Modified plant fiber polylactic acid composite material and preparation method thereof

Abstract

The invention discloses a modified plant fiber polylactic acid composite material and a preparation method thereof, and belongs to the technical field of composite materials. The modified plant fiber polylactic acid composite material comprises the following components in parts by weight: 11-13 parts of polylactic acid and 12-15 parts of thermal insulation gel liquid. According to the method, the performance of the polylactic acid material is improved in the mode that the thermal insulation gel liquid reinforced polylactic acid is prepared from the sisal fibers, meanwhile, the organic metal framework is prepared, the technical effect of reducing the water absorption of the sisal fibers is achieved, and meanwhile the bonding strength and damp-heat aging resistance of the composite material are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of composite materials, and specifically refers to a modified plant fiber polylactic acid composite material and a preparation method thereof. Background Art

[0002] Polylactic acid, also known as polylactide, is a polymer obtained by polymerization with lactic acid as the main raw material. It is one of the most widely used biodegradable materials because of its sufficient raw material source, pollution-free production process and biodegradable product. It has excellent advantages such as renewability and degradability. It is an excellent substitute for petroleum-based materials that are difficult to degrade in production and life. The poor crystallization performance and thermal stability of polylactic acid seriously affect its application. Natural plant fibers are often used to reinforce polylactic acid to prepare environmentally friendly and naturally degradable composite materials. However, natural fibers have strong water absorption and poor stability when used in durable composite materials. The expansion of fibers after absorbing water can easily cause cracks in the composite material, reducing the mechanical properties of the material. Natural fiber reinforced composite materials are currently widely used in the automotive, aerospace, construction and other fields. At the same time, because natural fibers have good sound insulation and heat insulation properties, they are widely used in the insulation and sound absorption of buildings.

[0003] The existing technology currently has the following main problems: the performance of polylactic acid materials is poor, and the strong water absorption of natural fibers affects the material performance. Summary of the invention

[0004] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a modified plant fiber polylactic acid composite material and a preparation method thereof. In order to solve the problem of poor performance of polylactic acid materials, the present invention proposes a method of strengthening polylactic acid by preparing a thermal insulation gel liquid with sisal fiber, thereby achieving the improvement of the performance of polylactic acid materials and preparing an organic metal framework at the same time, thereby achieving the technical effect of reducing the water absorption of sisal fiber and improving the bonding strength and moisture-heat aging resistance of the composite material.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: The present invention proposes a modified plant fiber polylactic acid composite material, which includes the following components in parts by weight: 11-13 parts of polylactic acid and 12-15 parts of thermal insulation gel liquid.

[0006] Preferably, the thermal insulation aerogel comprises the following components in parts by weight: 15-20 parts of sisal fiber, 9-12 parts of aminosulfonic acid, 12-16 parts of 2-methylimidazole, 10-12 parts of zinc nitrate, 15-18 parts of polyvinyl alcohol and 6-8 parts of borax.

[0007] Preferably, the method for preparing the thermal insulation gel liquid specifically comprises the following steps:

[0008] S1, mixing N,N-dimethylformamide with sisal fiber, adding aminosulfonic acid, ball milling at a speed of 800-900 rpm for 2 h, filtering, washing, and drying to obtain modified cellulose;

[0009] S2, dispersing zinc nitrate into a 5 wt % modified cellulose solution, and stirring in a water bath to obtain a modified cellulose solution;

[0010] S3, adding 2-methylimidazole to the modified cellulose solution obtained in S2, stirring for 30 minutes, standing for 20 minutes, filtering and drying to obtain an organic framework fiber;

[0011] S4. Add the organic framework fiber obtained in S3 into a 3 wt % polyvinyl alcohol aqueous solution, add borax, and stir to mix evenly to obtain a thermal insulation gel solution.

[0012] Preferably, in S1, the mass ratio of N,N-dimethylformamide to sisal fiber is 8-9:1.

[0013] Preferably, in S2, the water bath stirring temperature is 40-50°C, the speed is 60-80 rpm, and the time is 10-15 min.

[0014] Preferably, in S4, the stirring speed is 10000-12000 rpm, and the time is 30-40 min.

