Preparation method of buoyancy oriented continuous spinning hydrogel ultralight fiber

Abstract

The invention belongs to the technical field of functional composite material preparation, and particularly relates to a preparation method of buoyancy-oriented continuous spinning hydrogel ultralight fiber, the ultralight fiber is composed of a hydrogel matrix and a lightweight filler, and the buoyancy-oriented continuous spinning hydrogel ultralight fiber is prepared by adjusting the hydrophilic / hydrophobic property, the cross-linked network and the density of a lightweight functional microphase and the gel matrix. The interface interaction among multiple phases can be optimized, so that the overall mechanical property and the buoyancy orientation degree of the fiber are enhanced. Besides, continuous preparation of the composite fiber can be realized by skillfully using a buoyancy drafting orientation technology generated by density difference between a gel precursor and a coagulating bath, the method is lower in consumption and more efficient, and does not have complicated post-treatment procedures, and the hydrogel fiber prepared by the method has the characteristics of being ultra-light, high in orientation, continuous, low in consumption and efficient, and does not have complicated post-treatment procedures.

Description

Technical Field

[0001] The present invention relates to a method for preparing buoyancy-oriented continuous spinning hydrogel ultra-light fibers. The hydrogel fibers prepared by this method have the characteristics of ultra-light weight, high orientation, continuous production, low energy consumption and high efficiency, and no complicated post-treatment processes, and belong to the field of preparation of functional composite materials. Background Art

[0002] Hydrogel fiber materials have both the functional characteristics of hydrogels and the advantages of continuous and highly oriented fiber structures. One-dimensional hydrogel fibers have the characteristic of a small cross-section. When their dimension is expanded, they also have advantages such as easy weaving, good biocompatibility, soft and skin-friendly, fast heat and mass transfer, and expandable functions. They have been widely studied and reported. Such hydrogel fibers have extensive applications in fields such as flexible sensors, wound dressings, and artificial skin.

[0003] Currently, many spinning methods have been developed to prepare hydrogel fibers, such as microfluidic spinning, electrospinning, wet spinning, gel spinning, mechanical drawing method, etc. Among them, the electrospinning method is the most commonly used and widespread method. Electrospinning is a special fiber manufacturing process in which a polymer solution or melt is sprayed and spun in a strong electric field. Under the action of the electric field, the liquid droplets at the needle tip will change from a spherical shape to a conical shape (i.e., the "Taylor cone"), and fiber filaments are extended from the tip of the cone. However, in terms of practical applications, the output of electrospinning machines is very low, and the strength of the spun hydrogel fibers is relatively low. In addition, due to the need to use a relatively high voltage, the energy consumption is very high. Some electrospinning systems need to be carried out in strongly corrosive or highly toxic solvents. The cost of organic solvents is high, they are not easy to recycle, and it is easy to cause environmental pollution, resulting in limited practical applications.

[0004] In the design of high-performance engineering materials, nature has always been the source of inspiration for materials scientists. Muscle fibers have a natural oriented structure, which is composed of muscle fibers (hydrophilic) and fascia (lipophilic). This orientation and two-phase heterogeneous structure make muscles have excellent mechanical properties and have attracted much attention. In addition, high orientation is not only an important structural advantage of biological muscles with high strength and high driving force, but also a leap and qualitative change from plastics to fibers. Among them, the strategy of stretching and setting (orientation)-drying (crystallization cross-linking)-re-swelling (gelation) for orientation regulation has been favored by many scientists. However, compared with the natural growth of biological muscles and industrial spinning, the pre-orientation-drying and re-swelling strategy is difficult to continuously prepare for orientation.

[0005] The hydrogel composite fibers prepared by the prior art have poor mechanical properties, high energy consumption, heavy mass, and are difficult to continuously prepare for orientation, and the post-treatment process is complicated. Therefore, the preparation of strong and tough hydrogel fibers with low energy consumption, high efficiency, simplicity and continuity is of great significance for expanding the application of hydrogel fibers in the field of intelligent materials such as flexible sensors. Summary of the Invention

[0006] To overcome the deficiencies of the prior art, the present invention provides an ultra-light hydrogel composite fiber that simultaneously has strong mechanical properties and can be continuously prepared with low energy consumption and high efficiency. It consists of a hydrogel matrix and lightweight fillers. By adjusting the hydrophilic / hydrophobic properties, cross-linking network, and density of the lightweight functional microphase and the gel matrix, the interfacial interaction between multiple phases can be optimized, thereby enhancing the overall mechanical properties and buoyancy orientation degree of the fiber. In addition, by cleverly using the buoyancy stretching orientation technology generated by the density difference between the gel precursor and the coagulation bath, the continuous preparation of the composite fiber can be realized, which is more energy-efficient and has no complicated post-treatment processes.

