Uv absorbers based on sisal fibers, methods of making, and wood plastic composites

Abstract

The application discloses a kind of sisal fiber-based ultraviolet absorber and preparation method and wood-plastic composite material.The preparation method of the sisal fiber-based ultraviolet absorber of the application comprises the following steps:S1: performing carboxylation treatment on sisal fiber;S2: performing amination treatment on the carboxylated sisal fiber;S3: grafting ultraviolet absorber on the aminated sisal fiber to obtain sisal fiber-based ultraviolet absorber.The wood-plastic composite material is composed of sisal fiber-based ultraviolet absorber and polymer material.The application uses normal temperature acidification and microwave rapid synthesis, uses water as dispersion medium, does not use organic solvent, and has mild conditions, easy to purify, easy to industrialize.The ultraviolet absorber parent 2,4-dihydroxybenzophenone (UV-0) is bonded to sisal fiber, applied in wood-plastic composite material, has good dispersibility, is not easy to migrate, and can improve the anti-ultraviolet aging performance of wood-plastic composite material.

Description

Technical Field

[0001] This invention relates to the field of materials. More specifically, this invention relates to a sisal fiber-based ultraviolet absorber, its preparation method, and its uses. Background Technology

[0002] In recent years, with the continuous depletion of the ozone layer in the Earth's atmosphere, the intensity of ultraviolet radiation at the ground has been increasing, causing extremely adverse effects on humans and their living environment. Furthermore, long-term exposure to ultraviolet radiation accelerates the photo-oxidative aging of polymer materials, thus shortening their lifespan. Adding ultraviolet absorbers to polymer materials is an effective method to reduce this aging phenomenon caused by ultraviolet radiation.

[0003] Sisal fiber, due to its high strength and corrosion resistance, has a wide range of applications, including wood-plastic composites such as flooring and outdoor fences. When sisal fiber is combined with polymers like PE, PP, and PVC to create wood-plastic composites, long-term exposure to ultraviolet light easily leads to UV aging, thus shortening the lifespan of the composite material. Currently, UV aging protection for wood-plastic composites typically involves adding low-molecular-weight or high-molecular-weight organic UV absorbers. However, during the preparation process, low-molecular-weight UV absorbers are prone to decomposition during thermal processing and uneven dispersion within the polymer matrix. Furthermore, during the later stages of composite use, these absorbers are susceptible to migration, affecting the material's UV aging resistance. Therefore, it is necessary to design a technical solution that overcomes these shortcomings. Summary of the Invention

[0004] One object of the present invention is to provide a sisal fiber-based ultraviolet absorber, a preparation method thereof, and a wood-plastic composite material. The sisal fiber-based ultraviolet absorber can be used to improve the UV aging resistance of wood-plastic composite materials.

[0005] To achieve these objectives and other advantages of the present invention, according to one aspect of the present invention, a method for preparing a sisal fiber-based ultraviolet absorber is provided, comprising: S1: performing carboxylation treatment on sisal fibers; S2: performing amylation treatment on the carboxylated sisal fibers; S3: grafting an ultraviolet absorber onto the amylated sisal fibers to obtain a sisal fiber-based ultraviolet absorber.

[0006] Further, in S1, the method for performing carboxylation treatment on the sisal fiber includes: adding the sisal fiber to a mixed solution composed of TEMPO, sodium bromide, sodium hypochlorite, and water, adjusting the pH to 8-11, reacting at room temperature for 1-4 hours, washing and drying after the reaction is completed to obtain carboxylated sisal fiber.

[0007] Further, in S2, the method for performing amination treatment on carboxylated sisal fibers includes: dispersing carboxylated sisal fibers and polyethyleneimine, 2,5-diaminobenzenesulfonic acid or L-arginine in water, reacting under microwave conditions to obtain amination-treated sisal fibers.

[0008] Furthermore, the mass ratio of carboxylated sisal fiber to polyethyleneimine is 1:0.1-1.

[0009] Furthermore, the reaction was carried out at 90-100℃ and 500-600W for 30-50 minutes.

