Ghost Net Busters

Last Blog Post! Last Call! Call? Who’re You Gonna Call? Ghost Net Busters!!

5/20/2025

Hi everyone, we’re back with our final post - this is the homestretch of the quarter and our team’s project. In the past few weeks, we’ve successfully:

Made a dog bone by incrementally adding in clumps of melted plastic nets (May 8th).

Attempted making a levelized sheet of plastic (scrapped the dog bone mold for this) to then laser cut dog bones out of the cooled plastic (May 13th). We fed shredded nets, sandwiched by two metal sheets, into the heat press and took it out to cool before opening it up and putting more shreds on top to fill in any gaps between the cooled plastic. We cooled off the plastic by sandwiching the metal sheets with ice before separating the sheets and scraping off the plastic.

Created a fairly uniform dog bone using our previously-written-about “wax seal” method: using the negative of the dog bone mold to press down on semi-melted plastic and filling it from the top-down. This means we now have two dog bones!

Designed and machined a mold that would allow us to create 8 dog bones in the heat press simultaneously.

We finally received nets from PMDP, by way of CMDR, on May 20th. During unboxing, we realized that all the shredded nets are NOT prewashed (as we had anticipated). We realized that we might not have enough time left to prewash and test the materials, but this is still something that can be done in the future. Therefore, we divided up half of each biofouling level (clean, light, medium, heavy) for future pre-washing (see photo) and have set that aside for the time being.

Now, we can finally start working with the plastics from the Papahanaumokuakea Marine National Monument. We warmed up the clean (unwashed) shredded nets in the press, then proceeded to use the "wax seal" method with our new 8 dog bone mold! We left it to cool under pressure. Moving on, we will try creating dog bones for the four levels of biofouled, unwashed nets and hopefully perform enough tensile tests.

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1 Dog Bone Mold, 3 Failed Attempts, and a Whole Lot of Fishing Nets!

5/6/2025

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The past two weeks have been productive to say the least! Starting off strong with our biggest update - an (initial) completed dog bone mold, made by Zinnia in the Product Realization Lab. The type V dog bone was machined using the CNC machine (Computer Numerical Control).

This mold will become the basic unit for casting (no fishing net pun intended) our HDPE dog bones.

Now that we have the mold, we’ve been able to do some testing and experimentation, both literature-based as well as some trial and error, as to how we’re getting the bits of fishing net INTO the mold. And it’s not as easy as it sounds… Our first attempts have involved:

Manual shredding with scissors (and sharpening the scissors with aluminum foil), as well as...
A brief stint using a blender - this did not work because the pieces of unraveled net were getting tangled, instead of shredded, by the blade.

***We will ultimately get pre-shredded nets from CMDR, but the OVI nets and the shredding of them has been helpful for us to get an understanding of how we need to fill the dog bone mold.

Once we cut up enough nets into small enough pieces, we ran our first attempt (experiment?) for a dog bone. We filled the mold as much as we could (1.293g), and placed it in the heat press at 340ºF with 1.27 tons of pressure. We left it for 10 mins in the heat press and then pulled it off the heat but left it under pressure for another 10 mins. Afterwards, we removed the plastic from the mold.

In a change of strategy, our second attempt involved making a makeshift rectangular mold the right width for a type V dogbone with the idea that we can laser cut dog bones out of a flat sheet. We filled the rectangle as much as we could (~5g) and set it in the heat press at 370º, with a much higher pressure ( ~10 tons of force), and left it to cool inside the heat press for 5 minutes.

However when we released the pressure, the plastic all stuck to the top and bottom of the metal sheets (see photo) and looked/smelled…horrible. (pictured - results of rectangular mold heat press)

For our third (future) attempt, we are going to try one more strategy of filling, forming, and emptying the dog bone mold - similar to making a wax seal! This will involve using the aluminum dog bone mold as a negative and placing it on top of a mound of shredded nets bounded by an area (see initial concept sketch). We will press the mound of nets into the mold by covering them with the mold itself. Then, we will pressurize the loaded mold with the heat press. Essentially, we’re going to fill the mold from the top down, allow the plastic to harden, and laser cut any excess trim around it. Like a vintage wax seal!

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Melting some Marine Debris and Progress on Dog Bones

4/18/2025

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Welcome back! We have a couple updates on our progress so far and will also outline our next steps :D

We finally got our hands on some marine debris sourced by Ocean Voyages Institute (OVI), so we went straight to the lab to see what we could do. Unfortunately, the computer connected to the extruder is dead, so we went ahead and experimented with the heat press. We snipped off some fibers and fed them into the heat press at 270℉ (melting point of HDPE), left them in for 10 minutes, and set them at a pressure of around 11.5 (the pressure decreased over time as the plastic flattened out). The pressure was 11.05 when we took the sample out of the press.

The centers of the fibers melted together somewhat, but the edges were still pretty brittle. Without a shredder, we used a guillotine and scissors to snip the turquoise fibers into finer shreds before putting them through the heat press.

