The researchers created their sustainable plastics through a water-based process combining two types of ionic compounds. They mixed solutions of sodium hexametaphosphate with various guanidinium-based compounds, which underwent liquid-liquid phase separation.
This natural separation process expelled unwanted salts and created a concentrated phase that could be dried into solid plastic. They tested multiple variations of the guanidinium compounds and also created versions using chondroitin sulfate as the anionic component. The materials underwent extensive physical testing, including mechanical strength measurements, thermal analysis, and degradation studies.
The created plastics demonstrated remarkable properties: densities around 1.6 g/cm³, high optical transparency (97%), and impressive mechanical strength with Young's moduli ranging from 8.7 to 18.0 GPa. The materials showed thermal stability up to about 300°C and could be reshaped above their glass transition temperatures.
When exposed to saltwater, they completely dissociated into their component parts, which could be recovered at yields above 80%. The chondroitin sulfate versions showed even higher tensile strengths, reaching up to 94 MPa.
The materials showed sensitivity to water, particularly salt water, which while beneficial for environmental degradation, could limit some applications. The researchers addressed this by using protective coatings like parylene C. The study didn't include long-term durability testing under various environmental conditions, and scale-up considerations for manufacturing weren't fully explored. The economic viability of large-scale production wasn't addressed in detail.
This research demonstrates a new approach to creating sustainable plastics that combines practical durability with environmental degradability. The materials' ability to completely dissociate in salt water, rather than just fragmenting into microplastics, represents a significant advance in addressing marine plastic pollution. The successful incorporation of biological materials like chondroitin sulfate suggests the potential for further development using other natural polymers. The materials' thermal reshaping capability and recyclability offer practical advantages for manufacturing and end-of-life handling.
The research was supported by a JSPS Grant-in-Aid for Specially Promoted Research and RIKEN Strategic Partnership Collaborative Project with Eindhoven University of Technology. Several authors are inventors on a patent application related to this work. The study received additional support from Kao Corporation and various research fellowships. The authors declared no other competing interests.