A fully biodegradable nanocrystalline cellulose composite and a preparation method thereof

Abstract

This invention discloses a fully biodegradable nanofiber composite material and its preparation method, belonging to the field of polymer composite material technology. The composite material comprises the following components by mass percentage: 60-80% polybutylene terephthalate-adipate, 15-25% polylactic acid, 5-15% nanofiber, 0.1-2% chain extender, and 0-1% functional additives; wherein the nanofiber is obtained by hydrophobic modification of bamboo powder, and the surface hydroxyl groups are shielded by non-polar alkyl chains. The composite material has a tensile strength of not less than 23 MPa, an elongation at break of not less than 450%, and a transmittance of 79.6%-85.7% for visible light at 530 nm wavelength at a thickness of 0.10 mm, with a haze of 2.6%-3.2%. This invention, through molecular-level hydrophobic modification and in-situ nanofiber generation process, achieves uniform dispersion and excellent interfacial compatibility of bamboo fiber in biodegradable plastics, significantly improving the mechanical properties and optical transparency of the composite material, which can be widely used in transparent packaging, agricultural films, and disposable biodegradable products.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, and more specifically, to a fully biodegradable nano-bamboo fiber composite material and its preparation method. Background Technology

[0002] Bamboo fiber, as a natural, renewable, high-strength, and low-cost reinforcing material, has broad application prospects in the field of biodegradable polymer composites. Compared with traditional glass fiber or synthetic fiber, bamboo fiber itself possesses biodegradable properties. Combining it with biodegradable plastics can not only improve the mechanical properties of the products but also help reduce production costs and environmental impact.

[0003] However, existing technologies still face several challenges in preparing bamboo fiber / biodegradable plastic composites. First, the main components of bamboo fiber (cellulose, hemicellulose, lignin, etc.) are rich in hydroxyl groups (-OH), giving it a highly polar surface. In contrast, most biodegradable plastics (such as polylactic acid, polybutylene adipate terephthalate, etc.) have lower polarity, resulting in poor interfacial compatibility and difficulty in uniformly dispersing the fibers in the matrix. Second, bamboo fibers typically have a large aspect ratio, making them prone to physical entanglement during processing, further exacerbating the uneven dispersion problem and thus deteriorating the mechanical properties of the composite material. Furthermore, the introduction of bamboo fiber significantly reduces the transparency of the composite material, especially in the preparation of film products, limiting its application in areas such as transparent packaging.

[0004] To address the aforementioned issues, existing technologies have attempted to modify the surface of bamboo fibers to be hydrophobic or to prepare micron- or nano-scale bamboo fibers through mechanical grinding. However, surface modification struggles to completely alter the internal polarity of the fiber, and the bonding strength between the modifier and the fiber surface is limited; while mechanically prepared nanofibers are prone to agglomeration, resulting in unsatisfactory dispersion in polymer melts. For example, Chinese patent application CN202511800826.0 discloses a carboxymethyl-modified bamboo fiber conductive paper, its preparation method, and its application. This method effectively improves the hydrophilicity of bamboo fibers by introducing carboxymethyl groups, thereby increasing the conductivity of the carboxymethyl-modified bamboo fiber conductive paper. Furthermore, by mixing carboxymethyl-modified bamboo fibers with unmodified bamboo fibers, the carboxymethyl-modified bamboo fiber conductive paper also possesses ideal tensile strength. For example, Chinese patent application CN202511515892.3 discloses modified bamboo fiber, PBAT composite materials, and plastic objects. Modified bamboo fiber, due to its hot-pressing treatment in water, avoids the generation of volatile gases caused by high-temperature processing when applied to plastic materials, thus improving the interfacial interaction with the plastic material. The blocked aziridine crosslinking agent releases active groups at high temperatures, reacting with hydroxyl and carboxyl groups on the surface of bamboo fiber and plastic materials, improving the interfacial interaction between bamboo fiber and the plastic matrix, and increasing the tensile strength of the composite material. However, the overall performance of the resulting material still needs improvement.

