New approach to silicone waste recycling closes the loop
Summary author: Walter Beckwith
A new low-energy chemical recycling method using boron and gallium can convert common silicone waste into useful chlorosilanes with high efficiency and yield. The method offers a promising new chemical pathway toward circularity in silicone materials, addressing both resource sustainability and emissions reductions in the industry. Prized for their durability, heat and chemical resistance, and low toxicity, silicone polymers are found in countless everyday products, ranging from medical devices to car parts. Each year, millions of tons of silicone are produced globally. Producing silicones is highly energy-intensive, with over 70% of their carbon footprint stemming from the extraction and subsequent chemical processing of component materials. Thus, improving silicone recycling is critical – not only to conserve valuable raw materials like quartz but also to significantly reduce energy use and environmental waste. However, while recycling of carbon-based polymers has advanced, recycling silicone polymers remains challenging due to their complex chemical makeup and robust material properties. Here, Nam Duc Vu and colleagues present a versatile chemical recycling strategy to break down a wide range of silicone-based materials, including those commonly used in consumer and industrial products. Vu et al.’s approach uses a gallium catalyst and boron trichloride reagent to depolymerize silicone, at a mild 40° Celsius, into quantitative amounts (~97% yields) of high-purty chlorinated silane monomers, which are key building blocks in silicone manufacturing. According to the authors, the method is scalable and closes the loop on silicone materials by enabling re-synthesis of fresh silicones from waste. In a related Perspective, Koushik Ghosh discusses the study in greater detail.
For reporters interested in research integrity issues, Perspective author Koushik Ghosh notes, “recent efforts in my field have made strides toward addressing science integrity-related issues, particularly through initiatives aimed at improving transparency, reproducibility, and ethical research practices. However, one area I believe requires greater emphasis is prioritizing quality over quantity in scientific output. The current landscape often incentivizes the production of numerous publications, sometimes at the expense of originality and rigor. I would like to see a stronger focus on fostering truly innovative research, with an honest acknowledgment of the value of "failure experiments."
Journal
Science
Article Title
Gallium-catalyzed recycling of silicone waste with boron trichloride to yield chlorosilanes
Article Publication Date
25-Apr-2025
A new recycling process for silicones could greatly reduce the sector’s environmental impacts
CNRS
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.
Journal
Science
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Gallium-catalyzed recycling of silicone waste with boron trichloride to yield key chlorosilanes
Article Publication Date
24-Apr-2025
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