Nanocrystalline cellulose modified cement mortar composite material and preparation method
The preparation method of nanocrystalline cellulose modified cement mortar composite material solves the problem of insufficient reinforcement of cement-based composite materials at the nanoscale, improves the compressive and flexural strength of cement mortar, inhibits crack propagation, and achieves high strength and durability of the material.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- UNIV OF JINAN
- Filing Date
- 2024-01-19
- Publication Date
- 2026-06-30
AI Technical Summary
Existing cement-based composite materials have shortcomings in terms of tensile strength, deformation performance and durability, and traditional reinforcing materials are ineffective at the nanoscale, resulting in easy cracking of the structure and shortened service life.
A method for preparing cement mortar composite material modified with nanocrystalline cellulose was proposed. By adding nanocrystalline cellulose, the degree of hydration was improved, the porosity was reduced, the mechanical properties were enhanced, and the agglomeration problem of nanocrystalline cellulose was solved.
It improves the physical and mechanical properties of cement mortar, enhances compressive and flexural strength, inhibits crack propagation, optimizes the composition of hydration products, and achieves high strength and durability of the material.
Smart Images
Figure CN117843324B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of building materials technology, specifically relating to a nanocrystalline cellulose modified cement mortar composite material and its preparation method. Background Technology
[0002] Cement is the second most widely used material after water. Cement-based composites have advantages such as high compressive strength, low preparation cost, simple production process, and ease of use. However, these composites also have disadvantages such as low tensile strength, poor deformation performance, and susceptibility to cracking, affecting the long-term durability of structures. Furthermore, in harsh environments, they often suffer physical, chemical, and biological damage, leading to degradation and shortened service life. Moreover, it is well known that concrete has very low tensile strength, typically only one-tenth of its compressive strength. Overcoming these problems in cement-based materials is crucial for improving structural durability. Common improvement methods include the use of reinforcing materials, such as fibers and fillers, at both the macroscopic and microscopic scales; however, the cementitious matrix is prone to defects at the nanoscale, and traditional reinforcing materials are ineffective at the nanoscale.
[0003] As is well known, nanomaterials exhibit excellent physical and chemical properties, with better mechanical, electrical and thermal properties, low density and excellent chemical and thermal stability.
[0004] Nanocrystalline cellulose (NCC) is a type of rod-shaped nanoparticle extracted from plants and trees, typically produced in powder form. They possess several unique properties, such as high elastic modulus and strength, low density, reactive surface area, allowing for functionalization, and good dispersion in water without the need for surfactants or modification. Further advantages of NCC include its renewable, sustainable, low-toxicity, and low-cost nature. Because it is extracted from physical sources like plants and trees, NCC is biodegradable, carbon-neutral, and poses no environmental or health risks.
[0005] NCC can improve the mechanical properties of cement-based composites. Due to their small size, they can reduce the internal spacing of fibers, preventing microcracks and thus increasing matrix strength. They may increase the degree of hydration because they can provide channels for water to be transported through the hydration products to unhydrated cement particles. The addition of NCC can reduce porosity and improve the microstructure of the matrix.
[0006] High-intensity ultrasound is based on the cavitation effect of ultrasound. This refers to artificially creating a low-pressure, high-velocity state in a liquid flow path. When the liquid pressure is lower than the saturated vapor pressure, bubbles in the liquid continuously expand, increasing in volume. As the fluid moves, the bubbles collapse and burst when they reach the high-pressure, low-velocity region. Through the ultrasonic cavitation effect, microcrystalline cellulose (MCC) can be further dispersed and broken down into nanocrystalline cellulose. The extracted nanocrystalline cellulose has advantages such as size stability, large specific surface area, and high water absorption, exhibiting a nanoscale effect. This method is simple to operate, widely available, and low-cost, and its application in cement-based materials can produce good reinforcing and toughening effects. Summary of the Invention
[0007] The technical problem to be solved by this invention is to address the aforementioned shortcomings in the existing technology by proposing a nanocrystalline cellulose-modified cement mortar composite material and its preparation method. This solution improves the overall hydration level, densifies the cement matrix, reduces the porosity of the cement mortar, and enhances the physical and mechanical properties of the cement mortar by incorporating the prepared nanocrystalline cellulose, while also solving the problem of nanocrystalline cellulose agglomeration to a certain extent.
[0008] Technical Solution: To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing nanocrystalline cellulose-modified cement mortar composite material, characterized by comprising the following steps:
[0009] (1) Commercial microcrystalline cellulose was crudely purified to obtain nano-microcrystalline cellulose;
[0010] (2) Nanocrystalline cellulose is dispersed in an aqueous solution;
[0011] (3) The nanocrystalline cellulose dispersion was mixed evenly with cement and standard sand to obtain nanocrystalline cellulose modified cement mortar composite material.
