Green template self-assembled cement aerogel material and preparation method thereof

Abstract

The invention provides a green template self-assembly cement aerogel material and a preparation method thereof, and belongs to the technical field of building materials, the green template self-assembly cement aerogel material comprises a skeleton material and C-S-H gel nanoparticles attached to the skeleton material; the framework material comprises carboxylated nanocellulose; the density of the green template self-assembled cement aerogel material is 120-160 kg / m < 3 >, the porosity is 90%-95%, and the heat conductivity coefficient is 0.03-0.042 W / mK. According to the invention, carboxylated nano-cellulose is utilized to provide nucleation sites for the growth of C-S-H gel and perform highly ordered self-assembly, and C-S-H nanoparticles are tightly embedded into a cellulose skeleton under the complexation of Ca < 2 + > to form a bionic structure, so that the mechanical properties of the material are greatly improved, and meanwhile, the defect of flammability caused by exposure of cellulose in air is overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and particularly relates to a green template self-assembled cement aerogel material and a preparation method thereof. Background Art

[0002] Thermal insulation materials can effectively reduce heat transfer, reduce the energy consumption of winter heating and summer cooling, maintain a stable indoor temperature, and thus improve the living comfort. It can significantly reduce energy consumption and environmental pollution. Currently, commercially available conventional thermal insulation cotton includes expanded polystyrene, expanded polyurethane, rock wool, glass wool, etc., but most of them have defects such as non-biodegradability, poor thermal insulation performance, and flammability.

[0003] Compared with traditional thermal insulation materials, cellulose aerogel has performance advantages such as biodegradability, low thermal conductivity, and low cost. Its base material cellulose is the most abundant organic polymer on the earth, which is green and renewable. Although cellulose aerogel has excellent heat insulation performance, it has disadvantages such as flammability, low mechanical strength, and strong hygroscopicity as a building thermal insulation material. People have tried methods such as introducing chemical cross-linking agents (such as epoxy resin, polydopamine, etc.), nano-material composites (such as graphene, carbon nanotubes, silica nanoparticles), adding flame retardants (such as aluminum hydroxide, phosphate), etc., but the improvement effect is limited and the cost is high. This limits its application in the construction field.

[0004] Cement, as the most widely used building material in the world, has characteristics such as high mechanical strength, high temperature resistance, and strong durability, which can perfectly make up for the disadvantages of cellulose aerogel itself. However, when cellulose and cement components are compounded, the following problems are still faced: cellulose is prone to agglomeration in the cement matrix and is difficult to disperse evenly; the interfacial adhesion between cellulose fibers and the cement matrix is weak; excessive cellulose may introduce pores, reducing the density and strength of the material; the cellulose components from different sources vary greatly, which may lead to fluctuations in the performance of the composite material. Therefore, how to fully compound cellulose and cement components and improve the material performance is particularly important. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present invention provides a green template self-assembled cement aerogel material and a preparation method thereof, aiming to solve the technical problems that cellulose is prone to agglomeration, the interfacial adhesion between cellulose and cement is weak, and the mechanical properties of cellulose cement-based composites are limited in improvement in the existing cellulose cement-based composites.

[0006] In the first aspect, the present invention provides a green template self-assembled cement aerogel material. The green template self-assembled cement aerogel material includes a skeleton material and C-S-H gel nanoparticles attached to the skeleton material; the skeleton material includes carboxylated nanocellulose; the density of the green template self-assembled cement aerogel material is 120~160 kg / m3 , porosity is 90%~95%, and thermal conductivity is 0.03~0.042W / mK.

[0007] Preferably, the cross-sectional diameter of the carboxylated nanocellulose is 5-10 nm, the length is 500-1000 nm, and the aspect ratio is (50:1)-(200:1).

[0008] In a second aspect, the present invention provides a method for preparing a green template self-assembled cement aerogel material, comprising the following steps: Under stirring conditions, calcium salt solution and silicate solution were added dropwise to the carboxylated nanocellulose suspension, and the suspension was allowed to stand at room temperature and then placed in a solvent for aging treatment. After washing, freezing and drying, a green template self-assembled cement aerogel material was obtained.

[0009] Preferably, the concentration of the carboxylated nanocellulose suspension is 0.75 wt% to 1.25 wt%; The mass ratio of carboxylated nanocellulose to calcium salt is 1:(5~13).

