Prodrive Composites has developed a process for manufacturing recyclable composite components that can satisfy future end-of-life requirements without any compromise in the performance of the original parts. Called P2T (Primary to Tertiary), the process not only simplifies recycling, but endows a composite material with the potential to fulfil three or more useful lifetimes.
P2T composites do not require heat or pressure during manufacture, which means there is no need for an autoclave, reducing costs and enabling the scaling up of production without major investment. The basis of the process is the use of a reactive thermoplastic resin instead of the more usual thermosetting type; a plastic monomer is reacted with a catalyst in the presence of the fibres to produce a cured laminate. Prodrive believes it is the first to develop this technique, which emerged through a development programme with an automotive OEM customer who required a high performance structural material with lower environmental impact than conventional composites.
“End-of-life recycling is one of the biggest debates in the composites world today,” explains John McQuilliam, Chief Engineer, Prodrive Composites. “The issue affects automotive manufacturers and wider industries too, such as marine, where old fibreglass boats are often broken up and sent to landfill. The main barrier to recycling has been the type of resin used; thermosetting resins predominate but these cannot be readily recycled.”
Historically, the composites industry has been based on the supply of rolls of ‘pre-preg’ (woven fibre sheets pre-impregnated with resin) which customers then lay up in moulds to produce 3-D parts, curing through heating to fix the final shape. Thermosetting resins were highly convenient materials to support this supply chain but, as tighter end-of-life regulations are introduced, better alternatives are required.
Composites produced by the P2T process can be recycled multiple times. The highest mechanical properties are obtained during first use of the virgin fibres, enabling highly loaded structural items such as suspension wishbones to be manufactured. At the part’s end-of-life, the fibres and much of the resin can be recycled by chemical or thermal depolymerisation, supplying the raw material for a secondary part, such as a body panel.
When the secondary part reaches the end of its life, it can be chopped and remoulded into block material with properties suitable for 3-D solid components. This tertiary part can itself be recycled several times until, finally, just the re-melted resin is recovered and the fibres are milled to supply other, lower grade parts.
The P2T process is also compatible with advanced techniques, such as Tailored Fibre Placement (TFP), which is being adopted by many leading composite producers. TFP makes more efficient use of the fibres than a conventional weave and is highly complementary with the P2T approach to recycling.
“This is a really exciting development which finally addresses the recycling challenges faced by composites,” says McQuilliam. “We have developed and refined the process and could bring new customer applications into series production within as little as twelve months.”