Modified plant fiber and its preparation method and application

Abstract

The present invention relates to the field of organic polymer composite materials, and discloses a modified plant fiber and a preparation method and application thereof. The preparation method comprises the following steps: (1) placing the plant fiber after impurity removal in a dopamine hydrochloride solution for impregnation, followed by filtering, cleaning and drying in sequence to obtain a first plant fiber; (2) reacting cardanol glycidyl ether with a silane coupling agent to obtain cardanol siloxane; (3) mixing the first plant fiber, cardanol siloxane and ethanol, then reacting, and then filtering, cleaning and drying in sequence. The present invention co-deposits cardanol siloxane and dopamine on the surface of the plant fiber. The presence of long fatty chains enhances hydrophobicity, thereby obtaining a modified plant fiber composed of a hard phase and a soft phase. The modified plant fiber can promote the formation of a water-resistant interfacial phase in the fiber matrix, thereby improving the interfacial bonding force and water resistance of the fiber-reinforced composite material.

Description

Technical Field

[0001] The present invention relates to the field of organic polymer composite materials, and in particular to modified plant fibers and a preparation method and application thereof. Background Art

[0002] Under the background of "dual carbon", green and low-carbon development has increasingly become the focus of today's social development. Plant fibers have received more and more attention due to their excellent performance, low price, rich resources, and green and low-carbon nature. Plant fibers as reinforcements for reinforced composite materials are environmentally friendly green composite materials due to their strong designability, high specific strength and specific modulus, and biodegradability, showing broad development space.

[0003] Natural plant fibers have abundant hydroxyl groups on their surfaces, making them extremely hydrophilic. Plastic matrices, on the other hand, are often hydrophobic. This leads to poor interfacial compatibility between the natural plant fibers and the plastic matrix, preventing effective stress transfer at the interface. This weakens the plant fiber reinforcement effect and makes it difficult to significantly improve the mechanical properties of the composite material. Therefore, modifying the hydrophobic properties of plant fiber surfaces has become a new research direction for designing high-strength composite materials, providing new insights into the development of high-performance composite materials. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problem that natural plant fibers are highly hydrophilic, have poor interfacial compatibility with plastic matrices, and are difficult to significantly improve the mechanical properties of composite materials. The present invention provides modified plant fibers and their preparation method and application. This method can significantly improve the hydrophobicity of the fiber surface and effectively improve the interfacial strength and water resistance between the fiber and the resin.

[0005] In order to achieve the above object, the present invention provides a method for preparing modified plant fibers, the method comprising the following steps:

[0006] (1) placing the impurity-removed plant fiber in a dopamine hydrochloride solution for immersion, and then filtering, washing and drying in sequence to obtain a first plant fiber;

[0007] (2) reacting cardanol glycidyl ether with a silane coupling agent to obtain cardanol siloxane;

[0008] (3) The first plant fiber, cardanol siloxane and ethanol are mixed and reacted, followed by filtering, washing and drying.

[0009] Preferably, the concentration of dopamine hydrochloride in the dopamine hydrochloride solution is 1-3 g / L.

[0010] Preferably, the pH value of the dopamine hydrochloride solution is 8-9.

[0011] Preferably, the solid-liquid ratio of the removed plant fiber to the dopamine hydrochloride solution is 100 g: 1000-2000 mL.

[0012] Preferably, the immersion conditions include: a temperature of 20-30° C. and a time of 22-26 hours.

[0013] Preferably, the specific operation of step (2) includes: mixing cardanol glycidyl ether and a silane coupling agent, and then reacting under an inert atmosphere at a temperature of 70-80° C. and a reaction time of 1-2 h to obtain cardanol siloxane.

[0014] Preferably, the weight ratio of the cardanol glycidyl ether to the silane coupling agent is 1.5-3:1.

[0015] Preferably, in step (3), the solid-to-liquid ratio of the first plant fiber to the cardanol siloxane is 1.5-6 g / mL.

[0016] Preferably, the solid-to-liquid ratio of the first plant fiber to the ethanol is 0.05-0.2 g / mL.

[0017] Preferably, the reaction conditions include: temperature of 20-30° C. and time of 6-8 h.

[0018] Preferably, in step (3), the drying conditions include: a temperature of 50-60° C. and a drying time of 20-28 h.

[0019] A second aspect of the present invention provides a modified plant fiber prepared by the above-mentioned preparation method.

[0020] A third aspect of the present invention provides use of the modified plant fiber in preparing a composite material.

