Preparation method and application of stable foam based on biomass composite material

Abstract

The invention discloses a stable foam preparation method and application based on a biomass composite material, and the method comprises the following steps: firstly, carrying out crushing screening, mixed acid treatment and ultrasonication on cotton straws to obtain cellulose nanocrystals (CNC) with uniform size, and adding the CNC into water to prepare CNC suspensions with different mass fractions; and adding the CNC suspension into a surfactant cocamidopropyl betaine (CAB), stirring at 60 DEG C for 2 hours, adding hydroxypropyl methyl cellulose (HPMC), continuously stirring at the same temperature for 1 hour, and physically foaming the obtained dispersion liquid to obtain the super-stable foam suitable for cement paste. And finally, adding the foam into the cement paste to prepare the porous cement-based material with a uniform microporous structure. The stability of the foam and the application value of the foam in engineering are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of building energy-saving and emission-reduction materials, and particularly relates to a method for preparing and applying a foam stabilized by a biomass composite material. Background Art

[0002] Energy consumption in the building field and its associated greenhouse effect have always been a hot issue of global concern. Alleviating the large consumption of energy and avoiding the emergence of energy crises and the resulting carbon emission problems are in line with the main idea of energy conservation, environmental protection, and sustainable green energy currently advocated by the country. Energy consumption in the building field mainly comes from the production of building materials and the operation of buildings. Introducing porous cement-based building materials as thermal insulation layers in building walls can effectively slow down the energy loss caused by heat and cold exchange and improve the indoor living comfort. Moreover, this building material also has the advantages of low density and high strength, and is a popular development direction of lightweight wall materials at present.

[0003] Porous cement-based materials are prepared by introducing prefabricated water-air foam into cement paste, using the foam as a template to achieve a large number of dense and tiny pores in the cement base material. However, due to the large size and poor stability of the foam used, many current porous cement-based products have poor pore structure characteristics, such as too large pores, uneven distribution, and foam floating, resulting in obvious density stratification of the paste. These deteriorated pore structures will seriously affect the thermal insulation performance and strength of the products, and even cause local collapse of the cement-based materials. Therefore, developing foams with small size and high stability is of great significance for preparing porous cement-based materials with excellent thermal insulation performance and strength and realizing energy-saving and thermally comfortable buildings.

[0004] The formation of foam relies on the reduction of the surface tension of water by surfactants. During the process of sufficient contact with air, the surfactants will adhere to the water-air interface and form a boundary around the bubbles. However, the desorption energy of surfactants is low, and their adsorption on the water-air interface is reversible and cannot be maintained stably for a long time. Therefore, the stabilizing effect of surfactants on foam is poor. Due to their small size and high surface energy, nanoparticles can autonomously adsorb on the gas-liquid interface to balance the interfacial tension. Therefore, it is not only easy to attach nanoparticles to the foam surface, but also the solid particles or polymers closely and orderly arranged on the foam liquid film can increase the viscosity of the foam liquid film and effectively limit the drainage of the foam liquid film and the diffusion of gas between bubbles. Currently, the commonly used foam stabilizers are mainly inorganic nanoparticles such as nano-silica, nano-calcium carbonate, and nano-aluminum oxide. However, the connection between these inorganic nanoparticles is relatively weak, and the foam stabilization is achieved only by the accumulation of solid-phase particles on the foam liquid film, resulting in a relatively large amount of inorganic nanoparticles required. In addition, inorganic nanoparticles are not easily decomposed and metabolized biologically, have serious environmental and ecological hazards, their preparation raw materials are difficult to obtain from nature, the preparation process consumes high energy, and industrial wastewater will also be generated, causing adverse effects on the environment. CNC and HPMC are mainly derived from plant fibers, have a wide source, are a rich and renewable resource, have biocompatibility, and both surfaces are rich in hydroxyl groups, and they form connections through hydrogen bonds with each other. CNC nanoparticles can autonomously adsorb on the foam liquid film to form a closely arranged solid-phase boundary. HPMC with a relatively large aspect ratio forms a complex three-dimensional network structure on the foam liquid film through hydrogen bonding with CNC, can be stably adsorbed on the foam liquid film for a long time, and improve the foam stabilization effect. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a foam stabilizer composed of a composite of CNC and HPMC. Among them, CNC is obtained by successively performing crushing and sieving, mixed acid hydrolysis, and ultrasonic treatment on cotton straw, and is approximately spherical in shape, with a diameter that can reach 35±5nm. The prepared CNC and HPMC are mixed to obtain a foam stabilizer. The two are mainly connected through hydrogen bonding, form a three-dimensional network structure on the foam liquid film, improve the viscoelasticity of the foam liquid film, realize the stabilization of bubbles in porous cement-based materials and reduce the size of bubbles, thereby optimizing the pore structure of the porous material and improving its thermal insulation performance and strength.

