A method for preparing high retention performance foam-molded fiber composites based on physical retention technology

Abstract

This invention belongs to the field of fiber composite material preparation and discloses a method for preparing high-retention-performance foam-molded fiber composite materials based on physical retention technology. The method includes the following steps: adding fibers, fillers, and retention aids into water and dispersing them uniformly; then adding a foaming agent and fully foaming to obtain a foam slurry; firstly, dehydrating and defoaming the foam slurry under high vacuum; when the foam slurry reduces a certain volume or height, lowering the filtration vacuum; continuing dehydration, defoaming, and molding under low vacuum to obtain a fiber composite material preform; and finally, pressing and drying to obtain a high-retention-performance foam-molded fiber composite material. This invention enhances the physical retention of the fiber layer by adjusting the vacuum level during the foam molding process and using segmented filtration molding, further improving the retention rate of fine fibers and fillers in the slurry and promoting the uniform distribution of fillers on both sides and in the Z-direction of the foam-molded fiber composite material.

Description

Technical Field

[0001] This invention belongs to the field of fiber composite materials, and specifically relates to a method for preparing high retention performance foam-molded fiber composite materials based on physical retention technology. Background Technology

[0002] Foam molding is a material preparation technology that uses micron-sized water-based bubbles as a dispersion medium to uniformly disperse fibers in a foam system, followed by dehydration (defoaming) and drying to form the final product. This method has a wide range of applicable raw materials, and the resulting fiber composite materials have significant advantages such as high porosity, good uniformity, and easy control of fiber orientation. They are widely used in key areas such as thermal insulation materials, electrical insulation materials, and friction materials.

[0003] In the design of fiber composites, fillers with different functions and contents are typically added according to different application scenarios to improve the composite's heat resistance, thermal conductivity, and friction resistance. During preparation, the fillers, fibers, water, and surfactants form a foam slurry system, which is then filtered and molded in a molding apparatus. However, during molding, due to the large porosity and pore size of the composite material, some fillers smaller than the pore size are lost from the mesh, limiting the fiber structure's retention effect on the fillers. Furthermore, the filler loss intensifies with increasing filler dosage, reducing filler utilization. Therefore, a method to improve the filler retention rate in foam-molded fiber composites is urgently needed.

[0004] Currently, filler retention issues mainly occur in the paper forming industry, with retention mechanisms primarily involving physical retention and colloidal flocculation. Physical retention depends mainly on the morphology and type of fibers in the pulp, and there is currently no effective method to control it while ensuring the material formulation. Colloidal flocculation is widely used in filler retention technology. This method uses polymer intervention to bridge and aggregate fillers, effectively improving filler retention, but the improvement is limited, and excessive flocculation can reduce vacuum dewatering capacity, adversely affecting material uniformity. Furthermore, high-vacuum dewatering processes force denser filler particles to settle rapidly, resulting in a filler network distribution that is more prominent at the top than the bottom, which is also detrimental to the preparation of homogeneous fiber composite materials.

[0005] Therefore, it is of great significance to develop a novel retention technology that combines physical retention with colloidal flocculation to achieve both high retention rate and uniform filler distribution in foam-molded fiber composites. Summary of the Invention

[0006] To improve the retention performance of fillers in foamed fiber composites, the primary objective of this invention is to provide a method for preparing high-retention foamed fiber composites based on physical retention technology.

[0007] This invention improves the retention performance of fillers in fiber composites through a synergistic approach combining physical retention and colloidal flocculation. First, an anionic microparticle retention aid system is mixed with a slurry (fiber and filler) to prepare a foam slurry, promoting colloidal adsorption between the filler and fiber. Then, the foam slurry is subjected to high and low vacuum conditions, first rapidly then slowly, to maximize the physical retention effect of the fiber structure on the filler, thus jointly improving the filler retention performance. The foam-molded fiber composite material prepared by this invention exhibits a higher filler retention rate and more uniform distribution, solving the problems of limited retention rate improvement and uneven filler distribution inherent in single colloidal flocculation methods.

