A method of drying a gel foam material

Abstract

This invention proposes a drying method for gel foam materials, comprising the following steps: preparing a sol, forming a wet gel foam through physical foaming, sol-gel transition, and cross-linking curing; taking the wet gel foam for moisture content and DSC determination, taking the melting point T0 at the maximum moisture content M0 as the heating base, setting the heating temperature below the melting point T0, and measuring its moisture content and melting point at different times; and designing a drying route based on the relationship curve between moisture content and melting point. Compared with existing drying methods that affect the structure of gel foam materials, the drying method of this invention significantly improves the drying rate and has almost no impact on the structure of gel foam materials, providing a highly valuable theoretical basis for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of foaming materials technology, and more particularly to a drying method for gel foam materials. Background Technology

[0002] Current drying equipment for gel foam materials uses low-power constant temperature and humidity chambers to simulate a natural environment with a constant temperature of 25°C and a relative humidity of 50%, which has significant shortcomings in terms of drying rate; at the same time, the drying time is too long, and the drying cost is high. Differential scanning calorimetry (DSC) is a conventional method for comprehensive thermal analysis of substances. Under programmed temperature control, it measures the relationship between the power difference between the sample and the reference material and temperature. The recorded curve is called the DSC curve, which measures a variety of thermodynamic and kinetic parameters.

[0003] Patent CN111781240A discloses a peak fitting method for differential scanning calorimetry (DSC) curves. This method uses DSC experimental data to plot heat flow rate-temperature curves, determines the baseline required for peak area calculation, and thus accurately calculates the concentration of each substance. However, this method has not yet been seen applied to the drying process of gel foam materials.

[0004] Therefore, the drying process of existing gel foam material preparation methods still needs improvement. Summary of the Invention

[0005] In view of this, the present invention proposes a drying method for gel foam materials, which solves the technical problem in the prior art that poor drying effect leads to structural damage and performance degradation of gel foam materials.

[0006] The technical solution of this invention is implemented as follows:

[0007] This invention provides a method for drying gel foam materials, comprising the following steps:

[0008] Sol is prepared and wet gel foam is formed through physical foaming, sol-gel transition, and cross-linking curing.

[0009] Take 5-10 mg of the wet gel foam, test the initial moisture content and perform DSC test to obtain the DSC curve corresponding to the initial moisture content, where the initial moisture content is M0 and the corresponding melting point is T0;

[0010] The wet gel foam is dried at a drying temperature T1, where T1 < T0. After a predetermined drying time, the current moisture content is measured to be M1, and the corresponding melting point is T1'. The next stage of drying is then initiated, with the drying temperature set to T2, where T1' > T2 > T1. The above steps are repeated. During the nth stage of drying, the moisture content is measured to be Mn, and the corresponding melting point is Tn'. The drying temperature is set to Tn, where Tn' > Tn > Tn-1, and drying continues until the stopping condition is met. Here, n is a positive integer.

[0011] The dried gel foam material contains a certain amount of structural water. When the water concentration is high enough, it will form a multilayer of water. The monolayer wraps the helical structure, and the additional water layer constitutes the multilayer. The high concentration of unbound water is the free water that exists in the hydrogel network.

[0012] Therefore, more preferably, the stopping condition is that the measured water content of the wet gel foam is less than 10%.

[0013] More preferably, the drying temperature satisfies 0.9 < Tn / Tn' < 1.

[0014] More preferably, the 5-10 mg is taken from the same central part of the wet gel foam.

[0015] More preferably, 5-10 mg of the wet gel foam is sealed and then subjected to DSC testing to ensure that the moisture content remains unchanged.

[0016] More preferably, the relative humidity of the drying process is 0-5%.

[0017] More preferably, the drying wind speed is 5-10 m / s.

[0018] More preferably, the method for preparing the wet gel foam specifically includes the following steps:

[0019] Raw material preparation and weighing, including main materials, auxiliary materials, fillers, additives, and water; the main materials include natural polymers and sodium silicate.

[0020] The auxiliary materials include natural polymers, the fillers include vermiculite, perlite, plant fibers, and radiation-absorbing materials, and the additives include surfactants and plasticizers;

[0021] Slurry preparation involves dissolving the main ingredients, auxiliary ingredients, fillers, and additives in water and stirring at 40-80℃ until uniformly mixed to form a foamable sol.

[0022] Physical foaming involves injecting air into a sol, and through rapid shearing, uniformly dispersing the gas phase in the liquid phase to form liquid foam; molding.

