A plant fiber material and its preparation method

Abstract

This invention relates to the field of materials preparation technology, specifically to a plant fiber material composed of a matrix resin, plant fibers, a composite modifier, an antioxidant, and an ultraviolet absorber. The plant fibers are a single plant fiber or a mixture of at least two plant fibers. The composite modifier includes a silane coupling agent, maleic anhydride-grafted polypropylene, and calcium stearate, and may also contain nano-silica. This invention constructs a composite plant fiber system, combining the performance characteristics of different plant fibers to achieve complementary advantages. It overcomes the limitations of single plant fiber mechanical properties, significantly improving the tensile strength, bending performance, and impact toughness of the material, enabling it to adapt to more scenarios with diverse mechanical performance requirements.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, specifically to a plant fiber material and its preparation method. Background Technology

[0002] Plant fiber reinforced composites have gained widespread attention in various fields due to their environmental friendliness, low cost, and renewability, becoming a research hotspot in the field of composite materials. Currently, the preparation of plant fiber reinforced composites in existing technologies mostly uses a single plant fiber as the reinforcing phase. This approach makes it difficult to balance the strength and toughness of the material, resulting in limitations in the single mechanical property and failing to meet the application requirements of complex scenarios.

[0003] In terms of modification technology, existing solutions mostly rely on single coupling agents or simple mixtures of modifiers, lacking a systematic synergistic modification design. This results in weak interfacial bonding between plant fibers and matrix resins, making them prone to interfacial debonding and severely affecting the overall performance stability of the material. Meanwhile, some technologies use a single matrix resin, which either makes it difficult to balance mechanical properties and environmental friendliness, or suffers from poor processing compatibility, limiting the material's application range.

[0004] Furthermore, existing technologies suffer from narrow raw material ratio ranges and insufficient adaptability of process parameters. When adjusting plant fiber content or matrix composition, problems such as fiber agglomeration and resin degradation during processing easily occur, leading to low production efficiency and hindering large-scale production. Simultaneously, most existing materials have shortcomings in environmental friendliness and functionality, limiting their applications to single fields and failing to meet the diverse, high-performance, and environmentally friendly demands of various industries, thus restricting the industrialization of this type of composite material. Summary of the Invention

[0005] The primary objective of this invention is to provide a plant fiber material and a method for preparing the same.

[0006] A further objective of this invention is to provide a plant fiber material comprising a matrix resin, plant fibers, a composite modifier, an antioxidant, and an ultraviolet absorber; wherein the plant fibers are a single plant fiber or a mixture of at least two plant fibers; and the composite modifier comprises a silane coupling agent, maleic anhydride-grafted polypropylene, and calcium stearate, and may also contain nano-silica.

[0007] Preferably, the matrix resin is selected from one or a mixture of two of polypropylene and polylactic acid; the plant fiber is selected from one or a mixture of two of flax fiber and sisal fiber.

[0008] Preferably, when the plant fiber is a mixture of flax fiber and sisal fiber, the weight ratio of the two is 1:1 to 3:2.

[0009] Preferably, the silane coupling agent is selected from KH-550 or KH-560.

[0010] Preferably, the weight percentages of each raw material are as follows: 40-70 parts of matrix resin, 20-40 parts of plant fiber, 5-15 parts of composite modifier, 0.5-2 parts of antioxidant, and 0.5-2 parts of ultraviolet absorber.

[0011] A method for preparing the plant fiber reinforced composite material includes the following steps: (1) Plant fiber pretreatment: Dry the plant fiber and then crush it. If there are multiple plant fibers, mix them evenly. (2) Modifier pretreatment: The silane coupling agent is diluted with anhydrous ethanol and sprayed onto the surface of the pretreated plant fiber, stirred and dried; if the composite modifier contains nano silica, the nano silica is mixed with calcium stearate, or mixed with maleic anhydride grafted polypropylene and then mixed with calcium stearate. (3) Mixing: Mix the matrix resin, maleic anhydride grafted polypropylene, modified additives, antioxidants and ultraviolet absorbers evenly to obtain a mixed matrix; (4) Melt blending: The mixed matrix is ​​added to a twin-screw extruder, and the plant fiber is added by side feeding. After blending, the mixture is extruded and granulated. (5) Molding: The composite material particles are molded into samples by injection molding process; (6) Post-treatment: Dry the molded sample to remove surface moisture.

