Method for preparing bamboo-plastic composite material by using waste plastic

Abstract

The application discloses a method for preparing a bamboo-plastic composite material by using waste plastics, which uses bamboo, waste plastic particles, bamboo powder and bamboo fibers as raw materials to prepare modified bamboo tows, modified plastic particles, modified bamboo powder particle materials and modified bamboo fibers, respectively, then fully mixes the prepared modified plastic particles, modified bamboo powder particle materials and modified bamboo fibers according to quality to obtain a mixture, lays the mixture into a mold to obtain a mixture layer, and alternately lays the modified bamboo tows and the mixture layer; performs hot-pressing in the mold, naturally cools after forming, takes out the blank after cooling is completed to obtain a bamboo-plastic composite material product. The bamboo-plastic composite material has better structural strength and stability, and can effectively utilize the recycled HDPE particle materials.

Description

Technical Field

[0001] This invention relates to bamboo-plastic composite materials in the field of engineered wood products, and more specifically to a method for preparing bamboo-plastic composite materials using waste plastics. Background Technology

[0002] The development and utilization of bamboo resources plays a vital role in my country's forestry construction and national economic development. Bamboo is characterized by rapid growth, short cultivation cycle, high yield, early maturity, good properties, and wide range of uses, and has increasingly gained attention. Compared with wood, bamboo has higher strength, better toughness, and greater hardness, making it an ideal raw material for engineering structures. Furthermore, with the finite availability of timber resources, using bamboo as a substitute for wood in building materials can effectively reduce the demand for timber, saving costs and protecting the environment.

[0003] Currently, traditional bamboo-based panels mainly include three categories: bamboo plywood, bamboo woven plywood, and bamboo chipboard. However, bamboo plywood has a low utilization rate of bamboo raw materials, bamboo woven plywood and bamboo chipboard have insufficient performance, and bamboo chipboard also has problems with mold resistance. Therefore, their development is limited, and the application of bamboo resources as structural materials has not been fully utilized. Compared with wood-plastic composites, research on bamboo-plastic composites has not yet received sufficient attention. Bamboo-plastic composites are a new type of structural material that combines the characteristics of plant fibers and polymer materials. They have a series of advantages such as being lightweight, corrosion-resistant, high-temperature resistant, anti-aging, and easily degradable. They help to improve the utilization value of bamboo, reduce the amount of plastic used, and reduce environmental pollution, showing great potential for development and utilization.

[0004] Existing bamboo-plastic composite materials typically use pretreated and modified bamboo fibers or bamboo powder, mixed with molten recycled plastic in a certain proportion, and then processed through high-temperature mixing and molding with the aid of additives. However, this process mainly uses virgin plastics as raw materials, making it impossible to use recycled plastics. This not only leads to increasingly serious environmental pollution problems but also results in a significant waste of resources. If the resource-based recycling and reuse of waste plastics could be used to modify and composite bamboo-plastic composite materials, it would effectively reduce raw material costs and overcome the limitations of traditional bamboo and plastic applications, enabling the high-quality, multifunctional, and high-value-added utilization of bamboo-plastic composite materials. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a method for preparing bamboo-plastic composite materials using waste plastics. This method uses bamboo and waste plastics as raw materials, which can maximize the advantages of bamboo and plastics to produce bamboo-plastic reinforced composite materials, thereby solving the defects in the above-mentioned technical background.

[0006] The technical problem solved by this invention is achieved by the following technical solution:

[0007] A method for preparing bamboo-plastic composite materials using waste plastics specifically includes the following steps:

[0008] S1. Bamboo is subjected to a first alkali treatment to soften it. After treatment, the bamboo is cleaned and dried until the moisture content is below 15-18%. It is then crushed and the bamboo fibers are separated. The bamboo fibers are dried further until the moisture content is below 10%. After a second alkali treatment, the bamboo is cleaned and dried to obtain intermediate bamboo fiber material. Then, nano-TiO2 particles are modified using a silane coupling agent and deposited in situ on the surface of the intermediate bamboo fiber material to obtain modified bamboo fiber material with a transverse crystal layer on the surface.

[0009] S2 selects HDPE recycled material with a polyethylene content of more than 95% as waste plastic raw material, and performs acid washing and swelling treatment and swelling treatment with swelling agent in sequence. After the treatment, it is washed with clean water and floated to obtain recycled HDPE granules. The recycled HDPE granules are melted and then blended with HDPE virgin granules and polylactic acid granules in a mass ratio of 7:3:1 to obtain modified plastic granules.