[0006] The present invention first provides a preparation method for foam applicable to porous cement-based materials stabilized by a biomass composite material, and the method includes the following steps: S1. Nanostructuring of natural cotton straw, and cotton straw is processed into nanocellulose by successively using the methods of crushing and sieving, mixed acid hydrolysis, and ultrasonic treatment, which specifically includes the following sub-steps: S11. Obtain cotton straw fiber powder by crushing and sieving natural cotton straw to obtain cotton straw fiber powder with a mesh size of 100; S12. Prepare a mixed acid solution with the mass fraction of each acid being 98%. Mix 45 ml of sulfuric acid and 15 ml of hydrochloric acid and add deionized water to make up to 100 ml to obtain the mixed acid solution; S13. Add 4 g of cotton straw fiber powder to the above mixed acid solution and stir evenly to obtain a cellulose acid hydrolysis solution; S14. Use an ultrasonic cleaner to perform ultrasonic treatment on the solution described in step S3 for 10 h; S15. Neutralize the suspension after ultrasonic treatment by adding an appropriate amount of alkaline solution to the suspension.

[0007] S16. Centrifuge the solution after neutralization in step S5 to remove the liquid part. Add deionized water to the obtained solid-phase product, shake well, and then centrifuge again. Repeat this operation 3 times to obtain CNC; S17. Considering the agglomeration of the CNC obtained in step S16, it needs to be subjected to secondary ultrasonic treatment. Add the CNC obtained in S16 to water, shake well, and then use an ultrasonic cell disruptor to perform ultrasonic treatment on it for 10 minutes. Repeat three times, with an interval of 15 minutes each time, to obtain a uniformly dispersed CNC suspension.

[0008] S2. Preparation and application of foam, specifically including the following sub-steps: S21. Take the CNC and CAB prepared in step S1 and stir on a magnetic stirrer for 2 h, then add HPMC and stir for 1 h. The temperature is maintained at 60 °C throughout the stirring process to obtain a foaming liquid. The mass percentages of each component are as follows: CNC 0.05 wt% - 0.3 wt%, CAB 5 wt%, HPMC 0.5 wt%, NaCl 0.1%, and the remaining amount is water.

[0009] S22. Stir the foaming liquid obtained in S21 with a cantilever mixer at 6000 - 8000 rpm for sufficient foaming until the foam volume does not change significantly to obtain foam attached with CNC and HPMC composite foam stabilizer.

[0010] S23. Prepare a porous cement-based material. Take 760 g of sulfoaluminate cement and 335 g of water and add them to a cement mixer to stir for 3 min to obtain a cement paste. Further, take 850 ml of the foam obtained in S22 and add it to the cement paste and stir again for 3 min. Pour the obtained foam-containing cement paste into 100×100×100 mm molds and 50×50×15 mm molds, cover with a film, and let it stand at room temperature for 24 h. Then, demold the specimens and place them in a curing box for curing for 28 d. The curing conditions are relative humidity 90 ± 2% and temperature 20 ± 2 °C.

