Carbon nanotube modified polypropylene composite material and preparation method thereof

Abstract

The invention provides a carbon nanotube modified polypropylene composite material and a preparation method thereof, and belongs to the technical field of antibacterial materials. According to the method, plant fibers are used as precursors, carbon nanotubes are prepared through high-temperature calcination, and the carbon nanotubes are subjected to surface activation treatment by using aids such as L-cysteine hydrochloride, sodium ascorbate and ethylenediamine, so that the dispersity and interface bonding force of the carbon nanotubes in a polypropylene matrix are remarkably improved. And then, mixing the modified carbon nano tube with polypropylene, polyhydric alcohol and a catalyst, reacting, and granulating through a double-screw extruder to prepare the composite material with excellent performance. The composite material disclosed by the invention has excellent mechanical properties, thermal stability, antibacterial property and conductivity, and is suitable for the fields of automobile parts, electronic device shells, building materials, medical apparatuses and instruments and the like. The method is simple in process, environment-friendly and efficient, renewable resources are fully utilized, and the method has a wide industrial application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of antibacterial materials, and in particular to a carbon nanotube-modified polypropylene composite material and a preparation method thereof. Background Art

[0002] With the rapid development of science and technology, polymer-based composite materials have become a hot topic in materials science research due to their excellent performance and wide application fields. Among them, polypropylene (PP), as an important thermoplastic polymer, has been widely used in automobiles, home appliances, packaging, construction and other fields due to its low density, good mechanical properties, strong chemical corrosion resistance and excellent processing performance. However, polypropylene itself has some inherent defects, such as insufficient rigidity, low heat resistance and limited impact toughness, which to a certain extent limit its application in high-performance fields. Therefore, modifying polypropylene by adding functional fillers to improve its mechanical properties and thermal stability is an important research direction in the current field of materials science. In recent years, carbon nanotubes (CNTs), as a new type of nanomaterial, have attracted much attention due to their unique structure and excellent physical and chemical properties. Carbon nanotubes have ultra-high specific surface area, high modulus, high strength and excellent electrical and thermal conductivity, and are considered to be ideal fillers for enhancing the performance of polymer matrices. However, due to the strong van der Waals force and surface energy of carbon nanotubes, they are easy to agglomerate in the polymer matrix, resulting in uneven dispersion, thus affecting the performance of the composite material. Therefore, in order to give full play to the performance advantages of carbon nanotubes, surface modification of carbon nanotubes to improve their dispersibility and interfacial bonding in polymers is the key to achieving the preparation of high-performance composite materials. Carbon nanotube modification technology mainly includes two categories: physical modification and chemical modification. Physical modification mainly achieves uniform dispersion of carbon nanotubes in the matrix through ultrasonic dispersion, high-speed shear mixing and other methods, but this method is often difficult to fundamentally solve the problem of carbon nanotube agglomeration. Chemical modification improves the compatibility between carbon nanotubes and the matrix by introducing functional groups or chemical bonding methods. For example, the introduction of carboxyl or hydroxyl groups by acid treatment (such as nitric acid or sulfuric acid) significantly enhances the interfacial interaction between carbon nanotubes and the polymer matrix. In addition, functionalized molecules or polymer chains are introduced to the surface of carbon nanotubes by grafting polymerization or covalent bond grafting, thereby further improving their dispersion stability. Traditional polypropylene modification methods mainly include filling modification, blending modification and copolymerization modification. Among them, filling modification is to improve the mechanical properties and thermal stability of polypropylene by adding inorganic fillers (such as talcum powder, glass fiber) or organic fillers (such as wood powder, plant fiber). However, these traditional fillers usually have the problems of high density and limited reinforcement effect, which makes it difficult to meet the demand of modern industry for lightweight and high-strength materials. In contrast, the use of carbon nanotubes as fillers to prepare polypropylene-based composites has significant advantages. On the one hand, carbon nanotubes can significantly improve the tensile strength, flexural modulus and impact toughness of composite materials; on the other hand, their excellent electrical and thermal conductivity also makes composite materials have broad application prospects in electronic devices, conductive coatings and other fields.In addition, since carbon nanotubes have an extremely high aspect ratio, they can significantly improve the performance of composite materials at a relatively low addition amount, thus avoiding the problem of increased material density due to large-scale addition of traditional fillers.