[0010] Further, in S3, the method for grafting the aminated sisal fiber with the ultraviolet absorber includes: mixing paraformaldehyde with water, adjusting the pH to 3-5, sequentially adding a methanol or ethanol solution of 2,4-dihydroxybenzophenone and the aminated sisal fiber, reacting under microwave conditions to obtain the sisal fiber-based ultraviolet absorber.

[0011] Furthermore, the reaction is carried out at 50-70℃ and 500-600W.

[0012] Furthermore, the mass ratio of aminated sisal fiber to 2,4-dihydroxybenzophenone is 1:0.05-0.6.

[0013] According to another aspect of the invention, a sisal fiber-based ultraviolet absorber is also provided, prepared by the aforementioned preparation method.

[0014] According to another aspect of the present invention, an anti-UV aging wood-plastic composite material is also provided, which is composed of the aforementioned sisal fiber-based UV absorber and a polymer material. The present invention includes at least the following beneficial effects:

[0015] This invention sequentially carboxylates and aminations sisal fibers, then grafts a UV absorber onto them to obtain a sisal fiber-based UV absorber. The preparation process is green, environmentally friendly, and energy-efficient, easy to purify and separate, and exhibits good dispersibility. It can be used to improve the UV aging resistance of wood-plastic composites, and it does not accumulate in the biosphere, posing a low threat to human health. Furthermore, it does not migrate in subsequent wood-plastic composite applications. The high compatibility of sisal fibers with the polymer matrix enhances the UV aging resistance and stability of wood-plastic composites.

[0016] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0017] Figure 1The infrared spectrum of aminated sisal fiber (SF-PEI) and sisal fiber-based ultraviolet absorber (SF-PEI-g-UV-0) is shown in one embodiment of this application.

[0018] Figure 2 TGA curves of SF-PEI and SF-PEI-g-UV-0 in one embodiment of this application.

[0019] Figure 3 The UV absorption spectra (solid) of carboxylated sisal fibers (SF-COOH), SF-PEI, and SF-PEI-g-UV-0 are shown in one embodiment of this application.

[0020] Figure 4 SEM images of SF-COOH (row a), SF-PEI (row b), and SF-PEI-g-UV-O (row c) in one embodiment of this application.

[0021] Figure 5 Digital photographs of SF-COOH, SF-PEI, and SF-PEI-g-UV-0 in one example of this application under sunlight (a, b, c) and ultraviolet light (a′, b′, c′).

[0022] Figure 6 The ultraviolet absorption spectra (solid) of SF-PEI-g-UV-0 with different UV-0 contents. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0024] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0025] The embodiments of this application provide a method for preparing a sisal fiber-based ultraviolet absorber, comprising:

[0026] S1: Carboxylation treatment is performed on sisal fibers; optionally, the sisal fibers are carboxylated using an oxidizing agent;

[0027] S2: Aminoation treatment is performed on carboxylated sisal fibers; optionally, the carboxylated sisal fibers are aminoized using amine compounds.

[0028] S3: Grafting an ultraviolet absorber onto aminated sisal fibers yields a sisal fiber-based ultraviolet absorber. Optionally, the ultraviolet absorber is grafted onto aminated sisal fibers using the Mannich reaction. In this embodiment, sisal fibers are sequentially carboxylated and aminated before being grafted with an ultraviolet absorber to obtain a sisal fiber-based ultraviolet absorber. The entire preparation process is green, environmentally friendly, energy-efficient, easy to purify and separate, and exhibits good dispersibility. Verification was performed using infrared spectroscopy, ultraviolet absorption spectroscopy, SEM scanning, and TAG. The ultraviolet absorber in this embodiment was successfully grafted onto the sisal fibers and exhibits good thermal stability, making it suitable for improving the UV aging resistance of wood-plastic composites. It will not migrate in subsequent wood-plastic composite applications. The sisal fibers have high compatibility with the polymer matrix, enhancing the UV aging resistance and stability of the wood-plastic composite. Furthermore, as a macromolecular ultraviolet absorber, it will not accumulate in the biosphere and poses a low threat to human health.

