Preparation method of high-filling wood-plastic composite printing wire rod

Abstract

The invention discloses a preparation method of a high-filling wood-plastic composite printing wire rod, and belongs to the field of wood-plastic composite materials. The invention aims to solve the problem that the mechanical property, machinability and printing stability of a material are reduced due to poorer compatibility between wood and plastic when wood fibers are highly filled (greater than 30wt%) in an existing wood-plastic composite printing wire rod. The method comprises the following steps: 1, wood fiber modification; 2, weighing; 3, melt extrusion; and 4, preparing the wire rod. The preparation method is used for preparing the high-filling wood-plastic composite printing wire rod.

Description

Technical Field

[0001] This invention belongs to the field of wood-plastic composite materials. Background Technology

[0002] Fused deposition modeling (FDM), a mainstream additive manufacturing technology, constructs complex components by hot-melt extrusion of thermoplastic materials (such as polylactic acid) and stacking them layer by layer. Bio-based materials, represented by polylactic acid (PLA), are highly favored due to their biodegradability, low toxicity, and printability. However, their inherent drawbacks, such as high production costs, brittleness, and poor heat resistance, severely restrict the development of high-performance parts. Introducing natural fiber reinforcements into PLA is considered an effective way to improve performance and reduce carbon footprint. Wood fibers, as a byproduct of wood processing, have low density, low cost, and renewability, and their three main components (cellulose, hemicellulose, and lignin) provide abundant reaction sites.

[0003] However, in existing 3D printing wood-plastic composite materials processes, the amount of wood fiber filling is limited to 0 to 40 parts. When the wood fiber filling is high (>30wt%), the poor compatibility between wood and plastic leads to a decrease in the material's mechanical properties, processability, and printing stability. Summary of the Invention

[0004] This invention aims to address the problem that poor compatibility between wood and plastic leads to a decline in the mechanical properties, processability, and printing stability of existing wood-plastic composite printing filaments when wood fibers are highly filled (>30wt%). In this way, a method for preparing highly filled wood-plastic composite printing filaments is provided.

[0005] A method for preparing a highly filled wood-plastic composite printing filament, comprising the following steps:

[0006] I. Modification of wood fibers:

[0007] Wood fibers are added to a eutectic solvent and heated and stirred to obtain a mixture. The mixture is then added to deionized water and stirred. The solid fibers are then separated, washed, and dried to obtain modified wood fibers.

[0008] The eutectic solvent is composed of choline chloride and oxalic acid;

[0009] II. Weighing:

[0010] Weigh 10 to 60 parts of modified wood fiber, 30 to 85 parts of polylactic acid, 1 to 3 parts of polyethylene wax and 1 to 3 parts of stearic acid according to the mass ratio of polybutylene terephthalate to polylactic acid of 1:(6 to 9).

[0011] III. Melt Extrusion:

[0012] Modified wood fiber, polylactic acid, polybutylene terephthalate, polyethylene wax and stearic acid are mixed evenly, then melt-composite, and finally cooled, crushed and granulated and dried to obtain modified wood fiber / polylactic acid composite material.

[0013] IV. Wire Preparation:

[0014] Modified wood fiber / polylactic acid composite material was extruded using a single screw extruder, followed by water cooling and traction winding to obtain a highly filled wood-plastic composite printing filament.

[0015] The beneficial effects of this invention are:

[0016] 1. Breakthrough in high filler content: Successfully prepared printable composite material filaments with a wood fiber content of up to 60wt%, far exceeding the filler content of traditional methods.

[0017] 2. Mechanical properties of high-filler wood-plastic composite filaments: The tensile strength of the high-filler modified wood fiber / polylactic acid composite material is significantly improved compared with the unmodified composite material with the same content.

[0018] 3. The material has good rheological properties, which means it is printable.

[0019] 4. Excellent printing results: The printed products have a smooth surface, stable dimensions, no warping, and smooth edges. The S-shaped hook sample can withstand a load of 2500 times its own weight, meeting the requirements of 3D printing for molding accuracy and performance.

[0020] 5. Green, environmentally friendly and sustainable: It uses a low eutectic solvent as a green modification medium, which is low in energy consumption, environmentally friendly, and has a high biomass content, which is in line with the concept of sustainable development and reduces production costs. Attached Figure Description

[0021] Figure 1 This is a comparison chart of the percentage composition of wood fiber before and after modification in step one of Example 1;

[0022] Figure 2 The XRD patterns of the wood fibers before and after modification in step one of Example 1 are shown below.