[0012] Preferably, in step (1), the drying temperature is 50-80℃ and the length of the plant fiber after pulverization is 1-5 mm.

[0013] Preferably, in step (2), the stirring time between the diluted silane coupling agent and the plant fiber is 30-40 minutes, the drying temperature is 70-80℃, and the drying time is 2-3 hours.

[0014] Preferably, in step (4), the temperature of each section of the twin-screw extruder is 150-185℃ and the screw speed is 40-50 revolutions per minute.

[0015] Preferably, in step (5), the injection temperature is 160-190℃, the mold temperature is 30-45℃, the injection pressure is 70-85 MPa, the holding pressure is 55-60 MPa, the holding time is 10-12 seconds, and the cooling time is 30-35 seconds; in step (6), the drying temperature is 50-60℃, and the drying time is 1.5-2.5 hours.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention constructs a composite plant fiber system, which combines the performance characteristics of different plant fibers to achieve complementary advantages, breaks through the limitation of the single mechanical properties of a single plant fiber, and greatly improves the tensile strength, bending performance and impact toughness of the material, enabling the material to adapt to more scenarios with diverse mechanical performance requirements.

[0017] 2. This invention designs a multi-component synergistic modification mechanism of coupling agent-grafted polymer-lubricant-nanofiller. By optimizing the pretreatment process of the modifier, it promotes the full integration between the modifier and the fiber and matrix, significantly enhances the interfacial bonding force, effectively solves the core problem of interfacial debonding in the prior art, and improves the processing fluidity of the material, ensuring the stability of the production process.

[0018] 3. This invention optimizes the raw material ratio and process parameter design, broadens the compatibility range of matrix resin, plant fiber and modifier, and forms a wide range of process parameter system, effectively avoiding problems such as fiber agglomeration and resin degradation, improving production efficiency, and providing a feasible path for the large-scale and continuous production of materials.

[0019] 4. This invention uses an environmentally friendly matrix of polypropylene and polylactic acid blend, which balances the mechanical properties and biodegradability of the material, responding to the needs of environmental development. Furthermore, by adjusting the raw material ratio and adding functional additives, the material can be adapted to diverse functional requirements such as flame retardancy and wear resistance, expanding its application scenarios to multiple fields such as automotive interiors, building decoration, packaging materials, and electronic appliance housings, significantly enhancing the industrial value and market competitiveness of the product. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1: The raw material ratio, by mass fraction, is 60wt% polypropylene, 30wt% flax fiber, 5wt% maleic anhydride-grafted polypropylene, 2wt% silane coupling agent KH-550, 2wt% calcium stearate, 0.5wt% antioxidant, and 0.5wt% UV absorber.

[0022] All raw materials used are conventional commercial products. The polypropylene melt index is 10-20g / 10min, the flax fiber length is 2-5mm, the maleic anhydride grafted polypropylene grafting rate is 0.5-1.0%, the antioxidant is antioxidant 1010, and the ultraviolet absorber is UV-531.

[0023] Preparation steps: Plant fiber pretreatment: Place flax fiber in a drying oven and dry at 60℃ for 4 hours. After taking it out, pulverize it to a length of 2-5mm using a high-speed pulverizer and set aside. Modifier pretreatment: Dilute silane coupling agent KH-550 with anhydrous ethanol at a mass ratio of 1:10, spray it evenly on the surface of the pretreated flax fiber, stir for 30 min, and then dry at 80℃ for 2 h to obtain modified flax fiber. Mixing: Polypropylene, maleic anhydride-grafted polypropylene, calcium stearate, antioxidant, and ultraviolet absorber are placed in a high-speed mixer and mixed at 300 r / min for 15 min at room temperature to obtain a mixed matrix; Melt blending: The mixed matrix is ​​added to the hopper of a twin-screw extruder, and the modified flax fiber is added through a side feeding device. The temperature of each section of the extruder is set as follows: Zone 1 160℃, Zone 2 170℃, Zone 3 180℃, Zone 4 175℃, and Die head 170℃. The screw speed is 40 r / min. After blending, the mixture is extruded and granulated to obtain composite material particles. Molding: Place the composite material particles into the injection molding machine, with an injection temperature of 170-180℃, a mold temperature of 40℃, an injection pressure of 80MPa, a holding pressure of 60MPa, a holding time of 10s, and a cooling time of 30s. Injection mold standard samples are then formed. Post-processing: The molded sample was placed in a drying oven and dried at 50°C for 2 hours to remove surface moisture, thus obtaining the plant fiber reinforced composite material.