[0011] Compared with the prior art, the beneficial effects are as follows: The foam stabilizer materials used in the foam of the present invention are CNC and HPMC, which are derived from natural plants, are rich in sources and renewable, and also have the advantage of biocompatibility, meeting the current national development trend of vigorously promoting green environmental protection.

[0012] The CNC prepared in the present invention is spherical nanoparticles with uniform size, and the average size can reach 35 nm. When applied to foam stabilization, it can autonomously adsorb on the gas-liquid interface to form a tightly and orderly arranged solid-phase boundary, hindering the coarsening, coalescence and drainage of the foam.

[0013] The present invention uses CNC and HPMC together to stabilize the foam. The two act synergistically and have an excellent foam stabilization structure. Both the surfaces of CNC and HPMC are rich in hydroxyl groups. HPMC enhances the viscosity of the liquid film through its own hydrogen bond action and forms a complex three-dimensional network structure on the foam liquid film. CNC can further enhance the stability of the foam by filling the HPMC network to form a dense viscoelastic shell at the gas-liquid interface. Compared with inorganic nanoparticles, CNC and HPMC can achieve better foam stabilization effects with less dosage.

[0014] The foam of the present invention not only has advantages in stability, but also has smaller size. When this foam is applied to cement paste, a porous cement-based material with a microporous structure of uniform size can be obtained. The good pore structure is conducive to achieving a porous cement-based material with lower density, better heat insulation performance and higher strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is an electron microscope observation diagram of the CNC prepared in the present invention; Figure 2 It is the drainage half-life and foaming rate of the foams under different dosages of foam stabilizers in Comparative Examples 1-3 and Examples 1-3; Figure 3 It is an optical microscope diagram of the foams under different dosages of foam stabilizers in Comparative Examples 1-3 and Examples 1-3. Mean on the diagram is the average value of the diameters of all the foams in the corresponding example; Figure 4 It is the test result of the heat insulation performance of the porous cement-based material in the application example. DETAILED DESCRIPTION OF THE INVENTION

[0016] For the preparation of the foaming liquid, in combination with Specific Examples 1-4 and Comparative Examples 1-3, the foam stabilizer of the present invention is further described.

[0017] Example 1:

[0018] S1. Acid hydrolysis treatment: First, place the natural cotton straw flocs in an electrothermal blast drying oven at 60 °C and dry until the mass no longer changes. After taking it out, crush it with a multi-functional high-speed crusher, sieve it through a 100-mesh sieve to obtain cotton straw fiber powder. Then, prepare a mixed acid solution. The concentrations of sulfuric acid and hydrochloric acid used are 95 wt% and 36 wt% respectively. Mix 45 ml of sulfuric acid and 15 ml of hydrochloric acid and make up to 100 ml with deionized water to obtain the mixed acid solution. Slowly add 4 g of cotton straw fiber powder and stir evenly to obtain the cellulose acid hydrolysis solution; S2. CNC preparation: First, use an ultrasonic cleaner to perform ultrasonic treatment on the solution described in step S1 for 10 h. Then, perform neutralization treatment on the ultrasonic-treated suspension, and further perform washing treatment on the solid-phase product after neutralization treatment to remove the liquid phase in the suspension. Add deionized water, shake well, and centrifuge. Repeat this operation 3 times to obtain solid phase A. Considering the agglomeration of CNC in solid phase A, it needs to be subjected to secondary ultrasonic treatment. Then, add solid phase A to water at a mass ratio of 1:200 and shake well, and perform secondary ultrasonic treatment with an ultrasonic cell disruptor. The total ultrasonic time is 30 min, which is completed in three times, with an interval of 15 min each time. Finally, obtain the CNC suspension; Take a small amount of this CNC suspension and observe it through a scanning electron microscope. The observation results are as Figure 1 shown. After testing by the applicant, the CNC is approximately spherical with a diameter of 35 ± 5 nm.

