Method and device for preparing special-shaped structure of plant fiber composite material

Abstract

The invention relates to the technical field of fiber composite material preparation, in particular to a preparation method and device of a plant fiber composite material special-shaped structure. The preparation method comprises the following steps: sequentially overlapping reinforced lining cloth, a plant fiber unit and demolding cloth, and impregnating the obtained laminated raw material to obtain a continuous plant fiber composite base material; then carrying out pre-forming treatment to obtain a pre-formed body; stripping the demolding cloth from the surface of the preform; and completely curing the pre-formed body after stripping the demolding cloth to obtain the plant fiber composite material special-shaped structure. The reinforced lining cloth, the plant fiber unit and the demolding cloth are sequentially overlapped to form the laminated raw material, the plant fiber unit serves as a middle layer, the reinforced lining cloth and the demolding cloth are located on the outer side, and effective combination of the reinforced lining cloth and the plant fiber unit is achieved through the gum dipping and preforming process; and pultrusion, pultrusion and pultrusion winding can be directly selected subsequently according to actual requirements, so that the problems of discontinuity of plant fibers and weak load bearing capacity of continuous fibers are solved.

Description

Technical Field

[0001] This invention relates to the field of fiber composite material preparation technology, and in particular to a method and apparatus for preparing irregular structures of plant fiber composite materials. Background Technology

[0002] Traditional continuous fiber reinforced composite material manufacturing processes, such as pultrusion, pultrusion braiding, and pultrusion winding, all use high-performance continuous fibers (such as glass fiber, carbon fiber, or basalt fiber) as reinforcement. The core of these processes lies in achieving efficient, automated, and large-scale composite material production through precise tension control of the continuous fibers, uniform resin impregnation, and thermal curing. Specifically, the pultrusion process involves pulling continuous fiber bundles through a resin impregnation tank and a heated mold to achieve continuous shaping and curing of oriented fibers. Pultrusion and pultrusion winding processes involve precisely weaving and winding continuous fiber yarns along a predetermined path onto the surface of a mandrel, forming a core-shell component after curing. These processes highly rely on the continuity of the fibers, the consistency of their mechanical properties, and the interfacial stability with the resin system. However, plant fibers, due to their inherent discontinuity, length and performance dispersion, and the weak load-bearing capacity of continuous fibers, are difficult to directly apply to the aforementioned high-efficiency, high-precision existing automated production lines. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a method and apparatus for preparing irregularly shaped structures of plant fiber composite materials. The method provided by this invention solves the problem that discontinuous or continuous plant fibers have weak load-bearing capacity, making it difficult to prepare irregularly shaped composite structures. The apparatus provided by this invention enables the automated production of irregularly shaped plant fiber composite materials.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing irregular structures of plant fiber composite materials, comprising the following steps: sequentially stacking reinforcing lining, plant fiber units and release fabric to obtain laminated raw materials; The laminated raw material is impregnated with resin to obtain a continuous plant fiber composite substrate; The continuous plant fiber composite substrate is pre-formed to obtain a pre-formed body with a release cloth on the surface; Peel the release fabric off the surface of the preform; The preform after the release fabric is peeled off is completely cured to obtain the irregular structure of the plant fiber composite material.

[0005] Preferably, before complete curing, the preform after the release fabric is peeled off is further subjected to adhesive injection.

[0006] Preferably, before the glue injection, the preform after the release fabric is peeled off is further subjected to tufting or winding; the tufting is: using the preform as the core material to weave a fiber covering layer on its outer side; the winding is: using the preform as the core material to wind a fiber covering layer on its outer side.

[0007] Preferably, the plant fiber unit includes one or more of bamboo fiber, thin bamboo strips, and hemp fiber; the thickness of the thin bamboo strips is 0.01~5 mm.

[0008] Preferably, the reinforcing lining is a fabric, a mesh, or a strip; the material of the reinforcing lining includes one or more of cotton fiber, bamboo fiber, chemical fiber, glass fiber, carbon fiber, and basalt substrate.

[0009] Preferably, the injection molding process is employed.

