Preparation method and application of interface-modified flame-retardant polypropylene-based bamboo-plastic composite material

Abstract

The invention discloses a preparation method of an interface-modified flame-retardant polypropylene-based bamboo-plastic composite material. According to the method, a modification solution composed of a polyphenol component and a boron-containing component is adopted, bamboo powder is treated under the normal-temperature stirring condition, and the interface modified bamboo powder is successfully prepared. The mechanism is that polyphenol and a boron-containing component are subjected to a coordination reaction on the surface of bamboo powder, and a reversible borate dynamic covalent bond is constructed. The dynamic bond has a temperature response characteristic: reversible dissociation is realized during high-temperature processing, so that the melt viscosity of a composite system is reduced, and the processing fluidity is improved; the interface bonding force between the bamboo powder and the polypropylene matrix and the mechanical strength of the composite material are remarkably enhanced. In addition, the introduced boron element is used as an efficient flame-retardant component and promotes generation of a compact protective carbon layer during combustion, so that the flame-retardant property of the composite material is comprehensively improved.

Description

Technical Field

[0001] This invention relates to the field of polymer flame-retardant composite materials technology, specifically to a method for preparing an interface-modified, flame-retardant polypropylene-based bamboo-plastic composite material and its application. Background Technology

[0002] Bamboo's short growth cycle, renewability, abundant reserves, and high strength-to-weight ratio make it suitable for building materials, alleviating my country's timber resource shortage. However, natural bamboo is susceptible to moisture absorption, which reduces its mechanical properties, and it is also vulnerable to insect infestation, limiting its practical applications. Polymer plastics, on the other hand, generally possess chemical stability, are lightweight, and do not readily absorb water. Polypropylene, with its high cost-effectiveness and good processing characteristics, is the most commonly used general-purpose plastic; however, its non-degradability contributes to white pollution. In contrast, bamboo-plastic composites avoid these problems, offering excellent industrial applicability and alleviating the environmental pressure caused by the widespread use of plastics.

[0003] With the increasing demands for material performance, bamboo-plastic composites suffer from poor interfacial bonding due to the significant polarity difference between bamboo and polymers, resulting in defects in the composite's mechanical properties. Therefore, improving the interfacial compatibility and adhesion between bamboo and the polymer matrix is ​​a key issue in expanding the applications of bamboo-plastic composites.

[0004] Besides interfacial compatibility issues, the flame retardancy of bamboo-plastic composites is also a major challenge. Both bamboo powder and polypropylene are flammable materials, and their composite system exhibits rapid flame propagation and a high fire safety hazard, severely limiting its application in fields with high flame retardancy requirements (such as interior decoration and transportation). The multi-component nature of the composite necessitates more precise control of the flame-retardant formulation, often leading to complex processing and uneven filler dispersion in the matrix. Therefore, a simple method for interfacial modification and flame retardant polypropylene-based injection-molded composite materials is needed. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention aims to provide a method for preparing interface-modified, flame-retardant polypropylene-based bamboo-plastic composites. This invention develops a novel surface modification strategy by treating bamboo powder with an aqueous solution containing polyphenols and boron components under room-temperature stirring conditions to prepare functionalized bamboo powder. This method constructs reversible borate ester bonds on the bamboo powder surface through the coordination interaction between hydroxyl groups and polyphenols. These dynamic bonds exhibit temperature-responsive characteristics: they can dissociate at higher processing temperatures, thereby reducing melt viscosity and promoting composite material processing; and they can reform upon cooling, thereby enhancing interfacial bonding and mechanical strength. The introduced boron element not only serves as an intrinsic flame-retardant component, generating a protective char layer during combustion, but also synergistically works with phosphorus-containing flame retardants, thus comprehensively improving the flame-retardant properties of the composite material.