[0021] A fourth aspect of the present invention provides a composite material comprising 60-75 wt % of a plastic resin and 25-40 wt % of the modified plant fiber.

[0022] A fifth aspect of the present invention provides a method for preparing the composite material, comprising the following steps: mixing a plastic resin with modified plant fibers, and then performing extrusion granulation and injection molding.

[0023] The present invention co-deposits cardanol siloxane and dopamine on the surface of plant fibers. The presence of long fatty chains enhances hydrophobicity, thereby obtaining modified plant fibers composed of a hard phase and a soft phase. This can promote the formation of a water-resistant interfacial phase in the fiber matrix, thereby improving the interfacial bonding strength and water resistance of the fiber-reinforced composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1This is a surface scanning electron microscope image of the plant fiber after impurity removal obtained in step (1) of Example 1;

[0025] Figure 2 This is an electron microscope image of the cross-sectional morphology of the composite material D1 obtained in Comparative Example 1;

[0026] Figure 3 is a surface scanning electron microscope image of the modified plant fiber A2 in Example 2;

[0027] Figure 4 is an electron microscope image of the cross-sectional morphology of the composite material S2 obtained in Example 2;

[0028] Figure 5 This is a water contact angle test graph of the plant fiber surface after impurity removal obtained in step (1) of Example 1;

[0029] Figure 6 This is a water contact angle test diagram of the surface of modified plant fiber A2 in Example 2. DETAILED DESCRIPTION

[0030] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0031] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0032] One aspect of the present invention provides a method for preparing modified plant fibers, the method comprising the following steps:

[0033] (1) placing the impurity-removed plant fiber in a dopamine hydrochloride solution for immersion, and then filtering, washing and drying in sequence to obtain a first plant fiber;

[0034] (2) reacting cardanol glycidyl ether with a silane coupling agent to obtain cardanol siloxane;

[0035] (3) The first plant fiber, cardanol siloxane and ethanol are mixed and reacted, followed by filtering, washing and drying.

[0036] In the present invention, the method for preparing the impurity-removed plant fiber comprises: mixing the plant fiber with water, stirring for 1-2 hours, filtering and washing, and drying at 80-110° C. for 24-36 hours.

[0037] In the present invention, the usage ratio of the plant fiber to water is 90-120 g:1 L.

[0038] In a specific embodiment, the ratio of the plant fiber to water is 100g:1L.

[0039] In a specific embodiment, the stirring time can be 1 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h or 2 h.

[0040] In the present invention, the plant fiber can be various plant fibers commonly used in the art. Preferably, the plant fiber is selected from one or more of poplar fiber, flax fiber, bamboo fiber and cotton fiber.

[0041] In a specific embodiment, the plant fiber is bamboo fiber.

[0042] Preferably, the length of the plant fiber is 0.2-0.8 mm.

[0043] In a preferred embodiment of the present invention, in step (1), the concentration of dopamine hydrochloride in the dopamine hydrochloride solution is 1-3 g / L, specifically 1 g / L, 1.25 g / L, 1.5 g / L, 1.75 g / L, 2 g / L, 2.25 g / L, 2.5 g / L, 2.75 g / L or 3 g / L.

[0044] In a preferred embodiment of the present invention, in step (1), the pH value of the dopamine hydrochloride solution is 8-9, specifically 8, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9 or 9.

[0045] In a preferred embodiment of the present invention, in step (1), the solid-liquid ratio of the removed plant fiber to the dopamine hydrochloride solution is 100g:1000-2000mL, specifically 100g:1000mL, 100g:1100mL, 100g:1200mL, 100g:1300mL, 100g:1400mL, 100g:1500mL, 100g:1600mL, 100g:1700mL, 100g:1800mL, 100g:1900mL or 100g:2000mL.

[0046] In a preferred embodiment of the present invention, in step (1), the immersion conditions include: a temperature of 20-30° C. and a time of 22-26 h.

[0047] In a specific embodiment, in step (1), the impregnation temperature can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C or 30°C, and the impregnation time can be 22h, 22.5h, 23h, 23.5h, 24h, 24.5h, 25h, 25.5h or 26h.

[0048] In step (1) of the present invention, the drying conditions include: temperature of 80-120° C. and time of 20-26 h.

[0049] In step (2) of the present invention, the silane coupling agent is selected from one or more of KH550, KH560 and KH570.

[0050] In a specific embodiment, in step (2), the silane coupling agent is KH550.

