Nano-zinc oxide functionalized bamboo fiber and preparation method thereof, and PLA / bamboo fiber composite material and preparation method thereof

Abstract

The invention relates to the technical field of composite materials, and discloses a nano-zinc oxide functionalized bamboo fiber and a preparation method thereof, and a PLA / bamboo fiber composite material and a preparation method thereof, and the preparation method comprises the following steps: step 1, fully mixing a strong alkali solution and a zinc source A solution to obtain a ZnO seed solution; 2, the bamboo fibers are soaked in the ZnO seed solution to be fully infiltrated, and heat treatment is conducted; repeating the step for N times, and forming a ZnO crystal seed layer on the surface of the bamboo fiber to obtain an intermediate product; 3, dissolving a zinc source B, strong alkali and slow-release alkali in a solvent to obtain a growth solution; and 4, placing the intermediate product in a growth solution, and carrying out a hydrothermal reaction to obtain the required nano-zinc oxide functionalized bamboo fiber. According to the method, a two-step hydrothermal method is combined with'double zinc sources-double alkali sources' to construct a synergistic system, and the dense ZnO nano array grows on the surface of the bamboo fiber in situ; and introducing polydimethylsiloxane, and constructing an elastic interface layer between the BFO-ZnO and a PLA matrix, so as to obtain the high-strength and high-toughness PLA / bamboo fiber composite material.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, specifically to a nano-zinc oxide functionalized bamboo fiber and its preparation method, and a PLA / bamboo fiber composite material and its preparation method. Background Technology

[0002] With the increasing demand for "plastic-to-wood" and environmental protection, fully bio-based composite materials with polylactic acid (PLA) as the matrix and bamboo fiber (BFO) as the reinforcing phase have become a research hotspot. To further improve the performance of the composite material, nano-zinc oxide (ZnO) is often introduced onto the surface of bamboo fiber to impart antibacterial and UV-shielding functions, and the mechanical interlocking effect with PLA is enhanced by increasing the fiber roughness. However, this method suffers from a "reinforcement-degradation" competitive contradiction, a problem that is difficult to reconcile.

[0003] ZnO, as a metal oxide, catalyzes the hydrolysis of ester bonds in PLA molecular chains. During the high-temperature, high-shear-force processes of melt blending and hot pressing of composite materials, this catalytic effect is amplified dramatically, leading to severe PLA molecular chain breakage, matrix degradation, and significant damage to the intrinsic mechanical properties of the material, especially toughness. Although ZnO increases roughness, the interfacial compatibility between BFO-ZnO and the PLA matrix remains poor. The significant difference in modulus between the two leads to stress concentration at the rigid interface under stress, causing premature interface failure and preventing effective stress transfer from the plastic matrix to the reinforcing fibers, thus failing to fully realize the reinforcing effect of ZnO. Existing modification methods often struggle to simultaneously improve the strength and toughness of composite materials. The introduction of reinforcing fibers usually comes at the cost of sacrificing material ductility and toughness, resulting in increased brittleness. Overcoming this performance bottleneck and achieving a synergistic improvement in strength and toughness is an urgent problem to be solved. Summary of the Invention

[0004] This invention addresses the problems existing in the prior art by providing a nano-zinc oxide functionalized bamboo fiber and its preparation method, as well as a PLA / bamboo fiber composite material and its preparation method.

[0005] The technical solution adopted in this invention is: a method for preparing nano-zinc oxide functionalized bamboo fiber, comprising the following steps: Step 1: Mix the strong alkali solution and zinc source A solution thoroughly to obtain a ZnO seed solution; wherein zinc source A is zinc acetate dihydrate, and the molar ratio of strong alkali to zinc source is 8:5; Step 2: Immerse the bamboo fiber in ZnO seed solution until fully soaked, and heat treat; repeat this step N times to form a ZnO seed layer on the surface of the bamboo fiber, and obtain an intermediate product, N≥2; Step 3: Dissolve zinc source B, strong base and slow-release base in solvent to obtain growth solution; wherein zinc source B is zinc chloride, slow-release base is hexamethylenetetramine, and the molar ratio of zinc source B, strong base and slow-release base is 3:2:6. Step 4: Place the intermediate product obtained in Step 2 into the growth solution obtained in Step 3, and the desired nano-zinc oxide functionalized bamboo fiber can be obtained by hydrothermal reaction.

[0006] Furthermore, in step 2, the heat treatment temperature is 150 ℃ and the heat treatment time is 10 minutes.

