Method for preparing complex and precise wood structure device based on wood fiber raw material extrusion additive

Abstract

The invention discloses a method for preparing a complex and precise wood structure device based on wood fiber raw material extrusion additive. The method comprises the steps that lignin, cellulose and a binder are mixed, a wood fiber raw material extrusion additive is obtained, a green body is obtained through nozzle extrusion forming and layer-by-layer accumulation additive manufacturing, heat preservation, degreasing and curing are conducted on the green body, the surface is polished, and the complex precise wood structure device is obtained. The method is low in comprehensive cost, wide in raw material source and low in cost, waste recycling is achieved, the process scheme is simple, convenient and easy to implement, and the prepared complex wood structure device is good in performance and high in compressive strength gt; and the pressure is 200 MPa, which is 4-5 times that of the pine wood (40-50 MPa), so that the method has a very good popularization prospect.

Description

Technical Field

[0001] The present invention relates to a method for preparing complex and precise wooden structural components, and in particular to a method for preparing complex and precise wooden structural components based on extrusion and additive manufacturing of wood fiber raw materials. Background Art

[0002] Lignin, the second-most abundant natural aromatic polymer, has an annual global production of over 70 million tons, the vast majority of which comes from byproducts of the papermaking industry and biomass refining. Utilizing lignin at a high value is a major challenge.

[0003] Additive manufacturing, commonly known as 3D printing, is an advanced green manufacturing technology that has many advantages over traditional methods, such as the ability to form complex parts, short processing cycles, and savings in raw materials. It has been applied in many fields including aerospace, automotive parts, medical care, and art design. Additive manufacturing technology has the advantages of wide material adaptability, low equipment cost, fast forming speed, and low overall cost. It is expected to achieve low-cost and efficient mass production of complex parts and has broad development prospects. The materials currently used in 3D printing mainly include: plastic materials, metal materials, ceramic materials, photosensitive resins, wood, etc. Among them, wood 3D printing is in the emerging stage of additive manufacturing. Wood additive manufacturing mainly uses an extrusion process, which is to print by feeding a filamentary material containing wood fiber and polymer adhesive into an extruder. This method has problems such as insufficient structural strength, fragile finished products, long molding time, and severe shrinkage before and after curing.

[0004] To address the challenges of extruded wood additive manufacturing, existing wood-plastic composites (such as patent CN103665905B) use ABS / PLA composite wood powder (wood powder content ≤80%) for printing, which can address the brittleness of the finished product. However, the poor continuity of the plastic matrix leads to weak interlayer bonding, resulting in a compressive strength of ≤100 MPa. Patent CN116285404A, "A 3D-Printed Wood-Plastic Composite Material and Manufacturing Method," while increasing strength to 150 MPa by adding epoxy resin, requires high-temperature curing above 200°C (increasing energy consumption by 30%), and the molded samples lose the natural feel of wood. The preparation method proposed in patent CN105623290A uses hydrophobic silica to coat wood powder, resulting in poor particle flow and requiring a reduced printing speed to prevent clogging, resulting in a printing speed of only 15 mm / s. Patent CN107022176A's preparation method reduces shrinkage to 5% by adding glass microspheres, but this sacrifices the authenticity of the wood grain. It can be seen that the existing wood additive manufacturing technology has problems such as insufficient structural strength, low molding efficiency, and the contradiction between shrinkage rate and precision. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to address the shortcomings of wood additive manufacturing in the prior art and to provide a method for preparing complex and precise wood structural devices based on extrusion additive manufacturing of wood fiber raw materials.

[0006] Technical solution: The method of the present invention for preparing complex and precise wood structure components by extrusion and additive manufacturing of wood fiber raw materials comprises the following steps:

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

[0008] (2) Extruding the wood fiber raw material into additives through a nozzle to form a green body by accumulating additive manufacturing layer by layer;

[0009] (3) The blank is taken for heat preservation, degreasing and curing, and the surface is polished after curing to obtain a complex and precise wooden structure device.

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

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

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

[0013] The binder comprises 2% to 4% by weight of polyvinyl alcohol, 1% to 2% by weight of hydroxypropyl methylcellulose, 0.5% to 1.5% by weight of sodium lignin sulfonate, 0.5% to 1% by weight of glycerol, and the balance is water.

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

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

[0016] In step (3), the heat preservation degreasing and curing is carried out at a temperature of 160-200°C for 1-2 hours. The polishing is carried out step by step using 400-1200 mesh sandpaper. The curing is fixed temperature curing or gradient step-by-step temperature curing; the gradient step-by-step temperature curing is to bake the blank at 160-170°C for 20-40 minutes to promote the thermoplastic flow of lignin, and then cure at 180-190°C for 50-70 minutes to form a dense cross-linked structure, and finally bake at 190-200°C for 20-40 minutes to improve the final strength, thereby obtaining a high-precision structural device.

[0017] The present invention also discloses a complex and precise wood structure device manufactured by the above method. The device has an overall dense structure and a compressive strength greater than 200 MPa.