[0003] Although carbon nanotube-modified polypropylene composites have broad application prospects, their preparation process still faces some technical challenges: How to effectively solve the agglomeration problem of carbon nanotubes in the polypropylene matrix is ​​the key to achieving uniform distribution and improving the performance of composite materials. Since the surface of carbon nanotubes lacks polar functional groups, the interfacial bonding between them and the non-polar polypropylene matrix is ​​weak, and surface activation or functionalization treatment is required to enhance compatibility. How to simplify the process and reduce production costs while ensuring high performance is an important issue for achieving industrial production.

[0004] In response to the above problems, this study proposed a new preparation method, which uses plant fibers as precursors to prepare carbon nanotubes, and combines them with additives such as L-cysteine ​​hydrochloride to perform surface activation treatment, and then works with polyols and catalysts to achieve an efficient and environmentally friendly preparation process. This method not only effectively solves the problem of uneven dispersion of carbon nanotubes, but also significantly improves the mechanical properties and thermal stability of composite materials, providing new ideas for the development of high-performance lightweight composite materials.

[0005] In short, by functionalizing carbon nanotubes and combining them with polypropylene, not only the application scope of traditional plastics is expanded, but also important reference value is provided for the development of new green, environmentally friendly, high-performance composite materials. Summary of the invention

[0006] In view of this, the present invention provides a method for preparing a carbon nanotube-modified polypropylene composite material, which comprises the following steps in parts by weight: (1) providing 5-10 parts of plant fiber, 2-6 parts of calcium carbonate powder and 2-4 parts of gallic acid, mixing them, and homogenizing them to obtain a precursor carbon material; then, transferring them to a calcining furnace, calcining them at high temperature for 6-10 hours under a protective gas atmosphere, the high temperature calcination temperature being 400°C-600°C, collecting the solid product and rinsing it with acid, then rinsing it with deionized water, drying it, and vacuum freeze-drying it to obtain carbon nanotubes; (2) adding 1-3 parts of sodium ascorbate and 2-3 parts of ethylenediamine to 2.5-7.5 parts of L-cysteine ​​hydrochloride, and finally adding 50-80 parts of deionized water, transferring to a high-temperature reactor, reacting at 130-160° C. for 2-4 hours, adding 0.4 to 0.8 times the mass of the carbon nanotubes obtained in step (1) and 0.04 to 0.10 times the mass of the activator, stirring at room temperature for 3-6 hours, and performing activation treatment to obtain modified carbon nanotubes; the CAS number of L-cysteine ​​hydrochloride is 7048-04-6; (3) Mix 10-30 parts of the modified carbon nanotubes prepared in step (2) with 120-150 parts of polypropylene, then add 180-220 parts of polyol and 1-5 parts of catalyst, react at 80-95°C for 8-12 hours, and extrude and granulate using a twin-screw extruder after the reaction is completed.

[0007] Preferably, the plant fiber in step (1) is bamboo fiber, wheat straw fiber or coconut shell fiber; wherein the diameter of the plant fiber is 20 um and the length is 60 mm.

[0008] The particle size of the calcium carbonate powder in step (1) is 100um-200um; In step (1), the protective gas is nitrogen.

[0009] Preferably, the acid in step (1) is a 3% by weight dilute hydrochloric acid solution.

[0010] Preferably, the polyol in step (3) is glycerol, pentaerythritol, ethylene glycol or butanediol.

[0011] Preferably, the catalyst in step (3) is titanium tetrachloride or triethylaluminum.

[0012] A composite material is prepared by using the method for preparing a carbon nanotube-modified polypropylene composite material.

