A new way to recycle waste silicones

Researchers in France have devised a way to reclaim silicone building blocks for use in new materials

Silicones are used in a huge variety of products: cookware, cosmetics, medical devices, lubricants, sealants, and more. They’re prized for their flexibility, low toxicity, and heat resistance. But silicon-based polymers are also very energy- and carbon-intensive to produce. More than 70% of silicone’s carbon footprint comes from the processes to turn quartz into elemental silicon and silicon into polymerizable chlorosilanes. So having a way to regenerate chlorosilanes from waste silicone could save energy and reduce emissions.

Now, a team of researchers at the French National Center for Scientific Research (CNRS) have devised a strategy to turn nearly any silicone polymer back into chlorosilanes, which can be easily purified by distillation and reused to make new silicones (Science 2025, DOI: 10.1126/science.adv0919).

“The quality of the chlorosilanes that we make is on par with what is achieved industrially,” says Jean Raynaud, one of the lead researchers on the project. “You maintain the properties over and over again, so it's infinite recycling.”

The reaction gives high yields at relatively low temperatures and works on “a huge variety” of silicone polymers, including postconsumer and industrial waste, says Vincent Monteil, the project’s other coleader. It even works on the highly cross-linked silicones commonly used in bakeware, which other chemical recycling methods cannot handle.

The main drawback is that the reaction uses a large amount of toxic, corrosive boron trichloride to supply the necessary chlorine atoms. Raynaud says the group tried other chlorine sources without much success—not many other elements can compete with silicon in terms of wanting to form bonds to oxygen. The researchers also used gallium chloride as a catalyst to help break the silicon-oxygen bonds in the polymer backbone and shuttle chlorine and oxygen atoms around.

Joseph Furgal, a polymer chemist at Bowling Green State University who also researches silicone recycling but was not involved in the work, says that it’s a “very interesting and cool” approach to solving a major challenge in silicone recycling and that being able to produce chlorosilanes is certainly an attractive prospect for industry. “The biggest hurdle in the whole thing is the sacrificial boron,” he says. BCl₃ itself takes a lot of energy to produce, he explains, and that requirement may eat into the amount of energy saved by the recycling process. But overall, he thinks the method is a good step forward.

The reaction works best in dichloromethane, but the researchers found that it also proceeds in safer solvents such as toluene and heptane, albeit at a slightly slower rate. It gives boron trioxide as a by-product, which can be used to produce borosilicate glass or new BCl₃.

Monteil says that he and his team have taken the process up to a 100 g scale with help from industry collaborators at Activation and Elkem. He, Raynaud, and their team are continuing to work on making it more efficient and sustainable, including looking for ways to improve the catalyst and chlorine source.