A biomass aerogel-based thermal insulation and flame retardant material and its preparation method

Abstract

This invention discloses a biomass aerogel-based thermal insulation and flame retardant material and its preparation method. The invention involves sequentially mixing a lignocellulosic fiber suspension, a carboxymethyl cellulose nanoparticle suspension, and MOF nanoparticles, followed by directional freezing and freeze-drying to obtain the biomass aerogel-based thermal insulation and flame retardant material. The biomass aerogel-based thermal insulation and flame retardant material prepared by this invention exhibits low density, high porosity, and low thermal conductivity. Compared to other biomass-based thermal insulation and flame retardant materials, the aerogel obtained by this invention loads MOF nanoparticles into the lignocellulosic fiber network through a carboxymethyl cellulose nanoparticle "bridging" process. This avoids the self-aggregation of MOF nanoparticles and introduces a rich mesoporous structure into the aerogel, thereby endowing it with excellent flame retardant properties while reducing the thermal conductivity of the aerogel, showing great application potential in the field of energy-saving buildings.

Description

Technical Field

[0001] This invention relates to the field of heat-insulating and flame-retardant material preparation technology, specifically to a biomass aerogel-based heat-insulating and flame-retardant material and its preparation method. Background Technology

[0002] With increasing societal focus on energy efficiency and environmental sustainability, the construction, industrial, and energy sectors urgently need high-performance thermal insulation and flame-retardant materials to reduce heat conduction and loss, improve energy efficiency, and lower energy consumption and carbon emissions. Currently, most commercially available thermal insulation and flame-retardant materials are polymer foams and mineral wool, which typically have high thermal conductivity, low flame-retardant properties, and are prone to producing toxic gases during combustion and are not biodegradable. Therefore, developing a novel thermal insulation and flame-retardant material with low thermal conductivity, good flame-retardant properties, and biodegradability has become a research hotspot.

[0003] Due to the inherent complex porous structure of aerogels, which can reduce heat flow rates, and the abundance and biodegradability of cellulose, biomass-based aerogels made from cellulose have attracted widespread attention for thermal insulation. However, due to the inherent flammability of cellulose fibers, the prepared aerogels may burn at high temperatures, potentially causing a fire. To address this issue, flame retardants need to be added to cellulose aerogels. Metal-organic frameworks (MOFs), as a class of organic-inorganic hybrid materials with high porosity, excellent thermal stability, and abundant microporous structures, have good application potential in thermal insulation and flame retardancy. However, the processing and molding of MOF nanoparticles presents certain difficulties. Therefore, combining MOF nanoparticles with cellulose aerogels can achieve a win-win effect. In related research, researchers prepared CNF-MOF aerogels by directly blending nanocellulose filaments with MOF nanoparticles. However, since MOF nanoparticles cannot form an interconnected network with CNFs, they cannot effectively protect CNFs during combustion, and the resulting aerogels do not possess flame-retardant properties. While in-situ growth of MOFs onto the surface of cellulose fibers can improve the flame retardancy of aerogels, it also increases the thermal conductivity, which negatively impacts their thermal insulation performance. Furthermore, in-situ growth methods are typically complex, requiring chemical modification of the fibers and the addition of extra cross-linking agents, thus increasing production costs and causing environmental pollution. Therefore, there is a need to design a biomass aerogel-based insulation material that achieves a balance between thermal insulation and flame retardancy, meeting the demands of high-performance thermal insulation and flame retardant materials in the construction, industrial, energy, and transportation sectors. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention discloses a biomass aerogel-based thermal insulation and flame retardant material and its preparation method. This invention involves mixing lignocellulose, carboxymethyl cellulose nanoparticles, and metal-organic framework (MOF) nanoparticles, followed by directional freezing and freeze-drying to obtain the biomass aerogel-based thermal insulation and flame retardant material. The biomass aerogel-based thermal insulation and flame retardant material prepared by this invention has a low density (21.0 mg / cm³). 3 -35.1mg / cm 3 It possesses high porosity (97.8%-98.6%) and low thermal conductivity (30.6 mW / m / K-53.5 mW / m / K). Compared to other biomass-based thermal insulation and flame retardant materials, the aerogel obtained in this invention loads MOF nanoparticles into a wood fiber network through a carboxymethyl cellulose nanoparticle "bridging" process. This avoids the self-aggregation of MOF nanoparticles and introduces a rich mesoporous structure into the aerogel, thereby endowing it with excellent flame retardant properties while reducing its thermal conductivity, showing great application potential in the field of energy-saving buildings.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A biomass aerogel is made from wood fibers, with carboxymethyl cellulose nanoparticles grafted onto the wood fibers and metal-organic framework (MOF) nanoparticles loaded in the carboxymethyl cellulose nanoparticles.