[0018] Principle of the invention: The method of the present invention for preparing complex and precise wood structural devices based on extrusion additives of wood fiber raw materials uses wood fiber raw materials prepared in a special ratio as extrusion additives, and combines specific extrusion and curing conditions to obtain high-performance complex wood structural devices with extremely high compressive strength. First, a three-dimensional network of lignin-cellulose is constructed. When lignin (40-50%) and nanocellulose (40-50%) are cured at 160-200°C, the lignin thermoplastically flows to fill the gaps between the cellulose nanofibrils. The hydroxyl groups of the cellulose nanofibrils form hydrogen bonds with the phenylpropane units of the lignin. The polyvinyl alcohol (2-4%) and hydroxypropyl methylcellulose (1-2%) in the binder synergistically produce a shear thinning effect to form the required three-dimensional network. The samples were then molded using a low-temperature rapid curing mechanism. Sodium lignin sulfonate (0.5-1.5%) was used as a natural curing accelerator, which could reduce the curing temperature by 40°C compared to traditional wood-plastic materials. In addition, glycerol (0.5-1%) was added as a plasticizer to regulate the water evaporation rate, inhibit cracking, and accelerate curing and molding. The various material components synergistically improved the strength and precision of wooden structural devices.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The method for preparing complex and precise wooden structural devices of the present invention has good performance of the wooden structural devices prepared, with a compressive strength of >200MPa, which is 4-5 times that of pine wood (40-50MPa), and an improvement of up to 153% compared with the wood-plastic composite material molding method; and the structure of the device can be complex and precise, and the shear thinning properties regulated by hydroxypropyl methylcellulose can achieve 0.2mm ultra-fine flow channel printing; (2) The method has low overall cost, a wide source of raw materials, low cost, and realizes waste recycling; the process scheme is simple and easy to implement; and has good promotion prospects; (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%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The appearance and morphology of the complex and precise wooden structure device produced by additive manufacturing based on extrusion of wood fiber raw materials in Example 1;

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

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

[0023] Figure 4 This is the appearance and morphology of the complex and precise wooden structure device produced by additive manufacturing based on extrusion of wood fiber raw materials in Comparative Example 1. DETAILED DESCRIPTION

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

[0025] Example 1

[0026] The method of the present invention for preparing complex and precise wood structure components by extruding and adding wood fiber raw materials comprises the following steps:

[0027] (1) mixing lignin with a particle size of less than 15 μm and a purity of more than 85%, cellulose nanofibrils (CNF) with a diameter of 20 to 50 nm and a length of 5 to 10 μm, and a binder in a ratio of 50% lignin, 40% cellulose nanofibrils (CNF), and 10% binder, wherein the binder comprises 3% by weight of polyvinyl alcohol, 1.5% by weight of hydroxypropyl methylcellulose, 1% by weight of sodium lignin sulfonate, 0.5% by weight of glycerol, and the balance is water, to obtain a wood fiber raw material extrusion additive;

[0028] (2) Extruding the wood fiber raw material into additive manufacturing through a nozzle, and accumulating the additive manufacturing layer by layer to obtain a blank; the parameters used in the extrusion molding are: nozzle diameter 2.5 mm, extrusion pressure 0.6 MPa, printing layer thickness 0.4 mm, and printing speed 30 mm / s.

[0029] (3) The blank is taken and degreased in an oven for curing at a temperature of 200°C for 2 hours. After curing, the surface is polished step by step with 400-1200 mesh sandpaper to obtain a complex and precise wooden structure device.

[0030] The appearance photo of the complex wood structure device sample prepared in Example 1 is as follows: Figure 1As shown. It can be seen that the sample tissue is dense as a whole, with a density of 1.28g / cm 3 , compressive strength 215±8MPa, dimensional shrinkage before and after curing 3.2%, good performance.

[0031] Example 2

[0032] The method for preparing complex and precise wood structure components based on extrusion and additive manufacturing of wood fiber raw materials of the present invention, compared with Example 1, adjusts the ratio of extrusion and additive manufacturing of wood fiber raw materials, and comprises the following steps:

[0033] (1) mixing raw material lignin (from bamboo), cellulose nanofibrils (CNF) and a binder in a ratio of 45% lignin, 50% cellulose nanofibrils (CNF) and 5% binder, wherein the binder comprises 2% by weight of polyvinyl alcohol, 1.5% by weight of hydroxypropyl methylcellulose, 1% by weight of sodium lignin sulfonate, 0.5% by weight of glycerol, and the balance is water; adding natural pigment to obtain a wood fiber raw material extrusion additive;

[0034] (2) Extruding the wood fiber raw material into additive materials through a nozzle, and accumulating additive manufacturing layer by layer to obtain a green body; the parameters used in the extrusion molding are: nozzle diameter 2mm, extrusion pressure 0.3MPa, printing layer thickness 0.2mm, and printing speed 10mm / s;

[0035] (3) The blank is taken and degreased in an oven for curing at a temperature of 160°C for 1 hour. After curing, the surface is polished step by step with 400-1200 mesh sandpaper to obtain a complex and precise wooden structure device.

