Net plant fiber reinforced polylactic acid composite material forming equipment and method

Abstract

The application discloses a kind of net plant fiber reinforced polylactic acid composite forming equipment, including melt plasticizing device, casting roll, forming roller, longitudinal negative pressure guide pipe, transverse negative pressure guide pipe, press roller, dynamic press roller, dynamic hydraulic cylinder, guide roller, winding roller, the application can continuously fast weave the net reinforcing structure of hemp fiber, increase periodic mechanical vibration and promote the penetration efficiency of polylactic acid melt between net hemp fiber, also disclose a kind of net plant fiber reinforced polylactic acid composite forming method, the forming composite material produced has net hemp fiber skeleton and polylactic acid layer wrapped net hemp fiber gap and surface, can increase the comprehensive mechanical strength of composite material, also can solve the defect problem that traditional fiber reinforced polymer resin composite material is due to high length-diameter ratio fiber orientation degree, material mechanical property presents anisotropy.

Description

Technical Field

[0001] This invention relates to the field of equipment and methods for molding polymer composite materials, specifically to equipment and methods for molding polylactic acid composite materials reinforced with mesh plant fibers. Background Technology

[0002] Bio-based composite materials are gaining popularity due to their low-carbon, environmentally friendly, and biodegradable properties, and are being increasingly widely used in industrial and civilian fields to replace traditional petroleum-based plastics, showing excellent development and application prospects. However, these materials have relatively low mechanical strength, which cannot yet meet the needs of most application scenarios, especially since their rapid degradation performance accelerates the decline of their mechanical properties.

[0003] Currently, the most widely used and relatively mature fully biodegradable materials include copolymers of polylactic acid, butylene adipate, and butylene terephthalate. Methods to improve the mechanical properties of these materials mainly include inorganic particle filling and high aspect ratio mineral particle / fiber reinforcement. High aspect ratio fibers offer superior reinforcement; however, during the composite processing of high aspect ratio fibers and matrix resins, the fibers can fracture and become highly oriented under shear force. This high orientation imparts a directional, or anisotropic, mechanical property to the composite material. This anisotropy can lead to mechanical property defects in a specific direction during use, affecting the composite's performance.

[0004] Patent CN103102660B discloses a hemp fiber / polylactic acid biodegradable composite material and its preparation method. The material of this invention is made of the following components in weight percentage: 60~85wt% polylactic acid, 10~35wt% hemp fiber, 0.1~5wt% coupling agent, 0.1~1wt% antioxidant, 0.1~1wt% lubricant and 0.2~2wt% heat stabilizer. The preparation method of the material of this invention is as follows: 10-35 wt% of hemp fiber after surface flame retardant treatment, 60-85 wt% of polylactic acid after drying, 0.1-1 wt% of antioxidant, 0.1-1 wt% of lubricant, and 0.2-2 wt% of heat stabilizer are mixed uniformly at room temperature in a high-speed mixer; then, melt extrusion granulation is performed in a twin-screw extruder, with an extrusion temperature of 180-220℃ and a screw speed of 50-250 r / min; then, injection molding is performed at an injection temperature of 180-220℃ to obtain a hemp fiber / polylactic acid biodegradable composite material. During the composite processing, the high aspect ratio fibers will break and highly oriented under shear force. The anisotropy of mechanical properties causes mechanical property defects in a certain direction during the use of the composite material, affecting its performance. Summary of the Invention

[0005] To address the problems mentioned in the background section, this invention provides a molding equipment and method for polylactic acid composite materials reinforced with mesh plant fibers, thereby solving the existing problems.

[0006] The technical solution adopted in this invention is:

[0007] A molding equipment for a mesh plant fiber reinforced polylactic acid composite material includes a melt plasticizing device for melting and plasticizing a polylactic acid matrix material. A casting roller is provided below the melt plasticizing device, and a forming roller is provided on one side of the casting roller. A longitudinal negative pressure conduit and a transverse negative pressure conduit for conveying continuous hemp fibers are provided above the forming roller. Both the longitudinal negative pressure conduit and the transverse negative pressure conduit can move along the axial direction of the forming roller. A pressure roller is provided obliquely above the forming roller, and a dynamic pressure roller is provided on one side of the forming roller. The forming roller and the dynamic pressure roller are connected by a dynamic hydraulic cylinder. A guide roller and a take-up roller are provided on one side of the dynamic pressure roller.

[0008] Furthermore, the melting and plasticizing device includes a motor, a reducer, a mixing screw, and a casting die.