[0051] Preferably, the specific operation of step (2) includes: mixing cardanol glycidyl ether and a silane coupling agent, and then reacting under an inert atmosphere at a temperature of 70-80° C. and a reaction time of 1-2 h to obtain cardanol siloxane.

[0052] In step (2) of the present invention, the cardanol glycidyl ether is an epoxy compound containing a benzene ring and a long unsaturated C15 aliphatic hydrocarbon chain in its molecular structure, has a high boiling point, a low viscosity and is insoluble in water.

[0053] In the present invention, the inert atmosphere may be provided by at least one of helium, neon, argon, krypton, xenon and nitrogen.

[0054] In a specific embodiment, the inert atmosphere is provided by nitrogen.

[0055] In step (2) of the present invention, the weight ratio of the cardanol glycidyl ether to the silane coupling agent is 1.5-3:1, specifically 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1 or 3:1.

[0056] In a specific embodiment, in step (2), the reaction temperature can be 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C or 80°C, and the reaction time can be 1 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h or 2 h.

[0057] In a preferred embodiment of the present invention, in step (3), the solid-to-liquid ratio of the first plant fiber to the cardanol siloxane is 1.5-6 g / mL, specifically 1.5 g / mL, 2 g / mL, 2.5 g / mL, 3 g / mL, 3.5 g / mL, 4 g / mL, 4.5 g / mL, 5 g / mL, 5.5 g / mL or 6 g / mL.

[0058] In a preferred embodiment of the present invention, in step (3), the solid-liquid ratio of the first plant fiber to the ethanol is 0.05-0.2 g / mL, specifically 0.05 g / mL, 0.06 g / mL, 0.07 g / mL, 0.08 g / mL, 0.09 g / mL, 0.1 g / mL, 0.11 g / mL, 0.12 g / mL, 0.13 g / mL, 0.14 g / mL, 0.15 g / mL, 0.16 g / mL, 0.17 g / mL, 0.18 g / mL, 0.19 g / mL or 0.2 g / mL.

[0059] In a preferred embodiment of the present invention, in step (3), the reaction conditions include: temperature of 20-30° C. and time of 6-8 h.

[0060] In a specific embodiment of the present invention, in step (3), the reaction temperature can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C or 30°C, and the reaction time can be 6h, 6.2h, 6.4h, 6.5h, 6.7h, 6.8h, 7h, 7.2h, 7.4h, 7.5h, 7.7h, 7.9h or 8h.

[0061] In a preferred embodiment of the present invention, in step (3), the drying conditions include: a temperature of 50-60° C. and a drying time of 20-28 h.

[0062] A second aspect of the present invention provides a modified plant fiber prepared by the above-mentioned preparation method.

[0063] A third aspect of the present invention provides use of the modified plant fiber in preparing a composite material.

[0064] A fourth aspect of the present invention provides a composite material comprising 60-75 wt % of a plastic resin and 25-40 wt % of the modified plant fiber.

[0065] In a preferred embodiment, the plastic resin is a thermoplastic resin, specifically selected from one or more of polyethylene (molecular weight of 20,000-25,000, preferably 22,000), polypropylene (molecular weight of 500-600, preferably 550), polystyrene (molecular weight of 40,000-45,000, preferably 43,000), polyvinyl chloride (molecular weight of 2,500-4,000, preferably 3,000) and polylactic acid (molecular weight of 120-200, preferably 157.25).

[0066] In a specific embodiment, the plastic resin is polylactic acid, and the molecular weight of the polylactic acid is 157.25.

[0067] In a specific embodiment, the content of the plastic resin in the composite material can be 60wt%, 62wt%, 64wt%, 65wt%, 67wt%, 69wt%, 70wt%, 72wt% or 75wt%, and the content of the modified plant fiber in the composite material can be 25wt%, 27wt%, 30wt%, 33wt%, 35wt%, 37wt%, 39wt% or 40wt%.

[0068] A fifth aspect of the present invention provides a method for preparing the composite material, comprising the following steps: mixing a plastic resin with modified plant fibers, and then performing extrusion granulation and injection molding.

[0069] In the present invention, the operation of mixing the plastic resin with the modified plant fiber can be carried out in equipment commonly used in the art, for example, the mixing can be carried out in a high-speed mixer.

