RECYCLABILITY
Besides wood, all forms of composite suffer from the same problem; at end of life, it is very difficult to separate the component materials for re-use. This is why using materials such as steel or aluminium can make sense, despite the higher environmental cost of the virgin metal. They can be reused repeatedly.
The composite recycling systems developed to date, which include pyrolysis, burning and shredding, are all unsatisfactory because of the energy intensity of the processes or the fact they yield a lower quality material that has to be downcycled. In principle, it is possible to use resins that melt again at high temperatures and can be collected, refined and reused. Elium resin from
Arkema is capable of exactly that, and is already being used in recyclable wind turbine blades. They even built a 6.50m Mini Transat boat from it. The process also yields reusable glass, but carbon and flax don’t support the heat: carbon loses as much as two-thirds of its strength and flax simply combusts.
However, an Australian study has shown how carbon-fibre composite can first be heated without oxygen in a pyrolysis chamber to burn off resin, then oxidised to yield carbon-fibre with most of the strength of virgin fibre but only 10% of the environmental impact.
Cured laminates can also be separated using a chemical process proven in the lab at the National Composites Centre, with a big vat of acetic acid. Portsmouth University is researching enzymes to decompose plastic, starting with plastic bags. The approach could eventually handle boats as well. ‘You have to find the right enzyme that works for snipping the molecules of a particular polymer. Practically, it’s a decade away,’ says Ashley Parkinson of the NCC.