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In brief

This feature, published as the cover story of A*STAR Research Vol. 55, highlights A*STAR R&D initiatives and collaborations in advanced chemistries for a circular economy.

© A*STAR Research

Closing the loop

29 Oct 2024

Through advanced chemistries in materials and process engineering, A*STAR lends its support to national development goals for a more circular economy.

Our modern world is built on the idea of ‘take, make and dispose’. Consider the plastic water bottle: starting as crude oil extracted from the earth’s crust and subjected to carbon-emitting industrial processes, most of the 600 billion bottles that roll off factory lines each day are thrown away after just one use.

“Most products go through the ‘linear economy’; a one-way flow through extraction, production, use and end-of-use,” said Angeline Ong, Deputy Director of A*STAR’s Science and Engineering Research Council (SERC). “With the global threat posed by climate change, we not only need to transition from fossil fuels to low-carbon alternatives as feedstocks for material goods, but to also bring circularity to how we make these goods.”

‘Circularity’ is more than simply keeping our goods out of landfills; it’s about minimising waste by making the most of products, materials and resources, adds Lean Weng Yeoh, A*STAR Chief Sustainability Officer.

“Products must be designed for durability, reuse, refurbishment, remanufacturing and ease of recycling. Non-recyclable products must be biodegradable; otherwise, there must be cost-effective thermal treatment or incineration that reduces their waste volume and produces energy,” said Yeoh. “As incineration ash can then be used for carbon capture and construction, this lets us close the resource loop and reduce its environmental impact.”

For Singapore, the nation’s chemical manufacturing sector is a key part of closing that loop. As of 2022, the energy and chemicals (E&C) industry accounted for 25 percent of total national manufacturing output. Within Jurong Island alone—home to over 100 global chemicals firms—1.1 million barrels of oil are refined daily into fuels and feedstocks for thousands of products from plastics to fragrances.

“The Singapore Green Plan 2030 emphasises a transition away from fossil fuels and the development of circular production pathways,” said Ong. “To support that transition, A*STAR capabilities in chemistry R&D are focused on key enabling technologies to efficiently produce low-carbon commodities and speciality chemicals from alternative feedstocks.”

Greening chemical resources

A circular economy calls for advanced chemistries to develop new materials and processes. In the materials space, A*STAR research institutes such as the Institute of Sustainability for Chemicals, Energy and Environment (ISCE2) and the Institute of Materials Research and Engineering (IMRE) are exploring the potential of materials beyond crude oil.

“An innovation challenge is to devise alternative materials that are just as good as those in common use, but also recyclable and energy-efficient to produce,” said Andy Hor, Deputy Chief Executive (Research) of A*STAR. “Plastics like polystyrene (PS) remain popular despite being non-recyclable because they’re light, cheap and adaptable.”

Enter lignin: a natural plant polymer which grants structure and stiffness. A waste byproduct of the paper pulping industry, lignin is also a strong contender as an abundant, versatile and renewable alternative to today’s plastics, according to IMRE Principal Scientist Dan Kai.

“Lignin isn’t just biodegradable, but also has antioxidant, anti-UV and antibacterial properties that preserve active ingredients and offer bioactive solutions for skincare and medical applications,” said Kai, who is also the Group Leader of IMRE’s Green Infinity Lab.

Tapping into these features, Kai’s team is developing new and versatile lignin bioplastics while keeping an eye on sustainable production. Their processes emphasise green solvents and advanced manufacturing techniques such as 3D printing to minimise environmental impact while enhancing the resulting materials’ functional properties.

By using coconut husks and without adding synthetic resins, the team has created a durable bioplastic which can be used for disposable electronic sensors; as well as safe and biodegradable nanofibres which harness lignin’s natural antioxidant properties for osteoarthritis treatment. The team is also engineering a fully bio-based plastic from food and agricultural waste for high-performance applications such as insulation and adhesives.

Two-way materials

To improve the circularity of existing plastic materials, Shermin Goh, IMRE Senior Scientist and Functional and Dynamic Polymers Group Leader, is teaming up with colleagues from IMRE, ISCE2 and A*STAR’s Institute of High Performance Computing (IHPC) to combine the strengths of two broad classes of plastics—thermoplastics and thermosets—into a new third class: covalent adaptable networks (CANs).