[0023] Figure 3 The melt flow rate (MFI) curves are shown for the modified wood fiber / polylactic acid composite materials prepared in step three of Examples 1 to 4 and the wood fiber / polylactic acid composite materials prepared in step three of Comparative Experiments 1 to 3.

[0024] Figure 4 The image shows a physical picture of the modified wood fiber / polylactic acid composite wire prepared in Example 2.

[0025] Figure 5This is a photograph of an S-shaped hook 3D printed using the modified wood fiber / polylactic acid composite filament prepared in Example 2.

[0026] Figure 6 The images show actual leaf-shaped products 3D printed using the modified wood fiber / polylactic acid composite filament prepared in Example 2 and the wood fiber / polylactic acid composite filament prepared in Comparative Experiment 2. Detailed Implementation

[0027] Specific Implementation Method 1: This implementation method is a method for preparing a highly filled wood-plastic composite printing filament, which is carried out according to the following steps:

[0028] I. Modification of wood fibers:

[0029] Wood fibers are added to a eutectic solvent and heated and stirred to obtain a mixture. The mixture is then added to deionized water and stirred. The solid fibers are then separated, washed, and dried to obtain modified wood fibers.

[0030] The eutectic solvent is composed of choline chloride and oxalic acid;

[0031] II. Weighing:

[0032] Weigh 10 to 60 parts of modified wood fiber, 30 to 85 parts of polylactic acid, 1 to 3 parts of polyethylene wax and 1 to 3 parts of stearic acid according to the mass ratio of polybutylene terephthalate to polylactic acid of 1:(6 to 9).

[0033] III. Melt Extrusion:

[0034] Modified wood fiber, polylactic acid, polybutylene terephthalate, polyethylene wax and stearic acid are mixed evenly, then melt-composite, and finally cooled, crushed and granulated and dried to obtain modified wood fiber / polylactic acid composite material.

[0035] IV. Wire Preparation:

[0036] Modified wood fiber / polylactic acid composite material was extruded using a single screw extruder, followed by water cooling and traction winding to obtain a highly filled wood-plastic composite printing filament.

[0037] In this specific embodiment, a recyclable green modified eutectic solvent (DES) is used to modify wood fibers, depolymerizing and dissolving some hemicellulose and lignin. Then, the fibers are added to the antisolvent deionized water and mechanically stirred to disrupt the DES hydrogen bond network. This causes small lignin molecule fragments to re-attach to the wood fiber surface due to π–π stacking and hydrogen bonding, thus regenerating the fibers. Furthermore, the non-polar structure of the regenerated lignin may interact with PLA through van der Waals forces, optimizing the compatibility of wood fibers in the PLA matrix. By modifying wood fibers with amphiphilic regenerated lignin, the physical properties and printability of highly filled wood-plastic composite filaments are improved, enhancing the printing accuracy of 3D printed products and providing a new approach for developing high-performance, fully bio-based FDM printing materials.

[0038] The beneficial effects of this embodiment are:

[0039] 1. Breakthrough in high filler content: Successfully prepared printable composite material filaments with a wood fiber content of up to 60wt%, far exceeding the filler content of traditional methods.

[0040] 2. Mechanical properties of high-filler wood-plastic composite filaments: The tensile strength of the high-filler modified wood fiber / polylactic acid composite material is significantly improved compared with the unmodified composite material with the same content.

[0041] 3. The material has good rheological properties, which means it is printable.

[0042] 4. Excellent printing results: The printed products have a smooth surface, stable dimensions, no warping, and smooth edges. The S-shaped hook sample can withstand a load of 2500 times its own weight, meeting the requirements of 3D printing for molding accuracy and performance.

[0043] 5. Green, environmentally friendly and sustainable: It uses a low eutectic solvent as a green modification medium, which is low in energy consumption, environmentally friendly, and has a high biomass content, which is in line with the concept of sustainable development and reduces production costs.

[0044] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the eutectic solvent mentioned in step one is prepared according to the following steps: Choline chloride and oxalic acid are mixed, and then stirred until uniform and transparent at a temperature of 80℃~100℃ and a stirring speed of 500r / min~1500r / min to obtain the eutectic solvent; the molar ratio of choline chloride to oxalic acid is 1:(0.5~3). Everything else is the same as in Specific Implementation Method One.