[0010] This invention provides a device for preparing irregular structures of plant fiber composite materials by implementing the preparation method described above. The device is characterized by including a raw material rack 1, an impregnation tank 2, a preforming device 3, a curing device 6, and a traction device 7. The devices are connected in sequence to realize continuous transmission and processing of raw materials. A shelf is provided between the raw material rack 1 and the impregnation tank 2 to receive and support the laminated raw materials.

[0011] Preferably, a glue injection machine 5 is also provided between the preforming device 3 and the curing device 6 for glue injection.

[0012] Preferably, a weaving machine 4 is also provided between the preforming device 3 and the glue injection machine 5 for weaving or winding the preform after the release fabric has been peeled off.

[0013] Preferably, a cutter 8 is also provided at the end of the traction device 7.

[0014] This invention provides a method for preparing a shaped structure of plant fiber composite material, comprising the following steps: sequentially stacking a reinforcing lining, plant fiber units, and a release fabric to obtain a laminated raw material; impregnating the laminated raw material with resin to obtain a continuous plant fiber composite substrate; preforming the continuous plant fiber composite substrate to obtain a preform with a release fabric on its surface; peeling the release fabric from the surface of the preform; and completely curing the preform after peeling off the release fabric to obtain the shaped structure of the plant fiber composite material. This invention uses a sandwich structure laminated raw material formed by sequentially stacking a reinforcing lining, plant fiber units, and a release fabric, with the plant fiber units as the middle layer and the reinforcing lining and release fabric on the outermost layer. Through impregnation and preforming processes, an effective combination of the reinforcing lining and plant fiber units is achieved. Subsequently, it can be directly selected for pultrusion, pultrusion braiding, and pultrusion winding according to actual needs, thereby solving the problems of discontinuity in plant fibers or the weak load-bearing capacity of continuous plant fibers.

[0015] Furthermore, by injecting glue into the preform, or by performing stretching / winding followed by glue injection, the present invention can form a coating layer on the outside of the preform, which protects the inner structure and effectively enhances the durability of the composite material irregular structure.

[0016] Furthermore, this invention employs resin transfer molding (RTM) during injection, which reduces bubble formation and significantly lowers the internal porosity of the material, thereby greatly improving the resin's wetting effect on plant fibers. Due to the high hygroscopicity and weak interfacial adhesion of plant fibers, resin typically exhibits poor wetting properties.

[0017] This invention provides an apparatus for preparing irregularly shaped structures of plant fiber composite materials using the above-described method. By integrating the various process steps, energy losses in material transfer and process connection in traditional step-by-step molding are reduced, thus optimizing energy consumption in the preparation process. Attached Figure Description

[0018] Figure 1 A schematic diagram of one structure of the apparatus for preparing irregular structures of plant fiber composite materials provided by the present invention; Figure 2 This is a schematic diagram of a raw material rack structure; Figure 3 This is a schematic diagram of the dispensing machine and curing device. Figure 4 This is a schematic diagram of the structure of the curing device die and the pultruded product; Figure 5 This is a schematic diagram of the basic structure of a partial preform; Figures 1-5In the diagram, 1 is the raw material rack, 1-1 is the release cloth, 1-2 is the plant fiber unit, 1-3 is the reinforcing lining, 2 is the impregnation tank, 3 is the preforming device, 4 is the weaving machine, 5 is the glue injection machine, 5-1 is the second vacuum pump, 5-2 is the A glue, 5-3 is the B glue, 6 is the curing device, 6-1 is the heating equipment, 6-2 is the die, 6-3 is the first vacuum pump, 7 is the traction device, and 8 is the cutting machine. Detailed Implementation

[0019] This invention provides a method for preparing irregular structures of plant fiber composite materials, comprising the following steps: The reinforcing lining, plant fiber units, and release fabric are stacked in sequence to obtain the laminated raw material; The laminated raw material is impregnated with resin to obtain a continuous plant fiber composite substrate; The continuous plant fiber composite substrate is pre-formed to obtain a pre-formed body; Peel the release fabric off the surface of the preform; The preform after the release fabric is peeled off is completely cured to obtain the irregular structure of the plant fiber composite material.

