Modified bamboo fiber reinforced polypropylene composite material and preparation method thereof

Abstract

The invention discloses a modified bamboo fiber reinforced polypropylene composite material and a preparation method thereof, and belongs to the field of polypropylene composite materials, the modified bamboo fiber reinforced polypropylene composite material is characterized by comprising the following raw materials by mass: 1-10 parts of modified bamboo fiber, 80-90 parts of polypropylene, and 1-5 parts of a compatilizer. The modified bamboo fiber is prepared by modifying the surface of bamboo fiber by using acetic anhydride as an acetylation reagent and concentrated sulfuric acid and glacial acetic acid as a solvent system. Through acetylation modification of the bamboo fiber, the surface hydrophobic effect of the bamboo fiber is greatly improved, the bamboo fiber adapts to a polypropylene polymer non-polar material, and the interfacial compatibility between the bamboo fiber and polypropylene is improved. Fine fibers can be separated from the modified bamboo fibers through two screw extrusion processes under the shearing action of the screws and are uniformly dispersed in a polypropylene matrix, the fine fibers have the effect of a heterogeneous nucleating agent on polypropylene, the reinforcing effect of the bamboo fibers on the polypropylene is improved, and the composite material is endowed with more excellent mechanical performance and thermal stability.

Description

[0001] This invention belongs to the field of polypropylene composite materials, specifically relating to a modified bamboo fiber reinforced polypropylene composite material and its preparation method. Background Technology

[0002] Polypropylene (PP) is widely used in various fields such as automobiles, home appliances, construction, and medical applications due to its excellent properties, including light weight, high strength, high plasticity, and ease of processing. However, to further improve the mechanical properties, thermal stability, and dimensional stability of PP materials, reinforcing agents are usually added. These reinforcing agents generally include glass fiber, talc, and carbon fiber. PP is made from petroleum through refining and is a non-renewable resource that is not easily degraded. In recent years, with continuous technological advancements and increasing environmental awareness, PP materials need to develop towards new materials that are low-cost, recyclable, and biodegradable to meet modern needs. Bamboo fiber is one of the most abundant renewable resources in nature. It has advantages such as low cost, biodegradability, and high strength. Composite materials reinforced with bamboo fiber also exhibit excellent performance.

[0003] Due to the strong hydrophilicity of bamboo fiber, its compatibility with hydrophobic polypropylene resin is very poor. This makes it easy for voids and defects to form at the composite interface when bamboo fiber is used to reinforce polypropylene resin in the preparation of composites, resulting in poor mechanical properties. In existing technologies, bamboo fiber is treated to obtain a rough surface, and then compatibilizers are used to improve the interfacial bonding between the bamboo fiber and polypropylene. However, it is difficult to obtain polypropylene composites with excellent mechanical properties, and because bamboo fiber is difficult to disperse uniformly in the polypropylene matrix, it is difficult to improve its thermal stability.

[0004] Therefore, there is an urgent need to develop a polypropylene material with high interfacial compatibility between bamboo fiber and polypropylene and excellent performance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a modified bamboo fiber reinforced polypropylene composite material and its preparation method, thereby solving the problems in the prior art.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A modified bamboo fiber reinforced polypropylene composite material comprises the following raw materials in parts by weight: 1-10 parts modified bamboo fiber, 80-90 parts polypropylene, and 1-5 parts compatibilizer.

[0008] The modified bamboo fiber is prepared by modifying the surface of bamboo fiber using acetic anhydride as an acetylation reagent and concentrated sulfuric acid and glacial acetic acid as solvent system.

[0009] Furthermore, the polypropylene is one or more of homopolymer polypropylene, block copolymer polypropylene, and random copolymer polypropylene.

[0010] Furthermore, the bamboo fiber is one or more of the following: moso bamboo fiber, nephrolepis cordifolia fiber, styrax chinensis fiber, and basil fiber.

[0011] Furthermore, the compatibilizer is at least one of maleic anhydride-grafted polypropylene, acrylic acid-grafted polypropylene, ethylene / acrylic acid copolymer, and polyethylene / maleic anhydride-grafted copolymer.

[0012] Furthermore, the modified bamboo fiber preparation process includes:

[0013] S1. Soak bamboo fiber in analytical grade glacial acetic acid to fully swell the fiber and form a glacial acetic acid / fiber mixed solution.