[0023] Curing, through the synergistic effect of sol-gel transformation, physical cross-linking and surfactant, stabilizes the foam structure, thus obtaining wet gel foam;

[0024] Preferably, the preparation and weighing of the raw materials, by weight, includes 1-40 parts of main material, 0.01-10 parts of surfactant, and 50-98.99 parts of water. More preferably, the filler also includes vermiculite, perlite, plant fiber, and radiation-absorbing material.

[0025] More preferably, the molding refers to molding the liquid foam into one-dimensional (filaments for 3D printing), two-dimensional (films, sheets, plates), or three-dimensional (boxes, other complex shapes).

[0026] More preferably, the natural polymer includes at least one of gum arabic, xanthan gum, agar, alginic acid, gelatin, carrageenan, gellan gum, pectin, sucrose, transglutaminase, or chitosan.

[0027] More preferably, the surfactant includes one of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, or dodecyltrimethylammonium bromide.

[0028] The gel foam material drying method of the present invention has the following advantages over the prior art:

[0029] In existing technologies, conventional drying processes such as hot air drying, vacuum drying, and microwave drying cannot accurately determine the drying temperature, resulting in the drying temperature exceeding the instantaneous melting point of the foam material, causing the material to melt or its performance to decline significantly. This invention designs a drying route based on the relationship between moisture content and melting point, which greatly increases the drying rate and can shorten the drying time by more than 80%. At the same time, the drying conditions used in this invention have almost no impact on the structure and performance of the foam. The gel foam material dried by this invention has a stable cell structure, and its comprehensive mechanical and physical properties (thermal insulation, cushioning) are comparable to or better than those of traditional plastic foam materials. Attached Figure Description

[0030] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 The DSC curves of wet gel foam at different moisture contents of the present invention are shown.

[0032] Figure 2 This is a schematic diagram of the drying method of the present invention;

[0033] Figure 3 This is a scanning electron microscope image of the product after drying, as shown in Example 2 of the present invention.

[0034] Figure 4 This is a scanning electron microscope image of the product after drying, as shown in Example 3 of the present invention.

[0035] Figure 5 This is a scanning electron microscope image of the product after drying, as shown in Example 4 of the present invention.

[0036] Figure 6 This is a scanning electron microscope image of Comparative Example 1 of the present invention after drying. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] This invention provides a method for drying gel foam materials, comprising the following steps:

[0039] Sol is prepared and wet gel foam is formed through physical foaming, sol-gel transition, and cross-linking curing.

[0040] The preparation of the sol, through physical foaming, sol-gel transition, and cross-linking curing to form a wet gel foam, specifically includes the following steps:

[0041] Raw material preparation and weighing, including main materials, auxiliary materials, fillers, additives and water; the main materials include natural polymers and sodium silicate, the auxiliary materials include natural polymers, the fillers include vermiculite, perlite, plant fibers and radiation absorbing materials, and the additives include surfactants and plasticizers;

[0042] Slurry preparation involves dissolving the main ingredients, auxiliary ingredients, fillers, and additives in water. Since the stirring temperature has a significant impact on the preparation of foamable sol, gelation occurs at 25℃, making it impossible to prepare a fluid foamable slurry. Therefore, the mixture is stirred at 40-80℃ until it is uniformly mixed to form a foamable sol.

[0043] Physical foaming involves injecting air into a sol, and through rapid shearing, uniformly dispersing the gas phase in the liquid phase to form liquid foam; molding.

[0044] Curing is achieved through the synergistic effect of sol-gel transformation, physical cross-linking, and surfactants. Surfactants can stabilize the bubble structure by delaying or preventing bubble coarsening, bubble coalescence, and liquid drainage, thus obtaining wet gel foam.

[0045] The moisture inside the wet gel foam is then removed to obtain a solid foam product. Commonly used drying methods include hot air drying, vacuum drying, and microwave drying. However, when the drying temperature exceeds the instantaneous melting point of the wet gel foam material, the material will melt, damaging its structure and properties. Therefore, this invention uses variable temperature drying.

[0046] Take 5-10 mg of the wet gel foam, test the initial moisture content and perform DSC test to obtain the DSC curve corresponding to the initial moisture content, where the initial moisture content is M0 and the corresponding melting point is T0;

[0047] The DSC test process includes: placing 5-10 mg of wet gel foam into a crucible, covering it without drilling holes, setting the initial temperature to 25°C, decreasing it to 10°C at a rate of 10°C / min, holding it at that temperature for 5 min, and then increasing it to 100°C at a rate of 5°C / min and holding it at that temperature for 5 min.