[0020] In this invention, the reinforcing lining preferably comprises fabrics, meshes, or strips made of cotton fiber, bamboo fiber, chemical fiber, glass fiber, carbon fiber, and basalt-based materials; the plant fiber unit preferably comprises one or more of bamboo fiber, thin bamboo strips, and hemp fiber; the thickness of the thin bamboo strip is preferably 0.01~5 mm. Specifically, the hemp fiber can be one or more of jute fiber, kenaf fiber, sisal fiber, and ramie fiber; the release fabric is preferably made of polytetrafluoroethylene, polyolefin, polyester, or nylon. In this invention, the plant fiber unit can be continuous or discontinuous; for example, the bamboo fiber can be continuous or discontinuous; the thin bamboo strip can be continuous or discontinuous. Generally, plant fibers are mostly discontinuous, but this invention also applies to continuous plant fibers. Even continuous plant fibers have relatively weak load-bearing capacity, and there is still a problem that they are difficult to directly apply to existing automated production lines. The method of this invention can solve the problem of discontinuous plant fibers or the weak load-bearing capacity of continuous plant fibers, which makes it difficult to prepare composite irregular structures.

[0021] In this invention, the reinforcing lining and release fabric serve as the outermost layers, while the plant fiber units form the middle layer, creating a sandwich composite structure. The reinforcing lining supports and reinforces the plant fibers; the release fabric facilitates the demolding of the preform. In this invention, the plant fiber units can be flexibly configured, allowing for single-layer, double-layer, or triple-layer designs, and can be further expanded to four, five, or six layers depending on actual performance requirements, thus achieving customized control over the function and structure of the continuous plant fiber composite substrate. This invention does not impose specific limitations on the individual dimensions of the plant fibers; dimensions are flexibly adaptable. The release fabric and reinforcing lining should be determined according to the specifications of the plant fiber units.

[0022] After obtaining the laminated raw material, the present invention impregnates the laminated raw material with resin to obtain a continuous plant fiber composite substrate.

[0023] In this invention, the laminated raw material is specifically transported to the impregnation tank 2 for impregnation under the traction of the traction device 7. This invention does not have special requirements for the traction speed; it only needs to be adapted to the material type and the actual production requirements for product efficiency and performance. Under conventional process conditions, the typical range for adjusting the traction speed is 0.01-0.5 m / min, to balance the processing effect of the substrate in the process with production continuity.

[0024] The present invention does not impose any special limitations on the composition of the adhesive solution used for impregnation (referred to as the first adhesive solution). It can be specifically adjusted according to the specific type of plant fiber and the target application scenario of the product. This is a conventional technical means in the field. In addition, there is no uniform standard for the impregnation process conditions (such as impregnation temperature, time, pressure, etc.). It is necessary to make adaptability settings according to the determined type and characteristics of the first adhesive solution to ensure the uniform wetting of each layer of raw materials by the first adhesive solution and the integrated composite effect. In embodiments of the present invention, the first adhesive solution is specifically an epoxy resin system, molten polypropylene, or phenolic resin; the epoxy resin system is prepared by adding diethylenetriamine (curing agent), glass microspheres (50 μm particle size), antioxidant 1010, and carboxyl-terminated nitrile rubber (toughening agent) to a liquid epoxy resin in a mass ratio of 100:20:25:5:10. The mixture is stirred at 300-400 r / min at 30-40°C until homogeneous, resulting in the epoxy resin system; the viscosity of the epoxy resin system is 500-800 mPa·s (below 35°C). The core objective of this invention through impregnation is to achieve integrated composite of release fabric, plant fiber units, and reinforcing lining, constructing a continuous plant fiber composite substrate (the release fabric will be recycled in subsequent processes).

[0025] After obtaining a continuous plant fiber composite substrate, the present invention pre-forms the continuous plant fiber composite substrate to obtain a preform with a release cloth on the surface; and peels the release cloth off the surface of the preform.

[0026] In this invention, the purpose of preforming is to complete the initial shape shaping. This invention does not impose special limitations on the conditions for preforming, but the preforming process conditions must be compatible with the type of first adhesive used in the aforementioned impregnation process: if a room-temperature curing adhesive is used, the preforming process can be completed at room temperature, relying on the adhesive's own room-temperature curing characteristics to achieve the initial composite fixation of each layer of raw materials; if a heat-curing adhesive is used, heating control is required to initiate the curing reaction of the adhesive, thereby achieving the integrated shaping of multiple layers of raw materials and laying the structural foundation for subsequent curing and molding processes.

