Effect of thermal modification of wood on the rheology, mechanical properties and dimensional stability of wood composite filaments and 3D-printed parts

This study investigates the effects of thermal modification (TM) on wood-filled polylactic acid composite filaments for 3D printing. Nine composite formulations with different wood content were analysed. The wood particles came from unmodified and thermally modified beech wood (180 degrees C or 200 degrees C). The results showed that the incorporation of thermally modified (TMd) wood changed the filament properties, resulting in lower density and reduced surface roughness. The 3D-printed parts with TMd wood particles had a higher water contact angle, higher storage modulus, lower glass transition temperature, higher modulus of elasticity and higher indentation hardness. However, the tensile strength of the 3D-printed parts decreases, even though the results of parts with TMd wood showed higher strength compared to unmodified wood at the same filler content. Surprisingly, TMd wood had no effect on water absorption under humid conditions. Scanning electron micrographs showed improved interfacial adhesion between TMd wood particles and PLA, with smaller voids in the filament compared to filaments with unmodified wood particles. The study suggests that further research into use of TMd wood particles in composite holds promise for environmentally friendly 3D printing materials with favourable thermal and mechanical properties, impacting the expanding market for sustainable solutions in 3D printing.