At a molecular level, thermoplastics such as polyethylene terephthalate (PET), found in drink bottles, are made from linear polymer chains with no crosslinks between them. They tend to be weak but mechanically recyclable with heat. Meanwhile, thermosets such as polyurethane (PU), found in foams and cast-moulded parts, are stronger since they’re made of permanently-crosslinked polymer networks. But this makes them impossible to mechanically recycle; they burn before they can be reshaped.

“Conventional plastics with strong covalent bonds or permanently crosslinked chemical structures often end up in incineration plants as they can’t easily be recycled,” said Zibiao Li, Director of ISCE2’s Resource Circularity Division.

The trick to CANs is that their crosslinks are effectively reversible: with heat and pressure, they can be exchanged, or broken and reconnected, allowing them to switch between thermoset and thermoplastic-like structures. “This makes CANs not only tough and recyclable, but also able to ‘self-heal’, extending the life of CAN-based products,” said Goh. “Their stimuli-responsive nature also makes them potential active materials for smart electronics and recoverable adhesives.”

Li leads the MTC Programmatic ‘Developing a Toolbox for Next-Gen Circular Plastic Materials’, working with Goh and colleagues to engineer CANs from thermoplastics. “We aim to develop a chemical toolbox that can be assembled into high-performance new plastic materials for circular use, aiming to achieve zero waste and a lower carbon footprint in the long term,” said Li.

“We’re also exploring bio-based CANs from waste biomass with ISCE2 Scientist Zhuang Mao Png, and there is also potential to explore CANs derived from carbon dioxide (CO2),” added Goh.

Clearing the streams

In general, recycling aims to turn used products into new ones with identical properties. However, degradation and contaminants can make recycled materials more costly to produce than virgin raw materials.

“Circularity research largely focuses on recycling or valorisation technologies, which aim to restore waste to its highest possible value,” said Xinying Deng, Deputy Group Manager (Surface and Circular Processing) at A*STAR’s Singapore Institute of Manufacturing Technology (SIMTech). “However, there is often a gap in the availability of clean, homogenous feedstocks for these technologies.”

As such, Deng and colleagues are keenly focused on the pre-treatment of waste streams, developing process technologies for the separation, cleaning and secondary waste treatment of various mixed materials.

“Plastic products are often made of multiple materials, or have adhesives and other contaminants,” said Deng. “We’re looking to separate these materials into their individual types and clean them sufficiently to make good quality and homogenous feedstocks.”

The techniques developed by Deng’s team include a sonochemical separation process that separates carbon fibre sheets from honeycomb composite structures in end-of-life aircraft parts. Using power ultrasonics and mild chemicals, the process preserves the recovered material’s integrity and quality while making the subsequent fibre recovery process more efficient. The technology is being rolled out in collaboration with Nandina REM, a member company of A*STAR’s Advanced Remanufacturing and Technology Centre (ARTC).

“This work will also be extended in pipeline projects to other dissimilar material combinations, such as metal-plastic and plastic-plastic,” Deng added.

Separately, an engineering doctorate student from Deng’s team with the University of Warwick, UK, is developing a chemometric-enabled plastic sorting process which uses machine learning and analytical chemistry to better identify plastic types in waste streams.

Catalytic upgrades

Catalysts are vital in circular production processes as they help reduce the energy needed for chemical reactions. At IMRE’s Sustainable Supramolecular Materials Lab, Group Leader Jason Yuan Chong Lim and colleagues are exploring new catalytic processes, catalyst types and sustainable methods to valorise plastics. Their focus is on the most challenging, yet abundant plastic types: polyolefins (PO) and PS, which make up nearly 60 percent of all plastic waste.

“Unlike polyesters, these polymers are far less reactive and more difficult to upcycle due to their strong carbon molecular bonds,” said Lim. “We’ve developed a new metal-free, scalable method to turn mixed PS waste into good yields of benzoic acid—an antiseptic, preservative and vital precursor for the chemical industry—using an organic catalyst and vinegar as solvent.”

To further improve processes, Lim and IMRE Research Scientist Albert Ong teamed up with ISCE2 Senior Scientist Ming Hui Chua and IHPC Senior Scientist Shi Jun Ang to create a new computational method to help design and optimise photocatalysts capable of turning PS into benzoic acid. Their catalyst screening method, which uses far less resources than traditional ones, led to the team's discovery of a highly efficient but nonintuitive photocatalyst.

Another collaboration between Lim’s team with those of IMRE Nano+ Group Leader Enyi Ye; ISCE2 Catalysis and Green Process Engineering Division Director Lili Zhang; and researchers from Japanese universities showed that PEs and PPs could be turned into hydrocarbons using highly customisable metal organic frameworks (MOF) as catalysts. “This sets the scene for the development of next-generation catalysts with better reactivity control and product selectivity,” said Lim.

