阅读说明：本技术 一种绿色、质轻、隔热、高强度复合板材的制备方法 (Preparation method of green, light, heat-insulating and high-strength composite board ) 是由 宗鲁 张建明 彭倩倩 刘巧铃 马骋 于 2021-01-28 设计创作，主要内容包括：本发明属于功能复合材料制备领域,具体涉及一种含有不同浓度纳米纤维素/二氧化硅复合气凝胶粉末的复合板材的制备方法,该方法首先采用磁力搅拌器将所制备的纳米纤维素与水玻璃充分混合均匀,得到不同浓度的纳米纤维素/二氧化硅凝胶混合液,然后将该混合液通过静置、老化、疏水改性、常压干燥以及球磨等工艺制备出复合硅气凝胶粉末。然后,将复合硅气凝胶粉末与纳米纤维素按照不同比例进行均匀混合,制备绿色、质轻、隔热、高强度复合板材。(The invention belongs to the field of preparation of functional composite materials, and particularly relates to a preparation method of a composite board containing nano-cellulose/silicon dioxide composite aerogel powder with different concentrations. And then, uniformly mixing the composite silicon aerogel powder and the nano-cellulose according to different proportions to prepare the green, light, heat-insulating and high-strength composite board.)

1. A preparation method of a green, light, heat-insulating and high-strength composite board specifically comprises the following steps:

and uniformly mixing the nano-cellulose/silicon dioxide composite aerogel and the nano-cellulose dispersion liquid in a solvent to obtain a composite, then carrying out vacuum filtration, and drying when the composite is formed and does not collapse to obtain the nano-cellulose/composite silicon aerogel composite board.

2. The preparation method according to claim 1, wherein the mass ratio of the nanocellulose/silica composite aerogel to the nanocellulose in the nanocellulose dispersion is (1-5): 1.

3. the method according to claim 1, wherein the solvent is absolute ethanol.

4. The method of claim 1, wherein the drying is: drying in an oven at 80 ℃.

5. The preparation method according to any one of claims 1 to 4, wherein the nanocellulose/silica composite aerogel is prepared by:

(1) mixing the components in a volume ratio of (1-6): 1, uniformly mixing the water glass and the nano-cellulose dispersion liquid, slowly adding dilute hydrochloric acid into the mixture until the solution becomes viscous, and placing the solution at room temperature to gelatinize the solution to obtain wet gel;

(2) placing the wet gel obtained in the step into dilute hydrochloric acid for aging, then washing with water, and finally soaking in absolute ethyl alcohol to obtain alcogel;

(3) hydrophobic modification: soaking the obtained alcogel in a mixed solution of trimethylchlorosilane and normal hexane for surface modification; then, carrying out solvent exchange on the gel after surface modification by using absolute ethyl alcohol to replace unreacted trimethylchlorosilane so as to obtain replaced wet gel;

(4) gel drying-drying under normal pressure: and drying the displaced wet gel obtained in the step to finally obtain the nano-cellulose/silicon dioxide composite aerogel.

6. The preparation method according to claim 5, wherein the content of the nanocellulose in the nanocellulose/silica composite aerogel is 1% -30%.

7. The method of claim 5, wherein the nanocellulose dispersion has a diameter in the range of 40-100 nm and a solids content of 3.8%.

8. The method according to claim 5, wherein the dilute hydrochloric acid has a concentration of 1 mol/L.

9. The method according to claim 5, wherein the drying in the step (4) is: drying in an oven at 80 deg.C under normal pressure for 24 hr.

Technical Field

The invention relates to a method for preparing a green, light, heat-insulating and high-strength composite board by filling high-content nano-cellulose/silicon dioxide composite aerogel powder in nano-cellulose, belonging to the field of preparation of functional composite materials.

