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Mathias, J. D., Alzina, A., Grédiac, M., Michaud, P., Roux, P., De Baynast, H., Delattre, C., Dumoulin, N., Faure, T., Larrey-Lassalle, P., Mati-Baouche, N., Pennec, F., Sun, S., Tessier-Doyen, N., Toussaint, E., and Wei, W. (2015). "Upcycling sunflower stems as natural fibers for biocomposite applications," BioRes. 10(4), 8076-8088.

Abstract

One of the big global, environmental, and socioeconomic challenges of today is to make a transition from fossil fuels to biomass as a sustainable supply of renewable raw materials for industry. Growing public awareness of the negative environmental effects of petrochemical-based products adds to the need for alternative production chains, especially in materials science. One option lies in the value-added upcycling of agricultural by-products, which are increasingly being used for biocomposite materials in transport and building sector applications. Here, sunflower by-product (obtained by grinding the stems) is considered as a source of natural fibers for engineered biocomposite material. Recent results are shown for the main mechanical properties of sunflower-based biocomposites and the socioeconomic impact of their use. This paper demonstrates that sunflower stem makes a good candidate feedstock for material applications. This is due not only to its physical and chemical properties, but also to its socioeconomic and environmental rationales.



Full Article

Upcycling Sunflower Stems as Natural Fibers for Biocomposite Applications

Jean-Denis Mathias,a,* Arnaud Alzina,b Michel Grédiac,c,d Philippe Michaud,c,d Philippe Roux,eHélène De Baynast,c,d Cédric Delattre,c,d Nicolas Dumoulin,a Thierry Faure,a Pyrène Larrey-Lassalle,e Narimane Mati-Baouche,c,d Fabienne Pennec,b Shengnan Sun,c,d Nicolas Tessier-Doyen,bEvelyne Toussaint,c,d and Wei Wei a

One of the big global, environmental, and socioeconomic challenges of today is to make a transition from fossil fuels to biomass as a sustainable supply of renewable raw materials for industry. Growing public awareness of the negative environmental effects of petrochemical-based products adds to the need for alternative production chains, especially in materials science. One option lies in the value-added upcycling of agricultural by-products, which are increasingly being used for biocomposite materials in transport and building sector applications. Here, sunflower by-product (obtained by grinding the stems) is considered as a source of natural fibers for engineered biocomposite material. Recent results are shown for the main mechanical properties of sunflower-based biocomposites and the socioeconomic impact of their use. This paper demonstrates that sunflower stem makes a good candidate feedstock for material applications. This is due not only to its physical and chemical properties, but also to its socioeconomic and environmental rationales.

Keywords: Agricultural by-product; Biocomposite; Natural fiber; Sunflower stem; Waste management

Contact information: a: IRSTEA, Laboratoire d’Ingénierie pour les Systèmes Complexes, 9 avenue Blaise Pascal, CS 20085, 63178 Aubière, France, b: GEMH-CEC, 12, rue Atlantis, 87068 Limoges Cedex, France, c: Institut Pascal, Clermont Université, Université Blaise Pascal, BP 10448, F-63000 Clermont-Ferrand, France d: CNRS, UMR 6602, Institut Pascal, 63177 Aubière Cedex, France e: IRSTEA, UMR ITAP, 361 rue Jean-François Breton, BP5095, 34196 Montpellier cedex 5, France;

* Corresponding author: jean-denis.mathias@irstea.fr

INTRODUCTION

Over the last few decades, increasing environmental concerns have prompted a surge in research by the composite science community to develop natural-fiber biocomposites. These materials can be completely degraded in soil, or, by composting, do not emit volatile organic compounds, and are softer on the environment than petrochemical resource-based products (Mohanty et al. 2000; Lithner et al.2011). Agricultural by-products have several advantages over classical natural fibers: they do not need dedicated agricultural fields, they are already readily available, and they offer valuable environmental compatibility over standard-feedstock fibers (Reddy and Yang 2005). These factors are increasingly central now that biocomposites have found widespread use in all areas of life. The reason for this increasing use of biocomposites is performance at lower cost and reduced density when compared to classic synthetic materials (Reddy and Yang 2005). Nonetheless, some agricultural by-products are already exploited by second-generation biorefineries (Pfaltzgraff and Clark 2014). Therefore, the main objective for the bio-based material sector now is to find new sources of fibers to avoid competition with the growth of crops for human food or biofuels (Kopetz 2013). In this context, the present work focuses on a promising agricultural by-product, sunflower stems. Sunflower by-products are of interest because they are not currently exploited, their composition enables low-impact extractability from the field, and oilseed biorefineries can achieve greater economic viability by selling their by-products.

