Biocomposites Carbon
Biocomposites Carbon footprint of flax, hemp, jute and kenaf By: Martha Barth Michael Carus nova-Institute Hürth, Germany 1 Introduction Natural fibres are an environmentally friendly alternative to glass and mineral fibres. In the last twenty years more and more natural fibres have started being used in biocomposites, mainly for the automotive sector and also as insulation material. As a first step towards supporting the development of sustainably produced and innovative biorefinery products, a carbon footprint for various natural fibres was conducted. These natural fibres include: flax, hemp, jute and kenaf. In the year 2012, 30,000 tonnes of natural fibres were used in the European automotive industry, mainly in socalled compression moulded parts, an increase from around 19,000 tonnes of natural fibres in 2005. As shown in figure 1, in 2012 flax had a market share of 50 % of the total volume of 30,000 tonnes of natural fibre composites. Kenaf fibres, with a 20 % market share, are followed by hemp fibres, with a 12 % market share, while other natural fibres, mainly jute, coir, sisal and abaca, account for 18 %. The total volume of the insulation market in Europe is about 3.3 million tonnes – the share of flax and hemp insulation material is 10,000 – 15,000 tonnes (ca. 0.5 %). Globally, cotton is the largest natural fibre produced, with an estimated average production of 25 million tonnes during recent years (2004 – 2012). Jute accounts for around 3 million tonnes of production per year. Other natural fibres are produced in considerably smaller volumes. Globally, bast fibres play a rather small and specialized role in comparison to other fibres. The overview of worldwide production of other natural fibres for 1961 – 2013 based on FAO data (fig. 2) shows that jute has always been the most dominant of these materials. Apart from some fairly strong fluctuations, the overall volume of natural fibres produced globally has increased slightly over the last fifty years. The amount of jute has stayed more or less the same, coir has steadily increased its production volume, and production of flax and sisal has decreased. 2 Carbon footprint The goal of this carbon footprint calculation is to evaluate the carbon footprint of the four most important natural fibres used in the automotive and insulation industry: flax, hemp, jute and kenaf. This study covers the cultivation, harvest, retting, processing and transportation of natural-bast-fibres from the northwest of Europe (flax and hemp), India and Bangladesh (jute and kenaf) to non-woven-producers in Europe. One tonne of technical fibre for the production of non-wovens for biocomposites or insulation material is used as functional unit. In particular, inventory data related to current conditions (2013/2014) of the agricultural system, fibre processing and transportation were obtained from farmers and fibre producers and where necessary complemented with bibliographic sources. Allocation was necessary as all four fibre systems provide more than one product: e. g. the fibre process also produces shives and dust. In this study mass-based allocation was used for all four investigated systems, as it is more stable than economic allocation, which fluctuates more. Fig. 2: Development of worldwide natural fibre production 1961 – 2013 in million tonnes without cotton (based on FAOSTAT 2015) Fig. 1: Use of natural fibres for composites in the European automotive industry 2012 (total volume 30,000 tonnes, without cotton and wood); others are mainly jute, coir, sisal and abaca 7 6 18 % 5 12 % 50 % 4 3 Sisal Ramie Jute Hemp Flax Coir 2 20 % 1 Flax Kenaf Hemp Others 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 36 bioplastics MAGAZINE [03/15] Vol. 10
Biocomposites 2.1 Comparison of the carbon footprint of flax, hemp, jute and kenaf Figure 3 sums up the results of the greenhouse gas (GHG) emission calculation for flax, hemp, jute and kenaf. The result is that GHG emissions per tonne show no significant differences, especially when taking the uncertainty of the data into account. However there are some differences in results, which are described in more detail below: • The emissions related to the fertilizer subsystem are the most important contributors to greenhouse gas emissions of each considered bast fibre. However, the use of organic fertilizer for hemp cultivation (scenario 2) minimizes these emissions. Organic based fertilization is, however, not an option for all fibres, for different reasons (details see [1]). • Pesticides contribute relatively little to the carbon footprint of each fibre, except for the emissions stemming from pesticides used during flax cultivation. Due to its low shading capacity, flax is prone to weed infestation. Therefore, herbicides usually need to be applied for flax in higher doses. • Field operations, decortication and transportation differ for jute and kenaf and hemp and flax. Field operations and decortication of jute and kenaf are mainly done manually, which causes relatively low emissions. Since both are grown and processed outside of Europe, however, transportation must be taken into account, both overland transport from the farm to the processing site as well as marine transportation to the factory gate in Europe. • Another important contributor to overall greenhouse gas emissions for hemp and flax straw is their procession into fibres. These emissions are mainly caused by the energy consumption for decortication and fibre opening. Jute and kenaf fibre opening, is done by machines; on the other hand, decortication is done manually. Therefore the impact of fibre processing for jute and kenaf is smaller compared to hemp and flax fibre processing. 2.2 Comparison with fossil based fibres In the impact category greenhouse gas emission, natural fibres show lower emissions than fossil based materials. For instance, production of 1 tonne of continuous filament glass fibre products (CFGF) extracted and manufactured from raw materials for factory export has an average impact of 1.7 tonnes CO 2-eq . Based on data from Ecoinvent 3, glass fibre production has an impact of 2.2 tonnes CO 2-eq per tonne glass fibre. Compared with natural fibres, which have greenhouse gas emissions between 0.5–0.7 tonnes of CO 2-eq per tonne of natural fibre (from cultivation to fibre factory exit gate, excluding transport to the customer), impact on climate change from glass fibre production is three times higher than the impact from natural fibre production. This is also reflected in the impact category primary energy use. Figure 4 shows primary energy use for the production of hemp fibre compared to a number of non-renewable materials. With about 5 GJ/t, the production of hemp fibre shows the lowest production energy of all the materials by far. For example, primary energy for producing glass fibre accounts for up to 35 GJ/t of glass fibre, which is seven times as much primary energy as hemp fibre uses. Natural fibres are used in biocomposites, among other things. Biocomposites are composed of a polymer and natural fibres, the latter of which gives biocomposites their strength. Figure 5 indicates that hemp fibre composites show greenhouse gas emission savings of 10 – 50 % compared to their functionally equal fossil based counterparts; when carbon storage is included, greenhouse gas savings are consistently higher, at 30 – 70 %. However, the great advantage of natural fibres compared to glass fibres, in terms of greenhouse gas emissions, only partially remains for their final products, because further processing steps mitigate their benefits. Fig. 3: Comparison of greenhouse gas emissions per tonne natural fibre (flax, hemp, jute and kenaf) Hemp (scenario 1: mineral fertilizer) Hemp (scenario 2: organic fertilizer) Flax Jute Kenaf 0 100 200 300 400 500 600 700 800 900 kg CO 2-eq /t natural fibre Field operations Seeds Fertilizer Fertilizer-induced N 2 O-emissions Pesticides Transport I (field to processing) Fibre processing Transport II (Asia to Europe) Transport III (within Europe) bioplastics MAGAZINE [03/15] Vol. 10 37
