A high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel and its preparation method

Abstract

The invention discloses a high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel and a preparation method. The preparation method comprises the following steps: firstly, dissolving a benzoxazine resin in N,N-dimethylformamide; adding ammonium polyphosphate and a p-toluenesulfonic acid aqueous solution after complete dissolution; the benzoxazine resin undergoes ring opening in the p-toluenesulfonic acid aqueous solution and undergoes a polymerization reaction with the ammonium polyphosphate; secondly, adding a nanocellulose suspension to the ammonium polyphosphate / benzoxazine precursor system; and finally, adding polyvinyl alcohol to the system and adding an appropriate amount of γ-glycidyloxypropyltrimethoxysilane as a cross-linking agent, so that the polyvinyl alcohol undergoes cross-linking reactions with the ammonium polyphosphate / benzoxazine and the nanocellulose, respectively. The invention improves the inherent defects of the nanocellulose-based composite aerogel, such as lack of resilience and flammability, and provides a nanocellulose-based aerogel with excellent resilience and flame retardancy.

Description

Technical Field

[0001] The present invention relates to the field of material technology, and in particular to a high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel and a preparation method thereof. Background Art

[0002] Aerogels, one of the lightest materials in the world, offer advantages such as large surface area, low density, high porosity, and low thermal conductivity. Conventional aerogels primarily include inorganic, organic, and some composite aerogels. Compared to common carbon-based, silicon-based, and some metal oxide aerogels, cellulose-based aerogels, as the third generation of aerogel materials, offer advantages such as low cost, wide availability, simple storage, and good biocompatibility. Cellulose, a macromolecular polysaccharide composed of glucose, is one of the most common organic compounds found in nature and is a biomaterial essential for human survival. It is primarily found in the secondary cell walls of plants, animals, and a few fungi. Within the plant kingdom, wood, bamboo, cotton, and the straw of some plants are the primary sources of cellulose. Nanocellulose, on the other hand, is produced at the nanoscale through a series of raw material processing steps. This includes nanocellulose crystals, bacterial cellulose, and spherical nanocellulose. The abundant reactive hydroxyl groups on the surface of nanocellulose can cross-link with polymers to form stable hydrogen bonds, ultimately creating aerogel materials with a three-dimensional porous structure.

[0003] However, due to the limitations of the components of cellulose-based aerogels, pure cellulose-based aerogels have a high probability of catching fire, and the combustion process is violent. Therefore, in order to overcome the shortcomings of conventional cellulose-based aerogels, such as flammability and poor mechanical properties, researchers have introduced some halogen-containing flame retardants based on the microstructure of nanocellulose using in-situ polymerization and other technologies, aiming to improve the flame retardant properties of composite aerogels. However, these halogen-containing flame retardants not only pollute the environment, but the gases produced after combustion are extremely harmful to the human body. In addition, researchers have also introduced some inorganic particles, including graphene oxide, titanium dioxide, and silicon dioxide, etc. These inorganic particles not only improve the flame retardant properties of composite aerogels, but also improve the mechanical strength of the overall material. However, these inorganic particles are so expensive that they cannot be mass-produced.

[0004] Therefore, based on environmental protection and cost, how to improve the inherent defects of nanocellulose-based composite aerogels such as lack of resilience and fragility, further improve the flame retardant and mechanical properties of nanocellulose-based aerogels, and provide a green and efficient method to prepare flame-retardant nanocellulose-based aerogels is a technical problem that researchers in the field of biomaterials currently need to solve. Summary of the Invention

[0005] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid blurring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0006] Therefore, the purpose of the present invention is to provide a high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel and a preparation method, which can improve the inherent defects of nanocellulose-based composite aerogels such as lack of resilience and fragility, and improve the flame retardant and mechanical properties of nanocellulose-based aerogels.

[0007] To solve the above technical problems, according to one aspect of the present invention, the present invention provides the following technical solutions:

[0008] A high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel comprises a nanocellulose suspension, benzoxazine, ammonium polyphosphate, p-toluenesulfonic acid, γ-glycidyloxypropyltrimethoxysilane and water.