Sunflower-based oil ranks fourth in world oil crop production, with nearly 25 million hectares (FAOSTAT 2013). Seed and oil have been the main compounds exploited by industry. In most cases, seed and oil are both extracted from the head, and the stems are left in the fields. No significant industrial use of the stems that are shredded after seed harvesting has currently been proposed, although sunflower stems are exploited for combustion applications, animal feed, and/or fuel production (Chen and Lu 2006). These solutions consume only a small fraction of the sunflower by-product production. We propose to explore a new way of extracting value from sunflower stems by evaluating their potential as a natural fiber feedstock for biocomposite applications. Considering five tons of sunflower stalks per hectare, the potential production of this by-product reaches 125 million tons. In comparison with other natural fibers (not including wood), this potential production tonnage is higher than that of bamboo farming (30 million tons, mostly in Asia and South America), which, alongside cotton, is one of the most heavily produced sources of commercial fiber in the world (Faruk et al. 2012). The potential value of sunflower by-products as a biofiber is enhanced by the fact that sunflower is grown worldwide (FAOSTAT 2013). This could create opportunities to build a new worldwide agricultural economy and is a key advantage over other agricultural by-products, like bamboo, that are not available across the world. Furthermore, sunflower by-products are available in large amounts at zero or negligible price in an economic context, where the natural-fiber biocomposites market grew by 15% between 2005 and 2010 (Lucintel 2011). Indeed, the entire composite market is growing. For example, the polymer composites market has increased from 33 billion Euros in 2002 to 41.5 billion Euros in 2005 (Friedrich and Almajid 2013). This surge in the natural fibers market is primarily driven by the automotive and building sectors (John and Thomas 2008). In the automotive sector, EU and US legislations impose specific directives on the end-of-life of vehicles. For instance, the non-recycled fraction of materials will be cut by 5% in 2015 in Europe (European Commission. Directive 2000/53/EC 2000). In addition, natural fibers are expected to provide a 30% weight reduction and a 20% cost reduction compared to classic composites (Bledzki et al. 2006). Furthermore, the low density of natural fibers equates to significant energy savings (primarily fuel) and their economic value may be extended to all fields of transportation (railway, marine, aerospace) (Bledzki et al. 2006; Friedrich and Almajid 2013). Natural fibers are also exploited in building applications, not only for their low density but also for their thermal insulating properties. Their development was recently stimulated in the USA and in Europe by legislation imposing enhanced energy efficiency of existing buildings by 2020 (European Commission. Directive 2010/31/EU 2010), which yielded a significant market in green retrofit solutions.

This work presents the main results obtained from a project (Demether 2011) whose objective was to produce biocomposites for building insulation by factoring not only chemical and physical properties but also the environmental and socio-economic impacts tied to processing and use (Fig. 1). In view of the results obtained, it is argued that sunflower stems can be useful for other biocomposite-using applications such as automobiles. First, general results are presented corresponding to sunflower by-product properties, highlighting both unpublished and published data by giving associated references. Note that examples of biocomposite engineering using sunflower by-products can be found elsewhere (Mati-Baouche et al. 2014, 2015; Sun et al. 2015). In this context, the objective here was twofold: i) to report the main results of the project about the properties of the sunflower stems; ii) to report the general project conclusions on the use of sunflower by-products to give the interested reader a clear picture of what can be expected from this innovative type of biocomposite.

Fig. 1. General flowchart of the design of insulating biocomposite. The article focuses on the main physical and chemical properties of sunflower stems obtained under this project framework.

EXPERIMENTAL

Sample Description

This study characterized the material properties of the stems of LG5474 sunflower species harvested in September 2010 in Perrier, France. Two particular on-stem locations were defined as the bottom and the top of the stalk (Fig. 2). The bottom location was defined as the level of the first node above the roots. Note that no specific (mechanical or chemical) treatment was performed, as it has been shown that specific treatments may alter certain properties (Li et al. 2007), as will also be shown by results presented in the discussion that follows. However, as explained earlier, this paper focuses on the properties of fibers, and any investigation into the influence of mechanical or chemical treatments would require a dedicated companion paper. Evidence that these fibers are useable without any particular treatment can be found elsewhere (Mati-Baouche et al. 2014; Sun et al. 2015).