[0010] S3 adds bamboo powder to a polyurethane solution, adds a coupling agent, stirs and mixes, dehydrates, dries and granulates at room temperature to obtain polyurethane-modified bamboo powder granules.

[0011] S4 involves treating bamboo fiber with a coupling agent, followed by polyurethane impregnation. After treatment, the bamboo fiber is removed, filtered, separated, and dried to obtain polyurethane-modified bamboo fiber.

[0012] S5 uses the modified plastic granules obtained in step S2, the modified bamboo powder granules obtained in step S3, and the modified bamboo fiber obtained in step S4 as raw materials. The raw materials are thoroughly mixed according to the mass ratio of 45-55% modified plastic granules, 15-25% modified bamboo fiber, and the remainder modified bamboo powder granules to obtain a mixture. The mixture is then spread evenly into a mold. A layer of mixture is first laid to obtain a mixture layer. Then, the modified bamboo fiber bundles obtained in step S1 are laid on the surface of the mixture layer in the same direction. The mixture layer and the modified bamboo fiber bundles are cyclically laid in the above manner, and the mixture layer is used as the outer sealing layer.

[0013] S6 is hot-pressed in a mold, and then naturally cooled. After cooling, the blank is removed and trimmed to obtain the finished bamboo-plastic composite material.

[0014] As a further limitation, in step S1, when the bamboo is subjected to the first alkali treatment, the NaOH in the alkaline solution is controlled to be 30-35 g / L, and it is steamed at normal pressure for 45-90 min under the condition of a bath ratio of 1:15-1:20; when the bamboo is subjected to the second alkali treatment, the NaOH in the alkaline solution is controlled to be 25-30 g / L, and it is steamed for 3-4 h under the condition of a bath ratio of 1:15-1:20 and a pressure of 60-80 kPa.

[0015] As a further limitation, in step S1, the diameter of the stripped bamboo fiber bundle is 3 to 5 mm.

[0016] As a further limitation, in step S1, before the stripped bamboo fiber bundles are deposited in situ with nano-TiO2 particles, the bamboo fiber bundles are first treated with a chemical plating solution to obtain binary chemically plated bamboo fibers.

[0017] The electroless plating solution comprises 26–36 g / L nickel sulfate, 0.2–1.5 g / L sodium molybdate, and 1.5–3 g / L ferrous sulfate;

[0018] The chemical plating solution is controlled at a pH of 8.2–8.8, a temperature of 75–90°C, and a treatment time of 45–60 min.

[0019] As a further limitation, in step S2, during the blending modification process of the modified plastic particles, the particle size range of the corresponding HDPE recycled material particles, HDPE virgin material particles, and polylactic acid particles is controlled to be below 3 mm; while the particle size range of the modified plastic particles obtained through blending modification is controlled to be 2 to 3 mm.

[0020] As a further limitation, when preparing the mixture in step S5, heavy calcium carbonate is also added to the mixture as a reinforcing material, and the amount of the reinforcing material is 0.7 to 1.5% of the total mass of the modified plastic particles, modified bamboo powder particles, and modified bamboo fiber used as raw materials.

[0021] As a further limitation, when preparing the mixture in step S5, reinforcing aggregate is added to the mixture. The reinforcing aggregate is heavy calcium carbonate, and the amount added is 0.7 to 1.5% of the total mass of the modified plastic particles, modified bamboo powder particles, and modified bamboo fiber used as raw materials.

[0022] As a further limitation, when preparing the mixture in step S5, an additive is added to the mixture. The additive is maleic anhydride or modified maleic anhydride, and the amount added is 0.5 to 2% of the combined mass of the modified plastic particles, modified bamboo powder particles, and modified bamboo fiber used as raw materials.

[0023] As a further limitation, when the mixture is laid into the mold in step S5, the thickness of the mixture layer before hot pressing is 3 to 5 mm, and the modified bamboo fiber bundles are laid parallel and evenly spaced along the length of the mold on the surface of the mixture layer. The material mass of a single layer of modified bamboo fiber bundles is 1 / 20 to 1 / 15 of the material mass of a single layer of mixture.

[0024] As a further limitation, during hot pressing in step S6, the hot pressing temperature is controlled to be 175–190°C and the hot pressing pressure is 8–12 MPa.