[0029] In another embodiment, in step S1, the method for carboxylating the sisal fiber includes: adding the sisal fiber to a mixed solution of TEMPO, sodium bromide, sodium hypochlorite, and water; adjusting the pH to 8-11; reacting at room temperature for 1-4 hours; washing and drying after the reaction to obtain carboxylated sisal fiber; TEMPO, tetramethylpiperidine oxide, is a piperidine nitroxide radical that can oxidize primary alcohols to aldehydes and secondary alcohols to ketones; sodium hypochlorite can oxidize alcohols to carboxylic acids; sodium bromide acts as a co-catalyst; the combination of these three components can fully carboxylate the sisal fiber; preferably, the pH is adjusted to 10; preferably, the mass ratio of TEMPO, sodium bromide, sodium hypochlorite, and sisal fiber is 0.7-0.8; this embodiment uses room temperature acidification without the use of organic solvents, making the conditions mild and environmentally friendly.

[0030] In another embodiment, in S2, the method for amylating carboxylated sisal fibers includes: dispersing carboxylated sisal fibers and polyethyleneimine, 2,5-diaminobenzenesulfonic acid, or L-arginine in water, and reacting under microwave conditions to obtain aminated sisal fibers; polyethyleneimine has good water solubility, and after mixing with carboxylated sisal fibers, microwave treatment can fully achieve the amylation of carboxylated sisal fibers; optionally, the mass ratio of carboxylated sisal fibers to polyethyleneimine is 1:0.1-1; optionally, the reaction is carried out at 90-100℃ and 500-600W for 30-50 minutes; preferably, the reaction is carried out at 100℃ and 600W for 40 minutes; this embodiment uses microwave synthesis to prepare aminated sisal fibers, with water as the dispersion medium, which is environmentally friendly and under mild conditions.

[0031] In another embodiment, in step S3, the method for grafting the aminated sisal fiber with the ultraviolet absorber includes: mixing paraformaldehyde with water, adjusting the pH to 3-5, sequentially adding a methanol or ethanol solution of 2,4-dihydroxybenzophenone and the aminated sisal fiber, and reacting under microwave conditions to obtain the sisal fiber-based ultraviolet absorber; optionally, the reaction is carried out at 50-70°C and 500-600W, preferably at 70°C and 600W; optionally, the mass ratio of the aminated sisal fiber to 2,4-dihydroxybenzophenone is 1:0.05-0.6; optionally, the pH is adjusted to 4; this embodiment uses microwave rapid synthesis of the sisal fiber-based ultraviolet absorber, the synthesis process does not use organic solvents, the conditions are mild, water is used as the dispersion medium, it is easy to purify, environmentally friendly, and easy to industrialize.

[0032] Embodiments of this application also provide a sisal fiber-based ultraviolet absorber, prepared by the aforementioned preparation method.

[0033] Embodiments of this application also provide an anti-UV aging wood-plastic composite material, which is composed of the aforementioned sisal fiber-based UV absorber and polymer materials. Optionally, the anti-UV aging wood-plastic composite material comprises the following components in parts by weight: 100 parts low-density polyethylene, 5-10 parts maleic anhydride-grafted polyethylene, and 15-30 parts of the aforementioned UV absorber. The mixture is plasticized on an open-type mixing mill at 145°C. The plasticized sample is then molded into a 4mm thick sheet using a flat vulcanizing apparatus at a molding temperature of 150°C, a pressure of 15MPa, and a molding time of 15 minutes.

[0034] The following is a description of a specific embodiment.

[0035] Example 1:

[0036] Carboxylation treatment of sisal fibers:

[0037] To carboxylate sisal fibers, 600 mL of deionized water was added to a 1000 mL beaker. Then, 0.02 g of TEMPO, 0.2 g of sodium bromide, and 5.95 g of NaClO were weighed and mixed thoroughly. 8 g of sisal fibers were then added, and the pH of the system was adjusted to approximately 10 with NaOH. The mixture was stirred at room temperature for 4 hours to stop the reaction. The sisal fibers were then thoroughly washed with plenty of tap water until they were neutral and allowed to dry naturally to obtain the carboxylated sisal fiber intermediate (SF-COOH).

[0038] Aminolation treatment of sisal fibers:

[0039] The carboxylated sisal fiber and polyethyleneimine (PEI) were dispersed in 80 mL of water at a mass ratio of 1:0.2-1.0 and reacted at 100 °C and 600 W for 50 min to obtain aminated sisal fiber (SF-PEI).