[0027] In this invention, when the first adhesive is an epoxy resin system, the pre-forming temperature is preferably 60-70℃, the pressure is preferably 0.1-0.2MPa, and the time is preferably 0.5-1.5 hours. When the first adhesive is molten polypropylene, the pre-forming temperature is preferably 60-70℃, the pressure is preferably 0.1-0.3MPa, and the time is preferably 1-2 hours. When the first adhesive is phenolic resin, the pre-forming temperature is preferably 90-100℃, the pressure is preferably 0.3-0.5MPa, and the time is preferably 1-2 hours.

[0028] After obtaining the preform, the present invention peels off the release fabric from the surface of the preform, preferably by recycling the peeled release fabric, to obtain a preform with the release fabric removed, the basic local structure of which is as follows. Figure 5 As shown.

[0029] The preform after the release fabric is peeled off is completely cured to obtain the irregular structure of the plant fiber composite material.

[0030] In this invention, before complete curing, it is preferable to inject adhesive into the preform after peeling off the release fabric, or to perform tufting or winding of the preform after peeling off the release fabric before injecting adhesive, and finally perform complete curing. Alternatively, the preform after peeling off the release fabric can be directly subjected to complete curing.

[0031] In this invention, the adhesive used for injection (referred to as the second adhesive) can be a single-component adhesive or it can include adhesive A and adhesive B (i.e., a general term for a two-component composite adhesive system). Adhesive A and adhesive B need to be mixed before use. This invention does not impose fixed limitations on the specific type and dosage of the second adhesive. Specifically, the type of the second adhesive can be selected according to the performance requirements of the product (such as mechanical strength, weather resistance, curing rate, etc.).

[0032] In a specific embodiment, the second adhesive may specifically include a base resin, a curing agent, and a modifier; for example, adhesive A may include a base resin and some or all of the modifier, and adhesive B may include a curing agent and some or all of the modifier. In this invention, the base resin may specifically be polypropylene, polyethylene, epoxy resin, or silicone-based resin. In this invention, the modifier preferably includes one or more of polymerization inhibitors, functional agents, and interface promoters. The polymerization inhibitor is preferably a phenolic compound, a quinone compound, or an amine compound; the phenolic compound may specifically be hydroquinone or 2,6-di-tert-butyl-p-cresol; the quinone compound may be p-benzoquinone; and the amine compound may be diphenylamine. In this invention, the polymerization inhibitor mainly inhibits the polymerization reaction by capturing free radicals or reacting with active intermediates; the polymerization inhibitor imparts suitable storage and molding conditions to the prepreg. The functional agents preferably include one or more of the following: flame retardants (such as decabromodiphenyl ether, aluminum hydroxide), toughening agents (such as carboxyl-terminated nitrile rubber, polyethersulfone), diluents, fillers, colorants (such as carbon black, titanium dioxide), and antioxidants (such as hindered phenols, phosphites); these functional agents impart properties such as high tensile strength, high resilience, and high conductivity to the composite material. The interface accelerator is preferably one or more of the following: silane coupling agents (such as γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane), titanate coupling agents (such as isopropyltristearate titanate), and aluminate coupling agents; these interface accelerators can improve the performance of the composite material by improving the interfacial compatibility between the fiber and the resin.

[0033] The dosage requirements for each reagent should be determined comprehensively based on the curing characteristics of the adhesive system, the performance requirements of the composite material (such as mechanical strength, aging resistance, interfacial bonding strength, etc.), and process conditions (such as curing temperature and time): Resin, as the matrix phase, should be used in quantities sufficient to fully wet the preform and ensure the structural integrity of the product, typically accounting for 60-90% of the total adhesive mass; the amount of polymerization inhibitor is generally very low (usually 0.01-1% of the adhesive mass), just enough to inhibit premature curing of the adhesive during storage and pre-reaction stages; the amount of functional agents (such as flame retardants and toughening agents) needs to be adjusted according to the target functional strength, typically 1-10% of the resin mass; the amount of interfacial accelerator is typically 0.5-5% of the resin mass, based on ensuring effective chemical bonding at the fiber-resin interface.

