic bricks can be economically competitive and influential for structural and construction work. 

Graph showing stress vs. strain of bricks.
Graph of the Tensile Strengths of Four Tested Plastic Bricks from a Three-Point-Bend Test

Through this project, our team learned a lot about the recycling process – particularly, how difficult it is. Plastics are generally dangerous to work with. Plastics #3, 6 and 7 are unrecyclable because they emit toxic fumes when heated, and the other plastics can emit toxins if they are burned. Our team had to be incredibly careful to not burn the plastics, and all of our testing was conducted in a fumigation hood to protect us. At the end of the day, plastic is a very dangerous material, and while our research can be used to eliminate polluting plastics that have already been produced, we hope that the production of virgin plastics slows and eventually stops. 

Our team has shown that there can be demand for recycled products such as plastic bricks. Our research can be used to push for the elimination of unrecyclable plastics (#3, 6, 7) and to encourage the mass production of recycled products. Most importantly though, our research can motivate people to put in the effort to sort and recycle their waste. Taking a few extra seconds to properly sort waste can have a huge impact on how much plastic goes to the landfill and pollutes our environment. 


Making Recycled Plastic Bricks with Optimized Accessibility

Poster by Leonora Lee, Filip Bartel, Katherine Li, Jack Patterson and Chang Yan

Project poster.

Landing Page Image: Recycled Plastic Shreds, by Tony Webster, licensed under CC BY-SA 2.0