A method for preparing a complex and precise wood structure device based on wood fiber raw material extrusion addition

Abstract

The application discloses a method for preparing a complex and precise wood structure device based on wood fiber raw material extrusion additive manufacturing; the method comprises the following steps: mixing lignin, cellulose and a binder to obtain wood fiber raw material extrusion additive, extruding and forming through a nozzle, layer-by-layer additive manufacturing to obtain a blank, and performing heat preservation, degreasing and solidification on the blank, and polishing the surface to obtain the complex and precise wood structure device; the method has low comprehensive cost, wide raw material sources and low cost, realizes waste recycling, and has a simple and easy-to-implement process scheme; the prepared complex wood structure device has good performance, and the compressive strength is greater than 200 MPa, which is 4-5 times of that of pine wood (40-50 MPa), and has a good popularization prospect.

Description

Technical Field

[0001] This invention relates to a method for preparing complex and precision wood structure devices, and more particularly to a method for preparing complex and precision wood structure devices based on wood fiber raw material extrusion additive manufacturing. Background Technology

[0002] Lignin, the second most abundant natural aromatic polymer in the world, has a global annual production exceeding 70 million tons, the vast majority of which comes from the paper industry and as a byproduct of biomass refining. How to achieve high-value utilization of lignin is a major challenge.

[0003] Additive manufacturing, commonly known as 3D printing, is an advanced green manufacturing technology with many advantages over traditional methods, such as the ability to form complex parts, shorter processing cycles, and savings in raw materials. It has already been applied in numerous fields, including aerospace, automotive parts, medical, and art design. Additive manufacturing technology boasts advantages such as wide material adaptability, low equipment cost, fast forming speed, and low overall cost, and holds promise for low-cost, high-efficiency mass production of complex parts, showing broad development prospects. Currently, the main materials used in 3D printing include plastics, metals, ceramics, photosensitive resins, and wood. Among these, wood 3D printing is in its emerging stage of additive manufacturing. Wood additive manufacturing primarily employs an extrusion process, feeding filamentary materials containing wood fibers and polymer binders into an extruder for printing. This method suffers from problems such as insufficient structural strength, fragile finished products, long forming times, and significant shrinkage before and after curing.

[0004] To address the problems in extrusion-based wood additive manufacturing processes, existing wood-plastic composite materials (such as patent CN103665905B) use ABS / PLA composite wood powder (wood powder content ≤80%) for printing, which solves the problem of fragile finished products. However, due to the poor continuity of the plastic matrix, the interlayer bonding is weak, resulting in a compressive strength of ≤100MPa for the finished product. While patent CN116285404A, "A 3D Printed Wood-Plastic Composite Material and Manufacturing Method," increases the strength to 150MPa by adding epoxy resin, it requires high-temperature curing above 200℃ (increasing energy consumption by 30%), and the molded sample loses the natural feel of wood. The preparation method proposed in patent CN105623290A uses hydrophobic silica to coat wood powder, resulting in poor particle flowability and requiring a reduced printing speed to prevent clogging, resulting in a printing speed of only 15mm / s. The preparation method in patent CN107022176A can reduce its shrinkage rate to 5% by adding glass microspheres, but at the cost of sacrificing the authenticity of the wood texture. It is evident that existing wood additive manufacturing technologies suffer from problems such as insufficient structural strength, low forming efficiency, and a contradiction between shrinkage rate and precision. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to address the shortcomings of existing wood additive manufacturing technologies by providing a method for preparing complex and precision wood structure devices based on the extrusion additive manufacturing of wood fiber raw materials.

[0006] Technical solution: The method for preparing complex and precision wood structure devices based on extrusion additive manufacturing of wood fiber raw materials according to the present invention includes the following steps:

[0007] (1) Mix lignin, cellulose and binder to obtain wood fiber raw material extrusion additive manufacturing, wherein the binder is a water-based environmentally friendly binder, including polyvinyl alcohol (PVA), hydroxypropyl methylcellulose (HPMC), sodium lignosulfonate, glycerol and water;

[0008] (2) The wood fiber raw material is extruded and additively formed by nozzle extrusion, and the preform is obtained by layer-by-layer additive manufacturing;

[0009] (3) Take the blank and perform heat preservation, degreasing and curing. After curing, polish the surface to obtain complex and precision wooden structure devices.

[0010] In step (1), the lignin accounts for 40% to 50% of the weight, the cellulose accounts for 40% to 50% of the weight, the binder accounts for 5% to 10% of the weight, and the wood fiber raw material extrusion additive is a slurry with shear thinning properties.

