Researchers at the University of Tokyo have created a novel plastic that is more durable and flexible than the conventional type now in use. It retains its shape, is partially biodegradable, and can be repaired using heat. They produced it by mixing the plastic-type epoxy resin vitrimer with the molecule polyrotaxane. The substance, known as VPR, has strong internal chemical connections and the ability to maintain its shape at low temperatures.
Image Credit: Michael M.H. Ng/Shutterstock.com
However, when the temperature rises above 150 °C, those bonds recombine, allowing the material to take on new forms. Heat and a solvent are applied to break down VPR into its constituent parts.
After being submerged in seawater for 30 days, the polyrotaxane exhibited a 25% biodegradation, with the polyrotaxane breaking down into a food source for marine life.
This new material hols use potential in engineering, manufacturing, healthcare, and sustainable fashion, among other fields, to promote a more circular economy by recycling resources and cutting waste.
Despite worldwide efforts to reduce plastic consumption and waste, the presence of this pervasive material is hard to escape. It's found in everything from toys and clothing to homewares, electronics, vehicles, and infrastructure. While plastics offer undeniable utility, their life cycle and disposal pose significant challenges.
Creating alternatives that are more durable, easily recyclable, reusable, or sourced from eco-friendly materials is crucial in addressing these issues. Such innovations align closely with several of the United Nations' Sustainable Development Goals.
With this in mind, the University of Tokyo researchers developed a more sustainable plastic based on an epoxy resin vitrimer. Vitrimers are a relatively new family of polymers that are solid and robust at low temperatures (similar to thermoset plastics, which are used to produce heat-resistant tableware) but can be molded several times at high temperatures (similar to thermoplastics, which are used to make plastic bottles).
They are, however, often brittle and cannot be stretched far before breaking. The team was able to build a significantly superior version by adding a chemical called polyrotaxane, which they termed VPR (vitrimer integrated with polyrotaxane [PR]).
VPR is over five times as resistant to breaking as a typical epoxy resin vitrimer. It also repairs itself 15 times as fast, can recover its original memorized shape twice as fast, and can be chemically recycled 10 times as fast as the typical vitrimer. It even biodegrades safely in a marine environment, which is new for this material.
Shota Ando, Project Assistant Professor, Graduate School of Frontier Sciences, University of Tokyo
Polyrotaxane is gaining popularity in science and industry due to its capacity to improve the toughness of many materials. The enhanced toughness of VPR in this study meant that more intricate structures could be formed and held even at low temperatures (such as the origami crane in the video included with this release). Ando added that disposal or recycling was also simpler than with vitrimers that did not contain polyrotaxane.
Ando added, “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. It also showed 25% biodegradation after exposure to seawater for 30 days. By comparison, vitrimer without PR did not undergo any apparent biodegradation. These characteristics make it an ideal material in today's society, which demands resource recycling.”
VPR has potential uses ranging from engineering to fashion, robotics to healthcare, according to the team.
“Just to give some examples, 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,” Ando noted.
He continued, “Unlike conventional epoxy resins, this new material is hard but stretchable, so it could also be expected to strongly bond materials of different hardness and elongation, such as is needed for vehicle manufacture. Also, as it has shape memory, shape editing and shape recovery capabilities, you might also someday be able to rearrange the silhouette of your favorite clothes at home with a hair dryer or steam iron.”
The team’s next step will be to collaborate with companies to establish the viability of its numerous VPR ideas, while also continuing its lab research.
Ando concluded, “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.”
This study was funded in part by NEDO (grant JPNP18016), the JST- Mirai Program (grant JPMJMI18A2), and the AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory (OPERANDO-OIL).
Journal Reference:
Ando, S., et al. (2023) Environmentally Friendly Sustainable Thermoset Vitrimer-Containing Polyrotaxane. ACS Materials Letters. doi:10.1021/acsmaterialslett.3c00895
Source: https://www.u-tokyo.ac.jp/en/index.html