[0014] S2. Add analytical grade acetic anhydride reagent to the glacial acetic acid / cellulose mixed solution in step S1, followed by analytical grade concentrated sulfuric acid reagent. Stir continuously and heat in a water bath during the process to finally obtain a transparent solution.

[0015] S3. Add deionized water to the transparent solution in step S2 to precipitate the solid, filter and freeze-dry to obtain acetylated modified bamboo fiber.

[0016] Furthermore, in step S1, the bamboo fiber length is 4-5 mm, the mass ratio of bamboo fiber to glacial acetic acid is 1-5:7-10, the swelling temperature is 20-30℃, and the swelling time is 2-4 h.

[0017] Furthermore, in step S2, the mass ratio of analytical grade acetic anhydride, bamboo fiber, and analytical grade concentrated sulfuric acid is 1-9:1-5:0.01-0.05.

[0018] Furthermore, in step S2, the water bath heating reaction temperature is 40–60°C, and the reaction time is 2.5–3 hours.

[0019] Furthermore, in step S3, the freeze-drying temperature is -45℃ and the drying time is 48h.

[0020] A method for preparing a modified bamboo fiber reinforced polypropylene composite material includes the following steps:

[0021] A1. Soak bamboo fiber in analytical grade glacial acetic acid at a mass ratio of (1-5:7-10) to fully swell the fiber. Then add analytical grade acetic anhydride, bamboo fiber and analytical grade concentrated sulfuric acid at a mass ratio of 1-9:1-5:0.01-0.05. Heat in a water bath at 40-60℃ for 2.5-3 hours. After the reaction is complete, add deionized water to precipitate the solid, filter, and freeze-dry at -45℃ for 48 hours to obtain acetylated modified bamboo fiber.

[0022] A2. The modified bamboo fiber, compatibilizer, and polypropylene from step A1 are premixed evenly at high temperature to obtain a premix.

[0023] A3. Add the premix from step A2 to a twin-screw extruder and plasticize and granulate it by means of the high-temperature shearing action of the screw to obtain granules;

[0024] A4. Feed the granules obtained in step A3 back into the twin-screw extruder for plasticizing extrusion granulation to obtain composite material granules.

[0025] A5. Place the composite material particles obtained in step A4 into a mold and perform injection molding to obtain the desired modified bamboo fiber reinforced polypropylene composite material.

[0026] Furthermore, in step A2, the screw compressor speed is 30 r / min, and the temperatures of zones one through four are 170℃, 180℃, 185℃, and 190℃, respectively.

[0027] Furthermore, in step A3, the screw compressor speed is 30 r / min, and the temperatures of zones one through four are 170℃, 180℃, 185℃, and 190℃, respectively.

[0028] Furthermore, in step A5, the injection molding temperature is 190°C.

[0029] The above-mentioned modified bamboo fiber reinforced polypropylene composite material is used in the manufacture of automotive interiors.

[0030] The beneficial effects of this invention are:

[0031] 1. This invention uses acetic anhydride acetylation reagent, concentrated sulfuric acid, and glacial acetic acid as solvent systems to modify the surface of bamboo fiber; wherein, during the acetylation reaction between acetic anhydride acetylation reagent and bamboo fiber, acetyl groups replace hydroxyl groups on the fiber surface, reducing the surface polarity of the fiber and increasing the interfacial compatibility between bamboo fiber and polypropylene.

[0032] 2. The swelling pretreatment of bamboo fiber improves the surface roughness of the fiber, which facilitates the separation of fine fibers from the fiber surface by means of the screw shearing action during the subsequent two screw extrusion processes. These fine fibers reach the submicron and nanoscale, which can significantly improve the fiber size effect.

[0033] 3. The composite material prepared by melt extrusion of acetylated bamboo fiber with polypropylene and compatibilizer has significantly improved tensile, flexural and thermal stability, giving the composite material higher performance advantages. Attached Figure Description

[0034] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0035] Figure 1 This is a scanning electron microscope (SEM) image of the tensile fracture section of the composite material in Example 1 of the present invention.

[0036] Figure 2 This is a scanning electron microscope (SEM) image of the tensile fracture section of the composite material in Comparative Example 2 of this invention.