[0013] Beneficial effects: Enhance the mechanical properties of composite materials: By introducing modified carbon nanotubes into the polypropylene matrix, the tensile strength, bending modulus and impact toughness of the composite materials are significantly improved. Carbon nanotubes have the characteristics of high modulus and high strength. Their uniform dispersion in the matrix and good interfacial bonding force enable the composite material to effectively transfer stress when subjected to external force, thereby improving the overall mechanical properties. Improve the thermal stability of the composite material: The high thermal conductivity and thermal stability of carbon nanotubes enable the composite material to exhibit better thermal stability under high temperature environments. Compared with traditional fillers, the composite material prepared by the present invention can maintain structural integrity at higher temperatures and is suitable for a wider range of industrial application scenarios. Improve the dispersibility and compatibility of carbon nanotubes: The present invention performs surface activation treatment on carbon nanotubes by using additives such as L-cysteine ​​hydrochloride, sodium ascorbate and ethylenediamine, which significantly improves its dispersibility and interfacial bonding force in the polypropylene matrix and avoids the agglomeration of carbon nanotubes. This modification method not only simplifies the process flow, but also reduces production costs. Green environmental protection and resource utilization: The present invention uses plant fibers (such as bamboo fibers, wheat straw fibers or coconut shell fibers) as precursors to prepare carbon nanotubes, making full use of renewable resources and realizing resource recycling. At the same time, nitrogen protective atmosphere and dilute hydrochloric acid rinsing are used in the preparation process to reduce pollution to the environment, which is in line with the development concept of green environmental protection. The process is simple and suitable for industrial production: The present invention uses conventional equipment (such as calcining furnace, high-temperature reactor, twin-screw extruder) to complete the entire preparation process, with clear process steps and simple operation. By optimizing the reaction conditions (such as temperature, time and raw material ratio), the production efficiency is effectively improved and the energy consumption is reduced, providing for large-scale industrial production. Multifunctional application prospects: The prepared carbon nanotube modified polypropylene composite material not only has excellent mechanical properties and thermal stability, but also has good electrical conductivity and antibacterial properties. It can be widely used in automotive parts, electronic device housings, building materials, medical equipment and other fields, expanding the application range of traditional polypropylene materials.

[0014] In summary, the present invention not only solves the problems existing in traditional polypropylene modification through innovative design and green and environmentally friendly methods, but also significantly improves the comprehensive performance of composite materials, providing important reference value for the development of high-performance lightweight composite materials.

[0015] Advantages of the present invention will be partially explained in the following description, and partly will be obvious from the description, or will be learned through the implementation of the embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the content of the present invention, it is described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] Figure 1This is a scanning electron microscope characterization image of the composite material in Example 3 of the present invention. DETAILED DESCRIPTION

[0018] Described below are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications may be made without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

[0019] The present invention describes in detail the carbon nanotube-modified polypropylene composite material and its preparation method, as well as the prepared carbon nanotube-modified polypropylene composite material and its preparation method through the following examples.

[0020] Example 1: A method for preparing a carbon nanotube-modified polypropylene composite material, comprising the following steps in parts by weight: (1) 5 parts of plant fiber, 6 parts of calcium carbonate powder and 2 parts of gallic acid are provided and mixed, and a precursor carbon material is obtained after homogenization; then, the precursor carbon material is transferred to a calcining furnace, and calcined at high temperature for 6 hours under a protective gas atmosphere, and the high temperature calcination temperature is 600°C, and the solid product is collected and rinsed with acid, and then rinsed with deionized water and dried, and vacuum freeze-dried to obtain carbon nanotubes; in step (1), the plant fiber is bamboo fiber; in step (1), the particle size of the calcium carbonate powder is 100um; in step (1), the protective gas is nitrogen. In step (1), the acid is a 3% by mass dilute hydrochloric acid solution.

[0021] (2) Add 3 parts of sodium ascorbate and 2 parts of ethylenediamine to 2.5 parts of L-cysteine ​​hydrochloride, and finally add 80 parts of deionized water, transfer to a high-temperature reactor, react at 130° C. for 4 hours, add 0.4 times the mass of the carbon nanotubes obtained in step (1) and 0.10 times the mass of the activator, stir at room temperature for 3 hours, and activate the mixture to obtain modified carbon nanotubes; (3) 10 parts of the modified carbon nanotubes prepared in step (2) are mixed with 150 parts of polypropylene, and then 180 parts of polyol and 5 parts of catalyst are added, and the mixture is reacted at 80°C for 12 hours. After the reaction is completed, the mixture is extruded and granulated using a twin-screw extruder. The polyol in step (3) is pentaerythritol. The catalyst in step (3) is titanium tetrachloride.

[0022] The composite material is prepared by adopting the preparation method of the carbon nanotube modified polypropylene composite material.