Background

Cellulose is a natural polymer which is distributed most widely and has most content on the earth, is a macromolecular polysaccharide consisting of glucose units, and is insoluble in water and common organic solvents. One of the most prominent and useful features of cellulose is high hydroxylation along the polymer chain, with three hydroxyl groups per non-terminal monomer. Hydrogen bonding occurs between hydroxyl groups located on the same cellulose molecule (intramolecular) and adjacent cellulose chains (intermolecular). Intermolecular hydrogen bonding forms a fibrillar structure that controls the physical properties of cellulose, i.e., high strength and flexibility. Nanocellulose is an emerging nanomaterial with high strength, high specific surface area, and tunable surface chemistry properties. Can interact with polymers, nanoparticles, small molecules and biomaterials. High pressure homogenization, low temperature impact and grinding are several mechanical treatment methods for extracting nanocellulose, the chemical methods include acid, alkali, oxidant treatment, and the biological methods use enzyme treatment.

The silicon dioxide aerogel is a light nano porous amorphous solid material with excellent heat insulation performance, the porosity of the silicon dioxide aerogel is as high as 80-99.8%, the typical size of the pores is 1-10nm, and the specific surface area is 200-1000m²G, but a density as low as 3kg/m³The room temperature thermal conductivity coefficient can be as low as 0.012W/(m.k), and the characteristics enable the silicon dioxide aerogel to have wide application potential in the fields of scientific research, military industry, aerospace, seawater desalination and the like. There are many methods for preparing silica aerogels, such as sol-gel method, thermal cracking of organic metal compounds, solvent precipitation method, chemical vapor deposition method, etc., among which the sol-gel method is the most common and most commonly used method. However, in terms of practical application, since pure silica aerogel is subjected to capillary force during aging and drying processes, the mechanical properties are poor and the brittleness is high, so that the practical application is limited. In addition, the commercial promise of limited transparency and moisture absorption problems has been inhibited. Therefore, improving the quality and quality of silica aerogel is the main direction of silica aerogel research. In recent years, researchers have compounded aerogels with other materials to improve the performance of aerogels and expand the application of aerogels in the field of thermal insulationThe application is as follows.

In the design of high performance engineering materials, it is a natural source of biological inspiration for material scientists. Wood is one of the most common natural materials, and is attracting attention due to its light weight and high strength. Wood is grown by biocontrol, self-assembly from bottom to top, each structural level contributing to the remarkable properties of wood, including mechanical properties as well as multifunctional and adaptive properties. Wood derived materials have inherent outstanding advantages such as renewability, biodegradability, excellent toughness and the possibility of new functions.

Disclosure of Invention

The technical scheme of the invention provides a preparation method of a composite board containing nano-cellulose/silicon dioxide composite aerogel powder with different concentrations, which comprises the steps of firstly, fully and uniformly mixing the prepared nano-cellulose and water glass by adopting a magnetic stirrer to obtain nano-cellulose/silicon dioxide gel mixed liquor with different concentrations, and then preparing the composite silicon aerogel powder by the mixed liquor through the processes of standing, aging, hydrophobic modification, normal-pressure drying, ball milling and the like. And then, uniformly mixing the composite silicon aerogel powder and the nano-cellulose according to different proportions to prepare the green, light, heat-insulating and high-strength composite board.

The principle of preparing silica gel by water glass is as follows:

Na₂SiO₃+2HCl＝2NaCl+H₂SiO₃ (1)

H₂SiO₃＝H₂O+SiO₂ (2)

namely: under the acidic condition, the water glass slowly reacts with the dilute hydrochloric acid, and the dilute hydrochloric acid is slowly and stably added in order to prevent the occurrence of the implosion phenomenon in the experimental process. When the diluted hydrochloric acid is added in a proper amount, the solution becomes viscous, and the addition of the diluted hydrochloric acid is stopped, so that a transparent colloidal liquid, namely silicic acid, is produced, and simultaneously, colorless and tasteless sodium chloride salt is produced. The silicic acid in free form comprises orthosilicic acid (H)₄SiO₄) Metasilicic acid (H)₂SiO₃) Disilicic acid (H)₂Si₂O₅) Weak acidity and poor solubility in water and alcohol. Will be supersaturatedThe silicic acid solution, when left standing at room temperature, produces an amorphous silica precipitate that is milky white and appears as colloidal particles, precipitates or gels. Some of the water in the gel is evaporated to give a porous dry solid gel, i.e. a silica gel.

