Method for preparing sand willow cellulose reinforced heat-resistant salt brick by hot pressing densification

Abstract

This invention discloses a method for preparing heat-resistant salt bricks reinforced with *Salix psammophila* cellulose through hot pressing densification, belonging to the field of inorganic non-metallic composite material preparation technology. This invention uses sodium chloride as a raw material, incorporating a certain proportion of *Salix psammophila* cellulose as a reinforcing phase, and achieves densification of the salt bricks through a hot pressing process. The resulting salt bricks have a uniform structure, high strength, and excellent heat resistance. Experiments show that after heating at 350 ℃ for about 12 minutes, the crack length of the salt brick reaches 3 cm and stops extending; after continuous heating at 600 ℃ for about 4 minutes, the crack length reaches 5 cm and stops extending; and after heating for 90 minutes, the structure remains intact and does not crack. This invention fully utilizes the environmentally friendly properties and reinforcing effect of *Salix psammophila* cellulose, combined with a hot pressing process to improve the physical properties of the salt bricks, providing a new avenue for their application in high-temperature functional materials and diversified fields in the salt industry.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic composite material preparation technology, specifically relating to a method for preparing cellulose-reinforced heat-resistant salt bricks by hot pressing densification. Background Technology

[0002] my country is the world's largest producer and consumer of crude salt. In recent years, my country's salt supply capacity and level have remained stable; however, in terms of capacity utilization, the contradiction of overcapacity in my country's salt industry persists. Statistics show that approximately 10 million tons of crude salt in my country are used to produce edible salt, with edible salt production remaining stable at around 20 million tons, indicating that the edible salt industry still suffers from overcapacity.

[0003] The efficient utilization of edible salt is urgently needed, and functionalizing edible salt is an effective way to solve overproduction. In the catering industry, salt-pressed barbecue salt trays are cost-effective and produce delicious meat, making them popular with consumers. However, these salt trays are prone to cracking and damage after 10 minutes of heating, seriously affecting the consumer's barbecue experience. In animal husbandry, livestock need regular replenishment of their physiological salt requirements, but traditional salt bricks for livestock licking generally suffer from problems such as easy dampness and clumping, and easy breakage when licked by livestock, resulting in a short lifespan and significant waste. Fibrous willow cellulose is a natural fiber material that meets the requirements for food additives. Therefore, the synthesis of salt brick composite materials with high heat resistance through a one-step preparation process is of significant research importance. Summary of the Invention

[0004] In view of this, the purpose of this invention is to address the problems existing in the prior art by providing a method for preparing heat-resistant salt bricks reinforced with *Salix psammophila* cellulose through hot pressing and densification. This method involves mixing *Salix psammophila* cellulose with a specific particle size distribution with refined salt, and then hot-pressing the mixture under specific temperature and pressure conditions. This significantly improves the heat resistance, structural integrity, and mechanical strength of the salt bricks, resulting in excellent heat resistance. At 350 °C, the heat-resistant salt bricks prepared by this invention show a crack length of 3 cm that stops extending after approximately 12 minutes of heating; after continuous heating at 600 °C for approximately 4 minutes, the crack length reaches 5 cm and stops extending; and after heating for 90 minutes, the bricks maintain structural integrity and do not crack.

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

[0006] A method for preparing heat-resistant salt bricks reinforced with Salix psammophila cellulose by hot pressing densification involves using sodium chloride and Salix psammophila cellulose as raw materials, mixing them and molding them, and then pressing them into salt bricks through a hot pressing molding process.

[0007] It is worth noting that, considering that existing technologies have failed to effectively solve the problems of low success rate in the pressing process of salt bricks and rapid crack propagation during high-temperature processes, this invention evaporates some of the moisture in the salt bricks through the hot pressing process, reducing the moisture content to below the equilibrium moisture content. This allows the salt bricks to have a certain initial strength when demolded, reducing the risk of shrinkage and cracking during high-temperature heat treatment, and effectively optimizing the problem of brittle and easily crumbling salt bricks formed by pure pressure pressing.

[0008] Furthermore, the temperature of the hot pressing process is 155-160℃ and the directional pressure is 15-16 MPa.