[0007] The technical solution of the present invention provides a method for preparing a buoyancy-oriented continuous spinning hydrogel ultra-light fiber. Among them, the ultra-light fiber is prepared by adding lightweight fillers to a hydrogel matrix. The hydrogel matrix includes water-soluble polymers: sodium alginate, polyvinyl alcohol, sodium carboxymethyl cellulose, chitosan, and the lightweight fillers include: silica aerogel, hollow glass microspheres, paraffin, etc. This method first uses a magnetic stirrer to fully mix and homogenize the prepared hydrogel matrix and the added lightweight fillers to obtain a mixed solution of the two, and then injects the mixed solution into a salt solution under air pressure drive. Under the action of buoyancy and salting out, the hydrogel forms filaments.

[0008] The specific operation steps are as follows:

[0009] (1) Using water-soluble polymers as the matrix composition, after preparing an aqueous solution, add lightweight fillers to make a precursor solution;

[0010] (2) Prepare a coagulation bath solution, and the coagulation bath solution is a saturated sodium tripolyphosphate solution (15.7 wt%) and / or a saturated sodium sulfate solution (21.9 wt%);

[0011] (3) Pour the coagulation bath solution into a long tube with a closed bottom, pour the precursor solution into a syringe, and at a certain temperature (20 - 50 °C, preferably 25 °C), use an air pressure pump to drive the precursor solution in the syringe to be injected into the coagulation bath solution. Due to the density difference between the precursor solution and the coagulation bath solution, the continuous preparation of the composite fiber is realized under the action of buoyancy and salting out.

[0012] Further, in step (3), pour the coagulation bath solution into a long tube with a height of 1.5 m and an inner diameter of 3.6 cm. The bottom of the tube is blocked with a rubber stopper. The upper needle of the syringe: 19G / 21G, the inner rotating head: 1.6 mm, which is connected to the lower needle 16G through a silicone tube. The lower needle is inserted into the long tube through a rubber stopper. The air pressure during the air pressure pump drive is 25 psi.

[0013] Further, the water-soluble polymer is one of sodium alginate, polyvinyl alcohol, sodium carboxymethyl cellulose, chitosan, and the concentration of its aqueous solution is 5 - 20 wt%.

[0014] Furthermore, the lightweight filler is any one of silica aerogel, hollow glass microspheres, and paraffin. Among them, the mass fraction of the lightweight filler in the precursor solution is 1%-5%.

[0015] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0016] The present invention prepares a super-light, continuous, and strong mechanical property hydrogel composite fiber by means of a buoyancy orientation and two-phase heterogeneous composition strategy.

[0017] 1. The hydrogel matrix is mainly composed of water-soluble polymers: sodium alginate, polyvinyl alcohol, sodium carboxymethyl cellulose, and chitosan. Its water solubility and adjustable cross-linked network can provide a good basic structure, and its mechanical properties can be regulated by adjusting the degree of cross-linking.

[0018] 2. During the buoyancy spinning process, the buoyancy stretching orientation generated by the density difference between the gel precursor and the coagulation bath is skillfully utilized to improve the mechanical properties of the hydrogel composite fiber, and the tensile strength reaches 1.6 MPa;

[0019] 3. By adjusting the hydrophilic / hydrophobic properties, cross-linked network, and density of the lightweight functional microphase and the gel matrix, the interfacial interaction between multiple phases can be optimized. Good interfacial interaction can enhance the overall mechanical properties and buoyancy orientation degree of the fiber.

[0020] 4. Using the salting-out-buoyancy stretching continuous spinning technology, by controlling the rheological properties and composition of the spinning solution, the continuous preparation of composite fibers is realized. The spinning process can regulate the multi-level structure and properties of the fiber by adjusting process parameters (such as coagulation bath concentration / types, etc.) and adding different lightweight functional microphases (such as silica aerogel, hollow glass microspheres, paraffin, etc.).