[0009] Furthermore, the angle between the longitudinal negative pressure conduit and the transverse negative pressure conduit and the forming roller axis can be adjusted, and their moving speed can be controlled.

[0010] Furthermore, the longitudinal negative pressure conduit includes a three-way conduit, an air intake port, a fiber guide port, and a fiber inlet port. A heating device is provided on the outside of the longitudinal negative pressure conduit. A suction fan is provided at the air intake port. A mesh is provided between the air intake port and the fiber inlet port, and at the junction of the three-way conduit. The suction fan draws in air, which enters from the fiber inlet port and exits from the air intake port. The hemp fibers are output outward from the fiber inlet port and guided by the fiber guide port. The longitudinal negative pressure conduit has the same structure as the transverse negative pressure conduit.

[0011] A method for molding a polylactic acid composite material reinforced with mesh plant fibers, wherein the above-mentioned molding equipment for polylactic acid composite materials reinforced with mesh plant fibers is used.

[0012] Furthermore, it includes the following steps:

[0013] S1: The polylactic acid matrix material is melted and plasticized in a melt plasticizing device, and the polylactic acid melt sheet with a thickness of 0.3-2mm is extruded through a casting die.

[0014] S2: The longitudinal negative pressure duct and the transverse negative pressure duct suck in and export the hemp fibers that have been cut evenly and are less than 1.6m in length for continuous longitudinal and transverse laying. The exported hemp fibers come into contact with and adhere to the polylactic acid melt sheet on the forming roller.

[0015] S3: Hemp fibers and polylactic acid melt sheets laid out longitudinally and transversely are pressed together by pressure rollers;

[0016] S4: Then enter between the forming roller and the dynamic pressure roller. The dynamic pressure roller presses the hemp fibers into the polylactic acid melt and promotes the penetration of the polylactic acid melt between the network hemp fibers under the action of the dynamic hydraulic cylinder.

[0017] S5: After cooling, it passes through the guide roller and is wound up at the take-up roller to complete the preparation of the molded composite material.

[0018] Furthermore, in step S2, the gas temperature of the longitudinal negative pressure conduit and the transverse negative pressure conduit is controlled at 150-230℃, and the temperature range of the polylactic acid melt sheet on the forming roller is 160-200℃.

[0019] Furthermore, in step S4, the amplitude of the dynamic hydraulic cylinder is between 0.1-1mm, and the frequency is between 5-30Hz.

[0020] Furthermore, in step S2, the hemp fibers discharged from the longitudinal negative pressure conduit are evenly laid on the polylactic acid melt sheet along the circumference of the forming roller as the forming roller rotates. After completing one round of laying, the longitudinal negative pressure conduit moves a certain distance along the axial direction of the forming roller to lay the next set of hemp fibers. After the transverse negative pressure conduit adheres the first set of hemp fibers to the polylactic acid melt sheet, it quickly retracts along the axial direction of the forming roller to complete the laying of a set of hemp fibers, and then returns to the initial position to lay the next set of hemp fibers. This process is repeated to achieve continuous longitudinal and transverse laying of hemp fibers.

[0021] Furthermore, the molded composite material in step S5 includes a mesh hemp fiber skeleton and a polylactic acid layer that wraps the gaps and surface of the mesh hemp fiber skeleton. The mesh hemp fiber skeleton is formed by continuous hemp fibers with warp and weft intersections.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] (1) By using a woven mesh hemp fiber structure as the reinforcing component of the composite material, the negative influence of the anisotropy of the mechanical properties of the composite material caused by the high aspect ratio fiber orientation is eliminated, and the isotropy of the long fiber reinforced polylactic acid composite material is realized.

[0024] (2) An automatic weaving device for hemp fibers was invented, which can continuously and quickly weave a mesh-reinforced structure of hemp fibers, and at the same time realize the automatic adjustment of the fiber spacing in the warp and weft directions;

[0025] (3) By increasing periodic mechanical vibration at the pressure roller position of the multi-roller laminating device, the penetration efficiency of polylactic acid melt between the reticulated hemp fibers is improved, the interfacial interaction between hemp fibers and polylactic acid melt is enhanced, and the mechanical properties of the composite material are improved.

[0026] (4) After the hemp fiber is fully coated by the polylactic acid matrix, its contact with water is greatly reduced. The hemp fiber can maintain a high mechanical strength for a long time without decay in the anhydrous state, thereby indirectly reducing the decay rate of the mechanical properties of the composite material and extending the service life of the composite material. Attached Figure Description

[0027] Figure 1 A schematic diagram of a molding equipment for a mesh-like plant fiber reinforced polylactic acid composite material;

[0028] Figure 2 This is a schematic diagram of the longitudinal and transverse negative pressure conduits in a molding equipment for a mesh-like plant fiber reinforced polylactic acid composite material.

