Wood paste and objects made therefrom

Abstract

The invention generally concerns methods and printing inks comprising wood chips/wood powder and plant-extracted natural binders for constructing wood 3D structures.

Claims

1. A paste or plasticine-like mixture comprising water; at least one natural wood material selected from wood flour, wood chop and wood chips; cellulose nanocrystals (CNC); and at least one hemicellulose and/or lignin and/or starch, wherein the at least one natural wood material is free of unnatural or synthetic additives; the composition being for use in (a) a process of fabrication of 3D wood objects; or (b) a process for coating or covering a surface region of an object with the wood material; wherein the mixture is free of formaldehyde, synthetic resins and/or epoxy based materials; wherein the CNC is a crystalline rod-like material with a length of between 100 and 400 nm; and wherein the amount of CNC is between 0.01 wt % and 20 wt %.

2. The mixture according to claim 1, wherein the process of fabrication comprises casting, molding, extrusion, calendaring, injection, printing, hand-forming or manual processing.

3. The mixture according to claim 1, comprising all naturally derived materials.

4. The mixture according to claim 1, wherein the at least one wood material is a natural wood.

5. The mixture according to claim 4, wherein the natural wood material is derivable from wood stalks, branches, trunk or wood bark.

6. The mixture according to claim 4, wherein the wood material is obtained from a stalk, a branch, trunk or a bark of a tree or a bush selected from basswood, beech, birch, eucalyptus, walnut, pecan, cedar, cherry, elm, gum, hickory, lauan, mahogany, maple, oak, pine, poplar, redwood, rosewood, satinwood, sycamore, teak, alder, apple, aspen, chestnut, cottonwood, cypress, fir, hackberry, hemlock, holly, koa, laurel, locust, magnolia, pear-wood, spruce, tupelo and willow.

7. The mixture according to claim 6, wherein the tree is eucalyptus.

8. The mixture according to claim 1, wherein the at least one wood material is derived from hard or soft wood.

9. The mixture according to claim 1, wherein the at least one hemicellulose is selected from xylan, glucuronoxylan, arabinoxylan, glucomannan, galactoglucomannan and xyloglucan.

10. The mixture according to claim 9, wherein the hemicellulose is xyloglucan.

11. The mixture according to claim 1, the composition comprising at least one wood material, CNC and a hemicellulose or starch or lignin.

12. The mixture according to claim 1, the composition comprising at least one wood material, CNC and xyloglucan.

13. The mixture according to claim 1, wherein the object is a polymeric object formed of a material selected amongst thermoplastic polymers and thermoset polymers.

14. A wood object manufactured from a mixture according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 depicts DLS of two different CNC used in experimenters. DLS size: size of CNC #1 was measured to be 88.37 nm with 0.379 PdI and 48.34 nm with 0.204 PdI for CNC #2.

(3) FIG. 2 presents viscosity as a function of shear rate, shear thinning property can be seen in all inks ratio of XG:CNC.

(4) FIG. 3 presents the results of mold compression test of CNC ink with two different flour wood.

(5) FIGS. 4A-B depict (A) increase modulus as the addition of CNC (B) increasing in maximum compressive load as CNC concentration goes up.

(6) FIGS. 5A-B present (A) mold samples of wood with different ratio of XG:CNC for compression test (B) stress-strain curve of the measured objects.

(7) FIG. 6 presents the stress-strain curve of three point bending test of rectangular measured objects as a function of CNC concentration.

(8) FIGS. 7A-B present a three point bending test of wood flour as a depending of CNC concentration (A) Modulus (B) Stress at break

(9) FIG. 8 presents a stress-strain curve of 3D printed cylinder as compare to mechanical properties of XG:CNC:Wood ratio of mold sample.

(10) FIGS. 9A-D present various examples of 3D printed 100% wood objects by direct ink printing technology. Shown tree trunk, cube, and printed multi wood flour (maple and hard wood).

(11) FIGS. 10A-D show 3D printed 100% wood objects by binder-jet powder printing technology (T10 Come True Taiwan, each layer was printed with 1 pass of liquid) A—triangle (0.2% CNC), B—cookie shape (0.1% cnc). C cylinder (0.2% CNC) and D—Japanese carpentry (0.2% CNC).

(12) FIG. 11 presents a 3D printed 100% wood objects printed on 3D printed ABS using extrusion based technique.