[0009] As a preferred embodiment of the high resilience and high flame retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double network hybrid aerogel described in the present invention, the following components are present in percentage by weight:

[0010] 1% nanocellulose suspension;

[0011] 0.5% benzoxazine;

[0012] 0.5% ammonium polyphosphate;

[0013] 1% p-toluenesulfonic acid;

[0014] 0.5% γ-glycidoxypropyltrimethoxysilane;

[0015] 96.5% water.

[0016] A method for preparing a high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel comprises the following steps:

[0017] S1. Dissolve benzoxazine resin in N,N-dimethylformamide. After complete dissolution, add ammonium polyphosphate and p-toluenesulfonic acid aqueous solution. Ring-open the benzoxazine resin in the p-toluenesulfonic acid aqueous solution and undergo polymerization reaction with ammonium polyphosphate. Stir the reaction at low speed at room temperature for 0.5-1 hour.

[0018] S2, adding the nanocellulose suspension to the precursor system, and slowly raising the temperature of the reaction system to 90°C;

[0019] S3. After the temperature of the reaction system rises to 90°C, continue to add an appropriate amount of γ-glycidyloxypropyltrimethoxysilane to the precursor system and react at 90-95°C with high-speed stirring for 1-2 hours;

[0020] S4. Add polyvinyl alcohol to the precursor system and react at 90-95°C with high-speed stirring for 1-1.5 hours to cause a cross-linking reaction of the double-network hydrogen bond structure in the entire system;

[0021] S5. After the temperature of the reaction system drops to room temperature, continue stirring at a low speed for 0.2-0.5 hours. After stirring, add n-octanol to the solution to eliminate bubbles. After quick freezing in a refrigerator (-80°C) for 12 hours, place in a freeze dryer for 48 hours.

[0022] As a preferred embodiment of the method for preparing a high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel according to the present invention, in step S1, the mass ratio of nanocellulose to benzoxazine is 2:1-3:1, the mass ratio of ammonium polyphosphate to benzoxazine is 1:1, and the mass ratio of p-toluenesulfonic acid in the entire system is 1%.

[0023] As a preferred embodiment of the method for preparing a high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel described in the present invention, in step S2, the mass fraction of the nanocellulose dispersion is 1-1.5%, the ultrasonic oscillation time is 20 minutes, and the power is 400W.

[0024] As a preferred embodiment of the method for preparing the high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel of the present invention, in step S3, the amount of the silane coupling agent used is 1% of the entire system.

[0025] As a preferred embodiment of the method for preparing a high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel according to the present invention, the low-speed stirring is 200-250 r / min, and the high-speed stirring is 450-550 r / min.

[0026] As a preferred embodiment of the method for preparing the high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel described in the present invention, the water is deionized water.

[0027] Compared with the existing technology, the present invention has the following advantages: first, the present invention utilizes the ring-opening effect of the benzoxazine monomer and uses ammonium polyphosphate to modify the benzoxazine. Second, it utilizes polyvinyl alcohol and the hydroxyl groups on the surfaces of nanocellulose and polybenzoxazine to form a stable double-network hydrogen bond structure. Finally, due to the significant flame retardancy of the modified benzoxazine, a hybrid aerogel material with excellent heat resistance, flame retardancy, and mechanical properties is obtained. Compared with traditional pure cellulose-based aerogel materials, the defects of traditional nanocellulose-based aerogels, such as poor mechanical properties, lack of resilience, and fragility, are improved, and the involvement of halogen-containing substances is avoided, thereby improving the flame retardancy of the hybrid aerogel. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort. Among them:

[0029] Figure 1 The present invention is a flow chart of a method for preparing a high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel.

[0030] Attachment Figure 2 This is a comparison chart of the flame retardant data of nanocellulose-polyvinyl alcohol, nanocellulose / benzoxazine-polyvinyl alcohol and nanocellulose / modified benzoxazine-polyvinyl alcohol double network hydrogen bond structure hybrid aerogels.