[0029] Figure 3 This is a schematic diagram of the longitudinal negative pressure conduit and the transverse negative pressure conduit moving device in a molding equipment for a mesh plant fiber reinforced polylactic acid composite material.

[0030] The components are: 1. Motor; 2. Reducer; 3. Mixing screw; 4. Casting die; 5. Casting roller; 6. Longitudinal negative pressure guide; 7. Transverse negative pressure guide; 8. Forming roller; 9. Pressure roller; 10. Dynamic hydraulic cylinder; 11. Dynamic pressure roller; 12. Guide roller; 13. Polylactic acid melt sheet; 14. Take-up roller; 15. Air intake; 16. Fiber guide; 17. Mesh; 18. Fiber inlet; 19. Fixing screw; 20. Drive screw; 21. Gearbox; 22. Servo motor. Detailed Implementation

[0031] To clearly illustrate the technical features of this solution, the present invention will be described in detail below through specific embodiments and in conjunction with the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application; however, this application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited to the specific embodiments disclosed below. Furthermore, it should be understood in the description of this application that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified. In this application, unless otherwise explicitly specified and limited, the terms "installed," "connected," "linked," "fixed," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. In this application, unless otherwise explicitly specified and limited, "on" or "below" a second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In the description of this specification, references to terms such as "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples.

[0032] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0033] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods.

[0034] Example 1

[0035] Please see Figures 1 to 2 An embodiment of the present invention provides a molding equipment for a mesh plant fiber reinforced polylactic acid composite material, comprising a melting and plasticizing device, a casting roller 5, a molding roller 8, a longitudinal negative pressure conduit 6, a transverse negative pressure conduit 7, a pressure roller 9, a dynamic pressure roller 11, a dynamic hydraulic cylinder 10, a guide roller 12, and a take-up roller 14.

[0036] The melt plasticizing device melts and plasticizes the polylactic acid matrix material. The melt plasticizing device includes a motor 1, a reducer 2, a mixing screw 3, and a casting die 4. After the polylactic acid matrix enters the mixing screw 3, it is continuously melted under a certain processing temperature and the shearing and conveying action of the mixing screw 3. The molten polylactic acid enters the casting die 4. This process adopts general melt plasticizing technology, which will not be described in detail here. A polylactic acid melt sheet 13 with a thickness of 0.3-2mm is extruded through the casting die 4.

[0037] The casting roller 5, forming roller 8, dynamic pressure roller 11, and winding roller 14 are all actively driven rollers. The casting roller 5 is located below the melting and plasticizing device, and the forming roller 8 is located on one side of the casting roller 5.

[0038] Above the forming roller 8 are a longitudinal negative pressure conduit 6 and a transverse negative pressure conduit 7 for conveying continuous hemp fibers. The longitudinal negative pressure conduit 6 includes a three-way conduit, an air intake 15, a fiber guide 16, and a fiber inlet 18. A heating device is installed on the outside of the longitudinal negative pressure conduit 6. The air intake 15 is equipped with a suction fan. A mesh 17 is provided between the air intake 15 and the fiber inlet 18, at the junction of the three-way conduit. The suction fan draws in air, which enters from the fiber inlet 18, is heated, passes through the mesh 17, and is then extracted through the air intake 15. This creates a negative pressure inside the negative pressure conduit. Under the action of negative pressure, the hemp fibers are output from the fiber inlet 18 and guided by the fiber guide 16. The longitudinal negative pressure conduit 6 and the transverse negative pressure conduit 7 have the same structure. Both the longitudinal negative pressure conduit 6 and the transverse negative pressure conduit 7 can move along the axial direction of the forming roller 8. The conduit is fixedly connected to a servo motor 22, which controls the movement of the conduit in different directions. The hemp fibers can be transported through a movable negative pressure conduit, and under negative pressure, the hemp fibers can be tightly adhered to the polylactic acid melt sheet 13.