[0012] According to the above scheme, the preparation method of crude purified nanocrystalline cellulose includes the following steps:
[0013] S1. Prepare 250 g of 0.2% microcrystalline cellulose suspension.
[0014] S2. Initial dispersion is carried out for 10-20 min using a high-speed disperser at a speed of 10000-12000 r / min. The dispersed sample is then sonicated for 30-40 min. The sample is then divided into two parts and diluted to obtain a dispersion with a mass of 0.1%.
[0015] S3. Then, each part is subjected to ultrasonic treatment again for 30-40 minutes.
[0016] S4. Use a cell disruptor, set the ultrasonic power to 1000-1200 W, and sonicate for 1 hour.
[0017] S5. Place the dispersion in a reactor, add 3% hydrogen peroxide solution (hydrogen peroxide to microcrystalline cellulose mass ratio of 1:1-3:1), heat to 60-90℃, adjust the pressure inside the reactor to 0.9-1.5 MPa, stir for 2-4 h at a stirring speed of 200-240 r / min.
[0018] S6. The suspension after dispersion modification was centrifuged multiple times and finally freeze-dried to obtain powdered nanocrystalline cellulose.
[0019] According to the above scheme, the method for dispersing nanocrystalline cellulose in aqueous solution is as follows: dissolve nanocrystalline cellulose powder in deionized water and stir magnetically for 24-48 h, place the solution in an ultrasonic bath with a power of 180-360 W and an ultrasonic time of 1-2 h to obtain a nanocrystalline cellulose dispersion.
[0020] According to the above scheme, the method for uniformly mixing the nanocrystalline cellulose dispersion with cement and standard sand is as follows:
[0021] A. Mix cement and standard sand in a ratio of 1:3 by mass.
[0022] B. Add the nanocrystalline cellulose dispersion obtained in step (2) to water, stir evenly, and then slowly pour it into the prepared cement and standard sand until the required ratio is reached. Control the water-cement ratio to 0.45 to obtain a nanocrystalline cellulose modified cement mortar sample.
[0023] C. Pour the mortar sample prepared in step B into a mold to form it.
[0024] D. After curing at room temperature, the material is demolded and placed in a standard curing room for further curing to obtain a nanocrystalline cellulose modified cement mortar composite material.
[0025] According to the above scheme, the composition of the nanocrystalline cellulose modified cement mortar sample is as follows: cement: 450 parts; standard sand: 1350 parts; water: 202.5 parts; nanocrystalline cellulose: 0-2.25 parts.
[0026] According to the above scheme, in the nanocrystalline cellulose modified cement mortar samples, the amount of nanocrystalline cellulose added accounts for 0, 0.025%, 0.05%, 0.1%, 0.3% and 0.5% of the cement mass, respectively.
[0027] According to the above scheme, the amount of nanocrystalline cellulose added to the nanocrystalline cellulose-modified cement mortar sample shall not exceed 0.1% of the cement mass.
[0028] According to the above scheme, in the nanocrystalline cellulose modified cement mortar sample, the amount of nanocrystalline cellulose added accounts for 0.1% of the mass of cement.
[0029] According to the above scheme, the method of demolding after room temperature curing and placing it in a standard curing room is as follows: after standing in the mold for 24-48 hours in an indoor environment at (20±5)℃, the mold is removed. After demolding, the specimen should be placed in a standard curing room at (20±2)℃ and relative humidity above 95% for curing for 3 days, 7 days and 28 days.
[0030] The present invention also proposes a nanocrystalline cellulose modified cement mortar composite material prepared by any of the above preparation methods.
[0031] Compared with traditional technical solutions, this solution has the following advantages:
[0032] 1. Utilizing nanocrystalline cellulose, it possesses green, environmentally friendly, and sustainable characteristics, meeting the contemporary requirement of carbon neutrality;
[0033] 2. The preparation of oxidatively modified nanocrystalline cellulose by microcrystalline cellulose is a simple method that increases the hydroxyl content, enhances the mechanical properties and adhesion of the raw material itself, and produces no secondary pollution.
[0034] 3. Optimize cement hydration to suppress crack generation and propagation at the nanoscale and improve mechanical properties.
[0035] 4. It has solved the problem of agglomeration of nanocrystalline cellulose to a certain extent. Attached Figure Description
[0036] Figure 1 These are SEM images of commercially available microcrystalline fibers and nanocrystalline cellulose;
[0037] Figure 2 This is a TEM image of nanocrystalline cellulose;
[0038] Figure 3 This is a graph showing the variation of compressive and flexural strength of cement-based composite materials at different ages with the amount of nanocrystalline cellulose added.