[0048] Since temperature affects the drying rate of wet gel foam, and excessively high temperatures can also affect the structure of wet gel foam, the following drying route is designed to address the limitation of temperature on the drying of wet gel foam: the wet gel foam is dried at a drying temperature T1, where T1 < T0; after a predetermined drying time, the current moisture content is measured to be M1, corresponding to a melting point of T1', and then the next stage of drying is initiated, with the drying temperature set to T2, where T1' > T2 > T1; wet gel foams with different moisture contents M correspond to different melting points T, and the lower the moisture content M, the higher the melting point T of the wet gel foam;

[0049] Repeat the above steps. During the nth stage of drying, the moisture content is measured to be Mn, the corresponding melting point is Tn', and the drying temperature is set to Tn. Drying continues until the stopping condition is met, where n is a positive integer. This drying route results in a drying temperature that is closer to the instantaneous melting point of the wet gel foam, maximizing drying efficiency and avoiding damage to the foam structure and performance due to excessively high drying temperature when the moisture content of the wet gel foam is high.

[0050] This invention designs a drying route based on the relationship between moisture content and melting point, which significantly increases the drying rate and can shorten the drying time by more than 80%. At the same time, the drying conditions used in this invention have almost no impact on the structure and performance of the foam. Furthermore, the gel foam material dried by this invention has a stable cell structure, and its comprehensive mechanical and physical properties (thermal insulation, cushioning) are comparable to or better than those of traditional plastic foam materials.

[0051] Therefore, Example 1 of the present invention describes the preparation method of wet gel foam.

[0052] Example 1

[0053] The preparation method of the wet gel foam specifically includes the following steps:

[0054] Because excessively high mass fractions of natural polymers can lead to excessively high solution viscosity during stirring, making it impossible to form a foamable sol, and the absence of surfactants or the addition of small or excessive amounts of surfactants can also prevent successful foaming and stabilize the foam structure, ultimately leading to the collapse of the overall foam structure; therefore, 17.5% by mass of gum arabic and 2% by mass of sodium dodecyl sulfate surfactant were selected and dissolved in water.

[0055] Considering that excessively short stirring time will result in uneven mixing of the slurry, affecting foaming and the uniformity of the foam material, the gum arabic and sodium dodecyl sulfonate are dissolved in water and stirred at 50°C for 30 minutes to form a gum arabic sol. Then, a physical foaming machine is used to inject air into the sol at 50°C and use high-speed shearing to make it spread evenly, forming liquid foam. This direct air injection foaming method (liquid foaming) reduces energy consumption by 30-50% compared to the traditional melt foaming method and has no pollutant emissions.

[0056] Next, while forming the board, the foam structure is stabilized through the synergistic effect of sol-gel transformation, physical cross-linking, and surfactant, thus obtaining wet gel foam.

[0057] Temperature has a significant impact on the drying rate, but excessively high temperatures can affect the internal structure of gel foam. To address the limitations of temperature on the drying of wet gel foam, the thermal properties of gel foam materials are analyzed. Figure 1 The DSC curves of the wet gel foam at different moisture contents at different times show that although the moisture content decreases significantly in the higher moisture content stage, the melting point does not increase significantly. This is because water evaporation leads to stronger internal forces in the gel network, making the gel network denser and reducing porosity. The intermolecular forces of natural polymers are generally hydrogen bonds and electrostatic interactions, and these forces are more easily formed when moisture decreases. Therefore, while avoiding melting of the gel foam material, the drying temperature should be increased during the stage when the melting point increases significantly due to the large decrease in moisture content, thereby increasing the drying rate.

[0058] Therefore, the drying conditions were adjusted and a drying route was designed. A schematic diagram of the specific drying route is shown below. Figure 2 .

[0059] Example 2 is provided based on Example 1 to further illustrate the present invention.

[0060] Example 2

[0061] The drying method for the wet gel foam includes the following steps:

[0062] The moisture content of the wet gel foam was tested at different times, with 10 mg taken as the test sample each time. After the test, the test sample was sealed and stored to avoid changes in moisture content. Then, the test sample was subjected to DSC testing. The DSC test was set with 25°C as the starting temperature, decreasing to 10°C at a rate of 10°C / min, holding for 5 min, and then increasing to 100°C at a rate of 5°C / min, holding for 5 min.