[0009] It is worth noting that this invention employs a hot-pressing process with a limited temperature of 155-160℃. Firstly, edible salt (NaCl) undergoes plastic softening at 155℃. At this temperature, the salt particles no longer primarily deform elastically under pressure but exhibit certain plastic flow characteristics, fully filling the pores between particles and significantly increasing density. Secondly, the lignin accompanying the cellulose in *Salix psammophila* is a natural thermoplastic polymer that transitions from a glassy state to a gel-like state at 150-180℃, acting as a "binder" between particles and firmly binding the salt particles and cellulose fibers into a cohesive whole. Finally, some moisture evaporates during the hot-pressing process, giving the salt bricks a certain initial strength upon demolding and reducing the risk of drying shrinkage and cracking. Therefore, the hot-pressed salt bricks possess good initial strength, are not prone to cracking after demolding, and have a uniform structure.

[0010] Furthermore, the method for preparing *Salix psammophila* cellulose-reinforced heat-resistant salt bricks by hot pressing densification includes the following steps: S1. Grind the coarse salt for 60-90 min, then filter it twice through a 20-80 mesh sieve to obtain fine salt; S2. Mix the fine salt and sand willow cellulose evenly. After mixing evenly, filter the mixture through a 20-80 mesh sieve to obtain the mixture. S3. Pour the mixture evenly into a specific mold, then spray water evenly on the surface of the mixture 3-5 times, and then use a hot press molding machine to hold the pressure for 5 minutes at a temperature of 155-160℃ and a directional pressure of 15-16 MPa. Finally, press the mixture into salt bricks with a thickness of 4-25 mm.

[0011] It is worth noting that the heat-resistant salt bricks described in this invention are all sodium chloride heat-resistant salt bricks. During preparation, sodium chloride and sand willow cellulose are mixed and then immediately hot-pressed after being sprayed with water to avoid excessive water absorption by cellulose, which would lead to a decrease in interfacial bonding strength.

[0012] Furthermore, in step S1, the type of crude salt is refined salt, dust salt, and sun-dried salt.

[0013] Furthermore, in step S2, the *Salix psammophila* cellulose is fibrous *Salix psammophila* cellulose with a mesh size of 20-40, 40-60, or 60-80 mesh.

[0014] Furthermore, when the fine salt and the cellulose from Salix psammophila are mixed evenly, the mass ratio of the added cellulose from Salix psammophila is 0.1 wt%-0.9 wt%.

[0015] Furthermore, in step S3, the amount of water sprayed each time is controlled at 0.2-0.6 mL / cm².