[0005] Therefore, developing a fully biodegradable bamboo fiber composite material that combines excellent mechanical properties, high elongation at break, good transparency, uniform bamboo fiber dispersion, and good interfacial compatibility remains a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] Based on this, in order to solve one of the technical problems of the prior art, the present invention provides a fully biodegradable nano-bamboo fiber composite material and its preparation method, the specific technical solution of which is as follows:

[0007] A fully biodegradable nanofiber composite material, the nanofiber composite material comprising the following components by weight percentage: Polybutylene terephthalate (PET) 60-80%, polylactic acid 15-25%, nano bamboo fiber 5-15%, chain extender 0.1-2%, and functional additives 0-1%; The nano-bamboo fiber is obtained by hydrophobic modification of bamboo powder, and the surface hydroxyl groups are shielded by non-polar alkyl chains. Furthermore, the composite material has a tensile strength of not less than 23 MPa, an elongation at break of not less than 450%, and a transmittance of 79.6% to 85.7% for visible light at a wavelength of 530 nm when the thickness is 0.10 mm, and a haze of 2.6% to 3.2%.

[0008] Furthermore, at 190°C and 2.16 kg, the melt index of the polybutylene terephthalate is 1~40 g / 10 min.

[0009] Furthermore, at 190°C and 2.16 kg, the melt index of the polylactic acid is 1~40 g / 10 min.

[0010] Furthermore, the average size of the nano-bamboo fiber is 50~500nm.

[0011] Furthermore, the chain extender is an organic oligomer containing multiple epoxy functional groups, and the epoxy equivalent of the organic oligomer is 250~350 g / mol.

[0012] Furthermore, the functional additive is at least one of antioxidants, antistatic agents, antifogging agents, opening agents, and color masterbatches.

[0013] In addition, the present invention also provides a method for preparing a nano-bamboo fiber composite material, the method comprising the following steps: S1. Bamboo powder is washed with alkali, alcohol, and water, and then dried to obtain dried bamboo powder; S2. Add dried bamboo powder to a solvent and stir to obtain a semi-transparent solution; then add alkyl ketene dimer and continue stirring to obtain a hydrophobically modified nano-bamboo fiber solution. S3. Mix PBAT, PLA, chain extender and functional additives evenly, and feed them into a twin-screw extruder through the main feed port for melt blending to obtain plastic melt; at the same time, inject hydrophobically modified nano bamboo fiber solution into the extruder through a metering pump from the side feed port to melt and mix with the plastic melt; the mixed melt is extruded through the die, granulated, cooled and solidified, then collected, and then washed and dried to obtain nano bamboo fiber composite material.

[0014] Further, in step S2, the solvent is obtained by mixing choline chloride and lactic acid in a molar ratio of 1:2 and stirring at 100~120°C for 1~2 hours.

[0015] Further, in step S2, dried bamboo powder is added to the solvent and stirred at a speed of 50~300 r / min for 2~3 h to obtain a semi-transparent solution; then alkyl ketene dimer is added and the reaction is continued to be stirred for 1~2 h to obtain a hydrophobically modified nano bamboo fiber solution.

[0016] Furthermore, in step S3, the melting and mixing temperature is 170~220℃, the screw speed is 280~450rpm, and the cooling and solidification are carried out using cold water at a temperature of 0~6℃.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The mixed solvent obtained by melting choline chloride and lactic acid in a specific ratio in this invention exhibits good solubility for bamboo powder. Simultaneously, its acidic environment facilitates the breakdown of lignin in the bamboo powder, allowing for the full exposure and release of bamboo cellulose. Under the conditions of bamboo fiber dissolution, AKD is used for hydrophobic modification. AKD can fully react with the polar hydroxyl groups on the cellulose molecular chain, thereby replacing them with hydrophobic alkane long chains. Compared to existing technologies that only perform hydrophobic modification on the surface of bamboo fiber, the technical solution adopted in this invention reacts at the molecular chain level, resulting in better modification effects, improved dispersion of bamboo fiber in the plastic matrix, and better interfacial compatibility.

[0018] 2. The acidic environment provided by the lactic acid in the bamboo fiber solvent of this invention can cause partial degradation of PBAT and PLA polyester under high temperature conditions, and the molecular chain segments are reconnected under the action of chain extenders. This is a random transesterification process, which is beneficial to disrupting the molecular chain regularity of PBAT, thereby improving the transparency of the composite material. On the other hand, dissolving bamboo fiber into molecular-level (50~500nm) and then melt-blending it with biodegradable plastics such as PBAT results in better mixing and dispersion. By limiting the particle size of the melt and solidifying it with cold water, it is beneficial to fully solidify and precipitate the bamboo fiber to form nanofibers. Compared with the prior art, this invention, by generating nanofibers in situ in the polymer matrix, improves the mechanical properties of the composite material without affecting its transparency, representing a significant advancement.