[0025] Beneficial Effects: The method for preparing bamboo-plastic composite materials using waste plastics according to this invention can compensate for the material characteristic defects of recycled HDPE granules by blending with virgin HDPE granules and polylactic acid granules. Furthermore, it improves the bonding performance between modified plastic granules and bamboo by combining modified bamboo powder granules and modified bamboo fibers. The resulting bamboo-plastic composite material has superior mechanical properties, a realistic bamboo-wood texture, high hardness, good wear resistance, and good flatness. Moreover, the product exhibits dimensional stability and is less prone to structural delamination, deformation, collapse, and breakage during use. Detailed Implementation

[0026] To make the technical means, creative features, objectives, and effects of this invention easier to understand, the invention is further described below with reference to specific embodiments. The described embodiments are merely some, not all, of the embodiments of this invention.

[0027] In the following embodiments, those skilled in the art will understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. All other embodiments obtained by one of ordinary skill in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0028] In this embodiment, the specific operation method for preparing the board material in the bamboo-plastic composite material is as follows:

[0029] First, select moso bamboo aged 3 years or more as raw material. Cut the raw bamboo to a fixed length, then place the cut bamboo sections in a pressure vessel and use superheated steam to remove impurities such as lignin and pectin from the raw bamboo. Then soak it in an aqueous solution containing plant enzymes at a temperature of 27-35℃ to further remove lignin, pectin, sugar and fat from the bamboo fiber.

[0030] The bamboo sections of a fixed length treated in the above manner are then subjected to a first alkali treatment. For this first alkali treatment, a 35 g / L NaOH alkaline solution is prepared. Sodium silicate (1.5% by mass) and penetrant JFC (0.3% by mass) are then added to the alkaline solution. The bamboo sections of the fixed length are then boiled in the alkaline solution at a bath ratio of 1:18 under normal pressure for 70 minutes. This process removes residual gum from the bamboo fibers, softens the bamboo, and promotes further dispersion between the bamboo fibers. Furthermore, by enhancing the synergistic effect of sodium silicate and penetrant JFC, the fineness and toughness of the bamboo fibers are improved, as well as their strength. After treatment, the bamboo is rinsed with water to separate most of the lignin, pectin, and other impurities from the bamboo fibers.

[0031] After the bamboo is cleaned, it is dried naturally or by hot air drying until the moisture content is below 15-18%. Then, it is crushed and separated into bamboo bundles using a bamboo rolling machine, with the diameter of the separated bamboo bundles controlled at 3-5 mm. The separated bamboo bundles are then dried further using hot air drying equipment until the moisture content is below 10%, followed by a second alkali treatment. During the second alkali treatment, a 35 g / L NaOH alkaline solution is used, and the bamboo is steamed for 210 minutes at a bath ratio of 1:20 and a pressure of 70 kPa. After steaming, the bamboo is washed and dried to obtain intermediate bamboo bundle material.

[0032] Modified nano-TiO2 particles were treated with silane coupling agent KH570. During treatment, the modified nano-TiO2 particles were dispersed at 7200 rpm in KH570 for 90 minutes, and then removed to obtain silane coupling agent-modified nano-TiO2 particles. These silane coupling agent-modified TiO2 particles were then used to treat the obtained bamboo fiber bundle intermediate material, resulting in a modified bamboo fiber bundle with an in-situ deposition of the aforementioned nano-TiO2 particles. The in-situ treatment temperature was 120℃, the TiO2 modification solution concentration was 30 g / L, and the treatment time was 30 minutes. After treatment, a transverse crystalline interface structure was formed on the surface of the modified bamboo fiber bundle at the deposition sites of the nano-TiO2 particles.

[0033] HDPE recycled material with a polyethylene content of over 95% is used as waste plastic raw material. This waste plastic raw material is crushed to a particle size of less than 3mm. It is first acid-washed with a sulfuric acid solution with a solute mass fraction ≤60%, ensuring the sulfuric acid completely covers the material. The solution temperature is controlled at 65-70℃, and the mixture is stirred throughout the process. After 45 minutes, the material is removed and drained of surface moisture, then directly immersed in a swelling tank. Methacrylic acid is used as the swelling agent for swelling treatment, which lasts for 3 hours. Alternatively, ultrasonic-assisted treatment can be used during the swelling process, effectively reducing the required swelling time. However, the treatment effect is slightly inferior to natural swelling, specifically, the flexural strength of the molded bamboo-plastic composite material is 5%-8% lower.