[0010] Preferably, the molar ratio of calcium to silicon in the calcium salt solution and the silicate solution is (0.8-2):1.

[0011] Preferably, the calcium salt solution includes a Ca(NO3)2 solution, and the silicate solution includes a Na2SiO3 solution.

[0012] Preferably, the standing time at room temperature is 12 to 24 hours.

[0013] Preferably, the solvent includes any one of water, ethanol, acetone, and tert-butanol; and the aging time is 24 h to 48 h.

[0014] Preferably, the drying method is freeze drying, and the freeze drying conditions are: temperature of -100 to -50°C, pressure of 1 to 10 Pa, and freeze drying time of 36 to 48 hours.

[0015] Preferably, the stirring condition is specifically: the stirring rate is 100-200 r / min.

[0016] The principle of the technical solution of the present invention is: The orderly combination of collagen fibers and inorganic minerals (hydroxyapatite) in the hard tissue of teeth forms a continuous mineralized network, which gives teeth excellent mechanical properties (such as hardness and toughness). Among them, collagen fibers provide a template for mineralization, and mineral crystals are oriented along the long axis of collagen fibers. This combination method, similar to reinforced concrete, forms a highly ordered organic-inorganic composite structure. Inspired by this process, the present invention utilizes the morphological effect of nanocellulose and its effect on Ca 2+The complexing effect can provide nucleation sites for the crystallization and growth of C-S-H (calcium silicate hydrate). C-S-H nanoparticles are self-assembled in a nanocellulose solution. During the self-assembly process, Ca 2+ is complexed in the carboxylated nanocellulose framework, and SiO4 2- Using this as a template, C-S-H gel nanoparticles are in-situ grown. After the cellulose chains are cross-linked with each other, a three-dimensional network structure is formed. This bionic structure optimizes and solves the contradiction between high mechanical strength and high porosity, and also endows the aerogel with excellent fireproof and flame-retardant properties.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The green template self-assembled cement aerogel material provided by the present invention selects nanocellulose, which is widely sourced, easily degradable, and renewable, as the raw material, and has a simple and green preparation process, avoiding the defects of difficult degradation of raw materials and toxic by-products in traditional thermal insulation materials. Among them, carboxylated nanocellulose provides nucleation sites for the growth of C-S-H gel and undergoes highly ordered self-assembly. This bonding method similar to reinforced concrete ensures the high mechanical properties of the material; -COO - and -OH in carboxylated nanocellulose respectively form ionic bonds and coordination bonds under the action of Ca 2+ to make the nanocellulose chains overlap with each other to establish a three-dimensional network structure. The material has an extremely high porosity, greatly reducing the thermal conductivity of the material. Calcium silicate hydrate particles are tightly combined with the nanocellulose chains under the action of hydrogen bonds and are densely arranged to form a fireproof barrier, solving the defect of flammability when cellulose is used as a thermal insulation material. The high Young's modulus (100 - 150 GPa) and high aspect ratio of nanocellulose endow the material with excellent flexibility, enabling the material to be applicable to irregular spaces and curved structures, improving the design freedom and construction convenience. Description of the Drawings

[0018] Figure 1 is the scanning electron microscope image of the green template self-assembled cement aerogel material in Example 1 of the present invention; Figure 2 is the partially enlarged scanning electron microscope image of the green template self-assembled cement aerogel material in Example 1 of the present invention; Figure 3 is the transmission electron microscope image of the green template self-assembled cement aerogel material in Example 1 of the present invention; Figure 4 is the compression stress-strain curve of the green template self-assembled cement aerogel material in Example 1 of the present invention; Figure 5 is the combustion test result image of the green template self-assembled cement aerogel material in Example 1 of the present invention; Figure 6This is the compression stress-strain curve of the green template self-assembled cement aerogel material in Example 2 of the present invention. Detailed Implementation Modes

[0019] Hereinafter, embodiments of the technical solutions of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, and thus are only examples and cannot be used to limit the protection scope of the present invention.

[0020] For those technical or conditions not specified in the embodiments, they shall be in accordance with the technologies or conditions described in the literature in this field or in accordance with the product specifications. For the reagents or instruments not indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase or commonly used in this field.

[0021] In the following embodiments of the present invention, the carboxylated nanocellulose was purchased from Nanjing Tianlu Nano Technology Co., Ltd. The cross-sectional diameter of the carboxylated nanocellulose is 5 - 10 nm, the length is 500 - 1000 nm, and the aspect ratio is (50∶1) - (200∶1).