[0006] A polypropylene-based bamboo-plastic composite material with interface modification was prepared by compounding modified bamboo powder, polypropylene, and flame retardant. This process realizes the high-value utilization of bamboo powder, conforms to the current environmental protection concept of "replacing plastic with bamboo", not only takes into account the performance advantages of polypropylene and bamboo, but also improves the comprehensive mechanical properties of bamboo-plastic composite material and enhances the flame retardant properties of composite material. It has extremely high social and economic value and significance for industrialization.

[0007] The present invention provides the following technical solution: On the one hand, the present invention provides a method for modifying bamboo powder with a weakly acidic solution, wherein the solution is obtained by grafting polyphenolic components and boron-containing components together on the surface of bamboo powder.

[0008] Furthermore, the mass ratio of the polyphenolic component to the boron-containing component is 2:1.

[0009] Furthermore, the mass fraction of the polyphenolic component and the boron-containing component in the solution is 1.0–2.0 wt%.

[0010] Furthermore, the bamboo powder has a mass fraction of 5-15 wt% in the acidic solution.

[0011] Furthermore, the polyphenolic component is selected from one of tannic acid, ellagic acid, and gallic acid.

[0012] Furthermore, the boron-containing component is selected from one of borax, boric acid, disodium octaborate, and phenyldiboronic acid.

[0013] Furthermore, the tannic acid is reagent grade with a purity of 98%, purchased from Maclean's Reagents. The borax has a purity of 99% and was purchased from Beijing Chemical Plant.

[0014] In another aspect, the present invention provides a method for modifying the interface of bamboo powder as described above, comprising the following steps:

[0015] The polyphenolic component and the boron-containing component were dissolved in water in a certain proportion to obtain an acidic solution;

[0016] The acidic solution is used to soak the bamboo powder to obtain modified bamboo powder.

[0017] Furthermore, the bamboo powder is soaked in the acidic solution for 30 minutes;

[0018] The bamboo powder is soaked in an acidic solution at a temperature of 20–30°C.

[0019] The drying temperature is 60–80°C;

[0020] The drying time is 24 to 48 hours.

[0021] Furthermore, the preparation method includes the following steps:

[0022] S1. Dissolve the polyphenolic component and the boron-containing component together in deionized water at a mass ratio of 2:1 for 30 minutes at room temperature using magnetic stirring (500 rpm).

[0023] S2. Bamboo powder was then added, and the reaction continued for 30 minutes under the same stirring conditions. The resulting suspension was vacuum filtered and washed three times with deionized water to remove unreacted substances. Finally, the collected precipitate was placed in a vacuum oven and dried at 60–80°C for 24–48 hours until the mass was constant.

[0024] In another aspect, the present invention provides a method for preparing an interface-modified, flame-retardant polypropylene-based bamboo-plastic composite material, comprising polypropylene and the modified bamboo powder as described in any one of claims 3 to 5.

[0025] Furthermore, the raw materials in the bamboo-plastic composite material include the following components:

[0026] 100 parts by weight of a mixture of polypropylene and modified bamboo powder, and 10 to 18 parts of flame retardant.

[0027] Furthermore, the mass ratio of the polypropylene to the modified bamboo powder is maintained at 1:1.

[0028] Furthermore, the polypropylene is isotactic polypropylene with a melt index of 2.6 g / 10 min.

[0029] Furthermore, the flame retardant is piperazine pyrophosphate with a purity of 99%.

[0030] Further, the polypropylene, modified bamboo powder, and piperazine pyrophosphate were vacuum dried at 80°C for 12 hours to remove moisture and then mixed evenly.

[0031] Furthermore, a twin-screw extrusion process is used at 80–100 rpm and 170–190°C, followed by injection molding at 3–6 bar and 170–190°C.

