Mineral Plastics: Self-Repairing and Recyclable

Researchers are investigating mineral-based plastics as an alternative to plastics based on crude oil. Mineral plastics can be produced in a simple, low-cost and low-energy manner, and can be reused up to twenty times.

Packaging, toys, bottles and plastic bags are all made of polyethylene plastic. Considerable energy is required to produce plastics and to recycle them after use. The team of Helmut Cölfen, Professor of Physical Chemistry at the University of Konstanz, is hence developing greener mineral-based plastics that can be produced easily and be reused up to twenty times. The raw material of the mineral plastic is a sodium carbonate solution. The researchers drip this into a mixture of calcium chloride and polyacrylic acid, and, within minutes, a white, malleable compound forms in the solution – the plastic in the form of a hydrogel. The hydrogel’s ingredients are only lightly bonded, allowing the gel to be shaped into any form. The gel is suitable as a sealant in damp environments, for example. The gel can also repair itself: after externally induced bond cleavage, the two parts of the hydrogel can be immediately reconnected and subjected to load.

The hydrogel retains its shape when it dries. Compared with conventional plastic, this mineral plastic is five to six times harder, making it suitable as a housing material for electronic devices, for instance. Another advantage is the material’s reusability: when water is added, the dried plastic swells to form hydrogel again. This cycle of drying and swelling can be repeated at least twenty times without affecting the plastic’s mechanical properties.