[0007] The method for preparing a biomass aerogel involves using lignocellulose as raw material to prepare a lignocellulose suspension, then sequentially adding carboxymethyl cellulose nanoparticles and MOF nanoparticles to the lignocellulose suspension, mixing and stirring, followed by directional freezing and freeze-drying to obtain the aerogel.

[0008] The wood fiber is bagasse, rice straw, or aloe vera fiber, with a diameter of 10-100 nm, and the wood fiber suspension has a mass fraction of 1-4%.

[0009] The carboxymethyl cellulose nanoparticles have a diameter of 4–10 nm, a carboxymethyl content of 1.2–3.0 mmol / g, a carboxymethyl cellulose nanoparticle suspension mass fraction of 1%, and an addition amount of carboxymethyl cellulose of 10–30 wt% of the oven-dry weight of the wood fibers.

[0010] The amount of MOF nanoparticles added is 2.5 to 50 wt% of the oven-dry weight of the wood fibers.

[0011] The directional freezing conditions are as follows: the directional freezing angle is 0°, the freezing source is liquid nitrogen, and the freezing time is 20 to 50 minutes.

[0012] The freeze-drying is carried out in a freeze dryer under the following conditions: temperature -98.5 to -60°C, pressure 14 to 35 Pa, and freeze-drying time 36 to 72 hours.

[0013] The MOF nanoparticles are of type MIL-53(Al).

[0014] The application of a biomass aerogel in heat insulation and flame retardancy.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The biomass aerogel-based heat insulation and flame retardant material prepared by the present invention has a highly ordered vertically arranged pore structure that is not connected to each other in the axial direction to effectively reduce heat convection during the heat conduction process, thereby improving the heat insulation performance of the aerogel.

[0017] (2) The biomass aerogel-based heat-insulating and flame-retardant material prepared in this invention has a low density (21.0~35.1mg / cm³). 3 High porosity (97.7–98.5%).

[0018] (3) The aerogel obtained in this invention loads MOF nanoparticles into the aerogel network structure through carboxymethyl cellulose nanoparticles (CMNC) bridging, which not only imparts flame retardancy to it but also further reduces the thermal conductivity (30.6 mW / m / K) of the biomass aerogel-based heat insulation and flame retardant material, showing great application prospects in the field of energy-saving buildings.

[0019] (4) This invention can use agricultural and forestry waste as raw materials to prepare wood fiber through mechanical pulping, and is not affected by the source of raw materials. Attached Figure Description

[0020] Figure 1 This is a photograph of the actual sample from Example 3.

[0021] Figure 2 The temperature change of the sample obtained in Example 3 after heating on a heating table at 250°C for 30 minutes. Detailed Implementation

[0022] The present invention will be further illustrated below with reference to embodiments, but these should not be construed as limiting the invention. Simple modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and substance of the invention are all within the scope of the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0023] Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0024] In the following examples, the carboxymethyl cellulose nanoparticles have a diameter of 4–10 nm. The metal-organic framework (MOF) nanoparticles used are of type MIL-53(Al).