[0021] In summary, the hydrogel composite fiber prepared by the present invention has outstanding mechanical properties. The buoyancy stretching orientation generated by the density difference between the gel precursor and the coagulation bath is skillfully utilized to improve the mechanical properties of the hydrogel composite fiber. In addition, the continuous orientation of the composite fiber can be realized by using the buoyancy spinning technology, and then the continuous preparation can be achieved. Brief Description of the Drawings

[0022] Figure 1 It is a physical diagram of the hydrogel fiber prepared in Example 1 of the present invention, which proves the success of spinning.

[0023] Figure 2 It is a schematic diagram of the buoyancy orientation of the present invention. The buoyancy generated by the density difference between the gel precursor and the coagulation bath is greater than the gravity of the gel precursor, so as to stretch and orient.

[0024] Figure 3This is a physical picture of the hydrogel composite fiber obtained in Example 1 of the present invention, demonstrating the continuous orientation of the hydrogel composite fiber.

[0025] Figure 4 This is the stress-strain curve of the hydrogel composite fiber prepared in Example 1 of the present invention, showing that the tensile strength of the hydrogel fiber can reach 1.6 MPa and the elongation at break reaches 625%. Detailed implementation manners

[0026] To further elaborate on the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following combines some representative embodiments to describe the specific implementation manners, characteristics and properties of the preparation method of the buoyancy-oriented continuous spinning hydrogel ultra-light fiber according to the present invention.

[0027] Example 1 Preparation of hydrogel composite fiber with a mass ratio of silica aerogel to polyvinyl alcohol hydrogel of 1:20 (1) Preparation of precursor solution: Dissolve polyvinyl alcohol powder in deionized water to prepare a 5 wt% polyvinyl alcohol solution. Add silica aerogel to the polyvinyl alcohol solution and use a magnetic stirrer to fully mix the two to obtain a precursor solution (i.e., a composite solution of polyvinyl alcohol and silica aerogel: polyvinyl alcohol hydrogel, the same below), where the mass fraction of silica aerogel in the precursor solution is 5%.

[0028] 2. Preparation of coagulation bath solution: Dissolve sodium tripolyphosphate powder in deionized water to prepare a 15.7 wt% sodium tripolyphosphate solution.

[0029] 3. Pour the coagulation bath solution into a long tube with a height of 1.5 m and an inner diameter of 3.6 cm, and block the bottom of the tube with a rubber stopper. Pour the precursor solution into a syringe, with the upper needle: 19G / 21G, the inner rotating head: 1.6 mm, connect the lower needle (16G) through a 2 mm silicone tube. Insert the lower needle into the long tube through the rubber stopper. Use a pneumatic pump to drive the syringe, turn on the pump, and adjust the air pressure: 25 psi. The precursor solution is driven by the air pressure of the pump, passes through the upper needle, through the silicone tube, and then through the lower needle to reach the inside of the long tube. Utilize the buoyancy stretching orientation generated by the driving force and the density difference between the gel precursor and the coagulation bath (the density of the gel precursor is 0.38 g / cm 3 , and the density of the coagulation bath is 1.14 g / cm 3 ) until the precursor solution forms fibers. Finally, collect the hydrogel composite fiber at the top of the tube (1.5 m). Use a universal material testing machine to conduct mechanical property tests, and the tensile strength of the hydrogel composite fiber obtained by this method is measured to be 1.6 MPa, and the density is 0.3 g / cm 3 .

[0030] Example 2 Preparation of Hydrogel Composite Fibers with a Mass Ratio of Silica Aerogel to Polyvinyl Alcohol Hydrogel of 1:50

[0031] (1) Preparation of the precursor solution: Dissolve polyvinyl alcohol powder in deionized water to prepare a 5 wt% polyvinyl alcohol solution. Add silica aerogel to the polyvinyl alcohol solution and use a magnetic stirrer to mix the two evenly to obtain the precursor solution. Among them, the mass fraction of silica aerogel in the precursor solution is 2%.

[0032] (2) Preparation of the coagulation bath solution: Dissolve sodium tripolyphosphate powder in deionized water to prepare a 15.7 wt% sodium tripolyphosphate solution.

