JEC COMPOSITES MAGAZINE - Issue #46 - January/February 2009 - 35

Resources Table 2: Mechanical properties, chemical composition and structural parameters for a selection of vegetable fibres [1]. Fibre Flax Hemp Jute Ramie Coir Sisal Cotton Cellulose content (%) 71 78 61 83 43 67 82.7 Microfibrillar angle (°) 10.0 6.2 8.0 7.5 45 20 n.d. Section (mm²) 0.12 0.06 0.12 0.03 1.2 1.1 18-28 Length (mm) 20 23 2.3 154 3.3 2.2 25-64 L/D ratio 1,687 960 110 3,500 35 100 110 Max. tensile stress (MPa) 345-1,035 690 393-773 400-938 175 511-635 287-597 Young’s modulus (GPa) 27.6 35 26.5 61.4-128 4-6 9.4-22 5.5-12.6 Ultimate elongation (%) 2.7-3.2 1.6 1.3 3.6-3.8 30 2-2.5 7.0-8.0 10 40 70 250 Fig. 1: Changes in elastic modulus (GPa) (wood used as example) as a function of level of fibre extraction, from micro to nano. The micrographics do not represent wood fibres. for non-food crops, such an approach would help to: - ensure enough stable supply by using fibres from different sources for a single application, as shown in Table 1, or - optimize composite-material design by bringing the complementarity of properties into play – e.g. the fineness of flax fibre, the good mechanical properties of hemp, etc. Even if the resources are actually available, the real issue over the long term is being able to control the stability and quality of the fibre supply, and to standardize the fibres by type of use. specifications in terms of fibre types and manufacturing processes, you must first identify key properties. To address this challenge, FRD® (like other specialized technical centres) is developing its expertise in taking a set of industrial specifications, translating it into material properties, then expressing these in terms of key fibre properties. Understanding and controlling variability While understanding and controlling variability is not an issue for the organic/mineral fibre sector, these are still generating a lot of R&D in vegetable fibres. Like any plant resource, natural fibres present a wide quality range (also called variability), both within a single plant species and across the entire vegetable fibre category. Quality is affected by cultivation techniques and soil and climate characteristics; but also by the extraction and final forming processes that are used. For example, fibre quality might depend on: - fibre type (see Table 2), - fibre size (see Figure 1), as a function of the method and level of extraction, - fibre composition, which depends itself on soil and weather characteristics, - independent macroscopic parameters such as humidity and temperature. Fibre quality Many manufacturers, particularly in the building & construction and transport industries, are taking a greater interest in the properties of vegetable fibres. Material specifications – and therefore those for the constituent fibres – are very stiff, especially for a natural resource subject to unpredictable weather conditions that can affect growth. One of the industry’s major challenges is to control the links between the botanical fibre (composition, properties, and role of the fibre within the plant) and the industrial fibre (fibre properties and specifications of the industrial applications). Identifying key properties Before developing the solution that will best meet a set of No46 January-February 2009 / jec composites magazine 35

JEC COMPOSITES MAGAZINE - Issue #46 - January/February 2009

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #46 - January/February 2009