[0023] Example 2: A method for preparing a carbon nanotube-modified polypropylene composite material, comprising the following steps in parts by weight: (1) 10 parts of plant fiber, 2 parts of calcium carbonate powder and 4 parts of gallic acid are provided and mixed, and a precursor carbon material is obtained after homogenization; then, the precursor carbon material is transferred to a calcining furnace, and calcined at high temperature for 6 hours under a protective gas atmosphere, and the high temperature calcination temperature is 600°C. The solid product is collected and rinsed with acid, and then rinsed with deionized water and dried, and vacuum freeze-dried to obtain carbon nanotubes; the plant fiber in step (1) is wheat straw fiber; the particle size of the calcium carbonate powder in step (1) is 100um; the protective gas in step (1) is nitrogen. The acid in step (1) is a 3% by mass dilute hydrochloric acid solution.

[0024] (2) Add 1 part of sodium ascorbate and 3 parts of ethylenediamine to 7.5 parts of L-cysteine ​​hydrochloride, and finally add 50 parts of deionized water, transfer to a high-temperature reactor, react at 160° C. for 2 hours, add 0.8 times the mass of the carbon nanotubes obtained in step (1) and 0.04 times the mass of the activator, stir at room temperature for 6 hours, and activate to obtain modified carbon nanotubes; (3) Mix 30 parts of the modified carbon nanotubes prepared in step (2) with 120 parts of polypropylene, then add 220 parts of polyol and 1 part of catalyst, react at 95°C for 8 hours, and extrude and granulate using a twin-screw extruder after the reaction. The polyol in step (3) is ethylene glycol. The catalyst in step (3) is triethylaluminum.

[0025] The composite material is prepared by adopting the preparation method of the carbon nanotube modified polypropylene composite material.

[0026] Example 3: A method for preparing a carbon nanotube-modified polypropylene composite material, comprising the following steps in parts by weight: (1) 8 parts of plant fiber, 4 parts of calcium carbonate powder and 3 parts of gallic acid are provided and mixed, and a precursor carbon material is obtained after homogenization; then, the precursor carbon material is transferred to a calcining furnace, and calcined at high temperature for 8 hours under a protective gas atmosphere, and the high temperature calcination temperature is 500°C, and the solid product is collected and rinsed with acid, and then rinsed with deionized water and dried, and vacuum freeze-dried to obtain carbon nanotubes; in step (1), the plant fiber is coconut shell fiber; in step (1), the particle size of the calcium carbonate powder is 150um; in step (1), the protective gas is nitrogen. In step (1), the acid is a 3% by mass dilute hydrochloric acid solution.

[0027] (2) Add 2 parts of sodium ascorbate and 3 parts of ethylenediamine to 4.5 parts of L-cysteine ​​hydrochloride, and finally add 70 parts of deionized water, transfer to a high-temperature reactor, react at 150° C. for 3 hours, add 0.6 times the mass of the carbon nanotubes obtained in step (1) and 0.08 times the mass of the activator, stir at room temperature for 5 hours, and activate the mixture to obtain modified carbon nanotubes; (3) Mix 20 parts of the modified carbon nanotubes prepared in step (2) with 140 parts of polypropylene, then add 200 parts of polyol and 4 parts of catalyst, react at 88°C for 10 hours, and extrude and granulate using a twin-screw extruder after the reaction. The polyol in step (3) is butanediol. The catalyst in step (3) is titanium tetrachloride.

[0028] The composite material is prepared by adopting the preparation method of the carbon nanotube modified polypropylene composite material.

[0029] Comparative Example 1: A method for preparing a carbon nanotube-modified polypropylene composite material, comprising the following steps in parts by weight: (1) 8 parts of plant fiber and 4 parts of calcium carbonate powder are provided and mixed, and a precursor carbon material is obtained after homogenization; then, the precursor carbon material is transferred to a calcining furnace, and calcined at high temperature for 8 hours under a protective gas atmosphere, and the temperature of the high temperature calcination is 500° C. The solid product is collected and rinsed with acid, and then rinsed with deionized water and dried, and vacuum freeze-dried to obtain carbon nanotubes; in step (1), the plant fiber is bamboo fiber, wheat straw fiber or coconut shell fiber; in step (1), the particle size of the calcium carbonate powder is 150 μm; in step (1), the protective gas is nitrogen. In step (1), the acid is a 3% by mass dilute hydrochloric acid solution.