[0033] (3) Pour the coagulation bath solution into a long tube with a height of 1.5 m and an inner diameter of 3.6 cm, and block the bottom of the tube with a rubber stopper. Pour the precursor solution into a syringe. The upper needle: 19G / 21G, the inner rotating head: 1.6 mm, connect the lower needle (16G) through a 2 mm silicone tube. Insert the lower needle into the long tube through the rubber stopper. Use a pneumatic pump to drive the syringe, turn on the pump, and adjust the air pressure: 25 psi. The precursor solution is driven by the air pressure of the pump, passes through the upper needle, through the silicone tube, and then reaches the inside of the long tube through the lower needle. Utilize the buoyancy stretching orientation generated by the driving force and the density difference between the gel precursor and the coagulation bath (the density of the gel precursor is 0.49 g / cm 3 , and the density of the coagulation bath is 1.14 g / cm 3 ) to form fibers from the precursor solution. Finally, collect the hydrogel composite fibers at the top of the tube (1.5 m). Use a universal material testing machine to conduct mechanical property tests. The tensile strength of the hydrogel composite fibers obtained by this method is 1.2 MPa, and the density is 0.4 g / cm 3 .

[0034] Example 3 Preparation of Hydrogel Composite Fibers with a Mass Ratio of Silica Aerogel to Polyvinyl Alcohol Hydrogel of 1:100

[0035] (1) Preparation of the precursor solution: Dissolve polyvinyl alcohol powder in deionized water to prepare a 5 wt% polyvinyl alcohol solution. Add silica aerogel to the polyvinyl alcohol solution and use a magnetic stirrer to mix the two evenly to obtain the precursor solution. Among them, the mass fraction of silica aerogel in the precursor solution is 1%.

[0036] (2) Preparation of the coagulation bath solution: Dissolve sodium tripolyphosphate powder in deionized water to prepare a 15.7 wt% sodium tripolyphosphate solution.

[0037] (3) Pour the coagulation bath solution into a long tube with a height of 1.5 m and an inner diameter of 3.6 cm, and block the bottom of the tube with a rubber stopper. Pour the precursor solution into a syringe. The upper needle: 19G / 21G, the inner rotating head: 1.6 mm, connect the lower needle (16G) through a 2-mm silicone tube. The lower needle is inserted into the long tube through the rubber stopper. Use a pneumatic pump to drive the syringe, turn on the pump, and adjust the air pressure: 25 psi. The precursor solution is driven by the air pressure of the pump, passes through the upper needle, through the silicone tube, and then reaches the inside of the long tube through the lower needle. Utilize the buoyancy stretching orientation generated by the driving force and the density difference between the gel precursor and the coagulation bath (the density of the gel precursor is 0.8 g / cm 3 , and the density of the coagulation bath is 1.14 g / cm 3 ) to form fibers from the precursor solution. Finally, collect the hydrogel composite fibers at the top of the tube (1.5 m). Use a universal material testing machine to conduct mechanical property tests. The tensile strength of the hydrogel composite fibers obtained by this method is 0.8 MPa, and the density is 0.8 g / cm 3 .

[0038] Example 4 uses a saturated sodium sulfate solution (21.9 wt%) as the coagulation bath to prepare hydrogel composite fibers.

[0039] (1) Prepare the precursor solution: Dissolve polyvinyl alcohol powder in deionized water to prepare a 5 wt% polyvinyl alcohol solution. Add silica aerogel to the polyvinyl alcohol solution and use a magnetic stirrer to fully mix the two to obtain the precursor solution. Among them, the mass fraction of silica aerogel in the precursor solution is 1%.

[0040] (2) Prepare the coagulation bath solution: Dissolve sodium sulfate powder in deionized water to prepare a 21.9 wt% sodium sulfate solution.