[0039] Figure 4 This is a TGA-DTG diagram of the hydration products of cement-based composite materials;
[0040] Figure 5 This is the XRD pattern of the hydration phase of a cement-based composite material;
[0041] Figure 6 This is a SEM image of a crack in the cross-section of a cement-based composite material.
[0042] Figure 7 This is a SEM image of the NCC bridging effect of cement-based composite materials;
[0043] Figure 8 MIP diagram of porosity of cement-based composite materials Detailed Implementation
[0044] The present invention will be further described below with reference to embodiments. The raw materials, process conditions, and methods involved in the present invention are all well-known in the art. All other embodiments obtained by those skilled in the art without inventive effort, provided that the embodiments and comparative examples are given in the present invention, are within the protection scope of the present invention.
[0045] The following are all the main raw materials used in the embodiments and comparative examples of this invention: ordinary Portland cement (PC): produced by Shandong Shanshui Cement Group Co., Ltd., with a specific surface area of 350 m². 2 / kg, loss 2.14%; the standard sand is Chinese ISO standard quartz sand, produced by Xiamen Aisiou Standard Sand Co., Ltd., and the standard implemented is GB / T17671-1999; the commercial microcrystalline cellulose is MCC Avicel PH-101 standard type, produced by Sigma-Aldridge, extracted from cotton.
[0046] Example 1
[0047] A method for preparing a nanocrystalline cellulose-modified cement mortar composite material includes the following steps:
[0048] (1) Microcrystalline cellulose was crudely purified to obtain nanocrystalline cellulose; the preparation method was as follows:
[0049] S1. Prepare 250 g of 0.2% microcrystalline cellulose suspension.
[0050] S2. Initial dispersion was performed for 20 min using a high-speed disperser at 12000 r / min. The dispersed sample was then sonicated for 30 min. The sample was then divided into two parts and diluted to obtain a dispersion with a mass of 0.1%.
[0051] S3. Then, each part is subjected to ultrasonic treatment again for 30 minutes.
[0052] S4. Use a cell disruptor, set the ultrasonic power to 1000 W, and sonicate for 1 hour.
[0053] S5. Place the dispersion in a reactor, add 3% hydrogen peroxide solution (hydrogen peroxide to microcrystalline cellulose mass ratio of 2:1), heat to 80℃, adjust the pressure inside the reactor to 1.2 MPa, stir for 3 h at a stirring speed of 220 r / min.
[0054] S6. The suspension after dispersion modification was centrifuged multiple times and finally freeze-dried to obtain powdered nanocrystalline cellulose.
[0055] (2) Dissolve nanocrystalline cellulose powder in deionized water and stir magnetically for 24 h. Place the solution in an ultrasonic bath with a power of 180 W and an ultrasonic time of 1 h to obtain a nanocrystalline cellulose dispersion.
[0056] (3) The nanocrystalline cellulose dispersion is mixed evenly with cement and standard sand to obtain a nanocrystalline cellulose modified cement mortar composite material; the method for mixing the nanocrystalline cellulose dispersion with cement and standard sand is as follows:
[0057] A. Mix cement and standard sand in a ratio of 1:3 by mass.
[0058] B. Add the nanocrystalline cellulose dispersion obtained in step (2) to water, stir evenly, and then slowly pour it into the prepared cement and standard sand. The cement mortar sample composition is as follows: cement: 450 parts; standard sand: 1350 parts; water: 202.5 parts; nanocrystalline cellulose: 0.1125 parts (accounting for 0.025% of the cement mass), to obtain the nanocrystalline cellulose modified cement mortar sample.
[0059] C. Pour the mortar sample prepared in step B into a mold to form it.
[0060] D. After standing in the mold for 24 hours at (20±5)℃, the specimen should be removed from the mold. After removal from the mold, the specimen should be immediately placed in a standard curing room at (20±2)℃ and relative humidity above 95% for curing for 3 days, 7 days and 28 days.
[0061] Example 2
[0062] A method for preparing a nanocrystalline cellulose-modified cement mortar composite material includes the following steps:
[0063] (1) Microcrystalline cellulose was crudely purified to obtain nanocrystalline cellulose; the preparation method was as follows:
[0064] S1. Prepare 250 g of 0.2% microcrystalline cellulose suspension.
[0065] S2. Initial dispersion was performed for 20 min using a high-speed disperser at 12000 r / min. The dispersed sample was then sonicated for 30 min. The sample was then divided into two parts and diluted to obtain a dispersion with a mass of 0.1%.