[0034] In this invention, the braiding is preferably performed by weaving the preform as a core material onto its outer side to form a fiber covering layer; the winding is preferably performed by winding the preform as a core material onto its outer side to form a fiber covering layer. This invention does not have special requirements for the specific operations of the braiding and winding; well-known procedures in the art can be used.

[0035] This invention, by injecting glue into the preform or by performing stretching / winding followed by glue injection, can form a coating layer on the outside of the preform, which protects the inner structure and effectively enhances the durability of the composite material's irregular shape structure.

[0036] In this invention, when the dispensing process is involved, the fully curing process conditions need to be adapted to different types of dispensing adhesives (i.e., the second adhesive): if a room-temperature curing adhesive is used, the curing process can be carried out at room temperature, relying on the adhesive's own room-temperature curing characteristics to complete the curing reaction; if a heat-triggered curing adhesive is used, then heating control (e.g., controlling the curing environment temperature within the threshold range required for adhesive curing) is needed to provide the necessary energy for the adhesive curing reaction, ensuring the curing process proceeds fully and guaranteeing the final performance of the product. When the dispensing process is not involved, the fully curing process conditions can be based on a curing process well-known in the art, according to the composition of the first adhesive.

[0037] This invention provides a device for preparing irregular structures of plant fiber composite materials by implementing the preparation method described above, including a raw material rack 1, an impregnation tank 2, a preforming device 3, a curing device 6, and a traction device 7; the devices are connected in sequence to realize continuous transmission and processing of raw materials; a shelf is provided between the raw material rack 1 and the impregnation tank 2 for receiving and supporting the laminated raw materials.

[0038] The preparation apparatus provided by this invention includes a raw material rack 1; such as Figure 2 As shown, the raw material rack 1 provides a structural area for accommodating the release fabric 1-1, plant fiber units 1-2, and reinforcing lining 1-3. These structural areas are arranged in multiple layers from top to bottom, allowing for the stacking of each layer of raw materials. This invention does not impose any special requirements on the raw material rack 1; any raw material rack well-known in the art that can achieve the above functions is acceptable.

[0039] The preparation apparatus provided by this invention includes an impregnation tank 2. In this invention, the impregnation tank 2 contains a first adhesive solution for impregnation. Under the action of the traction device 7, the laminated raw material is transported to the impregnation tank 2, so that the raw material is fully impregnated with the adhesive solution.

[0040] In this invention, a shelf is provided between the raw material rack 1 and the impregnation tank 2 to receive and support the laminated raw materials. This invention does not impose any special requirements on the shelf; any shelf known in the art that can achieve the above functions is acceptable.

[0041] The preparation apparatus provided by the present invention includes a preforming device 3. The present invention does not impose any special limitations on the function of the preforming device 3, as long as it can provide the temperature for pre-curing (i.e., preforming). The die structure is also not subject to any special limitations, and can be a circular structure, a rounded square structure, an open structure (L-shaped), a trumpet-shaped structure, a gourd-shaped structure, etc.

[0042] The preparation apparatus provided by this invention includes a curing device 6. This invention does not specifically limit the function of the curing device 6, as long as it can provide a temperature for complete curing. The die structure is also not specifically limited, and can be a circular structure, a rounded square structure, an open structure (L-shaped), a trumpet-shaped structure, a gourd-shaped structure, etc. For example, as... Figure 3 As shown, it may include heating device 6-1, die 6-2, and a first vacuum pump 6-3. In this invention, the die of the preforming device 3 and the die of the curing device 6 have the same geometric shape (i.e., the former is a circular structure, and the latter is also a circular structure; the former is an open structure (L-shaped), and the latter is also an open structure (L-shaped)). The two can be set to the same size, or the curing die can be slightly larger than the preforming die. This size design difference is mainly based on the characteristics of subsequent processes—after the outer layer of fibers is laid by the braiding machine 4 and the glue is injected by the glue injection machine 5, the overall size of the composite structure formed by the inner layer structure and the outer layer (glue or fiber-glue system) will increase to a certain extent. The adaptive adjustment of the curing die size can ensure that the composite structure obtains a matching molding space during the curing process, ensuring the structural integrity and dimensional accuracy of the final product. In this invention, the die 6-2 can be replaced according to the irregular structure requirements of the material. Its cross-section includes, but is not limited to, circular, rounded square, open lines, trumpet-shaped lines, gourd-shaped lines, etc. (some are like...). Figure 4 (As shown).