[0039] As the forming roller 8 rotates, the hemp fibers are evenly laid along the circumference of the forming roller 8. After one round of laying is completed, the longitudinal negative pressure guide 6 moves a certain distance along the axial direction of the forming roller 8 to lay the next set of hemp fibers. After the transverse negative pressure guide 7 adheres the first set of hemp fibers to the polylactic acid melt sheet 13, it quickly retracts along the axial direction of the forming roller 8 to complete the laying of a set of hemp fibers, and then returns to the initial position to lay the next set of hemp fibers. This process is repeated to achieve continuous laying of hemp fibers.

[0040] A pressure roller 9 is positioned diagonally above the forming roller 8. The pressure roller 9 presses the hemp fibers and the polylactic acid melt sheet 13 together, strengthening their bonding force. A dynamic pressure roller 11 is located on one side of the forming roller 8. The forming roller 8 and the dynamic pressure roller 11 are connected by a dynamic hydraulic cylinder 10. The dynamic pressure roller 11 applies a fixed pressure to the composite sheet, pressing the hemp fibers into the polylactic acid melt. The melt, with its good fluidity, also flows to the surface of the sheet material, further coating the hemp fibers. Furthermore, the dynamic pressure roller 11 can obtain an additional sinusoidal dynamic pressure through the dynamic hydraulic cylinder 10. By adjusting the amplitude and frequency of the dynamic pressure, the penetration of the polylactic acid melt between the network of hemp fibers can be promoted, enhancing the interfacial interaction between the polylactic acid molecules and the hemp fiber surface, thereby improving the strength of the composite material.

[0041] The dynamic pressure roller 11 is provided with a guide roller 12 and a take-up roller 14 on one side, and the guide roller 12 and the take-up roller 14 complete the winding of the molded composite material.

[0042] Example 2

[0043] Please see Figures 1 to 3 An embodiment of the present invention provides a molding equipment for a mesh plant fiber reinforced polylactic acid composite material, comprising a melting and plasticizing device, a casting roller 5, a molding roller 8, a longitudinal negative pressure conduit 6, a transverse negative pressure conduit 7, a pressure roller 9, a dynamic pressure roller 11, a dynamic hydraulic cylinder 10, a guide roller 12, and a take-up roller 14.

[0044] The melt plasticizing device melts and plasticizes the polylactic acid matrix material. The melt plasticizing device includes a motor 1, a reducer 2, a mixing screw 3, and a casting die 4. After the polylactic acid matrix enters the mixing screw 3, it is continuously melted under a certain processing temperature and the shearing and conveying action of the mixing screw 3. The molten polylactic acid enters the casting die 4. This process adopts general melt plasticizing technology, which will not be described in detail here. A polylactic acid melt sheet 13 with a thickness of 0.3-2mm is extruded through the casting die 4.

[0045] The casting roller 5, forming roller 8, dynamic pressure roller 11, and winding roller 14 are all actively driven rollers. The casting roller 5 is located below the melting and plasticizing device, and the forming roller 8 is located on one side of the casting roller 5.

[0046] Above the forming roller 8 are a longitudinal negative pressure conduit 6 and a transverse negative pressure conduit 7 for conveying continuous hemp fibers. The longitudinal negative pressure conduit 6 includes a three-way conduit, an air intake 15, a fiber guide 16, and a fiber inlet 18. A heating device is installed on the outside of the longitudinal negative pressure conduit 6. The air intake 15 is equipped with a suction fan. A mesh 17 is provided between the air intake 15 and the fiber inlet 18, at the junction of the three-way conduit. The suction fan draws in air, which enters from the fiber inlet 18, is heated, passes through the mesh 17, and is then extracted through the air intake 15. This creates a negative pressure inside the negative pressure conduit. Under the action of negative pressure, the hemp fibers are output from the fiber inlet 18 and guided by the fiber guide 16. The longitudinal negative pressure conduit 6 and the transverse negative pressure conduit 7 have the same structure. Both the longitudinal negative pressure conduit 6 and the transverse negative pressure conduit 7 can move along the axial direction of the forming roller 8. The conduit is fixedly connected to a servo motor 22, which controls the movement of the conduit in different directions. The hemp fibers can be transported through a movable negative pressure conduit, and under negative pressure, the hemp fibers can be tightly adhered to the polylactic acid melt sheet 13.

[0047] Furthermore, the angles between the longitudinal negative pressure conduit 6 and the transverse negative pressure conduit 7 and the forming roller 8 along their axes can be adjusted using the fixing screws 19 connected to them. By adjusting the angles between the longitudinal and transverse negative pressure conduits and the forming roller 8 along their axes, different structures of hemp fibers can be interlaced to form a mesh-like hemp fiber reinforced structure with an interlaced pattern. The moving speed of the longitudinal negative pressure conduit 6 and the transverse negative pressure conduit 7 can be controlled by the drive screw 20 and the servo motor 22 connected to them. By controlling their moving speed, the distribution density of hemp fibers in the longitudinal and transverse directions can be adjusted, that is, the spacing between different hemp fibers in the mesh structure.

