Silicone rubber's exceptional properties have led to its widespread use across sectors such as healthcare, electronics, automotive, and kitchenware, with global consumption exceeding 2 million tons annually. However, its highly cross-linked three-dimensional network structure makes it difficult to degrade or reprocess after its service life ends—burning releases silica dust, while landfilling leaves it intact for over a century. With the advancement towards carbon neutrality goals and increased ESG requirements, the recycling and reuse of silicone rubber have become critical challenges that material science and environmental industries must overcome. While initial technical pathways are emerging, achieving large-scale, economically viable circular economy systems remains a long journey.

I. Why is Silicone Rubber Difficult to Recycle?

Thermosetting Nature: After vulcanization, C–Si–O–Si–C cross-links form, which do not melt when heated but begin to decompose only above 300°C.

Chemical Inertness: The backbone chain is stable and cannot be dissolved by conventional solvents.

Complex Composition: Contains fillers (such as silica), pigments, flame retardants, etc., making separation challenging.

Pollution Risk: Medical and food-grade waste requires strict sterilization and sorting, increasing processing costs.

Therefore, traditional "mechanical recycling" (crushing for filler) is limited to low-value applications with significantly reduced performance.

II. Mainstream Recycling Technology Approaches

Pyrolysis

Conducted in an oxygen-free environment at high temperatures (500–800°C), producing:

Silicon oils (cyclic/linear siloxanes) usable in new silicone synthesis after purification.

Silica ash suitable for construction materials or rubber reinforcement.

Advantages: Can handle mixed waste.

Challenges: High energy consumption, complex products requiring distillation separation; D4/D5 cyclic compounds need catalytic conversion.

Wacker has established a demonstration line with a recovery rate of about 60–70%.

Chemical Depolymerization

Uses strong bases (KOH), acids, or catalysts (e.g., tetramethylammonium hydroxide) to break Si–O bonds.

Produces low molecular weight siloxane monomers that can be repolymerized after purification.

Advantages: Closed-loop recycling with quality close to virgin materials.

Limitations: Harsh reaction conditions, high costs, suitable only for high-purity waste (like LSR scraps).

Shin-Etsu Chemical has developed a mild catalytic system effective at 200°C.

Mechanical Crushing and Reuse

Crushes waste silicone into micrometer-sized powder (<100 μm).

Used as filler in new silicone (typically ≤20%).

Applications include mats, sound insulation materials, garden paving.

Disadvantages: Decreased mechanical properties, considered downcycling.

Energy Recovery

High calorific value (～25 MJ/kg) makes it suitable for co-processing in cement kilns.

However, this does not align with the principle of material circulation and should be a last resort.

III. Industry Practices and Policy Promotion

EU Circular Economy Action Plan: Requires all plastic packaging to be recyclable by 2030, indirectly promoting research and development in elastomer recycling technologies.

China’s 14th Five-Year Plan for Circular Economy Development: Encourages high-value utilization of polymer waste.

Corporate Actions:

Dow has launched the "SILASTIC™ ReNew" series containing 30% recycled silicon oil.

Apple is experimenting with recycled silicone in Apple Watch bands.

Medical device companies are exploring "trade-in + professional recycling" models.

IV. Key Obstacles in the Circular Economy

表格

Obstacle Explanation

Difficulty in Collection Silicone products are widely distributed across various industries without unified recycling channels.

Poor Economics  Virgin silicone prices are low ( $ 3–5/kg), giving no cost advantage to recycled materials.

Lack of Standards No unified quality standards for recycled silicone, leading to hesitation from downstream users.

Technological Maturity      Depolymerization processes have yet to be scaled up, and pyrolysis product values are low.

V. Future Directions: From "Recycling" to "Design for Circularity"

Reversible Cross-linkable Silicone Rubbers: Incorporating dynamic covalent bonds like Diels-Alder and disulfide bonds for thermal/photo-triggered depolymerization.

Bio-based Siloxanes: Extracting silica from rice husks and bagasse to reduce carbon footprints.

Digital Passports: Embedding RFID in products to record material compositions for precise recycling.

Extended Producer Responsibility (EPR): Legislation requiring brand owners to assume responsibility for recycling.

Conclusion

The flexibility of silicone rubber has brought countless conveniences to mankind, yet its resistance to degradation poses new environmental challenges. Although the path to recycling is arduous, it is not insurmountable. Every technological breakthrough represents a reflection on the linear "use-and-dispose" model, and every gram of recycled silicone marks a step toward a circular economy. When material science not only focuses on "how to make better" but also considers "how to return properly," we truly learn to live gently with our planet—because true sustainability begins with reverence and appreciation for every resource.



Low compression set fluorosilicone rubber MY FHTV 3961 series