[0019] 3. This invention involves directly injecting a bamboo fiber solution in liquid form into a twin-screw extruder to mix with polyester melt, followed by rapid cooling and appropriate particle size control, allowing bamboo cellulose to crystallize in situ within the matrix to form nanofibers. This process avoids the defects of traditional mechanical grinding methods, such as easy fiber agglomeration and poor transparency; it generally meets the requirements of green material development and can be used in high-end transparent packaging, agricultural mulch films, disposable tableware, and other fields. Attached Figure Description

[0020] The invention will be further understood from the following description taken in conjunction with the accompanying drawings. The components in the drawings are not necessarily drawn to scale, but rather the emphasis is on illustrating the principles of the embodiments. In different views, the same reference numerals designate corresponding parts.

[0021] Figure 1 This is a schematic diagram of the process flow for a fully biodegradable nano-bamboo fiber composite material in Example 1 of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to its embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of the invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] An embodiment of the present invention provides a fully biodegradable nanofiber composite material, wherein the nanofiber composite material comprises the following components by mass percentage: Polybutylene terephthalate (PET) 60-80%, polylactic acid 15-25%, nano bamboo fiber 5-15%, chain extender 0.1-2%, and functional additives 0-1%; The nano-bamboo fiber is obtained by hydrophobic modification of bamboo powder, and the surface hydroxyl groups are shielded by non-polar alkyl chains. Furthermore, the composite material has a tensile strength of not less than 23 MPa, an elongation at break of not less than 450%, and a transmittance of 79.6% to 85.7% for visible light at a wavelength of 530 nm when the thickness is 0.10 mm, and a haze of 2.6% to 3.2%.

[0025] In one embodiment, at 190°C and 2.16 kg, the melt index of the polybutylene terephthalate is 1~40 g / 10 min, preferably 1~20 g / 10 min.

[0026] In one embodiment, at 190°C and 2.16 kg, the melt index of the polylactic acid is 1~40 g / 10 min, preferably 1~20 g / 10 min. By optimizing the melt index of PBAT and PLA, this invention not only meets the flowability requirements for processing and manufacturing but also helps to improve the overall performance of the materials and production efficiency.

[0027] In one embodiment, the average size of the nanofibers is 50-500 nm.

[0028] In one embodiment, the chain extender is an organic oligomer containing multiple epoxy functional groups, wherein the epoxy equivalent of the organic oligomer is 250-350 g / mol. The organic oligomer containing multiple epoxy functional groups of the present invention has epoxy groups that can react with hydroxyl or carboxyl groups on PBAT and PLA, thereby inhibiting the degradation of the plastic matrix and enhancing melt strength.

[0029] In one embodiment, the functional additive is at least one of antioxidants, antistatic agents, antifogging agents, opening agents, and color masterbatches.

[0030] In addition, the present invention also provides a method for preparing a nano-bamboo fiber composite material, the method comprising the following steps: S1. Bamboo powder is washed with alkali, alcohol, and water, and then dried to obtain dried bamboo powder; S2. Add dried bamboo powder to a solvent and stir to obtain a semi-transparent solution; then add alkyl ketene dimer and continue stirring to obtain a hydrophobically modified nano-bamboo fiber solution. S3. Mix PBAT, PLA, chain extender and functional additives evenly, and feed them into a twin-screw extruder through the main feed port for melt blending to obtain plastic melt; at the same time, inject hydrophobically modified nano bamboo fiber solution into the extruder through a metering pump from the side feed port to melt and mix with the plastic melt; the mixed melt is extruded through the die, granulated, cooled and solidified, then collected, and then washed and dried to obtain nano bamboo fiber composite material.

[0031] In one embodiment, in step S1, the moisture content of the dried bamboo powder is <5%.

[0032] In one embodiment, in step S2, the choline chloride and lactic acid need to be vacuum dried at 60~80°C for 1~2 hours.

