sustainability Tab. 2: Mechanical properties of various biocomposites Tab. 3: Acoustic properties of some traditional and natural fibre materials Fibre diameter (µm) Bulk density (g/cm3) Cotton 13.5 0.04 0.62 0.50 Flax 21.8 0.08 0.55 0.40 24.4 0.10 0.55 0.40 37.1 0.10 0.35 0.20 Biocomposite Property Tensile strength (MPa) Tensile modulus (GPa) Flexural strength (MPa) Flexural modulus (GPa) Fibre volume fraction (%) Density (g/cm3) Material Plain flax fabric (0/90) UD flax fabric (0°) / BUP* / BUP* Thickness (mm) Noise reduction Absorption coefcoefficient1 ficient2 at 500 Hz 87 112 8.6 14.0 138 162 Jute 81.2 0.07 0.35 0.20 8.9 11.5 Sisal 213.0 0.04 0.16 0.10 38 45 Glass wool --- 0.03 0.56 0.40 --- 0.07 0.65 0.70 1.23 1.46 --- 0.07 0.17 0.10 Tab. 4: Thermal properties of some natural and traditional insulating materials Material Thermal conductivity (W/mK) Hemp 0.040 Kenaf 0.044 Coco fibre 0.043 Sheep wool 0.044 Wood wool 0.065 Cork 0.039 Cellulose 0.037 Flax 0.040 Glass wool 0.040 Rock wool 0.045 Expanded polystryrene 0.031 conductivity values of natural fibres are in the range of traditional materials used in the transport and building industries such as glass or rock wool. Table 4 shows the thermal properties of both natural fibres and traditional materials . Vibrational damping Vibrational damping mechanisms in natural fibre composites differ entirely from those in conventional materials and energy dissipation depends on factors like the visco-elastic nature Ramie Wool Mineral wool 50 40 Polystyrene of the matrix and/or fibre, the interphase, damage and visco-plastic characteristics. Fig. 5 illustrates the vibrational damping behaviour of several natural fibres and conventional synthetic fibres as a function of fibre orientation. As can be seen from Fig.5, natural fibres such as flax exhibit a higher damping behaviour than traditional reinforcements such as glass or carbon fibres. Fig. 5: Vibrational damping behaviour of some natural fibres compared with conventional reinforcements (Source: Lineo n.v11) Applications Biocomposites obtained from both petroleum- and bio-based resins reinforced with natural fibres have gained interest over the past years. Regarding new applications of biocomposites, many companies and research institutes are currently conducting extensive work on natural fibre fabrics and polymers in order to develop parts for different areas of the transport industry including automotive, rail and aircraft applications. Some products developed from these Fig. 6: Examples of biocomposite applications in the transport industry: fireproof interior panels made from flax fabrics and thermosetting resins developed by AIMPLAS (a); biocomposite seat panelling element for suburban trains (b); fireproof sidewall panel made from natural fibres and thermoplastic polymers developed by AIMPLAS (c); tractor floor panel from flax and polylactic acid developed in the NATEX project (d); interior door panels from short natural fibres and thermoplastic polymers (e); under floor protection trim of the Mercedes Class A based on banana fibre and thermoplastic materials (f) 18 jec composites magazine / No92 October - November 2014