[0032] On the other hand, this invention also provides applications of the interface-modified, flame-retardant polypropylene-based bamboo-plastic composite material prepared by the above method. Based on the excellent comprehensive mechanical and flame-retardant properties of this composite material (limiting oxygen index >24.3%, UL-94 V-0 rating, tensile strength up to 19.9 MPa), it is particularly suitable for fields with high requirements for material strength and fire safety, such as the manufacture of automotive interior parts (e.g., door panels, dashboard back panels), building formwork, outdoor paving, logistics pallets, and furniture components. This not only realizes the high-value utilization of bamboo powder but also provides a high-performance solution for "replacing plastic with bamboo," possessing broad market prospects.

[0033] The beneficial effects of this invention are as follows:

[0034] By constructing dynamic and reversible borate ester bonds on the surface of bamboo powder using tannic acid / boron-containing components, the composite material's interfacial compatibility, processing fluidity, mechanical strength, and flame retardant properties are synergistically improved, successfully solving the technical challenge of traditional bamboo-plastic composite materials struggling to achieve multiple properties simultaneously. Attached Figure Description

[0035] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0036] Figure 1 The thermogravimetric analysis (TGA) curves of Example 1 and Comparative Example 3 under nitrogen atmosphere are compared, demonstrating the effect of modification treatment on improving the thermal stability and char-forming properties of the composite material.

[0037] Figure 2 The bar chart shows the comparison of tensile strength and impact strength between Example 2 and Comparative Example 2, reflecting the effect of flame retardant addition on the mechanical properties of the materials.

[0038] Figure 3 The images shown are cross-sectional scanning electron microscope (SEM) images of Example 3 and Comparative Example 1, illustrating the interfacial bonding and microscopic morphological differences before and after bamboo powder modification.

[0039] Figure 4 The comparison of the carbonyl index of Example 4 and Comparative Example 1 after 150 hours of UV aging shows that the modification treatment significantly slowed down the photo-oxidative aging process of the materials. Detailed Implementation

[0040] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0041] The tannic acid is reagent grade with a purity of 98%, purchased from Maclean's Reagents; the borax has a purity of 99%, purchased from Beijing Chemical Plant; the flame retardant is piperazine pyrophosphate with a purity of 99%, purchased from Sichuan Jingshida Technology Co., Ltd.; unless otherwise specified, other reagents are also commercially available.

[0042] Example 1

[0043] This embodiment provides a method for preparing an interface-modified, flame-retardant polypropylene-based bamboo-plastic composite material:

[0044] S1. Weigh 20g of tannic acid and 10g of borax, dissolve them in 1500mL of deionized water, and dissolve them together for 30min at room temperature using magnetic stirring (500rpm) to obtain an acidic solution with a mass fraction of approximately 2.0wt%.

[0045] S2. Subsequently, 150g of 100-mesh bamboo powder was added to the above solution, and the reaction was continued for 30 minutes under the same stirring conditions. The resulting suspension was vacuum filtered and washed three times with deionized water to remove unreacted substances. Finally, the collected precipitate was placed in a vacuum oven and dried at 80°C for 24 hours until the mass was constant, thus obtaining modified bamboo powder.

[0046] S3. 500g of polypropylene, 500g of the above-mentioned modified bamboo powder, and 120g of piperazine pyrophosphate were vacuum dried at 80℃ for 12h to remove moisture. Then, they were mixed in a high-speed mixer for 15min, followed by melt blending and extrusion granulation using a twin-screw extruder (screw speed 80rpm, barrel temperature 180℃). Finally, the masterbatch was injection molded into standard test strips in an injection molding machine (injection pressure 5bar, injection temperature 180℃).

[0047] Performance testing of the samples: The composite material achieved a limiting oxygen index (LOI) of 24.3% and passed the UL-94V-0 flammability test, demonstrating excellent flame retardant properties. Thermogravimetric analysis (TGA) results ( Figure 1 The results showed that, under a nitrogen atmosphere, the char residue of the material in Example 1 at 800°C was as high as 18.7%, which was significantly higher than that of Comparative Example 3 (with added unmodified bamboo powder) at 9.1%, further confirming that the char-forming properties and thermal stability of the modified system were significantly enhanced at high temperatures.