[0008] Another object of the present invention is to provide a foam-molded fiber composite material with high retention performance.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A method for preparing high retention performance foam-molded fiber composite materials based on physical retention technology includes the following steps:

[0011] (1) Add fiber, filler and retention aid to water and disperse evenly, then add foaming agent, pour into foaming tank and fully foam to obtain foam slurry;

[0012] (2) Pour the foam slurry described in step (1) into a glass molding machine and perform vacuum filtration molding. During the molding process, adjust the vacuum valve so that the slurry is first dehydrated and defoamed under high vacuum. When the foam slurry in the molding machine is reduced to a certain volume or height, reduce the vacuum degree of filtration so that the slurry completes the final molding process under low vacuum to obtain a fiber composite preform.

[0013] (3) Press and dry the fiber composite preform obtained in step (2) to obtain a foam-molded fiber composite material with high retention performance.

[0014] Preferably, the high vacuum degree in step (2) is 10-20 kPa and the low vacuum degree is 5-10 kPa.

[0015] Preferably, in step (2), when the volume or height of the foam slurry is reduced to 1 / 2 to 3 / 4 of the original volume or height of the foam slurry, the vacuum level is reduced.

[0016] Preferably, by mass percentage, the fiber in step (1) is 30-80%, the filler is 20-70%, and the retention aid is added at a rate of 0.1-0.5% of the total mass of the filler.

[0017] Preferably, the slurry concentration in step (1) is 0.5-1%, and the foaming agent concentration in the slurry is 2.5-4 g / L.

[0018] Preferably, the fiber in step (1) is one or more of cotton fiber, aramid fiber, carbon fiber, alumina fiber, aluminum silicate fiber, and glass fiber.

[0019] More preferably, the fiber comprises 10-30% carbon fiber, 10-30% aramid fiber, and 10-30% cotton fiber.

[0020] Preferably, the filler in step (1) is one or more of graphite, alumina, diatomaceous earth, silicon dioxide, and potassium titanate whiskers.

[0021] Preferably, the retention aid in step (1) is one or more of aluminum sulfate, cationic polyacrylamide, anionic polyacrylamide, and cationic potato starch.

[0022] Preferably, the foaming agent in step (1) is one or more of alkyl glycosides, sodium dodecyl sulfate, polyvinyl alcohol, and Tween-80.

[0023] Preferably, the air content in the foam slurry in step (1) is 50-80%.

[0024] Preferably, the pressing pressure in step (3) is 0.5 to 2 MPa, and the drying temperature is 80 to 105°C.

[0025] Preferably, the forming device includes a forming cylinder 1, a filtration flask 2, a pressure gauge 3, a flow regulating valve 4, and a vacuum pump 5. The forming cylinder 1 is connected to the filtration flask 2 via a rubber stopper, and the pressure gauge 3 is connected to the filtration flask 2 to ensure a seal. The vacuum pump 5 is connected to the filtration flask 2 via a polytetrafluoroethylene (PTFE) tube, through which a gas flow regulating valve 4, which controls changes in vacuum level, is connected.

[0026] A high retention performance foam-fiber composite material is prepared by the above method.

[0027] The present invention has the following advantages and beneficial effects:

[0028] (1) This invention proposes a method for preparing high retention performance foam-molded fiber composite materials based on physical retention technology. The above-mentioned fibers, fillers, retention aids, foaming agents, etc. are mixed evenly, and foam slurry is prepared by mechanical stirring. By using multiple vacuum degrees combined with dehydration and defoaming, the physical retention efficiency of fibers can be significantly increased, and foam-molded fiber composite materials with high retention rate and uniform filler distribution can be obtained.

[0029] (2) The present invention significantly improves the filler retention rate of fiber composite materials by 4.2% to 11.7% compared with the control group. At the same time, it improves the distribution state of fillers in fiber composite materials. The Z-direction distribution of fillers is uniform, the Z-direction concentration factor is increased by 2.7% to 79.2% compared with the control group, and the difference between the two sides of the filler distribution can be controlled within 0.7%. Attached Figure Description

[0030] Figure 1 This is a flowchart of the preparation process of the present invention.

[0031] Figure 2 An apparatus for preparing a high retention foam-molded fiber composite material includes a molding barrel 1, a filtration flask 2, a pressure gauge 3, a gas flow regulating valve 4, and a vacuum pump 5.

[0032] Figure 3 This is a Z-axis distribution diagram of the filler in foam-molded fiber composite materials.

[0033] Figure 4 This is a threshold screening diagram for fillers in the cross-section of foam-molded fiber composite materials.

[0034] Figure 5 This is a surface distribution diagram of the filler in a foam-molded fiber composite material. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. For process parameters not specifically noted, conventional techniques can be referred to.