[0007] Furthermore, in step 4, the hydrothermal reaction temperature is 95 ℃ and the heat treatment time is 2 hours.

[0008] Furthermore, in step 1, the strong base is sodium hydroxide, the concentration of the strong base in the ZnO seed solution is 20 mmol / L, and the concentration of zinc source A is 12.5 mmol / L.

[0009] Furthermore, in step 3, the strong base is sodium hydroxide, the concentration of the strong base in the growth solution is 80 mmol / L, the concentration of zinc source B is 120 mmol / L, and the concentration of the slow-release base is 240 mmol / L.

[0010] Furthermore, the bamboo fiber in step 2 is oxidized bamboo fiber, and the oxidation process is as follows: 2,2,6,6-Tetramethylpiperidine oxide and NaBr were dissolved in a solvent at a molar ratio of 1:10 to obtain a mixed solution; Add bamboo fiber to the mixed solution, then add NaClO, and oxidize thoroughly to obtain the desired oxidized bamboo fiber; the molar ratio of NaClO to NaBr is 4:1.

[0011] A nano-zinc oxide functionalized bamboo fiber.

[0012] A method for preparing a high-strength, high-toughness PLA / bamboo fiber composite material includes the following steps: S1: Polylactic acid and polydimethylsiloxane are premixed to obtain polylactic acid modified with polydimethylsiloxane; wherein the mass ratio of polylactic acid to polydimethylsiloxane is 100:1; S2: The polylactic acid modified with polydimethylsiloxane obtained in step S1 and the nano-zinc oxide functionalized bamboo fiber are melt-blended to obtain a mixture; wherein the mass ratio of polylactic acid modified with polydimethylsiloxane to nano-zinc oxide functionalized bamboo fiber is 100:1. S3: The mixture is hot-pressed to obtain the desired composite material.

[0013] Furthermore, the hot pressing process in step 3 is as follows: First, preheat at 170℃ for 3 minutes, then vent the air. Then, hot-press at 170 ℃ and 5 MPa for 10 minutes; Finally, cold press for 3 minutes at 3 MPa.

[0014] A high-strength, high-toughness PLA / bamboo fiber composite material.

[0015] The beneficial effects of this invention are: (1) This invention constructs a synergistic system by combining a two-step hydrothermal method with a “dual zinc source-dual alkali source” to grow a dense ZnO nano array in situ on the surface of bamboo fiber; the resulting structure can greatly increase the specific surface area and roughness of the fiber. When it is used as a reinforcement in PLA composite material, it can significantly improve the interfacial mechanical interlocking and chemical bonding, and simultaneously greatly improve the mechanical strength, toughness and functionality of the composite material. (2) The present invention introduces polydimethylsiloxane to construct an elastic interface layer between BFO-ZnO and PLA matrix, which solves the contradiction of "reinforcement-degradation" in composite material and obtains PLA / bamboo fiber composite material with high strength and high toughness. Attached Figure Description

[0016] Figure 1 The images shown are SEM images of the intermediate product obtained in step 2 of Example 1 of this invention, and SEM images of untreated bamboo fiber and oxidized bamboo fiber. a is BF, b is BFO, and c and d are both BFO-ZnO-Seed.

[0017] Figure 2 The images show the infrared spectra of the intermediate product obtained in step 2 of Example 1 of this invention, as well as the infrared spectra of untreated bamboo fiber and oxidized bamboo fiber.

[0018] Figure 3 The images show the XRD patterns of the intermediate product obtained in step 2 of Example 1 of this invention, as well as the XRD patterns of untreated bamboo fiber and oxidized bamboo fiber.

[0019] Figure 4 The images shown are SEM images of bamboo fibers obtained in Example 1, Comparative Example 1, and Comparative Example 2 of this invention. ad represents Comparative Example 1, eh represents Comparative Example 2, and il represents Example 1.

[0020] Figure 5 The images shown are SEM images of bamboo fibers obtained in Examples 1, 3, and 4 of this invention. ad represents Comparative Example 3, eh represents Example 1, and il represents Comparative Example 4.

[0021] Figure 6 The images shown are SEM images of bamboo fibers obtained in Examples 1, 5, and 6 of this invention. ad represents Comparative Example 5, eh represents Comparative Example 6, and il represents Example 1.

[0022] Figure 7 The images shown are SEM images of bamboo fibers obtained in Examples 1, 7, 8, and 9 of this invention. ac represents Comparative Example 7, df represents Comparative Example 8, gi represents Example 1, and jl represents Comparative Example 9.

