Soon a new, greener plastic for the automotive industry? Researchers are proposing to modify manufacturing processes to incorporate natural fibres, such as flax or hemp, into thermoformed objects. The recycling rate is important...
The automotive industry strives to produce lightweight, high-performance automotive parts that reduce fuel consumption and improve safety. Plastics have contributed to many advances over conventional metal parts. For example, polypropylene, a thermoplastic polymer that can be repeatedly softened by heating to different shapes, is currently used in bumpers, body panels and trim. Reinforced polymers are, as the name suggests, "filled" structures of fibrous reinforcing layers that improve mechanical properties.
Plant fibres to replace plastic?
More and more attention is being paid to natural fibre reinforcement using vegetable materials such as hemp, flax, jute and kenaf as they have high mechanical strength and are light. They also offer significant advantages over conventional reinforcements: low cost, durability in manufacture and recycling.
Why not enjoy unlimited reading of UP'? Subscribe from €1.90 per week.
However, their widespread use has been slowed down for a good reason: their performance decreases when subjected to the processing temperatures required for polymer extrusion. This is a process in which a compressed material is forced through a screw-shaped die into a mould that gives it a specific shape. European researchers associated with companies, including ESP Platics LTDTherefore, they have sought to make the use of natural fibre reinforcements more flexible by developing processing and treatment methods suitable for thermoforming (heat forming).
As a reminder, each flax stalk consists of 20 to 40 bundles each containing 20 to 40 plant fibres. They will now be able to be used in the automotive industry.
A reinforced plastic recyclable at 50 %
Extru CO project2 was specifically aimed at the use of supercritical carbon dioxide (scCO2) as a processing medium. The ultimate goal was to enable the extrusion of polypropylene sheets filled with natural fibres without the typical detrimental effects on mechanical characteristics, colour and odour.
Numerous innovations in composite development, natural fibre composite manufacturing and scCO2 injection equipment have reduced flow resistance, facilitating extrusion at lower temperatures. The mechanical properties of the extruded reinforced plates were well suited to the requirements of the automotive industry. The products manufactured from these plates offered superior quality at a reasonable cost while having an impressive recycling rate (up to 50 %). They could therefore be reused to produce new plates without detrimental effects on mechanical properties.
The Extru CO2 project team thus overcame the obstacle of high temperature processing previously required for extrusion. The innovative technology for producing natural fibre-reinforced thermoplastic sheets for the automotive industry is expected to stimulate more widespread use of affordable and recyclable materials.
Not to mention that, although it originated in the Middle East, flax has adapted to many regions, particularly in Europe, which has become the world's leading producer of flax fibre, with two thirds of the world's production grown on around 110,000 ha. In France, flax is cultivated from the Belgian border to the Caen plain in Normandy and accounts for more than 45 % of European production.
Article published in http://www.futura-sciences.com / August 2012
To fight against disinformation and to favour analyses that decipher the news, join the circle of UP' subscribers.