Making hardy plastics recyclable

Thermosetting polymers are a class of plastics commonly used in microelectronics and aerospace industry owing to their resistance to high temperatures, chemical stability and mechanical strength, but they can cause environmental hazards because they are non-recyclable. Researchers have now developed the first recyclable thermosets.

Thermosets are made up of chemical crosslinks that form between the monomers, which cannot be reversed by exposure to high temperatures like for other plastics.

However, a team of researchers led by James L. Hedrick at IBM, USA, and including researchers from Saudi Arabia, managed to retrieve the monomers from the thermosets they developed using acidic conditions — the first pH-based recycling strategy of its kind — and published their findings in Science¹.

The synthesis of the reported thermosets is based on the reaction between diamine monomers and paraformaldehyde. This set up allows the production of thermosets with versatile properties by changing the reaction conditions and the type of diamine used.

They produced a flexible thermoset at low temperature which retains the advantages of classical thermosets. By using the same diamine at a higher temperature, they produced a solvent-resistant thermoset of the highest mechanical strength reported among this class of polymers, which was further increased by adding carbon nanotubes. Separately, another diamine led to the development of an organogel that has the capacity to reform its initial shape upon cracking.

These new recyclable thermosets are expected to replace their conventional counterpart in many industrial applications, since they are more environment friendly and economically feasible. 

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