[0036] The appearance photo of the complex wood structure device sample prepared in Example 2 is as follows: Figure 2 As shown, the obtained sample has a clear appearance, high surface fineness, surface roughness Ra = 1.2μm, uniform color, and natural wood texture.

[0037] Example 3

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

[0039] (1) Lignin (from pine wood) with a particle size of less than 15 μm and a purity of more than 85%, cellulose nanofibrils (CNF) with a diameter of 20 to 50 nm and a length of 5 to 10 μm, and a binder are mixed in a ratio of 48% lignin, 47% cellulose nanofibrils (CNF), and 5% binder, wherein the binder comprises 3% by weight of polyvinyl alcohol, 1.2% by weight of hydroxypropyl methylcellulose, 0.8% by weight of sodium lignin sulfonate, 0.5% by weight of glycerol, and the balance is water to obtain a wood fiber raw material.

[0040] (2) Extruding the wood fiber raw material into additive materials through a nozzle, and accumulating additive manufacturing layer by layer to obtain a blank; the parameters used in the extrusion molding are: nozzle diameter 2.2 mm, extrusion pressure 0.4 MPa, and printing speed 25 mm / s.

[0041] (3) The green body is taken and degreased in an oven for heat preservation and curing. The green body is first baked at 160°C for 30 minutes to promote the thermoplastic flow of lignin, and then cured at 180°C for 1 hour to form a dense cross-linked structure. Finally, it is baked at 200°C for 30 minutes to improve the final strength, thus obtaining a high-precision structural device.

[0042] The appearance photo of the high-precision structural device sample prepared in Example 3 is as follows: Figure 3 As shown. Through the gradient curing process with staged temperature increase, the bending strength can reach 198MPa and the fracture toughness is 2.1MPa·m 1 / 2 , compressive strength increased by 4.6%.

[0043] Comparative Example 1

[0044] A method for making a wooden structure device, compared with the embodiment, does not add hydroxypropyl methylcellulose to the adhesive, and specifically comprises the following steps:

[0045] (1) Lignin with a particle size of less than 15 μm and a purity of more than 85%, cellulose nanofibrils (CNF) with a diameter of 20 to 50 nm and a length of 5 to 10 μm, and a binder are mixed in a ratio of 50% lignin, 40% cellulose nanofibrils (CNF), and 10% binder, wherein the binder comprises 3% by weight of polyvinyl alcohol, 0.5% by weight of glycerol, and the balance is water, to obtain a wood fiber raw material extrusion additive.

[0046] (2) Extruding the wood fiber raw material into additive manufacturing through a nozzle, and accumulating the additive manufacturing layer by layer to obtain a blank; the parameters used in the extrusion molding are: nozzle diameter 2.5 mm, extrusion pressure 0.6 MPa, printing layer thickness 0.4 mm, and printing speed 30 mm / s.

[0047] (3) The blank is taken and degreased in an oven for curing at a temperature of 200°C for 2 hours. After curing, the surface is polished step by step with 400-1200 mesh sandpaper to obtain a complex and precise wooden structure device.

[0048] The appearance photos of the complex wood structure device samples prepared in the comparative example are as follows: Figure 4 The comparative example adhesive lacks hydroxypropyl methylcellulose, which causes the slurry to lose its shear thinning properties, resulting in poor fluidity and insufficient interlayer adhesion. It can be seen that the resulting sample exhibits obvious cracks after curing, and its compressive strength decreases by 50%.

Claims

1. A method for preparing complex and precise wood structure components based on extrusion of wood fiber raw materials, characterized in that: The preparation method comprises the following steps: (1) mixing lignin, cellulose and a binder to obtain a wood fiber raw material extrusion additive, wherein the binder is a water-based environmentally friendly binder including polyvinyl alcohol, hydroxypropyl methylcellulose, sodium lignin sulfonate, glycerin and water; (2) Extruding the wood fiber raw material into additives through a nozzle to form a green body by accumulating additive manufacturing layer by layer; (3) The blank is taken for heat preservation, degreasing and curing, and the surface is polished after curing to obtain a complex and precise wooden structure device.

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

3. The method according to claim 1, characterized in that In step (1), the lignin is a by-product produced by the papermaking industry 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, wherein In step (1), the cellulose is nanocellulose, including one or a combination of cellulose nanofibrils or cellulose nanocrystals.

5. The method according to claim 1, wherein In step (1), the cellulose has a diameter ranging from 10 to 100 nm and a length ranging from 1 to 10 μm.

6. The method according to claim 1, characterized in that In step (1), the binder includes 2% to 4% by weight of polyvinyl alcohol, 1% to 2% by weight of hydroxypropyl methylcellulose, 0.5% to 1.5% by weight of sodium lignin sulfonate, 0.5% to 1% by weight of glycerol, and the balance is water.

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

8. The preparation 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° C. for 1-2 hours; and the polishing is carried out step by step using 400-1200 mesh sandpaper.

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

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

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