[0024] Example 2: The raw material ratio, by mass fraction, is as follows: polypropylene 55wt%, flax fiber 18wt%, sisal fiber 12wt%, maleic anhydride grafted polypropylene 6wt%, silane coupling agent KH-550 2wt%, calcium stearate 5wt%, antioxidant 0.5wt%, ultraviolet absorber 0.5wt%, and nano silica 1wt%.

[0025] The sisal fiber is 2-5 mm in length, the nano-silica particle size is 20-50 nm, and the specifications of the other raw materials are the same as in Example 1.

[0026] Preparation steps: Plant fiber pretreatment: Flax fiber and sisal fiber are dried at 60℃ for 4 hours, pulverized to a length of 2-5 mm, and mixed evenly at a mass ratio of 3:2 to obtain composite plant fiber. The high toughness of flax fiber and the high strength of sisal fiber are used to achieve complementary performance and solve the limitations of the mechanical properties of single fiber. Modifier pretreatment: The silane coupling agent KH-550 was diluted and sprayed onto the surface of the composite plant fiber, stirred for 30 min, and dried at 80℃ for 2 h; at the same time, nano silica and calcium stearate were mixed and ground at 500 r / min for 10 min to obtain a mixture of modified additives. The nano silica filled the interfacial voids and formed a synergistic reinforcing effect with the composite fiber. Mixing: Polypropylene, maleic anhydride-grafted polypropylene, modified additive mixture, antioxidant, and ultraviolet absorber are placed in a high-speed mixer and mixed at 300 r / min for 15 min at room temperature to obtain a mixed matrix; Melt blending: Using the same extruder temperature settings as in Example 1, the screw speed was adjusted to 45 r / min. The composite plant fiber was added through side feeding, and extrusion granulation was performed. The uniformity of the composite fiber dispersion in the matrix was improved by optimizing the speed. Molding and post-treatment: The injection temperature was adjusted to 175-185℃, and the remaining molding parameters and post-treatment steps were the same as in Example 1 to obtain composite material samples.

[0027] Compared to Example 1, this embodiment replaces single flax fiber with composite plant fiber and introduces nano-synergistic modification, which significantly improves tensile strength and heat distortion temperature, while solving the problem of uneven dispersion of composite fibers in the prior art.

[0028] Example 3: The raw material ratio, by mass fraction, is as follows: polypropylene 52wt%, flax fiber 20wt%, sisal fiber 10wt%, maleic anhydride grafted polypropylene 7wt%, silane coupling agent KH-560 1.5wt%, calcium stearate 4wt%, nano silica 4wt%, antioxidant 0.8wt%, and ultraviolet absorber 0.7wt%.

[0029] The silane coupling agents KH-560 and KH-550 have the same specifications, and the nano-silica particle size is maintained at 20-50nm, which is compatible with the optimized pretreatment process.

[0030] Preparation steps: Plant fiber pretreatment: consistent with Example 2, to obtain composite plant fiber, continue the complementary performance advantages of composite fiber, and ensure the continuity of technical path; Modifier pretreatment: Silane coupling agent KH-560 was used instead of KH-550 in Example 2. It was diluted with anhydrous ethanol at a mass ratio of 1:8 and sprayed onto the surface of the composite plant fiber. After stirring for 40 min, it was dried at 75°C for 2.5 h. Nano-silica and maleic anhydride-grafted polypropylene were first mixed, melted and stirred at 160°C for 10 min, cooled and pulverized, and then mixed and ground with calcium stearate to obtain a mixture of modifiers. By upgrading the pretreatment process, the modifiers were fully integrated with the fiber and matrix, and the synergistic effect of the multi-modifiers was brought into play. Mixing: Polypropylene, modified additive mixture, antioxidant, and ultraviolet absorber are placed in a high-speed mixer at 350 r / min and mixed at room temperature for 20 min to obtain a mixed matrix. The uniformity of matrix components is improved by optimizing the mixing parameters. Melt blending: The temperatures of each section of the extruder are adjusted to 165℃ in zone 1, 175℃ in zone 2, 185℃ in zone 3, 180℃ in zone 4, and 175℃ at the die head. The screw speed is 50 r / min. The remaining blending steps are the same as in Example 2. The temperature parameters are adjusted to adapt to the optimized modified system to ensure the blending effect. Molding and post-treatment: Injection temperature 180-190℃, mold temperature 45℃, injection pressure 85MPa, the remaining molding and post-treatment steps are the same as in Example 2, and composite material samples are obtained.

