Processing of natural-fibre reinforced polymers and the resulting dynamic–mechanical properties

By means of dynamic–mechanical analysis (DMA), selected application-specific properties of flax- and hemp-fibre reinforced polypropylenes (PPs) have been determined for material characterisation. The compound samples were manufactured both by consolidation of hybrid non-wovens and compounding and injection moulding with the addition of natural fibres. The conditioning (long and short fibres), the manufacturing process and the processing parameters are the most important influencing factors on the mechanical properties of the final product. The results also reveal that the elastic properties (stiffness, storage modulus) of the composite material are dependent on the type of coupling agent. Other influencing parameters are the specific surface and the content of added fibre. The parameters mentioned can be varied by fibre separation or post-treatment procedures. The recycling behaviour of natural-fibre reinforced PP shows that multiple processing has only an insignificant influence on the fibre lengths and the mechanical properties. In addition, it is possible to very quickly draw conclusions about the quality of the composite material, such as fibre–matrix adhesion and damping behaviour. Fractographic evaluations in the scanning electron microscope (SEM) confirm the quantitative characterisation obtained from DMA.