In order to achieve the purpose, the invention provides a preparation method of a green, light, heat-insulating and high-strength composite board, which comprises the following steps:

weighing a proper amount of nano-cellulose as a matrix, uniformly mixing the nano-cellulose/silicon dioxide composite aerogel and the nano-cellulose dispersion liquid in a solvent to obtain a composite, then carrying out vacuum filtration, and drying when the composite is formed and does not collapse to obtain the nano-cellulose/composite silicon aerogel composite board.

Further, the mass ratio of the nano-cellulose/silicon dioxide composite aerogel to the nano-cellulose in the nano-cellulose dispersion liquid is (1-5): 1, preferably (1-3): 1.

further, the solvent is absolute ethyl alcohol.

Further, the drying is as follows: drying in an oven at 80 ℃.

Further, the nano-cellulose/silicon dioxide composite aerogel is prepared by the following steps:

(1) mixing the components in a volume ratio of (1-6): 1 (preferably 3: 1), then slowly adding dilute hydrochloric acid into the mixture until the solution becomes viscous, and placing the solution at room temperature to gelatinize the solution to obtain wet gel;

(2) placing the wet gel obtained in the step into dilute hydrochloric acid for aging, then washing with water, and finally soaking in absolute ethyl alcohol to obtain alcogel;

(3) hydrophobic modification: soaking the obtained alcogel in a mixed solution of trimethylchlorosilane and normal hexane for surface modification; then, carrying out solvent exchange on the gel after surface modification by using absolute ethyl alcohol to replace unreacted trimethylchlorosilane so as to obtain replaced wet gel;

(4) gel drying-drying under normal pressure: and drying the displaced wet gel obtained in the step to finally obtain the nano-cellulose/silicon dioxide composite aerogel.

Further, the content of the nanocellulose in the nanocellulose/silica composite aerogel is 1% -30%, and preferably 10% -20%.

Further, the volume ratio of the trimethylchlorosilane to the normal hexane in the step (3) is 1: 9.

furthermore, the diameter range of the nano-cellulose dispersion liquid is 40-100 nm, and the solid content is 3.8%.

Further, the dilute hydrochloric acid is 1mol/L HCl.

Further, the drying in the step (4) is as follows: drying in an oven at 80 deg.C for 24 hr.

Due to the adoption of the technical scheme, the invention has the following advantages and beneficial effects:

1. the invention adopts nano-cellulose extracted from common plants in the nature as a raw material, obtains the nano-cellulose through TEMPO oxidation and high-pressure homogenization, has wide source of the nano-cellulose, low cost, no pollution, strong hydrogen bond interaction with the nano-cellulose in the composite silicon aerogel, and has the advantages of high strength, light weight, heat insulation and the like.

2. According to the invention, the nano-cellulose/silicon dioxide composite aerogel powder with different concentrations is prepared by taking water/ethanol as a dispersion medium and is added into a nano-cellulose matrix as a filler, so that the operation process is high in safety, time and cost are saved, the nano-cellulose can be effectively prevented from aggregating, and the composite aerogel powder with different contents can be stably dispersed in the nano-cellulose aggregate.

3. According to the invention, water glass is used as a precursor, high-concentration nano-cellulose is added to prepare the environment-friendly nano-cellulose/silicon dioxide composite aerogel, then the environment-friendly nano-cellulose/silicon dioxide composite aerogel is ground into powder and added to the nano-cellulose matrix to obtain the composite board of nano-cellulose/composite silicon aerogel particles. The nano-cellulose is embedded into the silicon dioxide aerogel, and can be uniformly mixed at high concentration under the action of a magnetic stirrer, so that the prepared nano-cellulose/silicon dioxide composite aerogel can achieve nano-scale uniform compounding, and the aggregation and agglomeration of the nano-cellulose can be effectively prevented. Because the molecular chain of the nano-cellulose in the composite silicon aerogel contains hydroxyl, a strong hydrogen bond interaction can be formed before the nano-cellulose and the nano-cellulose are combined, and the prepared composite board has good mechanical strength, and has the characteristics of light weight, heat insulation, greenness, low cost and the like, so that the composite board has potential application value in the fields of bio-based functional composite materials and the like.

