Stronger, heat-healable and biodegradable plastic developed

Researchers at the University of Tokyo developed an innovative plastic VPR by adding the molecule polyrotaxane to an epoxy resin vitrimer. The new material is stronger and stretchier than the existed standard type and can be healed with heat, remembers its shape and partially biodegradable.

Limitations of epoxy resin vitrimer

Vitrimers are a relatively new class of plastics, which are solid and strong at low temperatures, like thermoset plastics used to make heat-resistance tableware, but can also be reshaped multiple times at higher temperatures, like thermoplastics used for plastic bottles.

However, vitrimers are typically brittle and cannot be stretched far before breaking. By adding polyrotaxane, the researchers were able to create a dramatically improved version VPR.

Stronger, heat-healable and biodegradable VPR

VPR remembers its shape, holds its form and has strong internal chemical bonds at low temperatures.

Professor Shota Ando, Project Assistant from the Graduate School of Frontier Sciences, stated that VPR is over five times as resistant to breaking as a typical epoxy resin vitrimer. It also repairs itself 15 times as fast and recovers it is original memorized shape twice as fast.

The complex shape of an origami crane was restored using heat after being flattened.

The improved toughness of VPR implies that more complex shapes could be created and retained even at low temperatures.

Another feature of VPR is its ability to be healed with heat. At temperatures above 150°C, the material’s strong internal chemical bonds recombine and the material can be reformed into different shapes.

Shape recovery test of VPR (left) and vitrimer (right) heated to 120°C on a hot plate.

Last but not least, VPR can be chemically recycled and is partially biodegradable, which fulfils present demands on resource recycling.

Researchers discovered that by applying heat and a solvent, VPR breaks down into its raw components. VPR can be chemically recycled 10 times as fast as the typical vitrimer.

“Although this resin is insoluble in various solvents at room temperature, it can be easily broken down to the raw material level when immersed in a specific solvent and heated,” explained Prof Ando.

Originally, vitrimer does not undergo any apparent biodegradation. For VPR, however, submerging it in seawater for 30 days resulted in 25% biodegradation, with the polyrotaxane breaking down into a food source for marine life.

These all prove that disposal or recycling can be easier with VPR.

Wide range of practical and playful applications

Professor Ando pointed out that VPR is expected to fit both practical and playful applications from areas including engineering, fashion, robotics, medicine and so on.

Infrastructure materials for roads and bridges are often composed of epoxy resins mixed with compounds such as concrete and carbon. By using VPR, these would be easier to maintain as they would be stronger and healable using heat.

For vehicle manufacture, due to it hard but stretchable feature, VPR can strongly bond materials of different hardness and elongation.

Furthermore, for a more playful use, with its shape memory, editing and recovery capabilities, users may even be able to rearrange silhouette of clothes with hair dryer or steam iron.

“I have always thought that existing plastics are very difficult to recover and dispose of because they are subdivided according to their uses. It would be ideal if we could solve many of the world's problems with a single material like this,” said Prof Ando.

The team’s next step will be to work with companies to determine the feasibility of its various ideas for VPR, as well as continuing its research in the lab.

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Watch the demo: Features of heat-healable VPR