[0015] The present invention also provides a method for preparing a modified plant fiber polylactic acid composite material, which specifically comprises the following steps:

[0016] (1) dissolving polylactic acid in a dichloromethane solution to obtain a polylactic acid solution, and adding a thermal insulation aerogel liquid to the polylactic acid solution to obtain a mixed solution;

[0017] (2) The mixed solution obtained in step (1) was stirred at 100-200 rpm for 3 h, allowed to stand for 3 h, freeze-dried, and then dried at 100° C. for 24 h to obtain a modified plant fiber polylactic acid composite material.

[0018] Preferably, in step (1), the amount of polylactic acid added to dichloromethane is 0.04-0.06 g / mL.

[0019] Preferably, in step (2), the freeze-drying temperature is -60--80°C, the pressure is 50-60Pa, and the time is 60-80h.

[0020] The beneficial effects achieved by the present invention are as follows: the performance of the polylactic acid material is improved by preparing a thermal insulation gel liquid with sisal fiber to enhance the polylactic acid, and an organic metal framework is prepared at the same time to reduce the water absorption of the sisal fiber, while improving the bonding strength and resistance to moisture and heat aging of the composite material; the sisal fiber has the advantages of being long and tough, and is modified by aminosulfonic acid through a ball milling method to obtain modified cellulose, thereby enhancing its complexing ability with metal ions, and further adding zinc ions to the surface to prepare an organic metal framework to obtain an organic framework fiber with a hydrophobic effect, thereby reducing the water absorption effect of the fiber, improving the material's resistance to moisture and heat aging, and enhancing the bonding strength between the fiber and the polylactic acid, thereby improving the mechanical properties of the material; at the same time, borax is used as a cross-linking agent to undergo a gelation reaction with a hydroxyl group, thereby increasing the number of micropores in the material after freeze-drying, thereby improving the thermal insulation performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The results of the heat preservation experiments of Examples 1-3 and Comparative Examples 1-3 are shown in FIG.

[0022] Figure 2 The results of the tensile tests of Examples 1-3 and Comparative Examples 1-3 are shown in FIG.

[0023] Figure 3 It is a graph showing the results of the moisture and heat resistance test of Examples 1-3 and Comparative Examples 1-2.

[0024] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0026] Unless otherwise defined, all professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to those described herein may be applied to the present invention. The preferred implementation methods and materials described herein are for demonstration purposes only and are not intended to limit the content of this application.

[0027] The experimental methods in the following examples are conventional methods unless otherwise specified; the experimental materials used in the following examples are purchased from commercial channels unless otherwise specified.

[0028] Example 1

[0029] A modified plant fiber polylactic acid composite material comprises the following components in parts by weight: 130 parts of polylactic acid and 15 parts of thermal insulation gel liquid.

[0030] The thermal insulation gel liquid comprises the following components in parts by weight: 20 parts of sisal fiber, 12 parts of aminosulfonic acid, 16 parts of 2-methylimidazole, 12 parts of zinc nitrate, 18 parts of polyvinyl alcohol and 8 parts of borax.

[0031] S1, mixing N,N-dimethylformamide and sisal fiber in a mass ratio of 9:1, adding aminosulfonic acid, ball milling at a speed of 900 rpm for 2 h, filtering, washing, and drying to obtain modified cellulose;

[0032] S2, dispersing zinc nitrate into a 5 wt % modified cellulose solution, stirring at 80 rpm in a 50° C. water bath for 15 min to obtain a modified cellulose solution;

[0033] S3. Add 2-methylimidazole to the modified cellulose solution obtained in S2, stir for 30 minutes, let stand for 20 minutes, filter and dry to obtain organic framework fibers.

[0034] S4, adding the organic framework fiber obtained in S3 to a 3 wt % polyvinyl alcohol aqueous solution, adding borax, stirring at 12000 rpm for 40 min to obtain a thermal insulation gel solution;

[0035] The present invention also provides a method for preparing a modified plant fiber polylactic acid composite material, which specifically comprises the following steps:

[0036] (1) dissolving polylactic acid in a dichloromethane solution at an addition amount of 0.06 g / mL to obtain a polylactic acid solution, and adding a thermal insulation aerogel liquid to the polylactic acid solution to obtain a mixed solution;

[0037] (2) The mixed solution obtained in step (1) was stirred at 200 rpm for 3 h, allowed to stand for 3 h, freeze-dried at -80°C, 60 Pa for 80 h, and then dried at 100°C for 24 h to obtain a modified plant fiber polylactic acid composite material.