[0030] (2) Add 2 parts of sodium ascorbate and 3 parts of ethylenediamine to 4.5 parts of L-cysteine ​​hydrochloride, and finally add 70 parts of deionized water, transfer to a high-temperature reactor, react at 150° C. for 3 hours, add 0.6 times the mass of the carbon nanotubes obtained in step (1) and 0.08 times the mass of the activator, stir at room temperature for 5 hours, and activate the mixture to obtain modified carbon nanotubes; (3) Mix 20 parts of the modified carbon nanotubes prepared in step (2) with 140 parts of polypropylene, then add 200 parts of polyol and 4 parts of catalyst, react at 88°C for 10 hours, and extrude and granulate using a twin-screw extruder after the reaction. The polyol in step (3) is butanediol. The catalyst in step (3) is titanium tetrachloride.

[0031] The composite material is prepared by adopting the preparation method of the carbon nanotube modified polypropylene composite material.

[0032] Comparative Example 2: A method for preparing a carbon nanotube-modified polypropylene composite material, comprising the following steps in parts by weight: (1) 8 parts of plant fiber, 4 parts of calcium carbonate powder and 3 parts of gallic acid are provided and mixed, and a precursor carbon material is obtained after homogenization treatment; then, the precursor carbon material is transferred to a calcining furnace, and calcined at high temperature for 8 hours under a protective gas atmosphere, and the high temperature calcination temperature is 500°C, and the solid product is collected and rinsed with acid, and then rinsed with deionized water and dried, and vacuum freeze-dried to obtain carbon nanotubes; in step (1), the plant fiber is bamboo fiber, wheat straw fiber or coconut shell fiber; in step (1), the particle size of the calcium carbonate powder is 150um; in step (1), the protective gas is nitrogen. In step (1), the acid is a 3% by mass dilute hydrochloric acid solution.

[0033] (2) Add 70 parts of deionized water to 2 parts of sodium ascorbate and 3 parts of ethylenediamine, transfer to a high-temperature reactor, react at 150° C. for 3 hours, add 0.6 times the mass of the carbon nanotubes obtained in step (1) and 0.08 times the mass of the activator, stir at room temperature for 5 hours, and activate to obtain modified carbon nanotubes; (3) Mix 20 parts of the modified carbon nanotubes prepared in step (2) with 140 parts of polypropylene, then add 200 parts of polyol and 4 parts of catalyst, react at 88°C for 10 hours, and extrude and granulate using a twin-screw extruder after the reaction. The polyol in step (3) is butanediol. The catalyst in step (3) is titanium tetrachloride.

[0034] The composite material is prepared by adopting the preparation method of the carbon nanotube modified polypropylene composite material.

[0035] Comparative Example 3: A method for preparing a carbon nanotube-modified polypropylene composite material, comprising the following steps in parts by weight: (1) 8 parts of plant fiber, 4 parts of calcium carbonate powder and 3 parts of gallic acid are provided and mixed, and a precursor carbon material is obtained after homogenization treatment; then, the precursor carbon material is transferred to a calcining furnace, and calcined at high temperature for 8 hours under a protective gas atmosphere, and the high temperature calcination temperature is 500°C, and the solid product is collected and rinsed with acid, and then rinsed with deionized water and dried, and vacuum freeze-dried to obtain carbon nanotubes; in step (1), the plant fiber is bamboo fiber, wheat straw fiber or coconut shell fiber; in step (1), the particle size of the calcium carbonate powder is 150um; in step (1), the protective gas is nitrogen. In step (1), the acid is a 3% by mass dilute hydrochloric acid solution.

[0036] (2) Add 2 parts of sodium ascorbate to 4.5 parts of L-cysteine ​​hydrochloride, and finally add 70 parts of deionized water, transfer to a high-temperature reactor, react at 150° C. for 3 hours, add 0.6 times the mass of the carbon nanotubes obtained in step (1) and 0.08 times the mass of the activator, stir at room temperature for 5 hours, and activate the mixture to obtain modified carbon nanotubes; (3) Mix 20 parts of the modified carbon nanotubes prepared in step (2) with 140 parts of polypropylene, then add 200 parts of polyol and 4 parts of catalyst, react at 88°C for 10 hours, and extrude and granulate using a twin-screw extruder after the reaction. The polyol in step (3) is butanediol. The catalyst in step (3) is titanium tetrachloride.

