Small Molecule Organic Eutectics Show Potential for Replacing Plastics

Researchers at The University of Warwick have made significant progress in the search for sustainable alternatives to conventional plastics. In response to growing environmental concerns, the move towards a circular economy and changing consumer preferences, the research team has identified that certain mixtures of small organic molecules form interesting glasses and viscous liquids. These so-called organic eutectics are promising candidates for replacing polymers in various products.

Plastics have long been a mainstay in modern manufacturing, but their environmental impact has increased demand for eco-friendly alternatives. The Warwick research highlights eutectic molecular glasses and liquids—materials formed by mixing crystalline components—as underexplored yet highly promising options for this purpose.

The team successfully developed a series of hydrophobic eutectic molecular liquids and glasses, each carefully crafted by combining different crystalline components. Using advanced techniques like differential scanning calorimetry (DSC) and UV-vis spectroscopy, the eutectic compositions were precisely determined. The analysis was refined using a trained partial least squares regression model, ensuring accuracy in identifying the optimal material blends.

One key challenge in creating sustainable plastic alternatives is ensuring long-term stability. The Warwick team addressed this by testing the amorphous materials over an extended period of up to 14 months, using powder X-ray diffraction (PXRD) to confirm their resistance to crystallisation. This durability is crucial for ensuring that products maintain their integrity throughout their shelf life.

In addition to stability, the researchers investigated the processability of these materials by examining their rheological properties. They found that all the liquids exhibited low fragility indices, making them suitable for various manufacturing processes, including glassblowing, fibre pulling, film formation, and moulding. Importantly, the team demonstrated that the properties of these materials could be tailored to specific applications by blending different eutectic systems or incorporating plasticisers.

Prof. Dr. ir. Stefan Bon, lead investigator of the work, says: “The original plan was to develop an anything-but-plastic concept material for the formulation industry. Dr. Joshua Ryan, a talented former PhD researcher in my team, BonLab, undertook a systematic study of blending small hydrophobic organic molecules that could undergo a variety of non-covalent interactions with one another. That these hydrophobic eutectic systems had such remarkable physical properties, was beyond our initial expectations.

“We brought our colleague Prof. Gabriele Sosso on board to study by computer simulations how these eutectic mixtures interacted on a molecular level. These small molecule organic eutectic systems offer an opportunity to further develop high-performance materials that can replace conventional polymers in various applications. In a way, they can be seen as a non-covalent analogue to dynamic reversible macromolecular covalent materials, known as vitrimers.”

To showcase the practical potential of these materials, the researchers conducted a controlled release study using a eutectic system composed of 4-hydroxychalcone and bifonazole as a matrix. This study serves as a proof-of-concept, highlighting the versatility of eutectic materials in applications such as drug delivery and beyond.

The University of Warwick's groundbreaking research, published open access in Chemical Science, the flagship journal of the Royal Society of Chemistry, opens new avenues for developing sustainable, versatile alternatives to traditional plastics. As legislative changes and consumer preferences continue to push for greener solutions, these innovative organic materials offer a promising path forward.

Reference: Ryan JL, Sosso GC, Bon SAF. Small molecule organic eutectics as candidates to replace plastics. Chem Sci. 2024. doi: 10.1039/D4SC02574A

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