[0038] Example 2

[0039] A modified plant fiber polylactic acid composite material comprises the following components in parts by weight: 110 parts of polylactic acid and 12 parts of thermal insulation gel liquid.

[0040] The thermal insulation gel liquid comprises the following components in parts by weight: 15 parts of sisal fiber, 9 parts of aminosulfonic acid, 12 parts of 2-methylimidazole, 10 parts of zinc nitrate, 15 parts of polyvinyl alcohol and 6 parts of borax.

[0041] S1, mixing N,N-dimethylformamide and sisal fiber in a mass ratio of 8:1, adding aminosulfonic acid, ball milling at a speed of 800 rpm for 2 h, filtering, washing, and drying to obtain modified cellulose;

[0042] S2, dispersing zinc nitrate into a 5 wt % modified cellulose solution, stirring at 60 rpm in a 40° C. water bath for 10 min to obtain a modified cellulose solution;

[0043] S3. Add 2-methylimidazole to the modified cellulose solution obtained in S2, stir for 30 minutes, let stand for 20 minutes, filter and dry to obtain organic framework fibers.

[0044] S4, adding the organic framework fiber obtained in S3 to a 3 wt % polyvinyl alcohol aqueous solution, adding borax, stirring at 10000 rpm for 30 min to obtain a thermal insulation gel solution;

[0045] The present invention also provides a method for preparing a modified plant fiber polylactic acid composite material, which specifically comprises the following steps:

[0046] (1) dissolving polylactic acid in a dichloromethane solution at an addition amount of 0.04 g / mL to obtain a polylactic acid solution, and adding a thermal insulation aerogel liquid to the polylactic acid solution to obtain a mixed solution;

[0047] (2) The mixed solution obtained in step (1) was stirred at 100 rpm for 3 h, allowed to stand for 3 h, freeze-dried at -60°C, 50 Pa for 60 h, and then dried at 100°C for 24 h to obtain a modified plant fiber polylactic acid composite material.

[0048] Example 3

[0049] A modified plant fiber polylactic acid composite material comprises the following components in parts by weight: 120 parts of polylactic acid and 12-15 parts of thermal insulation gel liquid.

[0050] The thermal insulation gel liquid comprises the following components in parts by weight: 17 parts of sisal fiber, 10.5 parts of aminosulfonic acid, 14 parts of 2-methylimidazole, 11 parts of zinc nitrate, 17 parts of polyvinyl alcohol and 7 parts of borax.

[0051] S1, mixing N,N-dimethylformamide and sisal fiber in a mass ratio of 8-9:1, adding aminosulfonic acid, ball milling at a speed of 800-900 rpm for 2 h, filtering, washing, and drying to obtain modified cellulose;

[0052] S2, dispersing zinc nitrate into a 5 wt % modified cellulose solution, stirring in a 45° C. water bath at 70 rpm for 12.5 min to obtain a modified cellulose solution;

[0053] S3. Add 2-methylimidazole to the modified cellulose solution obtained in S2, stir for 30 minutes, let stand for 20 minutes, filter and dry to obtain organic framework fibers.

[0054] S4, adding the organic framework fiber obtained in S3 to a 3 wt % polyvinyl alcohol aqueous solution, adding borax, stirring at 11000 rpm for 35 min to obtain a thermal insulation gel solution;

[0055] The present invention also provides a method for preparing a modified plant fiber polylactic acid composite material, which specifically comprises the following steps:

[0056] (1) dissolving polylactic acid in a dichloromethane solution at an addition amount of 0.05 g / mL to obtain a polylactic acid solution, and adding a thermal insulation aerogel liquid to the polylactic acid solution to obtain a mixed solution;

[0057] (2) The mixed solution obtained in step (1) was stirred at 150 rpm for 3 h, allowed to stand for 3 h, freeze-dried at -70 °C, 55 Pa for 70 h, and then dried at 100 °C for 24 h to obtain a modified plant fiber polylactic acid composite material.

[0058] Comparative Example 1

[0059] This comparative example provides a modified plant fiber polylactic acid composite material, which differs from Example 1 only in that the component does not contain 2-methylimidazole, and the other components and component contents are the same as those in Example 1.