[0066] S3. Then, each part is subjected to ultrasonic treatment again for 30 minutes.
[0067] S4. Use a cell disruptor, set the ultrasonic power to 1000 W, and sonicate for 1 hour.
[0068] S5. Place the dispersion in a reactor, add 3% hydrogen peroxide solution (hydrogen peroxide to microcrystalline cellulose mass ratio of 2:1), heat to 80℃, adjust the pressure inside the reactor to 1.2 MPa, stir for 3 h at a stirring speed of 220 r / min.
[0069] S6. The suspension after dispersion modification was centrifuged multiple times and finally freeze-dried to obtain powdered nanocrystalline cellulose.
[0070] (2) Dissolve nanocrystalline cellulose powder in deionized water and stir magnetically for 24 h. Place the solution in an ultrasonic bath with a power of 180 W and an ultrasonic time of 1 h to obtain a nanocrystalline cellulose dispersion.
[0071] (3) The nanocrystalline cellulose dispersion is mixed evenly with cement and standard sand to obtain a nanocrystalline cellulose modified cement mortar composite material; the method for mixing the nanocrystalline cellulose dispersion with cement and standard sand is as follows:
[0072] A. Mix cement and standard sand in a ratio of 1:3 by mass.
[0073] B. Add the nanocrystalline cellulose dispersion obtained in step (2) to water, stir evenly, and then slowly pour it into the prepared cement and standard sand. The cement mortar sample composition is as follows: cement: 450 parts; standard sand: 1350 parts; water: 202.5 parts; nanocrystalline cellulose: 0.225 parts (accounting for 0.05% of the cement mass), to obtain the nanocrystalline cellulose modified cement mortar sample.
[0074] C. Pour the mortar sample prepared in step B into a mold to form it.
[0075] D. After standing in the mold for 24 hours at (20±5)℃, the specimen should be removed from the mold. After removal from the mold, the specimen should be immediately placed in a standard curing room at (20±2)℃ and relative humidity above 95% for curing for 3 days, 7 days and 28 days.
[0076] Example 3
[0077] A method for preparing a nanocrystalline cellulose-modified cement mortar composite material includes the following steps:
[0078] (1) Microcrystalline cellulose was crudely purified to obtain nanocrystalline cellulose; the preparation method was as follows:
[0079] S1. Prepare 250 g of 0.2% microcrystalline cellulose suspension.
[0080] S2. Initial dispersion was performed for 20 min using a high-speed disperser at 12000 r / min. The dispersed sample was then sonicated for 30 min. The sample was then divided into two parts and diluted to obtain a dispersion with a mass of 0.1%.
[0081] S3. Then, each part is subjected to ultrasonic treatment again for 30 minutes.
[0082] S4. Use a cell disruptor, set the ultrasonic power to 1000 W, and sonicate for 1 hour.
[0083] S5. Place the dispersion in a reactor, add 3% hydrogen peroxide solution (hydrogen peroxide to microcrystalline cellulose mass ratio of 2:1), heat to 80℃, adjust the pressure inside the reactor to 1.2 MPa, stir for 3 h at a stirring speed of 220 r / min.
[0084] S6. The suspension after dispersion modification was centrifuged multiple times and finally freeze-dried to obtain powdered nanocrystalline cellulose.
[0085] (2) Dissolve nanocrystalline cellulose powder in deionized water and stir magnetically for 24 h. Place the solution in an ultrasonic bath with a power of 180 W and an ultrasonic time of 1 h to obtain a nanocrystalline cellulose dispersion.
[0086] (3) The nanocrystalline cellulose dispersion is mixed evenly with cement and standard sand to obtain a nanocrystalline cellulose modified cement mortar composite material; the method for mixing the nanocrystalline cellulose dispersion with cement and standard sand is as follows:
[0087] A. Mix cement and standard sand in a ratio of 1:3 by mass.
[0088] B. Add the nanocrystalline cellulose dispersion obtained in step (2) to water, stir evenly, and then slowly pour it into the prepared cement and standard sand. The cement mortar sample composition is as follows: cement: 450 parts; standard sand: 1350 parts; water: 202.5 parts; nanocrystalline cellulose: 0.45 parts (accounting for 0.1% of the cement mass), to obtain the nanocrystalline cellulose modified cement mortar sample.
[0089] C. Pour the mortar sample prepared in step B into a mold to form it.
[0090] D. After standing in the mold for 24 hours at (20±5)℃, the specimen should be removed from the mold. After removal from the mold, the specimen should be immediately placed in a standard curing room at (20±2)℃ and relative humidity above 95% for curing for 3 days, 7 days and 28 days.