[0045] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the total mass fraction of the modified wood fiber, polylactic acid, polybutylene terephthalate-adipate, polyethylene wax, and stearic acid mentioned in step one is 100 parts; the wood fiber mentioned in step one is one or a mixture of several of poplar fiber, rice husk powder, bamboo powder, straw powder, fruit shell powder, and sugarcane bagasse; the wood fiber mentioned in step one is oven-dried wood fiber with a particle size of 80 mesh to 120 mesh. Everything else is the same as in Specific Implementation Method One or Two.

[0046] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: the mass ratio of wood fiber to eutectic solvent in step one is 1:(10~30); the mass ratio of eutectic solvent to deionized water in step one is 1:(5~8). Everything else is the same as in Specific Implementation Methods One to Three.

[0047] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: in step one, the wood fibers are added to a eutectic solvent and heated and stirred for 2 to 4 hours at a temperature of 80℃~110℃ and a stirring speed of 500 r / min~1500 r / min to obtain a mixture. The mixture is then added to deionized water and stirred for 3 to 5 hours at a temperature of 20℃~60℃ and a stirring speed of 500 r / min~1500 r / min. The solid fibers are then separated and washed until neutral, and finally dried to a moisture content below 3% to obtain modified wood fibers. The rest is the same as in Specific Implementation Methods One to Four.

[0048] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: in step three, under a stirring speed of 20 r / min to 50 r / min, modified wood fiber, polylactic acid, polybutylene terephthalate-adipate, polyethylene wax, and stearic acid are mixed for 5 min to 10 min. Then, using a torque rheometer or screw extruder, the mixture is melt-composite at a temperature of 155℃ to 185℃ and a rotation speed of 30 r / min to 60 r / min. Finally, it is cooled, crushed, granulated to a particle size of less than 3 mm, and dried to obtain the modified wood fiber / polylactic acid composite material. Everything else is the same as in Specific Implementation Methods One to Five.

[0049] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that, when using a screw extruder, the temperatures of each section of the screw extruder are set sequentially from the feeding section to the die head: Zone 1: 150℃~180℃; Zone 2: 155℃~185℃; Zone 3: 160℃~185℃; Zone 4: 165℃~185℃; Zone 5: 170℃~185℃; Zone 6: 160℃~185℃; and the die head temperature: 155℃~185℃. Melt compounding is then performed at a rotation speed of 30 r / min~60 r / min. Everything else is the same as in Specific Implementation Methods One through Six.

[0050] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: in step four, the modified wood fiber / polylactic acid composite material is extruded using a single-screw extruder at a temperature of 160℃~180℃ and a main extruder speed of 20r / min~60r / min. Everything else is the same as in Specific Implementation Methods One to Seven.

[0051] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One through Eight in that: in step four, the temperatures of each section of the single-screw extruder are set sequentially, from the feeding section to the die head, with zone one at 150℃~170℃ and zone two at 160℃~180℃. Then, the modified wood fiber / polylactic acid composite material is extruded under the condition that the main extruder speed is 20r / min~60r / min. Everything else is the same as in Specific Implementation Methods One through Eight.

[0052] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that the diameter of the highly filled wood-plastic composite printing filament prepared in step four is 1.60mm to 1.80mm. Everything else is the same as in Specific Implementation Methods One to Nine.

[0053] The beneficial effects of the present invention are verified using the following embodiments:

[0054] Example 1:

[0055] A method for preparing a highly filled wood-plastic composite printing filament, comprising the following steps:

[0056] I. Modification of wood fibers:

[0057] Wood fibers were added to a eutectic solvent and heated and stirred for 2 hours at 110°C and 600 r / min to obtain a mixture. The mixture was then added to deionized water and stirred for 3 hours at 30°C and 900 r / min. The solid fibers were then separated and washed until neutral. Finally, the mixture was dried until the moisture content was below 3% to obtain modified wood fibers.

[0058] The eutectic solvent is composed of choline chloride and oxalic acid; the eutectic solvent is specifically prepared according to the following steps: choline chloride and oxalic acid are mixed, and then stirred until uniform and transparent at a temperature of 80°C and a stirring speed of 500 r / min to obtain the eutectic solvent; the molar ratio of choline chloride to oxalic acid is 1:1.

[0059] The wood fiber is poplar fiber; the wood fiber is oven-dried wood fiber with a particle size of 100 mesh to 120 mesh.

[0060] The mass ratio of the wood fiber to the eutectic solvent is 1:15; the mass ratio of the eutectic solvent to deionized water is 1:5.