[0037] Figure 3 The above are TG test charts for thermal stability analysis of Examples 1-3 and Comparative Examples 1-2 of the present invention. Detailed Implementation

[0038] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments thereof. Those skilled in the art should understand that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0039] The preparation process of polypropylene composite materials is illustrated below through several examples, and the parts in the examples and comparative examples are all parts by weight; the raw materials and reagents used in the examples are conventionally purchased raw materials and reagents, as detailed below:

[0040] Polypropylene: T30S, homopolymer polypropylene, melt index 3g / 10min, purchased from Sinopec;

[0041] Bamboo fiber: Bamboo fiber, with an average fiber length of 4-5mm, purchased from Hedi Technology;

[0042] Compatibilizer: Maleic anhydride-grafted polypropylene, grafting rate 5%, purchased from Kingfa Science & Technology.

[0043] Example 1

[0044] Bamboo fiber was soaked in analytical grade glacial acetic acid at a mass ratio of 1:9 for 3 hours to allow the fiber to fully swell. Subsequently, analytical grade acetic anhydride and analytical grade concentrated sulfuric acid were added at a mass ratio of 5:5:0.05. The mixture was heated in a water bath at 50°C for 3 hours. After the reaction, deionized water was added to precipitate the solid, which was then filtered and freeze-dried at -45°C for 48 hours to obtain acetylated modified bamboo fiber. Five parts of modified bamboo fiber were premixed with three parts of maleic anhydride-grafted polypropylene and 85 parts of polypropylene at high temperature to obtain a premix. The premix was then added to a twin-screw extruder and plasticized by extrusion granulation using the high-temperature shearing action of the screw to obtain granules. The screw speed was 30 r / min, and the temperatures of zones one through four were 170°C, 180°C, 185°C, and 190°C, respectively. The granules were extruded and granulated again under the same conditions to obtain polypropylene composite granules. Finally, the granules were injection molded at 190°C.

[0045] Example 2:

[0046] Bamboo fiber was soaked in analytical grade glacial acetic acid at a mass ratio of 1:9 for 3 hours to allow the fiber to fully swell. Subsequently, analytical grade acetic anhydride and analytical grade concentrated sulfuric acid were added at a mass ratio of 2:5:0.05. The mixture was heated in a water bath at 50°C for 3 hours. After the reaction, deionized water was added to precipitate the solid, which was then filtered and freeze-dried at -45°C for 48 hours to obtain acetylated modified bamboo fiber. Five parts of modified bamboo fiber were premixed with three parts of maleic anhydride-grafted polypropylene and 85 parts of polypropylene at high temperature to obtain a premix. The premix was then added to a twin-screw extruder and plasticized by extrusion granulation using the high-temperature shearing action of the screw to obtain granules. The screw speed was 30 r / min, and the temperatures of zones one through four were 170°C, 180°C, 185°C, and 190°C, respectively. The granules were extruded and granulated again under the same conditions to obtain polypropylene composite granules. Finally, the granules were injection molded at 190°C.

[0047] Example 3:

[0048] Bamboo fiber was soaked in analytical grade glacial acetic acid at a mass ratio of 1:9 for 3 hours to allow the fiber to fully swell. Subsequently, analytical grade acetic anhydride and analytical grade concentrated sulfuric acid were added at a mass ratio of 8:5:0.05. The mixture was heated in a water bath at 50°C for 3 hours. After the reaction, deionized water was added to precipitate the solid, which was then filtered and freeze-dried at -45°C for 48 hours to obtain acetylated modified bamboo fiber. Five parts of modified bamboo fiber were premixed with three parts of maleic anhydride-grafted polypropylene and 85 parts of polypropylene at high temperature to obtain a premix. The premix was added to a twin-screw extruder and plasticized by extrusion granulation using the high-temperature shearing action of the screw to obtain granules. The screw speed was 30 r / min, and the temperatures of zones one to four were 170°C, 180°C, 185°C, and 190°C, respectively. The granules were extruded and granulated again under the same conditions to obtain polypropylene composite granules. Finally, the granules were injection molded at 190°C.

[0049] Comparative Example 1:

[0050] Five parts of bamboo fiber, three parts of maleic anhydride-grafted polypropylene, and 85 parts of polypropylene were premixed evenly at high temperature to obtain a premix. The premix was added to a twin-screw extruder and plasticized by extrusion granulation under the high-temperature shearing action of the screw to obtain granules. The screw speed was 30 r / min, and the temperatures of zones one to four were 170℃, 180℃, 185℃, and 190℃, respectively. The granules were extruded and granulated again under the same conditions to obtain polypropylene composite material granules. Finally, they were injection molded in a mold at 190℃.