[0040] Preparation of sisal fiber grafted with UV-0 ultraviolet absorber (SF-PEI-g-UV-0):

[0041] Add 0.025g of paraformaldehyde to a 150mL three-necked flask, then add 35mL of deionized water. Adjust the pH of the system to about 4 with hydrochloric acid, stir magnetically, add 0.107g of UV-0 dissolved in 35mL of methanol, stir and mix well, then add 0.5g of SF-PEI, place in a microwave reactor, and react for 1h at 70℃ and 500W microwave power. Then wash with tap water and air dry to obtain the final product SF-PEI-g-UV-0.

[0042] Example 2:

[0043] Carboxylation treatment of sisal fibers:

[0044] To carboxylate sisal fibers, 600 mL of deionized water was added to a 1000 mL beaker. Then, 0.02 g of TEMPO, 0.2 g of sodium bromide, and 6 g of NaClO were weighed and mixed thoroughly. 10 g of sisal fibers were then added, and the pH of the system was adjusted to about 10 with NaOH. The mixture was stirred at room temperature for 4 hours to stop the reaction. The sisal fibers were then thoroughly washed with plenty of tap water to neutralize them and allowed to dry naturally to obtain the carboxylated sisal fiber intermediate.

[0045] Aminolation treatment of sisal fibers:

[0046] The carboxylated sisal fiber and 2,5-diaminobenzenesulfonic acid (DMBSA) were dispersed in water (70 times the mass of the sisal fiber) at a mass ratio of 1:0.5, and reacted at 100°C and 600W for 50 minutes to obtain aminated sisal fiber (SF-DMBSA).

[0047] Preparation of sisal fiber grafted with UV-0 ultraviolet absorber (SF-DMBSA-g-UV-0):

[0048] Add 0.025g of paraformaldehyde to a 150mL three-necked flask, then add 35mL of deionized water. Adjust the pH of the system to about 4 with hydrochloric acid, stir magnetically, add 0.107g of UV-0 dissolved in 35mL of ethanol, stir and mix well, then add 0.5g of SF-PEI, place in a microwave reactor, and microwave at 70℃ and 600W for 1h. Then wash with tap water and air dry to obtain the final product SF-DMBSA-g-UV-0.

[0049] Example 3:

[0050] Carboxylation treatment of sisal fibers:

[0051] To carboxylate sisal fibers, 600 mL of deionized water was added to a 1000 mL beaker. Then, 0.02 g of TEMPO, 0.2 g of sodium bromide, and 6 g of NaClO were weighed and mixed thoroughly. 8 g of sisal fibers were then added, and the pH of the system was adjusted to approximately 10 with NaOH. The mixture was stirred at room temperature for 4 hours to stop the reaction. The sisal fibers were then thoroughly washed with plenty of tap water until they were neutral and allowed to dry naturally to obtain the carboxylated sisal fiber intermediate.

[0052] Aminolation treatment of sisal fibers:

[0053] 1 g of carboxylated sisal fiber and 0.8 g of polyethyleneimine were dispersed in 70 mL of deionized water and reacted at 100 °C and 600 W for 50 min to obtain aminated sisal fiber (SF-PEI).

[0054] Preparation of sisal fiber grafted with UV-0 ultraviolet absorber (SF-PEI-g-UV-0):

[0055] Add 0.025g of paraformaldehyde to a 150mL three-necked flask, then add 40mL of deionized water. Adjust the pH of the system to approximately 4 with hydrochloric acid, stir magnetically, add 0.214g of UV-0 dissolved in 40mL of ethanol, stir and mix thoroughly, then add 0.5g of SF-PEI, place in a microwave reactor, and microwave at 70℃ and 600W for 1 hour. Then wash with tap water and air dry to obtain the final product SF-PEI-g-UV-0.

[0056] Comparative Example 1:

[0057] Preparation of sisal fiber grafted with UV-0 ultraviolet absorber (SF-PEI-g-UV-0):

[0058] Add 0.025g of paraformaldehyde to a 150mL three-necked flask, then add 35mL of deionized water. Adjust the pH of the system to approximately 4 with hydrochloric acid, stir magnetically, add 0.054g of UV-0 dissolved in 35mL of methanol, stir until well mixed, then add 0.5g of SF-PEI, place in a microwave reactor, and microwave at 70℃ and 600W for 1 hour. After complete washing with tap water, the final product SF-PEI-g-UV-0 is obtained.

