A study on the influence of processing parameters on damping, elastic and ultimate properties of commingled flax-polypropylene composites

Abstract : Natural fibres such as flax are a promising replacement for synthetic fibres in polymer composites and achieve comparable specific properties due to their low density. Recent developments in the production of technical flax fabrics allow the use of sustainable natural fibres in the manufacture of structural composite parts. One of the other advantages of natural fibre composites is their high damping properties compared to that of glass and carbon fibre composites. The material properties that can be achieved with plant fibre based composites are highly sensitive to the composite manufacturing process. Although plant fibres have been shown to improve the damping coefficient of composite materials, there are no systematic studies of the effect of the processing conditions on the damping properties in correlation with the stiffness and strength of the composite. In this paper, the damping properties of flax fibre reinforced composites were investigated using the natural frequencies and modal damping obtained from vibration tests. The material selected for the study was flax/polypropylene (PP) fabric supplied by Composites Evolution as Biotex flax/PP. The composite laminates were manufactured by thermocompression using different conditions for temperature, pressure and consolidation time. The damping measurements were achieved on cantilever beams of the flax/PP composite that were clamped in a bench at one end and excited by a short impulse. A laser vibrometer sensor was used to measure the impulse response of the beam and the time signal was converted to frequency response by FFT. It was found that the damping factor is sensitive to the processing conditions and that factors such as porosities, fibre-matrix interface will affect the vibration response of the composite.