[0034] The waste granules after the above swelling treatment are washed with clean water and then floated to obtain recycled HDPE granules. The recycled HDPE granules are then melted with HDPE virgin granules (Maoming Petrochemical, HDPE, 2mm) and polylactic acid granules (Ningbo Jialian Technology, 2mm) in a mass ratio of 3:1:1. After melting, the mixture is blended and modified into granules under an extrusion pressure of 0.7-1.0MPa and a temperature of 120-130℃ to obtain modified plastic granules with a particle size range of 2-3mm.

[0035] Commercially available 70-90 mesh bamboo granules (from Lingchuan County Xinyuan Bamboo Products Factory) were added to a polyurethane solution along with coupling agent KH570 and stirred. The mixture was then dehydrated, dried, and granulated at room temperature to obtain polyurethane-modified bamboo powder granules. Simultaneously, commercially available bamboo fiber (from Lingchuan County Xinyuan Bamboo Products Factory) was treated with a coupling agent, followed by polyurethane impregnation. After treatment, the fiber was removed, filtered, separated, and dried to obtain polyurethane-modified bamboo fiber.

[0036] In this embodiment, the above-described process steps for obtaining modified bamboo filament bundles, modified plastic granules, modified bamboo powder granules, and modified bamboo fibers can simultaneously ensure production efficiency and continuous production.

[0037] After obtaining the modified bamboo fiber bundles, modified plastic granules, modified bamboo powder granules, and modified bamboo fiber, the raw materials are mixed according to the following mass ratio: 50% modified plastic granules, 22% modified bamboo fiber, and 28% modified bamboo powder granules. After mixing, 1.2% of heavy calcium carbonate (based on the total mass of the modified plastic granules, modified bamboo fiber, and modified bamboo powder granules) is added as a structural reinforcement, and 1.8% of maleic anhydride (based on the total mass of the modified plastic granules, modified bamboo fiber, and modified bamboo powder granules) is added as an additive. After thorough mixing, a mixture is obtained.

[0038] The above-mentioned mixture is laid flat into the mold. First, a layer of mixture is laid to obtain a mixture layer. Then, modified bamboo fiber bundles are laid in the same direction on the surface of the mixture layer. That is, the modified bamboo fiber bundles are laid parallel and spaced along the length of the mold. After laying one layer, another layer of mixture layer is laid. The mixture layer and modified bamboo fiber bundles are laid in a cycle of mixture layer-bamboo fiber bundle-mixed layer-bamboo fiber bundle... until the mixture layer is used as the outer sealing surface layer.

[0039] Then, hot pressing is performed on the mold surface. The processing temperature during hot pressing is controlled at 165-195℃ and the hot pressing pressure is 8MP. After hot pressing for 10 minutes, it is naturally cooled. After cooling, it is demolded and taken out to obtain the blank. After the blank is trimmed, the finished bamboo-plastic composite material is obtained.

[0040] Under the technical conditions of this embodiment, the density of the prepared bamboo-plastic composite material is 1405.1 kg / m³. 3 With a water absorption rate of 0.22%, strips with a cross-sectional size of 10mm×10mm were prepared. Five groups of 10 strips each were subjected to bending and compressive strength treatments. The average bending strength and compressive strength were 17.15MPa and 19.62MPa, respectively, demonstrating good performance. Furthermore, after being continuously placed outdoors for 30 and 90 days, the performance loss rates of the bending strength and compressive strength of the above-mentioned strip test materials were between 1.5% and 3.2% and 3.5% and 4.2%, respectively, thus also demonstrating good weather resistance and stability.

[0041] In this embodiment, recycled HDPE material, after acid washing and swelling treatment, is blended with virgin HDPE granules and polylactic acid granules to obtain modified plastic granules with better structural strength and bonding performance with bamboo fiber. These modified plastic granules also possess better structural strength. To further optimize this bonding performance, this technical solution continues to use coupling agent modification treatment during the processing of bamboo powder and bamboo fiber. Using coupling agents such as silanes on natural fibers or plastic matrices is a common method to improve the interfacial compatibility between the two, which can improve the bonding performance between bamboo powder / bamboo fiber and the corresponding plastic granules.