[0041] (3) Pour the coagulation bath solution into a long tube with a height of 1.5 m and an inner diameter of 3.6 cm, and block the bottom of the tube with a rubber stopper. Pour the precursor solution into a syringe. The upper needle: 19G / 21G, the inner rotating head: 1.6 mm, connect the lower needle (16G) through a 2-mm silicone tube. The lower needle is inserted into the long tube through the rubber stopper. Use a pneumatic pump to drive the syringe, turn on the pump, and adjust the air pressure: 25 psi. The precursor solution is driven by the air pressure of the pump, passes through the upper needle, through the silicone tube, and then reaches the inside of the long tube through the lower needle. Utilize the buoyancy stretching orientation generated by the driving force and the density difference between the gel precursor and the coagulation bath (the density of the gel precursor is 0.8 g / cm 3 , and the density of the coagulation bath is 1.11 g / cm 3)The buoyancy-induced stretching orientation is generated until the precursor solution forms fibers. Finally, the hydrogel composite fibers are collected at the top of the tube (1.5 m). The mechanical properties are tested using a universal material testing machine. The tensile strength of the hydrogel composite fibers obtained by this method is 1.3 MPa, and the density is 0.28 g / cm 3 .

[0042] Example 5 uses a 10 wt% sodium sulfate solution as the coagulation bath to prepare hydrogel composite fibers

[0043] (1) Preparation of the precursor solution: Dissolve polyvinyl alcohol powder in deionized water to prepare a 5 wt% polyvinyl alcohol solution. Add silica aerogel to the polyvinyl alcohol solution and use a magnetic stirrer to mix the two thoroughly to obtain the precursor solution. Among them, the mass fraction of silica aerogel in the precursor solution is 1%.

[0044] (2) Preparation of the coagulation bath solution: Dissolve sodium sulfate powder in deionized water to prepare a 10 wt% sodium sulfate solution.

[0045] (3) Pour the coagulation bath solution into a long tube with a height of 1.5 m and an inner diameter of 3.6 cm, and block the bottom of the tube with a rubber stopper. Pour the precursor solution into a syringe. The upper needle: 19G / 21G, the inner rotating head: 1.6 mm, connect the lower needle (16G) through a 2-mm silicone tube. Insert the lower needle into the long tube through the rubber stopper. Use a pneumatic pump to drive the syringe, turn on the pump, and adjust the air pressure: 25 psi. The precursor solution is driven by the air pressure of the pump, passes through the upper needle, through the silicone tube, and then through the lower needle to reach the inside of the long tube. Utilize the driving force and the density difference between the gel precursor and the coagulation bath (the density of the gel precursor is 0.8 g / cm 3 , and the density of the coagulation bath is 1.07 g / cm 3 ) to generate the buoyancy-induced stretching orientation until the precursor solution forms fibers. Finally, the hydrogel composite fibers are collected at the top of the tube (1.5 m). The mechanical properties are tested using a universal material testing machine. The tensile strength of the hydrogel composite fibers obtained by this method is 1.1 MPa, and the density is 0.25 g / cm 3 .

[0046] In the above examples, the spinning temperature is about room temperature (25 °C).

[0047] Example 6 prepares hydrogel composite fibers at a spinning temperature of 50 °C

[0048] (1) Preparation of precursor solution: Dissolve polyvinyl alcohol powder in deionized water to prepare a 5wt% polyvinyl alcohol solution. Add silica aerogel to the polyvinyl alcohol solution and use a magnetic stirrer to mix the two evenly to obtain the precursor solution. Among them, the mass fraction of silica aerogel in the precursor solution is 5%.

[0049] 2. Preparation of coagulation bath solution: Dissolve sodium tripolyphosphate powder in deionized water to prepare a 15.7wt% sodium tripolyphosphate solution.

[0050] 3. Pour the coagulation bath solution into a long tube with a height of 1.5 m and an inner diameter of 3.6 cm. Block the bottom of the tube with a rubber stopper and wrap the outside of the long tube with a heat-insulating film to ensure that the coagulation bath solution remains at 50 °C. Pour the precursor solution into a syringe. The upper needle: 19G / 21G, the inner rotating head: 1.6 mm, and connect the lower needle (16G) through a 2-mm silicone tube. Insert the lower needle into the long tube through the rubber stopper. Use a pneumatic pump to drive the syringe, turn on the pump, and adjust the air pressure: 25 psi. The precursor solution is driven by the air pressure of the pump, passes through the upper needle, through the silicone tube, and then through the lower needle to reach the inside of the long tube. Utilize the buoyancy stretching orientation generated by the driving force and the density difference between the gel precursor and the coagulation bath until the precursor solution forms a hydrogel composite fiber collected at the top of the tube (1.5 m). Conduct a mechanical property test using a universal material testing machine. The tensile strength of the hydrogel composite fiber obtained by this method is 1.1 MPa, and the density is 0.3 g / cm 3 。

[0051] Compared with the room-temperature spinning in Example 1, the tensile strength of the composite fiber spun at 50 °C in this example is slightly reduced.