[0023] Figure 8 The TG curves are those of bamboo fiber obtained in Example 1 of this invention, as well as untreated bamboo fiber and oxidized bamboo fiber.

[0024] Figure 9 XPS images of bamboo fiber obtained in Example 1 of the present invention, untreated bamboo fiber, and oxidized bamboo fiber are shown. a is XPS, b is C spectrum of untreated bamboo fiber and oxidized bamboo fiber, c is O spectrum of oxidized bamboo fiber and bamboo fiber of Example 1, and d is Zn spectrum of Example 1.

[0025] Figure 10 The images show polydimethylsiloxane-modified polylactic acid and polylactic acid SEM images obtained in step S1 of Example 2 of this invention.

[0026] Figure 11 The images show SEM images of the polylactic acid modified with polydimethylsiloxane obtained in S1 of Example 2 of the present invention, the composite material, and the composite materials obtained in Comparative Examples 10 and 11.

[0027] Figure 12 The tensile strength and elongation at break of the composite materials obtained in Examples 2, 12, 13 and 14 of this invention are shown.

[0028] Figure 13 The tensile strength and elongation at break of the composite materials obtained in Example 2 and Comparative Example 15 of the present invention are shown. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] A method for preparing nano-zinc oxide functionalized bamboo fiber includes the following steps: Step 1: Mix the strong alkali solution and zinc source A solution thoroughly to obtain a ZnO seed solution; wherein zinc source A is zinc acetate dihydrate, and the molar ratio of strong alkali to zinc source is 8:5; the strong alkali is sodium hydroxide, and the concentration of strong alkali in the ZnO seed solution is 20 mmol / L, and the concentration of zinc source A is 12.5 mmol / L.

[0031] Step 2: Immerse the bamboo fiber in ZnO seed solution until fully soaked, then heat-treat; repeat this step N times to form a ZnO seed layer on the surface of the bamboo fiber, obtaining an intermediate product, where N≥2; the heat treatment temperature is 150 ℃ and the heat treatment time is 10 minutes. The bamboo fiber is oxidized bamboo fiber, and the oxidation process is as follows: 2,2,6,6-Tetramethylpiperidine oxide and NaBr were dissolved in a solvent at a molar ratio of 1:10 to obtain a mixed solution; Add bamboo fiber to the mixed solution, then add NaClO, and oxidize thoroughly to obtain the desired oxidized bamboo fiber; the molar ratio of NaClO to NaBr is 4:1.

[0032] Step 3: Dissolve zinc source B, strong base, and slow-release base in a solvent to obtain a growth solution; wherein zinc source B is zinc chloride, slow-release base is hexamethylenetetramine, and the molar ratio of zinc source B, strong base, and slow-release base is 3:2:6; the strong base is sodium hydroxide, and the concentration of strong base in the growth solution is 80 mmol / L, the concentration of zinc source B is 120 mmol / L, and the concentration of slow-release base is 240 mmol / L.

[0033] Step 4: Place the intermediate product obtained in Step 2 into the growth solution obtained in Step 3, and perform a hydrothermal reaction to obtain the desired nano-zinc oxide functionalized bamboo fiber. The hydrothermal reaction temperature is 95 ℃, and the heat treatment time is 2 hours.

[0034] A method for preparing a high-strength, high-toughness PLA / bamboo fiber composite material includes the following steps: S1: Polylactic acid and polydimethylsiloxane are premixed to obtain polylactic acid modified with polydimethylsiloxane; wherein the mass ratio of polylactic acid to polydimethylsiloxane is 100:1; S2: The polylactic acid modified with polydimethylsiloxane obtained in step S1 and the nano-zinc oxide functionalized bamboo fiber in claim 7 are melt-blended to obtain a mixture; wherein the mass ratio of polylactic acid modified with polydimethylsiloxane to nano-zinc oxide functionalized bamboo fiber is 100:1; S3: The mixture is hot-pressed to obtain the desired composite material. The hot-pressing process is as follows: First, preheat at 170℃ for 3 minutes, then vent the air. Then, hot-press at 170 ℃ and 5 MPa for 10 minutes; Finally, cold press for 3 minutes at 3 MPa.