[0031] Attachment Figure 3 This is a comparison chart of the compression-rebound properties of nanocellulose-polyvinyl alcohol and nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hydrogen bond structure hybrid aerogels. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0033] Next, the present invention is described in detail with reference to schematic diagrams. For ease of illustration, cross-sectional views of device structures may be partially enlarged and not to scale when describing the embodiments of the present invention. Furthermore, the schematic diagrams are merely illustrative and should not limit the scope of protection of the present invention. Furthermore, in actual production, three-dimensional dimensions, including length, width, and depth, should be included.

[0034] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0035] The present invention provides a high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel and a preparation method, which can improve the inherent defects of nanocellulose-based composite aerogels such as lack of resilience and flammability, and propose a nanocellulose-based aerogel with excellent rebound and flame-retardant properties.

[0036] The high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel includes a nanocellulose suspension, benzoxazine, ammonium polyphosphate, p-toluenesulfonic acid, γ-glycidyloxypropyltrimethoxysilane and water. Specifically, in this embodiment, the weight percentage is: 1% nanocellulose suspension, 0.5% benzoxazine, 0.5% ammonium polyphosphate, 1% p-toluenesulfonic acid, 0.5% γ-glycidyloxypropyltrimethoxysilane and 96.5% deionized water.

[0037] like Figure 1 As shown, the preparation method of the high resilience and high flame retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double network hydrogen bond structure hybrid aerogel is as follows:

[0038] S1. Dissolve benzoxazine resin in N,N-dimethylformamide. After complete dissolution, add ammonium polyphosphate and p-toluenesulfonic acid aqueous solution. Ring-open the benzoxazine resin in the p-toluenesulfonic acid aqueous solution and undergo polymerization reaction with ammonium polyphosphate. Stir the reaction at low speed at room temperature for 0.5-1 hour.

[0039] S2, adding the nanocellulose suspension to the precursor system, and slowly raising the temperature of the reaction system to 90°C;

[0040] S3. After the temperature of the reaction system rises to 90°C, continue to add an appropriate amount of γ-glycidyloxypropyltrimethoxysilane to the precursor system and react at 90-95°C with high-speed stirring for 1-2 hours;

[0041] S4. Add polyvinyl alcohol to the precursor system and react at 90-95°C with high-speed stirring for 1-1.5 hours to cause a cross-linking reaction of the double-network hydrogen bond structure in the entire system;

[0042] S5. After the temperature of the reaction system drops to room temperature, continue stirring at a low speed for 0.2-0.5 hours. After stirring, add n-octanol to the solution to eliminate bubbles. After quick freezing in a refrigerator for 12 hours, place it in a freeze dryer for 48 hours.

[0043] In the above method steps, the mass ratio of nanocellulose to benzoxazine is 2:1-3:1, the mass ratio of benzoxazine to ammonium polyphosphate is 1:1, the mass ratio of p-toluenesulfonic acid in the entire system is 1%, the mass fraction of the nanocellulose dispersion is 1-1.5%, the ultrasonic oscillation time is 20 minutes, the power is 400w, the amount of silane coupling agent is 1% of the entire system, the low-speed stirring is 200-250r / min, the high-speed stirring is 450-550r / min, and the water is deionized water.