[0091] Example 4
[0092] A method for preparing a nanocrystalline cellulose-modified cement mortar composite material includes the following steps:
[0093] (1) Microcrystalline cellulose was crudely purified to obtain nanocrystalline cellulose; the preparation method was as follows:
[0094] S1. Prepare 250 g of 0.2% microcrystalline cellulose suspension.
[0095] S2. Initial dispersion was performed for 20 min using a high-speed disperser at 12000 r / min. The dispersed sample was then sonicated for 30 min. The sample was then divided into two parts and diluted to obtain a dispersion with a mass of 0.1%.
[0096] S3. Then, each part is subjected to ultrasonic treatment again for 30 minutes.
[0097] S4. Use a cell disruptor, set the ultrasonic power to 1000 W, and sonicate for 1 hour.
[0098] S5. Place the dispersion in a reactor, add 3% hydrogen peroxide solution (hydrogen peroxide to microcrystalline cellulose mass ratio of 2:1), heat to 80℃, adjust the pressure inside the reactor to 1.2 MPa, stir for 3 h at a stirring speed of 220 r / min.
[0099] S6. The suspension after dispersion modification was centrifuged multiple times and finally freeze-dried to obtain powdered nanocrystalline cellulose.
[0100] (2) Dissolve nanocrystalline cellulose powder in deionized water and stir magnetically for 24 h. Place the solution in an ultrasonic bath with a power of 180 W and an ultrasonic time of 1 h to obtain a nanocrystalline cellulose dispersion.
[0101] (3) The nanocrystalline cellulose dispersion is mixed evenly with cement and standard sand to obtain a nanocrystalline cellulose modified cement mortar composite material; the method for mixing the nanocrystalline cellulose dispersion with cement and standard sand is as follows:
[0102] A. Mix cement and standard sand in a ratio of 1:3 by mass.
[0103] B. Add the nanocrystalline cellulose dispersion obtained in step (2) to water, stir evenly, and then slowly pour it into the prepared cement and standard sand. The cement mortar sample composition is as follows: cement: 450 parts; standard sand: 1350 parts; water: 202.5 parts; nanocrystalline cellulose: 1.35 parts (accounting for 0.3% of the cement mass), to obtain the nanocrystalline cellulose modified cement mortar sample.
[0104] C. Pour the mortar sample prepared in step B into a mold to form it.
[0105] D. After standing in the mold for 24 hours at (20±5)℃, the specimen should be removed from the mold. After removal from the mold, the specimen should be immediately placed in a standard curing room at (20±2)℃ and relative humidity above 95% for curing for 3 days, 7 days and 28 days.
[0106] Example 5
[0107] A method for preparing a nanocrystalline cellulose-modified cement mortar composite material includes the following steps:
[0108] (1) Microcrystalline cellulose was crudely purified to obtain nanocrystalline cellulose; the preparation method was as follows:
[0109] S1. Prepare 250 g of 0.2% microcrystalline cellulose suspension.
[0110] S2. Initial dispersion was performed for 20 min using a high-speed disperser at 12000 r / min. The dispersed sample was then sonicated for 30 min. The sample was then divided into two parts and diluted to obtain a dispersion with a mass of 0.1%.
[0111] S3. Then, each part is subjected to ultrasonic treatment again for 30 minutes.
[0112] S4. Use a cell disruptor, set the ultrasonic power to 1000 W, and sonicate for 1 hour.
[0113] S5. Place the dispersion in a reactor, add 3% hydrogen peroxide solution (hydrogen peroxide to microcrystalline cellulose mass ratio of 2:1), heat to 80℃, adjust the pressure inside the reactor to 1.2 MPa, stir for 3 h at a stirring speed of 220 r / min.
[0114] S6. The suspension after dispersion modification was centrifuged multiple times and finally freeze-dried to obtain powdered nanocrystalline cellulose.
[0115] (2) Dissolve nanocrystalline cellulose powder in deionized water and stir magnetically for 24 h. Place the solution in an ultrasonic bath with a power of 180 W and an ultrasonic time of 1 h to obtain a nanocrystalline cellulose dispersion.
[0116] (3) The nanocrystalline cellulose dispersion is mixed evenly with cement and standard sand to obtain a nanocrystalline cellulose modified cement mortar composite material; the method for mixing the nanocrystalline cellulose dispersion with cement and standard sand is as follows:
[0117] A. Mix cement and standard sand in a ratio of 1:3 by mass.