[0019] S3. Foaming solution preparation: Take CAB, HPMC, the CNC prepared in step S2, and NaCl and add them to a beaker. Stir at 60 °C on a magnetic stirrer for 3 h to obtain the foaming solution. Among them, the mass percentages of each component are as follows: CAB 5 wt%, HPMC 0.5 wt%, CNC 0.05 wt%, NaCl 0.1%.

[0020] S4. Foam preparation: Divide the foaming solution obtained in step S3 into two parts, and respectively perform foaming by fully stirring with a cantilever mixer at 6000 - 8000 rpm until the foam volume does not change significantly to obtain two foams prepared from the foaming solution of Example 1 for foam property analysis.

[0021] S5. Foam property analysis: Add the first foam obtained in step S4 to a glass graduated cylinder with a diameter of 6.5 cm to obtain the foaming rate (foaming multiple = foam volume ÷ required foaming solution volume), and at the same time record the time required for half of the liquid in the foam to precipitate, which is recorded as the drainage half-life; Place the other foam on a glass slide and observe the microscopic morphology of the bubbles through an optical microscope.

[0022] Example 2:

[0023] S1. Acid hydrolysis treatment: First, place natural cotton straw flocs in an electrothermal blast drying oven at 60 °C and dry until the mass no longer changes. After taking it out, crush it with a multi-functional high-speed crusher, sieve it through a 100-mesh sieve to obtain cotton straw fiber powder. Then, prepare a mixed acid solution. The concentrations of sulfuric acid and hydrochloric acid used are 95 wt% and 36 wt% respectively. Mix 45 ml of sulfuric acid and 15 ml of hydrochloric acid and make up to 100 ml with deionized water to obtain a mixed acid solution. Slowly add 4 g of cotton straw fiber powder and stir evenly to obtain a cellulose acid hydrolysis solution; S2. CNC preparation: First, use an ultrasonic cleaner to perform ultrasonic treatment on the solution described in step S1 for 10 h. Then, perform neutralization treatment on the ultrasonic-treated suspension, and further perform washing treatment on the solid-phase product after neutralization treatment to remove the liquid phase in the suspension. Add deionized water, shake well, and then centrifuge. Repeat this operation 3 times to obtain solid phase A. Considering the agglomeration of CNC in solid phase A, it needs to be ultrasonically treated again. Then add solid phase A to water at a mass ratio of 1:200, shake well, and perform secondary ultrasonic treatment with an ultrasonic cell disruptor. The total ultrasonic time is 30 min, which is completed in three times, with an interval of 15 min each time. Finally, obtain a CNC suspension; S3. Foaming solution preparation: Take CAB, HPMC, the CNC prepared in step S2, and NaCl and add them to a beaker. Stir at 60 °C on a magnetic stirrer for 3 h to obtain a foaming solution. Among them, the mass percentages of each component are as follows: CAB 5 wt%, HPMC 0.5 wt%, CNC 0.1 wt%, NaCl 0.1%.

[0024] S4. Foam preparation: Divide the foaming solution obtained in step S3 into two parts, and respectively perform foaming by fully stirring with a cantilever mixer at 6000 - 8000 rpm until the foam volume does not change significantly, to obtain two foams prepared from the foaming solution of Example 1 for foam performance analysis.

[0025] S5. Foam performance analysis: Add the first foam obtained in step S4 to a glass graduated cylinder with a diameter of 6.5 cm to obtain the foaming rate (foaming multiple = foam volume ÷ required foaming solution volume). At the same time, record the time required for half of the liquid in the foam to precipitate, which is recorded as the drainage half-life; Place the other foam on a glass slide and observe the microscopic morphology of the bubbles through an optical microscope.

