FRP composites have considerable potential in various sectors because of specific properties such as long-term durability, light-weight and ability to be produced in complex shapes. The increase in their usage over the past decade has brought benefits in many areas. However, most composites use thermosetting resin matrices which are not easily recycled since they cannot be remelted and remoulded, unlike thermoplastic resins. Technology has been developed to address this issue and several methods have been proven to recycle thermoset-based FRP composites.
Volumes of waste produced
Reliable figures for composite waste material volumes are difficult to obtain, but it is estimated that the volume of GFRP manufacturing waste produced in the UK in 2009 was estimated at 22,750 tonnes and end-of-life waste at 5 times that amount. Around 3000 tonnes of carbon fibre FRP scrap is generated annually in the USA and Europe. Since CFRP is a relatively new material, volumes of end-of-life waste remain fairly small and so it is presumed that the majority of the waste produced comes from manufacturing.
Although GFRP production volumes are far greater than CFRP, more investment has gone into CFRP recycling. This is because the value of the fibre is an order of magnitude higher, and so an economically viable recycling process is easier to achieve. Nevertheless, several companies manufacturing GFRP products have invested in this area and solutions are also available for the material.
According to the waste hierarchy, the options for FRP waste management in order of preference are waste minimisation, reuse, recycling, incineration with energy recovery / composting, and lastly incineration without energy recovery / landfill.
Recovery of waste
To make recycling procedures as easy and cost effective as possible, FRP waste needs to be recovered in as clean and pure a condition as is feasible. This can be difficult to achieve since the materials are often used in association with other materials, often being joined together by adhesive or mechanical means. Materials need to be clearly labelled for rapid and accurate identification of component contents. The reclaimed materials will require storage and transportation to a recycling facility. This requires the development of supply chains and a robust infrastructure.
Several methods have been developed including:
- Mechanical grinding – primarily for GFRP waste. The material is ground in a hammer mill or similar and graded into different fractions. This method can be economically challenging since it is difficult to produce finely ground recyclate at a cost comparable to fillers such as calcium carbonate.
- Pyrolysis – partial pyrolysis has been used for CFRP where the resin matrix is burned off with limited oxygen. Carbon fibres processed this way retain at least 90% of their original mechanical properties. Pyrolysis can also be used for GFRP but the process significantly reduces the mechanical properties of the glass fibre – the has to be factored into resultant recyclate applications.
- Cement kiln – approximately 2/3 of the material is transferred into raw materials for cement and 1/3, the organic part. Is burnt, generating energy.
- Fluidised bed – this process can be used for CFRP and GFRP, although the method reduces the strength of the resultant fibres considerable (20% and 50% respectively), but has little effect on stiffness. The key advantage of fluidised bed is that it is can be used for mixed and contaminated materials.
- Solvolysis – this process is being developed for GFRP in current research projects. The process allows chemicals in the resin to be reclaimed.
Applications for recyclate
Few application routes have been commercialised as yet but research is ongoing to assess the feasibility of using FRP recyclate in a variety of applications.
The European Composites Industry Association (EuCIA) www.eucia.org
The European Composite Recycling Service Company (ECRC) www.ecrc-greenlabel.org
NCN Report – End of Life Options
Materials KTN report – Composites Recycling Research