[0118] B. Add the nanocrystalline cellulose dispersion obtained in step (2) to water, stir evenly, and then slowly pour it into the prepared cement and standard sand. The cement mortar sample composition is as follows: cement: 450 parts; standard sand: 1350 parts; water: 202.5 parts; nanocrystalline cellulose: 2.25 parts (accounting for 0.5% of the cement mass), to obtain the nanocrystalline cellulose modified cement mortar sample.
[0119] C. Pour the mortar sample prepared in step B into a mold to form it.
[0120] D. After standing in the mold for 24 hours at (20±5)℃, the specimen should be removed from the mold. After removal from the mold, the specimen should be immediately placed in a standard curing room at (20±2)℃ and relative humidity above 95% for curing for 3 days, 7 days and 28 days.
[0121] Example 6
[0122] A method for preparing a nanocrystalline cellulose-modified cement paste composite material includes the following steps:
[0123] (1) Microcrystalline cellulose was crudely purified to obtain nanocrystalline cellulose; the preparation method was as follows:
[0124] S1. Prepare 250 g of 0.2% microcrystalline cellulose suspension.
[0125] S2. Initial dispersion was performed for 20 min using a high-speed disperser at 12000 r / min. The dispersed sample was then sonicated for 30 min. The sample was then divided into two parts and diluted to obtain a dispersion with a mass of 0.1%.
[0126] S3. Then, each part is subjected to ultrasonic treatment again for 30 minutes.
[0127] S4. Use a cell disruptor, set the ultrasonic power to 1000 W, and sonicate for 1 hour.
[0128] S5. Place the dispersion in a reactor, add 3% hydrogen peroxide solution (hydrogen peroxide to microcrystalline cellulose mass ratio of 2:1), heat to 80℃, adjust the pressure inside the reactor to 1.2 MPa, stir for 3 h at a stirring speed of 220 r / min.
[0129] S6. The suspension after dispersion modification was centrifuged multiple times and finally freeze-dried to obtain powdered nanocrystalline cellulose.
[0130] (2) Dissolve nanocrystalline cellulose powder in deionized water and stir magnetically for 24 h. Place the solution in an ultrasonic bath with a power of 180 W and an ultrasonic time of 1 h to obtain a nanocrystalline cellulose dispersion.
[0131] (3) The nanocrystalline cellulose dispersion is mixed evenly with cement to obtain a nanocrystalline cellulose modified cement paste composite material; the method for mixing the nanocrystalline cellulose dispersion with cement is as follows:
[0132] A. Add the nanocrystalline cellulose dispersion obtained in step (2) to water, and pour the cement and nanocrystalline cellulose solution into the mixing pot of the cement paste mixer according to the proportion. The cement paste sample composition is: cement: 450 parts; water: 202.5 parts; nanocrystalline cellulose: 0.225 parts (accounting for 0.05% of the cement mass).
[0133] B. Stir at low speed for 120 seconds, stop stirring for 15 seconds, then stir at high speed for 120 seconds.
[0134] C. After mixing, the cement paste is poured into a standard mold of 20 x 20 x 20 mm. The mold is left to stand in the room at (20±5)℃ for 24 h before demolding. After demolding, the specimens should be placed in a standard curing room at (20±2)℃ and relative humidity of more than 95% for curing until the specified age of 3 days, 7 days and 28 days.
[0135] D. After standing in the mold for 24 hours at (20±5)℃, the specimen should be removed from the mold. After removal from the mold, the specimen should be immediately placed in a standard curing room at (20±2)℃ and relative humidity above 95% for curing for 3 days, 7 days and 28 days.
[0136] Comparative Example 1
[0137] The difference from Examples 1-5 is that no nanocrystalline cellulose is added.
[0138] Comparative Example 2
[0139] The difference from Example 6 is that no nanocrystalline cellulose is added.
[0140] Performance testing:
[0141] Morphology and size of microcrystalline cellulose and nanocrystalline cellulose: Microcrystalline cellulose and nanocrystalline cellulose with a concentration of 0.05% were prepared and dropped onto clean tin foil. The morphology was observed by SEM. For TEM, a nanocrystalline cellulose suspension with a concentration of 0.05% was prepared, stirred thoroughly, sonicated for 30 min, dropped onto a copper grid, and observed after air drying. The size of the nanocrystalline cellulose was quantitatively analyzed using ImageJ software.
[0142] Strength testing of cement mortar composite materials: The strength of the mortar is tested according to the GB / T50081-2002 testing standard.
[0143] Testing of hydration products of cement paste: The hydration products and degree of hydration were analyzed by thermogravimetric analysis (TGA-DTG) and X-ray diffraction (XRD).
[0144] Microscopic analysis of cement mortar: The hydration products, crack size and porosity of cement mortar were tested using SEM and MIP methods.