[0061] II. Weighing:

[0062] Weigh out 30 parts of modified wood fiber, 61.2 parts of polylactic acid, 6.8 parts of polybutylene terephthalate-adipate, 1 part of polyethylene wax and 1 part of stearic acid by weight.

[0063] III. Melt Extrusion:

[0064] Modified wood fiber, polylactic acid, polybutylene terephthalate-adipate, polyethylene wax and stearic acid were mixed for 8 minutes at a stirring speed of 40 r / min. Then, using a screw extruder, the temperatures of each section of the twin-screw extruder were set as follows: from the feeding section to the die head, the temperatures of the first section were 160℃, the second section was 170℃, the third section was 175℃, the fourth section was 180℃, the fifth section was 175℃, the sixth section was 170℃, and the die head was 160℃. The mixture was then melt-composite at a stirring speed of 35 r / min. Finally, the mixture was cooled, crushed and granulated to a particle size of less than 3 mm and dried to obtain the modified wood fiber / polylactic acid composite material.

[0065] IV. Wire Preparation:

[0066] Using a single-screw extruder, the temperatures of each section of the single-screw extruder are set. From the feeding section to the die head, the temperature of the first section is 165℃ and the temperature of the second section is 180℃. Then, under the condition that the main machine speed is 30r / min, the modified wood fiber / polylactic acid composite material is extruded. Finally, it is water-cooled and traction-wound to obtain the modified wood fiber / polylactic acid composite wire.

[0067] The diameter of the modified wood fiber / polylactic acid composite wire prepared in step four is 1.75±0.05mm.

[0068] Example 2: This example differs from Example 1 in that, in step 2, 40 parts by weight of modified wood fiber, 52.2 parts by weight of polylactic acid, 5.8 parts by weight of polybutylene terephthalate-adipate, 1 part by weight of polyethylene wax, and 1 part by weight of stearic acid are weighed. Everything else is the same as in Example 1.

[0069] Example 3: This example differs from Example 1 in that, in step 2, 50 parts by weight of modified wood fiber, 43.2 parts by weight of polylactic acid, 4.8 parts by weight of polybutylene terephthalate-adipate, 1 part by weight of polyethylene wax, and 1 part by weight of stearic acid are weighed. Everything else is the same as in Example 1.

[0070] Example 4: This example differs from Example 1 in that, in step 2, 60 parts by weight of modified wood fiber, 34.2 parts by weight of polylactic acid, 3.8 parts by weight of polybutylene terephthalate-adipate, 1 part by weight of polyethylene wax, and 1 part by weight of stearic acid are weighed. Everything else is the same as in Example 1.

[0071] Comparative Experiment 1: This comparative experiment differs from Example 1 in that: in step 2, the modified wood fiber is replaced with wood fiber; the wood fiber is poplar fiber; the wood fiber is oven-dried wood fiber with a particle size of 100-120 mesh; step 4 yields wood fiber / polylactic acid composite wire. Everything else is the same as in Example 1.

[0072] Comparative Experiment 2: This comparative experiment differs from Example 2 in that: in step 2, the modified wood fiber is replaced with wood fiber; the wood fiber is poplar fiber; the wood fiber is oven-dried wood fiber with a particle size of 100-120 mesh; step 4 yields wood fiber / polylactic acid composite wire. Everything else is the same as in Example 2.

[0073] Comparative Experiment 3: This comparative experiment differs from Example 3 in that: in step two, the modified wood fiber is replaced with wood fiber; the wood fiber is poplar fiber; the wood fiber is oven-dried wood fiber with a particle size of 100-120 mesh; step four yields wood fiber / polylactic acid composite wire. Everything else is the same as in Example 3.

[0074] Figure 1This is a comparison chart of the percentage composition of lignocellulose before and after modification in step one of Example 1. As shown in the chart, compared to the original lignocellulose, the modified lignocellulose has a higher relative cellulose content (55.0%), a lower relative hemicellulose content (8%), and a lignin content (21.58%). This change is mainly due to the H⁺ generated by the dissociation of oxalic acid, which directionally hydrolyzes the glycosidic bonds and acetyl groups in the hemicellulose, causing it to dissolve. Cellulose, however, is retained due to the stability of its crystalline regions and the lack of easily hydrolyzable groups. Simultaneously, DES can break the ether bonds between phenylpropane units, causing lignin depolymerization and dissolution. The addition of deionized water increases the polarity of the system, disrupts the DES hydrogen bond network, and reduces the solubility of lignin. This leads to regeneration and deposition on the fiber surface through π–π stacking and hydrogen bonding, ultimately resulting in fibers with a surface covered in regenerated lignin.