[0025] Example 1

[0026] This embodiment is an example of a method for preparing biomass aerogel according to the present invention. The specific steps are as follows:

[0027] S1. Prepare a lignocellulose suspension with a mass fraction of 1 wt%;

[0028] S2. Add a carboxymethyl cellulose nanoparticle suspension with a solid content of 1 wt% (carboxymethyl content of 1.2 mmol / g) and MOF nanoparticles sequentially to the lignocellulosic suspension obtained in step S4, and stir at room temperature for 15 min; the amount of carboxymethyl cellulose added is 10 wt% of the dry weight of the lignocellulosic fiber; the amount of MOF nanoparticles added is 2.5 wt% of the dry weight of the lignocellulosic fiber; adjust the concentration of the lignocellulosic suspension to 1 wt%.

[0029] S3. Freeze the mixed solution obtained in step S5 in a directional freezing device. The directional freezing conditions are: freezing angle 0°, freezing source is liquid nitrogen, freezing time is 20 min; after directional freezing, place it in a freeze dryer for freeze drying. The freeze drying conditions are: -60.0℃, 35 Pa, freeze drying for 36 h.

[0030] The density of the biomass aerogel-based thermal insulation and flame retardant material prepared in this embodiment was determined by weighing at room temperature and pressure, and its density at room temperature and pressure was 23.8 mg / cm³. 3 .

[0031] The porosity of the biomass aerogel-based thermal insulation material prepared in this embodiment was determined by mass density method at room temperature and pressure, and the porosity at room temperature and pressure was 98.4%.

[0032] The pore size of the biomass aerogel-based heat-insulating and flame-retardant material prepared in this embodiment was determined by mercury porosimetry, and the pore size was 8.9 μm.

[0033] The biomass aerogel-based thermal insulation and flame retardant material prepared in this embodiment was tested for its heat release and smoke emission during combustion using a cone calorimeter. The heat release and smoke emission were both 10.2 mJ / m³. 2 and 10.7m 2 .

[0034] The biomass aerogel-based heat-insulating and flame-retardant material (1.5 cm thick) prepared in this embodiment was placed on a 250°C heating platform and the change in the top temperature during the heating process was recorded. After heating for 30 minutes, the top temperature rose to 69.5°C.

[0035] The thermal conductivity of the biomass aerogel-based heat-insulating and flame-retardant material prepared in this embodiment was measured using a thermal conductivity meter, and the thermal conductivity was 42.0 mW / m / K.

[0036] Example 2

[0037] A method for preparing a biomass aerogel-based thermal insulation and flame retardant material, comprising the following specific steps:

[0038] S1. Prepare a 2 wt% lignocellulose suspension;

[0039] S2. Add a carboxymethyl cellulose nanoparticle suspension with a solid content of 1 wt% (carboxymethyl content of 1.8 mmol / g) and MOF nanoparticles sequentially to the lignocellulosic suspension obtained in step S4, and stir at room temperature for 20 min; the amount of carboxymethyl cellulose added is 15 wt% of the dry weight of the lignocellulosic fiber; the amount of MOF nanoparticles added is 10 wt% of the dry weight of the lignocellulosic fiber; adjust the concentration of the lignocellulosic suspension to 1.5 wt%.

[0040] S3. Freeze the mixed solution obtained in step S5 in a directional freezing device. The directional freezing conditions are: freezing angle 0°, freezing source is liquid nitrogen, freezing time is 30 min; after directional freezing, place it in a freeze dryer for freeze drying. The freeze drying conditions are: -75.0℃, 30 Pa, freeze drying for 48 h.

[0041] The density of the biomass aerogel-based thermal insulation and flame retardant material prepared in this embodiment was determined by weighing at room temperature and pressure, and its density at room temperature and pressure was 22.1 mg / cm³. 3 .

[0042] The porosity of the biomass aerogel-based thermal insulation material prepared in this embodiment was determined by mass density method at room temperature and pressure, and the porosity at room temperature and pressure was 98.5%.