[0052] Example 7 selects hollow glass microspheres as the lightweight functional microphase to prepare hydrogel composite fibers

[0053] On the basis of Example 1, replace the silica aerogel with the same amount of hollow glass microspheres. The strength of the obtained hydrogel composite fiber is 1.6 MPa, and the density is 0.4 g / cm 3 .。

[0054] Example 8 selects paraffin as the lightweight functional microphase to prepare hydrogel composite fibers

[0055] On the basis of Example 1, replace the silica aerogel with the same amount of paraffin. The strength of the obtained hydrogel composite fiber is 1.6 MPa, and the density is 0.9 g / cm 3 。

[0056] The comparative example uses electrospinning technology to prepare hydrogel composite fibers

[0057] 1. Dissolve polyvinyl alcohol powder in deionized water to prepare a 5wt% polyvinyl alcohol solution. Add silica aerogel to the polyvinyl alcohol solution and use a magnetic stirrer to mix the two evenly. Among them, the mass fraction of silica aerogel in the mixed solution is 5%.

[0058] 2. Preparation of electrospinning equipment: Fill the spinning solution into a syringe, connect the syringe pump, and ensure that the connection between the syringe and the nozzle is tight and leak-free. Connect the nozzle to the positive electrode of the high-voltage power supply, and ground the collection device. Set the voltage of the high-voltage power supply to 15 kV, set the flow rate of the syringe pump to 0.3 mL / h, adjust the distance between the nozzle and the collection device to 10 cm, and use a 19G / 21G metal needle.

[0059] 3. Electrospinning operation: Turn on the syringe pump to make the spinning solution spray out from the nozzle at the set flow rate. Start the high-voltage power supply to apply a high voltage so that the spinning solution forms a Taylor cone under the action of the electric field and is stretched into fibers. The fibers are deposited on the collection device under the action of the electric field to form a PVA fiber membrane. During the electrospinning process, keep the ambient temperature at room temperature of 25 °C to ensure the uniform formation and stable collection of fibers. The collection device is a grounded roller. In order to compare with the hydrogel composite fibers prepared by the buoyancy orientation method, no post-treatment steps such as drying treatment and heat treatment are performed on the obtained fibers. After collection, the mechanical properties are tested using a universal material testing machine. The tensile strength of the hydrogel composite fibers obtained by this method is 0.6 MPa, and the density is 0.7 g / cm 3 。

Claims

1. A preparation method of buoyancy-oriented continuous spinning hydrogel ultra-light fibers, the operation steps are as follows: (1) Composed of a water-soluble polymer as a matrix, after being formulated into an aqueous solution, a lightweight filler is added to make a precursor solution; (2) Prepare a coagulation bath solution, and the coagulation bath solution is a saturated sodium tripolyphosphate solution and / or a saturated sodium sulfate solution; (3) Pour the coagulation bath solution into a long tube with a closed bottom, pour the precursor solution into a syringe, and use an air pressure pump to drive the precursor solution in the syringe to be injected into the coagulation bath solution. Due to the density difference between the precursor solution and the coagulation bath solution, continuous preparation of composite fibers is achieved under the action of buoyancy and salting out.

2. The preparation method according to claim 1, characterized in that, In step (3), the coagulation bath solution is poured into a long tube with a height of 1.5 m and an inner diameter of 3.6 cm, and the bottom of the tube is blocked with a rubber stopper. The upper needle of the syringe: 19G / 21G, the inner rotating head: 1.6 mm, which is connected to the lower needle 16G through a silicone tube, and the lower needle is inserted into the long tube through a rubber stopper. When the air pressure pump is driven, the air pressure is 25 psi.

3. The preparation method according to claim 1, characterized in that, The water-soluble polymer is one of sodium alginate, polyvinyl alcohol, sodium carboxymethyl cellulose, and chitosan, and the concentration of its aqueous solution is 5-20 wt%.

4. The preparation method according to claim 1, characterized in that, The lightweight filler is any one of silica aerogel, hollow glass microspheres, and paraffin. Among them, the mass fraction of the lightweight filler in the precursor solution is 1%-5%.

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