Industrial activity is undergoing a perpetual revolution, in a context of increasingly demanding global production, which raises new constraints on manufacturing quality. It therefore generates environmental repercussions, particularly in the field of recycling. This concerns mainly the construction, aeronautics, aerospace, nautical, naval as well as the automotive industry.
These sectors are becoming major consumers of composite materials that are known for their durability, resistance and long-life cycle. However, the manufacture of these complex materials is responsible for the production of a large volume of waste that must be recycled in order to protect the environment in the long term. This recycling still remains a real headache today and research for innovative solutions is becoming essential.
What are composite materials?
Composites are the combination of two or more elements, of different nature, which are assembled to create a single product. A wide variety of materials are involved in their composition, coming from two main families: the matrix on the one hand, and the reinforcement on the other.
The materials that make up the matrix
There are three main categories:
• organic matrix composites (OMC) which use natural and synthetic substances. This category of materials is the most widespread, itself classified into two by-products: mass-produced composites, representing nearly 85% of CMOs, and high-performance composites, which are the most in demand in the high-tech industry.
• ceramic matrix composites (CMC): these are ceramic fibers, as their name suggests; these are known for their thermal resistance and weight reduction
• metal matrix composites (MMC): they are made from light metals such as magnesium, titanium and aluminum
The materials that make up the reinforcement
These materials are made from fibers which constitute the framework of the body and which are also classified into three main groups: the organic, mineral and metallic type. There are several structures of those reinforcements, which are in the form of particles, three-dimensional assembly for multiaxial weaving, braiding or even short or long fibers.
What about recycling composites?
These complex materials must follow a specific process in their recycling in order to limit their environmental impact. Indeed, once decomposed, they can be reused again to obtain new products.
However, recycling is still proving to be a challenge today, with the need to implement innovative concept solutions for safe, sustainable and profitable reuse. Added to this is the search for added value through the creation of new products. Indeed, different treatment process must be considered in consideration of not only the environmental but also economic and social issues, in accordance with the principle of the circular economy.
Recovery techniques differ depending on the composition of the composites, taking into account the potential for transformation, energy recovery and disposal. Each element is separated mechanically, then the treatment and actual recycling depend on the nature of the decomposed elements.
Among the various processes used, one must take into account the nature of the materials:
• grinding and reincorporation, for dry fiber and glass fiber composites
• pyrolysis or thermolysis, for carbon fiber composites, consisting in using high temperature for the degradation of certain molecules
• cement works, for fiberglass composites
• steam-thermolysis which is the combination of pyrolysis and steam treatment, adapted to the decomposition of the organic matrix
• solvolysis, which involves solvents for chemical decomposition
In summary, high performance composite materials have gradually found a place in high-tech sectors due to their wide application. The amount of waste associated with these materials is increasing and the problem of recycling them is proving to be a challenge. Whatever is the decision, it must be taken into account today in order to provide, when the time comes, a technically efficient and economically bearable solution to limit its environmental impact.