[0011] The lignin is a byproduct of papermaking or biomass refining using wood, bamboo, and crop straw. It is a waste recycling product with low cost, turning waste into treasure. The particle size range of the lignin is less than 15μm.

[0012] The cellulose is nanocellulose, including one or a combination of two of cellulose nanofibers (CNF) or cellulose nanocrystals (CNC); the diameter of the cellulose ranges from 10 to 100 nm and the length ranges from 1 to 10 μm.

[0013] The adhesive comprises 2% to 4% polyvinyl alcohol by weight, 1% to 2% hydroxypropyl methylcellulose by weight, 0.5% to 1.5% sodium lignosulfonate by weight, 0.5% to 1% glycerol by weight, and the balance being water.

[0014] Pigments can also be added to adjust the color of the additive during the extrusion of the wood fiber raw material.

[0015] In step (2), the parameters used for extrusion molding are: nozzle diameter 2-2.5 mm, extrusion pressure 0.3-0.6 MPa, printing layer thickness 0.2-0.4 mm, and printing speed 10-30 mm / s.

[0016] In step (3), the heat preservation, degreasing, and curing are carried out at a temperature of 160–200°C for 1–2 hours. The sanding is performed using 400–1200 grit sandpaper in progressively smaller increments. The curing process is either fixed-point temperature curing or gradient-stage temperature-increasing curing. The gradient-stage temperature-increasing curing involves baking the blank at 160–170°C for 20–40 minutes to promote lignin thermoplastic flow, followed by curing at 180–190°C for 50–70 minutes to form a dense cross-linked structure, and finally baking at 190–200°C for 20–40 minutes to improve the final strength, thus obtaining a high-precision structural device.

[0017] The present invention also discloses a complex and precision wooden structure device made by the above method, wherein the device has a dense overall structure and a compressive strength >200MPa.

[0018] Invention Principle: This invention relates to a method for preparing complex and precision wood structure devices based on extrusion additive manufacturing of lignocellulose raw materials. The method utilizes lignocellulose raw materials prepared with a special ratio as the extrusion additive, and combines specific extrusion and curing conditions to obtain high-performance complex wood structure devices with extremely high compressive strength. First, a three-dimensional lignin-cellulose network is constructed. When lignin (40-50%) and nanocellulose (40-50%) are cured at 160-200℃, the lignin thermoplastically flows and fills the gaps between cellulose nanofibers. The hydroxyl groups of the cellulose nanofibers form hydrogen bonds with the lignin phenylpropane units. In the binder, polyvinyl alcohol (2-4%) and hydroxypropyl methylcellulose (1-2%) synergistically produce a shear-thinning effect, forming the desired three-dimensional network. Then, samples are formed using a low-temperature rapid curing mechanism. Sodium lignosulfonate (0.5-1.5%) is used as a natural curing accelerator, which can reduce the curing temperature by 40°C compared to traditional wood-plastic composites. In addition, glycerol (0.5-1%) is added as a plasticizer, which can also regulate the rate of moisture evaporation, inhibit cracking, and accelerate curing. The various material components work together to improve the strength and precision of the wood structure components.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The method of preparing complex and precise wood structure devices of the present invention produces wood structure devices with good performance and compressive strength >200MPa, which is 4-5 times that of pine wood (40-50MPa), and the improvement is up to 153% compared with the wood-plastic composite molding method; and the structure of the device can achieve complex precision. Through the shear thinning characteristics regulated by hydroxypropyl methylcellulose, 0.2mm ultrafine flow channel printing can be achieved; (2) The method has low overall cost, wide availability of raw materials, low cost, and realizes waste recycling; the process scheme is simple and easy to implement; it has a good prospect for promotion; (3) The printing speed of the preparation method of the present invention can be increased by 100% compared with the existing additive manufacturing technology (such as CN103665905B), and the reduction in surface roughness and curing shrinkage can reach about 60%. Attached Figure Description

[0020] Figure 1 The image shows the appearance of the complex and precision wood structure device produced by extrusion additive manufacturing based on wood fiber raw materials in Example 1.

[0021] Figure 2 This is a photograph of a complex and precise wood structure device produced by extrusion additive manufacturing based on wood fiber raw materials in Example 2.

[0022] Figure 3 This is a photograph of the high-precision structural device produced by extrusion additive manufacturing based on wood fiber raw materials in Example 3;

[0023] Figure 4 The appearance of the complex and precision wood structure device produced by extrusion additive manufacturing based on wood fiber raw materials in Comparative Example 1 is shown. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the embodiments. The test materials used in the embodiments can all be purchased through conventional means.

