Living in a Plastic World: Tackling the Plastic Pollution Problem

Since plastics are non-biodegradable, they accumulate in the environment, disrupting habitats and natural processes. Every year, millions of wildlife are affected by plastic waste.

As plastics break down, they release toxic compounds into the environment and form small plastic particles called microplastics. These microplastics are now ubiquitous and are associated with severe health effects such as metabolic disorders and organ damage.

Recycling plastics reduces the amount of waste and conserves natural resources. However, only about 10 percent of plastic is currently recycled globally. This low figure is partly due to the difficulty of recycling certain types of plastic, such as e-waste and marine plastic litter. Additionally, chemical processes to break down plastics into reusable components are energy-intensive.

Researchers at NTU Singapore are addressing these significant challenges and making progress in reducing plastic pollution.

Repurposing E-Waste Plastics for Biomedical Applications

Plastics form a large portion of electronic waste (e-waste), driven by rapid technological advancements and high consumer demand. According to a UN report, e-waste is growing five times faster than the official recycling rate. In 2022, e-waste generated 17 million tonnes of plastic globally.

Single-use plastics are also extensively used in research and healthcare, particularly in cell culture.

Acrylonitrile butadiene styrene (ABS) is a common e-plastic used in devices like keyboards and laptops. Repurposing ABS for high-value biomedical applications can effectively reduce plastic waste.

Scientists at NTU developed a synthetic matrix to culture cells using ABS from discarded keyboards. The porous matrix acts as a scaffold, providing a structure for cells to attach and grow.

This matrix can culture spherical clusters of cells, called cancer spheroids, which more accurately represent actual tumors due to their 3D shape compared to traditional cell cultures.

To fabricate the matrix, scientists dissolved plastic scraps from discarded keyboards in an organic solvent, acetone, and poured the solution into a mold. The matrix supported the growth of breast, colorectal, and bone cancer spheroids. These cancer spheroids exhibited properties similar to those grown using commercially available matrices and could be used for biomedical applications such as drug testing.

“Our innovation not only offers a practical means to reuse e-waste plastics but could also reduce the use of new plastics in the biomedical industry,” said Assoc Prof Dalton Tay from NTU’s School of Materials Science and Engineering, who led the research. The study was published in *Resources, Conservation & Recycling* in 2024.

Converting Hard-to-Recycle Plastic Waste into Useful Materials

While some plastics can be repurposed into new products, others, like household plastics, packaging waste, and marine plastic litter, are harder to recycle. Moreover, treating mixed and contaminated plastics offers limited economic benefits.

NTU researchers explored using difficult-to-recycle plastics as a source of solid carbon material for polymer foams. The process involves heating different types of plastic waste at high temperatures (600 degrees Celsius) in the absence of oxygen to obtain gas and oil, which are then heated to over 1000 degrees Celsius to break down into solid carbon and hydrogen. The solid carbon can be added to polymer foam to enhance its strength and abrasion resistance for cushioning applications. The foam containing synthesized solid carbon from plastic waste exhibited properties comparable to other carbon-based and conventional reinforcing materials.

The hydrogen produced can be collected and used as fuel.

Published in the *Journal of Hazardous Materials* in 2024, the research marks a milestone in repurposing previously unrecyclable plastic waste. “We have developed a feasible approach to repurpose hard-to-recycle plastics, which is an important aspect of the circular economy,” said lead investigator Assoc Prof Grzegorz Lisak from NTU’s School of Civil and Environmental Engineering.

A Greener Way to Break Down Plastics

Conventional methods of breaking down plastics involve heating them at high temperatures, which is energy-intensive and generates greenhouse gases, contributing to global warming.

Addressing the need for greener methods, NTU scientists have developed a process to upcycle most plastics into valuable chemical compounds useful for energy storage. This reaction uses light-emitting diodes (LEDs) and a commercially available catalyst at room temperature and can break down a wide range of plastics, including polypropylene, polyethylene, and polystyrene, all commonly used in packaging and discarded as waste.

Compared to traditional plastic recycling methods, this process requires much less energy.

First, the plastics are dissolved in the organic solvent dichloromethane to make the polymer chains more accessible to the photocatalyst. The solution is then mixed with the catalyst and flowed through transparent tubes where LED light is shone on it. The light provides the initial energy to break the carbon-carbon bonds with the help of the vanadium catalyst. The plastics' carbon-hydrogen bonds are oxidized, making them less stable and more reactive, followed by the breakdown of carbon-carbon bonds.

The resulting end products are compounds such as formic acid and benzoic acid, which can be used to make other chemicals for fuel cells and liquid organic hydrogen carriers (LOHCs) – organic compounds that absorb and release hydrogen through chemical reactions. LOHCs are being explored by the energy sector as storage media for hydrogen.

According to Assoc Prof Han Soo Sen from NTU’s School of Chemistry, Chemical Engineering, and Biotechnology, who led the study, this breakthrough not only addresses the growing plastic waste problem but also reuses the carbon trapped in these plastics instead of releasing it as greenhouse gases through incineration. The method was reported in the journal *Chem* in 2023.

Source: Nanyang Technological University