Damping of thermoset and thermoplastic flax fibre composites

The mechanical and damping properties of unidirectional (UD) and twill 2/2 flax fibre (FF) reinforced thermoset (epoxy) and thermoplastic (polypropylene (PP) and polylactic acid (PLA)) composites containing 40 vol% of fibres have been compared with those of carbon (CF) and glass (GF) fibre reinforced epoxy composites. Thanks to the relatively low density of the FF, the specific mechanical properties of the UD FF based composites were comparable with those of the GF epoxy composites. The composites reinforced with FF also showed improved damping as reflected by dynamic mechanical analysis with respect to composites reinforced with synthetic CF and GF. For example, the addition of UD FF to epoxy led to an approximately 100% increase in loss factor with respect to both the matrix and GF reinforced epoxy. FF/PP showed the highest damping at 25 °C and 1 Hz of all the composites investigated (tan δ=0.033). However the best compromise between stiffness and damping was obtained with FF reinforced semicrystalline PLA.