[0035] Example 1 A method for preparing nano-zinc oxide functionalized bamboo fiber includes the following steps: Step 1: Dissolve 20 mM sodium hydroxide in 280 mL of ethanol to obtain a sodium hydroxide solution, and dissolve 12.5 mM zinc acetate dihydrate in 720 mL of ethanol to obtain a zinc acetate dihydrate solution; heat the sodium hydroxide solution and the zinc acetate dihydrate solution to 60 °C respectively, then mix them, and stir continuously at this temperature for 10 minutes, then quench to room temperature to obtain a ZnO seed solution.

[0036] Step 2: First, oxidize the bamboo fiber: Add 0.1 mmol of 2,2,6,6-tetramethylpiperidine oxide (TEMPO) and 1 mmol of NaBr to 1 L of deionized water, mix well, and then add bamboo fiber (BF). Adjust the pH of the solution to 10 using sodium hydroxide solution.

[0037] Add 4 mmol of NaClO and oxidize at room temperature for 2 h. After the reaction is complete, quench with ethanol to end the reaction. Then, ultrasonically wash with deionized water and dry at 80 ℃ for 12 h to obtain oxidized bamboo fiber BFO.

[0038] The BFO was immersed in the ZnO seed solution obtained in step 1, and stirred thoroughly for 10 minutes at 200 r / min. The immersed bamboo fiber was then annealed at 150 ℃ for 10 minutes to complete one loading cycle. This loading cycle can be repeated and adjusted as needed. In this embodiment, five loading cycles were performed to form a uniformly distributed ZnO seed layer on the surface of the bamboo fiber, obtaining the intermediate product BFO-ZnO-Seed.

[0039] Step 3: Dissolve 12 mmol of ZnCl2, 24 mmol of hexamethylenetetramine (HMTA), and 8 mmol of sodium hydroxide in 100 mL of deionized water to obtain the growth solution.

[0040] Step 4: Add the BFO-ZnO-Seed obtained in Step 2 to the growth solution and react in a water bath at 95 ℃ for 2 h; after the reaction is complete, wash with deionized water and dry in a vacuum oven at 80 ℃ for 24 h to obtain nano zinc oxide functionalized bamboo fiber BFO-ZnO.

[0041] The following comparative examples are provided to illustrate the effects of the present invention. Comparative Example 1 The other steps in this comparative example are the same as in Example 1, except that ZnCl2 in step 3 is replaced with Zn(CH3COO)2.

[0042] Comparative Example 2 The other steps in this comparative example are the same as those in Example 1, except that ZnCl2 in step 3 is replaced with Zn(NO3)2.

[0043] Comparative Example 3 The other steps in this comparative example are the same as those in Example 1, except that the water bath reaction time in step 4 is 1 h.

[0044] Comparative Example 4 The other steps in this comparative example are the same as those in Example 1, except that the water bath reaction time in step 4 is 4 hours.

[0045] Comparative Example 5 The other steps in this comparative example are the same as in Example 1, except that in step 3, ZnCl2 and hexamethylenetetramine (HMTA) are 4 mmol and 8 mmol, respectively.

[0046] Comparative Example 6 The other steps in this comparative example are the same as in Example 1, except that in step 3, ZnCl2 and hexamethylenetetramine (HMTA) are 8 mmol and 12 mmol, respectively.

[0047] Comparative Example 7 The other steps in this comparative example are the same as in Example 1, except that in step 3, ZnCl2 and hexamethylenetetramine (HMTA) are 8 mmol and 4 mmol, respectively.

[0048] Comparative Example 8 The other steps in this comparative example are the same as in Example 1, except that in step 3, ZnCl2 and hexamethylenetetramine (HMTA) are 8 mmol and 8 mmol, respectively.

[0049] Comparative Example 9 The other steps in this comparative example are the same as in Example 1, except that in step 3, ZnCl2 and hexamethylenetetramine (HMTA) are 8 mmol and 32 mmol, respectively.

[0050] Example 2 A method for preparing a high-strength, high-toughness PLA / bamboo fiber composite material includes the following steps: S1: Polylactic acid (PLA) and the nano-zinc oxide functionalized bamboo fiber obtained in Example 1 were vacuum dried at 80 °C for 24 hours to remove moisture.

[0051] Dry PLA and polydimethylsiloxane (PDMS) are premixed to uniformly coat the PLA surface with PDMS, wherein the mass ratio of polylactic acid to polydimethylsiloxane is 100:1.

[0052] S2: The polylactic acid modified with polydimethylsiloxane obtained in step S1 and BFO-ZnO were placed in a torque rheometer at a mass ratio of 100:1 and melt-blended at 170 °C and 30 rpm for 10 minutes.