[0037] The composite material is prepared by adopting the preparation method of the carbon nanotube modified polypropylene composite material.

[0038] Effect embodiment: A carbon nanotube-modified polypropylene composite material is added to a melt spinning machine, and is extruded into filaments after being heated and melted. The spinning temperature is 220°C, the extrusion pressure is controlled at 6 MPa, the spinneret hole diameter is 0.5 mm, and the extruded melt passes through the spinneret hole to form nascent fibers, which enter the cooling water tank for rapid cooling and solidification. The water tank temperature is 25°C. The solidified nascent fibers are stretched, the stretching multiple is 6 times, and the stretching temperature is 90°C.

[0039] Material characterization: The modified polypropylene fiber prepared in Example 3 was observed using a scanning electron microscope. Figure 1 As shown, a smooth fiber surface is seen.

[0040] Mechanical properties test: The tensile stress of the fabric was determined using the ASTM D100 test method. Briefly, a fabric with a size of 1×11 cm2 was tested using a 1 kN load cell with a sensor length of 5 cm and a test speed of 100 mm / min. Five repetitions were used for each test, and the average values ​​in the warp and weft directions were reported.

[0041] Table 1 Mechanical properties

[0042] Antimicrobial performance test: The antimicrobial effect of the fabrics against Staphylococcus aureus (ATCC25923) and Escherichia coli (ATCC 8739) was evaluated using the ASTM 2149 test method. Briefly, a bacterial suspension of known concentration was prepared, and then 1 g of the treated sample was placed in 50 mL of the prepared bacterial suspension in a 250 mL sterile glass bottle. After stirring for the specified contact time in a wrist vibrator, serial dilutions were prepared using phosphate buffered solution. The solution was then cultured on LB agar and incubated at 37°C for 24 h. The surviving colonies were counted and the kill rate was calculated.

[0043] Table 2 Antibacterial test

[0044] The present invention proposes a carbon nanotube modified polypropylene composite material and a preparation method thereof, which significantly improves the comprehensive performance of the composite material through innovative technical design and green and environmentally friendly process flow. The following is a summary of the technical effects: Mechanical properties are significantly improved: By introducing modified carbon nanotubes into the polypropylene matrix, the tensile strength, bending modulus and impact toughness of the composite material are significantly improved. For example, in the mechanical properties test, the longitudinal fracture stress of Example 3 reached 40.3 MPa, and the latitudinal fracture stress was 78.0 MPa, which is significantly better than the comparative example. This is mainly due to the high modulus and high strength characteristics of carbon nanotubes, as well as their uniform dispersion in the matrix and good interfacial bonding, which enables the material to effectively transfer stress when subjected to external forces.

[0045] Enhanced thermal stability: Carbon nanotubes have excellent thermal conductivity and thermal stability, which makes the composite material show better thermal stability in high temperature environment. Compared with traditional fillers, the composite material prepared by the present invention can maintain structural integrity at higher temperatures and is suitable for a wider range of industrial application scenarios.

[0046] Excellent antibacterial performance: The composite material of the present invention exhibits excellent antibacterial performance. According to the ASTM 2149 test results, the killing rates of Escherichia coli and Staphylococcus aureus in Example 3 reached 97.2% and 92.5%, respectively. This performance is due to the good interface between the modified carbon nanotubes and the polypropylene matrix after surface activation treatment, thereby enhancing the antibacterial effect.

[0047] Improved dispersibility and compatibility: The surface activation of carbon nanotubes by using additives such as L-cysteine ​​hydrochloride, sodium ascorbate and ethylenediamine significantly improves their dispersibility and interfacial bonding in the polypropylene matrix, effectively avoiding the problem of traditional carbon nanotube agglomeration. This modification method not only improves material performance, but also simplifies the process and reduces production costs.

[0048] Green environmental protection and resource utilization: The present invention uses plant fibers (such as bamboo fibers, wheat straw fibers or coconut shell fibers) as precursors to prepare carbon nanotubes, realizing the recycling of renewable resources. At the same time, nitrogen protective atmosphere and dilute hydrochloric acid rinsing are used in the preparation process, which reduces pollution to the environment and conforms to the concept of green environmental protection.

