JEC COMPOSITES MAGAZINE - Issue #37 - December 2007 - 35

Properties Table 1: Tensile mechanical properties of various fibres, where E: Young’s modulus, σ: breaking stress, A: elongation at break, d: density and df: average fibre diameter. Variety Glass Jute Sisal Hemp Flax Flax Flax Flax Nettle Viscose Lyocell Ariane Agatha Hermes Urtica Dioica E (GPa) 72 10-25 46 26-30 40-85 58 (±15) 71 (±25) 76.7 (±20.8) 87 (±28) 11.6 22.3 σ (MPa) 2200 400-800 700 500-900 800-2000 1339 (±486) 1381 (±419) 1795 (±1127) 1594 (±640) 310 750 A (%) 3 1-2 2-3 1-6 2.4-3 3.27 (±0.4) 2.1 (±0.8) 2.4 (±0.7) 2.11 (±0.81) 8 12 d (g/cm3) 2.54 1.46 1.33 1.48 1.54 1.53 1.53 1.53 ~1.5 1.3 1.3 Reference [7] [8] [8] [8] [8] [9] [10] [11] [12] [13] [13] the parameters were controlled. As far as we know, nettle fibres are no longer available for industry. Studying them is still of interest, however: the plant is well adapted to the European climate, the fibres have good mechanical properties, and there is potential for upgrading a whole group of co-products. We can see from Table 1 that: - the tensile stiffness of Hermes flax fibre (E=77 GPa) and nettle fibre (E=87 GPa) is higher than that of glass fibre; - natural-fibre density (d~1.5) is lower than that of glass fibre (d=2.54). When part weight is being used as a selection criteria, the specific mechanical properties of the materials are compared (E/d, σ/d); - Compared to glass fibres, the natural fibres presented here have higher specific stiffness and equivalent specific strength; - a solution being explored by a number of researchers is the use of regenerated cellulose fibres like viscose and lyocell as reinforcement for composite materials. The main arguments given are that such fibres are in continuousfilament form and that their mechanical properties are Table 2: Comparison of the specific tensile properties of various fibres. Variety Glass Flax Flax Flax Nettle Viscose Lyocell Ariane Agatha Hermes Urtica Dioica E/d 28.3 37.9 46.4 50.1 58 8.9 14.9 σ /d 866 875 903 1173 1063 238 576 d (g/cm3) 2.54 1.53 1.53 1.53 ~1.5 1.3 1.3 reproducible. Note that these mechanical properties are still relatively unexceptional, and that the non-neutral impact of the fibre production process needs to be factored into the life-cycle analysis; The values for the properties of natural fibres are widely distributed – a common reproach. This should not be overlooked, but inspires a few remarks: - other reinforcement fibres (glass, carbon, etc.) – like most other materials, for that matter – also show widely distributed values for mechanical properties, - the scattering can be reduced by controlling the set of parameters (species, variety, growth conditions, extraction techniques, etc.), - the textile, paper and wood industries, among others, have long used natural raw materials with success to manufacture products with consistent quality, - recent research [11] has focused on the influence of the location on the stem (close to the root, middle, or top) from which the fibre is taken. Conditions such as the amount of water and sunlight received or the daily temperature range change throughout a plant’s growth cycle, with an influence on cell development. In future, it will be possible to factor this in during the fibre extraction and upgrading stages. Obviously the mechanical properties of an anisotropic fibre are not limited to three tensile properties, and the thermomechanical behaviour under different stress/strain conditions should also be studied. In addition, research needs to be carried out on the fibre/matrix bond and ply properties of a composite material. However, all this is beyond the purview of this paper. In the near future, we will need to set up channels that are specific to each area of plastics processing. There is also a need to draw up reference documents establishing specifications for natural fibres that are suitable for use in composite materials. Setting up No37 December 2007 / JEC Composites Magazine
JEC COMPOSITES MAGAZINE - Issue #37 - December 2007

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #37 - December 2007