[0022] I. Preparation Method Example 1 A preparation method of a green template self-assembled cement aerogel material, comprising the following steps: (1) Prepare 100 g of a carboxylated nanocellulose solution with a mass fraction of 1.2%, disperse it by ultrasonic treatment with an ultrasonic cell disruptor for 25 min, and let it stand at room temperature for 30 min to obtain a carboxylated nanocellulose suspension.

[0023] (2) Place the nanocellulose suspension on a magnetic stirrer and slowly stir at a rate of 160 r / min. Dropwise add 55 mL of a Ca(NO3)2 solution (1 mol / L) at a constant rate of 7 mL / min and 50 mL of a Na2SiO3 solution (1 mol / L) at a constant rate of 3 mL / min. After the addition is completed, let it stand at room temperature for 12 h. After the sample is aged in an ethanol solution for 1 d, wash it with deionized water three times to remove NaNO3 in the sample, soak it in liquid nitrogen for freezing, and after the freezing is completed, freeze-dry it for 36 h to obtain a cement-based aerogel induced by nanocellulose self-assembly.

[0024] The morphological characterization results of the green template self-assembled cement aerogel prepared by this method are as Figures 1-5 shown; Figure 1 、 Figure 2 are the scanning electron microscope images of the sample. It can be seen from the scanning electron Figure 1 microscope that the cement aerogel material presents a highly porous structure, the nanocellulose chains overlap with each other to form a three-dimensional network structure, and there are dense C-S-H gel particles aggregated and embedded on the cellulose chains. From the enlarged Figure 2It can be seen that the C-S-H gel is spherical and arranged orderly along the cellulose chain, with a particle size in the range of 10-20 nm. Figure 3 It is the transmission electron micrograph of the sample. It can be seen that the nanocellulose chains are intertwined into a network structure, and the surface of the cellulose chain is tightly wrapped by a layer of C-S-H gel, presenting a structure similar to that of steel bars - concrete. The organic flexible cellulose is reinforced by the inorganic rigid material, which brings an improvement in the mechanical properties of the material.

[0025] Example 2 A preparation method of a green template self-assembled cement aerogel material, comprising the following steps: 1) Prepare 100 g of a carboxylated nanocellulose solution with a mass fraction of 1%, disperse it by ultrasonic treatment with an ultrasonic cell disruptor for 10 min, and let it stand at room temperature for 30 min to obtain a carboxylated nanocellulose suspension.

[0026] 2) The nanocellulose suspension is slowly stirred in a magnetic stirrer at a rate of 150 r / min. A Ca(NO3)2 solution (1 mol / L) of 50 mL is added dropwise at a constant rate of 6 mL / min and a Na2SiO3 solution (1 mol / L) of 40 mL is added dropwise at a constant rate of 2.5 mL / min. After the addition is completed, it is left standing at room temperature for 12 h. After the sample is aged in an aqueous solution for 2 d, it is washed 3 times with deionized water to remove NaNO3 in the sample, soaked in liquid nitrogen for freezing, and freeze-dried for 40 h after freezing to obtain a cement-based aerogel induced by self-assembly of nanocellulose.

[0027] Comparative Example 1 The difference between this comparative example and Example 1 is that only the mass fraction of the carboxylated nanocellulose solution in step (1) is adjusted from 1.2% to 2.5%, and other preparation methods are the same as those in Example 1.

[0028] During the experiment, it was found that when the concentration of the nanocellulose solution was too high, when the Ca(NO3)2 solution was added dropwise at a constant rate, it would cause the cellulose solution to gelify rapidly. Shortly after the addition was completed, the reaction solution became solid, the molecules could not move freely, and it was even more impossible to in-situ grow calcium silicate hydrate particles along the cellulose chain template.

[0029] Comparative Example 2 The difference between this comparative example and Example 1 is that only "add a Ca(NO3)2 solution (1 mol / L) of 55 mL at a constant rate of 7 mL / min and a Na2SiO3 solution (1 mol / L) of 50 mL at a constant rate of 3 mL / min" in step (2) is changed to "add 55 mL of a Ca(NO3)2 solution (1 mol / L) and 50 mL of a Na2SiO3 solution (1 mol / L) at one time".