Zhang’s team also has an eye on carbon itself: the elemental backbone of both plastic and organic waste. According to Jennet Li Ying Ong, an ISCE2 Research Engineer, the team has recently filed patents for two successful catalytic technologies they developed for waste plastics: one to create carbon nanotubes, and another for light olefins.

“Carbon nanotubes are widely useful in reinforcement materials and electronics, while light olefins are precursors for synthetic rubber, coatings and versatile plastics,” said Ong. “Currently, we have an ongoing industrial partnership with ExxonMobil and Nanyang Technological University (NTU), with a corporate laboratory set up for low-carbon solutions.”

A milestone project in this area is the Accelerate Catalyst Development Platform (ACDP), an automated high-throughput machine learning system to speed up design and development for industrial catalysts. Jointly set up by ISCE2, IHPC and IMRE, and with industry contributions from IHI and Mitsui Chemicals, its main focus is on catalysts for CO2 and hydrocarbon conversion. In 2023, the platform was awarded the IES Sustainability Award and the ASEAN Outstanding Engineering Achievement Award.

Filters at the frontier

Membranes are one technological area that brings together circular materials and circular processes. ISCE2 Principal Investigator Bofan Li notes their versatile uses in various sectors including wastewater treatment, food processing, pharmaceuticals and chemical manufacturing.

“Being highly adaptable, modular and customisable to specific applications, membranes enable efficient separation and purification processes,” said Li. “They facilitate closed-loop systems where valuable resources such as water, solvents and chemicals can be recovered and reused.”

However, most membranes today aren’t themselves recyclable, leading them to landfills; a problem Li and colleagues intend to fix by pushing the boundaries of membrane technology.

“We’re developing membranes that can be easily recycled and reused after end-of-life; modular membranes that can be easily reconfigured to different separation processes; bio-based membranes derived from renewable sources and processed with green solvents; as well as membranes which can handle more complex, challenging mixed solvent streams,” said Li.

Working with IMRE and the National Taiwan University of Science and Technology, Li and colleagues have developed closed-loop recyclable membranes for dye/salt fractionation in textile production, which can potentially be adopted by other industries. Another IMRE collaboration saw the creation of advanced nanofibrous membranes for efficient water/oil separation, which can help tackle oil pollution in environmental protection efforts.

Harnessing nature’s chemists

Beyond bio-based materials, A*STAR researchers are also looping in nature’s own chemical factories, especially given the 755,000 tonnes of food waste generated in 2023 within Singapore alone—of which only 18 percent was recycled.

“We use biological catalysts such as enzymes and microorganisms to chemically transform organic compounds,” said Melanie Weingarten, Head of the Biotransformation Department at A*STAR’s Singapore Institute of Food and Biotechnology Innovation (SIFBI). “Biotransformation enables us to convert food waste into high-value products such as nutraceuticals, biofuels and enzymes, going beyond food waste’s conventional use as animal feed or fertilisers.”

A key advantage of biotransformation is its environmental efficiency. Unlike traditional processes, it requires neither high heat nor pressure, and achieves highly selective reactions with good space-time yields, making it both energy-efficient and sustainable.

“At SIFBI, we leverage fermentation and biotransformation technologies to develop sustainable processes that valorise food waste. Instead of using sugar—a food ingredient—as fermentation feedstock, we convert what would otherwise be discarded into value-added ingredients, such as bioactives, for food and consumer care products,” said Weingarten.

In collaboration with ISCE2, Weingarten’s team partnered with agricultural producer Dole to reduce fruit loss on farms and transform unutilised fruit parts, such as peels, into specialty ingredients—enzymes, seed oil, dietary fibre, extracts and more—for pharmaceuticals, human nutrition and cosmetics.

“Under the Singapore Food Story R&D Programme, we are also working on an alternative protein production platform that develops functional food ingredients from homogenous agrifood sidestreams such as okara and spent brewers’ grains, providing a sustainable solution for the growing demand,” Weingarten added.

Out in the field

A*STAR’s close working relationships with public sector entities, industry partners and institutes of higher learning continue to strengthen its support for national challenges like the circular economy. These ecosystem partnerships are also integral in bringing A*STAR innovations in advanced chemistry into the circular transition.