[0060] A modified plant fiber polylactic acid composite material comprises the following components in parts by weight: 130 parts of polylactic acid and 15 parts of thermal insulation gel liquid.

[0061] The thermal insulation gel liquid comprises the following components in parts by weight: 20 parts of sisal fiber, 12 parts of aminosulfonic acid, 12 parts of zinc nitrate, 18 parts of polyvinyl alcohol and 8 parts of borax.

[0062] S1, mixing N,N-dimethylformamide and sisal fiber in a mass ratio of 9:1, adding aminosulfonic acid, ball milling at a speed of 900 rpm for 2 h, filtering, washing, and drying to obtain modified cellulose;

[0063] S2, dispersing zinc nitrate into a 5 wt % modified cellulose solution, stirring at 80 rpm in a 50° C. water bath for 15 min to obtain a modified cellulose solution;

[0064] S3, stirring the modified cellulose solution obtained in S2 for 30 minutes, letting it stand for 20 minutes, filtering and drying to obtain modified cellulose.

[0065] S4, adding the modified cellulose obtained in S3 to a 3 wt % polyvinyl alcohol aqueous solution, adding borax, stirring at 12000 rpm for 40 min to obtain a thermal insulation gel solution;

[0066] The present invention also provides a method for preparing a modified plant fiber polylactic acid composite material, which specifically comprises the following steps:

[0067] (1) dissolving polylactic acid in a dichloromethane solution at an addition amount of 0.06 g / mL to obtain a polylactic acid solution, and adding a thermal insulation aerogel liquid to the polylactic acid solution to obtain a mixed solution;

[0068] (2) The mixed solution obtained in step (1) was stirred at 200 rpm for 3 h, allowed to stand for 3 h, freeze-dried at -80°C, 60 Pa for 80 h, and then dried at 100°C for 24 h to obtain a modified plant fiber polylactic acid composite material.

[0069] Comparative Example 2

[0070] This comparative example provides a modified plant fiber polylactic acid composite material, which differs from Example 1 only in that the component does not contain aminosulfonic acid, that is, the fiber is not modified, and the remaining components and component contents are the same as those in Example 1.

[0071] A modified plant fiber polylactic acid composite material comprises the following components in parts by weight: 130 parts of polylactic acid and 15 parts of thermal insulation gel liquid.

[0072] The thermal insulation gel liquid comprises the following components in parts by weight: 20 parts of sisal fiber, 16 parts of 2-methylimidazole, 12 parts of zinc nitrate, 18 parts of polyvinyl alcohol and 8 parts of borax.

[0073] S1, mixing N,N-dimethylformamide and sisal fiber in a mass ratio of 9:1, ball milling at a speed of 900 rpm for 2 h, filtering, washing, and drying to obtain sisal cellulose;

[0074] S2, dispersing zinc nitrate into a 5 wt % sisal cellulose solution, stirring at 80 rpm in a 50° C. water bath for 15 min to obtain a sisal cellulose solution;

[0075] S3. Add 2-methylimidazole to the sisal cellulose solution obtained in S2, stir for 30 minutes, let stand for 20 minutes, filter and dry to obtain organic framework fibers.

[0076] S4, adding the organic framework fiber obtained in S3 to a 3 wt % polyvinyl alcohol aqueous solution, adding borax, stirring at 12000 rpm for 40 min to obtain a thermal insulation gel solution;

[0077] The present invention also provides a method for preparing a modified plant fiber polylactic acid composite material, which specifically comprises the following steps:

[0078] (1) dissolving polylactic acid in a dichloromethane solution at an addition amount of 0.06 g / mL to obtain a polylactic acid solution, and adding a thermal insulation aerogel liquid to the polylactic acid solution to obtain a mixed solution;

[0079] (2) The mixed solution obtained in step (1) was stirred at 200 rpm for 3 h, allowed to stand for 3 h, freeze-dried at -80°C, 60 Pa for 80 h, and then dried at 100°C for 24 h to obtain a modified plant fiber polylactic acid composite material.

[0080] Comparative Example 3

[0081] This comparative example provides a modified plant fiber polylactic acid composite material, which is different from Example 1 only in that the component does not contain borax, and the other components and component contents are the same as those in Example 1.