[0070] Preferably, the conditions for mixing the plastic resin and the modified plant fiber include: a mixing time of 500-700s and a rotation speed of 1500-2500rpm. Specifically, the mixing time can be 500s, 520s, 540s, 560s, 580s, 600s, 620s, 640s, 660s, 680s or 700s, and the mixing speed can be 1500rpm, 1600rpm, 1700rpm, 1800rpm, 1900rpm, 2000rpm, 2100rpm, 2200rpm, 2300rpm, 2400rpm or 2500rpm.

[0071] In the present invention, the extrusion granulation operation can be carried out in equipment commonly used in the art, for example, the extrusion granulation can be carried out in a twin-screw extruder.

[0072] In a preferred embodiment of the present invention, when a twin-screw extruder is used for extrusion granulation, the heating zone in the twin-screw granulator is set to zone 3-4. Further preferably, the heating zone in the twin-screw granulator is set to zone 4, and the heating zone temperatures are: 155-165°C in the first zone, 160-170°C in the second zone, 165-175°C in the third zone, and 155-165°C in the fourth zone.

[0073] In a specific embodiment, the temperatures of the heating zones are: 160°C in the first zone, 165°C in the second zone, 170°C in the third zone, and 160°C in the fourth zone.

[0074] In a preferred embodiment of the present invention, the twin screw speed of the twin screw extruder is 10-30 rpm, specifically 10 rpm, 12 rpm, 14 rpm, 16 rpm, 18 rpm, 20 rpm, 22 rpm, 24 rpm, 26 rpm, 28 rpm or 30 rpm.

[0075] In a specific embodiment, the twin-screw speed of the twin-screw extruder is 20 rpm.

[0076] In a preferred embodiment, the material obtained after extrusion granulation by a twin-screw granulator needs to be crushed and then injection molded.

[0077] In a preferred embodiment of the present invention, the injection pressure is controlled to be 5-7 MPa, the injection time is 8-10 s, and the mold closing time is 4-6 s.

[0078] In a specific embodiment, the injection pressure is controlled to be 6 MPa, the injection time is 9 s, and the mold closing time is 5 s.

[0079] The pressure described in the present invention refers to absolute pressure.

[0080] Compared with the prior art, the present invention has the following beneficial effects:

[0081] 1. The composite material, using common plant fibers as the primary reinforcement, is a renewable, biodegradable, green, natural polymer material that is widely available, inexpensive, and easy to prepare. This can expand the application of plant fiber materials and achieve high-value utilization of common plant fibers.

[0082] 2. The cardanol siloxane synthesized from cardanol glycidyl ether and silane coupling agent retains the chemical properties of aromatic compounds and unsaturated aliphatic hydrocarbons, and also retains the excellent interfacial bonding ability of silane coupling agent with plant fibers, thereby improving the interfacial properties of fiber composite materials.

[0083] 3. Due to its superior adhesion and high reactivity, the dopamine coating can effectively improve the interfacial compatibility between plant fibers and plastic matrices. At the same time, the dopamine excitation reaction can also induce the simultaneous silicification and fixation of epoxy and amino-terminated long-chain molecules to prepare high-performance fiber-reinforced composites. The hydrophobic cardanol siloxane is fixed to the surface of the plant fiber. The presence of long fatty chains enhances the hydrophobicity, and a modified plant fiber composed of a hard phase and a soft phase is obtained, which can promote the formation of a water-resistant interfacial phase in the fiber matrix and improve the interfacial bonding strength and water resistance of the fiber-reinforced composite material.

[0084] 4. Plant fiber-reinforced composites have enormous market potential and can be applied in automotive, green building materials, military, aerospace, home building materials, food packaging, industrial agriculture, and other fields. Plant fiber-reinforced composites are not only environmentally friendly but also enable the high-value utilization of plant fibers and the transformation and upgrading of the industrial chain. These materials offer advantages such as low cost, short production cycles, energy conservation, environmental friendliness, and biodegradability, meeting the requirements of green chemistry.

[0085] The present invention will be described in detail below through examples, but the scope of protection of the present invention is not limited thereto.

[0086] The plant fibers used in the examples and comparative examples were purchased from Anhui Sentai Wood Plastic Group Co., Ltd., with a length of 0.2-0.8 mm; cardanol glycidyl ether was purchased from Wuhan Kemik Biopharmaceutical Technology Co., Ltd., and polylactic acid (molecular weight 157.25) was purchased from NatureWorks, Inc., USA.

[0087] The room temperature below refers to 25℃.

