Have you ever left a plastic water bottle in a hot car, only to find it warped and distorted? That's ‘creep’ in action. This tendency of solid materials to gradually deform under constant stress can be seen everywhere, from the sagging insulation of old electrical wires to tire indents in old, tarred roads. For heavy industries like aerospace and construction, creep has serious consequences, as even tiny changes in precisely designed parts can affect their structural integrity enough for catastrophic failures.
This issue is particularly significant for vitrimers, a unique class of polymers being eyed for a new generation of recyclable tough plastics. With dynamic covalent bonds that can break and reform under certain conditions, the traits that allow vitrimers to be easily reshaped also make them more prone to creep, even at usage temperatures.
To address this, Research Scientist Zibiao Li led a team at the A*STAR Institute of Sustainability for Chemicals, Energy and Environment (A*STAR ISCE2), and worked with colleagues at the A*STAR Institute of Materials Research and Engineering (A*STAR IMRE) to develop a new foundational chemical reaction platform for vitrimers: one which would only activate at temperatures above 140 °C.
“Using the α-acetyl cinnamate/acetoacetate (α-AC/A) exchange reaction, vitrimers exhibit high creep resistance at common service temperatures, ensuring their stability during regular use while maintaining the ability to be reshaped, repaired or recycled,” said Wang Sheng, the co-corresponding author of the work. “This selective behaviour makes α-AC/A vitrimers ideal for applications that need long-term stability, like car or aerospace parts.”
During stress tests, the team found their α-AC/A-based vitrimers showed no signs of creep even after being exposed to 120 °C for six hours. After two rounds of reprocessing, the vitrimers also maintained tensile strength and stiffness similar to the original raw material.
Wang highlighted that their novel reaction was catalyst-free, simplifying the resulting vitrimers’ production process while reducing their economic and environmental costs.
“While catalysts are commonly used to enhance the reactivity and control of dynamic covalent bonds in vitrimers, they often bring complications such as increased system complexity, potential toxicity and reduced long-term stability,” said Wang. “Catalyst residues can also interfere with material stability or performance.”
Beyond their functionality, α-AC/A vitrimers hold exciting potential for customisation. As their dynamic bonds can be selectively triggered by heat or light, they could form the base of self-healing or ‘smart’ plastics that adapt to environmental changes.
The research team is now focused on improving the α-AC/A exchange platform by lowering its activation temperatures, explore new polymer designs based on it, and testing its vitrimers in real-world scenarios.
“We hope this work leads to new breakthroughs in sustainable polymers that are both high-performance and fully reprocessable,” said Wang.
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 A*STAR Institute of Materials Research and Engineering (A*STAR IMRE).