[0025] Example 1

[0026] The method for preparing complex and precision wood structure devices based on extrusion additive manufacturing of wood fiber raw materials according to the present invention includes the following steps:

[0027] (1) A mixture of lignin with a particle size of less than 15 μm and a purity of >85%, cellulose nanofibers (CNF) with a diameter of 20-50 nm and a length of 5-10 μm and a binder is prepared in a ratio of 50% lignin, 40% cellulose nanofibers (CNF) and 10% binder. The binder includes 3% polyvinyl alcohol by weight, 1.5% hydroxypropyl methylcellulose by weight, 1% sodium lignin sulfonate by weight, 0.5% glycerol by weight, and the remainder is water, to obtain wood fiber raw material extrusion additive manufacturing.

[0028] (2) The wood fiber raw material is extruded and additively formed by nozzle, and the preform is obtained by layer-by-layer additive manufacturing; the parameters used for extrusion forming are: nozzle diameter 2.5mm, extrusion pressure 0.6MPa, printing layer thickness 0.4mm, and printing speed 30mm / s.

[0029] (3) Take the blank and keep it in the oven for degreasing and curing. The baking temperature is 200℃ and the time is 2h. After curing, the surface is polished step by step with 400-1200 grit sandpaper to obtain complex and precision wooden structure devices.

[0030] An appearance photograph of the complex wooden structure component sample obtained in Example 1 is shown below. Figure 1As shown in the figure, the obtained sample tissue is dense overall, with a density of 1.28 g / cm³. 3 It has a compressive strength of 215±8MPa and a dimensional shrinkage rate of 3.2% before and after curing, exhibiting good performance.

[0031] Example 2

[0032] The method for preparing complex and precision wood structure devices based on extrusion additive manufacturing of wood fiber raw materials of the present invention, compared with Example 1, adjusts the proportion of wood fiber raw material extrusion additive manufacturing and includes the following steps:

[0033] (1) The raw material lignin (from bamboo), cellulose nanofibers (CNF) and binder are mixed in a ratio of 45% lignin, 50% cellulose nanofibers (CNF) and 5% binder. The binder includes 2% polyvinyl alcohol by weight, 1.5% hydroxypropyl methylcellulose by weight, 1% sodium lignin sulfonate by weight, 0.5% glycerol by weight, and the balance is water. Natural pigments are added to obtain wood fiber raw material extrusion additive manufacturing.

[0034] (2) The wood fiber raw material is extruded and additively formed through a nozzle, and the preform is obtained by layer-by-layer additive manufacturing; the parameters used for the extrusion forming are: nozzle diameter 2mm, extrusion pressure 0.3MPa, printing layer thickness 0.2mm, and printing speed 10mm / s;

[0035] (3) Take the blank and keep it in the oven for degreasing and curing. The baking temperature is 160℃ and the time is 1h. After curing, the surface is polished step by step with 400-1200 grit sandpaper to obtain complex and precision wooden structure devices.

[0036] An appearance photograph of the complex wooden structure component sample prepared in Example 2 is shown below. Figure 2 As shown, the obtained sample has a clear appearance, high surface fineness, surface roughness Ra=1.2μm, uniform color, and a natural wood texture.

[0037] Example 3

[0038] The method for preparing high-precision structural devices based on extrusion additive manufacturing of wood fiber raw materials according to the present invention includes the following steps:

[0039] (1) A mixture of lignin (from pine wood) with a particle size of less than 15 μm and a purity of >85%, cellulose nanofibers (CNF) with a diameter of 20-50 nm and a length of 5-10 μm and a binder is prepared in a ratio of 48% lignin, 47% cellulose nanofibers (CNF) and 5% binder. The binder includes 3% polyvinyl alcohol by weight, 1.2% hydroxypropyl methylcellulose by weight, 0.8% sodium lignin sulfonate by weight, 0.5% glycerol by weight, and the balance being water, to obtain wood fiber raw material.

[0040] (2) The wood fiber raw material is extruded and additively formed by nozzle, and the preform is obtained by layer-by-layer additive manufacturing; the parameters used for extrusion forming are: nozzle diameter 2.2mm, extrusion pressure 0.4MPa, and printing speed 25mm / s.

[0041] (3) Take the blank and degrease it in the oven. First, bake the blank at 160℃ for 30 minutes to promote the thermoplastic flow of lignin. Then, cure it at 180℃ for 1 hour to form a dense cross-linked structure. Finally, bake it at 200℃ for 30 minutes to improve the final strength, thus obtaining a high-precision structural device.