[0016] It is worth noting that in step S3, the principle for spraying water onto the mixture is as follows: after the mixture is evenly poured into the mold, water is sprayed evenly onto the surface of the mixture 3-5 times using a spray bottle. The amount of water sprayed each time is controlled at 0.2-0.6 mL / cm² to ensure that the water wets the surface without penetrating to the bottom, so as to maintain the orderly rearrangement of ionic bonds between salt particles and the densification of the structure during hot pressing.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention significantly improves the heat resistance of salt bricks. The heat-resistant salt bricks reinforced with willow cellulose obtained by the present invention have a crack length of 3 cm and no longer extend after heating at 350 ℃ for about 12 minutes, which is 60.5% lower than that of pure salt bricks; after continuous heating at 600 ℃ for about 4 minutes, the crack length is 5 cm and no longer extends, which is 45.7% lower than that of pure salt bricks; after heating for 90 minutes, the structure remains intact and does not break, which shows good heat resistance. (2) The heat-resistant salt bricks prepared by the present invention achieve plastic flow of salt particles and bonding effect of cellulose through hot pressing densification molding process, which greatly improves the density, hardness and overall strength of the salt bricks. (3) The addition of fibrous cellulose from sand willow wood can effectively absorb and inhibit crack propagation, and the main crack extension rate is greatly reduced under high temperature environment, giving salt bricks good thermal shock resistance and mechanical support. (4) The heat-resistant salt brick prepared by the present invention has the characteristics of high hardness and strength after heat treatment. During the heat treatment process, the carboxyl groups on the surface of fibrous cellulose can form ionic bonds with sodium ions or chloride ions, which can greatly improve the strength and hardness of the salt brick. (5) The heat-resistant salt brick prepared by the present invention has ideal adsorption characteristics. During the heat treatment process at 650 °C, the fibrous cellulose will be locally carbonized to form a large number of pore structures. These pore structures can effectively adsorb gases and fumes generated by oils in the surrounding environment. (6) The method of the present invention is simple and the conditions are controllable, making it suitable for large-scale production. The salt bricks prepared have both excellent weather resistance and functionality, and can be widely used in high-temperature roasting salt plates, long-lasting livestock licking salt bricks, and other fields, effectively expanding the high-value-added application of sodium chloride. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1 The image shows a 7.78 mm thick hot-pressed densified fibrous cellulose-reinforced heat-resistant salt brick obtained in Example 1 of this invention. Figure 2 The image shows the 8.15 mm thick hot-pressed densified fibrous cellulose-reinforced heat-resistant salt brick obtained in Example 2 of the present invention. Figure 3 This is a length diagram of the 7.78 mm thick hot-pressed densified fibrous cellulose-reinforced heat-resistant salt brick obtained in Example 1 of the present invention. Figure 4 This is a length diagram of the 8.15 mm thick hot-pressed densified fibrous cellulose-reinforced heat-resistant salt brick obtained in Example 2 of the present invention. Figure 5 The images show the 8.15 mm thick hot-pressed densified fibrous cellulose-reinforced heat-resistant salt brick obtained in Example 2 of this invention, heated at 600°C for 10 min (left) and 90 min (right). Figure 6 A diagram of the 22.39 mm thick pure salt brick obtained in Example 4 of this invention; Figure 7 Laser confocal images (a: surface morphology, b: 3D morphology) of the 8.15 mm thick hot-pressed densified fibrous cellulose-reinforced heat-resistant salt brick obtained in Example 2 of the present invention. Figure 8 Laser confocal images (a: surface morphology, b: 3D morphology) of a 7.78 mm thick fibrous cellulose-reinforced heat-resistant salt brick obtained in Example 1 of the present invention. Figure 9 The graphs show the relationship between crack length and heat treatment time for 8.15 mm thick pure salt bricks and hot-pressed, densified fibrous cellulose-reinforced heat-resistant salt bricks obtained in Comparative Example 1 and Example 2 of this invention, respectively, after high-temperature heat treatment at 350 °C and 600 °C (a: pure salt brick, b: 0.5% 40-mesh cellulose-reinforced salt brick). Figure 10The graphs show the relationship between crack length and heat treatment time after different proportions of 40-mesh cellulose were added to the 8.15 mm thick hot-pressed densified fibrous cellulose-reinforced heat-resistant salt bricks obtained in Example 2 of the present invention, after high-temperature heat treatment at 350 ℃ and 600 ℃ respectively (a: 0.1% 40-mesh cellulose-reinforced salt brick, b: 0.3% 40-mesh cellulose-reinforced salt brick, c: 0.5% 40-mesh cellulose-reinforced salt brick, d: 0.7% 40-mesh cellulose-reinforced salt brick). Figure 11 The graphs show the relationship between temperature and room temperature standing time after high-temperature heat treatment at 350 ℃ and 600 ℃ for pure salt bricks and hot-pressed densified fibrous cellulose-reinforced heat-resistant salt bricks with a thickness of 8.15 mm obtained in Example 3 and Comparative Example 1 of the present invention (a: pure salt brick, b: 0.5% 60 mesh cellulose-reinforced salt brick). Figure 12 The graphs show the relationship between crack length and heat treatment time for 8.15 mm thick hot-pressed densified fibrous cellulose-reinforced heat-resistant salt bricks and un-hot-pressed densified heat-resistant salt bricks obtained in Example 2 and Comparative Example 2 of the present invention after high-temperature heat treatment at 350 °C and 600 °C, respectively (a: pure pressure-formed 0.5% 40-mesh cellulose-reinforced salt brick, b: hot-pressed densified 0.5% 40-mesh cellulose-reinforced salt brick). Figure 13 This is a diagram illustrating the high-temperature modification mechanism of sodium chloride in the heat-resistant salt bricks obtained in the embodiments of the present invention. Figure 14 This is a flowchart of the preparation process of the present invention. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in the embodiments of this application, unless otherwise specified, employs conventional testing methods in the art. It should be understood that the terminology used in this application is merely for describing particular implementations and is not intended to limit the scope of this disclosure.

[0022] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; other experimental methods and technical means not specifically mentioned herein refer to experimental methods and technical means commonly used by one of ordinary skill in the art.

[0023] To better illustrate the content of this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented even without certain specific details. In the embodiments, some methods, means, instruments, and devices well-known to those skilled in the art are not described in detail in order to highlight the main points of this application.

