While many everyday plastics like water bottles are recyclable, not all plastics are so forgiving. Heat-hardened plastics known as thermosets are widely used in electronics and aerospace components, but their durability also means they often persist in landfills for decades.
“Once they are set, thermosets are almost impossible to re-engineer, reshape or recycle, creating a critical sustainability challenge. This motivated us to rethink thermoset design at a fundamental chemical level,” said Jie Zheng, a Scientist at the A*STAR Institute of Sustainability for Chemicals, Energy and Environment (A*STAR ISCE2).
To engineer more adaptable thermoset materials, Zheng teamed up with Zibiao Li, Director of the Resource Circularity Division, and colleagues from A*STAR ISCE2, along with researchers from the A*STAR Institute of Materials Research and Engineering (A*STAR IMRE) and King Abdullah University of Science and Technology in Saudi Arabia.
They set out to combine two parent thermosets—one that primarily carried bonds between carbon atoms (C=C), and another that had mostly carbon and nitrogen bonds (C=N)—through a chemical fusion process called a metathesis reaction.
“Much like partners switching in a dance, metathesis reactions allow molecules to exchange bonding partners in a seamless and orderly way,” explained Li. These reactions determine how tightly the atomic network within the plastic is connected, which in turn influences the material’s rigidity and recyclability.
By inducing efficient bond exchange, the team fused an optimal balance of the two parent thermosets to create a new material with uniform mechanical strength throughout. Heat tests showed that the material behaved as a single cohesive unit, indicating the formation of a cross-linked network with complete molecular-level mixing.
“Through the active exchange of internal bonds, the thermoset network is rearranged to allow the material to be reshaped or recycled without losing its structural integrity,” said Zheng.
Moreover, the researchers showed that adjusting the mixing ratio of the parent thermosets alters the tune of the bond exchange dance between the C=C and C=N bonds. This tunability influences the flexibility and thermal behaviour of the resulting material, enabling a wide range of potential applications—from rigid, high-performance components to more adaptable plastics that can be easily reprocessed.
As the approach is already compatible with existing industrial systems and heat-processing equipment, the team believes it could simplify large-scale production and help reduce costs.
“For practical deployment, we will need reliable methods to identify and sort suitable thermoset materials,” said Zheng. Pilot-scale demonstrations will also be needed to validate performance, scalability and cost-competitiveness of these fused materials.
The A*STAR-affiliated researchers contributing to this research are from the A*STAR Institute of Sustainability for Chemicals, Energy and Environment (A*STAR ISCE2) and the A*STAR Institute of Materials Research and Engineering (A*STAR IMRE).