[0043] The pore size of the biomass aerogel-based heat-insulating and flame-retardant material prepared in this embodiment was determined by mercury porosimetry, and the pore size was 9.5 μm.

[0044] The biomass aerogel-based thermal insulation and flame retardant material prepared in this embodiment was tested for its heat release and smoke emission during combustion using a cone calorimeter. The heat release and smoke emission were 55.8 mJ / m³. 2 and 5.7m 2 .

[0045] The biomass aerogel-based heat-insulating and flame-retardant material (1.5 cm thick) prepared in this embodiment was placed on a 250°C heating platform and the change in the top temperature during the heating process was recorded. After heating for 30 minutes, the top temperature rose to 72.6°C.

[0046] The thermal conductivity of the biomass aerogel-based heat-insulating and flame-retardant material prepared in this embodiment was measured using a thermal conductivity meter, and the thermal conductivity was 40.2 mW / m / K.

[0047] Example 3

[0048] A method for preparing a biomass aerogel-based thermal insulation and flame retardant material, comprising the following specific steps:

[0049] S1. Prepare a 3 wt% lignocellulose suspension;

[0050] S2. Add a carboxymethyl cellulose nanoparticle suspension with a solid content of 1 wt% (carboxymethyl content of 2.5 mmol / g) and MOF nanoparticles sequentially to the lignocellulosic suspension obtained in step S4, and stir at room temperature for 40 min; the amount of carboxymethyl cellulose added is 20 wt% of the dry weight of the lignocellulosic fiber; the amount of MOF nanoparticles added is 10 wt% of the dry weight of the lignocellulosic fiber; adjust the concentration of the lignocellulosic suspension to 2.0 wt%.

[0051] S3. Freeze the mixed solution obtained in step S5 in a directional freezing device. The directional freezing conditions are: freezing angle 0°, freezing source is liquid nitrogen, freezing time is 40 min; after directional freezing, place it in a freeze dryer for freeze drying. The freeze drying conditions are: -90.0℃, 25 Pa, freeze drying for 60 h.

[0052] The density of the biomass aerogel-based thermal insulation and flame retardant material prepared in this embodiment was determined by weighing at room temperature and pressure, and its density at room temperature and pressure was 21.0 mg / cm³. 3 .

[0053] The porosity of the biomass aerogel-based thermal insulation material prepared in this embodiment was determined by mass density method at room temperature and pressure, and the porosity at room temperature and pressure was 98.6%.

[0054] The pore size of the biomass aerogel-based heat-insulating and flame-retardant material prepared in this embodiment was determined by mercury porosimetry, and the pore size was 11.5 μm.

[0055] The biomass aerogel-based thermal insulation and flame retardant material prepared in this embodiment was tested for its heat release and smoke emission during combustion using a cone calorimeter. The heat release and smoke emission were 4.0 mJ / m³. 2 and 0.5m 2 .

[0056] The biomass aerogel-based heat-insulating and flame-retardant material (1.5 cm thick) prepared in this embodiment was placed on a 250°C heating platform and the change in the top temperature during the heating process was recorded. After heating for 30 minutes, the top temperature rose to 50.2°C.

[0057] The thermal conductivity of the biomass aerogel-based heat-insulating and flame-retardant material prepared in this embodiment was measured by a thermal conductivity meter, and the thermal conductivity was 30.6 mW / m / K.

[0058] Example 4

[0059] A method for preparing a biomass aerogel-based thermal insulation and flame retardant material, comprising the following specific steps:

[0060] S1. Prepare a lignocellulose suspension with a mass fraction of 4 wt%;

[0061] S2. Add a carboxymethyl cellulose nanoparticle suspension with a solid content of 1 wt% (carboxymethyl content of 3.0 mmol / g) and MOF nanoparticles sequentially to the lignocellulosic suspension obtained in step S4, and stir at room temperature for 60 min; the amount of carboxymethyl cellulose added is 30 wt% of the dry weight of the lignocellulosic fiber; the amount of MOF nanoparticles added is 50 wt% of the dry weight of the lignocellulosic fiber; adjust the concentration of the lignocellulosic suspension to 3 wt%.