[0059] The remaining processes and parameters are the same as in Example 1.

[0060] Comparative Example 2:

[0061] Add 0.025g of paraformaldehyde to a 150mL three-necked flask, then add 35mL of deionized water. Adjust the pH of the system to about 4 with hydrochloric acid, stir magnetically, add 0.160g of UV-0 dissolved in 35mL of methanol, stir and mix well, then add 0.5g of SF-PEI, place in a microwave reactor, and microwave at 70℃ and 600W for 1h. After washing completely with tap water, the final product SF-PEI-g-UV-0 is obtained.

[0062] The remaining processes and parameters are the same as in Example 1.

[0063] Example 4:

[0064] 100 parts of low-density polyethylene, 15 parts of SF-PEI-g-UV-0 (3-5cm) obtained in Example 1, and 10 parts of maleic anhydride-grafted polyethylene were mixed in a high-speed mixer for 1 minute, and then plasticized in an open-type mixer at 145°C. The plasticized sample was then molded into a 4mm thick sheet using a flat vulcanizing apparatus at a molding temperature of 150°C, a pressure of 15MPa, and a molding time of 15 minutes. This yielded a polyethylene / sisal fiber wood-plastic composite board.

[0065] Example 5:

[0066] 100 parts of low-density polyethylene, 20 parts of SF-PEI-g-UV-0 (3-5cm) obtained in Example 1, and 10 parts of maleic anhydride-grafted polyethylene were mixed in a high-speed mixer for 1 minute, and then plasticized on an open-type mixer at 145°C. The plasticized sample was then molded into a 4mm thick sheet using a flat vulcanizing apparatus at a molding temperature of 150°C, a pressure of 15MPa, and a molding time of 15 minutes. This yielded a polyethylene / sisal fiber wood-plastic composite board.

[0067] Example 6:

[0068] 100 parts of low-density polyethylene, 25 parts of SF-PEI-g-UV-0 (3-5cm) obtained in Example 1, and 10 parts of maleic anhydride-grafted polyethylene were mixed in a high-speed mixer for 1 minute, and then plasticized in an open-type mixer at 145°C. The plasticized sample was then molded into a 4mm thick sheet using a flat vulcanizing apparatus at a molding temperature of 150°C, a pressure of 15MPa, and a molding time of 15 minutes. This yielded a polyethylene / sisal fiber wood-plastic composite board.

[0069] Example 7:

[0070] 100 parts of low-density polyethylene, 30 parts of SF-PEI-g-UV-0 (3-5cm) obtained in Example 1, and 10 parts of maleic anhydride-grafted polyethylene were mixed in a high-speed mixer for 1 minute, and then plasticized in an open-type mixer at 145°C. The plasticized sample was then molded into a 4mm thick sheet using a flat vulcanizing apparatus at a molding temperature of 150°C, a pressure of 15MPa, and a molding time of 15 minutes. This yielded a polyethylene / sisal fiber wood-plastic composite board.

[0071] Comparative Example 3:

[0072] 100 parts low-density polyethylene, 20 parts SF (3-5cm), and 10 parts maleic anhydride-grafted polyethylene were mixed in a high-speed mixer for 1 minute, and then plasticized in an open-type mixer at 145℃. The plasticized sample was then molded into a 4mm thick sheet using a flat vulcanizing apparatus at a molding temperature of 150℃, a pressure of 15MPa, and a molding time of 15 minutes. This yielded a polyethylene / sisal fiber wood-plastic composite board.

[0073] Comparative Example 4:

[0074] 100 parts low-density polyethylene, 30 parts SF (3-5cm), and 10 parts maleic anhydride-grafted polyethylene were mixed in a high-speed mixer for 1 minute, and then plasticized in an open-type mixer at 145℃. The plasticized sample was then molded into a 4mm thick sheet using a flat vulcanizing apparatus at a molding temperature of 150℃, a pressure of 15MPa, and a molding time of 15 minutes. This yielded a polyethylene / sisal fiber wood-plastic composite board.

