Natural fibres are increasingly used as reinforcements for thermoplastic composites. Additive manufacturing,
also known as 3D printing, is a common material extrusion process using (bio)polymers reinforced with natural
fibres. However, there is a lack of understanding of the effect of printing parameters on themechanical properties
involved in this new process, and more particularly in the case of Fused Deposition Modeling (FDM).
Hygromorphic biocomposites represent a novel use of natural fibres for the production of original self-bending
devices that actuate in a moisture gradient. By mimicking natural actuators and their bilayer microstructure
adapted for seed dispersal, hygromorphic biocomposites take advantage of the hygro-elastic behaviour of natural
fibres.
The FDM of wood fibre reinforced biocomposites leads to mechanical properties that are strongly dependent on
printing orientation (0 or 90°) due to fibre anisotropy. Mechanical properties depend also on printing width
(overlapping of filaments), with a lower Young's modulus than in the compressed samples. Indeed, printed
biocomposites have a microstructurewith relatively high porosity (around 20%) that conjointly leads to damage
mechanisms but also water absorption and swelling.
The FDM of hygromorphic biocomposites enables a shift towards 4D printing since the material is able to evolve
over time in response to an external stimulus. Typical microstructures achieved by printing could be used advantageously
to produce biocomposites with a faster moisture-induced bending response compared to compressed
samples.
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