[0024] In the description of this invention, it should be understood that the terms "inner," "outer," "first," "last," etc., indicating orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing this invention, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Similarly, the terms "first," "second," etc., indicating differences in components are only for the convenience of describing this invention, and do not indicate or imply that the device or element referred to must have a specific order or sequence, and therefore should not be construed as a limitation of this invention.

[0025] Without conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the resulting technical solution belongs to the content disclosed in the embodiments of this application.

[0026] This invention discloses a method for preparing heat-resistant salt bricks reinforced with *Salix psammophila* cellulose through hot pressing densification, belonging to the field of inorganic non-metallic composite material preparation technology. This invention uses sodium chloride as a raw material, incorporating a certain proportion of *Salix psammophila* cellulose as a reinforcing phase, and achieves densification of the salt bricks through a hot pressing process. The resulting salt bricks have a uniform structure, high strength, and excellent heat resistance. Experiments show that after heating at 350 ℃ for about 12 minutes, the crack length of the salt brick reaches 3 cm and stops extending; after continuous heating at 600 ℃ for about 4 minutes, the crack length reaches 5 cm and stops extending; and after heating for 90 minutes, the structure remains intact and does not crack. This invention fully utilizes the environmentally friendly properties and reinforcing effect of *Salix psammophila* cellulose, combined with a hot pressing process to improve the physical properties of the salt bricks, providing a new avenue for their application in high-temperature functional materials and diversified fields in the salt industry.

[0027] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0028] Example 1 A method for preparing Salix psammophila cellulose-reinforced heat-resistant salt bricks by hot pressing densification includes the following steps ( Figure 14 ): S1. Grind the coarse salt using a pulverizer for 60 minutes, and then filter it twice using a 20-mesh sieve. S2. Peeled sand willow is crushed into 20-mesh fibrous cellulose using a pulverizer; S3. Add 0.1wt%-0.9wt% of Salix psammophila cellulose to the ground fine salt and mix evenly. After mixing evenly, filter through a 20-mesh sieve to obtain the mixture. S4. Pour the mixture evenly into the mold, spray water evenly on the surface of the mixture 3-5 times, and then use a hot press molding machine to hold the pressure for 5 minutes at a temperature of 155-160 ℃ and a directional pressure of 15-16 MPa. Finally, press the mixture into salt bricks with a thickness of 4-25 mm.

[0029] Testing showed that the heat-resistant salt brick prepared in this embodiment was successfully pressed and formed, with a thickness of 7.78 mm. Figure 1 ), length 149 mm ( Figure 3 ).

[0030] Example 2 A method for preparing Salix psammophila cellulose-reinforced heat-resistant salt bricks by hot pressing densification includes the following steps: S1. Grind the coarse salt using a pulverizer for 90 minutes, and then filter it twice using a 40-mesh sieve. S2. Peeled sand willow is crushed into 40-mesh fibrous cellulose using a pulverizer; S3. Add 0.1wt%-0.9wt% of sand willow cellulose to the ground fine salt and mix evenly. After mixing evenly, filter through a 40-mesh sieve to obtain the mixture. S4. Pour the mixture evenly into the mold, spray water evenly on the surface of the mixture 3-5 times, and then use a hot press molding machine to hold the pressure for 5 minutes at a temperature of 155-160℃ and a directional pressure of 15-16 MPa. Finally, press the mixture into salt bricks with a thickness of 4-25 mm.

[0031] Testing showed that the heat-resistant salt bricks prepared in this embodiment were successfully pressed and formed, with a thickness of 8.15 mm. Figure 2 ), length 151mm ( Figure 4 ).

[0032] Example 3 A method for preparing Salix psammophila cellulose-reinforced heat-resistant salt bricks by hot pressing densification includes the following steps: S1. Grind the coarse salt using a pulverizer for 30 minutes, and then filter it twice using a 60-mesh sieve. S2. Peeled sand willow is crushed into 60-mesh fibrous cellulose using a pulverizer; S3. Add 0.1wt%-0.9wt% of Salix psammophila cellulose to the ground fine salt and mix evenly. After mixing evenly, filter through a 60-mesh sieve to obtain the mixture. S4. Pour the mixture evenly into the mold, spray water evenly on the surface of the mixture 3-5 times, and then use a hot press molding machine to hold the pressure for 5 minutes at a temperature of 155-160℃ and a directional pressure of 15-16 MPa. Finally, press the mixture into salt bricks with a thickness of 4-25 mm.