[0062] S3. Freeze the mixed solution obtained in step S5 in a directional freezing device. The directional freezing conditions are: freezing angle 0°, freezing source is liquid nitrogen, freezing time is 50 min; after directional freezing, place it in a freeze dryer for freeze drying. The freeze drying conditions are: -98.5℃, 14 Pa, freeze drying for 72 h.

[0063] The density of the biomass aerogel-based thermal insulation and flame retardant material prepared in this embodiment was determined by weighing at room temperature and pressure, and its density at room temperature and pressure was 35.1 mg / cm³. 3 .

[0064] The porosity of the biomass aerogel-based thermal insulation material prepared in this embodiment was determined by mass density method at room temperature and pressure, and the porosity at room temperature and pressure was 97.8%.

[0065] The pore size of the biomass aerogel-based heat-insulating and flame-retardant material prepared in this embodiment was determined by mercury porosimetry, and the pore size was 10.1 μm.

[0066] The biomass aerogel-based thermal insulation and flame retardant material prepared in this embodiment was tested for its heat release and smoke emission during combustion using a cone calorimeter. The heat release and smoke emission were 5.3 mJ / m³. 2 and 1.5m 2.

[0067] The biomass aerogel-based heat-insulating and flame-retardant material (1.5 cm thick) prepared in this embodiment was placed on a 250°C heating platform and the change in the top temperature during the heating process was recorded. After heating for 30 minutes, the top temperature rose to 85.3°C.

[0068] The thermal conductivity of the biomass aerogel-based heat-insulating and flame-retardant material prepared in this embodiment was measured using a thermal conductivity meter, and the thermal conductivity was 53.3 mW / m / K.

[0069] Comparative Example 1

[0070] Unlike Example 2, this comparative example did not perform step S2, but all other steps and conditions were the same as in Example 2.

[0071] The density of the biomass aerogel-based thermal insulation and flame retardant material prepared in this embodiment was determined by weighing at room temperature and pressure, and its density at room temperature and pressure was 60.5 mg / cm³. 3 .

[0072] The porosity of the biomass aerogel-based thermal insulation material prepared in this embodiment was determined by mass density method at room temperature and pressure, and the porosity at room temperature and pressure was 89.7%.

[0073] The pore size of the biomass aerogel-based heat-insulating and flame-retardant material prepared in this embodiment was determined by mercury porosimetry, and the pore size was 3.5 μm.

[0074] The biomass aerogel-based thermal insulation and flame retardant material prepared in this embodiment was tested for its heat release and smoke emission during combustion using a cone calorimeter. The heat release and smoke emission were 88.2 mJ / m³. 2 and 42m 2 .

[0075] The biomass aerogel-based heat-insulating and flame-retardant material (1.5 cm thick) prepared in this embodiment was placed on a 250°C heating platform and the change in the top temperature during the heating process was recorded. After heating for 30 minutes, the top temperature rose to 100°C.

[0076] The thermal conductivity of the biomass aerogel-based heat-insulating and flame-retardant material prepared in this embodiment was measured using a thermal conductivity meter, and the thermal conductivity was 90.3 mW / m / K.

[0077] The table below compares the density, porosity, pore size, heat release, flue gas emission, temperature change, and thermal conductivity of the heat-insulating and flame-retardant materials prepared in Examples 1-4 and Comparative Example 1.