[0048] Example 2

[0049] This embodiment provides a method for preparing an interface-modified, flame-retardant polypropylene-based bamboo-plastic composite material:

[0050] S1. Weigh 20g of tannic acid and 10g of borax, dissolve them in 1500mL of deionized water, and dissolve them together for 30min at room temperature using magnetic stirring (500rpm) to obtain an acidic solution with a mass fraction of approximately 2.0wt%.

[0051] S2. Subsequently, 150g of 100-mesh bamboo powder was added to the above solution, and the reaction was continued for 30 minutes under the same stirring conditions. The resulting suspension was vacuum filtered and washed three times with deionized water to remove unreacted substances. Finally, the collected precipitate was placed in a vacuum oven and dried at 80°C for 24 hours until the mass was constant, thus obtaining modified bamboo powder.

[0052] S3. 500g of polypropylene, 500g of the above-mentioned modified bamboo powder, and 140g of piperazine pyrophosphate were vacuum dried at 80℃ for 12h to remove moisture. Then, they were mixed in a high-speed mixer for 15min, followed by melt blending and extrusion granulation using a twin-screw extruder (screw speed 80rpm, barrel temperature 180℃). Finally, the masterbatch was injection molded into standard test strips in an injection molding machine (injection pressure 5bar, injection temperature 180℃).

[0053] Perform performance testing on the spline: such as Figure 2 As shown, the composite material prepared in Example 2 exhibits superior comprehensive mechanical properties, with a tensile strength of 17.5 MPa and an impact strength of 3.2 kJ / m. 2 In contrast, in Comparative Example 2, with the flame retardant addition increased to 200g, both tensile strength and impact strength decreased significantly, reaching only 13.9MPa and 1.9kJ / m², respectively. 2 The above results indicate that increasing the amount of flame retardant added within a certain range helps to enhance the flame retardant properties of the material, but excessive addition will have an adverse effect on the mechanical properties of the composite material.

[0054] Example 3

[0055] This embodiment provides a method for preparing an interface-modified, flame-retardant polypropylene-based bamboo-plastic composite material:

[0056] S1. Weigh 20g of tannic acid and 10g of borax, dissolve them in 1500mL of deionized water, and dissolve them together for 30min at room temperature using magnetic stirring (500rpm) to obtain an acidic solution with a mass fraction of approximately 2.0wt%.

[0057] S2. Subsequently, 150g of 100-mesh bamboo powder was added to the above solution, and the reaction was continued for 30 minutes under the same stirring conditions. The resulting suspension was vacuum filtered and washed three times with deionized water to remove unreacted substances. Finally, the collected precipitate was placed in a vacuum oven and dried at 80°C for 24 hours until the mass was constant, thus obtaining modified bamboo powder.

[0058] S3. 500g of polypropylene, 500g of the above-mentioned modified bamboo powder, and 160g of piperazine pyrophosphate were vacuum dried at 80℃ for 12h to remove moisture. Then, they were mixed in a high-speed mixer for 15min, followed by melt blending and extrusion granulation using a twin-screw extruder (screw speed 80rpm, barrel temperature 180℃). Finally, the masterbatch was injection molded into standard test strips in an injection molding machine (injection pressure 5bar, injection temperature 180℃).

[0059] Perform performance testing on the spline: such as Figure 3 As shown in the electron micrograph of the cross-section of the composite material prepared from unmodified bamboo powder, obvious interfacial gaps and piperazine pyrophosphate agglomeration are visible, indicating poor interfacial compatibility between bamboo powder and the polypropylene matrix, and uneven dispersion of the flame retardant. These structural defects easily lead to stress concentration, thereby reducing mechanical properties. In contrast, the composite material prepared from bamboo powder modified by the tannic acid / borax system exhibits a uniform phase in its cross-section, with the interfacial gaps and piperazine pyrophosphate agglomeration essentially disappearing, and a continuous tear ridge morphology appearing. This indicates a significantly enhanced interfacial bonding between bamboo powder and polypropylene, improved flame retardant dispersion, and effective stress transfer and dissipation under stress, resulting in superior overall mechanical properties.