[0031] This embodiment constructs a multi-element synergistic modification mechanism by replacing the type of silane coupling agent and upgrading the pretreatment process of the modifier. Compared with the simple mixing of modifiers in Example 2 and the prior art, the interfacial bonding force is greatly improved, and the bending performance and impact toughness of the material are significantly optimized.

[0032] Example 4: The raw material ratio, by mass fraction, is as follows: polypropylene 32wt%, polylactic acid 20wt%, flax fiber 20wt%, sisal fiber 10wt%, maleic anhydride grafted polypropylene 8wt%, silane coupling agent KH-560 1.5wt%, calcium stearate 4wt%, nano silica 3wt%, antioxidant 0.8wt%, and ultraviolet absorber 0.7wt%.

[0033] The melt index of polylactic acid is 8-15 g / 10 min. The blending ratio with polypropylene was determined through multiple sets of adaptation tests to ensure the processing stability of the blend system.

[0034] Preparation steps: Plant fiber pretreatment: consistent with Example 3, to obtain composite plant fibers, maintain the continuity of the fiber system, and focus on the environmental optimization of the matrix resin; Modifier pretreatment: consistent with Example 3, a mixture of modified composite plant fiber and modifier was obtained, continuing the optimized modification process to ensure the advantages of interfacial bonding; Mixing: Polypropylene, polylactic acid, maleic anhydride-grafted polypropylene, a mixture of modified additives, antioxidants, and ultraviolet absorbers are placed in a high-speed mixer at 350 r / min and mixed at room temperature for 20 min to obtain a mixed matrix. The introduction of polylactic acid improves the environmental friendliness of the material, and the optimization of polylactic acid drying parameters ensures the stability of the blend. Melt blending: The temperatures of each section of the extruder are adjusted to 155℃ in zone 1, 165℃ in zone 2, 175℃ in zone 3, 170℃ in zone 4, and 165℃ at the die head. The screw speed is 45r / min. The composite plant fiber is added through side feeding, extruded and granulated. The temperature parameters are adjusted to match the characteristics of the blended matrix to avoid polylactic acid degradation. Molding and post-processing: Injection temperature 165-175℃, mold temperature 35℃, injection pressure 75MPa, holding pressure 55MPa, the remaining molding and post-processing steps are the same as in Example 3, and composite material samples are obtained. By optimizing the molding parameters to adapt to the properties of the blended matrix, the molding quality is ensured.

[0035] This embodiment replaces the single matrix with a polypropylene and polylactic acid blend matrix, taking into account the mechanical properties, biodegradability and processing stability of the material. Compared with the single matrix or blend matrix solutions with poor adaptability in Example 3 and the prior art, the environmental application scenarios are greatly expanded.

[0036] Example 5: The raw material ratio, by mass fraction, is: polypropylene 30wt%, polylactic acid 20wt%, flax fiber 22wt%, sisal fiber 13wt%, maleic anhydride-grafted polypropylene 6wt%, silane coupling agent KH-560 1wt%, calcium stearate 3wt%, nano silica 4wt%, antioxidant 0.5wt%, and ultraviolet absorber 0.5wt%. The total plant fiber content is increased to 35wt%, a proportion verified through multiple tests to ensure reinforcement while avoiding agglomeration.

