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Building blocks of sustainability

Since their discovery in the early 20th century, polymeric materials have revolutionized many aspects of our lives. Perhaps the most recognizable polymers in our daily lives are plastics.

Despite their enormous value, we produce more plastic than we recycle, and this is becoming a major environmental challenge. The figures are staggering: Just 9 percent of the global supply of plastic is recycled. Most plastic produced is incinerated or placed in landfills, leading to pollution. A significant amount of plastic waste is also found in the seas, creating not just an eyesore but damage to aquatic life and marine ecosystems.

At Khalifa University, Sharmarke Mohamed and his team at the Advanced Materials Chemistry Center (AMCC) are developing a new method for recycling post-consumer plastic waste that uses a combination of mechanical force (as part of mechanochemistry), light and catalysts.

The value of this technology is that it uses no corrosive or harmful chemicals.

– Sharmarke Mohamed, Khalifa University

While mechanical methods are common as a means for reducing the size of plastics prior to recycling, it is not possible to apply this for the depolymerization of most plastic waste. Instead, the researchers are looking for ways to perform low-cost recycling using a range of stimuli.

“Despite the enormous environmental challenge posed by plastic waste, we felt a sense of duty to develop these new mechanochemical tools. Most researchers around the world are exploring mechanical force as a means to build new chemicals. In other words, building complexity from simple structures. We decided to use the same principles and use mechanical force as well as light and catalysts to break down complex polymer waste materials into smaller building blocks that can then either be recycled or upcycled,” he says.

“Solar energy is responsible for the photodegradation of plastics in the environment, particularly in the UV region of the electromagnetic spectrum. We also know that some biological catalysts (e.g. enzymes) are adapted to using organic macromolecules such as plastics as fuel sources. So in essence, we are learning from nature as we try to develop a lab-scale protocol that uses these tried-and-tested methods for turning plastic waste into high-value chemicals,” Mohamed says.

“As the UAE declares 2023 to be the Year of Sustainability, our research group is very much leading this effort in a challenging area. But we are motivated by solving the environmental challenges posed by plastic waste,” Mohamed says.

About 380 million metric tons of plastic are produced each year. Of that, only about 9 percent is recycled, Mohamed tells the KUST Review. Some plastics are treated with harsh chemicals, like acid. But most plastic is incinerated, he says.

“But the problem (with incineration) is that it releases carbon dioxide and adds to the global carbon footprint. The other problem is that if you burn the plastic you can’t reuse it. Our group is trying to take the end-user plastic and come up with new low-cost mechanical methods that are able to break down these polymers into their constituent parts.”

Those constituent parts might then be reused to make new plastic products or chemicals for other uses.

Mohamed’s team is working on a three-year project to investigate a three-part process for recycling plastics. This research is supported by AMCC and funded by ASPIRE, the technology program management pillar of Abu Dhabi’s Advanced Technology Research Council (ATRC), via the ASPIRE Award for Research Excellence.

The first part involves mechanochemistry: using mechanical energy to induce the chemical depolymerization of the plastic waste.

“Mainly we use ball mills to grind the polymers in the presence of proprietary chemicals we are developing in our lab. This leads to the polymer essentially breaking down and releasing its constituent building blocks, known as the monomers. Preliminary results in our lab suggest this process can be done under ambient conditions in the solid-state with yields of up to about 70 percent or higher,” he says.

We are trying to think outside the box and look at the problem from a non-conventional perspective using a mechanocatalytic approach.

– Zeinab Mohamed Saeed, Khalifa University

The value of this technology is that it uses no corrosive or harmful chemicals, which is important as it makes the entire process much more environmentally friendly than incineration or land-filling the plastic waste.

The next step is to examine the influence of light on the process, followed by experiments with inorganic catalysts (i.e. metal salts) or enzymes to break down the plastics.

“Once we understand each of these processes on their own, we can see how they can be stitched up together to create what we refer to as a photolytic and mechanoenzymatic degradation (PMED) protocol. We envisage the PMED process will be implemented serially as part of a batch process, much like a conveyor belt in a factory. Our long-term goal is to take post-consumer plastic waste and to efficiently produce the chemical building blocks of the plastic waste via our PMED process.”

Different forms of plastic break down in different ways under mechanical force, complicating the process, Mohamed says. But he says the initial work is promising.

Zeinab Mohamed Saeed, a Ph.D. candidate working on the project, says she’s excited by the non-conventional approach to a long-standing problem.

“The field of polymer degradation was there for decades,” she says. “People have been trying to come up with different ways to tackle the issue using their expertise, and now we are trying to think outside the box and look at the problem from a non-conventional perspective using a mechanocatalytic approach. I find this research challenging but exciting, and can’t wait to see what kind of results we will end up with.”