[0053] The blended materials were pulverized and placed in a flat vulcanizing mold. The mold was preheated at 170 °C for 3 minutes and vented 10 times to remove air bubbles. Then, it was hot-pressed at the same temperature and 5 MPa for 10 minutes, and finally cold-pressed at 3 MPa for 3 minutes to obtain the composite material PLA-P / BFO-ZnO.

[0054] Comparative Example 10 The other steps in this comparative example are the same as in Example 2, except that in steps S1 and S2, BFO-ZnO is replaced with untreated bamboo fiber BF to obtain the composite material PLA-P / BF.

[0055] Comparative Example 11 The other steps in this comparative example are the same as in Example 2, except that in steps S1 and S2, BFO-ZnO is replaced with oxidized bamboo fiber BFO that has undergone oxidation treatment, resulting in the composite material PLA-P / BFO. The oxidation method of bamboo fiber is as described in Example 1.

[0056] Comparative Example 12 The other steps in this comparative example are the same as those in Example 2, except that BFO-ZnO is not added in step S2.

[0057] Comparative Example 13 The other steps in this comparative example are the same as in Example 2, except that the mass ratio of polydimethylsiloxane-modified polylactic acid to BFO-ZnO in step S2 is 100:3.

[0058] Comparative Example 14 The other steps in this comparative example are the same as in Example 2, except that the mass ratio of polydimethylsiloxane-modified polylactic acid to BFO-ZnO in step S2 is 100:5.

[0059] Comparative Example 15 The other steps in this comparative example are the same as those in Example 2, except that step S1 is not included, and step S2 is prepared by mixing polylactic acid and BFO-ZnO.

[0060] SEM images of the intermediate product obtained in step 2 of Example 1 and SEM images of untreated bamboo fiber and oxidized bamboo fiber are shown below. Figure 1 As shown in the figure, a is BF, b is BFO, and c and d are both BFO-ZnO-Seed. It can be seen from the figure that after oxidation, the surface of BF partially breaks down, forming grooves, and the surface roughness increases. Figure 1 As shown in Figure b, uniform zinc oxide nanodots are formed on the surface of the bamboo fiber after the seed crystals are attached. These nanodots can serve as growth sites for zinc oxide crystals, which helps in the formation of subsequent structures.

[0061] The infrared spectra of the intermediate product obtained in step 2 of Example 1, and the infrared spectra of untreated bamboo fiber and oxidized bamboo fiber are as follows: Figure 2 As shown in the figure, BF is 3356 cm. -1 and 2895 cm -1 With wide OH stretch and sp3 Hybridized CH stretching. The stretching peak of OH in BFO appears at 3340 cm⁻¹. -1 At the oxidation site, the OH stretching peaks of both samples shifted to lower wavelengths, indicating that the distribution of H bonds and -OH groups in cellulose changed after oxidation, leading to a change in the hybridization state of cellulose C6. (1730 cm⁻¹) -1 The stretching vibration of C=O, attributed to hemicellulose, disappeared significantly after the oxidation of bamboo fiber. This is because hemicellulose is soluble in alkaline media, and the sodium hydroxide solution, used to adjust the pH of the oxidation process, removed some of the hemicellulose. Meanwhile, the peak at 1600 cm⁻¹... -1 The characteristic peaks were enhanced after oxidation, indicating that the hydroxyl groups on C6 of cellulose were oxidized into carboxylic acid groups in the form of sodium salts.

[0062] Because carboxylic acid groups have a chemisorption effect on ZnO, the intensity of the characteristic peak at this location decreases significantly after zinc oxide grows from the BFO substrate, and drops to 436 cm⁻¹. -1 A tensile vibration peak of Zn-O appears at the location.

[0063] The XRD patterns of the intermediate product obtained in step 2 of Example 1 and the XRD patterns of untreated bamboo fiber and oxidized bamboo fiber are shown below. Figure 3 As shown in the figure, all samples exhibit diffraction peaks at 16.4° and 22.3°, which are typical cellulose I peaks, belonging to the (101) and (002) crystal planes, indicating that the growth of ZnO does not change the crystal structure of bamboo fiber. In addition to the characteristic peaks of cellulose, BF-ZnO shows new diffraction peaks at 32.1°, 35.1°, 36.3°, 47.6°, 56.8°, 63.2°, and 69.2°, corresponding one-to-one with the (100), (002), (101), (102), (110), (103), and (201) crystal planes of hexagonal zinc oxide crystals. This demonstrates that zinc oxide was successfully loaded onto the BFO surface using the hydrothermal method.