[0030] Comparative Example 3 The difference between this comparative example and Example 1 is that only the carboxylated nanocellulose in step (1) is replaced with uncarboxylated nanocellulose, and other preparation methods are the same as those in Example 1.

[0031] Comparative Example 4 The difference between this comparative example and Example 1 is that only the carboxylated nanocellulose in step (1) is replaced with polyvinyl alcohol. A 100 g polyvinyl alcohol solution with a mass fraction of 1.2% is prepared by magnetic stirring at 80 °C, and after returning to room temperature, the polyvinyl alcohol solution is obtained for use in step (2).

[0032] Comparative Example 5 The difference between this comparative example and Example 1 is that only "55 mL of Ca(NO3)2 solution (1 mol / L) and 50 mL of Na2SiO3 solution (1 mol / L)" in step (2) is replaced with "45 mL of Ca(NO3)2 solution (1 mol / L) and 60 mL of Na2SiO3 solution (1 mol / L)", that is, the calcium-silicon ratio is adjusted from 1.1 to 0.75.

[0033] II. Test methods The Nanosem430 field emission scanning electron microscope of Philips in the Netherlands is used to observe the microscopic morphology of the cement aerogel material prepared by the method of the present invention.

[0034] The FEI Tecnai G2 F20 transmission electron microscope (TEM) is used to observe the microscopic structure of the cellulose chain template and C-S-H gel. When preparing the sample, the cement aerogel powder is dispersed in absolute ethanol by an ultrasonic disperser, dropped on a carbon film copper mesh and dried.

[0035] A physical adsorption analyzer (ASAP2460, 77K) is used to obtain the nitrogen adsorption / desorption isotherm curve. Before the test, the sample is vacuum heated at 473 K for 10 hours to completely remove the physically adsorbed molecules in the sample. The pore size distribution of the sample is calculated by the BJH model.

[0036] The HFM300 thermal conductivity tester of Linseis in Germany is used to measure the thermal conductivity of the cement-based double-network aerogel material. First, the sample is dried at (105 ± 5) °C for 4 h; then it is cooled to room temperature for thermal conductivity measurement.

[0037] The compression performance of the aerogel sample is tested by Sansi in Shenzhen. The shape of the tested sample is a cylinder with a height of 1 cm and a diameter of 2 cm. The stress-strain curve is collected, and the elastic modulus of the sample is calculated through the curve.

[0038] The flame retardancy of the sample is tested by the direct observation method. The outer flame of a lighter is used to burn the sample, and the morphological changes of the sample are observed.

[0039] III. Analysis of Test Results of Each Example and Comparative Example The test results of the samples prepared in the examples and comparative examples are shown in Table 1.

[0040] Table 1

[0041] As can be seen from Table 1, the elastic modulus of the sample prepared in Example 1 reaches 8.75 MPa (calculated from the Figure 4 stress-strain curve), and the compressive strength reaches 4.16 MPa, showing an order-of-magnitude improvement compared with conventional cellulose aerogels. This structural form in which the organic material is wrapped by the inorganic material also changes the material from flammable to non-flammable. As Figure 5 shown, Figure 5 (a) is the state diagram of the material in Example 1 before combustion, Figure 5 (b) is the state diagram of the material in Example 1 after 5 minutes of combustion, improving the fire resistance. This benefits from the highly porous network structure formed by the overlapping of cellulose templates. The material density is only 151 kg / m 3 , the porosity reaches 92.4%, and the thermal conductivity is as low as 0.038 W / mK.

[0042] The physical properties of the sample prepared in Example 2 are also excellent. Its density is 132 kg / m 3 , the porosity reaches 93.1%, and the thermal conductivity is even as low as 0.036 W / mK. Limited by the raw material dosage, the mechanical properties decline. The elastic modulus is 5.83 Mpa (calculated from the Figure 6 stress-strain curve), and the compressive strength is 3.62 Mpa.

[0043] Although the material dosage of Comparative Example 2 is the same as that of Example 1, the dropping rate and sequence are changed, resulting in part of the Ca 2+ not being complexed on the cellulose chain to provide growth sites. The C-S-H gel is mostly suspended in the solution and precipitates on the surface of the template after drying, unable to provide mechanical support. The density and thermal conductivity decrease, the porosity increases, but the mechanical properties decrease significantly.