[0145] Figure 1 a represents commercially available microcrystalline cellulose (MCC). Figure 1 b represents nanocrystalline cellulose (NCC) obtained through mechanical processing. The mechanical crushing method successfully decomposed MCC into smaller NCC particles. These NCC particles are short rod-shaped, with diameters on the nanometer scale, exhibiting a small size effect and a large specific surface area. Furthermore, TEM was used to observe the size of the NCC more clearly (e.g., ...). Figure 2 As shown in the image. Through ImageJ software analysis, more than 200 points were selected from the image for labeling. The average diameter of NCC was 63.3 nm, mainly distributed between 20-80 nm, accounting for 66%, and the overall particle size distribution was relatively uniform.
[0146] Figure 3 The compressive and flexural strengths of cement mortar composites modified with nanocrystalline cellulose (NCC) at different addition levels are shown. The results indicate that at curing ages of 3, 7, and 28 days, both compressive and flexural strengths initially increase and then decrease with increasing NCC concentration. When the NCC content is too high, the strength is lower than the control (CK) value. Modified cement mortars with NCC additions of 0.025%, 0.05%, 0.1%, 0.3%, and 0.5% of the cement mass showed the following increases in compressive strength compared to the control (CK): at 3 days: 5.69%, 7.36%, 7.05%, -1.89%, and 0.03%, respectively; at 7 days: 8.02%, 8.15%, 12.58%, -3.49%, and 6.52%, respectively; and at 28 days: 12.50%, 15.59%, 14.67%, 7.61%, and 9.86%, respectively. Similarly, flexural strength also showed similar changes. At curing ages of 3 days, 7 days, and 28 days, compared to the control (CK), the strength increase was greatest when the addition amount was 0.1%, increasing by 1.06%, 9.91%, and 17.17%, respectively. The enhancing effect of NCC on flexural strength confirms its bridging role. However, high concentrations reduced the mechanical properties of cement mortar, indicating that excessively high NCC concentrations can cause agglomeration, resulting in defects in certain areas and deteriorating the cementitious material.
[0147] The improvement in mechanical properties may be due to the water retention of NCC, which acts as a nucleation site during cement hydration, promoting the formation of more hydration products and making the internal structure more compact. It may also play a bridging role, inhibiting the propagation of cracks in the cement matrix under stress.
[0148] To avoid agglomeration caused by excessive NCC, we selected an addition amount of 0.05% of NCC, which has good dispersibility in cement matrix, to study the hydration products and microstructure, and elucidated the mechanism of action in cement paste.
[0149] Figure 4 The TGA-DTG curves for Example 6 and Comparative Example 2 at different ages are shown. DTG can be used to determine the temperature range corresponding to the thermal decomposition of different hydration phases in cement paste. TGA can be used to further analyze the bound water and calcium hydroxide (CH) content of the hydration products calcium silicate hydrate (CSH). Compared with the control (CK), the weight loss of the samples at 900°C was different. The weight loss of the NCC-containing samples increased to varying degrees at different ages, indicating that the formation of cementitious hydration products was greater in the presence of NCC. At the same time, the formation of CSH and CH increased to varying degrees at different ages, which may be due to NCC promoting the formation of hydration products through nucleation effect.
[0150] Furthermore, the hydration products were further analyzed using XRD patterns. Figure 5 In each sample, the XRD patterns showed the same hydrated crystal structure, consistent diffraction peaks, typical hydration products, and all peaks confirmed the expected presence of hydration products. With the addition of NCC, the intensities of the 2θ = 18° and 34° peaks associated with the CH crystal plane increased significantly, indicating that NCC promoted CH formation through a nucleation effect.
[0151] Figure 6 The images show SEM images of cement mortar cracks at 28 days in Example 2 and Comparative Example 1. Figure 6 'a' represents plain mortar. Figure 6 b represents a cement mortar composite material with an added amount of 0.1% NCC. It is evident that NCC has a higher specific surface area and elastic modulus, which can better control cracks at the nanoscale. Figure 6 The average crack size in a is 3.96 μm. Figure 6 The average crack size in b is 1.85 μm. Furthermore, through... Figure 7 (a and b are plain mortar, c and d are cement mortar with 0.1% NCC addition) Observe the morphology of micro-hydration products. The NCC-modified cement mortar composite sample has a relatively dense structure, and fibers can be seen extending from the crack surface, indicating that NCC plays a bridging role in the deformation and fracture of cement mortar. At the same time, we observed that NCC can exist alone, indicating that NCC has good dispersion in the cement matrix.
