Industrial Crops and Products 33 (2011) 317–324 Contents lists available at ScienceDirect Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop Biocomposites based on flax short fibres and linseed oil J. Lazko ∗ , B. Dupré, R.M. Dheilly, M. Quéneudec Laboratoire des Technologies Innovantes (EA 3899), Université de Picardie Jules Verne, CODEM Picardie, 41, rue Paul Claudel, 80480 Dury, France article info Article history: Received 2 September 2010 Received in revised form 18 November 2010 Accepted 20 November 2010 Available online 10 December 2010 Keywords: Biocomposites Flax short fibres Linseed oil Hydrophobicity Polymerization abstract Insulating materials based on flax short fibres were prepared and their functional properties enhanced using linseed oil. In order to improve biocomposites hydrophobicity, the linseed oil was added to the initial formulation, mixed with the fibres and finally dried after the moulding process. Thus, the average water absorption of 10–40/140 g/g oil/fibres samples was reduced up to 10 times during the first hour of immersion, compared to the reference oil-free materials. Moreover, the linseed oil polymerization inside the lignocellulosic matrix, which occurred after 20 days of drying at 50 ◦ C, also improved mechanical and thermal behaviour of biocomposites. Spontaneous combustion phenomena related to the exothermic oxidation–polymerization of linseed oil were described as well. Therefore, the process parameters such as oil/fibres ratio, drying time and temperature, were optimized to ensure the safety of the process and to avoid self ignition of the lignocellulosic fraction at temperatures below 200 ◦ C. © 2010 Elsevier B.V. All rights reserved. 1. Introduction In flax (Linum usitatissimum) long high-quality textile fibres are considered as the noble fraction, and the rest, not <80% of the plant mass, are low-cost by-products. These short fibres, also called “tow”, containing a large proportion of shives, are nevertheless potential lignocellulosic raw materials, perfectly corresponding to actual demand on renewable, recyclable and biodegradable resources. The increasing interest for flax fibres and shives in thermal insulation is particularly well described in literature, and a large number of flax based composites and nonwovens already have their share in transportation and building markets (Satyanarayana et al., 2009; Bos et al., 2006; Flambard et al., 2005; Klamer et al., 2004; Kymäläinen and Sjöberg, 2008; Schartel et al., 2003; Aamr- Daya et al., 2008). However, these new biocomposites generally contain an important synthetic polymer fraction (10–40%), such as polypropylene for example. Other polyesters and polyamides from petrochemical resources are used to enhance the mechanical prop- erties of the materials, but they also have a quite negative impact on the global biodegradability and recycling aspects. Natural insulation materials from flax short fibres only, without any mineral or synthetic additive, were developed and patented in our laboratory (Queneudec t’Kint et al., 2005). The scale of their thermal and mechanical performances should be suitable for numerous industrial applications. The main disadvantage of these ∗ Corresponding author. Tel.: +32 0 68 27 47 80. E-mail address: Jevgenij.Lazko@materianova.be (J. Lazko). materials is nevertheless, their high hydrophilic character, as it is the case for almost all composites based on vegetal lignocellulosic raw materials. Surface treatments or homogeneous chemical modifications (esterification, acetilation, acylation) are commonly applied to var- ious cellulosic substrates in order to enhance their hydrophobicity (Heinze and Liebert, 2001; Pasquini et al., 2006; Vaca-Garcia and Borredon, 1999). Grafting of aliphatic chains was performed onto flax fibres and shives as well (Hill et al., 1998; Joffe et al., 2003; Sain and Fortier, 2002; Tserki et al., 2005). Results indicate a signif- icant improvement of moisture resistance, mechanical properties and microbial degradation resistance. However, in most chemical modification procedures concerning lignocellulosic substrate, the use of harmful organic reagents, solvents and catalysts, obviously contrasts with the very intrinsic biodegradable and renewable properties of these natural raw materials. The hydrophobisation of biocomposites described in this arti- cle was realized with full respect of green chemistry approach. In fact, the hydrophobic treatment was not based on chemical mod- ifications but on formulation modifications: a hydrophobic agent, linseed oil, was introduced into the reaction medium during the process. Thus, the whole biocomposite preparation was realized in aqueous medium, without any use of potentially toxic organic sol- vent (acetone, toluene, methanol) or acyl chloride and anhydride. The particularity of linseed oil – the latter being commonly used for industrial applications from paints to linoleum – is its high drying ability. In fact, this oil consists of mixed glycerides composed of about 50% linolenic acid, 20% oleic acid, 15% linoleic acid and also containing palmitic and stearic acid (Güner et al., 2006; Sharma and Kundu, 2006). The drying of the linseed oil is 0926-6690/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.indcrop.2010.11.015