The “RecycloSil” research project aims to evaluate the recycling potential of crosslinked silicone polymers and to develop a suitable process for breaking down crosslinked silicone products (e.g. old silicone baking moulds or silicone sealants) back into their molecular building blocks in a controlled and energy-efficient manner after the end of their product lifetime. After separation, purification and analytical characterisation, these are to be recycled as secondary raw materials into the process of silicone production or other applications. The aim is, in the future, to protect both natural resources and the environment, to reduce waste, and to make savings on the costly, energy-intensive process steps for producing silicones. The project is funded by the STAEDTLER Foundation.

A number of different process steps are needed for the targeted degradation of elastomer silicone products, from mechanical comminution to chemical degradation, and subsequent isolation of products and by-products. The chemical degradation step is primarily carried out using mild digestion methods that are able to cleave the Si–O bonds contained in silicones and to obtain defined, low-molecular cleavage products. The use of sustainable digestion reagents and/or solvents is particularly important here. The main focus is the systematic investigation of digestion methods using different acids, which ideally also occur in nature and are therefore “green”, as well as the use of metal and non-metal compounds that allow catalytic degradation of silicone polymers. For example, preliminary studies have already shown that solid silicones can be completely dissolved in the presence of suitable reagents at low temperatures (< 100 °C) or even at room temperature, resulting in mixtures of silicon-containing cleavage products, some of which even occur in the established value-added and process chain for silicones and could be recycled into the production of new silicone products.

As part of the “RecycloSil” research project, the dissolution and digestion behaviour of defined commercial silicone products in relation to various digestion reagents and mixtures will be systematically investigated and comprehensively evaluated with regard to the resulting cleavage products. Targeted approaches will then be further adapted and optimised with regard to yield and selectivity of the reaction being investigated, the silicon-containing cleavage products obtained will be isolated and used as examples for the production of new silicone products (especially silicone oils), in order to demonstrate and evaluate the completeness of the material cycle on the basis of examples.

At the end of the project, at least one process that allows controlled cleavage and recycling of silicones and the silicon-containing components contained therein should have been obtained. This should provide the basis for follow-up projects aimed at the targeted development of economically viable processes for recycling silicones, in collaboration with industrial partners.

Project leader: Prof. Dennis Troegel

Researchers: Students of the Faculty of Applied Chemistry

Funded by: STAEDTLER Foundation

Dates: 1 October 2021 – 31 March 2023