[0033] In one embodiment, in step S2, the solvent is obtained by mixing choline chloride and lactic acid in a molar ratio of 1:2 and stirring at 100-120°C for 1-2 hours.

[0034] In one embodiment, in step S2, dried bamboo powder is added to a solvent and stirred at a speed of 50-300 r / min for 2-3 hours to obtain a semi-transparent solution; then alkyl ketene dimer is added and the reaction is continued to be stirred for 1-2 hours to obtain a hydrophobically modified nano-bamboo fiber solution.

[0035] In one embodiment, the mass ratio of the dried bamboo powder to the solvent is (5~10):100.

[0036] In one embodiment, the amount of the alkyl ketene dimer added accounts for 1% to 2% of the mass of the dried bamboo powder.

[0037] In one embodiment, in step S3, the melting and mixing temperature is 170~220℃, the screw speed is 280~450rpm, and the cooling and solidification are carried out using cold water at a temperature of 0~6℃.

[0038] In one embodiment, in step S3, the melt is extruded through a die with a diameter of 0.4~2.0 mm, cut into particles with a length of 0.5~2.0 mm by a granulation system, and then fully cooled and solidified in a cold water bath at 0~6°C.

[0039] After optimization of the composition and process, the above scheme can obtain a nano-bamboo fiber composite material with excellent compatibility, significant mechanical properties and transparency.

[0040] The embodiments of the present invention will be described in detail below with reference to specific examples. The equipment and raw materials used are all commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0041] Example 1: A fully biodegradable nanofiber composite material comprises the components listed in Table 1 below by mass percentage; Table 1: Raw materials for the preparation of fully biodegradable nanofiber composite material in Example 1

[0042] A method for preparing a fully biodegradable nanofiber composite material includes the following steps: S1. Bamboo powder of 60 mesh is washed with alkali, alcohol, and water and then dried to obtain dried bamboo powder with a moisture content of <5%; S2. Choline chloride and lactic acid were vacuum dried at 80℃ for 2 hours, mixed in a molar ratio of 1:2, and stirred at 100℃ for 1.5 hours to obtain a solvent; 10g of dried bamboo powder was added to 100g of solvent, and stirred at 100r / min at 120℃ for 3 hours to obtain a translucent solution; then 0.2g of alkyl ketene dimer was added, and the reaction was continued to be stirred for 1.5 hours to obtain a hydrophobically modified nano-bamboo fiber solution. S3. The dried PBAT, PLA, chain extender and functional additives are mixed evenly and fed into a twin-screw extruder through the main feed port for melt blending to obtain a plastic melt. At the same time, the hydrophobically modified nano bamboo fiber solution is injected into the extruder through the side feed port via a metering pump and melt-mixed with the plastic melt. The melt mixing temperature is set at 180℃ and the screw speed is 400rpm. The mixed melt is extruded through a die with a diameter of 1.0mm, cut into 0.5mm particles by the granulation system, and then fully cooled and solidified in a 0℃ cold water bath. The particles are then collected, washed, and dried to obtain the nano bamboo fiber composite material.

[0043] Example 2: A fully biodegradable nanofiber composite material comprises the components listed in Table 1 below by mass percentage; Table 1: Raw materials for the preparation of fully biodegradable nanofiber composite material in Example 2

[0044] A method for preparing a fully biodegradable nanofiber composite material includes the following steps: S1. Bamboo powder with a 40-mesh surface is washed with alkali, alcohol, and water, and then dried to obtain dried bamboo powder with a moisture content of <5%. S2. Choline chloride and lactic acid were vacuum dried at 60℃ for 2 hours, mixed in a molar ratio of 1:2, and stirred at 110℃ for 1.5 hours to obtain a solvent; 5g of dried bamboo powder was added to 100g of solvent, and stirred at 100r / min at 110℃ for 2 hours to obtain a translucent solution; then 0.05g of alkyl ketene dimer was added, and the reaction was continued to be stirred for 1.5 hours to obtain a hydrophobically modified nano-bamboo fiber solution. S3. The dried PBAT, PLA, chain extender and functional additives are mixed evenly and fed into a twin-screw extruder through the main feed port for melt blending to obtain a plastic melt. At the same time, the hydrophobically modified nano bamboo fiber solution is injected into the extruder through the side feed port via a metering pump and melt-mixed with the plastic melt. The melt mixing temperature is set to 200℃ and the screw speed is 350rpm. The mixed melt is extruded through a die with a diameter of 2.0mm, cut into granules with a length of 2.0mm through a granulation system, and then fully cooled and solidified in a 4℃ cold water bath. The granules are then collected, washed, and dried to obtain a nano bamboo fiber composite material.

