Hawaii faces a growing plastic waste challenge. Recycling on the islands is expensive and difficult, and large amounts of marine debris continue to wash ashore or remain in surrounding waters. Researchers are now exploring innovative solutions to turn discarded fishing nets and household plastic waste into asphalt for roads. Initial results suggest this approach could provide a practical new destination for plastics that would otherwise end up in landfills or oceans.
Jeremy Axworthy, a researcher at Hawaii Pacific University’s Center for Marine Debris Research (CMDR), presented the findings at the American Chemical Society (ACS) Spring Meeting.
“This study investigates whether using recycled plastics on Hawaii’s roads is responsible,” Axworthy said. “Reusing plastic waste already in Hawaii reduces the environmental and economic impact of transporting waste plastic off the islands, incinerating it, or disposing of it in Hawaii’s overflowing landfills.”
Why Hawaii is experimenting with recycled plastic roads
Since 2020, most roads in Hawaii have been constructed using polymer-modified asphalt (PMA), which is designed to improve strength and durability. Compared to traditional asphalt, PMA is more flexible and better resistant to cracking, rutting, and water damage, making it suitable for Hawaii’s tropical climate.
To make PMA, pellets of styrene-butadiene-styrene (SBS, a type of copolymer) are melted into a sticky petroleum-based asphalt binder. That binder is then mixed with heated aggregate (rock or sand) to coat the material before it is laid as pavement.
The researchers wondered if they could replace some of the virgin polymer with discarded plastic. They also wanted to know whether roads made from recycled plastic would work well and whether microplastics and other chemicals would be released into the environment. These questions led the Hawaii Department of Transportation (HDOT) to partner with environmental chemist Jennifer Lynch, CMDR director and research team leader.
Recycling fishing nets into asphalt
HDOT asked Lynch’s team to address two important challenges. The first was to provide abandoned fishing nets collected from Hawaiian waters for use as recycled plastic asphalt for experiments.
“Abandoned foreign plastic fishing gear is the biggest contributor to Hawaii’s marine debris problem,” Lynch said. “To date, CMDR’s bounty project, which pays financial rewards to licensed commercial fishermen for marine debris removal, has removed 84 tons of large derelict fishing gear from the Pacific Ocean.”
The second goal was to determine whether pavements made with recycled plastic release more microplastics than standard SBS-modified asphalt.
“The CMDR laboratory is equipped with state-of-the-art chemical equipment to quantify and characterize microplastics in environmental samples,” explains Lynch. “This capability is incredibly unique and impactful, especially when combined with our marine debris removal projects and our mission to recycle debris into locally needed infrastructure products for the long term.”
After the U.S. company processed the recovered plastic into a material suitable for making asphalt, HDOT moved the project into the real world. A local paving company used three different asphalt mixtures to repave a portion of a residential area on Oahu. One used standard SBS, one used recycled polyethylene from Honolulu’s residential recycling program, and the other was made from polyethylene recovered from discarded fishing nets.
About 11 months later, Lynch’s team returned to collect road dust from each section to measure the microplastics released into the surrounding environment.
Measuring microplastic shedding
Scientists have isolated different types of polymers from road dust, including microplastics, large plastic debris, and tire rubber. They then used pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) to determine where the material came from. Analysis identified styrene and butadiene from standard PMA, polyethylene from recycled plastic and fishing net pavement, and isoprene and butadiene rubber from vehicle tires.
Initial findings indicate that pavements containing recycled polyethylene do not release more polymer than conventional SBS pavements. The same pattern appeared in laboratory performance tests and simulated rainwater collected from experimental road sections.
Researchers detected microplastic-sized particles, but only a small number were identified as polyethylene, regardless of pavement type. Researchers believe this is because the plastic dissolves into the asphalt binder. As roads wear over time, the particles that flake off are made up of rocks, asphalt binders, and polymers together, rather than just plastic alone.
The researchers are also comparing polymer emissions from pavements to the amount of tire material in road dust.
“Our initial Py-GC-MS data showed tire wear overwhelming the polyethylene signal by orders of magnitude like a giant peak. We had to search through the weeds of the chromatogram to find signs of polyethylene,” continues Lynch.
A new possible future for plastic waste
More testing is needed to assess how well these recycled plastic roads will hold up over time. Still, researchers believe this approach could ultimately reduce both landfill waste and marine debris across Hawaii.
“Some people think recycling plastic is a hoax. It’s ineffective and too difficult,” Lynch said. “But this study shows that recycling works when society prioritizes sustainability.”
This study was funded by the Hawaii Department of Transportation.
meeting
ACS Spring 2026
title
Recovery of ocean plastics for paving Hawaii’s roads: assessing the release of microplastics and plastic additives from asphalt incorporating recycled plastics from various waste streams
abstract
Polymer-modified asphalt (PMA) is used to increase the strength and durability of roads. In Hawaii, PMA is typically manufactured using the virgin copolymer styrene-butadiene-styrene (SBS). Recycled plastics such as high-density polyethylene (HDPE) can also be added to asphalt to help sequester plastic waste. Derelict fishing gear (DFG) is a significant problem in Hawaii, but it is also a source of HDPE that can be recycled. However, the performance of asphalt and the effects of adding recycled polymers to asphalt are not well understood. In collaboration with the Hawaii Department of Transportation (HDOT) and the University of Hawaii (UH), the Center for Marine Debris Research (CMDR) is testing the feasibility of using recycled HDPE in asphalt by quantifying the microplastics and plastic additives released from asphalt roads made with various combinations of virgin and recycled polymers. The specific asphalt combinations tested are SBS (control-PMA), DFG with or without SBS (DFG-PMA and DFG-NEET), community waste recycled HDPE with or without SBS (LW-PMA and LW-NEET), and commercial industrial waste recycled HDPE with or without SBS (CA-PMA and CA-NEET). The release of microplastics and plastic additives under laboratory conditions was performed using the Hamburg Wheel Tracker Test (HWTT) with water sample analysis. The field test was conducted on a residential road on Oahu, Hawaii. We swept road dust and analyzed microplastics by direct analysis and solvent extraction, separated bound plastics from asphalt, and separated plastic additives by water extraction. Pyrolysis gas chromatography-mass spectrometry was utilized to analyze the microplastic samples. Plastic additives are solid-phase extracted and analyzed using gas chromatography-mass spectrometry. The results obtained using these new analytical methods provide guidance on the use of recycled rather than virgin plastics on roads. Furthermore, the results of this study provide a viable fate for ending the lifespan of plastic marine debris, which could lead to cleaner and healthier oceans.