[0042] An appearance photograph of the high-precision structural device sample prepared in Example 3 is shown below. Figure 3 As shown, by using a gradient curing process with staged temperature increases, the flexural strength can reach 198 MPa, and the fracture toughness is 2.1 MPa·m. 1 / 2 The compressive strength is increased by 4.6%.

[0043] Comparative Example 1

[0044] A method for constructing wooden structures, compared to the embodiments, in which hydroxypropyl methylcellulose is not added to the adhesive, specifically includes the following steps:

[0045] (1) A mixture of lignin with a particle size of less than 15 μm and a purity of >85%, cellulose nanofibers (CNF) with a diameter of 20-50 nm and a length of 5-10 μm and a binder is prepared in a ratio of 50% lignin, 40% cellulose nanofibers (CNF) and 10% binder. The binder includes 3% polyvinyl alcohol by weight, 0.5% glycerol by weight, and the balance being water, to obtain wood fiber raw material extrusion additive manufacturing.

[0046] (2) The wood fiber raw material is extruded and additively formed by nozzle, and the preform is obtained by layer-by-layer additive manufacturing; the parameters used for extrusion forming are: nozzle diameter 2.5mm, extrusion pressure 0.6MPa, printing layer thickness 0.4mm, and printing speed 30mm / s.

[0047] (3) Take the blank and keep it in the oven for degreasing and curing. The baking temperature is 200℃ and the time is 2h. After curing, the surface is polished step by step with 400-1200 grit sandpaper to obtain complex and precision wooden structure devices.

[0048] The appearance photos of the complex wooden structure device samples prepared in the comparative scale are as follows: Figure 4 As shown, the binder in the comparative example lacked hydroxypropyl methylcellulose, resulting in the slurry losing its shear-thinning properties, exhibiting poor fluidity, and insufficient interlayer adhesion. This is evident in the obvious cracks that appeared after curing of the resulting sample, with a 50% decrease in compressive strength.

Claims

1. A method for fabricating complex and precision wood structure devices based on lignocellulose extrusion additive manufacturing, characterized in that, The method includes the following steps: (1) Mix lignin, cellulose and binder to obtain wood fiber raw material extrusion additive manufacturing, wherein the binder is a water-based environmentally friendly binder, including polyvinyl alcohol, hydroxypropyl methylcellulose, sodium lignosulfonate, glycerol and water; (2) The wood fiber raw material is extruded and additively formed by nozzle extrusion, and the preform is obtained by layer-by-layer additive manufacturing; (3) Take the blank and perform heat preservation, degreasing and curing. After curing, polish the surface to obtain complex and precision wooden structure devices.

2. The method according to claim 1, characterized in that, In step (1), the lignin accounts for 40% to 50% by weight, the cellulose accounts for 40% to 50% by weight, and the binder accounts for 5% to 10% by weight.

3. The method according to claim 1, characterized in that, In step (1), the lignin is a byproduct of papermaking or biomass refining using wood, bamboo, or crop straw, and has a particle size range of less than 15 μm.

4. The method according to claim 1, characterized in that, In step (1), the cellulose is nanocellulose, including one or a combination of two of cellulose nanofibers or cellulose nanocrystals.

5. The method according to claim 1, characterized in that, In step (1), the cellulose has a diameter range of 10-100 nm and a length range of 1-10 μm.

6. The method according to claim 1, characterized in that, In step (1), the adhesive comprises 2% to 4% polyvinyl alcohol by weight, 1% to 2% hydroxypropyl methylcellulose by weight, 0.5% to 1.5% sodium lignosulfonate by weight, 0.5% to 1% glycerol by weight, and the balance being water.

7. The method according to claim 1, characterized in that, In step (2), the parameters used for extrusion molding are: nozzle diameter 2-2.5 mm, extrusion pressure 0.3-0.6 MPa, printing layer thickness 0.2-0.4 mm, and printing speed 10-30 mm / s.

8. The method according to claim 1, characterized in that, In step (3), the heat preservation, degreasing and curing is carried out at a temperature of 160-200℃ for 1-2 hours; the polishing is carried out by polishing with 400-1200 grit sandpaper in stages.

9. The method according to claim 8, characterized in that, In step (3), the curing is either fixed-point temperature curing or gradient-stage temperature curing; the gradient-stage temperature curing first involves baking the blank at 160-170℃ for 20-40 minutes, then curing at 180-190℃ for 50-70 minutes to form a dense cross-linked structure, and finally baking at 190-200℃ for 20-40 minutes.

10. A complex and precise wooden structure device manufactured using the method of claim 1, characterized in that, The device has a dense overall structure and a compressive strength >200MPa.

Images