[0060] Example 4

[0061] This embodiment provides a method for preparing an interface-modified, flame-retardant polypropylene-based bamboo-plastic composite material:

[0062] S1. Weigh 20g of tannic acid and 10g of boric acid, dissolve them in 1500mL of deionized water, and dissolve them together for 30min at room temperature using magnetic stirring (500rpm) to obtain an acidic solution with a mass fraction of approximately 2.0wt%.

[0063] S2. Subsequently, 150g of 100-mesh bamboo powder was added to the above solution, and the reaction was continued for 30 minutes under the same stirring conditions. The resulting suspension was vacuum filtered and washed three times with deionized water to remove unreacted substances. Finally, the collected precipitate was placed in a vacuum oven and dried at 80°C for 24 hours until the mass was constant, thus obtaining modified bamboo powder.

[0064] S3. 500g of polypropylene, 500g of the above-mentioned modified bamboo powder, and 160g of piperazine pyrophosphate were vacuum dried at 80℃ for 12h to remove moisture. Then, they were mixed in a high-speed mixer for 15min, followed by melt blending and extrusion granulation using a twin-screw extruder (screw speed 80rpm, barrel temperature 180℃). Finally, the masterbatch was injection molded into standard test strips in an injection molding machine (injection pressure 5bar, injection temperature 180℃).

[0065] By comparing the carbonyl indices of Example 4 and Comparative Example 1 after 150 hours of UV aging, the carbonyl index of Example 4 was only 3.1, far lower than that of Comparative Example 1 (6.6). This result indicates that bamboo powder modified with a combination of tannic acid and boric acid can significantly enhance the resistance of polypropylene-based composites to UV-induced oxygen aging, effectively suppressing the content of carbonyl compounds generated during the aging process due to molecular chain breakage and oxidation, thereby slowing down the aging rate and improving durability.

[0066] Comparative Example 1

[0067] This comparative example provides a method for preparing a polypropylene-based bamboo-plastic composite material:

[0068] S1. 500g of polypropylene, 500g of unmodified bamboo powder, and 160g of piperazine pyrophosphate were vacuum dried at 80℃ for 12h to remove moisture. Then, they were mixed in a high-speed mixer for 15min, followed by melt blending and extrusion granulation using a twin-screw extruder (screw speed 80rpm, barrel temperature 180℃). Finally, the masterbatch was injection molded into standard test strips using an injection molding machine (injection pressure 5bar, injection temperature 180℃).

[0069] Comparative Example 2

[0070] This comparative example provides a method for preparing a polypropylene-based bamboo-plastic composite material:

[0071] S1. Weigh 20g of tannic acid and 10g of borax, dissolve them in 1500mL of deionized water, and dissolve them together for 30min at room temperature using magnetic stirring (500rpm) to obtain an acidic solution with a mass fraction of approximately 2.0wt%.

[0072] S2. Subsequently, 150g of 100-mesh bamboo powder was added to the above solution, and the reaction was continued for 30 minutes under the same stirring conditions. The resulting suspension was vacuum filtered and washed three times with deionized water to remove unreacted substances. Finally, the collected precipitate was placed in a vacuum oven and dried at 80°C for 24 hours until the mass was constant, thus obtaining modified bamboo powder.

[0073] S3. 500g of polypropylene, 500g of the above-mentioned modified bamboo powder, and 200g of piperazine pyrophosphate were vacuum dried at 80℃ for 12h to remove moisture. Then, they were mixed in a high-speed mixer for 15min, followed by melt blending and extrusion granulation using a twin-screw extruder (screw speed 80rpm, barrel temperature 180℃). Finally, the masterbatch was injection molded into standard test strips in an injection molding machine (injection pressure 5bar, injection temperature 180℃).