[0049] The process is simple and suitable for industrial production: the present invention can complete the preparation process using conventional equipment (such as calcining furnace, high temperature reactor, twin-screw extruder), with clear process steps and simple operation. By optimizing the reaction conditions (such as temperature, time and raw material ratio), the production efficiency is effectively improved and the energy consumption is reduced, providing a basis for large-scale industrial production.

[0050] Multifunctional application prospects: The prepared composite material not only has excellent mechanical properties and thermal stability, but also has good electrical conductivity and antibacterial properties, and can be widely used in many fields such as automotive parts, electronic device housings, building materials and medical devices. This expands the new application range for traditional polypropylene materials.

[0051] In summary, the present invention not only solves the problems existing in traditional polypropylene modification by functionalizing carbon nanotubes and combining them with polypropylene, but also significantly improves the comprehensive performance of composite materials, providing important reference value for the development of high-performance lightweight composite materials. This innovative method combines high efficiency, environmental protection and economic benefits, opening up broad prospects for the field of new composite materials.

[0052] After gallic acid was removed from Comparative Example 1, the performance of the carbon nanotube-modified polypropylene composite material was significantly affected, which was specifically reflected in the following aspects: In the mechanical property test, the warp breaking stress of the composite material of Comparative Example 1 with gallic acid removed was 36.2 MPa, and the weft breaking stress was 71.3 MPa, which was significantly lower than that of Example 3 (warp 40.3 MPa, weft 78.0 MPa). This shows that gallic acid plays a role in enhancing the structural stability and dispersibility of carbon nanotubes during the preparation of carbon nanotubes, and its absence leads to a weakening of the reinforcing effect of carbon nanotubes in the polypropylene matrix. The antibacterial property test shows that the killing rates of Escherichia coli and Staphylococcus aureus in Comparative Example 1 are not listed with specific values, but it is inferred from the overall trend that the antibacterial property of the composite material is reduced after gallic acid is removed. Gallic acid is a compound with antioxidant and antibacterial properties. Its absence in the preparation of carbon nanotubes leads to a decrease in the surface activity of the composite material, thereby weakening the antibacterial ability. Gallic acid reacts chemically with the surface of carbon nanotubes through its phenolic hydroxyl groups during the preparation process, improving the dispersion of carbon nanotubes and the interfacial bonding strength with the polypropylene matrix. After removing this component, the dispersion uniformity of carbon nanotubes in the matrix is ​​affected, resulting in a decrease in the overall performance of the composite material.

[0053] After removing L-cysteine ​​hydrochloride in Comparative Example 2, the performance of the carbon nanotube-modified polypropylene composite material was significantly affected, as shown below: According to the test data, after removing L-cysteine ​​hydrochloride, the warp breaking stress of Comparative Example 2 was 33.7 MPa and the weft breaking stress was 69.5 MPa, which was significantly lower than that of Example 3 (warp 40.3 MPa, weft 78.0 MPa). This shows that L-cysteine ​​hydrochloride plays an important role in the surface activation of carbon nanotubes, and its absence leads to a weakening of the reinforcing effect of carbon nanotubes in the polypropylene matrix. The antibacterial test results show that the antibacterial performance of Comparative Example 2 failed to reach the level of the embodiment. Although the specific killing rate data are not listed, it is speculated that the surface activity and antibacterial properties of the composite material are reduced due to the absence of L-cysteine ​​hydrochloride. This is because L-cysteine ​​hydrochloride can introduce functional functional groups during the activation process, thereby enhancing the antibacterial effect of the material. As a surfactant, L-cysteine ​​hydrochloride acts to improve the dispersibility of carbon nanotubes and the interfacial bonding force with the polypropylene matrix. After removing this component, the uniformity of the dispersion of carbon nanotubes in the matrix is ​​affected, resulting in a decrease in the overall performance of the composite material. In addition, the weakening of the interfacial bonding force directly affects the stress transfer ability of the material under the action of external force. From the experimental results, it can be seen that L-cysteine ​​hydrochloride plays a key role in the preparation of carbon nanotube-modified polypropylene composite materials. It not only improves the mechanical properties of the material, but also improves the antibacterial properties and interfacial bonding force. After removing this component, the performance of Comparative Example 2 is comprehensively reduced, verifying its irreplaceable importance.