[0075] Experiment 1:

[0076] The infrared spectra of SF-PEI and SF-PEI-g-UV-0 were detected, such as... Figure 1 As shown. Figure 1 In the curve a, the absorption peak at 3280 cm⁻¹ is the absorption peak of the free -OH stretching vibration in SF fiber, and the peak at 2892 cm⁻¹ is the absorption peak of the free -OH stretching vibration in SF fiber. -1 The absorption peak at 1598.7 cm⁻¹ is the stretching vibration absorption peak of CH. -1 The peaks are characteristic absorption peaks of the amide group in SF-PEI. Curve b is the infrared spectrum after the addition of 2,4-dihydroxybenzophenone. The characteristic peaks are at 1736 cm⁻¹ for the ester group, 1621.4 cm⁻¹ for the ketone carbonyl group (-C=O) in benzophenone, and 1053 cm⁻¹ for the COC group. The introduction of UV-0 significantly broadens these absorption peaks, indicating that the target product SF-PEI-g-UV-0 has been successfully synthesized.

[0077] Experiment 2:

[0078] The TGA curves of SF-PEI and SF-PEI-g-UV-0 were detected, and the results are as follows: Figure 2As shown, SF-PEI-UV-0 experiences only about 5% weight loss at temperatures below 275℃, likely due to the thermal decomposition of the introduced UV-0 small molecules. The comparison of residual carbon content reveals that SF-PEI-UV-0 has a significantly higher residual carbon content than the intermediate product SF-PEI. This indicates that UV-0 molecules were successfully grafted onto sisal fibers, and SF-PEI-UV-0 also exhibits good heat resistance and stability.

[0079] Experiment 3:

[0080] The ultraviolet absorption spectra (solid) of SF-COOH, SF-PEI, and SF-PEI-g-UV-0 were detected. Figure 3 As can be seen, SF-COOH exhibits some ultraviolet light absorption in the 200-400nm range, mainly due to the contribution of cellulose and hemicellulose in sisal fibers. When PEI is introduced into sisal fibers, it not only shows some ultraviolet absorption but also some absorption in the visible light region, proving that PEI was successfully introduced. Furthermore, when SF-PEI is grafted with UV-0, the ultraviolet absorption intensity increases, further demonstrating that UV-0 was successfully grafted onto the sisal fibers.

[0081] Experiment 4:

[0082] SEM scans were performed on SF-COOH, SF-PEI, and SF-PEI-g-UV-0, and the results are as follows: Figure 4 As shown in the image, SEM images of SF-COOH (row a), SF-PEI (row b), and SF-PEI-g-UV-0 (row c) reveal that the surface of SF-COOH is relatively smooth, somewhat resembling the appearance of bamboo. Row b shows SEM images of SF-PEI at different resolutions, indicating that the surface becomes relatively rougher, and the last high-resolution image shows a patina-like substance, indicating that PEI was successfully introduced onto the sisal fiber. Row c shows SEM images of the SF-PEI-g-UV-0 product at different resolutions, clearly showing that it is rougher than SF-PEI, and cloud-like substances appear, indicating that UV-0 was successfully grafted onto the sisal fiber.

[0083] Experiment 5:

[0084] Digital photographs of SF-COOH, SF-PEI, and SF-PEI-g-UV-0 were taken under sunlight (a, b, c) and ultraviolet light (a′, b′, c′), and the results are as follows: Figure 5As shown in the image, the colors gradually deepen, which preliminarily confirms the synthesis of the target product. The second row contains digital photographs of the three products under 365nm ultraviolet light. It can be seen that SF-COOH shows no fluorescence, while SF-PEI exhibits pale yellow fluorescence, indicating that PEI underwent a carbonization reaction with the functional groups in sisal fiber, forming carbon dots. However, when UV-0 is grafted onto SF-PEI, its fluorescence disappears, indicating that the UV-0 molecules disrupt the surface structure of the carbon dots, causing fluorescence quenching. This further proves that the target product was successfully synthesized in this application.