[0075] Figure 2 The figures show the XRD patterns of lignocellulose before and after modification in step one of Example 1. As can be seen from the figures, DES treatment did not change the crystal structure of cellulose. The increased crystallinity may be due to the effective removal of some amorphous components of hemicellulose by DES, and the synergistic effect of the hydrogen bond network formed between regenerated lignin and cellulose.

[0076] Table 1

[0077]

[0078] As shown in the table, tensile tests were conducted on the highly filled wood-plastic composite filaments according to ISO 527-2 standard, and the impact properties of printed standard parts (printing conditions as shown in Table 2) were tested according to ASTM D6110 standard. When the wood fiber content was 30wt%, 40wt%, and 50wt%, the tensile strength of the modified wood fiber / polylactic acid composite filaments increased by 45.9%, 78.5%, and 99.1%, respectively, and the impact properties increased by 74.2%, 29.9%, and 61.5%, respectively, compared with the unmodified group. At the highest filling amount, the modified wood fiber / polylactic acid composite material still exhibited good tensile strength (20.81 MPa) and impact resistance (2.71 KJ / m²). 2 This study demonstrates that modified wood fibers exhibit good compatibility and dispersibility in a polylactic acid matrix, effectively improving stress transfer and resistance to damage in highly filled and complex printed structures.

[0079] Figure 3The melt flow rate (MFI) curves are shown for the modified wood fiber / polylactic acid composite materials prepared in step three of Examples 1 to 4 and the wood fiber / polylactic acid composite materials prepared in step three of Comparative Experiments 1 to 3. All samples were tested according to ISO 1133-1 standards at a temperature of 190℃ and a load of 2.16 kg, with each sample tested five times. The average melt flow rates for Comparative Experiments 1 to 3 were 6.302 g / 10 min, 3.836 g / 10 min, and 2.464 g / 10 min, respectively, while the average melt flow rates for Examples 1 to 3 were 10.278 g / 10 min, 7.428 g / 10 min, and 5.198 g / 10 min, respectively. MFI directly reflects the flowability of the material during extrusion processing. A high MFI value can reduce material wear on the printing nozzle and improve interlayer melt diffusion, thus resulting in better interlayer bonding quality and printing accuracy. Compared with the unmodified wood fiber / polylactic acid composite material, the modified composite filament has a higher MFI value; and the melt flow rate of commercially available printing consumables under the same test conditions is 5g / 10min~7g / 10min. This result confirms that the modified wood fiber / polylactic acid composite material has good processability and printability.

[0080] Figure 4 The image shows a physical picture of the modified wood fiber / polylactic acid composite wire prepared in Example 2. Figure 5 The image shows an S-shaped hook 3D printed using the modified wood fiber / polylactic acid composite filament prepared in Example 2. As shown in the image, the S-shaped hook weighs 1.96g and can support an item weighing 5kg. Figure 6 The images show actual leaf-shaped products 3D printed using the modified wood fiber / polylactic acid composite filament prepared in Example 2 and the wood fiber / polylactic acid composite filament prepared in Comparative Experiment 2. As can be seen from the images, the modified wood fiber / polylactic acid composite filament has better printing stability, and its products have a smooth surface, clear outline, and complete shape, exhibiting high dimensional accuracy and low surface roughness. This shows that products printed with high-content wood-plastic composite filament have good processability and printability, and have certain application prospects.

[0081] The printing conditions for 3D printed impact test specimens, S-shaped hooks, and leaf-shaped products made from modified wood fiber / polylactic acid composite filaments and wood fiber / polylactic acid composite filaments are shown in Table 2:

[0082] Table 2

[0083]

Claims

1. A method for preparing a highly filled wood-plastic composite printing filament, characterized in that... It is done in the following steps: I. Modification of wood fibers: Wood fibers are added to a eutectic solvent and heated and stirred to obtain a mixture. The mixture is then added to deionized water and stirred. The solid fibers are then separated, washed, and dried to obtain modified wood fibers. The eutectic solvent is composed of choline chloride and oxalic acid; II. Weighing: Weigh 10 to 60 parts of modified wood fiber, 30 to 85 parts of polylactic acid, 1 to 3 parts of polyethylene wax and 1 to 3 parts of stearic acid according to the mass ratio of polybutylene terephthalate to polylactic acid of 1:(6 to 9). III. Melt Extrusion: Modified wood fiber, polylactic acid, polybutylene terephthalate, polyethylene wax and stearic acid are mixed evenly, then melt-composite, and finally cooled, crushed and granulated and dried to obtain modified wood fiber / polylactic acid composite material. IV. Wire Preparation: Modified wood fiber / polylactic acid composite material was extruded using a single screw extruder, followed by water cooling and traction winding to obtain a highly filled wood-plastic composite printing filament.