[0048] As the forming roller 8 rotates, the hemp fibers are evenly laid along the circumference of the forming roller 8. After one round of laying is completed, the longitudinal negative pressure guide 6 moves a certain distance along the axial direction of the forming roller 8 to lay the next set of hemp fibers. After the transverse negative pressure guide 7 adheres the first set of hemp fibers to the polylactic acid melt sheet 13, it quickly retracts along the axial direction of the forming roller 8 to complete the laying of a set of hemp fibers, and then returns to the initial position to lay the next set of hemp fibers. This process is repeated to achieve continuous laying of hemp fibers.

[0049] A pressure roller 9 is positioned diagonally above the forming roller 8. The pressure roller 9 presses the hemp fibers and the polylactic acid melt sheet 13 together, strengthening their bonding force. A dynamic pressure roller 11 is located on one side of the forming roller 8. The forming roller 8 and the dynamic pressure roller 11 are connected by a dynamic hydraulic cylinder 10. The dynamic pressure roller 11 applies a fixed pressure to the composite sheet, pressing the hemp fibers into the polylactic acid melt. The melt, with its good fluidity, also flows to the surface of the sheet material, further coating the hemp fibers. Furthermore, the dynamic pressure roller 11 can obtain an additional sinusoidal dynamic pressure through the dynamic hydraulic cylinder 10. By adjusting the amplitude and frequency of the dynamic pressure, the penetration of the polylactic acid melt between the network of hemp fibers can be promoted, enhancing the interfacial interaction between the polylactic acid molecules and the hemp fiber surface, thereby improving the strength of the composite material.

[0050] The dynamic pressure roller 11 is provided with a guide roller 12 and a take-up roller 14 on one side, and the guide roller 12 and the take-up roller 14 complete the winding of the molded composite material.

[0051] Example 3

[0052] Please see Figures 1 to 3 A method for molding a polylactic acid composite material reinforced with mesh plant fibers, wherein the molding equipment for the polylactic acid composite material reinforced with mesh plant fibers described in Example 1 above is used.

[0053] Includes the following steps:

[0054] S1: The polylactic acid matrix material is melted and plasticized in a melt plasticizing device, and polylactic acid melt sheet 13 with a thickness of 0.3-2mm is extruded through the casting die 4;

[0055] S2: The longitudinal negative pressure conduit 6 and the transverse negative pressure conduit 7 draw in and guide uniformly cut hemp fibers with a length of less than 1.6m for continuous longitudinal and transverse laying. In step S2, the hemp fibers guided by the longitudinal negative pressure conduit 6 are evenly laid on the polylactic acid melt sheet 13 along the circumference of the forming roller 8 as the forming roller 8 rotates. After completing one round of laying, the longitudinal negative pressure conduit 6 moves a certain distance along the axial direction of the forming roller 8 to lay the next group of hemp fibers; the transverse negative pressure conduit 7 carries the first group of hemp fibers... After adhering to the polylactic acid melt sheet 13, the fibers are quickly retracted along the axial direction of the forming roller 8 to complete the laying of a set of hemp fibers. Then, the fibers return to the initial position to lay the next set of hemp fibers. This process is repeated to achieve continuous longitudinal and transverse laying of hemp fibers. The gas temperature of the longitudinal negative pressure conduit 6 and the transverse negative pressure conduit 7 is controlled at 150-230℃. The hemp fibers are brought into contact with and adhered to the polylactic acid melt sheet 13 on the forming roller 8. The temperature range of the polylactic acid melt sheet 13 on the forming roller 8 is 160-200℃.

[0056] S3: The longitudinally and transversely laid hemp fibers and polylactic acid melt sheets 13 are pressed by the pressure roller 9;

[0057] S4: Then enter between the forming roller 8 and the dynamic pressure roller 11. The dynamic pressure roller 11 presses the hemp fibers into the polylactic acid melt and promotes the penetration of the polylactic acid melt between the network hemp fibers under the action of the dynamic hydraulic cylinder 10. In step S4, the amplitude of the dynamic hydraulic cylinder 10 is between 0.1-1mm and the frequency is between 5-30Hz.

