Japanese researchers have developed a new type of temperature-resistant plastic that is easily decomposable with a solvent and capable of self-repair or returning to its original shape when heated. To top it off, it can biodegrade in seawater and transform into food for marine life. The applications of this material range from engineering to medicine, including both light and heavy infrastructure and sustainable fashion.
Despite global efforts to reduce plastic production and use, the material remains ubiquitous in our daily lives. While significant advances have been made in recycling technologies, plastic production has continued to increase every year. Its disposal in landfills and oceans dramatically impacts not only the environment but also public health.
To mitigate these impacts, scientists are now working on circular production solutions for plastic. To do this, materials must exhibit both resilience and malleability, self-repair properties, shape memory, recyclability, and marine biodegradability. It is in this context that researchers at the University of Tokyo have created a new durable plastic material based on epoxy vitrimer resin.
However, while vitrimers possess most of the characteristics of durability and circular production, they are generally fragile and can easily break when stretched. By adding a molecule called polyrotaxane, Japanese researchers have created a significantly improved alternative. Details are available in the ACS Publications journal.
Marine Biodegradation in Just 30 Days
Epoxy vitrimer resins are a new category of rigid plastics at room temperature that can be reshaped at will when heated. The exchange of bonds and changes in the cross-linked network topology of the material are activated above 150 °C. As a result, the material gains in malleability but does not melt, giving it strong potential as a durable and environmentally friendly polymer.
The new material, called vitrimer incorporated into polyrotaxane (VPR), possesses the resilience lacking in conventional epoxy vitrimer resins. Polyrotaxanes are assemblies of interlocked supramolecules in the shape of collars and numerous cyclic molecules wound on axial polymers. Through cross-linking (the formation of one or more three-dimensional networks between macromolecules) with other polymers, they significantly enhance the material’s resilience. This property is due to the ability of cyclic molecules to slide along their polymer axes.
The addition of polyrotaxane has allowed the new material to retain even the most complex shapes at room temperature. “VPR is over five times as resistant to breaking as a typical epoxy resin vitrimer,” explains Shota Ando, the lead designer and assistant project professor at the University of Tokyo, in a statement. The VPR has retained the inherent malleability of epoxy vitrimers and can be reshaped at will starting at 150 °C. However, it self-repairs 15 times faster and regains its original shape two times faster than conventional vitrimers.
Japanese experts demonstrated these feats with an origami crane-shaped VPR. After being completely disassembled and flattened, the object quickly returned to its initial shape (with all its details) when heated. After being cut with a scalpel, it self-repaired in just 60 seconds when exposed to a temperature of 150 °C (hot air gun).
Furthermore, when heated and immersed in a specific solvent, it breaks down into its raw components and can be chemically recycled 10 times faster. “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,” explains Ando.
To top it all off, VPR biodegrades by 25% in just 30 days when immersed in seawater. The resulting polyrotaxane fragments can serve as food for marine animals—a first for this type of material. In comparison, polyrotaxane-free vitrimers showed no notable marine biodegradation.
Practical and Playful Applications
The characteristics of VPR make it an ideal material for today’s society, which demands resource recycling and environmentally friendly plastic alternatives. Prospects for applications range from robotic engineering to sustainable fashion, medicine, car coatings, and various infrastructures.
For example, roads and bridges could be easier to maintain by adding VPR to the concrete mix. Typically, these structures are made of a combination of epoxy resins and concrete or carbon. By adding VPR, it would only require heating a high-temperature area to see it self-repair.
Its shape memory and modification capability could also interest fashion designers in reshaping clothing, for example, using a simple hairdryer or iron. It’s important to note that synthetic textiles are responsible for 35% of microplastic pollution in the oceans. Sustainable materials like VPR could help reduce the sector’s impacts.
Shota Ando, Masaki Hirano, Lisa Watakabe, Hideaki Yokoyama, and Kohzo Ito, “Environment-friendly sustainable thermoset vitrimer-containing polyrotaxane,” ACS Materials Letters: October 31, 2023, doi:10.1021/acsmaterialslett.3c00895.