[0064] SEM images of bamboo fibers obtained in Example 1, Comparative Example 1, and Comparative Example 2 are shown below. Figure 4 As shown in the figure, the surface morphology of nano-ZnO obtained in Comparative Example 1, Comparative Example 2 and Example 1 is granular, but the ZnO obtained in Example 1 has the most uniform and dense distribution.

[0065] SEM images of bamboo fibers obtained in Example 1, Comparative Example 3, and Comparative Example 4 are shown below. Figure 5As shown in the figure, the ZnO density increases with increasing growth time. When the growth time is 1 hour, some areas on the fiber surface do not have ZnO grown, while the bamboo fiber obtained in Example 1 shows continuous and uniform ZnO growth on the surface. After 4 hours of increased growth time, ZnO accumulates on the surface. This indicates that the hydrothermal time cannot be arbitrarily selected.

[0066] SEM images of bamboo fibers obtained in Example 1, Comparative Example 5, and Comparative Example 6 are shown below. Figure 6 As shown in the figure, the amount and density of ZnO on the surface of bamboo fiber increase with the increase of growth concentration, and the ZnO growth obtained in Example 1 is the most continuous and dense.

[0067] SEM images of bamboo fibers obtained in Example 1, Comparative Example 7, Comparative Example 8, and Comparative Example 9 are shown below. Figure 7 As shown in the figure, hexamethylenetetramine acts as an alkali source in the growth solution during the hydrothermal reaction. When the HMTA concentration is too low, the OH- in the solution... -1 The content is low, resulting in less ZnO formation. As the HMTA concentration increases, at the reaction equilibrium, OH... -1 As the concentration increases, the generated ZnO becomes more continuous and uniform; when the molar ratio reaches 1:4, the HMTA concentration is too high, and the OH- in the solution... -1 Excessive concentration leads to overly rapid ZnO growth and nucleation, resulting in fiber delamination. Therefore, the molar ratio in this invention is irreplaceable.

[0068] The TG curves of bamboo fiber obtained in Example 1, as well as those of untreated bamboo fiber and oxidized bamboo fiber, are shown below. Figure 8 As shown in the figure, during the low-temperature stage (25 ℃~200 ℃), all three types of bamboo fibers exhibited weight loss peaks due to the evaporation of intermolecular water and volatiles. This is caused by the removal of weakly bound small molecules from the fiber. BFO-ZnO showed a smaller weight loss amplitude. The nano-ZnO on the surface of the bamboo fiber adheres to the surface or penetrates into the fiber structure, which can inhibit the escape of small molecules to a certain extent, effectively reducing the mass loss during this stage and improving the low-temperature thermal stability of the fiber. BFO, on the other hand, has a slightly higher low-temperature weight loss rate than BF due to the introduction of carboxyl groups caused by oxidation, and some amorphous chain segments break prematurely. However, the difference in the initial weight loss temperature is not significant.

[0069] As the temperature rises (>200 ℃), the carbon skeleton of the fiber body decomposes under heat, and it is almost completely decomposed at about 370 ℃. During this stage, the weight loss rate of the three types of fibers accelerates, reflecting the thermal degradation process of the fiber body structure. As the temperature continues to rise (>370 ℃), the curve tends to flatten out, corresponding to the carbonization of residual organic matter.

[0070] The residual mass of BFO-ZnO is significantly higher than that of BF and BFO. Surface nano-ZnO not only inhibits the escape of small molecules at low temperatures, but also exerts a "physical barrier effect" (such as the barrier layer formed by ZnO particles on / inside the fiber) and a "chemical synergistic effect" (such as Zn) at high temperatures. 2+ (Interaction with fiber degradation products) effectively inhibited the excessive decomposition of the carbon skeleton and slowed down the carbonization process.

[0071] XPS images of bamboo fiber obtained in Example 1, untreated bamboo fiber, and oxidized bamboo fiber are shown below. Figure 9 As shown in the figure, the BFO-ZnO curve exhibits distinct characteristic peaks for Zn 2p, O 1s, and C 1s, indicating successful synthesis of ZnO on BFO. Compared to BF, the O 1s characteristic peak of BFO is enhanced because the reaction yields more carboxyl groups. The decrease in the O1s characteristic peak of BFO-ZnO is due to the consumption of carboxyl groups required for ZnO growth on the BFO surface, and the shrinking of the C1s characteristic peak as the BFO surface is covered by ZnO.