[0058] S5: After cooling, the material passes through the guide roller 12 and is wound up at the take-up roller 14 to complete the preparation of the molded composite material. The molded composite material in step S5 includes a mesh hemp fiber skeleton and a polylactic acid layer that wraps the gaps between the mesh hemp fiber skeleton and the surface. The mesh hemp fiber skeleton is formed by continuous hemp fibers with warp and weft intersections.

[0059] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for molding a polylactic acid composite material reinforced with mesh-like plant fibers, characterized in that, The method is based on molding equipment, which includes a melting and plasticizing device for melting and plasticizing polylactic acid matrix material. A casting roller is provided below the melting and plasticizing device, and a forming roller is provided on one side of the casting roller. A longitudinal negative pressure conduit and a transverse negative pressure conduit for conveying continuous hemp fibers are provided above the forming roller. Both the longitudinal negative pressure conduit and the transverse negative pressure conduit can move along the axial direction of the forming roller. A pressure roller is provided obliquely above the forming roller, and a dynamic pressure roller is provided on one side of the forming roller. The forming roller and the dynamic pressure roller are connected by a dynamic hydraulic cylinder. A guide roller and a take-up roller are provided on one side of the dynamic pressure roller. The longitudinal negative pressure conduit includes a three-way conduit, an air intake, a fiber guide, and a fiber inlet. A heating device is installed on the outside of the longitudinal negative pressure conduit. A suction fan is installed at the air intake. A mesh is provided between the air intake and the fiber inlet, at the junction of the three-way conduit. The suction fan draws in air, which enters through the fiber inlet and exits through the air intake. Hemp fibers are output from the fiber inlet and guided by the fiber guide. The longitudinal negative pressure conduit has the same structure as the transverse negative pressure conduit. The angle between the longitudinal and transverse negative pressure conduits and the forming roller axis can be adjusted, and their movement speed can be controlled. The steps include: S1: The polylactic acid matrix material is melted and plasticized in a melt plasticizing device, and the polylactic acid melt sheet with a thickness of 0.3-2mm is extruded through a casting die. S2: The longitudinal negative pressure duct and the transverse negative pressure duct suck in and export hemp fibers that have been cut evenly and are less than 1.6m in length for continuous longitudinal and transverse laying. The exported hemp fibers come into contact with and adhere to the polylactic acid melt sheet on the forming roller. The hemp fibers, guided by the longitudinal negative pressure conduit, are evenly laid on the polylactic acid melt sheet along the circumference of the forming roller as the forming roller rotates. After completing one round of laying, the longitudinal negative pressure conduit moves a certain distance along the axial direction of the forming roller to lay the next set of hemp fibers. After the transverse negative pressure conduit adheres the first set of hemp fibers to the polylactic acid melt sheet, it retracts along the axial direction of the forming roller to complete the laying of a set of hemp fibers, and then returns to the initial position to lay the next set of hemp fibers. This process is repeated to achieve continuous longitudinal and transverse laying of hemp fibers. S3: Hemp fibers and polylactic acid melt sheets laid out longitudinally and transversely are pressed together by pressure rollers; S4: Then enter between the forming roller and the dynamic pressure roller. The dynamic pressure roller presses the hemp fibers into the polylactic acid melt and promotes the penetration of the polylactic acid melt between the network hemp fibers under the action of the dynamic hydraulic cylinder. S5: After cooling, it passes through the guide roller and is wound up at the take-up roller to complete the preparation of the molded composite material.

2. The molding method for a mesh-like plant fiber reinforced polylactic acid composite material according to claim 1, characterized in that, The melting and plasticizing device includes a motor, a reducer, a mixing screw, and a casting die.

3. The molding method for a mesh-like plant fiber reinforced polylactic acid composite material according to claim 1, characterized in that, In step S2, the gas temperature of the longitudinal negative pressure conduit and the transverse negative pressure conduit is controlled at 150-230℃, and the temperature range of the polylactic acid melt sheet on the forming roller is 160-200℃.

4. The molding method for a mesh-like plant fiber reinforced polylactic acid composite material according to claim 1, characterized in that, In step S4, the amplitude of the dynamic hydraulic cylinder is between 0.1-1mm and the frequency is between 5-30Hz.

5. The molding method for a mesh-like plant fiber reinforced polylactic acid composite material according to claim 1, characterized in that, The molded composite material in step S5 includes a mesh hemp fiber skeleton and a polylactic acid layer that wraps the gaps between the mesh hemp fiber skeleton and the surface. The mesh hemp fiber skeleton is woven from continuous hemp fibers with warp and weft intersections.

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