[0033] Tests showed that the heat-resistant salt bricks prepared in this embodiment were successfully pressed and formed with a thickness of 8.15 mm.

[0034] Example 4 A method for preparing Salix psammophila cellulose-reinforced heat-resistant salt bricks by hot pressing densification includes the following steps: S1. Grind the coarse salt using a pulverizer for 90 minutes, and then filter it twice using an 80-mesh sieve. S2. Peeled sand willow is crushed into 80-mesh fibrous cellulose using a pulverizer; S3. Add 0.1wt%-0.9wt% of sand willow cellulose to the ground fine salt and mix evenly. After mixing evenly, filter through an 80-mesh sieve to obtain the mixture. S4. Pour the mixture evenly into the mold, spray water evenly on the surface of the mixture 3-5 times, and then use a hot press molding machine to hold the pressure for 5 minutes at a temperature of 155-160℃ and a directional pressure of 15-16 MPa. Finally, press the mixture into salt bricks with a thickness of 4-25 mm.

[0035] Testing showed that the heat-resistant salt bricks prepared in this embodiment were successfully pressed and formed, with a thickness of 22.39 mm. Figure 6 ).

[0036] To further demonstrate the beneficial effects of the present invention and to better understand the present invention, the following comparative examples and experimental examples further illustrate the characteristics and application performance of the method for preparing cellulose-reinforced heat-resistant salt bricks by hot pressing densification disclosed in the present invention. However, these should not be construed as limiting the present invention. Other methods and applications obtained by those skilled in the art based on the above-described invention and their results are also considered to fall within the protection scope of the present invention.

[0037] Comparative Example 1 A method for preparing pure salt bricks by hot pressing densification: S1. Grind the coarse salt for 60-90 min, and filter it twice through a 20-80 mesh sieve to obtain fine salt; S2. Without adding sand willow cellulose, directly sieve the fine salt again through a 20-80 mesh sieve to obtain pure salt material; S3. Pour the pure salt material evenly into the mold, and spray water evenly on the surface of the material 3-5 times, with a water volume of 0.2-0.6 mL / cm² each time. S4. Using a hot press molding machine, press the pure salt bricks with a thickness of 8.15 mm by holding the pressure for 5 minutes at 155-160 ℃ and directional pressure of 15-16 MPa.

[0038] Compared to Example 2, the only difference is that only coarse salt (refined salt / dust salt / sun-dried salt) is used as the raw material, without the addition of willow cellulose. Testing showed that the thickness of the conventional thickness pure salt brick prepared in this comparative example was 8.15 mm.

[0039] Comparative Example 2 A method for producing a heat-resistant salt brick reinforced with cellulose from *Salix psammophila* includes the following steps: S1. Grind the coarse salt using a pulverizer for 90 minutes, and then filter it twice using a 40-mesh sieve. S2. Peeled sand willow is crushed into 40-mesh fibrous cellulose using a pulverizer; S3. Mix the ground fine salt with 0.5 wt% saxaul cellulose evenly, and filter the mixture through a 40-mesh sieve to obtain the mixture. S4. Pour the mixture evenly into the mold, spray water evenly on the surface of the mixture 3-5 times, and then use a molding machine to press at room temperature for 5 minutes to finally press the mixture into salt bricks with a thickness of 4-25 mm.

[0040] Compared to Example 2, the only difference is that it did not undergo hot-press densification treatment.

[0041] Testing revealed that the salt bricks prepared in this comparative example had low density and numerous internal pores. They cracked rapidly and continued to expand upon heating at 350°C, and collapsed after a short period of heating at 600°C, failing to maintain structural integrity. In contrast, the heat-resistant salt bricks prepared in Example 2, through a hot-pressing densification process at 155-160°C and 15-16 MPa, exhibited plastic flow of salt particles and thermal bonding of cellulose and lignin, significantly improving density, mechanical strength, and high-temperature stability. This molding process greatly enhances the overall strength of the salt bricks. Figure 12 The control group (a) was compared with the salt brick obtained in Example 2 (b) of the present invention. The relationship between crack length and heat treatment time at 350 ℃ and 600 ℃ was compared with that of the salt brick obtained in Example 2 of the present invention. The salt brick obtained in Example 2 of the present invention has better heat resistance and crack resistance. The cracks stopped quickly at 350 ℃ and the structure remained intact after heating at 600 ℃ for 90 min. This verifies the effect of hot pressing densification process on improving heat resistance and crack resistance.