[0042] The modification of bamboo fiber bundles is mainly based on transcrystallinity (TC) structure modification. Inducing semi-crystalline polymers on the surface of natural fibers forms a special interfacial crystal structure, namely a transcrystallinity layer. This interfacial crystal structure can improve the interfacial bonding performance between the composite bamboo fiber bundles and the plastic material. This reinforcement method can enhance interfacial compatibility independently of silane coupling agent treatment. A highly efficient dispersed silane coupling agent-modified nano-TiO2 suspension is used to deposit nano-TiO2 particles in situ on the surface of bamboo fiber bundles, improving the heterogeneous nucleation ability of the bamboo fiber surface, thereby inducing the formation of a stable TC structure at the interface of the bamboo-plastic composite material.

[0043] For the reasons mentioned above, in the technical solution of this embodiment, bamboo fiber can undergo fiber cross-linking in the mixture layer during the molding process to improve the single-layer structural strength and stability of the molded mixture layer. However, under this molding method, the thickness of the mixture layer should not be too thick, otherwise it will destroy the interfacial compatibility gain brought by the silane coupling agent. Under this premise, by molding modified bamboo fiber bundles between two mixture layers, a layer of bamboo fiber bundles can be fixed between the two mixture layers in another reinforcement form, achieving a similar effect to that of steel bars in concrete, thereby enhancing load-bearing capacity, preventing cracking, improving durability, and providing seismic resistance. This effectively improves the structural stability of the molded bamboo-plastic material and extends its service life. Based on this, the corresponding bamboo fiber bundles need to have a certain bundle diameter requirement, usually 3-5 mm, and the material weight of a single layer of modified bamboo fiber bundles should be 1 / 20 to 1 / 15 of the material weight of a single layer of mixture.

[0044] In another embodiment, before the stripped bamboo filament bundles undergo in-situ deposition of nano-TiO2 particles, the bamboo filament bundles can be treated with a chemical plating solution to obtain binary chemically plated bamboo fibers:

[0045] The corresponding electroless plating solution consists of a main salt, a complexing agent, an accelerator, and a pH adjuster. The main salt includes 26–36 g / L nickel sulfate, 0.2–1.5 g / L sodium molybdate, and 1.5–3 g / L ferrous sulfate. The complexing agent is 15 g / L sodium pyrophosphate, the accelerator is 5 mL / L triethanolamine, and the pH adjuster is ammonia. When treating the electroless plating solution, ammonia is used to control the pH value to be maintained at 8.2–8.8. The treatment temperature is 75–90℃, and the treatment time is 45–60 minutes. Under these conditions, a structural coating can be formed inside the transcrystalline layer before in-situ deposition of highly dispersed silane coupling agent-modified nano-TiO2 particles on the surface of bamboo fiber bundles. This coating effectively improves the toughness and corrosion resistance of the bamboo fiber bundles and enhances the stress transfer efficiency of the modified bamboo fiber bundles in the cross-sectional area of ​​the mixture layer. This allows for the formation of a spatially linked bamboo fiber bundle-bamboo fiber crosslinking system, further leveraging the advantages of natural fibers as mechanical reinforcement, particularly their higher modulus and specific strength. Calculations show that this method increases costs by approximately 10%, but improves the strength of the molded bamboo-plastic composite by approximately 8%, allowing for selection based on actual needs.

