Wood Warping Composite by 3D Printing

Abstract

Wood warping is a phenomenon known as a deformation in wood that occurs when changes in moisture content cause an unevenly volumetric change due to fiber orientation. Here we present an investigation of wood warped objects that were fabricated by 3D printing. Similar to natural wood warping, water evaporation causes volume decrease of the printed object, but in contrast, the printing pathway pattern and flow rate dictate the direction of the alignment and its intensity, all of which can be predesigned and affect the resulting structure after drying. The fabrication of the objects was performed by an extrusion-based 3D printing technique that enables the deposition of water-based inks into 3D objects. The printing ink was composed of 100% wood-based materials, wood flour, and plant-extracted natural binders cellulose nanocrystals, and xyloglucan, without the need for any additional synthetic resins. Two archetypal structures were printed: cylindrical structure and helices. In the former, we identified a new length scale that gauges the effect of gravity on the shape. In the latter, the structure exhibited a shape transition analogous to the opening of a seedpod, quantitatively reproducing theoretical predictions. Together, by carefully tuning the flow rate and printing pathway, the morphology of the fully dried wooden objects can be controlled. Hence, it is possible to design the printing of wet objects that will form different final 3D structures.

Keywords: 3D printing; nanocellulose; shape programming; wood.

Figure A1

Wood flour particles in the powder starting material.

Figure A2

SEM images of a cylindrical sample printed at $\overrightarrow{v}=150\mathrm{mm}/\min$ (arrows indicating printing pathway direction.

Figure A3

SEM images of a cylindrical sample printed at $\overrightarrow{v}=600\mathrm{mm}/\min$ (arrows indicating printing pathway direction.

Figure A4

SEM images of a cylindrical sample printed at $\overrightarrow{v}=1500\mathrm{mm}/\min$ (arrows indicating printing pathway direction.

Figure 1

Examples of shrinking-induced shape changes in drying natural materials. (a) Crack propagation in Pinus halepensis tree trunk due to volume decrease by water evaporation in a cylindrical geometry constrain. (b) Delonix regia seed pod twists into a chiral shape. (c) A drying thin slice of an oak tree trunk buckles out-of-plane releasing the internal stresses instead of breaking (credit: Pascal Oudet [7]).

Figure 2

Schematic drawing of the printing and drying process. Wood ink consists of WF, and CNC and XG are extruded in a 2D predesign pathway on a plastic wrap placed on a Teflon substrate. The obtained object reduces its volume as a result of gradual evaporation of water and glides on the Teflon substrate. The anisotropic shrinkages result in a 3D wood warped object.

Figure 3

90° oriented bilayers. (a) printed object “as printed”, wet length = 60 mm, wet width = 15 mm. (b) Curvature as a function of printing speed measured at two different locations: center and side, blue and orange markers, respectively. (c) Dried 3D warped objects at different velocities, scale bar indicates 10 mm, demonstrating an increased effect at higher velocities.

Figure 4

Applying the curvature model on 3D warped objects at different velocities. The dashed lines are the profiles resulting from our numerical model for different values of ${\kappa }_0$. The resulting values vary from 0.1 ${\mathrm{mm}}^{-1}$ to 0.14 ${\mathrm{mm}}^{-1}$.

Figure 5

45° oriented bilayers. (a) Dried, 3D-warped helical objects at different velocities and width, scale bar indicates 10 mm. (b) Dimensionless radius versus dimensionless width. (c) Dimensionless pitch with versus dimensionless width. The vertical dotted line represents the threshold of the shape transition.

Figure 6

3D printed wood warped seedpod. These were made by printing to helical ribbons of opposite chirality with a relative angle of 45°.