2. The method for preparing a highly filled wood-plastic composite printing filament according to claim 1, characterized in that... The eutectic solvent mentioned in step one is prepared according to the following steps: choline chloride and oxalic acid are mixed, and then stirred until uniform and transparent at a temperature of 80℃~100℃ and a stirring speed of 500r / min~1500r / min to obtain the eutectic solvent; the molar ratio of choline chloride to oxalic acid is 1:(0.5~3).

3. The method for preparing a highly filled wood-plastic composite printing filament according to claim 1, characterized in that... The total mass fraction of the modified wood fiber, polylactic acid, polybutylene terephthalate-adipate, polyethylene wax and stearic acid mentioned in step one is 100 parts; the wood fiber mentioned in step one is one or a mixture of several of poplar fiber, rice husk powder, bamboo powder, straw powder, fruit shell powder and sugarcane bagasse; the wood fiber mentioned in step one is oven-dried wood fiber with a particle size of 80 mesh to 120 mesh.

4. The method for preparing a highly filled wood-plastic composite printing filament according to claim 1, characterized in that... The mass ratio of wood fiber to eutectic solvent in step one is 1:(10~30); the mass ratio of eutectic solvent to deionized water in step one is 1:(5~8).

5. The method for preparing a highly filled wood-plastic composite printing filament according to claim 1, characterized in that... In step one, wood fibers are added to a eutectic solvent and heated and stirred for 2 to 4 hours at a temperature of 80℃ to 110℃ and a stirring speed of 500 r / min to 1500 r / min to obtain a mixture. The mixture is then added to deionized water and stirred for 3 to 5 hours at a temperature of 20℃ to 60℃ and a stirring speed of 500 r / min to 1500 r / min. The solid fibers are then separated and washed until neutral, and finally dried until the moisture content is below 3% to obtain modified wood fibers.

6. The method for preparing a highly filled wood-plastic composite printing filament according to claim 1, characterized in that... In step three, under a stirring speed of 20 r / min to 50 r / min, modified wood fiber, polylactic acid, polybutylene terephthalate-adipate, polyethylene wax and stearic acid are mixed for 5 min to 10 min. Then, using a torque rheometer or screw extruder, the mixture is melt-composite at a temperature of 155℃ to 185℃ and a rotation speed of 30 r / min to 60 r / min. Finally, the mixture is cooled, crushed and granulated to a particle size of less than 3 mm and dried to obtain the modified wood fiber / polylactic acid composite material.

7. The method for preparing a highly filled wood-plastic composite printing filament according to claim 6, characterized in that... When using a screw extruder, the temperatures of each section of the screw extruder are set as follows: from the feeding section to the die head, the temperatures are: Zone 1: 150℃~180℃, Zone 2: 155℃~185℃, Zone 3: 160℃~185℃, Zone 4: 165℃~185℃, Zone 5: 170℃~185℃, Zone 6: 160℃~185℃, and the die head temperature: 155℃~185℃. Then, the extruder is melt-compounded at a speed of 30r / min~60r / min.

8. The method for preparing a highly filled wood-plastic composite printing filament according to claim 1, characterized in that... In step four, the modified wood fiber / polylactic acid composite material is extruded using a single screw extruder at a temperature of 160℃~180℃ and a main machine speed of 20r / min~60r / min.

9. The method for preparing a highly filled wood-plastic composite printing filament according to claim 1, characterized in that... In step four, the temperatures of each section of the single-screw extruder are set. From the feeding section to the die head, the temperature of zone one is 150℃~170℃ and the temperature of zone two is 160℃~180℃. Then, the modified wood fiber / polylactic acid composite material is extruded under the condition that the main machine speed is 20r / min~60r / min.

10. The method for preparing a highly filled wood-plastic composite printing filament according to claim 1, characterized in that... The diameter of the highly filled wood-plastic composite printing filament prepared in step four is 1.60mm~1.80mm.

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