[0037] Preparation steps: Plant fiber pretreatment: flax fiber and sisal fiber are dried at 70℃ for 3 hours, pulverized to a length of 1-4 mm, and mixed evenly at a mass ratio of 22:13 to obtain composite plant fiber, increasing the total fiber content to 35 wt%, and optimizing drying and pulverizing parameters to avoid fiber agglomeration; Modifier pretreatment: The silane coupling agent KH-560 was diluted and sprayed onto the surface of the composite plant fiber, stirred for 35 min, and dried at 70℃ for 3 h to obtain the modified composite plant fiber. The pretreatment parameters were adjusted according to the fiber content to ensure the stability of the modification effect. Mixing: Polypropylene, polylactic acid, maleic anhydride-grafted polypropylene, calcium stearate, nano silica, antioxidant, and ultraviolet absorber are placed in a high-speed mixer at 400 r / min and mixed at room temperature for 18 min to obtain a mixed matrix. The mixing speed and time are optimized to improve the uniformity of the matrix under high fiber content. Melt blending: The temperatures of each section of the extruder are adjusted to 150℃ in zone 1, 160℃ in zone 2, 170℃ in zone 3, 165℃ in zone 4, and 160℃ at the die head. The screw speed is 40r / min. The feeding speed of the composite plant fiber side is adjusted to 35% of the total feeding speed. Extrusion granulation is carried out, and the temperature, speed and feeding speed are fully optimized to meet the processing requirements of high fiber content. Molding and post-treatment: Injection temperature 160-170℃, mold temperature 30℃, injection pressure 70MPa, holding time 12s, cooling time 35s, post-treatment temperature 60℃, drying for 1.5h to obtain composite material samples. Optimize molding and post-treatment parameters to ensure the molding quality and performance stability of materials with high fiber content.

[0038] This embodiment increases the total plant fiber content and optimizes process parameters, thereby further reducing material costs while ensuring the mechanical properties and environmental friendliness of the materials. At the same time, it significantly expands the compatibility range of plant fiber content and process parameters.

[0039] Comparative Example 1: This comparative example simulates the conventional scheme in the existing technology that uses only a single coupling agent for modification and a single plant fiber for reinforcement. The raw material ratio is as follows by mass fraction: polypropylene 65wt%, flax fiber 30wt%, silane coupling agent KH-550 2wt%, calcium stearate 2wt%, antioxidant 0.5wt%, and ultraviolet absorber 0.5wt%.

[0040] Preparation steps: Except for not adding maleic anhydride-grafted polypropylene, the other steps are completely the same as in Example 1, and a composite material sample is obtained.

[0041] This scheme lacks the core multi-component composite modification mechanism of this technology, and only adopts the single coupling agent modification approach in the existing technology. It has weak interfacial bonding and poor mechanical properties, representing the typical level of the existing technology. The comparison with Example 1 can directly confirm the technical advantages of the composite modification system of this technology.

[0042] Comparative Example 2: This comparative example simulates the existing technology that simply adds a compatibilizer but does not adopt the technical combination of composite fiber and nano-modification. The raw material ratio by mass fraction is: polypropylene 60wt%, flax fiber 30wt%, maleic anhydride grafted polypropylene 6wt%, silane coupling agent KH-550 2wt%, calcium stearate 1.5wt%, antioxidant 0.5wt%, and ultraviolet absorber 0.5wt%.

[0043] Preparation steps: Except for using single flax fiber and not adding nano silica, the other steps are completely the same as in Example 2, and a composite material sample is obtained.

[0044] This solution is merely a simple superposition of compatibilizer and single fiber in the existing technology, without achieving complementary fiber properties and nano-synergistic enhancement. The performance improvement is limited and there is no substantial improvement. The comparison with Example 2 confirms the technical advantages of the composite fiber plus nano-synergistic system of this technology.

[0045] Comparative Example 3: This comparative example simulates the existing technology's scheme of simply mixing modifiers without optimized pretreatment, and the raw material ratio is completely consistent with Example 3.

[0046] Preparation steps: Except for the modified agent pretreatment step, which is simplified to directly mixing silane coupling agent KH-560, nano silica, and calcium stearate with plant fibers without dilution spraying and melt pretreatment, the other steps are completely consistent with Example 3, and the composite material sample is obtained.

[0047] This solution lacks the modifier-synergistic pretreatment process of this technology, and only simply mixes the modifier, which cannot achieve full integration of the modifier with the fiber and matrix, thus limiting the performance improvement. It represents a typical defect of the rough modification process in the prior art. The comparison with Example 3 can confirm the technical value of the optimized modification process of this technology.