Among the challenges, however, is creating vessels that can hold the material but also allow in light of a certain wavelength. And the enzymes known to break down plastics are expensive.

The hope, however, is to scale up the technology to levels required by industry. That’s still some time off, however.

“Now we can do up to a gram or two. This is fine for feasibility and patenting,” Mohamed says.

The Advanced Materials Chemistry Center (AMCC) was formed in 2022 and combines expertise from different disciplines to tackle major environmental problems. Its methods for treating plastic waste “align with the UAE’s ambitions to transition to a green circular economy and achieve its net-zero targets” Mohamed says.

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Microplastics:
The invisible threat

Over 300 million tons of plastics are produced each year, out of which only up to 40 percent are recycled or incinerated. The majority end up in landfills or are improperly discarded in the environment, leading over time to their fragmentation into smaller plastic items.


CREDIT: Khalifa University
Ludovic Dumée

Ludovic (Ludo) Dumée is an assistant professor within the Chemical Engineering Department at Khalifa University who leads the Advanced Separation Materials team. Read more›››

His research interests span from functional and reactive materials engineering to their application across environmental applications. In 2020, he received the Membrane Society of Australasia Science award for his work on microplastics separation. He can be reached at Ludovic.dumee@ku.ac.ae.‹‹‹ Read less

Such “microplastics,” whose maximum dimension falls below 5 millimeters, are ultimately released into waterways and represent a major threat to global ecosystems, the entire food chain as well as many human industrial activities that rely on river or sea-water intake.

The fragmentation of such microplastics may also lead to the formation of nanoplastics, with dimensions below the micrometer level. These are much more difficult to quantify and identify, and they represent key challenges for engineers and researchers.

Why may microplastics enter the food chain and affect humans? Microplastics are reported in the guts of multiple avian or sea-life species that often mistake microplastics for food. Ingested microplastics may accumulate in their digestive system. Besides representing a major source of pain, it can lead to the animals’ premature death. Scavengers then feed on their carcasses, leading to further ingestion of microplastics up the food chain.

Over time microplastics contamination carries over to greater predators and human beings. It is estimated that humans ingest between 50,000 and 100,000 microplastics every year, arising from overusage of plastic bottles for soft drinks or packaged-water consumption, but also through uncontrolled fragmentation and release from packaging materials.

Examples of risks associated to plastic ingestion for human and their uptake by our body through diffusion in the blood system are multiple and daunting, not only due to the increased risk of cancer for exposed organs, but also because microplastics may carry over pathogenic contaminants, such as heavy metals or persistent organic pollutants. Such surface-contaminated microplastics, given the high buoyancy of plastic materials and their ability to float, may therefore act as cargos to further disseminate other contaminants over much larger distances than the single contaminants could achieve.

How can microplastics impact human industrial activities? Besides the food industry, a key area affected by the presence of micro or nanoplastics is the water industry.

Microplastics that enter the waterways may carry over pathogenic contaminants, such as heavy metals or persistent organic pollutants. CREDIT: Unsplash

The intake waters, feeding wastewater-treatment and desalination plants, may contain, depending on their location and origin, various levels of nano or microplastics, which may damage existing treatment processes.

For instance, the presence of microplastics in microbial-digestion bioreactors would disturb the microbial ecosystem and floc formation, that is the size of the colonies and their stability, thus reducing the efficiency of the process.

Deposits of nano or microplastics may directly damage membrane-separation steps, potentially leading to mechanical abrasion, as well as to accumulation onto the membranes, reducing the separation and flux performance. These phenomena were found to increase substantially the cost of water desalination and processing, sometimes detrimentally affecting the quality of produced water.

In addition, studies showed also that, depending on the treatment trains in place, microplastics may be further concentrated across the treatment units, leading to discharge of sludge or downstream waters richer in microplastics at the end of the water-treatment process.

How can you help? Discard your plastic wastes properly and ensure that you put them in the right bin without leaving a chance for discarded items to get into our beautiful waterways. Also privilege sustainable-packaging options and limit your usage of single-use items.

What is needed at this point to better understand risks? Researchers are developing advanced tools and platforms to detect nano and microplastics in wastewaters, to better understand their interactions with microbial organisms, water-treatment operations and assess their health and economic impact. We develop strategies to reveal the true extent of pollution within local ecosystems and understand the impact of plastic fragments of various sizes or shapes on the performance of separation systems. We also study the impact of microplastics on human health and their potential diffusion into our bodies to better prevent long-term diseases.