Cheaper, Lighter, Safer Composite Materials for Aircraft Interiors

To meet the strict fire and weight requirements for aircraft interiors, the current solution is to use a fire-resistant composite made of phenolic resin with glass fibre reinforcement. But phenolic parts have many drawbacks. One EU project has found a greener, cheaper alternative.

Phenolic resin combined with glass fibres has been the go-to solution for the aircraft industry when it comes to the fitting of airplane interiors. The aim of the EU-supported IntAir project was to refine the materials and upscale the manufacturing process for a new generation of aircraft interior composites that are cheaper, lighter and safer than the toxic materials that are currently used.

The project was focussed on a particular type of composite material - preimpregnated carbon or glass fibre fabrics, or ‘prepregs’. Prepregs are high-performance composites in which a textile is impregnated with a thermosetting resin, which is then partially cured. The result is a material that is very easy to handle and cut, and which offers a high fibre-to-polymer ratio (and therefore a high performance). To produce a finished part, the prepreg is normally laid-up in a mould and consolidated using heat and pressure to fully cure the polymer.

PFA (polyfurfuryl alcohol) resins are not, in themselves, new. “For example,” explains Dr Joe Carruthers, the managing director of Composites Evolution, the company behind the IntAir project, “they have been used in the foundry industry for many years. PFA resins for composites have been in development for several years. We have been working on PFA prepregs since around 2010. However, the challenge has been getting them to the quality (consistency) and performance levels demanded by the aerospace industry. So, in terms of ‘why now’, it’s not something that has happened overnight. Rather it is the result of a significant long-term R&D effort.”

Prior to the project Composites Evolution had been able to produce small quantities of prepreg on a laboratory scale. One of the aims of the project was to demonstrate that it was possible to up-scale the prepreg production process to commercially viable volumes.

The team had to overcome a variety of challenges. They needed to prove that the mechanical properties, such as strength and stiffness, along with fire performance were as good or better than the materials currently used.

Then there were the characteristics of the prepreg and how it could be handled: too tacky and the material is hard to work with, not tacky enough and it is difficult to layup during the moulding process. Finally, the team had to refine the curing process. “PFAs cure through a condensation process and the resulting steam needs to be carefully managed in order to ensure that the escaping moisture doesn’t compromise the surface finish of the part.”

IntAir managed to address all these factors through a combination of chemistry, (formulating the resin to give the required cure characteristics), and process engineering, (development of a precision manufacturing process that ensures the maintenance of an accurate fibre-to-resin ratio with well-impregnated fibres).

Qualifying a product for use on aircraft is a relatively lengthy process, but the company is already in discussions with a number of aircraft interiors manufacturers. “However, other sectors such as rail and maritime also have stringent fire requirements and they have shown a high level of interest. We have sold materials to both of those sectors,” explains Carruthers.

He is clear that the time and effort have paid off. “I’m proud of the fact that a truly viable commercial product, generating post-project sales, has emerged from the project. Many collaborative projects struggle to cross the so-called ‘Valley of Death’ from R&D to commercialisation. But in this case we have been able to bring to market a disruptive product that offers our customers a number of advantages over a long-established but compromised incumbent.”

Commercial recognition is clearly significant but the project is also garnering industry recognition. The rail seat component that the partners made within the project has recently been nominated as a finalist in the 2019 JEC World Exhibition Innovation awards. “We’ll find out whether we won on 13th March 2019” says Carruthers.

Reference source: Cheaper, Lighter, Safer Composite Materials for Aircraft Interiors