4. After hydrophobic modification, the high-quality composite aerogel can be obtained under normal pressure and low temperature environment, so that the production cost and the energy consumption are greatly reduced.

Drawings

FIG. 1 is a schematic view of the interaction between nano-cellulose and composite silica aerogel particles according to the present invention.

FIG. 2 shows the microstructure of the nanocellulose used in the examples under a polarization microscope (POM).

The two figures show the mechanism of interaction of the nanocellulose with the composite silica aerogel particles and the microstructure of the nanocellulose matrix. As shown in the figure: because the molecular chain of the nano-cellulose contains a large amount of hydroxyl, a large amount of hydrogen bond interaction can be generated among the nano-celluloses in the composite silicon aerogel particles, among the nano-celluloses in the composite silicon aerogel particles and the nano-celluloses of the matrix and among the molecular chains of the nano-celluloses in the matrix, so that the composite silicon aerogel particles and the nano-celluloses of the matrix are tightly combined.

Fig. 3 is a result of a specific surface area test of the composite aerogel prepared in example 2 (in the figure, the silica aerogel of example 1, the nanocellulose/silica composite silica aerogel having a nanocellulose content of 10%, and the nanocellulose/silica composite aerogel having a nanocellulose content of 20%, respectively, are illustrated from left to right). The specific surface area of the gel particles is 790-890 m²The specific surface area of the composite aerogel nano particles is slightly reduced compared with that of silicon dioxide aerogel, and the nano cellulose can play a role of framework support and resist the shrinkage stress during normal pressure drying, so that the volume of gel particles is relatively increased, and the nano cellulose can be containedThe rice cellulose has low density and small addition amount, so the mass can be ignored, and the density and the specific surface area of the composite aerogel are reduced.

FIG. 4 shows the density of the composite board in examples 3 and 4 as a function of the amount of silica composite aerogel powder added.

As can be seen from the figure: along with the increase of the adding amount of the silicon dioxide composite aerogel in sequence, the density of the composite board is obviously reduced.

The main reasons for the above phenomena are: in one aspect, ρ (SiO)₂Nano particles) < rho (nano cellulose), SiO (sodium oxide) is increased along with the addition of the nano particles₂The proportion of the nano particles is increased, so that the density of the composite board is reduced; on the other hand, compared with pure SiO₂The nano particles and the composite silicon aerogel nano particles contain nano cellulose and SiO₂The proportion of the nano particles is reduced, so that the density of the composite board added with the composite nano particles is slightly increased.

Fig. 5 is a stress-strain graph of the nanocellulose/composite silicon aerogel composite board in example 4, fig. 6 is an actual graph of the strength test of the nanocellulose/composite silicon aerogel composite board, and the stress-strain graph and the actual graph show that: the composite board has stress of over 90MPa under 70% strain, which is mainly because the strong hydrogen bond interaction exists between the nano-cellulose and the composite gel particles, so that the gel nano-particles are uniformly distributed in the nano-cellulose matrix, and the composite board has better mechanical strength. And the composite board can still keep good blockiness when placed under a 500g weight.

FIG. 7 shows the thermal conductivity of the nano-cellulose/composite silica aerogel composite sheet material compared with other sheet materials, wherein the thermal conductivity of the silica particles is usually very low, about 0.012 W.m^-1·K^-1The powder is added into the nano cellulose matrix, the heat conductivity coefficient of the composite board is greatly lower than that of boards such as a polystyrene board, an electrodeless foaming insulation board and the like, and the superiority of the composite board is shown.

Detailed Description

The silica content of the water glass used in the following examples is: 25.5% -28.5%, modulus: 3.2-3.5.