[0036] Reference Figure 2 A device for preparing high-retention foam-forming fiber composite materials is described. A forming barrel 1 is connected to a filtration flask 2 via a rubber stopper. A pressure gauge 3 is connected to the filtration flask 2 to ensure a tight seal. A vacuum pump 5 is connected to the filtration flask 2 via a polytetrafluoroethylene (PTFE) tube, with a gas flow regulating valve 4 in between to control changes in vacuum level.

[0037] The present invention will now be further described with reference to the embodiments:

[0038] Example 1

[0039] Step 1: By mass percentage, calculate the fiber composite material weight as 300 g / m³. 2 Weigh the raw materials, which specifically include 20% carbon fiber, 20% aramid fiber, 10% cotton fiber, and 50% silicon dioxide.

[0040] Step 2: Add the above raw materials to water at a slurry concentration of 0.5%, mix and decompose them in a decomposer for 10,000 revolutions, add 0.2% cationic polyacrylamide by mass of filler silica, continue decomposition for 100 revolutions, and add foaming agent alkyl glycoside. The concentration of alkyl glycoside in the slurry is 2.5 g / L.

[0041] Step 3: After mixing evenly, pour the slurry into the foamer and mechanically stir and foam at 2000 rpm for 3 minutes to obtain a foam slurry with an air content of about 65%.

[0042] Step 4: Pour the foam slurry into the molding device (e.g., Figure 2 In this process, the vacuum pump switch is turned on while the vacuum valve is adjusted to control the vacuum level at 15 kPa. Under this condition, vacuum dehydration and defoaming are performed. When the foam slurry level drops to 3 / 4 of its original height, the vacuum valve is adjusted again to control the vacuum level at 7.5 kPa. The foam slurry continues to dehydrate and defoam under this condition to obtain a fiber composite preform. Finally, it is pressed at 0.5 MPa and dried at 105°C to obtain the foam-molded fiber composite material.

[0043] Example 2

[0044] During the foam slurry molding process, the vacuum pump switch is turned on while the vacuum valve is adjusted to control the vacuum level at 15 kPa. When the foam slurry level drops to half of its original height, the vacuum valve is adjusted again to control the vacuum level at 7.5 kPa. Under these conditions, the foam slurry continues to dehydrate and defoam, thus obtaining a foam-molded fiber composite material. Other steps are consistent with those in Example 1.

[0045] Example 3

[0046] During the foam slurry molding process, the vacuum pump switch is turned on while the vacuum valve is adjusted to control the vacuum level at 20 kPa. When the foam slurry level drops to 3 / 4 of its original height, the vacuum valve is adjusted again to control the vacuum level at 5 kPa. Under these conditions, the foam slurry continues to dehydrate and defoam, thus obtaining the foam-molded fiber composite material. Other steps are consistent with those in Example 1.

[0047] Comparative Example 1

[0048] Step 1: By mass percentage, calculate the fiber composite material weight as 300 g / m³. 2 Weigh the raw materials, which specifically include 20% carbon fiber, 20% aramid fiber, 10% cotton fiber, and 50% silicon dioxide.

[0049] Step 2: Add the above raw materials to water at a slurry concentration of 0.5%, mix and decompose them in a decomposer for 10,000 revolutions, add 0.2% cationic polyacrylamide, continue decomposition for 100 revolutions, and add foaming agent alkyl glycoside. The concentration of alkyl glycoside in the slurry is 2.5 g / L.

[0050] Step 3: After mixing evenly, pour the slurry into the foamer and mechanically stir and foam at 2000 rpm for 3 minutes to obtain a foam slurry with an air content of about 65%.

[0051] Step 4: Pour the foam slurry into the molding device (e.g., Figure 2 In a process where a constant vacuum of 15 kPa is applied, vacuum dehydration and defoaming are performed to obtain foam-molded fiber composite materials.

[0052] Comparative Example 2

[0053] During the foam slurry molding process, vacuum dehydration and defoaming were performed under a constant vacuum of 7.5 kPa to obtain foam-molded fiber composite materials. Other steps were the same as in Comparative Example 1.

[0054] Comparative Example 3

[0055] During the foam slurry molding process, the vacuum pump switch is turned on while the vacuum valve is adjusted to control the vacuum level at 15 kPa. When the foam slurry level drops to 1 / 4 of its original height, the vacuum valve is adjusted again to control the vacuum level at 7.5 kPa. Under these conditions, the foam slurry continues to dehydrate and defoam, thus obtaining the foam-molded fiber composite material. Other steps are consistent with Comparative Example 1.