[0063] The maximum moisture content of the wet gel foam was determined to be 85%, corresponding to a melting point of 35.94℃. Based on the DSC curves of wet gel foams with different moisture contents, the foams were placed in a constant temperature and humidity chamber for hot air temperature-variable drying. The relative humidity of the constant temperature and humidity chamber was 5%, and the drying air velocity was 5 m / s.

[0064] The drying process is divided into three stages. In the first stage, the drying temperature is set at 35°C. After 5 hours, the moisture content is measured. If it is below 50%, the temperature is increased to 40°C. If it is above 50%, the drying temperature is maintained at 35°C until the moisture content is below 50%. In the second stage, the drying temperature is 40°C. After 3 hours, the moisture content is measured. If it is below 30%, the temperature is increased to 50°C. If it is above 30%, the drying temperature is maintained at 40°C until the moisture content is below 30%. In the third stage, the drying temperature is 50°C. After 2 hours, the moisture content is measured. If it is below 20%, the temperature is increased to 60°C. If it is above 20%, the drying temperature is maintained at 50°C until the drying is complete and the moisture content is below 10%.

[0065] Due to uneven drying, the moisture content differs between the inside and outside of the wet gel foam. Taking 10mg of wet gel foam material each time, sampling from the same central location, helps reduce errors and improve repeatability. Simultaneously, during the drying process, the cell structure of the wet gel foam gradually changes from closed-cell to open-cell. Initially, the wet gel foam is in a closed-cell state with no connection between pores. During drying, the internal moisture begins to evaporate, and air enters the foam. Over time, the internal moisture gradually evaporates, leading to connections between the internal pores and gradually connecting with the external environment, thus transforming from a closed-cell to an open-cell state. This transformation is crucial for the drying of wet gel foam. In the closed-cell state, internal moisture cannot contact the external environment, limiting the drying rate. Once it transforms into an open-cell state, internal moisture can evaporate freely, allowing for full contact with the outside environment, thus increasing the drying rate. Figure 3 The image shown is a scanning electron microscope image of the dried gel foam material in this embodiment. It is clearly visible that, under a microscopic view, the gel foam material exhibits a uniform, fully open-cell structure.

[0066] Example 3

[0067] In atmospheric pressure drying, the lower the relative humidity, the shorter the drying time. To improve drying efficiency, the drying method for the gel foam material described in this embodiment differs from that in Embodiment 2 in that the relative humidity of the constant temperature and humidity chamber is 0%. Figure 4 This is a scanning electron microscope image of the dried gel foam material in this embodiment.

[0068] Example 4

[0069] During atmospheric pressure drying, provided the foam structure is not damaged, the higher the drying air velocity, the shorter the drying time. To improve drying efficiency, the drying method for the gel foam material described in this embodiment differs from that in Embodiment 2 in that the drying air velocity is 10 m / s. Figure 5 This is a scanning electron microscope image of the dried gel foam material in this embodiment.

[0070] In addition, Comparative Examples 1 and 2 were also provided based on Example 1.

[0071] Comparative Example 1

[0072] The drying method for the gel foam material employs a room temperature drying mode, with a temperature of 25°C and a relative humidity of 50%. Figure 6 This is a scanning electron microscope image of the dried gel foam material in this embodiment.

[0073] Comparative Example 2

[0074] The drying method for the gel foam material adopts a vacuum drying method. The prepared wet gel foam is placed in a vacuum dryer, the vacuum degree of the vacuum dryer is set to 0.05MPa, the temperature is set to 35℃, the vacuum pump is turned on to draw a vacuum, the corresponding vacuum degree is drawn, the corresponding temperature is set, and the dried sample is observed with the naked eye during the vacuuming process.

[0075] The drying time of the wet gel foam materials in Examples 2-4 and Comparative Example 1 was statistically analyzed. All samples taken from the examples and comparative examples were 4cm × 4cm × 2cm, as shown in Table 1.

