The challenge of recycling composite materials

18-04-2024 | Posted by Joaquín Martí

Composite materials are engineered by combining two or more different materials to create a final product with enhanced properties. Because of those enhanced properties, composite materials are widely used in various industries, such as aerospace, automotive, wind power, construction, consumer goods, and sporting goods, among others.

As a drawback against their good properties, disposing of composite materials presents unique challenges. The difficulties posed by the recycling of composite materials stem primarily from their complex and heterogeneous nature. The main types of composite materials include:

• Fibre-reinforced composites: These consist of a matrix (polymer, metal, or ceramic) reinforced with fibres (e.g., carbon, glass, or aramid).
• Particle-reinforced composites: In these materials, the matrix contains embedded particles (e.g., metal, ceramic) to enhance properties.
• Structural composites: These are used to build complex structures, like sandwich panels, with different materials for skins and cores.

While composites offer numerous advantages in terms of properties like strength-to-weight ratio and durability, their recycling is hindered by several factors:

• Material complexity: Composites are a mix of different materials, often chemically bonded together, making it difficult to separate the constituents during the recycling process.
• Degraded properties: Recycling can cause a loss of material properties due to the need for mechanical or thermal processing to separate the components.
• Environmental impact: Conventional recycling techniques may release hazardous chemicals or generate harmful byproducts.
• Lack of standardization: The lack of standardized recycling processes and regulations for composite materials hinders widespread recycling efforts.

The growing concern for sustainability and the necessity for these materials to be part of the circular economy are leading researchers and industry to work very actively on the development of innovative methods. Some of the recycling techniques currently being explored include:

• Mechanical recycling: Involves shredding or grinding composite waste to create smaller pieces that can be used as fillers in new composite materials.
• Thermal recycling: Involves using high temperatures to break down the composite materials into their constituent parts. For example, pyrolysis can be used to convert composites into their original fibres and matrix materials.
• Solvent recycling: Involves dissolving the matrix material with a suitable solvent to recover the fibres or particles.
• Biological recycling: Some researchers are investigating biodegradable composite materials that can be broken down by microorganisms.
• Hybrid methods: Combining several of those techniques to achieve better results.

To improve recycling rates, it is essential to develop cost-effective and environmentally friendly techniques and encourage the adoption of these methods by industries. Additionally, designing composites with better recyclability in mind from the outset can be an effective strategy to address this issue.

With the great service that composites are providing, it would be a shame if we were unable to manage their end of life in a sustainable manner.