[0046] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing bamboo-plastic composite materials using waste plastics, characterized in that, Specifically, the following steps are included: S1. Bamboo is subjected to an initial alkali treatment to soften it. After treatment, the bamboo is cleaned and dried until the moisture content is below 15-18%. It is then crushed and the bamboo fibers are separated. The bamboo fibers are dried further until the moisture content is below 10%. After a second alkali treatment, the bamboo is cleaned and dried to obtain intermediate bamboo fiber material. Then, nano-TiO2 particles are modified using a silane coupling agent and deposited in situ on the surface of the intermediate bamboo fiber material to obtain modified bamboo fiber material with a transverse crystal layer on the surface. Before in-situ deposition of nano-TiO2 particles, the stripped bamboo fiber bundles are first treated with a chemical plating solution to obtain binary chemically plated bamboo fibers. The electroless plating solution includes 26-36 g / L nickel sulfate, 0.2-1.5 g / L sodium molybdate, and 1.5-3 g / L ferrous sulfate; The chemical plating solution is controlled at a pH of 8.2-8.8, a temperature of 75-90℃, and a treatment time of 45-60 minutes. S2 selects HDPE recycled material with a polyethylene content of more than 95% as waste plastic raw material. The waste plastic is subjected to acid washing treatment and swelling treatment with swelling agent in sequence. After the treatment is completed, it is washed with clean water and floated to obtain recycled HDPE granules. The recycled HDPE granules are melted and then blended with HDPE virgin granules and polylactic acid granules in a mass ratio of 7:3:1 to obtain modified plastic granules. S3 adds bamboo powder to a polyurethane solution, adds a coupling agent, stirs and mixes, and then dehydrates, dries and granulates at room temperature to obtain polyurethane-modified bamboo powder granules. S4 involves treating bamboo fiber with a coupling agent, followed by polyurethane impregnation. After treatment, the bamboo fiber is removed, filtered, separated, and dried to obtain polyurethane-modified bamboo fiber. S5 uses the modified plastic granules obtained in step S2, the modified bamboo powder granules obtained in step S3, and the modified bamboo fiber obtained in step S4 as raw materials. The raw materials are thoroughly mixed according to the mass ratio of 45-55% modified plastic granules, 15-25% modified bamboo fiber, and the remainder modified bamboo powder granules to obtain a mixture. The mixture is then spread evenly into a mold. A layer of mixture is first laid to obtain a mixture layer. Then, the modified bamboo fiber bundles obtained in step S1 are laid on the surface of the mixture layer in the same direction. The mixture layer and the modified bamboo fiber bundles are cyclically laid in the above manner, and the mixture layer is used as the outer sealing layer. S6 is hot-pressed in a mold, and then naturally cooled. After cooling, the blank is removed and trimmed to obtain the finished bamboo-plastic composite material.

2. The method for preparing bamboo-plastic composite materials from waste plastics according to claim 1, characterized in that, In step S1, when the bamboo is subjected to the first alkali treatment, the NaOH in the alkaline solution is controlled to be 30~35g / L, and it is steamed at normal pressure for 45~90min under the condition of a bath ratio of 1:15~1:20; when the bamboo is subjected to the second alkali treatment, the NaOH in the alkaline solution is controlled to be 25~30g / L, and it is steamed for 3~4h under the condition of a bath ratio of 1:15~1:20 and a pressure of 60~80KPa.

3. The method for preparing bamboo-plastic composite materials from waste plastics according to claim 1, characterized in that, In step S1, the diameter of the stripped bamboo fiber bundles is 3~5mm.

4. The method for preparing bamboo-plastic composite materials from waste plastics according to claim 1, characterized in that, In step S2, during the blending modification of the modified plastic particles, the particle size range of the corresponding HDPE recycled material particles, HDPE virgin material particles, and polylactic acid particles is controlled to be below 3 mm; while the particle size range of the modified plastic particles obtained through blending modification is controlled to be 2~3 mm.

5. The method for preparing bamboo-plastic composite materials from waste plastics according to claim 1, characterized in that, In step S5, when preparing the mixture, heavy calcium carbonate is added to the mixture as a reinforcing material. The amount of the reinforcing material is 0.7 to 1.5% of the total mass of the modified plastic particles, modified bamboo powder particles, and modified bamboo fiber used as raw materials.

6. The method for preparing bamboo-plastic composite materials from waste plastics according to claim 1, characterized in that, In step S5, when preparing the mixture, reinforcing aggregate is added to the mixture. The reinforcing aggregate is heavy calcium carbonate, and the amount added is 0.7 to 1.5% of the total mass of the modified plastic particles, modified bamboo powder particles, and modified bamboo fiber used as raw materials.

7. The method for preparing bamboo-plastic composite materials from waste plastics according to claim 1, characterized in that, In step S5, when preparing the mixture, an additive is added to the mixture. The additive is maleic anhydride or modified maleic anhydride, and the amount added is 0.5 to 2% of the total mass of the modified plastic particles, modified bamboo powder particles, and modified bamboo fiber used as raw materials.

8. The method for preparing bamboo-plastic composite materials from waste plastics according to claim 1, characterized in that, When the mixture is laid into the mold in step S5, the thickness of the mixture layer before hot pressing is 3~5mm, and the modified bamboo fiber bundles are laid parallel and evenly spaced along the length of the mold on the surface of the mixture layer. The material weight of a single layer of modified bamboo fiber bundles is 1 / 20~1 / 15 of the material weight of a single layer of mixture.

9. The method for preparing bamboo-plastic composite materials from waste plastics according to claim 1, characterized in that, In step S6, the hot pressing temperature is controlled at 175~190℃ and the hot pressing pressure is 8~12MPa.