[0045] Example 3: A fully biodegradable nanofiber composite material comprises the components listed in Table 1 below by mass percentage; Table 1: Raw materials for the preparation of fully biodegradable nanofiber composite material in Example 3

[0046] A method for preparing a fully biodegradable nanofiber composite material includes the following steps: S1. Bamboo powder with a 40-mesh surface is washed with alkali, alcohol, and water, and then dried to obtain dried bamboo powder with a moisture content of <5%. S2. Choline chloride and lactic acid were vacuum dried at 75℃ for 1.8h, mixed in a molar ratio of 1:2, and stirred at 100℃ for 1h to obtain a solvent; 10g of dried bamboo powder was added to 100g of solvent, and stirred at 100r / min at 120℃ for 3h to obtain a translucent solution; then 0.12g of alkyl ketene dimer was added, and the reaction was continued to be stirred for 1.5h to obtain a hydrophobically modified nano-bamboo fiber solution. S3. The dried PBAT, PLA, chain extender and functional additives are mixed evenly and fed into a twin-screw extruder through the main feed port for melt blending to obtain a plastic melt. At the same time, the hydrophobically modified nano bamboo fiber solution is injected into the extruder through the side feed port via a metering pump and melt-mixed with the plastic melt. The melt mixing temperature is set at 220℃ and the screw speed is 450rpm. The mixed melt is extruded through a die with a diameter of 0.4mm, cut into 0.5mm particles by the granulation system, and then fully cooled and solidified in a 4℃ cold water bath. The particles are then collected, washed, and dried to obtain the nano bamboo fiber composite material.

[0047] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that no chain extender was added in Comparative Example 1, but otherwise it is the same as Example 1.

[0048] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that no alkyl ketene dimer was added in the preparation of the hydrophobic modified bamboo fiber nanofiber solution in Comparative Example 2, but otherwise it was the same as Example 1.

[0049] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that the preparation method of the hydrophobic modified nano-bamboo fiber solution in Comparative Example 3 is different, while the rest is the same as in Example 1. The preparation method of the composite material in Comparative Example 3 is as follows: S1. Bamboo powder with a 40-mesh surface is washed with alkali, alcohol, and water, and then dried to obtain dried bamboo powder with a moisture content of <5%. S2. Choline chloride and lactic acid were vacuum dried at 75℃ for 1.8h, mixed in a molar ratio of 1:2, and stirred at 100℃ for 1h to obtain a solvent; 10g of dried bamboo powder was added to 100g of solvent, and stirred at 100r / min at 120℃ for 3h to obtain a translucent solution; then 0.12g of alkyl ketene dimer was added, and the reaction was continued to be stirred for 1.5h to obtain a hydrophobically modified nano-bamboo fiber solution. S3. Directly inject the hydrophobically modified nano bamboo fiber solution into sufficient cold water to allow the nano bamboo fibers to fully precipitate, and collect the precipitated nano bamboo fibers; S4. The dried PBAT, PLA, chain extender, nano bamboo fiber and functional additives from step S3 are mixed evenly and fed into a twin-screw extruder for melt blending from the main feed port. The melt mixing temperature is set to 220℃ and the screw speed is 450rpm. The mixed melt is extruded through a die with a diameter of 0.4mm, cut into 0.5mm particles by a granulation system, and then fully cooled and solidified in a 4℃ cold water bath. The particles are then collected, washed, and dried to obtain the nano bamboo fiber composite material.

[0050] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that the mixed melt in Comparative Example 4 was extruded through a die with a diameter of 5.0 mm, cut into 10 mm long particles by a granulation system, and then fully cooled and solidified in a 4°C cold water bath. Comparative Example 5: The difference between Comparative Example 5 and Example 1 is that the cooling and solidification temperature in Comparative Example 5 is 15°C, while the rest is the same as in Example 1.

