In STEM I, we work on a seven month long independent research project on a topic of our choosing. As someone who cares deeply about the environment, I wanted to do a project that targeted a major environmental issue: plastic pollution. In narrowing down the project, I landed on the idea to manage plastic waste in paper cups.
Paper cups are widely used because they effectively hold water while being cheap and disposable. These valuable traits are due to the paper-plastic composite material in paper cups, but the presence of this plastic makes paper cups a major pollutant. While there are many proposed solutions, there is no effective means of managing this waste. The goal of this project was to build machine prototypes to separate the paper and plastic components of paper cups for separate recycling. Ad hoc testing showed that the optimal process involved rubbing an abrasive against wet, exposed paper using Arduino-controlled motors. Two designs were built: Design 1 with easier component access, and Design 2 with simpler water management. They were tested for percent of paper removed. Analysis for a confidence interval for population mean at the 95% confidence level revealed Design 1 cleaned 23.4 % ± 2.42% (n = 4), while Design 2 cleaned 12.8% ± 0.946% (n = 4). In a test for rate of cleaning, neither machine was able to completely clean a cup, therefore both have a mean rate of 0 cups per hour. Using a decision matrix for prototype analysis, Design 1 scored 144.9 points, while Design 2 scored 181.3 points, making Design 2 more successful. This project could introduce a largely unexplored waste management route in order to increase the reuse of raw materials, which will help support sustainability and mitigate climate issues arising from waste management. Areas of further improvement to the prototypes were also identified.
Due to their plastic lining and extensive use in society, paper cups are a major pollutant.
Build a machine that will separate the paper and plastic components of paper cup to allow them to be recycled separately.
Paper cups are made of a paper-plastic composite material, which is made by extruding a thin layer of plastic (low density polyethylene) onto a sheet of paper. These sheets are then cut up, rolled, and formed into cups. By extruding the plastic on, the paper and plastic are heat pressed together, which causes the two materials to be tightly attached to each other. This material is both cheap and waterproof, which makes it convenient to use in society, but it becomes more difficult to manage after use.
This is because the mixed materials nature of the cups makes it very difficult to recycle. The current recycling system does not contain the infrastructure to separate different materials within mixed materials items. This is because current recycling models rely on the collection of pure items, such as water bottles, sheets of paper, and metal cans. As a result, mixed materials items such as paper cups whose components have the potential to be recycled, end up being sent to the landfill.
This is a problem because Americans along use 25 billion paper cups annually, amounting to amount 3 million tons of paper cup waste being sent to landfills. On top of that, plastic has a lifespan of 500 years before it can be considered broken down. Combining these facts, paper cup usage causes large amounts of indestructible waste to be sent to landfills and environments, which is highly problematic.
The first part of the project involved ad hoc testing to determine how the separation process would work in the machine. Because the idea of the separation was created from scratch, multiple tests had to be run in order to narrow down how exactly the machines would function. The first test was a test to determine the best liquid to apply to the paper. To test this, the ease of separation was compared after the paper cups were submerged in water (control), a solution with white vinegar, and a solution with baking soda for an hour. After, the ease of separation was ranked on a scale. The second was a test to determine if the separation process should rely on mechanical separation or if it was possible to involve chemical separation. The paper cup was soaked in the optimal solution of baking soda and water for 24 hours, and from there the solution was observed to see if any paper shreds were removed from the cup. There were none found in the solution, which indicated that the chemicals could not separate. Since it was found that the chemical separation was not able to separate the materials, there would be a need for mechanical separation. The third test was a test to determine the application of the abrasive on the paper. The applications of rubbing the abrasive and rolling the abrasive were compared in how much paper was removed in the one minute, and it was found that rubbing the abrasive against the paper was able to separate far more than rolling the abrasive against the paper.