[0043] In one embodiment of the present invention, a dispensing machine 5 is further provided between the preforming device 3 and the curing device 6 for dispensing adhesive. The present invention does not have special requirements for the dispensing machine 5; any RTM dispensing machine well-known in the art is acceptable. In an embodiment of the present invention, the dispensing machine 5 is equipped with a 5-1 second vacuum pump, a 5-2 mixing mechanism for adhesive A and adhesive B (e.g., ...). Figure 3 (As shown).

[0044] As an embodiment of the present invention, a braiding machine 4 is further included between the preforming device 3 and the glue injection machine 5 for stretching or winding the preform.

[0045] In this invention, the braiding machine 4 is equipped with at least four functional rollers. The first roller is used to recover the release fabric, and the remaining rollers are used to form the covering layer. In this invention, the braiding machine 4 is preferably an integrated braiding / winding machine.

[0046] The preparation apparatus provided by the present invention includes a traction device 7. In the present invention, the traction device 7 provides traction force, enabling the continuous fiber units to pass sequentially through the aforementioned devices.

[0047] The preparation apparatus provided by the present invention includes a cutting machine 8. In the present invention, the cutting machine 8 is capable of cutting materials according to dimensional requirements for later use.

[0048] The following is combined with Figure 1 and Figure 2 The working principle of the preparation apparatus of the present invention will be explained. For example... Figure 1-2 As shown, in this invention, the release fabric 1-1, plant fiber units 1-2, and reinforcing lining 1-3 are placed on the raw material rack 1 and sequentially conveyed to the impregnation tank 2 under the pulling force of the traction device 7, allowing the plant fiber units to be fully impregnated with resin. The impregnated laminated raw material enters the preforming device 3 for preliminary shaping, and then enters the weaving machine 4 for weaving and winding, forming a core-shell structure by creating a covering layer outside the inner layer, while simultaneously performing preliminary recycling of the release fabric. The woven material enters the injection machine 5, where A and B adhesives are mixed and injected, and then enters the curing device 6 to complete the curing and molding process, resulting in the prepared morphology as shown. Figure 4 Structure ( Figure 4 The exhibition showcases circular structures, rounded square structures, open structures (L-shaped), and other irregularly shaped structures such as trumpet and gourd shapes. Finally, the cured composite material is pulled out by the traction device 7 and cut to size requirements by the cutting machine 8.

[0049] The method and apparatus for preparing irregularly shaped plant fiber composite materials provided by this invention achieve automated continuous production, integrating raw material transportation to finished product cutting. It can be widely applied in various fields such as construction, water conservancy, packaging, furniture, agriculture, automobiles, and aerospace. In the construction field, it can be used to prepare new environmentally friendly building materials; in the water conservancy field, it can be used to prepare water pipelines; in the packaging field, it can be used to prepare transport pallets; in the furniture field, it can be used to prepare furniture panels, storage cabinet frames, etc.; in the agricultural field, it can be used to prepare greenhouse supports, seedling pots, and agricultural packaging boxes; in the automotive field, it can be used to manufacture automotive interior parts and body components, reducing vehicle weight and improving fuel efficiency; in the aerospace field, it can be used to manufacture some non-critical structural components, meeting the requirements for lightweight and high-strength materials. The preparation method and apparatus provided by this invention can stably and efficiently produce plant fiber composite materials that meet the needs of various fields, possessing good practicality and broad market application prospects.

[0050] The following detailed description of the preparation method and apparatus for the irregular structure of plant fiber composite material provided by the present invention, with reference to the embodiments, should not be construed as limiting the scope of protection of the present invention.