[0074] Comparative Example 3

[0075] This comparative example provides a method for preparing a polypropylene-based bamboo-plastic composite material to investigate the effect of insufficient flame retardant on performance:

[0076] S1. Weigh 20g of tannic acid and 10g of borax, dissolve them in 1500mL of deionized water, and dissolve them together for 30min at room temperature using magnetic stirring (500rpm) to obtain an acidic solution with a mass fraction of approximately 2.0wt%.

[0077] S2. Subsequently, 150g of 100-mesh bamboo powder was added to the above solution, and the reaction was continued for 30 minutes under the same stirring conditions. The resulting suspension was vacuum filtered and washed three times with deionized water to remove unreacted substances. Finally, the collected precipitate was placed in a vacuum oven and dried at 80°C for 24 hours until the mass was constant, thus obtaining modified bamboo powder.

[0078] S3. 500g of polypropylene, 500g of the above-mentioned modified bamboo powder, and 80g of piperazine pyrophosphate were vacuum dried at 80℃ for 12h to remove moisture. Then, they were mixed in a high-speed mixer for 15min, followed by melt blending and extrusion granulation using a twin-screw extruder (screw speed 80rpm, barrel temperature 180℃). Finally, the masterbatch was injection molded into standard test strips in an injection molding machine (injection pressure 5bar, injection temperature 180℃).

[0079] Comparative Example 4

[0080] This comparative example provides a method for preparing a polypropylene-based bamboo-plastic composite material to investigate the effect of the type of flame retardant on the properties of the composite material.

[0081] S1. Weigh 20g of tannic acid and 10g of borax, dissolve them in 1500mL of deionized water, and dissolve them together for 30min at room temperature using magnetic stirring (500rpm) to obtain an acidic solution with a mass fraction of approximately 2.0wt%.

[0082] S2. Subsequently, 150g of 100-mesh bamboo powder was added to the above solution, and the reaction was continued for 30 minutes under the same stirring conditions. The resulting suspension was vacuum filtered and washed three times with deionized water to remove unreacted substances. Finally, the collected precipitate was placed in a vacuum oven and dried at 80°C for 24 hours until the mass was constant, thus obtaining modified bamboo powder.

[0083] S3. 500g of polypropylene, 500g of the modified bamboo powder described above, and 160g of ammonium polyphosphate were vacuum dried at 80℃ for 12h to remove moisture. Then, they were mixed in a high-speed mixer for 15min, followed by melt blending and extrusion granulation using a twin-screw extruder (screw speed 80rpm, barrel temperature 180℃). Finally, the masterbatch was injection molded into standard test specimens using an injection molding machine (injection pressure 5bar, injection temperature 180℃).

[0084] The conventional mechanical properties and combustion performance of polypropylene-based bamboo-plastic composites were tested according to the following standards, and the results are shown in Table 1.

[0085] Impact strength of cantilever beam: Tested according to GB / T1043.1-2018 standard, the impact energy is 2J;

[0086] Tensile strength: Tested according to GB / T1040.1-2018 standard, at a test speed of 5 mm / min;

[0087] Flammability: Tested according to LOI standard in accordance with GB / T2406-2015 and UL-94 standard in accordance with GB / T2408-2008.

[0088] Figure 1 This is a comparison graph of the thermogravimetric analysis (TGA) curves of Example 1 and Comparative Example 3 under nitrogen atmosphere;

[0089] Figure 2 This is a bar chart comparing the tensile strength and impact strength of Example 2 and Comparative Example 2.

[0090] Figure 3 Cross-sectional scanning electron microscope (SEM) images of Example 3 and Comparative Example 1;

[0091] Figure 4 This is a comparison of the carbonyl index of Example 4 and Comparative Example 1 after 150 hours of UV aging.