[0042] Pure salt bricks showed cracks after 1 minute at 600 ℃, with a crack length of approximately 7.8 cm, and reached 9.2 cm after 15 minutes. At 350 ℃, the crack length reached 5.8 cm after 1 minute and 7.6 cm after 15 minutes, indicating severe thermal stress concentration and poor crack resistance in the salt matrix without reinforcement. However, the 40-mesh Salix psammophila cellulose-reinforced composite exhibited excellent overall performance: no cracks appeared within 6 minutes at 350 ℃, and the crack length was only 3.0 cm after 15 minutes, a reduction of 60.5% compared to pure salt; at 600 ℃, the crack length was 4.0 cm after 1 minute and 5.0 cm after 15 minutes, a reduction of 45.7%.

[0043] Tests and results: The salt bricks prepared in the examples and comparative examples were placed in a high-temperature test furnace and subjected to heat treatment using a programmed temperature control method. 1. 350 ℃ heat treatment: Heat to 350 ℃ at a conventional heating rate, keep at a constant temperature, and record the crack propagation and crack arrest time; 2. 600 ℃ heat treatment: Heat to 600 ℃ at a conventional heating rate, maintain the temperature for 90 min, and observe the structural integrity.

[0044] like Figure 5 As shown, the heat-resistant salt brick with a thickness of 8.15 mm obtained in Example 2 was heated at 600 °C for 10 min (left) and 90 min (right). The salt brick still maintained its complete structure, which verifies that the heat-resistant salt brick with cellulose-reinforced by hot pressing and densification has excellent heat resistance.

[0045] like Figure 7 As shown, the 8.15 mm thick heat-resistant salt brick obtained from Example 2, after heat treatment at 350 °C, has a low surface roughness. The presence of fibrous cellulose can be clearly observed in the figure, verifying that the hot-pressed densified fiber-reinforced composite material of the present invention has been successfully synthesized.

[0046] like Figure 8 As shown, the 7.78 mm thick heat-resistant salt brick obtained from Example 1 still maintains its complete structure and has a large surface roughness after high-temperature heat treatment at 600 °C. Similarly, the presence of fibrous cellulose can be clearly observed in the figure, further verifying that the present invention has successfully synthesized fiber-reinforced composite materials.

[0047] Pure salt bricks with a thickness of 8.15 mm (Comparative Example 1, Figure a) and cellulose-reinforced heat-resistant salt bricks (Example 2, Figure b) were subjected to high-temperature heat treatment at 350 °C and 600 °C, respectively. The relationship between crack length and heat treatment time is as follows: Figure 9As shown, the crack length and crack initiation time of the heat-resistant salt brick prepared by the present invention are significantly better than those of pure salt brick, which verifies that the heat-resistant salt brick reinforced with cellulose by hot pressing and densification has excellent heat resistance.

[0048] like Figure 10 As shown, the *Salix psammophila* cellulose-reinforced heat-resistant salt bricks with a thickness of 8.15 mm, obtained by adding 0.1% (Figure a), 0.3% (Figure b), 0.5% (Figure c), and 0.7% (Figure d) of 40-mesh fibrous cellulose as disclosed in Example 2 of this invention, were subjected to high-temperature heat treatment at 350 ℃ and 600 ℃, respectively. The data show that the crack length and crack initiation time of the heat-resistant salt bricks prepared by this invention are affected by the proportion of fibrous cellulose added. When the proportion of fibrous cellulose added is 0.5%, the heat-resistant salt bricks prepared by this invention have the best heat resistance, verifying that the *Salix psammophila* cellulose-reinforced heat-resistant salt bricks prepared by hot pressing densification have excellent heat resistance.

[0049] Pure salt bricks (Fig. a) and cellulose-reinforced heat-resistant salt bricks (Fig. b) with a thickness of 8.15 mm prepared in Comparative Example 1 and Example 3 were subjected to high-temperature heat treatment at 350 °C and 600 °C, respectively, and then left to stand at room temperature. The temperature of the salt bricks was measured at different standing times. Figure 11 It can be observed that the heat-resistant salt bricks prepared by this invention have significantly better thermal insulation performance than pure salt bricks, verifying that the heat-resistant salt bricks reinforced with cellulose from *Salix psammophila* prepared by hot pressing and densification have excellent thermal insulation performance.