DETAILED DESCRIPTION OF EMBODIMENTS

(13) Binder Ink Description

(14) The binder is composed of CNC particles dispersed in water. The concentration of CNC can be up to 20 wt % or as low as 0.01 wt %. Once mixed with wood flour or chips, it adheres to the surface of the wood chips and after the water evaporates, the CNC serves as a binder between the wood pieces. The binder can be mixed with the wood flour/chips into a homogenous mixture for deposition methods such as dispenser printing or to be printed directly onto layers of the wood flour/chips to be used in binder jetting/powder printer.

(15) FIG. 1 shows the viscosity of the binder ink without the wood chips. Xyloglocan (XG) can be used as an additive.

(16) Rheology of the Ink

(17) Low surface charge density CNC suspension ((DLS size: 88.37 nm (0.379 PdI), FIG. 1.) prepared from sulfuric acid hydrolysis of kraft pulp sheets (TEMBEC), were mixed with Xyloglucan (XG) from tamarind seed (Megazyme) according to the compositions presented in Table 1.

(18) TABLE-US-00001 TABLE 1 Name by ratio XG:CNC Material 0:1 1:100 1:50 1:10 1:4 1:0 CNC wt. % 3 2.97 2.94 2.72 2.4 0 XG wt. % 0 0.0297 0.0588 0.272 0.6 3

(19) Controlled rate mode rheology measurements of compositions with different XG:CNC ratios were performed at room temperature (Haake Rheostress 6000 coupled with RS6000 temperature controller, lower plate—TMP60, higher plate P60 TiL, Thermo Fisher Scientific Inc.). Four independent 1 mL samples were prepared and evaluated; one representative curve is presented in FIG. 2.

(20) Shear thinning behavior can be seen for all samples. As more XG been added initial viscosity raises up while slope remains the same. This important behavior of the ink is crucial for direct ink writing 3D printing technique.

(21) Mechanical Properties of Molds

(22) Mold—Compression Test,

(23) Compression Test of Plain CNC Based Ink

(24) High surface charge density CNC suspension (DLS size: 48.34 nm (0.204 PdI), FIG. 1), with surface charge density of 0.6 e/nm.sup.2), prepared from sulfuric acid hydrolysis of kraft pulp sheets (TEMBEC), mixed with two types of flour wood (made from Cupressus and Eucalyptus) (Table 2).

(25) TABLE-US-00002 TABLE 2 Ink name DW [g] 2.4% CNC [g] Flour wood [g] 0% CNC 4 0 2 0.5% CNC 3.167 0.833 2 1.5% CNC 1.5 2.5 2 2.4% CNC 0 4 2

(26) 1.5 g of different ratios of CNC samples were dried in a cylinder mold (D=10 mm, H=20 mm), for at least 48 Hr at 60° C. The samples were evaluated by a compression test by Instron Universal Testing Machine (Model 3345, Instron Corp. equipped with a 100N load cell) with a speed rate of 2 mm/min until the samples broke (FIG. 3). It was found that the mechanical properties increased dramatically with the addition of CNC. Young's modulus has improved by an order of magnitude from below 1 MPa for samples without CNC (0% CNC), to 11-17 MPa for 5 wt. % CNC, depending on the origin of the wood, while maximum stress load has improved with the same trend (FIG. 4). It should be noted that while using small particle size wood flour (75 um) the modules of the printed samples increased from 1.5 to >20 MPa.

(27) Mold—Compression Test of XG and CNC Based Ink

(28) Low surface charge density CNC suspension ((DLS size: 88.37 nm (0.379 PdI)), prepared from sulfuric acid hydrolysis of kraft pulp sheets (TEMBEC), were mixed with Xyloglucan (XG) from tamarind seed (Megazyme) according to the compositions presented in Table 3. For ink preparation, 4 g of samples with different XG:CNC were mixed with 4 g of DW and 2 g of wood flour (Eucalyptus).

(29) TABLE-US-00003 TABLE 3 Name by ratio XG:CNC Material 0:1 1:100 1:50 1:10 1:4 1:0 CNC wt. % 3 2.97 2.94 2.72 2.4 0 XG wt. % 0 0.0297 0.0588 0.272 0.6 3

(30) 1.5 g of ink samples were dried in a cylinder mold (D=10 mm, H=20 mm), for at least 48 Hr at 60° C. The samples were compression tested by Instron universal testing machine (Model 3345, Instron Corp. equipped with a 100N load cell) with a speed rate of 2 mm/min until samples broke (FIG. 5).