[0082] A modified plant fiber polylactic acid composite material comprises the following components in parts by weight: 130 parts of polylactic acid and 15 parts of thermal insulation gel liquid.

[0083] The thermal insulation gel liquid comprises the following components in parts by weight: 20 parts of sisal fiber, 12 parts of aminosulfonic acid, 16 parts of 2-methylimidazole, 12 parts of zinc nitrate and 18 parts of polyvinyl alcohol.

[0084] S1, mixing N,N-dimethylformamide and sisal fiber in a mass ratio of 9:1, adding aminosulfonic acid, ball milling at a speed of 900 rpm for 2 h, filtering, washing, and drying to obtain modified cellulose;

[0085] S2, dispersing zinc nitrate into a 5 wt % modified cellulose solution, stirring at 80 rpm in a 50° C. water bath for 15 min to obtain a modified cellulose solution;

[0086] S3. Add 2-methylimidazole to the modified cellulose solution obtained in S2, stir for 30 minutes, let stand for 20 minutes, filter and dry to obtain organic framework fibers.

[0087] S4, adding the organic framework fiber obtained in S3 to a 3 wt % polyvinyl alcohol aqueous solution, stirring at 12000 rpm for 40 min to obtain a thermal insulation gel solution;

[0088] The present invention also provides a method for preparing a modified plant fiber polylactic acid composite material, which specifically comprises the following steps:

[0089] (1) dissolving polylactic acid in a dichloromethane solution at an addition amount of 0.06 g / mL to obtain a polylactic acid solution, and adding a thermal insulation aerogel liquid to the polylactic acid solution to obtain a mixed solution;

[0090] (2) The mixed solution obtained in step (1) was stirred at 200 rpm for 3 h, allowed to stand for 3 h, freeze-dried at -80°C, 60 Pa for 80 h, and then dried at 100°C for 24 h to obtain a modified plant fiber polylactic acid composite material.

[0091] Experimental example

[0092] 1. Insulation experiment

[0093] In an open 20°C environment, the heating platform was kept at a constant temperature of 100°C. Examples 1-3 and Comparative Examples 1-3 were respectively prepared into thin sheets with a length and width of 5 cm and a thickness of 0.5 cm, placed on the platform, and the upper surface temperature was observed by an infrared thermal imager to perform a constant temperature heating platform test.

[0094] Figure 1 The result diagram of the thermal insulation experiment of Example 1-3 and Comparative Example 1-3 is shown in the figure. As shown in the figure, the upper surface temperatures of Example 1-3 are 31.2°C, 33.5°C, and 31.6°C, and the upper surface temperatures of Comparative Example 1-2 are 56.3°C, 55.9°C, and 69.5°C, respectively. The upper surface temperature of Example 1-3 is significantly lower than that of Comparative Example 1-3; it indicates that the thermal insulation effect of Example 1-3 is better than that of Comparative Example 1-3, and the use of 2-methylimidazole, aminosulfonic acid, and borax improves the thermal insulation effect of the material.

[0095] 2. Tensile test

[0096] The examples 1-3 and comparative examples 1-3 were tested using a universal material testing machine at a test temperature of 25° C. and a tensile rate of 25 mm / min. The specimens used in the experiment were 15 mm in length, 2 mm in thickness, and 2 mm in width. The tensile strength was calculated using the following formula:

[0097] Tensile strength = maximum load the specimen withstands during tension / original cross-section of the specimen.

[0098] Figure 2 The results of the tensile tests of Examples 1-3 and Comparative Examples 1-3 are shown in the figure. As shown in the figure, the tensile strengths of Examples 1-3 are 45.5 MPa, 45.2 MPa, and 45.6 MPa, and the upper surface temperatures of Comparative Examples 1-2 are 36.5 MPa, 37.1 MPa, and 39.2 MPa, respectively. The tensile strength of Example 1-3 is significantly higher than that of Comparative Examples 1-3, indicating that the mechanical properties of Example 1-3 are better than those of Comparative Examples 1-3, and the use of 2-methylimidazole, aminosulfonic acid, and borax improves the mechanical properties of the material.

