The natural combination

Materials World magazine
,
1 Apr 2015

Biocomposites ignite the imagination, but the market needs more convincing. Eoin Redahan reports from Fibre Developments for Biocomposite Materials, in Bristol, UK. 

You’re probably out of touch with the way teenagers speak. Try to talk like them and you will embarrass everybody in the vicinity, including yourself. So, if you were to say something like, ‘That’s a sweet ride,’ when talking about your car, any teens present would probably cringe.

In your defence, this may not be an attempt to relate to juveniles at all. You may merely be describing a bio-based sugar resin that binds the flax fibres on your seatback. It is a frequent misunderstanding.

Biocomposites pop up in places you wouldn’t expect. In cars, they are present in parcel shelves, flooring underlay, door trim, wheel arch liners, instrument panels and, as mentioned, seatbacks. They are also found in compostable plastic bottles, home insulation and in the drinks trolley that rolls down aeroplane aisles. 

Flax, linseed, coir, rayon, hemp, sheep wool, cotton, miscanthus, willow, oats, rye grass and sugar are just some of the natural materials that have been incorporated into biocomposites. At their best, they are lighter than their synthetic alternatives, strong, recyclable and energy efficient to produce. 

In many cases, they are also more straightforward to manufacture. Cambridge-based company EcoTechnilin uses flax in its products. Once grown, the crop is uprooted and allowed to partially decompose under the sun before a mechanical process extracts the fibres. The flax is transformed into a non-woven fibre using a needle-punch process to align the fibres and maintain consistent properties. The mat is then impregnated with a sugar-based bioresin.

EcoTechnilin produces a flax, bioresin and paper sandwich for the load floors in cars, a flax and bioresin composite for seatbacks and, perhaps most interestingly, a flax, bioresin and basalt composite called FibriRock, which is used in aeroplane galley carts. According to William Anthony, EcoTechnilin’s Marketing Director, these carts are 6kg lighter than the competition and are produced more quickly. ‘FibriRock also has a 150-second process time,’ he said. ‘This process usually takes 40–70 minutes.’ 

The brittle and the blended

Of course, biocomposites have less flattering features, ones that confine them to the edges of industry. Firstly, they suffer from embrittlement, uneven dispersion and alignment issues. Secondly, crop properties vary from season to season. This can make them unusable when material consistency is vital, such as in aerospace. Thirdly, many natural materials have long suffered from a data gap. Producers knew their materials were fit for purpose, but they weren’t always able to back this up with data on acoustic properties, fire performance statistics and other metrics that are required by standards bodies.

There is also the issue of public awareness. Ceri Loxton, of the BioComposites Centre, in Bangor, Wales, noted that bio-based materials such as sheep wool, hemp and recycled paper are present in 20% of insulating materials in Germany (a contentious statistic), 10% in France, but only 1% in the UK. Simply put, many people aren’t aware of the bio-based alternatives available to them, but some of the UK manufacturers involved lack the resources to increase public awareness. 

However, manufacturers are addressing some of these problems. Dr Luke Savage, of the University of Exeter, noted that fibre bundling is mitigating the embrittlement problem in cellulosic fibres. To address the problem of seasonal variability, crops from different years are blended to create more consistent composites year on year, as is done in the wine industry.

Oh, brave new biocomposite

The potential, however, for the biocomposite industry is huge. With lightweighting such a central issue in automotive and aerospace applications, biocomposites are well placed to take advantage, especially if material consistency is improved. Biocomposite insulation could also benefit from recent industry trends. Loxton noted that with homes becoming increasingly airtight, volatile organic compounds (VOCs) are more of an issue. Natural insulation materials, such as wool, can eliminate these VOCs.  

Then there is cellulose, the world’s most abundant polymer. According to Dr Sameer Rahatekar, of the University of Bristol, plants generate 40 billion tonnes of cellulose every year, but only four million tonnes are used for cellulose-based fibres. While the processing involved remains a challenge, it is hard not to be smitten by the sheer breadth of possibility.