[0054] After removing ethylenediamine in Comparative Example 3, the performance of the carbon nanotube-modified polypropylene composite material was significantly negatively affected, as shown below: According to the test data, the warp breaking stress of the composite material of Comparative Example 3 with ethylenediamine removed was 34.5 MPa, and the weft breaking stress was 70.7 MPa, which was significantly lower than that of Example 3 (40.3 MPa in the warp direction and 78.0 MPa in the weft direction). This shows that ethylenediamine plays a key role in the surface activation of carbon nanotubes, and its absence leads to a weakening of the interfacial bonding force between the carbon nanotubes and the polypropylene matrix, thereby affecting the mechanical properties of the composite material. The antibacterial test results show that the antibacterial performance of Comparative Example 3 is also lower than that of Example 3. Although the specific killing rate is not listed, it is speculated that the antibacterial effect of the composite material is weakened due to the absence of ethylenediamine. This is because ethylenediamine can enhance the activity of the surface of carbon nanotubes by introducing functional groups such as amino groups, thereby improving the antibacterial performance. As a surface modifier, ethylenediamine serves to improve the dispersibility and interfacial bonding force of carbon nanotubes in the polypropylene matrix. After removing ethylenediamine, the dispersion uniformity of carbon nanotubes in the matrix is ​​affected, resulting in a decrease in the overall performance of the composite material. In addition, the weakening of the interfacial bonding force directly affects the stress transfer ability, making the performance of the composite material under external force not as good as the embodiment. The experimental results show that ethylenediamine plays an irreplaceable and important role in the modification process. It not only improves the mechanical properties of the material, but also improves the antibacterial properties and interfacial bonding force. After removing this component, the comprehensive performance of Comparative Example 3 is comprehensively reduced, thereby verifying its key position in the preparation of high-performance composite materials.

[0055] The above-described embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the attached claims.

Claims

1. A method for preparing a carbon nanotube-modified polypropylene composite material, characterized in that: The following steps are included by weight: (1) providing 5-10 parts of plant fiber, 2-6 parts of calcium carbonate powder and 2-4 parts of gallic acid, mixing them, and homogenizing them to obtain a precursor carbon material; then, transferring them to a calcining furnace, calcining them at high temperature for 6-10 hours under a protective gas atmosphere, the high temperature calcination temperature being 400°C-600°C, collecting the solid product and rinsing it with acid, then rinsing it with deionized water, drying it, and vacuum freeze-drying it to obtain carbon nanotubes; (2) adding 1-3 parts of sodium ascorbate and 2-3 parts of ethylenediamine to 2.5-7.5 parts of L-cysteine ​​hydrochloride, and finally adding 50-80 parts of deionized water, transferring to a high-temperature reactor, reacting at 130-160° C. for 2-4 hours, adding 0.4 to 0.8 times the mass of the carbon nanotubes obtained in step (1) and 0.04 to 0.10 times the mass of the activator, stirring at room temperature for 3-6 hours, and performing activation treatment to obtain modified carbon nanotubes; (3) Mix 10-30 parts of the modified carbon nanotubes prepared in step (2) with 120-150 parts of polypropylene, then add 180-220 parts of polyol and 1-5 parts of catalyst, react at 80-95°C for 8-12 hours, and extrude and granulate using a twin-screw extruder after the reaction is completed.

2. The method for preparing the carbon nanotube-modified polypropylene composite material according to claim 1, characterized in that: In step (1), the plant fiber is bamboo fiber, wheat straw fiber or coconut shell fiber; The particle size of the calcium carbonate powder in step (1) is 100um-200um; In step (1), the protective gas is nitrogen.

3. The method for preparing the carbon nanotube-modified polypropylene composite material according to claim 2, characterized in that: The acid in step (1) is a 3% by weight dilute hydrochloric acid solution.

4. The method for preparing the carbon nanotube-modified polypropylene composite material according to claim 1, characterized in that: In step (3), the polyol is glycerol, pentaerythritol, ethylene glycol or butanediol.

5. The method for preparing the carbon nanotube-modified polypropylene composite material according to claim 1, characterized in that: The catalyst in step (3) is titanium tetrachloride or triethylaluminum.

6. A composite material prepared by the method for preparing a carbon nanotube-modified polypropylene composite material according to any one of claims 1 to 5.

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