(31) As seen, the mechanical properties were improved as more XG was added until a threshold of 1:50 XG:CNC.

(32) Mold—Three Point Bending

(33) 2.5 g of industrial hardwood wood flour FIBER-75, LA.SO.LE) was mixed with 10 g of different weight concentration of CNC (Table 4) using a planetary centrifugal mixer for 5 min (Thinky). 5 g of sample was placed in a rectangle mold (D=20 mm, L=100 mm) and left to completely dry for at least 48 Hr in room temperature. The samples were evaluated by three point bending method by Instron Universal Testing Machine (Model 3345, Instron Corp. equipped with a 5 kN load cell) with a speed rate of 2 mm/min and support span of 30 mm

(34) TABLE-US-00004 TABLE 4 Ink name suspension [g] Wood flour [g] TDW 10 2.5 0.5% CNC 10 2.5 1% CNC 10 2.5 3% CNC 10 2.5

(35) It was found that all mechanical properties improved dramatically with the addition of CNC by at least an order of magnitude (FIG. 6). For example, flexure stress at break had improved from 0.1 MPa for TDW sample to overt 1.2 MPa for 3% CNC sample (FIG. 7).

(36) Printed Samples

(37) Direct Write Printing

(38) The ability to 3D print with dispenser based techniques depends on tailoring the properties of the ink. Pseudo-plastic liquid property is essential to the deposition of the ink, as it liquefies while the ink extrudes out of the nozzle and maintains its shape after deposition. The flow rate printing parameters should be tailored as well for the specific inks. First, the rheological properties of the ink and the obtained mechanical properties of the dry ink were studied by using molds. As optimal parameters were found, 3D printing of 100% wood structures was performed. CNC suspensions exhibit shear thinning behavior due to particle loading and size, and these parameters can be used to control the rheology. Since the inks can be used with high viscosity, the addition of XG and its effect on viscosity and mechanical properties of the resulting molded objects was also investigated.

(39) The dependence of mechanical properties, compression test and rheology, on the ratio of XG:CNC were considered. Once optimal ink parameters such as viscosity and mechanical properties were obtained, the inks were 3D printed and the printed objects characterized.

(40) Compression Test of 3D Printed Samples

(41) 3D printed cylinders were printed using HYREL3D printer mounted with a 10 ml syringe. Two different wood flour were used, homemade grinded Eucalyptus and industrial hardwood wood flour (FIBER-75, LA.SO.LE), with dry weight ratio of 1:0.74:0.06 for Wood-flour:CNC:XG. The samples were compression tested by Instron universal testing machine (Model 3345, Instron Corp. equipped with a 5 kN load cell) with a speed rate of 2 mm/min, measurement stopped by load cell limitation, none of the samples broke (FIG. 8). It was found that the mechanical properties of the 3D printed structures were improved by 400% as compared to objects prepared in molds which is an advantage of 3D printing process compared to conventional extrusion and mold fabrication processes.

(42) Example of 3D Printed Wood Objects

(43) 3D printed wood objects can be seen in FIG. 9, showing for the first time fully 3D printed 100% wood without addition of synthetic polymeric binders, by using the direct write technology.

(44) Binder Jetting/Powder Printing Ink Characterization and Results

(45) The ability to 3D print with inkjet based technology requires tailoring the properties of the ink. The typical surface tension and viscosity should be about 15 cP and 30 mN/m respectively (these parameters may vary, depending on the type of printer and print head). Therefore, low concentration of CNC should be used in order to meet typical DOD inkjet print head. The printing parameters of and the printer such as frequency should be tailored as well for the specific inks. The rheological properties of the ink and the obtained mechanical properties of the dry ink were first studied by using molds. Upon finding the optimal parameters, 3D printing experiments of 100% wood structures were performed.

(46) Example of 3D Printed Wood Objects

(47) As can be seen in FIG. 10, various structures can be printed while using binder jetting of the CNC based binder onto hard wood flour. In this approach more complex structures can be obtained due to the unbound wood flour that serves as support material for complex structures. The various structures can be immersed in another natural liquid binder solution for final hardening.

(48) ABS plate was coated by 3D printed wood showing coating/covering/packaging ability. The ABS was printed initially by an FDM head followed by extrusion\dispensing of the wood-based ink onto the formed ABS structures. The printing of the hybrid structure can be formed in the same layer, different layer, sequential layer—resulting in a wood texture structure with inner plastic body, as shown in FIG. 11.