[0051] Comparative Example 6: Compared with Example 1, Comparative Example 6 differs in that the nano-bamboo fiber in Comparative Example 6 is commercially available conventional hydrophobic modified bamboo powder (60 mesh, coupling agent modified bamboo powder), which is then directly mixed evenly with dried PBAT, PLA, chain extender, and functional additives, and then melt-mixed and extruded. The rest is the same as in Example 1.

[0052] The performance of the nano-bamboo fiber composite material samples prepared in Examples 1-3 and the nano-bamboo fiber composite material samples prepared in Comparative Examples 1-6 were tested, and the results are shown in Table 1 below.

[0053] The test methods for tensile strength and elongation at break are as follows: According to the requirements of national standard GB / T 1040.1-2018, a universal testing machine is used to test the tensile strength and elongation at break of the samples. Each sample is tested repeatedly 5 times, and the average value is recorded. The tensile rate is fixed at 200 mm / min.

[0054] The test method for visible light transmittance is as follows: Prepare a circular sample with a thickness of 0.10 mm and a diameter of 50 mm. According to GB / T2410-2008, test the transmittance of the sample using spectrophotometry. Repeat the test 5 times for each sample and record the average value. The incident light wavelength is fixed at 530 nm.

[0055] The standard for testing haze is GB / T 2410-2008, and it is measured directly using an integrating sphere haze meter.

[0056] Table 1: Performance Test Results

[0057] Analysis of the data in Table 1 shows that, by optimizing the raw materials and preparation process of the nano-bamboo fiber composite material, this invention achieves a fully biodegradable bamboo fiber composite material with good mechanical properties, high elongation at break, and good transparency, as well as uniform bamboo fiber dispersion and good interfacial compatibility. Compared with Example 1, in Comparative Example 1, due to the absence of a chain extender, the plastic matrix underwent a more significant degradation reaction during processing, resulting in lower mechanical strength. Simultaneously, PBAT and PLA could not form an effective transesterification process, leading to lower transparency compared to Example 1. The interfacial bonding force between the nano-bamboo fiber and the matrix weakened, resulting in increased light scattering (increased haze). In Comparative Example 2, the nano-bamboo fiber was not modified with AKD for hydrophobicity, resulting in higher polarity. In the low-polarity plastic matrix, it was unevenly dispersed, easily forming agglomerates that created stress concentration points, leading to lower mechanical strength, elongation at break, and light transmittance. In Comparative Example 3, the nano-bamboo fibers were not generated in situ but added later. The nano-bamboo fibers were dispersed at the molecular level in the solution, precipitated, and then blended with the polyester melt. The precipitated nano-sized fibers, due to their large specific surface area, were prone to agglomeration, resulting in uneven dispersion in the high-viscosity plastic melt and causing more stress defects. Therefore, their performance was inferior to Example 1. This illustrates that in this invention, dispersing the cellulose solution before precipitating the nano-cellulose is a key process. This is because dispersing the cellulose solution in the plastic matrix is ​​a "solid-liquid" dispersion, which offers better liquid permeability and a higher degree of dispersion. Subsequently, cooling water is used to displace the solvent, precipitating the cellulose from the solution. The uniform precipitation of cellulose from the solution allows for in-situ generation of nano-sized cellulose. Simultaneously, the high viscosity of the plastic melt effectively prevents the agglomeration of nanofibers. Therefore, the dispersion method of this invention can achieve in-situ dispersion of nano-cellulose, which is beneficial for balancing the transparency and mechanical strength of the material. In Comparative Example 4, the melt particle size was too large, resulting in a significant amount of bamboo fiber and solvent being trapped inside the plastic, failing to be fully wetted by the cooling water. The residual solvent created structural defects in the material, forming large fibers or agglomerates, leading to a decrease in performance. In Comparative Example 5, the cooling water temperature was too high, and the melt cooling rate was slow, causing the nano-bamboo fibers to fail to fully precipitate from the solvent and instead be drawn away by the cooling water. This resulted in a lower actual fiber content, insufficient tensile strength, and uneven fiber dispersion, making the overall performance inferior to Example 1. In Comparative Example 6, commercially available conventional hydrophobically modified bamboo powder was used. Commercially available bamboo powder only performs surface modification and does not achieve molecular-level dissolution and re-precipitation. Although bamboo powder can significantly improve the tensile strength of the composite material, conventional bamboo powder is a high-rigidity material with excessively large particle size, causing a sharp decrease in the material's toughness and transparency, resulting in a less significant improvement in the overall performance compared to Example 1.