[0088] Example 1

[0089] (1) 150 g of plant fiber (bamboo fiber) was added to 1.5 L of water, mixed and stirred for 1 h, and then filtered. The filtered solid was washed and then dried in an oven at 105 ° C for 24 h to obtain the plant fiber after impurities were removed;

[0090] (2) 100 g of the plant fiber after impurity removal was placed in 1 L of dopamine hydrochloride solution (the concentration of dopamine hydrochloride was 2 g / L, and the pH value of the dopamine hydrochloride solution was 8.5), and immersed at room temperature for 24 h under stirring, and then filtered. The solid obtained by filtration was washed and then dried in an oven at 105° C. for 24 h to obtain a first plant fiber;

[0091] (3) 20 g of cardanol glycidyl ether and 10 g of silane coupling agent (KH550) were placed in a three-necked flask and mixed, with the weight ratio of cardanol glycidyl ether to silane coupling agent being 2:1. Then, nitrogen was introduced to react at a temperature of 75 ° C. for 1 h to obtain cardanol siloxane;

[0092] (4) 50 g of the first plant fiber was added to 500 mL of anhydrous ethanol, and then 10 mL of cardanol siloxane was added and mixed, and the mixture was reacted under stirring at a temperature of 25° C. for 6 h. The mixture was then filtered, and the filtered solid was washed and then dried in an oven at 55° C. for 24 h to obtain a modified plant fiber A1.

[0093] (5) 30 g of modified plant fiber A1 and 70 g of polylactic acid were mixed in a high-speed mixer. The mixing conditions included: time of 600 s and speed of 2000 rpm. The mixed materials were then added to a twin-screw extruder for melt extrusion granulation. The heating zone in the twin-screw granulator was set to 4 zones, and the twin-screw temperatures were: 160°C in the first zone, 165°C in the second zone, 170°C in the third zone, and 160°C in the fourth zone. The twin-screw speed of the twin-screw extruder was 20 rpm. The materials were then crushed and added to an injection molding machine for injection molding. The injection pressure was controlled to 6 MPa, the injection time was 9 s, and the mold closing time was 5 s to obtain a composite material S1.

[0094] Example 2

[0095] The method of Example 1 was followed, except that 15 mL of cardanol siloxane was added in step (4), i.e., the solid-liquid ratio of the first plant fiber to the cardanol siloxane was 3.33 g / mL, to obtain modified plant fiber A2, and thus prepare composite material S2.

[0096] Example 3

[0097] The method of Example 1 was followed, except that 20 mL of cardanol siloxane was added in step (4), i.e., the solid-liquid ratio of the first plant fiber to the cardanol siloxane was 2.5 g / mL, to obtain modified plant fiber A3, and thus prepare composite material S3.

[0098] Comparative Example 1

[0099] The method of Example 1 was followed, except that the plant fiber obtained in step (1) of Example 1 after impurities removal was directly used to replace the first plant fiber to prepare the composite material D1. The specific steps were as follows:

[0100] 30 g of the impurity-removed plant fiber obtained in step (1) of Example 1 was mixed with 70 g of polylactic acid in a high-speed mixer. The mixing conditions included: a time of 600 s and a speed of 2000 rpm. The mixed material was then added to a twin-screw extruder for melt extrusion and granulation. The heating zone in the twin-screw granulator was set to 4 zones, the twin-screw temperature was: 160°C in the first zone, 165°C in the second zone, 170°C in the third zone, and 160°C in the fourth zone. The twin-screw speed of the twin-screw extruder was 20 rpm. The material was then crushed and added to an injection molding machine for injection molding. The injection pressure was controlled to 6 MPa, the injection time was 9 s, and the mold closing time was 5 s to obtain a composite material D1.

[0101] Test Example 1

[0102] The surface scanning electron micrograph of the plant fiber after impurity removal obtained in step (1) of Example 1 and the cross-sectional morphology of D1 were observed using a scanning electron microscope. Figure 1 and 2 The surface scanning electron microscope images of A2 and the cross-sectional morphology of S2 were observed using scanning electron microscope, respectively. Figure 3 and 4 shown.

[0103] As shown in the figure, the surface of the unmodified fiber is neat and smooth, and the parallel grooves inherent in the natural fiber are clearly visible. The modified coating attached to the surface of the plant fiber modified with cardanol siloxane reduces the defects on the fiber surface. At the same time, the co-deposited coating is tightly bonded to the fiber to form a uniform and compact hydrophobic modified coating, which effectively improves the surface performance of the fiber.