[0076] Table 1. Drying times of Examples 2-4 and Comparative Example 1

[0077]

[0078]

[0079] In room temperature drying, provided the foam material does not melt, the higher the drying temperature, the shorter the drying time. However, wet gel foam with high water content has a low melting point, making it impossible to use temperatures exceeding the melting point for drying. Lower drying temperatures also significantly increase drying time, resulting in low production efficiency. During vacuum drying, since the initial stage primarily involves a closed-cell structure, the wet gel foam expands with increasing vacuum, causing changes in its structure and properties. Furthermore, due to the high water content of the wet gel foam in the initial stage, vacuum drying generates a large amount of water mist. Currently, the vacuum level can only be reached to -0.02 MPa. Drying at 25°C with the vacuum valve closed is inefficient, even less efficient than room temperature drying. As shown in Table 1, compared to existing room temperature and vacuum drying methods, the drying route designed in this invention significantly shortens drying time and improves production efficiency. Additionally, comparing Examples 2 with Examples 3-4 shows that higher drying wind speeds and lower relative humidity result in higher drying efficiency. Figure 3-5 It is evident that the drying route of this invention has almost no impact on the structure of the gel foam material, making it relatively stable; while Figure 6 The results show that the structure of the gel foam material in this embodiment is unstable, presumably because the excessively high drying temperature damaged the cell structure of the foam material.

[0080] In addition, there are composite drying methods, such as first drying with variable temperature hot air and then vacuum drying, first drying with microwave and then hot air drying, and first drying with microwave and then vacuum drying, which can significantly improve drying efficiency; for example, composite gel methods can also improve drying efficiency by increasing the melting point without affecting foaming performance.

[0081] In summary, the drying method of the present invention significantly improves drying efficiency and has almost no impact on the structure of gel foam materials, providing a highly valuable theoretical basis for the large-scale production of gel foam materials.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for drying a gel foam material, characterized in that, Includes the following steps: Sol is prepared and wet gel foam is formed through physical foaming, sol-gel transition, and cross-linking curing. Take 5-10 mg of the wet gel foam, test the initial moisture content and perform DSC test to obtain the DSC curve corresponding to the initial moisture content, where the initial moisture content is M0 and the corresponding melting point is T0; The wet gel foam is dried at a drying temperature T1, where T1 < T0. After a predetermined drying time, the current moisture content is measured to be M1, corresponding to a melting point of T1'. The next drying stage begins, with the drying temperature set to T2, where T1' > T2 > T1. The above steps are repeated. During the nth drying stage, the moisture content is measured to be Mn, corresponding to a melting point of Tn'. The drying temperature is set to Tn, where Tn' > Tn > Tn-1. Drying continues until the stopping condition is met. Here, n is a positive integer, and Tn-1 is the drying temperature of the (n-1)th stage. Wet gel foams with different moisture contents M correspond to different melting points T. The lower the moisture content M, the higher the melting point T of the wet gel foam.

2. The drying method for the gel foam material as described in claim 1, characterized in that, The stopping condition is that the measured water content of the wet gel foam is less than 10%.

3. The drying method for the gel foam material as described in claim 2, characterized in that, The drying temperature satisfies 0.9 < Tn / Tn' < 1.

4. The drying method for the gel foam material as described in claim 1, characterized in that, The 5-10 mg samples were all taken from the same central part of the wet gel foam.

5. The drying method for the gel foam material as described in claim 1, characterized in that, After sealing 5-10 mg of the wet gel foam, perform DSC testing to ensure that the moisture content remains unchanged.

6. The drying method for the gel foam material as described in claim 1, characterized in that, The preparation of the sol, through physical foaming, sol-gel transition, and cross-linking curing to form a wet gel foam, specifically includes the following steps: Raw material preparation and weighing, including main materials, auxiliary materials, fillers, additives and water; the main materials include natural polymers and sodium silicate, the auxiliary materials include natural polymers, the fillers include vermiculite, perlite, plant fibers and radiation absorbing materials, and the additives include surfactants and plasticizers; Slurry preparation involves dissolving the main ingredients, auxiliary ingredients, fillers, and additives in water and stirring at 40-80°C until uniformly mixed to form a foamable sol. Physical foaming involves injecting air into a sol, and through rapid shearing, uniformly dispersing the gas phase in the liquid phase to form liquid foam; molding. Curing, through the synergistic effect of sol-gel transformation, physical cross-linking, and surfactants, stabilizes the foam structure, thus obtaining wet gel foam.

7. The drying method for the gel foam material as described in claim 6, characterized in that, The natural polymers include at least one of gum arabic, xanthan gum, agar, alginic acid, gelatin, carrageenan, gellan gum, pectin, sucrose, transglutaminase, or chitosan.

8. The drying method for the gel foam material as described in claim 6, characterized in that, The surfactant includes one of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, or dodecyltrimethylammonium bromide.

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