Example 1

(1) Taking a proper amount of water glass, so that the water glass: deionized water 1: 4 (volume ratio) is mixed in a 100mL beaker, stirred uniformly on a magnetic stirrer rapidly, then 1mol/L HCl is added slowly until the solution becomes viscous, and the solution is immediately transferred to a PE culture dish and placed at 25 ℃ to be gelatinized;

(2) putting the wet gel obtained in the step into 0.1mol/L HCl for aging, then washing with water, and finally soaking in absolute ethyl alcohol for 12 hours to obtain alcogel;

(3) hydrophobic modification: placing the obtained alcogel in a mixture of trimethylchlorosilane and normal hexane according to the volume ratio of 1: 9, soaking for 3 times, each time for 12 hours, and carrying out surface modification; then, carrying out solvent exchange on the gel after surface modification by using absolute ethyl alcohol to replace unreacted trimethylchlorosilane for 3 times, and obtaining replaced wet gel after 12 hours each time;

(4) gel drying-drying under normal pressure: and (3) placing the displaced wet gel obtained in the step above in an oven at 80 ℃ for drying for 24 hours to finally obtain the silicon dioxide aerogel.

Example 2

The procedure was as in example 1, except that the dispersion of the nanocellulose provided by Jinan holy spring group GmbH, Shandong was replaced with deionized water in the diameter range of 40-100 nm and the solid content was 3.8%. Meanwhile, as a dispersion: water glass 1: 2 (volume ratio), obtaining the nano-cellulose/silicon dioxide composite silica aerogel with the nano-cellulose content of 10%, and mixing the nano-cellulose/silicon dioxide composite silica aerogel with the dispersion liquid: water glass 1: 1 (volume ratio), and obtaining the nano-cellulose/silicon dioxide composite aerogel with the nano-cellulose content of 20 percent. The obtained composite silica aerogel is subjected to BET test, and the specific surface area of the composite silica aerogel is found to be in the range of 790-860 m²The ratio of the specific component to the specific component is/g. FIG. 3 shows the results of the specific surface area test of the composite aerogel obtained in this example (in the figure, from left to right, the silica aerogel obtained in example 1, and the nanofibers having a nanocellulose content of 10%Cellulose/silica composite silica aerogel, nanocellulose/silica composite aerogel having a nanocellulose content of 20%).

Example 3

Grinding the silica aerogel obtained in the example 1 by using a mortar, placing the ground silica aerogel into a gauze with 100 meshes, sieving the ground silica aerogel to obtain powder, weighing a proper amount of nano-cellulose as a matrix, and respectively mixing the silica aerogel powder and the nano-cellulose in the nano-cellulose dispersion liquid according to the mass ratio of 1: 1. 2: 1. 3: 1, dispersing the nano-cellulose dispersion liquid and the silicon dioxide aerogel powder in absolute ethyl alcohol, and stirring for 30min on a magnetic stirrer to obtain a uniformly mixed compound. And (3) separating out the water in the nano-cellulose and the added ethanol by vacuum filtration, and placing the nano-cellulose in an oven at 80 ℃ to continuously volatilize the residual ethanol until the nano-cellulose is dried when the composite is formed and does not collapse to obtain the composite board.

Example 4

The process flow is the same as that in example 3, except that the used silica aerogel powder in example 1 is replaced with the nanocellulose/silica composite aerogel powder with the nanocellulose content of 10% in example 2, and the nanocellulose/composite silicon aerogel composite board is prepared.

FIG. 4 shows the density of the composite board in examples 3 and 4 as a function of the amount of silica composite aerogel powder added.

Detecting that the mass ratio of the composite gel powder to the nano-cellulose in the nano-cellulose dispersion liquid is 3: 1 the relevant performance results of the prepared nanocellulose/composite silica aerogel composite boards are shown in fig. 5-7.

As shown in fig. 5, it can be seen that: the obtained nano-cellulose/silicon dioxide powder composite board has excellent compression strength.

The composite board still maintained good block integrity when placed under a 500g weight (as shown in figure 6). The heat conductivity coefficient of the material is far lower than that of other heat-insulating materials (as shown in figure 7) through a heat insulation coefficient test, and the material can be applied to the fields of buildings, heat insulation and the like.