[0026] Example 3:

[0027] S1. Acid hydrolysis treatment: First, place natural cotton straw flocs in an electrothermal blast drying oven at 60 °C and dry until the mass no longer changes. After taking it out, crush it with a multi-functional high-speed crusher, sieve it through a 100-mesh sieve to obtain cotton straw fiber powder. Then, prepare a mixed acid solution. The concentrations of sulfuric acid and hydrochloric acid used are 95 wt% and 36 wt% respectively. Mix 45 ml of sulfuric acid and 15 ml of hydrochloric acid and make up to 100 ml with deionized water to obtain a mixed acid solution. Slowly add 4 g of cotton straw fiber powder and stir evenly to obtain a cellulose acid hydrolysis solution; S2. CNC preparation: First, use an ultrasonic cleaner to perform ultrasonic treatment on the solution described in step S1 for 10 h. Then, perform neutralization treatment on the ultrasonic-treated suspension, and further perform washing treatment on the solid-phase product after neutralization treatment to remove the liquid phase in the suspension. Add deionized water, shake well, and then centrifuge. Repeat this operation 3 times to obtain solid phase A. Considering the agglomeration of CNC in solid phase A, it needs to be subjected to secondary ultrasonic treatment. Then, add solid phase A to water at a mass ratio of 1:200, shake well, and perform secondary ultrasonic treatment with an ultrasonic cell disruptor. The total ultrasonic time is 30 min, which is completed in three times, with an interval of 15 min each time. Finally, obtain CNC; S3. Foaming liquid preparation: Take CAB, HPMC, the CNC prepared in step S2, and NaCl and add them to a beaker. Stir at 60 °C on a magnetic stirrer for 3 h to obtain a foaming liquid. Among them, the mass percentages of each component are as follows: CAB 5 wt%, HPMC 0.5 wt%, CNC 0.3 wt%, NaCl 0.1%.

[0028] S4. Foam preparation: Divide the foaming liquid obtained in step S3 into two parts, and respectively perform foaming by fully stirring with a cantilever mixer at 6000 - 8000 rpm until the foam volume does not change significantly, to obtain two foams prepared from the foaming liquid of Example 1 for foam performance analysis.

[0029] S5. Foam performance analysis: Add the first foam obtained in step S4 to a glass graduated cylinder with a diameter of 6.5 cm to obtain the foaming rate (foaming multiple = foam volume ÷ required foaming liquid volume). At the same time, record the time required for half of the liquid in the foam to precipitate, which is denoted as the half-life of liquid drainage; Place the other foam on a glass slide and observe the microscopic morphology of the bubbles through an optical microscope.

[0030] Comparative Example 1: S1. Foaming liquid preparation: Take CAB and NaCl and add them to a beaker. Stir at 60 °C on a magnetic stirrer for 3 h to obtain a foaming liquid. Among them, the mass percentages of each component are as follows: CAB 5 wt%, NaCl 0.1%.

[0031] S2. Foam preparation: The foaming liquid obtained in step S2 is sufficiently stirred at 6000 - 8000 rpm by a cantilever mixer for foaming until there is no obvious change in the foam volume, obtaining the foam prepared from the foaming liquid of Comparative Example 1.

[0032] S3. Foam property analysis: Add the first portion of the foam obtained in step S2 into a glass graduated cylinder with a diameter of 6.5 cm to obtain the foaming rate (foaming multiple = foam volume ÷ required foaming liquid volume). At the same time, record the time required for half of the liquid in the foam to precipitate, denoted as the half-life of liquid precipitation. Place the other portion of the foam on a glass slide and observe the microscopic morphology of the bubbles through an optical microscope.