[0051] Comparative Example 2:

[0052] Bamboo fiber was soaked in analytical grade glacial acetic acid at a mass ratio of 1:9 for 3 hours to allow the fiber to fully swell. Subsequently, analytical grade acetic anhydride and analytical grade concentrated sulfuric acid were added at a mass ratio of 5:5:0.05. The mixture was heated in a water bath at 50°C for 3 hours. After the reaction, deionized water was added to precipitate the solid, which was then filtered and freeze-dried at -45°C for 48 hours to obtain acetylated modified bamboo fiber. Five parts of modified bamboo fiber were premixed with three parts of maleic anhydride-grafted polypropylene and 85 parts of polypropylene at high temperature to obtain a premix. The premix was added to a twin-screw extruder and plasticized by extrusion granulation using the high-temperature shearing action of the screw to obtain granules. The screw speed was 30 r / min, and the temperatures of zones one to four were 170°C, 180°C, 185°C, and 190°C, respectively. Finally, the granules were injection molded at 190°C.

[0053] The tensile strength and flexural strength of the molded parts obtained by injection molding of polypropylene composite material particles in Examples 1-3 and Comparative Examples 1-2 were tested. The test results are shown in the table below.

[0054] Table 1. Tensile test results of polypropylene composite materials obtained in Examples 1-3 and Comparative Examples 1-2.

[0055]

[0056] As shown in Table 1, the modified bamboo fiber reinforced polypropylene composite material prepared by the method of this invention exhibits excellent tensile and flexural properties. Comparing Example 1 and Comparative Example 1, it was found that the tensile strength of the composite material with modified bamboo fiber added was 35.67 MPa, an increase of 17.1% compared to the 30.47 MPa of the unmodified bamboo fiber composite material, and the flexural strength increased by 72.4%. Therefore, adding modified bamboo fiber can significantly improve the physical properties of polypropylene materials. This is because the modification of bamboo fiber increases its surface hydrophobicity, changing it from hydrophilic to hydrophobic. This greatly increases the interfacial compatibility between the modified bamboo fiber and polypropylene, thus significantly improving the mechanical properties.

[0057] Comparative Example 2 is a composite material obtained through a single screw extrusion process, and its physical properties are somewhat reduced compared to Example 1. This is because the shearing action of the screw is lacking. Although the acetylation reaction greatly increases the roughness and surface hydrophobicity of the fibers, agglomeration is prone to occur during the compounding process with polypropylene, such as... Figure 1 , Figure 2 As shown, the present invention employs a double screw extrusion method, which results in more uniform fiber dispersion in the polypropylene matrix. Without reducing the performance of the polypropylene material, the screw shearing action can separate submicron and nano-sized filaments from the fiber surface, significantly leveraging the fiber size effect and improving the physical properties of the composite material.

[0058] The thermal stability (TG) of the molded parts obtained by injection molding of polypropylene composite particles from Examples 1-3 and Comparative Examples 1-2 was tested. The test results are shown in the table below.

[0059] Depend on Figure 3 As shown in Table 2, the thermal stability of the composite material with modified bamboo fiber is improved. Furthermore, the thermogravimetric curves of Examples 1-3 and Comparative Examples 1-2 show a shift to the right, indicating a steady improvement in the thermal stability of the composite material. The composite material of Example 1 exhibits the best thermal stability. Table 2 provides a more intuitive understanding of this information. The maximum thermal decomposition temperature of Example 1 is 474.92℃, which is higher than the other examples. This is because acetyl groups were introduced during the modification process, and acetyl groups have higher thermal stability than the hydroxyl groups in bamboo fiber. Adding bamboo fiber to the polypropylene matrix restricts the movement of polypropylene molecular chains. The small-sized fibers separated by the screw shearing action are uniformly dispersed within the polypropylene, filling the gaps between polypropylene molecules and making the structure denser. Additionally, bamboo fiber acts as a heterogeneous nucleating agent, further enhancing the thermal stability of the composite material.

[0060] Table 2. Thermal stability (TG) test results of polypropylene composite materials obtained in Examples 1-3 and Comparative Examples 1-2.

[0061]

[0062] Note: Samples are in T 05 This indicates the temperature at which a 5% mass loss of the sample occurs, where the sample is at a temperature of T. 10 The temperature at which the sample mass loss is 10% is represented by Rmax, and the temperature at which the sample mass loss is at its maximum is represented by Rmax.