[0044] Attachment Figure 1 The preparation method of nanocellulose-polyvinyl alcohol aerogel and nanocellulose / modified benzoxazine-polyvinyl alcohol double network hybrid aerogel is included. The preparation process of nanocellulose / benzoxazine-polyvinyl alcohol double network hybrid aerogel does not include the addition of ammonium polyphosphate, and the other steps are consistent with the sample preparation of modified benzoxazine. Figure 2 The limiting oxygen index is an important parameter in flame retardancy testing, which mainly evaluates the volume fraction of oxygen required for a composite material to maintain combustion in a mixture of nitrogen and oxygen. According to the GB2406-80 test standard, the test results show that the limiting oxygen index of cellulose-polyvinyl alcohol aerogel (CNF-PVA), nanocellulose / benzoxazine-polyvinyl alcohol double network hybrid aerogel (CNF / BZ-PVA), and nanocellulose / modified benzoxazine-polyvinyl alcohol double network hybrid aerogel (CNF / BZA-PVA) are 19.5%, 23.5%, and 34.5%, respectively. It can be seen that cellulose-polyvinyl alcohol aerogel is a flammable material (<22%), while the oxygen index of nanocellulose / benzoxazine-polyvinyl alcohol double network hybrid aerogel has a significant improvement effect, which is attributed to the heat resistance and flame retardant effect of benzoxazine, and the polymer reaches the flammable level (22%-27%). However, hybrid aerogel samples with a double-network hydrogen-bonded structure containing modified benzoxazine required a higher volume of oxygen under the same oxygen and nitrogen concentration conditions, exceeding the flame retardant level (>27%). This shows that modified benzoxazine has excellent flame retardancy, far exceeding the requirements for ultra-flame-retardant materials.

[0045] Attachment Figure 3 The stress curves of nanocellulose-polyvinyl alcohol (Figure a) and nanocellulose / modified benzoxazine-polyvinyl alcohol double network hybrid aerogel (Figure b) under 60% strain are shown. It can be seen that when the strain is 60%, the compression rebound rate of nanocellulose-polyvinyl alcohol aerogel is only about 5%, while the compression rebound rate of nanocellulose / modified benzoxazine-polyvinyl alcohol double network hybrid aerogel under the same conditions is close to 99%. Therefore, the addition of modified benzoxazine has a significant effect on improving the mechanical properties of the composite aerogel.

[0046] Although the present invention has been described above with reference to embodiments, various modifications may be made thereto and equivalent components may be substituted without departing from the scope of the present invention. In particular, as long as there are no structural conflicts, the various features of the embodiments disclosed herein may be combined with each other in any manner, and the omission of an exhaustive description of such combinations in this specification is solely for the sake of space and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel, characterized in that: The raw materials for preparing high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel include: nanocellulose suspension, benzoxazine, ammonium polyphosphate, p-toluenesulfonic acid, γ-glycidyloxypropyltrimethoxysilane, polyvinyl alcohol and water; The preparation steps are as follows: S1. Dissolve benzoxazine in N,N-dimethylformamide. After complete dissolution, add ammonium polyphosphate and p-toluenesulfonic acid aqueous solution. Ring-opening of benzoxazine in the p-toluenesulfonic acid aqueous solution and polymerization reaction with ammonium polyphosphate are carried out. The reaction is stirred at low speed at room temperature for 0.5-1 hour. S2, adding the nanocellulose suspension to the precursor system, and slowly raising the temperature of the reaction system to 90°C; S3. After the temperature of the entire reaction system rises to 90°C, continue to add an appropriate amount of γ-glycidyloxypropyltrimethoxysilane to the precursor system and react at 90-95°C with high-speed stirring for 1-2 hours; S4. Add polyvinyl alcohol to the precursor system and react at 90-95°C with high-speed stirring for 1-1.5 hours to cause a cross-linking reaction of the double-network hydrogen bond structure in the entire system; S5. After the temperature of the reaction system drops to room temperature, continue stirring at a low speed for 0.2-0.5 hours. After stirring, add n-octanol to the solution to eliminate bubbles. Quick-freeze in a refrigerator at -80°C for 12 hours to complete cross-linking, and finally place in a freeze dryer for 48 hours.

2. The method for preparing a high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel according to claim 1, characterized in that: In step S2, the mass fraction of the nanocellulose suspension is 1-1.5%, the ultrasonic oscillation time is 20 minutes, and the power is 400W.

3. The method for preparing a high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel according to claim 1, characterized in that: The low-speed stirring is 200-250 r / min, and the high-speed stirring is 450-550 r / min.

4. The method for preparing a high-resilience and high-flame-retardant nanocellulose / modified benzoxazine-polyvinyl alcohol double-network hybrid aerogel according to claim 1, characterized in that: The water is deionized water.

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