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Hygromorph BioComposites: Effect of fibre content and interfacial strength on the actuation performances

Le Duigou, Antoine, Castro, Mickael
Industrial crops and products 2017 v.99 pp. 142-149
actuators, biocomposites, drying, fiber content, flax, microstructure, polysaccharides, porosity, water uptake
Hygromorph biocomposites (HBCs) are hygroscopically active materials with moprhing ability upon a moisture variation. They turned the water sensitivity of natural fibres into the driving force of the HBC actuation. A novel asymmetric 0/90° microstructure, where both passive and active layers have included flax fibres, has been used. Faster actuation (x2) was reached compared to pure matrix as a passive layer. The present study has also evidenced that flax fibre content and the interfacial bonding strength control the actuation properties. Indeed, increasing the fibre content from 17 to 60% in volume has drastically improved the actuation amplitude (x4) and speed (≈x90) leading to competitive performance with synthetic actuators. Improving interfacial strength by using PP+MAPP leads to more efficient actuation (≈x2) with water uptake even if actuation amplitude is slightly reduced (−12%). Hygromechanical fatigue cycles (wetting/drying) have greatly weakened the return to initial position of non-compatibilized HBC due to porosity generation and polysaccharide leashing. Fatigue resistance of HBCs has been largely improved with improved interfacial bond strength (+20%).