[0092] Table 1

[0093] Conclusion: The interface-modified, flame-retardant polypropylene-based bamboo-plastic composite material of the present invention exhibits excellent comprehensive performance. As shown in Table 1, all examples achieved UL-94V-0 flame retardancy, with limiting oxygen index (LOI) above 24.3%, and char residue at 800℃ reaching 18.7%–21.5%, significantly better than the unmodified control group (Comparative Example 1). This demonstrates that the present invention, by modifying bamboo powder with a tannic acid-boron system and compounding it with piperazine pyrophosphate, can significantly improve the flame retardancy and char formation of the material. In terms of mechanical properties, the examples maintained excellent flame retardancy while exhibiting a good balance of mechanical properties. Comparative Example 2 (excessive flame retardant) showed excellent flame retardancy but significantly decreased mechanical properties, while Comparative Example 3 (insufficient flame retardant) had high mechanical properties but failed to meet the flame retardancy standard (V-2), which conversely confirms the rationality of the flame retardant dosage range of the present invention. Comparative Example 4 (changing the type of flame retardant) showed a comprehensive decline in performance, further demonstrating the specific synergistic effect of piperazine pyrophosphate and the modified system. In summary, this invention successfully solves the technical challenge of balancing flame retardancy and mechanical properties in bamboo-plastic composites, providing an effective solution for the industrial application of high-performance bamboo-plastic composites.

[0094] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. An interface-modified, flame-retardant polypropylene-based bamboo-plastic composite material, characterized in that, The polypropylene-based bamboo-plastic composite material includes polypropylene, modified bamboo powder, and flame retardant; The modified bamboo powder was obtained by treating it with polyphenolic substances and boron-containing components.

2. The polypropylene-based bamboo-plastic composite material according to claim 1, characterized in that, The polypropylene-based composite material comprises the following components in parts by weight: 100 parts by weight of a mixture of polypropylene and modified bamboo powder; wherein the mass ratio of polypropylene to modified bamboo powder is 1:1; Flame retardant piperazine pyrophosphate 10-18 parts; The modified bamboo powder has a mesh size of 50-100 mesh.

3. A method for preparing the polypropylene-based bamboo-plastic composite material according to claim 1, characterized in that, The preparation method includes the following steps: (I) Preparation of modified bamboo powder: bamboo powder is soaked in an acidic solution composed of polyphenols and boron-containing components, stirred and dispersed evenly, and after soaking for a period of time, the bamboo powder is filtered, washed and dried to obtain modified bamboo powder; (II) Polypropylene, modified bamboo powder and flame retardant are mixed evenly according to the proportions described in claim 2, and then the mixture is fed into a twin-screw extruder. After melt plasticization and extrusion molding, bamboo-plastic composite material masterbatch is prepared. Then the masterbatch is injection molded to obtain the final polypropylene-based bamboo-plastic composite material.

4. The preparation method according to claim 3, characterized in that, In step (I), the mass fraction of the acidic solution is 1.0–2.0 wt%. In the acidic solution, the mass ratio of polyphenols to boron-containing components is 2:1; The ratio of bamboo powder to acidic solution is 5-15g:100mL; The bamboo powder is soaked in the acidic solution for 30 minutes; The bamboo powder is soaked in an acidic solution at a temperature of 20–30°C. The drying temperature is 60–80°C; The drying time is 24 to 48 hours.

5. The preparation method according to claim 3, characterized in that, The screw speed of the twin-screw extruder is 80-100 rpm; The barrel temperature of the twin-screw extruder is 170–190°C; The injection molding temperature is 170–190°C; The injection molding pressure is 3 to 6 bar.

6. An article, characterized in that, The article is made of polypropylene-based bamboo-plastic composite material prepared by any one of claims 1 to 5.

7. The article of claim 6, characterized in that, The products are automotive interior parts, building formwork, outdoor flooring, logistics pallets, or furniture components.

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