[0099] 3.Wet and hot stability test

[0100] The examples 1-3 and comparative examples 1-2 were placed at 50°C and 100% RH for 3 days, and then the above tensile test was performed. The tensile strength data of the examples 1-3 and comparative examples 1-2 in Experiment 2 were taken as the initial tensile strength, and the tensile strength data obtained after the wet heat treatment in this embodiment were taken as the experimental tensile strength. The tensile strength reduction rate was calculated by the following formula:

[0101] Tensile strength decrease rate = (initial tensile strength - experimental tensile strength) / initial tensile strength × 100%

[0102] Figure 3 It is a result graph of the moisture and heat resistance test of Example 1-3 and Comparative Example 1-2. As shown in the figure, the reduction rates of tensile strength of Example 1-3 and Comparative Example 1-2 are 9.6%, 9.3%, 10.1%, 22.6% and 19.9%, respectively. The reduction rate of tensile strength of Example 1-3 is significantly lower than that of Comparative Example 1-2, indicating that the use of 2-methylimidazole and aminosulfonic acid improves the moisture and heat stability of the material.

[0103] While the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that many changes, modifications, substitutions and variations can be made to the embodiments without departing from the principles and spirit of the invention.

[0104] The present invention and its implementation methods are described above, which is not restrictive. The drawings are only one of the implementation methods of the present invention, and the actual application is not limited thereto. In short, if ordinary technicians in the field are inspired by it and design methods and embodiments similar to the technical solution without creativity without departing from the purpose of the invention, they should all fall within the protection scope of the present invention.

Claims

1. A modified plant fiber polylactic acid composite material, characterized in that: The thermal insulation aerogel comprises the following components in parts by weight: 11-13 parts of polylactic acid and 12-15 parts of thermal insulation gel liquid; the thermal insulation aerogel comprises the following components in parts by weight: 15-20 parts of sisal fiber, 9-12 parts of aminosulfonic acid, 12-16 parts of 2-methylimidazole, 10-12 parts of zinc nitrate, 15-18 parts of polyvinyl alcohol and 6-8 parts of borax.

2. A method for preparing the modified plant fiber polylactic acid composite material according to claim 1, characterized in that: The specific steps include: (1) dissolving polylactic acid in a dichloromethane solution to obtain a polylactic acid solution, and adding a thermal insulation aerogel liquid to the polylactic acid solution to obtain a mixed solution; (2) The mixed solution obtained in step (1) was stirred at 100-200 rpm for 3 h, allowed to stand for 3 h, freeze-dried, and then dried at 100° C. for 24 h to obtain a modified plant fiber polylactic acid composite material.

3. The method for preparing the modified plant fiber polylactic acid composite material according to claim 2, characterized in that: In step (1), the amount of polylactic acid added to dichloromethane is 0.04-0.06 g / mL.

4. The method for preparing the modified plant fiber polylactic acid composite material according to claim 3, characterized in that: In step (2), the freeze-drying temperature is -60--80°C, the pressure is 50-60Pa, and the time is 60-80h.

5. The method for preparing the modified plant fiber polylactic acid composite material according to claim 4, characterized in that: The method for preparing the thermal insulation gel liquid specifically comprises the following steps: S1, mixing N,N-dimethylformamide with sisal fiber, adding aminosulfonic acid, ball milling at a speed of 800-900 rpm for 2 h, filtering, washing, and drying to obtain modified cellulose; S2, dispersing zinc nitrate into a 5 wt % modified cellulose solution, and stirring in a water bath to obtain a modified cellulose solution; S3, adding 2-methylimidazole to the modified cellulose solution obtained in S2, stirring for 30 minutes, standing for 20 minutes, filtering and drying to obtain an organic framework fiber; S4. Add the organic framework fiber obtained in S3 into a 3 wt % polyvinyl alcohol aqueous solution, add borax, and stir to mix evenly to obtain a thermal insulation gel solution.

6. The method for preparing the modified plant fiber polylactic acid composite material according to claim 5, characterized in that: In S1, the mass ratio of N,N-dimethylformamide to sisal fiber is 8-9:

1.

7. The method for preparing the modified plant fiber polylactic acid composite material according to claim 6, characterized in that: In S2, the water bath stirring temperature is 40-50°C, the speed is 60-80 rpm, and the time is 10-15 min.

8. The method for preparing the modified plant fiber polylactic acid composite material according to claim 7, characterized in that: In S4, the stirring speed is 10000-12000 rpm, and the time is 30-40 min.

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