The drive to use green materials has led PSA Peugeot Citroën and Boeing to explore applications for flax-based biocomposites.
Automotive Tier One supplier Faurecia has developed and patented a composite material called Flaxpreg which uses natural flax fibres in a thermoset resin matrix.
At a conference on flax and hemp organised by JEC Group and the European Confederation of Linen and Hemp (CELC) in Leuven, Belgium, in December 2012, the French company said it is working on a project with PSA Peugeot Citroën to use Flaxpreg in a car trunk load floor. Other project partners are the University of Reims and Lineo, a French company which produces flax prepregs.
The project was presented at the conference by Valérie Marcel, research engineer in Faurecia's interior systems division. The presentation was prepared jointly with Frédéric Rousseau, innovation project manager in the research and engineering department at PSA Peugeot Citroën.
The project is part of PSA's programme to increase the amount of “green” materials in its cars. The sandwich panel floor being developed has a 65% green content and will be lighter than a comparable part which is currently produced using the Baypreg system. The targeted weight reduction is 2,000 g/m for the panel, which has flax-thermoset composite skins and a structured cardboard core.
Lineo is developing uni-directional (UD) flax tapes for the project to enable large volume production at a relatively low cost. The first mechanical performance tests, though, as discussed in the presentation, were on a panel made with woven flax fabric prepregs. This showed a good performance versus the Baypreg version.
Francois Vanfleteren, CEO of Lineo, told European Plastics News that mechanical performance using UD tape prepregs is expected to be similar or better than the fabric version. Lineo's UD tape production line for the project makes tape that is 40cm wide, but when scaled up for series production 1m wide tape will be possible.
According to Faurecia, PSA is expected to use the flax composite part in a demonstration car in 2014. Series production, if approved, would start in 2015 or 2016. PSA has exclusive rights to use the flax composite process for one car, after which Faurecia can use the process for other car manufacturers' applications.
In his presentation, Pedro Martin, material scientist in the materials and fuel cells department at Boeing Research & Technology Europe, discussed the Cayley project. In this, Boeing is working with partners to develop a biocomposite sandwich panel which can be used, for example, for sidewalls in the interior of its aircraft. The project has a target to produce panels in an automated one-step process at a rate of one panel every 15 minutes.
Boeing's partners in the Cayley project are Lineo, composites company Invent, based in Germany, and plastics research institute Aimplas, based in Spain. Boeing's work has focused on panels with skins made of flax in a thermoset resin matrix, and a foam core, while other partners are investigating PP and PLA.
“Fire resistance is the most challenging issue to overcome when working with natural fibres,” said Martin.
In the project work, the flax fabrics were treated with halogen-free flame retardants. At laboratory scale, the biocomposite achieved compliance with fire resistance requirements of the US Federal Aviation Administration and the European Aviation Safety Agency.
But the project must still overcome other issues. Martin said it was working on the proof of concept for the prepreg system. Curing time for the thermoset resin is also very long and needs to be reduced, and shelf life for the prepreg needs to be increased.
During the project, Boeing produced a sidewall panel for a 737 aircraft made with the flax-thermoset composite. Using a vacuum bag process, the part was produced at full scale.
However, the production cycle was two hours due to a long curing time for the resin.
Martin said Boeing would work to solve these issues with the thermoset-based composite. The company may instead use the PP-based or PLA-based composite being developed by other Cayley partners. Whatever Boeing decides, the tough certification procedures of the aviation sector could take up to 10 years, said Martin.