[0104] The impact cross-section morphology of the composite material was observed. Figure 2 There are a lot of holes in the cross section of the composite material left after the fibers are pulled out. There are large gaps at the boundary between the unmodified plant fibers after impurity removal and the polylactic acid matrix, and the interfacial compatibility between the unmodified plant fibers and the polylactic acid matrix is poor. Figure 4 The fibers are tightly wrapped in the polylactic acid matrix at the cross section. When subjected to external force, the fibers break at the interface and are rarely pulled out of the matrix. The holes in the cross section almost disappear, indicating that the modified plant fibers have good bonding strength with the polylactic acid matrix at the interface.

[0105] Test Example 2

[0106] The contact angle detection system was used to detect the change of water contact angle of the plant fiber after impurity removal obtained in step (1) of Example 1 and the surface of A2 over time. The contact angle data was the angle at which the water droplet contacted the fiber surface for 10 seconds, respectively. Figure 5 and Figure 6 As shown;

[0107] Depend on Figure 5 and Figure 6 Yes, the introduction of modifiers can reduce the number of hydroxyl groups on the surface of plant fibers, thereby enhancing the hydrophobicity of the fibers and showing excellent hydrophobic properties.

[0108] Test Example 3

[0109] The mechanical properties of S1, S2, S3, and D1 were tested respectively, wherein the flexural properties (flexural strength and flexural modulus) were tested according to the standard ASTM D790-03 (2003), the tensile properties (tensile strength and tensile modulus) were tested according to the standard ASTM D638-03 (2003), and the impact properties (impact strength) were tested according to the standard ASTM D256-03 (2003). The results are shown in Table 1.

[0110] Table 1

[0111]

[0112] The results in Table 1 show that the plant fiber in Comparative Example 1 was not modified, resulting in poor interfacial compatibility between the bamboo fiber and polylactic acid in the resulting composite material. Consequently, the mechanical properties of the composite material were inferior to those of the other examples. In the examples, the mechanical properties of the composite material were significantly improved because dopamine has good interfacial compatibility and reactivity. This allows for molecular entanglement with the plastic matrix, enhancing the interaction between the two phases. Furthermore, it increases the grafting rate of the cardanol siloxane, strengthening interfacial bonding.

[0113] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A composite material, characterized in that The composite material contains 60-75 wt% of a plastic resin and 25-40 wt% of a modified plant fiber, wherein the preparation method of the modified plant fiber comprises the following steps: (1) placing the impurity-removed plant fiber in a dopamine hydrochloride solution for immersion, and then filtering, washing and drying in sequence to obtain a first plant fiber; (2) reacting cardanol glycidyl ether with a silane coupling agent to obtain cardanol siloxane; (3) mixing the first plant fiber, cardanol siloxane and ethanol, and then reacting, followed by filtering, washing and drying; The concentration of dopamine hydrochloride in the dopamine hydrochloride solution is 1-3 g / L, the pH value of the dopamine hydrochloride solution is 8-9, and the solid-liquid ratio of the plant fiber after impurity removal to the dopamine hydrochloride solution is 100 g: 1000-2000 mL; The weight ratio of the cardanol glycidyl ether to the silane coupling agent is 1.5-3:1; The solid-to-liquid ratio of the first plant fiber to the cardanol siloxane is 1.6:1-6 g / mL; The solid-to-liquid ratio of the first plant fiber to the ethanol is 0.05-0.2 g / mL; The plastic resin is a thermoplastic resin, selected from one or more of polyethylene with a molecular weight of 20,000-25,000, polypropylene with a molecular weight of 500-600, polystyrene with a molecular weight of 40,000-45,000, polyvinyl chloride with a molecular weight of 2,500-4,000 and polylactic acid with a molecular weight of 120-200.

2. The composite material according to claim 1, characterized in that The immersion conditions include: a temperature of 20-30° C. and a time of 22-26 hours.

3. The composite material according to claim 1, characterized in that The specific operation of step (2) includes: mixing cardanol glycidyl ether and a silane coupling agent, and then reacting under an inert atmosphere at a temperature of 70-80° C. and a reaction time of 1-2 hours to obtain cardanol siloxane.

4. The composite material according to claim 1, characterized in that In step (3), the reaction conditions include: temperature of 20-30°C and time of 6-8h.

5. The composite material according to claim 1 or 4, characterized in that In step (3), the drying conditions include: temperature of 50-60°C and time of 20-28 hours.

6. A method for preparing the composite material according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: mixing plastic resin with modified plant fiber, and then performing extrusion granulation and injection molding.

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