[0051] Example 1 30 g of bamboo fiber with a fixed length of 40 mm was randomly selected and introduced into the traction system. At a traction speed of 200 m / h, the release cloth, bamboo fiber, and reinforcing lining (glass fiber) were layered sequentially and continuously fed into the epoxy resin system for 5 min to ensure thorough fiber impregnation. Specifically, diethylenetriamine (curing agent), glass microspheres (50 μm particle size), antioxidant 1010, and carboxyl-terminated nitrile rubber (toughening agent) were added sequentially to the liquid epoxy resin in a mass ratio of 100:20:25:5:10. The mixture was stirred at 300 r / min for 30 minutes at 30°C until homogeneous. The viscosity of the prepared epoxy resin system was approximately 650 mPa·s (below 35°C). Subsequently, the impregnated material was placed in a pre-forming mold and hot-pressed at 70°C and 0.1 MPa for 0.5 hours to pre-set the core material with a preliminary structure. The pre-formed core material is then fed into a weaving machine, the release fabric is recycled, and carbon fibers with a single filament diameter of 7 μm are used as the weaving material. The core material is then woven at a weaving angle of ±45° and a mesh size of 20 meshes / cm. 2 The carbon fiber braided reinforcing core material was prepared by weaving the fiber at a specific density. The core material was then placed in a curing mold and sealed. The mold temperature was set to 30°C and the injection pressure to 3 MPa. Epoxy resin was injected into the mold cavity through the injection port, and injection was stopped when excess resin overflowed. A stepped curing process was then employed: first, the temperature was increased to 80°C at a rate of 2°C / min and held for 40 min; then, the temperature was increased to 130°C at a rate of 2°C / min and held for 90 min; finally, the temperature was decreased to 60°C at a rate of 2°C / min to release the pressure. A molding pressure of 0.6 MPa was applied during curing to ensure material density. After complete curing, the molded composite material was cut into 100 mm × 100 mm square samples using a CNC cutting machine at a cutting speed of 50 mm / s, ensuring a smooth, burr-free cut. Before performance testing, the specimens were equilibrated according to ASTM D618-08 at 23°C and 50% relative humidity for 88 hours. Performance testing was conducted according to ASTM D 638, using dumbbell IV specimens with a total length of 115 mm, width of 33 mm, clamping distance of 65 mm, narrow section length of 33 mm, and narrow section width of 6 mm. The tensile speed was 2 mm / min, and 5 valid samples were obtained for each group. The tensile strength of the prepared composite material was 180–250 MPa, and the impact strength was 25–40 KJ / m². 2 .

[0052] Example 2 A 30 g sample of thin bamboo strips, with a fixed length of 2000 mm, a fixed width of 10 mm, and a fixed thickness of 0.5 mm, was randomly selected and introduced into the traction system at a traction speed of 150 m / h. The release fabric, thin bamboo strips, and reinforcing lining were alternately layered and continuously impregnated in molten polypropylene. The impregnated material was then placed in a pre-forming mold and pre-pressed for 1.5 h at 60℃ and 0.3 MPa to form the core material with a preliminary structure. The pre-formed core material was then fed into a weaving machine. The release fabric was recovered, and glass fiber with a monofilament diameter of 10 μm was used as the winding material. The winding speed was set to 20 m / min, the winding angle to ±45°, the winding tension to 8 N, and the winding density to 20 mesh / cm². 2 The glass fiber wound core material was prepared by winding. The glass fiber wound core material was placed in a curing mold and the mold was closed. The mold temperature was set to 30℃ and the injection pressure to 3MPa. Molten polypropylene at 210℃ was injected into the mold cavity through the injection port, ensuring that the gaps between the wound layers were fully filled. Injection was stopped when excess polypropylene flowed out from the overflow port. Afterwards, the material was cured and held under pressure at 50℃ and 0.5 MPa for 3 hours to achieve stable curing, utilizing the crystallization characteristics of polypropylene to avoid high-pressure overflow. After complete curing, the molded composite material was cut into 80 mm × 100 mm L-shaped specimens using a CNC cutting machine at a cutting speed of 50 mm / s, ensuring a smooth, burr-free cut. Before performance testing, the specimens were equilibrated according to ASTM D 618-08 at 23℃ and 50% relative humidity for 88 hours. Performance testing was conducted according to ASTM D 638. The specimen size used was dumbbell type IV, with a total length of 115 mm, a width of 33 mm, a clamping distance of 65 mm, a narrow section length of 33 mm, and a narrow section width of 6 mm. The tensile speed was 2 mm / min, and 5 valid samples were ensured for each group. The tensile strength of the prepared composite material was 60–90 MPa, and the impact strength was 30–50 KJ / m². 2 .