[0048] Comparative Example 4: This comparative example simulates an existing technology that uses a single environmentally friendly resin but has poor compatibility with fibers. The raw material ratios by mass fraction are: polylactic acid 52wt%, flax fiber 20wt%, sisal fiber 10wt%, maleic anhydride grafted polypropylene 8wt%, silane coupling agent KH-560 1.5wt%, calcium stearate 4wt%, nano silica 3wt%, antioxidant 0.8wt%, and ultraviolet absorber 0.7wt%.

[0049] Preparation steps: Except for using a single polylactic acid matrix and adjusting the extruder temperature to 170-190℃, the other steps are completely consistent with those in Example 4, and a composite material sample is obtained.

[0050] This solution simply replaces the matrix with an environmentally friendly one, without solving the compatibility problem between the matrix and the fiber. It has poor mechanical properties and processing stability. Compared with the blended matrix solution of this technology, it has no obvious technical advantages. The comparison with Example 4 can confirm the rationality of the blended matrix design of this technology.

[0051] Comparative Example 5: This comparative example simulates the existing technology's approach of blindly increasing fiber content without employing synergistic modification. The raw material ratios, by mass fraction, are: polypropylene 25wt%, polylactic acid 20wt%, flax fiber 28wt%, sisal fiber 17wt%, maleic anhydride-grafted polypropylene 6wt%, silane coupling agent KH-560 1wt%, calcium stearate 3wt%, antioxidant 0.5wt%, and ultraviolet absorber 0.5wt%.

[0052] Preparation steps: Except that the total plant fiber content is 45wt% and no nano-silica is added, the other steps are completely the same as in Example 5, and a composite material sample is obtained.

[0053] This scheme does not follow the fiber content optimization range and synergistic modification mechanism of this technology. Blindly increasing the fiber content leads to poor fiber dispersibility and a significant decrease in mechanical properties, which reflects the typical defects of blindly adjusting the ratio in the prior art. The comparison with Example 5 can confirm the scientific nature of the raw material ratio and process adaptation optimization of this technology.

[0054] Performance testing and results analysis: Test samples: Standard samples prepared in Examples 1-5 and Comparative Examples 1-5, with 5 samples in each group, and the test results are taken as the average value.

[0055] Meanwhile, three sets of typical samples from existing technologies were selected as references for comparison: Existing Technology 1: single flax fiber modified with a single coupling agent; Existing Technology 2: single polylactic acid matrix modified with composite fiber; and Existing Technology 3: composite fiber modified with a simple mixture of modifiers, to ensure the comprehensiveness and relevance of the comparison.

[0056] All samples were prepared according to the steps of the corresponding examples and comparative examples, and the molding dimensions met the requirements of each test standard.

[0057] Test items and standards: (1) Tensile strength: Tested according to GB / T1447-2005 Tensile properties test method for fiber reinforced plastics, with a tensile speed of 5 mm / min; (2) Bending strength and bending modulus: Tested according to GB / T1449-2005 Test method for bending properties of fiber reinforced plastics, with a bending speed of 2 mm / min and a span of 100 mm; (3) Impact strength: Tested according to GB / T1451-2005 Test method for impact strength of fiber reinforced plastic simply supported beams, with no notch and impact energy of 5J; (4) Heat distortion temperature: According to GB / T1634.2-2004 Determination of heat distortion temperature of plastics under load Part 2 Plastics, hard rubber and long fiber reinforced composites, the load is 1.80 MPa; (5) Interfacial bonding strength: The tensile fracture surface of the sample was observed using a scanning electron microscope to evaluate the interfacial bonding state between the plant fiber and the matrix resin, which was divided into four grades: excellent, good, medium and poor.

[0058] (6) Test results: The performance test data of each sample are shown in the table below. All data have been repeatedly tested and verified to ensure the accuracy and reliability of the data.

[0059] The test results are shown in Table 1 below: Table 1: Test Result Analysis: Based on the test data of the embodiments, comparative examples and prior art samples, this technical solution shows a more outstanding overall performance compared with the prior art and simple combinations of the prior art.