This time, the shreds still didn’t uniformly melt together, so we raised the temperature to 350℉, set the pressure to 10, and kept the time constant—the result: a flexible, film-like sheet.

With proof that we can melt the nets into a more even material with the heat press, we can start designing and creating a mold for dog bones by next week. Our biggest challenge is figuring out the design and creation of the molds. Once we have that down, the process can be more streamlined and be a rinse-and-repeat of making dog bones and running the flexural and tensile tests! After finishing those tests, we will test for the melt flow index if time allows.

We are still expecting a shipment of HDPE nets from CMDR that will come in various contamination levels and include washed, unwashed, and clean nets as a control. In the meantime, we will continue experimenting with the OVI nets. During our meeting with Mafalda (CMDR), we identified the nets that are most likely HDPE. We will shred the HDPE-identified nets into 2-inch sizes, create initial dog bones, and determine the density of the dog bones. We also plan on getting our hands on some heat-resistant gloves and mold-release spray before we hit the lab again.

Outside of lab time, we will simultaneously start researching infrastructural (long-term) end-use products to incorporate these plastics into. This aligns with the mission of promoting a more circular economy in the Hawaiian islands by decreasing the need for virgin plastic imports and minimizing waste.

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Recycling Ghost Nets for Public Infrastructure: Investigating the Role of Biofouling in Determining the Material Properties

4/14/2025

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Introduction:
The problem of ghost nets in our oceans continues to be a major environmental challenge. These discarded, lost, or abandoned fishing nets, which float in the ocean for years, have devastating impacts on marine life and ecosystems, particularly in sensitive regions like the Northwestern Hawaiian Islands. At the same time, they present an opportunity for innovative recycling solutions that can serve both environmental and economic needs. This quarter, our collaboration with the Center for Marine Debris Research (CMDR) and Papahānaumokuākea Marine Debris Project (PMDP) takes a critical step forward in tackling this issue by exploring the potential for transforming these ghost nets into sustainable infrastructure materials, like plastic lumber and concrete reinforcement ties.
Project Focus:
This quarter, our team’s focus is on determining the tensile and flexural properties of ghost nets with varying degrees of biofouling, specifically analyzing whether washing the nets prior to recycling adds any functional benefit. Our hypothesis is that more biofouling, especially the naturally accumulated calcium carbonate (CaCO3) on the nets, could actually reinforce the plastic, making the washing process unnecessary. This could streamline the recycling process, saving time, energy, and resources by eliminating the need for power washing and chemical treatments typically used to remove biofouling in standard plastic recycling.

Testing Plan and Methodology:
We’re working with nets that have been retrieved from the ocean and are divided into two groups: those that have been prewashed to remove biofouling and those that have not. The main goal of this testing is to understand the mechanical properties of these nets to determine if they can be used effectively in producing long-lasting, durable infrastructure materials.
To achieve this, we will:

Create Dogbone Specimens: We will begin by shredding and extruding the recovered ghost nets into the shape of “dogbones” – a standard specimen for tensile testing (pictured below). These dogbones will be manufactured in our lab using a specialized extruder. This step is critical because it turns the debris into usable testable forms that can be evaluated for their material properties.

Tensile and Flexural Testing: We will test the dogbones in the MTS Criterion 43 materials testing machine, which is available in the Stanford lab. This allows us to evaluate the tensile strength (how much force the material can withstand before breaking) and flexural properties (how the material bends before failure). Our objective is to compare the mechanical properties of prewashed versus non-prewashed nets, and determine whether biofouling enhances or weakens the material.
Melt Flow Index (If Time Permits): If we have time, we will also test the melt flow index, which is a measure of how easily the material flows when heated. This is important for understanding the processing behavior of the plastic when it is extruded into products like plastic lumber of reinforcement ties.

We aim to conduct 10 trials for each specimen type to generate reliable results that can guide the recycling process and inform future applications of the material.

Why This Matters:
The unique aspect of our project is the access we have to advanced materials testing equipment at Stanford, which is not available at Hawaii Pacific University (HPU) or with CMDR. This collaboration allows us to conduct detailed, high-precision tests that will help CMDR and PMDP understand the full potential of the ghost nets for reuse in the local Hawaiian infrastructure market. By demonstrating that washing the nets might not be necessary and that the biofouling itself may enhance the plastic’s strength, we could potentially streamline the entire recycling process—reducing costs, labor, and environmental impact.

The Bigger Picture:
Ultimately, our goal is to transform the waste problem into a resource. By proving that the biofouling on ghost nets can be an asset rather than a hindrance, we hope to support CMDR’s efforts to recycle these materials into long-lasting products like plastic lumber and concrete reinforcement ties. These products could help reduce the reliance on new plastic production and contribute to a circular economy in Hawaii, where ocean plastic is given a second life in building materials that can be used in the community.

As the project moves forward, we will continue working closely with CMDR and PMDP to finalize the testing and push the boundaries of what is possible with recycled ghost nets. Stay tuned for more updates as we move closer to a solution that could not only address ocean pollution but also support sustainable development on the islands.

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