[0085] Experiment 6:

[0086] Figure 6 The UV absorption spectra (solid) of SF-PEI-g-UV-0 with different UV-0 contents (Comparative Example 1, Example 1, and Comparative Example 2) are shown. All three products with different UV-0 contents exhibit good UV absorption in the 280nm-390nm region. With increasing UV-0 content, the UV absorption intensity first increases and then decreases, with the best UV absorption observed at 0.107g of UV-0. When the amount of UV-0 is too high (0.160g), the absorbance of the sample begins to decrease. This may be because the reactive group -NH2 in sisal fiber reaches its reaction limit with UV-0, and further increases do not result in a reaction, indicating that the UV absorber ratio in Example 1 is optimal.

[0087] Experiment 7:

[0088] The polyethylene / sisal fiber wood-plastic composite boards obtained in Examples 4-7 and Comparative Examples 3-4 were cut into dumbbell-shaped standard specimens according to GBT1040.4-2006 standard. Then, according to GBT16422.3-2014 standard, ultraviolet aging tests were conducted using a YN-UV-A type ultraviolet aging test chamber. After 30 days of aging, the appearance was observed and the changes in tensile properties were tested. The test results are shown in Table 1. It can be seen that compared with Comparative Examples 3-4, the tensile strength change of Examples 4-7 after 30 days of aging was significantly smaller, and the color change was significantly lower. This indicates that the polyethylene / sisal fiber wood-plastic composite boards of Examples 4-7 have better resistance to ultraviolet aging and can better maintain mechanical properties and color quality, thereby expanding the application range of polyethylene / sisal fiber wood-plastic composite boards.

[0089] Table 1 Ultraviolet Aging Test

[0090]

[0091]

[0092] The number of devices and processing scale described herein are for simplification of the invention. Applications, modifications, and variations of the sisal fiber-based ultraviolet absorber, its preparation method, and the wood-plastic composite material of this invention will be readily apparent to those skilled in the art.

[0093] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing a sisal fiber-based ultraviolet absorber, characterized in that, include: S1: Carboxylation treatment is performed on sisal fibers; S2: Aminolation treatment is performed on carboxylated sisal fibers; S3: Grafting an amino-modified sisal fiber with an ultraviolet absorber to obtain a sisal fiber-based ultraviolet absorber; In S1, the method for performing carboxylation treatment on the sisal fibers includes: Sisal fibers were added to a mixed solution of TEMPO, sodium bromide, sodium hypochlorite and water, the pH was adjusted to 8-11, and the reaction was carried out at room temperature for 1-4 hours. After the reaction was completed, the fibers were washed and dried to obtain carboxylated sisal fibers. In S2, the method for performing amination treatment on carboxylated sisal fibers includes: Carboxylated sisal fibers and polyethyleneimine or 2,5-diaminobenzenesulfonic acid or L-arginine are dispersed in water and reacted under microwave conditions to obtain aminated sisal fibers. In S3, the method of grafting an ultraviolet absorber onto aminated sisal fibers includes: Paraformaldehyde was mixed with water, and the pH was adjusted to 3-5. Then, a methanol or ethanol solution of 2,4-dihydroxybenzophenone and aminated sisal fibers were added sequentially. The mixture was reacted under microwave conditions to obtain a sisal fiber-based ultraviolet absorber.

2. The method for preparing the sisal fiber-based ultraviolet absorber as described in claim 1, characterized in that, The mass ratio of carboxylated sisal fiber to polyethyleneimine is 1:0.1-1.

3. The method for preparing the sisal fiber-based ultraviolet absorber as described in claim 1, characterized in that, In S2, the reaction is carried out at 90-100℃ and 500-600W for 30-50 minutes.

4. The method for preparing the sisal fiber-based ultraviolet absorber as described in claim 1, characterized in that, In S3, the reaction is carried out at 50-70℃ and 500-600W.

5. The method for preparing the sisal fiber-based ultraviolet absorber as described in claim 1, characterized in that, The mass ratio of aminated sisal fiber to 2,4-dihydroxybenzophenone is 1:0.05-0.

6.

6. A sisal fiber-based ultraviolet absorber, characterized in that, It is prepared by any one of the preparation methods described in claims 1-5.

7. A UV-resistant wood-plastic composite material, characterized in that, It is composed of the sisal fiber-based ultraviolet absorber as described in claim 6 and a polymer material.

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