DaimlerChrysler is using natural fibers with extremely high tensile strength from the abaca banana plant in the standard underbody cover for the spare-wheel compartment of the 3-door version of the Mercedes-Benz A-Class model. After using natural fibers such as flax, hemp, sisal and coconut in the interior of Mercedes-Benz passenger cars and commercial vehicles for many years, now a component is in use in the exterior of a car for the first time.

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DaimlerChrysler research engineers patented a novel mixture of polypropylene (PP)-thermoplastic and abaca fibers in 2002. Manila Cordage, a Philippine producer of semi-finished materials, supplies the fibers of the musa textilis plant, which is related to the banana. The components are manufactured by Rieter, an automotive supplier in Switzerland.

The direct long-fiber thermoplastics (d-LFT) method was further developed for the production of the components. The challenge consisted of adapting the machines’ precision to the natural fibers, which are subject to natural fluctuations in their length and thickness, and fulfilling the particular demands placed on a component used in the exterior of a vehicle, such as stone impact, weathering and water resistance.

Natural fibers protect scarce resources and are renewable. Their concrete benefits for the environment compared with glass fibers are a result of the very good ecological balance of abaca fibers in terms of their manufacture, application and recycling. The production of glass fibers, which are almost completely replaced in the cover for the spare-wheel compartment for the A-Class, is very energy intensive. With abaca fibers, however, up to 60% of the energy can be saved, thus significantly reducing CO2 emissions in the manufacturing phase of the raw materials. The waste material that arises as a byproduct of fiber production can be used as an organic fertilizer.

Rieter, an automotive supplier, made use of the DaimlerChrysler research engineers’ know-how to master the challenge of adapting the manufacturing process for natural fibers and distributing the fibers evenly in the polypropylene (PP) matrix. After passing all of DaimlerChrysler’s functional tests, the component was put into use in the 3-door version of the A-Class starting in September 2004.

Abaca fibers are 1.5 to 2.7 meters long, have very high tensile strength, are rot resistant and are traditionally used in ropes. The abaca-banana tree, whose leaves are held on a pseudo trunk with extremely long, fiber-reinforced and interwoven leaf stems, is cultivated in the Philippines. After harvest, these leaf sheaths are separated and the fibers are taken out by hand using a metal comb. The farmers comb the long white fibers again and hang them out to dry. The fibers are then transported in bales to Manila Cordage, a producer of semi-finished materials, where they are sorted by hand according to quality criteria, spun into yarn, put onto bobbins and sent to Rieter.

At Rieter, the bobbins of abaca fiber are transported to the compounding unit where the fibers are embedded in the polypropylene matrix at a temperature of 180° Celsius. The fiber-matrix mats are then put into presses whilst they are still formable and pressed into the shape of the component. Due to the use of the natural fibers, this step is very complex, as the material is more viscose and has to be well distributed in the mold.