[0072] From the C 1s peak curve, BF contains a small amount of HO-C=O, which is a carboxylic acid group from the reduced end of BF hemicellulose or cellulose / hemicellulose. After oxidation, its content increased by 3.53%, while the proportion of C-OH and COC peaks decreased by 11.55%. The results indicate that after oxidation, some C-OH on the cellulose is converted into -OC=O and HO-C=O, and BFO produces carboxylic acid groups. From the O 1s peak curve, the peak at 530.31 eV corresponds to the Zn-O bond, and the peak at 532.16 eV corresponds to the CO bond, proving that zinc oxide was successfully synthesized. There are two peaks in the Zn 2p curve, with peaks at 1044.5 eV and 1021.2 eV corresponding to Zn 2p1 / 2 and Zn 2p3 / 2, respectively.

[0073] In Example 2, the polydimethylsiloxane-modified polylactic acid obtained in step S1 and the SEM image of polylactic acid are shown below. Figure 10 As shown, SEM images of the polylactic acid modified with polydimethylsiloxane obtained in S1 of Example 2, the composite material, and the composite materials obtained in Comparative Examples 10 and 11 are shown. Figure 11 As shown.

[0074] The tensile strength and elongation at break of the composite materials obtained in Examples 2, 12, 13, and 14 are as follows: Figure 12 As shown in the figure, the tensile strength and elongation at break of the composite material obtained in Example 2 are significantly higher than those of the comparative example.

[0075] The tensile strength and elongation at break of the composite materials obtained in Example 2 and Comparative Example 15 are as follows: Figure 13As shown in the figure, the mechanical properties of the composite material are significantly improved after the introduction of PDMS. Its tensile strength increases dramatically from 19.2 MPa in the unmodified system to 48.5 MPa, a strength increase of 153%. The elongation at break increases from 1.25% to 3.49%, and the toughness increases by 179%.

[0076] The test results above demonstrate that a synergistic increase in the strength and toughness of PLA composite materials was achieved, rather than a trade-off between the two. This effect overcomes the technical biases of those skilled in the art and provides a novel pathway for developing high-performance, high-durability bio-based composite materials.

[0077] This invention utilizes a two-step hydrothermal method and a "dual zinc source-dual alkali source" approach to obtain bamboo fibers with a dense and uniform nano-ZnO surface. In the seeding stage, a zinc acetate / ethanol system is used to generate tiny ZnO nuclei at low temperatures. Multiple cycles of impregnation and heat treatment ensure a high-density, uniform distribution of seed crystals on the bamboo fiber surface, providing numerous and uniform nucleation sites for subsequent vertical growth. In the growth stage, the second hydrothermal stage, a zinc oxide / water system is used, introducing a dual alkali source of NaOH and HMTA. NaOH, as a strong alkali, provides high OH- content. - Concentration promotes rapid crystal growth. HMTA, acting as a slow-release alkali and structure-directing agent, slowly hydrolyzes to provide OH-. - It preferentially adsorbs onto the ZnO crystal plane, guiding the crystal to preferentially grow along the c-axis. The two work together to achieve controllable and ordered growth from "high-density seed crystals" to "dense nanoarrays".

[0078] Through the aforementioned synergistic control, a ZnO nanoarray with high sub-height ratio, uniform size, and dense arrangement is obtained on the surface of bamboo fiber. This can greatly increase the specific surface area and roughness of bamboo fiber. When used as a reinforcement in composite materials such as PLA, it can significantly improve interfacial mechanical interlocking and chemical bonding, and simultaneously and substantially enhance the mechanical strength, toughness, and functionality of the composite material.

[0079] This invention introduces polydimethylsiloxane (PDMS) to construct an elastic interface layer between the surface of bamboo oxidized fiber (BFO-ZnO) with nano-ZnO grown on it and the polylactic acid matrix. The resulting composite material solves the contradiction between poor interfacial compatibility and the "enhancement-degradation" competition between ZnO and PLA catalytic degradation.