Second part of the process involved mapping and drawing out the designs. It was decided that there would be two main functions of the machine: supply water and rub and abrasive against the exposed edge of the unrolled paper cup. Two design ideas were created, one of them with a focus on having an easy access to the separated parts in the machine, and one that focused on having a simpler method of water management. The first idea was more catered towards a machine with optimal features, whereas the second design was expected to have a higher chance of running. These designs were then drawn out in CAD, which helped in detecting potential issues within the machine, and also provided a clean idea which could be easily communicated with others.
These ideas were then built after collecting the necessary parts from Amazon and Home Depot. There was a bit of circuitry and coding involved in order to control the timing of the motors so that they run as necessary.
The final stage involved testing the designs with two tests. The first was a test of efficiency, where the percent of paper cleaned off the cup in 5 minutes was determined. This percent was calculated by measuring the areas of the places that had been cleaned, and areas that were completing cleaned were multiplied by a factor of 1, and areas that had been partially cleaned and were translucent were multiplied by a factor of 0.5. After summing these areas and multiplying appropriate factors, the sum was divided by the total area of the cup in order to determine the percent cleaned in five minutes. Originally, this test was run without holding the cup at a sample size of eight, however the paper was constantly moving and along with high variability in the numbers, the tests were re run with the paper cup being held down at a sample size of four. The second test run was a test to determine cleaning rate, where first the time taken to clean all the paper off would be measured. From there, a mean could be taken from which the cleaning rate could be determined. The final step involved using this data to evaluate the designs in a decision matrix, as well as compare the success of the designs to a competitor.
Figure 1: The first design
Figure 2: The second design
Figure 3: A piece of paper cup that had been cleaned
Figure 4: Paper shreds attached to the abrasive
The histograms above show the data collected on the percent cleaned in five minutes with holding the cup down, as well as without holding the cup down on the machine. Data for the test on the rate of cleaning is not shown, because neither machine was able to completely clean a cup, therefore there was no realistic data to analyze.
The chart above shows the mean percentages cleaned by the machines in 5 minutes by taking a confidence interval at the 95% confidence level. The data is separated by trials conducted while holding the paper down, and without holding the paper down.
The decision matrix above was used to evaluate the based on multiple criteria. These criteria include:
Consistent: This refers to how much paper can be removed by the machine, which was based on the the percent cleaned in 5 minutes. After the mean with holding was calculated, the mean percent was divided by ten and inputted into the matrix.
Easy Product Access: The refers to how easy it is to access the separated products from within the machine
Low Time: This refers to how much time is required to clean each cup, evaluated by the rate of output by the machine. The machines scored 0's in this department, because they were not able to completely clean a cup and therefore provide a rate.
Safe: This refers to how safe it is to handle the machine
Low Water Usage: The refers to the amount of water used to clean a cup
Protected Motors: This refers to how likely a motor or electrical part is to receive water damage
Low Cost: This refers to how expensive the machine is to get
Note that values for the competitor are estimates, as it was not possible to acquire and test a HydroFiner.
This was a successful proof of concept, which revealed that this is a viable path to explore in order to separate paper and plastic within paper cups. Interestingly, though Design 1 cleaned more than Design 2 with a mean percent cleaned off 23.38% ± 2.42% (n=4), Design 2 had a lower variability in the amount cleaned, with a much smaller margin error from the mean of 12.83% ± 0.946% (n=4). This shows that Design 1 is able to clean paper more efficiently than Design 2, however Design 2 is much more predictable and stable in terms of how much it cleans. However, both machines display a high level of consistency with small margins of errors despite the small sample size, which indicates that holding the paper helped more accurately reflect the capabilities of the machine. From the results of the decision matrix, Design 2 scored higher than Design 1 with a score of 181.3 points, making it the more successful prototype after this first design and build cycle. However, neither prototype was able to compare to the competitor, the HydroFiner, which had a score of 248 points. Given how the evaluation of the different designs, the prototypes must be refined to be more efficient and able to clean a full piece of paper in order to be comparable to other recycling aids. Given the success of this method separation, this is a viable path which can become comparable with the market given more refinement.
References (APA Format)
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PDF of February Poster