[0050] like Figure 12 As shown, a pure pressure-molded 0.5% 40-mesh cellulose-reinforced salt brick (Figure a) with a thickness of 8.15 mm and a hot-pressed densified 0.5% 40-mesh cellulose-reinforced salt brick (Figure b) were subjected to high-temperature heat treatment at 350 ℃ and 600 ℃, respectively. The hot-pressed densified heat-resistant salt brick prepared by this invention has significantly better heat resistance and crack resistance than the pure pressure-molded salt brick, verifying the effect of the hot-pressing densification process on improving heat resistance and crack resistance.

[0051] like Figure 13As shown, the heat-resistant salt bricks prepared by the method of this invention possess ideal physical properties, mainly based on the combined effects of the high-temperature modification mechanism of sodium chloride and the synergistic effect of multiple components: sodium chloride transforms from a glassy state to a plastic flow state at 155–160 °C, and recrystallizes upon cooling, significantly improving the mechanical strength of the salt bricks; simultaneously, through the synergistic effect of high-temperature plastic softening of sodium chloride, reinforcement and toughening by willow cellulose, and hot-pressing densification, the heat resistance and structural stability are further significantly improved. Sodium chloride undergoes plastic flow and particle rearrangement densification at hot-pressing temperature, significantly improving the density and initial strength of the salt bricks; willow cellulose, as a natural reinforcing phase, can effectively inhibit crack initiation and propagation, and its accompanying lignin transforms into a gel-like state at hot-pressing temperature, strengthening the interfacial bonding force between salt particles and fibers; the hot-pressing process simultaneously completes the densification of salt, the bonding and fixation of fibers, and the rapid removal of moisture, resulting in a uniform internal structure, fewer defects, and strong thermal shock resistance in the salt bricks. With the synergy of these three elements, salt bricks are less prone to cracking and breakage at high temperatures. Their heat resistance, mechanical strength, and structural stability are far superior to pure salt bricks and unheat-pressed cellulose-reinforced salt bricks, achieving an integrated technical effect of high density, high heat resistance, and high stability.

[0052] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing *Salix psammophila* cellulose-reinforced heat-resistant salt bricks by hot pressing and densification, characterized in that, Salt bricks are made from sodium chloride and willow cellulose as raw materials, mixed and molded, and then pressed into salt bricks through a hot pressing process.

2. The method for preparing *Salix psammophila* cellulose-reinforced heat-resistant salt bricks by hot pressing densification according to claim 1, characterized in that, The temperature of the hot pressing process is 155-160℃ and the directional pressure is 15-16 MPa.

3. The method for preparing *Salix psammophila* cellulose-reinforced heat-resistant salt bricks by hot pressing densification according to claim 2, characterized in that, Includes the following steps: S1. Grind the coarse salt for 60-90 min, then filter it twice through a 20-80 mesh sieve to obtain fine salt; S2. Mix the fine salt and sand willow cellulose evenly. After mixing evenly, filter the mixture through a 20-80 mesh sieve to obtain the mixture. S3. Pour the mixture evenly into a specific mold, then spray water evenly on the surface of the mixture 3-5 times, and then use a hot press molding machine to hold the pressure for 5 minutes at a temperature of 155-160℃ and a directional pressure of 15-16 MPa. Finally, press the mixture into salt bricks with a thickness of 4-25 mm.

4. The method for preparing *Salix psammophila* cellulose-reinforced heat-resistant salt bricks by hot pressing densification according to claim 3, characterized in that, In step S1, the type of crude salt is refined salt, dust salt, and sun-dried salt.

5. The method for preparing *Salix psammophila* cellulose-reinforced heat-resistant salt bricks by hot pressing densification according to claim 3, characterized in that, In step S2, the *Salix psammophila* cellulose is fibrous *Salix psammophila* cellulose with mesh sizes of 20-40, 40-60, and 60-80 mesh.

6. The method for preparing *Salix psammophila* cellulose-reinforced heat-resistant salt bricks by hot pressing densification according to claim 5, characterized in that, When the fine salt and sand willow cellulose are mixed evenly, the mass ratio of sand willow cellulose added is 0.1 wt%-0.9 wt%.

7. The method for preparing *Salix psammophila* cellulose-reinforced heat-resistant salt bricks by hot pressing densification according to claim 3, characterized in that, In step S3, the amount of water sprayed each time is controlled at 0.2-0.6 mL / cm².

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