[0056] Comparative Example 4

[0057] During the foam slurry molding process, the vacuum pump switch is turned on while the vacuum valve is adjusted to control the vacuum level at 7.5 kPa. When the foam slurry level drops to 3 / 4 of its original height, the vacuum valve is adjusted again to control the vacuum level at 15 kPa. Under these conditions, the foam slurry continues to dehydrate and defoam, thus obtaining the foam-molded fiber composite material. Other steps are consistent with Comparative Example 1.

[0058] The foam-molded fiber composite material samples from the examples and comparative examples were subjected to a series of performance characterizations, and the characterization methods are as follows:

[0059] Retention rate test: The sample was dried at 105℃, and the composite material was cut into pieces of approximately 1cm. 2 Weigh 2g of the sample into a crucible, taking small pieces. Thoroughly ashing the sample on an electric furnace, then transferring it to a muffle furnace and igniting at 925℃ to constant weight. Transferring it to a desiccator to cool and dry to constant weight, and weighing the ash content. The retention rate is calculated using the following formula:

[0060]

[0061] Composite material surface filler distribution test: Scanning electron microscopy (SEM) in backscatter mode was used to photograph the surface of the composite materials. Four consecutive images (100x magnification) were taken for each sample to observe the distribution of inorganic elements on the material surface. Then, ImageJ software was used to perform thresholding on the images, and filler components were further distinguished by color. Based on this, the area ratio of filler on the material surface was calculated using software.

[0062]

[0063] Composite material cross-section filler distribution test: Cross-section images of the composite material were taken using the same method as described above. Three consecutive images (100x magnification) were captured for each sample to observe the distribution of inorganic elements in the material cross-section. The images were then stitched together to form a continuous cross-section. The cross-section was divided into five equal parts along the Z-axis. ImageJ software was used to process each of the five regions as described above, and the area proportion of filler in each region was calculated. The concentration factor of the filler was calculated based on the filler proportion in each region to evaluate the cross-sectional distribution of the filler. The formula is as follows:

[0064]

[0065]

[0066] The performance of Examples 1 to 3 was compared with that of Comparative Examples 1 to 4.

[0067] use Figure 1 Fiber composite materials were prepared using a specific process flow. By controlling different molding process parameters, samples from various examples and comparative examples were obtained, and their retention properties are shown in Table 1. The data shows that, among fiber composite materials with the same filler, the filler retention rate of samples subjected to dehydration and defoaming molding under both vacuum conditions was higher than that of samples dehydrated and defoamed under either vacuum degree alone. Specifically, Example 1 showed an increase of 11.6% and 7.4% compared to Comparative Examples 1 and 2, respectively, while Example 2 showed an increase of 8.5% and 4.3% compared to Comparative Examples 1 and 2, respectively. For foam-molded samples under two vacuum conditions and different vacuum degree transition points, the earlier the transition from high vacuum to low vacuum, the higher the filler retention rate. It is evident that the filler retention rate is: Example 1 > Example 2 > Comparative Example 3. For foam-molded samples under two vacuum conditions and different vacuum degree application sequences, samples with a high-to-low vacuum degree dehydration and defoaming process often have a higher retention rate than samples with a low-to-high vacuum degree process. It is evident that Example 1 and Example 3 showed filler retention rates 6.9% and 5.8% higher than those of Comparative Example 3, respectively. In summary, this demonstrates that rapidly forming a deposited layer from the slurry using high-vacuum molding, followed by slow molding of the remaining slurry under low vacuum, effectively leverages the physical retention effect of the fiber layer on the filler, thereby improving the filler retention rate. Furthermore, filler loss primarily occurs under higher vacuum conditions, where the fiber deposited layer has not yet formed, and the physical retention effect is weaker.