[0078] project Example 1 Example 2 Example 3 Example 4 Comparative Example 1 <![CDATA[Density (mg / cm 3 )]]> 23.8 22.1 21.0 35.1 60.5 Porosity (%) 98.4 98.5 98.6 97.8 89.7 Aperture (μm) 8.9 9.5 11.5 10.1 3.5 <![CDATA[Heat release rate (mJ / m 2 )]]> 10.2 55.8 4.0 5.3 88.2 <![CDATA[Flue gas emission (m 2 )]]> 10.7 5.7 0.5 1.5 42.0 Temperature change (°C) 69.5 72.6 50.2 85.3 100 Thermal conductivity (mW / m / K) 42 40.2 30.6 53.3 90.3

[0079] The technical principle of this invention is as follows: A biomass aerogel-based thermal insulation and flame retardant material with an anisotropic structure is rationally designed by "bridging" MOF nanoparticles and wood fibers with carboxymethyl cellulose nanoparticles (CMNC) through directional freezing and freeze-drying. Key parameters were systematically studied. Compared to disordered structures, the anisotropic aerogel structure can suppress thermal localization and reduce heat flow in directions with lower thermal conductivity, thereby further reducing the thermal conductivity of the aerogel. Secondly, the abundant active groups (hydroxyl / carboxyl groups) and nanoscale diameter (4-10 nm) on the CMNC surface act as a "bridge," embedding MIL-53(Al) nanoparticles into the fiber network structure through coordination bonds, hydrogen bonds, and electrostatic adsorption, thus preventing the self-aggregation of MOF nanoparticles. With the increase of MOF nanoparticle content, the thermal conductivity of the aerogel shows a trend of first decreasing and then increasing. This is because, on the one hand, the intermolecular interactions between cellulose nanofibers and MOF nanoparticles can reflect and scatter phonons, thereby reducing thermal conductivity; on the other hand, the mesopore size of MOF nanoparticles is significantly lower than the path of freedom (70 nm) of common gases in air, further limiting gas thermal conductivity. However, when the MOF nanoparticle content is increased to 50%, the inherent high thermal conductivity of MOF nanoparticles leads to agglomeration and an increase in aerogel density, resulting in a decrease in thermal insulation performance. Furthermore, due to the strong intermolecular interactions between MOF nanoparticles and wood fibers, the aerogel can acquire good flame retardancy during combustion by forming a char layer and highly thermally stable alumina.

Claims

1. A biomass aerogel, characterized in that, Using wood fiber as raw material, carboxymethyl cellulose nanoparticles are grafted onto the wood fiber, and MOF nanoparticles are loaded in the carboxymethyl cellulose nanoparticles. The preparation method of the biomass aerogel is as follows: a lignocellulose suspension is prepared using lignocellulose as raw material; carboxymethyl cellulose nanoparticle suspension and MOF nanoparticles are sequentially added to the lignocellulose suspension, mixed and stirred, and then obtained by directional freezing and freeze-drying; the MOF nanoparticles are... .

2. The method for preparing the biomass aerogel according to claim 1, characterized in that, The wood fiber is bagasse, rice straw, or aloe vera fiber, with a diameter of 10–100 nm, and the wood fiber suspension has a mass fraction of 1–4%.

3. The method for preparing the biomass aerogel according to claim 1, characterized in that, The carboxymethyl cellulose nanoparticles have a diameter of 4–10 nm, a carboxymethyl content of 1.2–3.0 mmol / g, a carboxymethyl cellulose nanoparticle suspension mass fraction of 1%, and an addition amount of carboxymethyl cellulose of 10–30 wt% of the oven-dry weight of the wood fibers.

4. The method for preparing the biomass aerogel according to claim 1, characterized in that, The amount of MOF nanoparticles added is 2.5 to 50 wt% of the oven-dry weight of the wood fibers.

5. The method for preparing the biomass aerogel according to claim 1, characterized in that, The directional freezing conditions are as follows: the directional freezing angle is 0°, the freezing source is liquid nitrogen, and the freezing time is 20 to 50 minutes.

6. The method for preparing the biomass aerogel according to claim 1, characterized in that, The freeze-drying is carried out in a freeze dryer under the following conditions: temperature [temperature value missing]. The pressure is 14–35 Pa, and the freeze-drying time is 36–72 h.

7. The application of the biomass aerogel according to claim 1 in heat-insulating and flame-retardant materials.

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