[0060] The comprehensive mechanical and thermal properties of Examples 1 to 5 are optimized and improved to varying degrees compared to the corresponding proportions and all prior art samples. Specifically, Example 3 achieves a tensile strength of 52.1 MPa, an improvement of 55.5% compared to Prior Art 1 and 27.1% compared to Prior Art 3; its heat distortion temperature reaches 140℃, an improvement of 20.7% compared to Prior Art 1. Even Example 1, as the basic scheme, shows improvements of 26.3% and 40.4% in tensile strength and impact strength, respectively, compared to Prior Art 1. These performance improvements are not minor adjustments but rather represent a significant advancement, demonstrating that this technical solution, compared to existing technologies and simple combinations of existing technologies, possesses considerable technological progress and practical application potential.

[0061] Based on the complementary properties of high toughness of flax fiber and high strength of sisal fiber, this technical solution designs a composite plant fiber system. At the same time, it optimizes the fiber ratio and pretreatment process, effectively improving the problems of single fiber mechanical properties and insufficient dispersion.

[0062] Compared to the irregular fiber composite schemes in existing technologies, the composite fiber system of this technology achieves better results in synergistic improvement of strength and toughness through precise proportioning. Fiber dispersion uniformity is improved by more than 25%, and it can be adapted to subsequent multi-element modification and blending matrix systems, resulting in an overall optimized effect. Test data shows that Examples 2 to 5, which use composite plant fibers, exhibit significantly improved tensile strength and impact strength compared to Example 1, which uses single fibers, further confirming the rationality of the composite fiber system.

[0063] The construction of a multi-component synergistic modification mechanism is another important improvement of this technical solution. Compared with the existing technologies that use a single modifier or a simple mixture of modifiers, this technology designs a multi-component modification system of coupling agent-graft polymer-lubricant-nanofiller: the coupling agent reduces the surface polarity of the fiber, the graft polymer promotes chemical bonding, the lubricant improves processing fluidity, and the nanofiller fills the interfacial voids, ultimately achieving a synergistic enhancement effect on interfacial bonding.

[0064] Compared to existing technologies, this technical solution improves the overall mechanical properties by more than 30%, playing a positive role in addressing the core technical issue of interfacial debonding. Furthermore, the modification process and system are precisely matched, further enhancing synergistic effectiveness. Test data shows that the interfacial bonding strength of Examples 2 to 4 all reached the "excellent" level, superior to the "medium" and "poor" levels of existing technologies and their corresponding proportions. This, to a certain extent, verifies the feasibility and effectiveness of the multi-element synergistic modification mechanism.

[0065] The optimized design of raw material proportions and processes also provides strong support for the implementation of the technical solution. Addressing the narrow range of raw material proportions and insufficient adaptability of process parameters in existing technologies, this technology, through optimization using multiple embodiments, has determined a wide-adaptability range of raw material proportions: 40-70wt% matrix resin, 20-40wt% plant fiber, 5-15wt% composite modifier, and 0.5-2wt% other additives. The corresponding process parameter ranges are: drying temperature 50-80℃, extrusion temperature 150-185℃, and injection molding temperature 160-190℃. Simultaneously, a side-feed continuous production process was designed, reducing fiber agglomeration and breakage, achieving a fiber length retention rate ≥80%, and increasing production efficiency by 15-20%. Compared to existing technologies, the technical flexibility and industrial adaptability have been further improved, providing a feasible path for large-scale production.

[0066] Example 5, by broadening the fiber content range and optimizing process parameters, still maintained good mechanical properties even when the total fiber content was increased to 35 wt%, which fully demonstrates the rationality and adaptability of the ratio and process range.

[0067] The raw materials used in this technical solution are all conventional commercially available products, which are readily available and cost-controllable. The plant fibers include flax fiber, sisal fiber, and bamboo fiber, with flax fiber length 1-10mm and fineness 20-50μm, sisal fiber length 2-12mm and fineness 30-60μm, and bamboo fiber length 0.5-8mm and fineness 15-40μm. The matrix resins include polypropylene, polyethylene, and polylactic acid, with polypropylene melt index 10-20g / 10min and polylactic acid melt index 8-15g / 10min. The composite modifiers include silane coupling agents KH-550 and KH-560, maleic anhydride-grafted polypropylene, calcium stearate, and nano-silica, with maleic anhydride-grafted polypropylene grafting rate of 0.5-1.0% and nano-silica particle size of 20-50nm. Other additives include antioxidant type 1010 and ultraviolet absorber type UV-531. The availability of standard raw materials further ensures the feasibility of the solution, eliminating the need for additional special preparation or procurement processes.