[0080] In this invention, PDMS, with its extremely low surface energy and excellent chemical inertness, forms a dense, hydrophobic physical barrier on the BFO-ZnO surface. This effectively blocks the physical contact between ZnO nanoparticles and the ester bonds in the PLA molecular chain, inhibiting the hydrolytic catalytic activity of ZnO on PLA during processing. This significantly improves the chemical stability of the composite material during processing and use, preserving the molecular weight integrity of the PLA matrix. The flexible siloxane segments of PDMS can simultaneously interact with ZnO on the fiber surface through hydrogen bonding, and with the PLA matrix through diffusion entanglement and possible covalent bonding, constructing a multi-level interfacial bridging structure of "BFO-ZnO-PDMS-PLA". This structure not only achieves a fundamental improvement in interfacial strength, ensuring efficient stress transfer from the matrix to the reinforcing fibers, but its inherent flexibility also endows the interfacial region with excellent deformation capacity. While absorbing impact energy, it avoids premature interfacial failure caused by stress concentration, thereby significantly improving the toughness of the material and resolving the contradiction between reinforcement and toughening.

Claims

1. A method for preparing nano-zinc oxide functionalized bamboo fiber, characterized in that, Includes the following steps: Step 1: Mix the strong alkali solution and zinc source A solution thoroughly to obtain a ZnO seed solution; wherein zinc source A is zinc acetate dihydrate, and the molar ratio of strong alkali to zinc source is 8:5; Step 2: Immerse the bamboo fiber in ZnO seed solution until fully soaked, then heat treat. Repeat this step N times to form a ZnO seed layer on the surface of bamboo fiber, and obtain an intermediate product, where N≥2; Step 3: Dissolve zinc source B, strong base and slow-release base in solvent to obtain growth solution; wherein zinc source B is zinc chloride, slow-release base is hexamethylenetetramine, and the molar ratio of zinc source B, strong base and slow-release base is 3:2:

6. Step 4: Place the intermediate product obtained in Step 2 into the growth solution obtained in Step 3, and the desired nano-zinc oxide functionalized bamboo fiber can be obtained by hydrothermal reaction.

2. The method for preparing nano-zinc oxide functionalized bamboo fiber according to claim 1, characterized in that, In step 2, the heat treatment temperature is 150 ℃ and the heat treatment time is 10 minutes.

3. The method for preparing nano-zinc oxide functionalized bamboo fiber according to claim 1, characterized in that, In step 4, the hydrothermal reaction temperature is 95 ℃ and the heat treatment time is 2 hours.

4. The method for preparing nano-zinc oxide functionalized bamboo fiber according to claim 1, characterized in that, In step 1, the strong base is sodium hydroxide, the concentration of the strong base in the ZnO seed solution is 20 mmol / L, and the concentration of zinc source A is 12.5 mmol / L.

5. The method for preparing nano-zinc oxide functionalized bamboo fiber according to claim 1, characterized in that, In step 3, the strong base is sodium hydroxide, the concentration of the strong base in the growth solution is 80 mmol / L, the concentration of zinc source B is 120 mmol / L, and the concentration of the slow-release base is 240 mmol / L.

6. The method for preparing nano-zinc oxide functionalized bamboo fiber according to claim 1, characterized in that, The bamboo fiber in step 2 is oxidized bamboo fiber, and the oxidation process is as follows: 2,2,6,6-Tetramethylpiperidine oxide and NaBr were dissolved in a solvent at a molar ratio of 1:10 to obtain a mixed solution; Add bamboo fiber to the mixed solution, then add NaClO, and oxidize thoroughly to obtain the desired oxidized bamboo fiber; the molar ratio of NaClO to NaBr is 4:

1.

7. Nano-zinc oxide functionalized bamboo fiber obtained by any of the preparation methods described in claims 1 to 6.

8. A method for preparing a high-strength, high-toughness PLA / bamboo fiber composite material, characterized in that, Includes the following steps: S1: Polylactic acid and polydimethylsiloxane are premixed to obtain polylactic acid modified with polydimethylsiloxane; wherein the mass ratio of polylactic acid to polydimethylsiloxane is 100:1; S2: The polylactic acid modified with polydimethylsiloxane obtained in step S1 and the nano-zinc oxide functionalized bamboo fiber in claim 7 are melt-blended to obtain a mixture; wherein the mass ratio of polylactic acid modified with polydimethylsiloxane to nano-zinc oxide functionalized bamboo fiber is 100:1; S3: The mixture is hot-pressed to obtain the desired composite material.

9. The method for preparing a high-strength, high-toughness PLA / bamboo fiber composite material according to claim 8, characterized in that, The hot pressing process in step 3 is as follows: First, preheat at 170℃ for 3 minutes, then vent the air. Then, hot-press at 170 ℃ and 5 MPa for 10 minutes; Finally, cold press for 3 minutes at 3 MPa.

10. The high-strength, high-toughness PLA / bamboo fiber composite material obtained by any of the preparation methods described in claims 9 to 10.

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