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Renewable

BackgroundEurope’s transition towards a Circular Economy, where new materials and better designed products will play an important role. Life cycle analysis is an important technique that is used to assess the environmental impact of a product, associated with all the stages of its life. This means comparing the resources needed to make these materials (energy, water, raw materials), the emissions (CO2, pollution of air, water and soil) during the transformation and the

in-service life use as well as their end-of-life disposal, recycling or reuse options. For example, for packaging materials, which have a short life cycle, the energy required to make these materials and to dispose or recycle them, is primordial. On the contrary for transportation products, which have a long life cycle, the in-service-life use of fuel and the maintenance of the product will be dominating the total environmental impact.

Many composite materials consist of fibers and a surrounding matrix. Typically the fibers are responsible for the strength and the stiffness of the structure while the matrix binds them together ensuring the load transfer between the fibers. In 2016 the worldwide composites market accounted for 11 million tonnes. The largest market benefiting from composite materials is the transportation sector, followed by the construction and aerospace sector. The newest airplanes consist for 50 % out of composite materials, with the majority of them carbon fibre reinforced. The high quantities of composites in these sectors are not surprising, not only due to their low weight, also because they enable the production of complex 3D structures and with the layered structure, strength can be provided where needed. 

In the composites of today, the majority of the fibers is synthetic (for example carbon fibers glass fibers ) and the matrix is mostly petroleum based. Carbon fibers will at least for the coming decade be the fibers of choice for aeronautic applications, due to their unequalled performance in relation to their density. For synthetic fibers, care should be taken on how to assess their impact on the environment. As stated before, a life cycle analysis will point out that the in-service-life phase is the dominating phase in the life cycle analysis of transportation products and by making the airplanes lighter and larger, due to the use of highly technological materials, the ratio fuel per passenger can be lowered which can result in a lower environmental impact. 

However, there are possibilities to further lower the environmental impact by making composite materials more ‘green’. The last 10 years, research on ‘green’ composites is increasing, where the fibers are replaced by natural fibers and/or the resin by a biobased alternative. In Europe the wood polymer composites (WPC) and natural fibre reinforced composites (NFRC) account for 15% of the total amount of the European composite market of 2.4 million tonnes. The Nova Institute determined that 1/3 of this 15% consists out of natural fibre reinforced composites, mainly produced for the automotive sector, with flax and hemp the most important natural fibers. A total amount of 15.000 tonnes of flax fibers and 3.800 tonnes of hemp fibers were used in 2012 in automotive. More recent figures of 2017 indicate a 15% growth of WPC and NFRC, with the main growth area located in other applications (technical, furniture and consumer goods). This clearly indicates that the potential of natural fibers has still not been reached, as many new application areas are still emerging.

If this trend continues, and the share of NFRC keeps growing also in the other continents, then it is easy to understand that we need to look at the potential of other natural fibers.

Typical stiffness values (Young's modulus) for natural fibers compared to glass fibers, at standard environmental conditions.