[0044] The density of the sample prepared in Comparative Example 3 is similar to that of the sample in Example 1, but the porosity decreases slightly and the thermal conductivity increases significantly. Since carboxylated nanocellulose carries a large number of -COO - , under the action of Ca 2+ , ionic bonds (-COO - -Ca 2+ - -Crosslinked by OOC-), while conventional nanocellulose can only achieve coordination bonds or hydrogen bonds. The higher binding energy of ionic bonds endows the material with better mechanical properties. The elastic modulus of this comparative example decreased to 3.96 MPa, and the compressive strength decreased to 1.58 MPa.

[0045] Although the density and porosity of the sample prepared in Comparative Example 4 are close to those in Example 1, the thermal conductivity is significantly increased. This is because the pore size of the three-dimensional network formed by polyvinyl alcohol is relatively large (micrometer level), and the heat conduction path is short. At the same time, the thermal conductivity of polyvinyl alcohol itself is also higher than that of cellulose. The mechanical properties also decrease. Although polyvinyl alcohol also has a large number of hydroxyl groups that can form hydrogen bonds with each other, the number of hydroxyl groups is less than that of cellulose, and there is no carboxyl ionic bond binding. As a result, the interfacial connection force is weak.

[0046] The density, porosity and thermal conductivity of the sample prepared in Comparative Example 5 are not much different from those in Example 1, but the mechanical properties are significantly decreased. This is because when the calcium-silicon ratio is too low, the generated C-S-H gel structure is loose, the degree of crosslinking is low, and the mechanical properties are weak, which cannot provide sufficient mechanical support for the material.

[0047] It should be noted that the present invention is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same constitution and achieving the same effect within the technical scope of the present invention are included in the technical scope of the present invention. In addition, within the scope not departing from the gist of the present invention, various modifications that can be conceived by those skilled in the art to the embodiments, and other embodiments constructed by combining some constituent elements of the embodiments are also included in the scope of the present invention.

Claims

1. A green template self-assembled cement aerogel material, characterized in that, The green template self-assembled cement aerogel material includes a framework material and C-S-H gel nanoparticles attached to the framework material; the framework material includes carboxylated nanocellulose; the density of the green template self-assembled cement aerogel material is 120~160 kg / m 3 , the porosity is 90%~95%, and the thermal conductivity is 0.03~0.042 W / mK.

2. The green template self-assembled cement aerogel material according to claim 1, characterized in that The cross-sectional diameter of the carboxylated nanocellulose is 5-10 nm, the length is 500-1000 nm, and the aspect ratio is (50:1)-(200:1).

3. The preparation method of the green template self-assembled cement aerogel material according to any one of claims 1 to 2, characterized in that, It includes the following steps: Under stirring conditions, a calcium salt solution and a silicate solution are dropped into the carboxylated nanocellulose suspension. After standing at room temperature, it is placed in a solvent for aging treatment, and a green template self-assembled cement aerogel material is obtained after washing, freezing and drying.

4. The preparation method of a green template self-assembled cement aerogel material according to claim 3, wherein, The concentration of the carboxylated nanocellulose suspension is 0.75 wt%-1.25 wt%; The mass ratio of the carboxylated nanocellulose to the calcium salt is 1:(5-13).

5. The preparation method of a green template self-assembled cement aerogel material according to claim 3, characterized in that, The molar ratio of calcium to silicon elements in the calcium salt solution and the silicate solution is (0.8-2):

1.

6. The preparation method of a green template self-assembled cement aerogel material according to claim 3, characterized in that, The calcium salt solution includes a Ca(NO3)2 solution, and the silicate solution includes a Na2SiO3 solution.

7. The preparation method of a green template self-assembled cement aerogel material according to claim 3, characterized in that, The standing time at room temperature is 12-24 h.

8. The preparation method of a green template self-assembled cement aerogel material according to claim 3, characterized in that, The solvent includes any one of water, ethanol, acetone, and tert-butanol; the aging time is 24 h-48 h.

9. The preparation method of a green template self-assembled cement aerogel material according to claim 3, characterized in that, The drying method is freeze-drying, and the conditions for freeze-drying are: the temperature is -100~-50 °C, the pressure is 1~10 Pa, and the freeze-drying time is 36~48 h.

10. The preparation method of a green template self-assembled cement aerogel material according to claim 3, characterized in that, The stirring conditions are specifically: the stirring rate is 100~200 r / min.

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