[0053] Example 3 30 g of sisal fiber, 70 mm in length, was randomly selected and introduced into the traction system. At a traction speed of 80 m / h, the release fabric, sisal fiber, and reinforcing lining were alternately laid in sequence and continuously impregnated with phenolic resin. The impregnated material was then placed in a pre-forming mold and pre-compressed at 100℃ and 0.5 MPa for 1.5 hours to form a sisal fiber / phenolic resin composite material. The material was then fed into a weaving machine to recover the release fabric. After pre-compression and shaping, the temperature was increased to 160℃ at 2℃ / min and held for 2 hours, then increased to 190℃ and held for 3 hours, with a pressure of 0.5 MPa applied throughout. After complete curing, the composite material was cut into tubular blanks with a length of 500 mm, an outer diameter of 100 mm, and an inner diameter of 90 mm using a CNC cutting machine at a cutting speed of 50 mm / s, ensuring smooth, burr-free cuts. Before performance testing, the specimens were equilibrated according to ASTM D 618-08 at 23°C and 50% relative humidity for 88 hours. Performance testing was conducted according to ASTM D 638, using dumbbell IV specimens with a total length of 115 mm, a width of 33 mm, a clamping distance of 65 mm, a narrow section length of 33 mm, and a narrow section width of 6 mm. The tensile speed was 2 mm / min, and 5 valid samples were obtained for each group. The tensile strength of the prepared composite material was 40–70 MPa, and the impact strength was 15–30 KJ / m². 2 .

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a heterogeneous structure of plant fiber composite material, characterized in that, Includes the following steps: The reinforcing lining, plant fiber units, and release fabric are stacked in sequence to obtain the laminated raw material; The laminated raw material is impregnated with resin to obtain a continuous plant fiber composite substrate; The continuous plant fiber composite substrate is pre-formed to obtain a pre-formed body with a release cloth on the surface; Peel the release fabric off the surface of the preform; The preform after the release fabric is peeled off is completely cured to obtain the irregular structure of the plant fiber composite material.

2. The preparation method according to claim 1, characterized in that, Before complete curing, the preform after the release fabric is peeled off is injected with adhesive.

3. The preparation method according to claim 2, characterized in that, Before the glue injection, the preform after the release fabric is peeled off is further subjected to tufting or winding; the tufting is: using the preform as the core material to weave a fiber covering layer on its outer side; the winding is: using the preform as the core material to wind a fiber covering layer on its outer side.

4. The preparation method according to claim 1, characterized in that, The plant fiber unit includes one or more of bamboo fiber, thin bamboo strips, and hemp fiber; the thickness of the thin bamboo strips is 0.01~5 mm.

5. The preparation method according to claim 1, characterized in that, The reinforcing lining is a fabric, mesh, or strip; the material of the reinforcing lining includes one or more of cotton fiber, bamboo fiber, chemical fiber, glass fiber, carbon fiber, and basalt substrate.

6. The preparation method according to claim 2 or 3, characterized in that, The injection molding process uses resin transfer molding.

7. An apparatus for preparing irregularly shaped structures of plant fiber composite materials according to any one of claims 1 to 6, characterized in that, It includes a raw material rack (1), a dipping tank (2), a preforming device (3), a curing device (6), and a traction device (7); each device is connected in sequence to realize continuous transmission and processing of raw materials; a shelf is provided between the raw material rack (1) and the dipping tank (2) to receive and support the laminated raw materials.

8. The preparation apparatus according to claim 7, characterized in that, A glue injection machine (5) is also provided between the preforming device (3) and the curing device (6) for glue injection.

9. The preparation apparatus according to claim 7, characterized in that, A weaving machine (4) is also provided between the preforming device (3) and the glue injection machine (5) for weaving or winding the preform after the release fabric is peeled off.

10. The preparation apparatus according to claim 7, characterized in that, A cutting machine (8) is also installed at the end of the traction device (7).

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