Enhanced Self-Repairing Plastic Invented by Tokyo Researchers

A team from the University of Tokyo has created a new type of plastic, designated VPR, which exhibits superior strength, increased elasticity, and self-healing properties upon heating, outperforming conventional plastics. This plastic can be remolded at elevated temperatures and shows partial biodegradation in marine environments. Such advancements promise to revolutionize recycling processes and waste management across numerous sectors, aiding in fulfilling Sustainable Development Goals. VPR presents benefits such as improved resilience, rapid shape restoration, and efficient chemical recyclability, with potential applications across diverse fields including engineering, production, healthcare, and the textile industry. (Illustrative concept)

This advanced material is capable of preserving intricate forms and biodegrading in ocean water.

The University of Tokyo’s research team has introduced a groundbreaking plastic that exceeds traditional plastics in robustness and flexibility, and also mends itself when exposed to heat.

This polymer, which exhibits shape memory and is partially biodegradable, was produced by incorporating polyrotaxane with an epoxy resin vitrimer. The plastic, termed VPR, maintains its form at lower temperatures due to strong internal chemical bonds.

An origami crane able to revert to its original form after flattening with the application of heat demonstrates this property. (Image credit: 2023, Shota Ando)

Beyond a threshold of 150 degrees Celsius, the material’s bonds can reconfigure, allowing it to assume different forms. Both heat and solvent exposure can break down VPR into its basic constituents.

Its immersion in seawater for a month led to a biodegradation of 25%, with polyrotaxane decomposing into substances that marine organisms can consume. This material paves the way for a more sustainable, circular economy, with uses extending from engineering and manufacturing to medical applications and eco-friendly fashion.

Confronting Challenges of Plastic Consumption and Waste

Global initiatives continue to strive against the widespread use and disposal of plastics, which permeate numerous aspects of modern life, from toys and clothing to electronics, transportation, and infrastructure.

Although plastics are prevalent and serve multiple functions, their production, usage, and disposal present numerous environmental challenges. Developing durable, reusable, and environmentally benign alternatives is crucial for addressing these issues and achieving the United Nations’ Sustainable Development Goals.

Advantages of VPR

In pursuit of sustainable solutions, the Tokyo researchers have engineered a novel plastic from an epoxy resin vitrimer. Vitrimers are modern plastics that are solid and robust at lower temperatures (similar to thermosets used in heat-resistant products), but are also malleable at higher temperatures (like thermoplastics used in bottles).

Ordinarily, vitrimers are fragile and have limited stretchability. However, by integrating polyrotaxane, the researchers have significantly enhanced the plastic, which they have called VPR (vitrimer with polyrotaxane).

A test comparing vitrimer plastic with and without polyrotaxane at 120 degrees Celsius showcased the superior performance of VPR. (Image credit: 2023, Shota Ando)

“VPR showcases more than a fivefold increase in break resistance compared to a typical epoxy resin vitrimer,” explained Project Assistant Professor Shota Ando of the Graduate School of Frontier Sciences. “It also self-heals 15 times quicker, returns to its initial shape doubly fast, and can be chemically recycled at a rate ten times quicker than standard vitrimers. Additionally, it safely biodegrades in a marine setting, which is a novel feature for this type of material.”

Polyrotaxane is attracting attention for its potential to reinforce various materials. In this study, the enhanced durability of VPR allowed for the creation and maintenance of more complex structures at cooler temperatures, such as the showcased origami crane.

The disposal or recycling of VPR is also more straightforward compared to traditional vitrimers, as stated by Ando: “While this resin is insoluble in different solvents at ambient temperature, it easily degrades to its original materials when heated in a specific solvent. It also experienced 25% biodegradation after a month in seawater. Unlike vitrimers lacking PR, no significant biodegradation occurred. These properties make it exceptionally suitable for today’s resource-recycling demands.”

Potential Uses and Continued Research

The team envisions VPR’s application in fields ranging from engineering to fashion, robotics, and healthcare.

For instance, Ando suggests that infrastructure materials, typically comprising epoxy resins mixed with substances like concrete and carbon, would benefit from VPR’s enhanced properties. This new material could also be advantageous in vehicle manufacturing due to its rigidity coupled with stretchability, as well as in fashion where its shape memory and editing features could allow for home customization of garments with common appliances.

Further research and collaboration with industry partners will explore VPR’s viability for these varied uses.

Ando reflects on the broader implications: “Given the complexity of recovering and disposing of current plastics, a material like this, which can address numerous global challenges, would be ideal.”

The study has been backed by NEDO, the JST-Mirai Program, and the AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory, and is published in “ACS Materials Letters” journal.

Reference: “Environmentally Friendly Sustainable Thermoset Vitrimer-Containing Polyrotaxane” by Shota Ando, et al., 30 October 2023, ACS Materials Letters.
DOI: 10.1021/acsmaterialslett.3c00895

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More about Self-healing plastic

• University of Tokyo
• ACS Materials Letters
• Sustainable Development Goals
• Epoxy Resin Vitrimers
• Polyrotaxane Properties