One key project has been the multi-party collaboration on carbon capture and mineralisation technology developed by ISCE2 Principal Scientist Jie Bu and colleagues with the National University of Singapore (NUS), NTU and industry partners, with added inputs by public agencies in Singapore such as the National Environment Agency (NEA), the Building and Construction Authority (BCA), and the Economic Development Board (EDB).

The patented ammonium-based mineralisation technology converts three major waste streams into valuable carbonated alternative sand for construction, coastal protection and land reclamation. These consist of incinerator bottom ash (IBA), of which up to 1.5 kilotonnes would otherwise go to landfill daily; recycled concrete aggregate (RCA), which makes up 70 percent of Singapore’s construction and demolition waste; and lower-carbon concentration flue gas, which accounts for at least 26 megatonnes of annual CO2 emissions, and can be partially captured and used for mineralisation.

According to ISCE2 representatives, the process can be done at ambient conditions, making the alternative sand cost-competitive with those from existing technologies which need high CO2 concentrations, temperatures and pressures. It also effectively prevents the leeching of heavy metals from IBA into the environment.

Further upstream, A*STAR and sustainable waste management solutions provider KL Enviro have co-developed an artificial intelligence (AI)-powered waste profiling system that provides detailed insights into the composition of waste streams. “Those insights help optimise waste management processes and determine the most suitable recycling pathways across value chains,” said Spencer Soong, KL Enviro Executive Director.

Andy Hor noted that as circularity is not a single domain subject, A*STAR’s ability to form cross-disciplinary research teams, as well as its excellent working relationships with the private and public sectors, empowers it to create real-world solutions for the specific yet complex problems involved in the field.

“We can bring together experts in materials science, AI, biomaterials and biomechanical design to address challenges like low-energy process production,” said Hor. “Circularity is also a topic under consideration for our upcoming series of Strategic Research and Translational Thrusts (SRTT), a new centralised initiative that harnesses our multidisciplinary expertise to tackle problems of national importance.”

Closing the national loop

In the last five years, A*STAR has made significant contributions towards Singapore’s circular economy aspirations, with over 80 major research projects in this area undertaken in collaboration with ecosystem partners, notes A*STAR Chief Executive Officer Frederick Chew.

“These research projects have led to the publication of more than 300 papers since 2019, highlighting breakthroughs in technologies for smart manufacturing; improved energy efficiency; waste reduction; recycling and upcycling of polymers; CO2 conversion to sustainable fuels; and circular urban planning,” said Chew.

Chew added that the agency is well-equipped to drive transformative R&D initiatives in the space due to its ability to pull intellectual property from low to high translational readiness levels, as well as to assemble multidisciplinary capabilities.

“Since its relaunch in 2022, ISCE2 has spearheaded several circular economy research initiatives including the Singapore Integrative Biosystems and Engineering Research (SIBER) programme, which aims to develop enzyme-based technologies for manufacturing specialty chemicals,” said Chew. “Both ISCE2 and IMRE are also directing research efforts to develop alternative low-carbon feedstocks from CO2 and biomass for chemicals, fuels and materials. Simultaneously, ISCE2, IMRE and IHPC are working with NTU and NUS on next-generation plastic materials that support end-of-life circularity.”

To support Singapore’s targeted overall recycling rate of 70 percent by 2030, as laid out in its Zero Waste Masterplan, A*STAR’s waste profiling and valorisation solutions can be deployed across value chains to enhance the sorting of mixed waste; facilitate more efficient downstream processing methods; and identify new uses for waste materials. Chew cited the example of life-cycle costing/assessment (LCC/LCA) capabilities developed by SIMTech, which are now in use by a range of public agencies and companies to map out their carbon footprint across Scope 1, 2 and 3 greenhouse gas emissions.

The agency’s strategic partnerships in this area also go beyond national borders. Chew highlighted the launch of bilateral grant calls with Australia’s Commonwealth Scientific and Industrial Research Organisation, Italy’s Ministry of Foreign Affairs and International Cooperation, and Germany’s Federal Ministry of Education and Research within the last two years.

“To achieve a circular economy and foster a resilient, sustainable society, we need a fundamental change in how we design products, source for materials, manufacture goods, consume resources and produce waste,” concluded Chew. “A*STAR will continue to strengthen its world-class capabilities in circularity through robust talent development, synergistic collaborations and targeted research strategies, creating impact that extends well beyond Singapore’s borders and shapes a more sustainable future for all.”

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This article was made for A*STAR Research by Wildtype Media Group