[0068] In terms of application scenarios, compared with the limited application scenarios of plant fiber reinforced composite materials in existing technologies, this technical solution, by adjusting the raw material ratio and process parameters, takes into account the mechanical properties, environmental protection and functionality of the material, and further expands the scope of application. It can be widely used in many fields such as automotive interiors, building decoration, packaging materials, electronic and electrical appliance housings, and furniture components.

[0069] Adding flame retardants allows for the preparation of flame-retardant composite materials with tensile strength ≥45MPa and oxygen index ≥28%, making them suitable for the construction and electronics industries requiring flame retardancy. Adding wear-resistant agents allows for the production of wear-resistant parts, meeting the needs of mechanical manufacturing. This technology effectively broadens its application scope and further enhances its industrial value, offering a wider market prospect compared to the single application scenarios of existing technologies.

[0070] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A plant fiber material, characterized in that, It is composed of a matrix resin, plant fibers, a composite modifier, an antioxidant, and an ultraviolet absorber; the plant fibers are a single plant fiber or a mixture of at least two plant fibers; the composite modifier includes a silane coupling agent, maleic anhydride-grafted polypropylene, and calcium stearate, and may also contain nano-silica.

2. The plant fiber reinforced composite material according to claim 1, characterized in that, The matrix resin is selected from one or a mixture of two of polypropylene and polylactic acid; the plant fiber is selected from one or a mixture of two of flax fiber and sisal fiber.

3. The plant fiber reinforced composite material according to claim 2, characterized in that, When the plant fiber is a mixture of flax and sisal fibers, the weight ratio of the two is 1:1 to 3:

2.

4. The plant fiber reinforced composite material according to claim 1, characterized in that, The silane coupling agent is selected from KH-550 or KH-560.

5. The plant fiber reinforced composite material according to claim 1, characterized in that, The weight percentages of each raw material are as follows: 40-70 parts of matrix resin, 20-40 parts of plant fiber, 5-15 parts of composite modifier, 0.5-2 parts of antioxidant, and 0.5-2 parts of ultraviolet absorber.

6. A method for preparing a plant fiber reinforced composite material as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Plant fiber pretreatment: Dry the plant fiber and then crush it. If there are multiple plant fibers, mix them evenly. (2) Modifier pretreatment: The silane coupling agent is diluted with anhydrous ethanol and sprayed onto the surface of the pretreated plant fiber, stirred and dried; if the composite modifier contains nano silica, the nano silica is mixed with calcium stearate, or mixed with maleic anhydride grafted polypropylene and then mixed with calcium stearate. (3) Mixing: Mix the matrix resin, maleic anhydride grafted polypropylene, modified additives, antioxidants and ultraviolet absorbers evenly to obtain a mixed matrix; (4) Melt blending: The mixed matrix is ​​added to a twin-screw extruder, and the plant fiber is added by side feeding. After blending, the mixture is extruded and granulated. (5) Molding: The composite material particles are molded into samples by injection molding process; (6) Post-treatment: Dry the molded sample to remove surface moisture.

7. The preparation method according to claim 6, characterized in that, In step (1), the drying temperature is 50-80℃, and the length of the plant fiber after pulverization is 1-5 mm.

8. The preparation method according to claim 6, characterized in that, In step (2), the silane coupling agent is diluted and stirred with plant fiber for 30-40 minutes, the drying temperature is 70-80℃, and the drying time is 2-3 hours.

9. The preparation method according to claim 6, characterized in that, In step (4), the temperature of each section of the twin-screw extruder is 150-185℃, and the screw speed is 40-50 revolutions per minute.

10. The preparation method according to claim 6, characterized in that, In step (5), the injection temperature is 160-190℃, the mold temperature is 30-45℃, the injection pressure is 70-85 MPa, the holding pressure is 55-60 MPa, the holding time is 10-12 seconds, and the cooling time is 30-35 seconds; in step (6), the drying temperature is 50-60℃, and the drying time is 1.5-2.5 hours.

Images