A study conducted by CNRS1 researchers describes a new method of recycling silicone waste (caulk, sealants, gels, adhesives, cosmetics, etc.). It has the potential to significantly reduce the sector's environmental impacts. This is the first universal recycling process that brings any type of used silicone material back to an earlier state in its life cycle where each molecule has only one silicon atom. And there is no need for the raw materials currently used to design new silicones. Moreover, since it is chemical and not mechanical recycling, the reuse of the material can be carried out infinitely. The associated study is to be published in Science on 24 April 2025.
The raw material used to make silicones is naturally occurring quartz2. Its constituents are decomposed using metallurgy at high temperature to obtain pure silicon. That then reacts with methyl chloride to form chlorosilanes, molecules essential to all silicone-based polymers. These first two transformations are very energy intensive and emit CO2, the main greenhouse gas causing climate change. Consequently, this new recycling technique would make it possible to circumvent one of the most harmful impacts of the silicone sector. Moreover, as this chemical recycling process gives direct access to (methyl)chlorosilanes, which can be separated and purified industrially, it guarantees the quality of silicone materials from recycling, and can do that infinitely without loss of properties.
At a time when key chemical elements – and the associated mineral resources – are increasingly sought after, a recycling process like this also opens up a path to easing potential tensions around the crucial quartz resource, and the resulting silicon that is one of the key components used by the electronics industry. Together with their scientific and industrial partners3, the authors continue their research, both on improving this process to make it industrially applicable, and by proposing recycling methods for other stages of silicone processing. Finally, they are also working on recycling other materials to make their use more sustainable.
Notes
1 – From the « Catalyse, Polymérisation, Procédés et Matériaux » laboratory (CNRS/CPE Lyon /Université Claude Bernard Lyon 1).
2 – Critstalline silica with fewer impurities than sand.
3 – This study was conducted alongside the Centre de RMN à très haut champs at Lyon (CNRS/ENS de Lyon/Université Claude Bernard Lyon 1), the Institut de chimie et biochimie moléculaires et supramoléculaires (CNRS/Université Claude Bernard Lyon 1) and private companies Activation and Elkem Silicones.