[0033] Comparative Example 2: S1. Acid hydrolysis treatment: First, place natural cotton straw flocs in an electrothermal blast drying oven at 60 °C and dry until the mass no longer changes. After taking it out, crush it with a multi-functional high-speed crusher, sieve it through a 100-mesh sieve to obtain cotton straw fiber powder. Then, prepare a mixed acid solution with the concentrations of sulfuric acid and hydrochloric acid being 95 wt% and 36 wt% respectively. Mix 45 ml of sulfuric acid and 15 ml of hydrochloric acid and make up to 100 ml with deionized water to obtain the mixed acid solution. Slowly add 4 g of cotton straw fiber powder and stir evenly to obtain the cellulose acid hydrolysis solution. S2. CNC preparation: First, use an ultrasonic cleaner to perform ultrasonic treatment on the solution described in step S1 for 10 h. Then, perform neutralization treatment on the ultrasonic-treated suspension, and further perform washing treatment on the solid-phase product after neutralization treatment. Remove the liquid phase in the suspension, add deionized water, shake well, and centrifuge. Repeat this operation 3 times to obtain solid phase A. Then, add solid phase A into water, shake well, and perform secondary ultrasonic treatment with an ultrasonic cell disruptor. The total ultrasonic time is 30 min, completed in three times with an interval of 15 min each time, and finally obtain CNC. S3. Foaming liquid preparation: Take CAB, the CNC prepared in step S2, and NaCl and add them into a beaker. Stir at 60 °C on a magnetic stirrer for 3 h to obtain the foaming liquid. Among them, the mass percentages of each component are as follows: CAB 5 wt%, CNC 0.3 wt%, NaCl 0.1%.

[0034] S4. Foam preparation: Divide the foaming liquid obtained in step S3 into two portions, and respectively perform sufficient stirring at 6000 - 8000 rpm by a cantilever mixer for foaming until there is no obvious change in the foam volume, obtaining two portions of foam prepared from the foaming liquid of Example 1 for foam property analysis.

[0035] S5. Foam performance analysis: The first portion of foam obtained in step S4 was added to a glass measuring cylinder with a diameter of 6.5 cm to obtain the foaming rate (foaming multiple = foam volume ÷ required foaming liquid volume). At the same time, the time required for the foam to precipitate half of the liquid was recorded, which was recorded as the precipitation half-life; another portion of foam was placed on a glass slide, and the microscopic morphology of the bubbles was observed under an optical microscope.

[0036] Comparative Example 3: S1. Preparation of foaming liquid: CAB, HPMC and NaCl were added into a beaker and stirred on a magnetic stirrer at 60°C for 3 h to obtain a foaming liquid, wherein the mass percentages of the components were as follows: CAB 5wt%, HPMC 0.5wt%, and NaCl 0.1%.

[0037] S2. Foam preparation: The foaming liquid obtained in S2 was fully stirred at 6000~8000rpm by a cantilever stirrer for foaming until the foam volume did not change significantly, to obtain the foam prepared from the foaming liquid of Comparative Example 3.

[0038] S3. Foam performance analysis: The first portion of foam obtained in step S2 was added to a glass measuring cylinder with a diameter of 6.5 cm to obtain the foaming multiple (foaming multiple = foam volume ÷ required foaming liquid volume). The time required for the foam to precipitate half of the liquid was recorded, which was recorded as the precipitation half-life. Another portion of foam was placed on a glass slide, and the microscopic morphology of the bubbles was observed under an optical microscope.

[0039] Among them, the sulfuric acid and hydrochloric acid used in the above examples and comparative examples are from Guangzhou Zixing Chemical Instrument Co., Ltd., cocamidopropyl betaine (CAB) is from Shandong Yousuo Chemical Technology Co., Ltd., and hydroxypropyl methylcellulose (HPMC) is from Shanghai Chenqi Chemical Technology Co., Ltd. The CNC used in Examples 1 to 3 and Comparative Example 2 is the same, and its electron microscope observation diagram is shown in Figure 1 The liquid separation half-life and optical microscope images of the foams prepared in Comparative Examples 1 to 3 and Examples 1 to 3 are shown in Figure 2 and Figure 3 (Mean in the figure represents the average diameter of the foam shown in the corresponding example).

[0040] With respect to the application of the foaming liquid, combined with application examples, the application of the modified foam of the present invention in the field of energy-saving buildings is further explained.