[0058] In summary, this invention utilizes a dissolution-precipitation method to induce in-situ precipitation of bamboo fibers from bamboo powder within a biodegradable plastic matrix. This reduces fiber size and improves the dispersibility of nanofibers within the matrix. Simultaneously, the degradation-chain extension and reconstruction method disrupts the regularity of polyester molecules, further enhancing the material's transparency. Through these methods, a fully biodegradable composite material exhibiting superior mechanical strength, toughness, and transparency is obtained.

[0059] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0060] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A fully biodegradable nanofiber composite material, characterized in that, The nano-bamboo fiber composite material comprises the following components by mass percentage: Polybutylene terephthalate (PET) 60-80%, polylactic acid 15-25%, nano bamboo fiber 5-15%, chain extender 0.1-2%, and functional additives 0-1%; The nano-bamboo fiber is obtained by hydrophobic modification of bamboo powder, and the surface hydroxyl groups are shielded by non-polar alkyl chains. Furthermore, the composite material has a tensile strength of not less than 23 MPa, an elongation at break of not less than 450%, and a transmittance of 79.6% to 85.7% for visible light at a wavelength of 530 nm when the thickness is 0.10 mm, and a haze of 2.6% to 3.2%.

2. The nano-bamboo fiber composite material according to claim 1, characterized in that, At 190°C and 2.16 kg, the melt index of the polybutylene terephthalate is 1~40 g / 10 min.

3. The nano-bamboo fiber composite material according to claim 1, characterized in that, At 190°C and 2.16 kg, the melt index of the polylactic acid is 1~40 g / 10 min.

4. The nano-bamboo fiber composite material according to claim 1, characterized in that, The average size of the nano-bamboo fiber is 50~500nm.

5. The nano-bamboo fiber composite material according to claim 1, characterized in that, The chain extender is an organic oligomer containing multiple epoxy functional groups, and the epoxy equivalent of the organic oligomer is 250~350 g / mol.

6. The nano-bamboo fiber composite material according to claim 1, characterized in that, The functional additive is at least one of antioxidants, antistatic agents, antifogging agents, opening agents, and color masterbatches.

7. A method for preparing a nano-bamboo fiber composite material, characterized in that, The preparation method is used to prepare the fully biodegradable nano-bamboo fiber composite material as described in any one of claims 1 to 6, and the preparation method includes the following steps: S1. Bamboo powder is washed with alkali, alcohol, and water, and then dried to obtain dried bamboo powder; S2. Add dried bamboo powder to a solvent and stir to obtain a semi-transparent solution; then add alkyl ketene dimer and continue stirring to obtain a hydrophobically modified nano-bamboo fiber solution. S3. Mix PBAT, PLA, chain extender and functional additives evenly, and feed them into a twin-screw extruder through the main feed port for melt blending to obtain plastic melt; at the same time, inject hydrophobically modified nano bamboo fiber solution into the extruder through a metering pump from the side feed port to melt and mix with the plastic melt; the mixed melt is extruded through the die, granulated, cooled and solidified, then collected, and then washed and dried to obtain nano bamboo fiber composite material.

8. The preparation method according to claim 7, characterized in that, In step S2, the solvent is obtained by mixing choline chloride and lactic acid in a molar ratio of 1:2 and stirring at 100~120℃ for 1~2 hours.

9. The preparation method according to claim 7, characterized in that, In step S2, dried bamboo powder is added to the solvent and stirred at 50-300 r / min for 2-3 h to obtain a semi-transparent solution; then alkyl ketene dimer is added and the reaction is continued for 1-2 h to obtain a hydrophobically modified nano-bamboo fiber solution.

10. The preparation method according to claim 7, characterized in that, In step S3, the melting and mixing temperature is 170~220℃, and the screw speed is 280~450rpm; cooling and solidification are carried out using cold water at a temperature of 0~6℃.

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