Fibreglass, being a composite material (glass fibre reinforced with polymer resin), is not easily recyclable in traditional recycling plants. However, there are innovative technologies that make it possible to recover glass fibres from end-of-life products, separating them from the resin so they can be reused in new production processes. These technologies are available at different levels of technological maturity, and not all of them are available on an industrial scale.
To date, the main technology for recycling composite materials is through cement production kilns (also known as co-processing), in which the waste partly becomes part of the cement’s composition and partly acts as fuel.
Composite materials can also be recycled through mechanical and electromechanical recycling (high-voltage pulse fragmentation), or through thermal recycling processes (pyrolysis, fluidised bed and depolymerisation) or thermochemical processes (solvolysis).
Co-processing is an innovative technology used in cement plants that makes it possible to valorise fibreglass-based waste within the cement production process. This method is specific to materials containing glass fibres and is not suitable for treating composites reinforced with carbon fibres.
In co-processing, the glass fibres and inorganic fillers present in composite materials partly replace the raw materials (such as calcium carbonate) normally used to produce clinker. At the same time, the resin component is used as an alternative fuel to traditional fossil fuels, such as pet coke.
This dual function makes co-processing a process that is:
- efficient (materials and fuels are valorised simultaneously),
- scalable,
- fast.
It also makes it possible to reduce the carbon footprint of cement production by around 16%.
This reduction in emissions results from:
- the use of already decarbonised raw materials, such as the calcium oxide present in glass fibres, which avoids the CO₂ release associated with the decomposition of mineral calcium carbonate;
- the optimal dispersion between resin and mineral filler, which improves combustion efficiency and optimises the kiln’s energy performance.
Thanks to co-processing, waste materials can be integrated into a virtuous industrial cycle, reducing the use of natural resources and avoiding landfill disposal.
Controlled mechanical grinding is a method for recycling composite materials based on the controlled crushing of end-of-life material. It is an effective, low-cost process with low energy requirements, making it a sustainable solution for numerous composite waste streams.
This process yields:
- short fibres, which can be reused as reinforcing elements;
- polymer matrix powder, which can be used as a filler.
Although grinding reduces the material’s original performance — with a partial loss of physical-mechanical properties — the recycled material still retains useful characteristics that make it suitable for numerous applications, including:
- furniture products,
- industrial components,
- solutions where the recycled material performs a secondary structural function.
This process allows for good overall energy recovery, is flexible with respect to the different types of composites treated, and offers benefits in terms of cost reduction and lower environmental impact.
Pyrolysis is a thermal recovery process that separates and recovers both the fibres and the hydrocarbon products generated by the decomposition of the polymer matrix. The hydrocarbons obtained can be reused to reduce the overall energy consumption of the process.
Compared with other recycling technologies, pyrolysis makes it possible to obtain higher-value recycled materials, particularly with regard to fibres. However:
- glass fibres still undergo a loss of quality, due to the removal of the surface sizing (essential for adhesion to the original matrix);
- exposure to high temperatures can further damage the fibres, reducing their mechanical strength.
From an economic standpoint, pyrolysis:
- requires high initial investment,
- has higher operating costs compared with other recycling methods.
Solvolysis is a chemical decomposition process for composite materials that uses solvents (such as water, alcohol or other chemicals) to separate the fibres from the polymer matrix. The treatment takes place under controlled temperatures and pressures, generally lower than those required for pyrolysis.
Thanks to the lower temperatures, solvolysis:
- reduces the risk of damage to the fibres,
- better preserves the original mechanical properties.
One of the most promising technologies is subcritical water solvolysis, which not only allows fibres to be recovered with almost intact properties, but also enables the recovery of liquid chemical substances from the degraded matrix. These compounds can be reused to produce new resins for composite materials, further improving the circularity of the process.
Solvolysis also offers:
- good industrial scalability, but also involves:
- high initial investment,
- significant operating costs,
- a potential environmental impact that must be carefully managed, particularly in relation to the handling of the solvents used.
Currently, the process is economically viable mainly for carbon fibres, thanks to their high market value. However, pyrolysis is not yet widely adopted on an industrial scale, mainly due to the limited volumes of material available for recycling.
Fluidised bed gasification is a thermal decomposition process similar to pyrolysis, but with different operating methods and a different type of end products.
During gasification:
- the polymer matrix of the composite materials is decomposed mainly into gaseous products,
- these gases are recovered and used to generate energy within the same process.
Unlike solvolysis, gasification does not allow for the direct recovery of chemical substances reusable in the formulation of new polymer matrices, as most of the organic matter is completely converted into gas.
A major advantage of this process is its ability to treat complex, mixed composite materials, such as:
- painted laminates,
- materials bonded to foams or other substrates.
This makes gasification particularly suitable for recovering complex structural components that are difficult to recycle using other technologies.
High-voltage pulse fragmentation is an electromechanical separation technology that effectively separates the polymer matrix from the fibres in composite materials, using electrical discharges instead of heat or solvents.
This method stands out for its ability to:
- preserve fibre integrity, resulting in longer, cleaner fibres compared with those obtained using traditional mechanical techniques (such as grinding),
- minimise contamination between matrix and reinforcement during separation.
However, this technology requires:
- amounts of electricity,
- significant investment, both for the plant and for operations.
For these reasons, it is an attractive solution for high-value-added applications, where the quality of the recycled material justifies the cost of the process.
Thermochemical depolymerisation is an innovative process that recovers both the reinforcing fibres and the polymer matrix of composite materials, through a thermal treatment carried out in a carbon dioxide (CO₂) atmosphere.
Unlike other thermal methods, this technique:
- does not require the use of aggressive chemical reagents,
- produces a reusable organic liquid fraction,
- can treat complex composites, including those containing core materials (such as PS, PU, PET), metal inserts or wood (e.g. balsa).
How the process works
- Matrix depolymerisation — In the presence of CO₂, the polymer decomposes at molecular level, producing condensable vapours which, once purified, generate an organic liquid compatible with virgin resins (unsaturated polyester, vinylester or epoxy). This liquid can be blended and re-polymerised, contributing to the production of new composite materials. In some cases, it is also possible to recover valuable chemical compounds, such as phthalic anhydride.
- Calcination of the solid residue — In this phase, the remaining organic residues are eliminated, and the reinforcing fibres and any inorganic fillers are recovered.
Main advantages
- Recovery of both composite components (fibres + matrix)
- Direct compatibility with virgin resins
- Sustainable treatment, thanks to the reuse of CO₂ and the absence of toxic reagents
- More cost-effective than other thermal processes, thanks to the high yield of reusable product