[0041] Application examples: S1. Preparation of porous cement-based specimens: Take 760 g of cement and 335 g of water and add them to a small concrete mixer to mix at low speed for 3 min to obtain a cement paste. Take 850 ml of the foams obtained in Examples 1-3 and Comparative Examples 1-3 respectively and add them to the cement paste and stir again for 3 min. Pour the obtained cement paste containing foam into 100×100×100 mm molds and 50×50×15 mm molds respectively, cover with a film, and let stand at room temperature for 24 h. Then demold the specimens and cure them in a curing box for 28 d. The curing conditions are relative humidity 90±2% and temperature 20±2°C; S2. Detection of dry density and compressive strength: Take the 100×100×100 mm specimens cured for 28 d in S1 and test the dry density and compressive strength of the specimens according to the standard of JG / T266-2011; S3. Detection of thermal insulation performance: Take the 50×50×15 mm specimens cured for 28 d in S1 and place them on a heating table. Set the heating temperature to 400°C, and use an infrared camera (T540, FLIR, USA) to monitor the temperature distribution of the sample during the heating process, and obtain the temperatures at the top of the specimen after heating for 5 min, 15 min and 30 min.

[0042] Among them, 42.5 sulphoaluminate cement is used, which comes from Zhucheng Jiuqi Building Materials Co., Ltd. The main chemical components of the cement are shown in Table 1. The dry densities and compressive strengths of 6 groups of specimens prepared by adding the foams of Comparative Examples 1-3 and Examples 1-3 are shown in Table 2, and the thermal insulation test results are shown in Figure 4 .

[0043]

[0044] From Figure 2 、 Figure 3 It can be seen that the liquid drainage half-lives of the foams of Comparative Example 1, Comparative Example 2 and Comparative Example 3 are 0.13 h, 0.18 h and 3 h respectively, indicating that adding CNC alone cannot effectively improve the stability of CAB foam. As a polymer, HPMC can increase the viscosity of the foaming liquid. Adding HPMC alone can improve the stability of CAB foam to a certain extent. When CNC and HPMC are added simultaneously, the liquid drainage half-life of the obtained foam can be further improved and the bubble diameter is reduced. This change amplitude increases significantly with the increase of the CNC content. When the dosage of CNC is 0.3 wt%, the liquid drainage half-lives of the foams are increased by 15233%, 12678% and 667% respectively compared with those of the foams of Comparative Example 1, 2 and 3, and the bubble diameters are reduced by 60 μm, 64 μm and 58 μm respectively. The foam also becomes more uniform. Therefore, the foam stabilizer of the present invention can significantly increase the stability of the foam and reduce the diameter of the foam.

[0045] Table 2 and Figure 4The compressive strength and heat insulation capacity of the specimens with different foams added are shown. It can be seen that the mechanical properties of the specimens with the foams of Comparative Examples 1, 2, and 3 are all worse than those of the specimens with the foams of Examples 1 to 3. Among them, the specimen with the foam of Example 3 has the best mechanical properties, which are improved by 112%, 122%, and 104% compared with Comparative Examples 1, 2, and 3 respectively. Place each specimen on a heating table and heat it at 400 °C for 30 min. Except for Example 1, the top temperatures of the specimens prepared with the foams of Examples 2 and 3 are lower than those of Comparative Examples 1 to 3. The specimen with the foam of Example 3 has the lowest top temperature, which is 153.2 °C, and the heat insulation rate reaches 61.7%.

[0046] The foam modified by the CNC / HPMC composite foam stabilizer is applied to building materials and has obvious advantages in mechanical properties and heat insulation performance. The reason is that the stability of the foam modified by the CNC / HPMC composite foam stabilizer and its diameter relative to the unmodified foam diameter are both optimized. Using it as a template can provide a better pore structure for porous materials, which is beneficial to forming an effective support structure to ensure mechanical properties and effectively dividing heat to achieve the purpose of preventing temperature transfer.