[0068] Figure 3The diagram shows the Z-axis distribution of fillers in the foam-molded fiber composite material. Based on this, the Z-axis concentration factor of the fillers in Table 1 can be calculated. The higher the value, the closer the proportion of fillers in each layer and the more uniform the distribution. Data shows that the Z-axis concentration factors of the examples are all above 0.75, and are 2.7% to 79.2% higher than the comparative examples. This indicates that during the molding process, switching from high vacuum to low vacuum, and ensuring the transition point occurs before the foam slurry volume decreases by half, can produce a fiber composite material with a more uniform Z-axis filler distribution. Furthermore, from... Figure 3 It can be seen that for composite materials formed under a single vacuum degree, the distribution of filler in each layer shows a trend of gradually increasing from the top surface to the inner surface, eventually resulting in a difference between the two surfaces. Composite materials formed under two vacuum degrees reduce this phenomenon. Figure 4 As can be seen, after thresholding, the filler distribution in Example 1 is more uniform than that in Comparative Example 1.

[0069] Figure 5 This is a surface distribution diagram of the filler in the foam-molded fiber composite material, from which the two-sided difference of the filler distribution in the material can be obtained. In the two vacuum-molded composite materials of the examples, due to their higher retention rates, the proportion of filler on both the mesh surface and the top surface is greater than that of the comparative examples. The difference between the proportion of filler on the mesh surface and the top surface is calculated to evaluate the two-sided difference of the material. The examples and comparative examples 3 and 4 all have two-sided difference values ​​below 0.7%, while the two-sided differences of comparative examples 1 and 2 both exceed 0.9%. This indicates that this process has a good improvement effect on the filler retention rate, Z-direction, and two-sided distribution.

[0070] Table 1

[0071] Retention rate Z-axis concentration factor mesh filler ratio Top surface filler ratio Example 1 88.8％ 0.86 5.1％ 4.6％ Example 2 85.7％ 0.76 5.1％ 4.4％ Example 3 87.7％ 0.81 5.1％ 4.9％ Comparative Example 1 77.2％ 0.48 5.7％ 3.3％ Comparative Example 2 81.4％ 0.74 4.4％ 3.5％ Comparative Example 3 81.9％ 0.68 3.8％ 3.2％ Comparative Example 4 80.7％ 0.56 3.7％ 3.3％

[0072] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing high retention performance foam-molded fiber composite materials, characterized in that, Includes the following steps: (1) Add fiber, filler and retention aid to water and disperse evenly, then add foaming agent and foam thoroughly to obtain foam slurry; (2) The foam slurry described in step (1) is first dehydrated and defoamed under high vacuum. When the foam slurry is reduced to a certain volume or height, the vacuum degree of filtration is reduced, and dehydration and defoaming are continued under low vacuum to obtain the fiber composite material preform. (3) Press and dry the fiber composite preform obtained in step (2) to obtain a high retention performance foam molding fiber composite material. In step (2), when the volume or height of the foam slurry is reduced to 1 / 2 to 3 / 4 of the original volume or height, the vacuum level is reduced. The high vacuum level in step (2) is 15~20 kPa, and the low vacuum level is 5~10 kPa; The concentration of the foaming agent in the slurry in step (1) is 2.5~4g / L.

2. The method for preparing high retention performance foam-molded fiber composite materials according to claim 1, characterized in that, By mass percentage, the fiber in step (1) is 30-80%, the filler is 20-70%, and the retention aid is 0.1-0.5% of the total mass of the filler.

3. The method for preparing high retention performance foam-molded fiber composite materials according to claim 1, characterized in that, The slurry concentration in step (1) is 0.5~1%.

4. The method for preparing high retention performance foam-molded fiber composite materials according to any one of claims 1 to 3, characterized in that, The fiber mentioned in step (1) is one or more of cotton fiber, aramid fiber, carbon fiber, alumina fiber, aluminum silicate fiber, and glass fiber.

5. The method for preparing high retention performance foam-molded fiber composite materials according to claim 1, characterized in that, The filler in step (1) is one or more of graphite, alumina, diatomaceous earth, silicon dioxide, and potassium titanate whiskers.

6. The method for preparing high retention performance foam-molded fiber composite materials according to claim 1, characterized in that, The retention aid mentioned in step (1) is one or more of aluminum sulfate, cationic polyacrylamide, anionic polyacrylamide, and cationic potato starch; The foaming agent in step (1) is one or more of alkyl glycosides, sodium dodecyl sulfate, polyvinyl alcohol, and Tween-80.

7. The method for preparing high retention performance foam-molded fiber composite materials according to claim 1, characterized in that, The pressing pressure in step (3) is 0.5~2 MPa, and the drying temperature is 80~105℃.

8. A high retention performance foam-molded fiber composite material, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

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