[0063] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A modified bamboo fiber reinforced polypropylene composite material, characterized in that, The raw material composition includes the following parts by weight: 1-10 parts modified bamboo fiber, 80-90 parts polypropylene, and 1-5 parts compatibilizer; The modified bamboo fiber is prepared by modifying the surface of bamboo fiber using acetic anhydride as an acetylation reagent and concentrated sulfuric acid and glacial acetic acid as solvent system.

2. The modified bamboo fiber reinforced polypropylene composite material according to claim 1, characterized in that, The polypropylene is one or more of homopolymer polypropylene, block copolymer polypropylene, and random copolymer polypropylene. The bamboo fiber is one or more of moso bamboo fiber, bamboo stalk fiber, square bamboo fiber, and hemp bamboo fiber. The compatibilizer is at least one of maleic anhydride-grafted polypropylene, acrylic acid-grafted polypropylene, ethylene / acrylic acid copolymer, and polyethylene / maleic anhydride-grafted copolymer.

3. The modified bamboo fiber reinforced polypropylene composite material according to claim 1, characterized in that, The modified bamboo fiber preparation process includes: S1. Soak bamboo fiber in analytical grade glacial acetic acid to fully swell the fiber and form a glacial acetic acid / fiber mixed solution. S2. Add analytical grade acetic anhydride reagent to the glacial acetic acid / cellulose mixed solution in step S1, followed by analytical grade concentrated sulfuric acid reagent. Stir continuously and heat in a water bath during the process to finally obtain a transparent solution. S3. Add deionized water to the transparent solution in step S2 to precipitate the solid, filter and freeze-dry to obtain acetylated modified bamboo fiber.

4. The modified bamboo fiber reinforced polypropylene composite material according to claim 3, characterized in that, In step S1, the bamboo fiber length is 4-5 mm, the mass ratio of bamboo fiber to glacial acetic acid is 1-5:7-10, the swelling temperature is 20-30℃, and the swelling time is 2-4 h.

5. The modified bamboo fiber reinforced polypropylene composite material according to claim 3, characterized in that, In step S2, the mass ratio of analytical grade acetic anhydride, bamboo fiber and analytical grade concentrated sulfuric acid is 1-9:1-5:0.01-0.

05.

6. The modified bamboo fiber reinforced polypropylene composite material according to claim 3, characterized in that, In step S2, the water bath heating reaction temperature is 40-60℃, and the reaction time is 2.5-3h.

7. A method for preparing a modified bamboo fiber reinforced polypropylene composite material, characterized in that, Includes the following steps: A1. Soak bamboo fiber in analytical grade glacial acetic acid at a mass ratio of (1-5:7-10) to fully swell the fiber. Then add analytical grade acetic anhydride, bamboo fiber and analytical grade concentrated sulfuric acid at a mass ratio of 1-9:1-5:0.01-0.

05. Heat in a water bath at 40-60℃ for 2.5-3 hours. After the reaction is complete, add deionized water to precipitate the solid, filter, and freeze-dry at -45℃ for 48 hours to obtain acetylated modified bamboo fiber. A2. The modified bamboo fiber, compatibilizer, and polypropylene from step A1 are premixed evenly at high temperature to obtain a premix. A3. Add the premix from step A2 to a twin-screw extruder and plasticize and granulate it by means of the high-temperature shearing action of the screw to obtain granules; A4. Feed the granules obtained in step A3 back into the twin-screw extruder for plasticizing extrusion granulation to obtain composite material granules. A5. Place the composite material particles obtained in step A4 into a mold and perform injection molding to obtain the desired modified bamboo fiber reinforced polypropylene composite material.

8. The method for preparing a modified bamboo fiber reinforced polypropylene composite material according to claim 7, characterized in that, In step A2, the screw compressor speed is 30 r / min, and the temperatures of zones one through four are 170℃, 180℃, 185℃, and 190℃, respectively.

9. The method for preparing a modified bamboo fiber reinforced polypropylene composite material according to claim 7, characterized in that, In step A3, the screw compressor speed is 30 r / min, and the temperatures of zones one through four are 170℃, 180℃, 185℃, and 190℃, respectively.

10. The method for preparing a modified bamboo fiber reinforced polypropylene composite material according to claim 7, characterized in that, In step A5, the injection temperature is 190℃.

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