[0047] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of them. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention. Although the specific implementation manners of the present invention have been described above, it is not a limitation to the protection scope of the present invention. Those skilled in the art should understand that various modifications or deformations that can be made without creative labor on the basis of the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a stable foam based on a biomass composite material, characterized in that: The method comprises the following steps: S1. The natural cotton straw is nano-processed by crushing and screening, mixed acid hydrolysis and ultrasonic treatment to process the cotton straw into nanocellulose, which specifically includes the following sub-steps: S11 obtain cotton straw fiber powder, the natural cotton straw was crushed and sieved to obtain 100 mesh cotton straw fiber powder; S12. Prepare a mixed acid solution by mixing 45 ml of 95% sulfuric acid and 15 ml of 36% hydrochloric acid and adding deionized water to a volume of 100 ml to obtain a mixed acid solution; S13. Take 4 g of the cotton straw fiber powder obtained in step S11 and add it to the mixed acid solution configured in step S12, stir evenly, and obtain a cellulose acid hydrolysis solution; S14. The cellulose acid hydrolyzate solution obtained in step S13 is subjected to ultrasonic treatment using an ultrasonic cleaning machine for 10 h to obtain a suspension; S15. The suspension after ultrasonic treatment in step S14 is neutralized by adding an alkaline solution to the suspension until the pH of the suspension is neutral; S16. Centrifuge the suspension after neutralization in step S15, remove the liquid portion, add water to the obtained solid phase product, shake well, and then centrifuge again. Repeat this operation 3 times to obtain cellulose nanocrystals (CNC); S2. Preparation of foam, specifically comprising the following sub-steps: S21. Take the CNC and cocamidopropyl betaine (CAB) prepared in step S1 and stir them on a magnetic stirrer for 2 hours, then add hydroxypropyl methylcellulose (HPMC) and stir for 1 hour. The temperature is kept at 60°C during the whole stirring process to obtain a foaming liquid, wherein the mass percentage of each component is as follows: CNC 0.05wt%~0.3wt%, CAB 5wt%, HPMC 0.5wt%, NaCl 0.1%, and the rest is water; S22. The foaming liquid obtained in S21 is fully stirred at 6000-8000 rpm by a cantilever stirrer for foaming until the foam volume does not change significantly, thereby obtaining a foam containing a composite foam stabilizer of CNC and HPMC.

2. The method for preparing a stable foam based on a biomass composite material according to claim 1, characterized in that: The method also includes the step of performing a secondary ultrasonic treatment on the CNC obtained from S16. The specific method is to add the CNC obtained from S16 into water at a mass ratio of 1:200, shake it thoroughly, and then use an ultrasonic cell disruptor to perform ultrasonic treatment on it for 10 minutes. The process is repeated three times, with an interval of 15 minutes each time, to obtain a uniformly dispersed CNC suspension.

3. A foam stabilized by biomass composite material, characterized in that: The stable foam based on biomass composite material is prepared by the method described in claim 1, and includes cellulose nanocrystals CNC, cocamidopropyl betaine CAB, and hydroxypropyl methylcellulose HPMC, and the mass percentage of each component is as follows: CNC 0.05wt%~0.3wt%, CAB 5wt%, HPMC 0.5wt%, NaCl 0.1%, and the rest is water.

4. An application of the foam stabilized by biomass composite materials as claimed in claim 3, characterized in that: The biomass composite material stabilized foam is used to prepare a porous cement-based material, and the method is as follows: 760 g of sulphoaluminate cement and 335 g of water were added into a cement mixer and stirred for 3 min to obtain cement paste; Then take 850 ml of the stable foam of the biomass composite material and add it to the cement slurry and stir again for 3 minutes. The obtained foamed cement slurry is poured into a mold and covered with a film and allowed to stand at room temperature for 24 hours. Thereafter, the specimen is demolded and placed in a curing box for curing for 28 days. The curing conditions are a relative humidity of 90±2% and a temperature of 20±2°C.

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