[0152] Figure 8Mercury intrusion porosimetry (MIP) was used to determine the porosity changes in the mortar. The maximum volumetric porosity of NCC mortar and CK mortar were ~43 nm and ~95 nm, respectively. In all analyzed samples, the average size of the gel pores was approximately 8 nm, but the number of pores of different sizes increased and the number of large pores decreased in NCC-modified cement mortar, indicating that NCC increased the number of gel pores to some extent. NCC led to the refinement of the porosity of cement hydration products due to the increased degree of hydration, resulting in the formation of more CSH phase.
[0153] The effective dispersion of nanocrystalline cellulose in cement mortar has a significant impact on improving the mechanical properties of cement-based materials. Results show that an appropriate amount of nanocrystalline cellulose can increase the hydration degree of cement paste, optimize the composition of hydration products, reduce the porosity of cement mortar, decrease damage cracks, and improve the mechanical properties of cement mortar. The optimal dosage of nanocrystalline cellulose is 0.1% of the cement mass, resulting in a significant increase in compressive and flexural strength at 28 days of age, with increases of 14.67% and 17.17%, respectively.
Claims
1. A method for preparing a nanowhite cement mortar composite material, characterized by, Includes the following steps: (1) The crude purification of commercial microcrystalline cellulose to obtain nano-microcrystalline cellulose, specifically including: S1. Prepare 250 g of a 0.2% concentration microcrystalline cellulose suspension made from commercial microcrystalline cellulose. S2. Initial dispersion is carried out using a high-speed disperser at a speed of 10000-12000 r / min for 10-15 min. The dispersed sample is then sonicated for 30-40 min. The sample is then divided into two parts for dilution to obtain a dispersion with a mass concentration of 0.1%. S3. Each dispersion obtained in step S2 is subjected to ultrasonic treatment again for 30-40 minutes. S4. Using a cell disruptor, set the ultrasonic power to 1000-1200 W, and sonicate the dispersion after step S3 for 1 h. S5. Place the dispersion treated in step S4 into a reaction vessel, add 3% hydrogen peroxide solution, the mass ratio of hydrogen peroxide to microcrystalline cellulose is 1:1-3:1, heat to 60-90℃, adjust the pressure inside the reaction vessel to 0.9-1.5 MPa, and stir at a stirring speed of 200-240 r / min for 2-4 h. S6. The suspension after dispersion and modification in step S5 is centrifuged multiple times and then freeze-dried to obtain powdered nanocrystalline cellulose. (2) The nanocrystalline cellulose obtained in step (1) is dispersed in an aqueous solution to obtain a nanocrystalline cellulose dispersion; (3) The nanocrystalline cellulose dispersion is mixed with cement and standard sand at a mass ratio of "cement:standard sand = 1:3" and a water-cement ratio of 0.45 to obtain nanocrystalline cellulose modified cement mortar composite material.
2. The production method according to claim 1, wherein In step (2), the method for dispersing the nanocrystalline cellulose in the aqueous solution is as follows: dissolve the nanocrystalline cellulose powder in deionized water and stir magnetically for 24-48 h, place the solution in an ultrasonic bath with a power of 180-360 W and an ultrasonic time of 1-2 h to obtain a nanocrystalline cellulose dispersion.
3. The production method according to claim 2, wherein In step (3), the method for uniformly mixing the nanocrystalline cellulose dispersion with cement and standard sand is as follows: A. Mix cement and standard sand in a ratio of 1:3 by mass. B. Add the nanocrystalline cellulose aqueous dispersion obtained by magnetic stirring and ultrasonic dispersion in step (2) to water, stir evenly, and then slowly pour it into the prepared cement and standard sand until the required ratio is reached. Control the water-cement ratio to 0.45 to obtain a nanocrystalline cellulose modified cement mortar sample. C. Pour the mortar sample prepared in step B into a mold to form it; D. After curing at room temperature, the material is demolded and placed in a standard curing room for further curing to obtain a nanocrystalline cellulose modified cement mortar composite material.
4. The production method according to claim 3, wherein In step B, the amount of nanocrystalline cellulose added to the nanocrystalline cellulose modified cement mortar sample is 0.025%, 0.05%, 0.1%, 0.3%, or 0.5% of the cement by mass, respectively.
5. The production method according to claim 3, wherein In step B, the amount of nanocrystalline cellulose added to the nanocrystalline cellulose modified cement mortar sample does not exceed 0.1% of the cement mass.
6. The production method according to claim 3, wherein In step B, the amount of nanocrystalline cellulose added to the cement mortar sample is 0.1% of the mass of cement.
7. A nanocrystalline cellulose-modified cement mortar composite material prepared by any one of the preparation methods described in claims 1-6.