A high-slip lightweight foamed gypsum and an environment-friendly simple preparation method thereof

Abstract

This invention relates to the field of building materials and discloses a high-smoothness, lightweight foamed gypsum and its environmentally friendly and simple preparation method. The raw materials for this high-smoothness, lightweight foamed gypsum include a mixed powder and water. The mixed powder comprises 70-90 wt% gypsum powder, 5-15 wt% expanded foamed microspheres, and 5-15 wt% filler; the mass ratio of water to gypsum powder is (0.8-1.2):1; the filler includes one or more of heavy calcium carbonate, light calcium carbonate, and microcrystalline cellulose. This invention uses the volume-stabilizing support of the foamed microspheres and the filling of the filler to suppress the formation of high surface roughness in the gypsum. This invention prepares foamed gypsum by mixing and curing the foamed microspheres with gypsum powder, avoiding secondary foaming, gas escape, and surface blistering, effectively reducing the weight of the gypsum and achieving cost reduction and efficiency improvement. The foamed gypsum of this invention does not require the use of a release agent during the demolding process and leaves no chemical residue.

Description

Technical Field

[0001] This invention relates to the field of building materials, and in particular to a high-smoothness, lightweight foamed gypsum and its environmentally friendly and simple preparation method. Background Technology

[0002] Gypsum, due to its excellent moisture absorption, heat insulation, fire resistance, and plasticity, is widely used in model making, ceilings, and relief decoration. However, traditional gypsum products are often heavy, leading to high material costs and difficulties in installation and fixation. To address this, the industry has introduced foaming technology to reduce the density of gypsum, developing lightweight foamed gypsum. Currently, in the field of lightweight gypsum technology, existing technologies mainly rely on physical and chemical foaming methods to achieve lightweighting, but these methods still have several significant drawbacks.

[0003] Chemical foaming typically relies on the reaction of carbonates with acidic components to release carbon dioxide (such as the reaction of aluminum sulfate with calcium carbonate) to form pores within the gypsum slurry. However, the gas release rate is greatly affected by the system's pH, temperature, and raw material purity, making it difficult to precisely control the pore structure and distribution. This can easily lead to uneven pore size or excessive interconnected pores, reducing material strength. Furthermore, gypsum systems are neutral or slightly acidic, resulting in low reaction efficiency with common foaming agents. Additional acidic or alkaline regulators are often required, which may interfere with the gypsum hydration process, affecting the final performance stability and posing a risk of pollution from chemical residues.

[0004] Physical foaming primarily involves introducing air bubbles through mechanical stirring of a surfactant solution, followed by mixing with the gypsum slurry. However, the air bubbles introduced by stirring are prone to coalescing, bursting, or escaping within the slurry, making it difficult to maintain a uniform and fine pore structure during the hardening process, resulting in large fluctuations in the density of the finished product. Furthermore, the escape of air bubbles during physical foaming is not synchronized with the curing of the gypsum; air bubbles rise and burst before hardening, easily forming depressions or holes on the surface, causing a rough surface. For example, invention patent CN116396044A proposes using a foaming agent supplemented with fiber fillers, aiming to balance lightweight and mechanical properties; however, the materials prepared in this way often have high surface porosity and roughness, affecting the decorative effect. This reflects that current foamed gypsum technology still has significant shortcomings in practical applications.

[0005] In summary, regardless of whether chemical or physical foaming methods are used, the foaming process in existing technologies occurs during the hydration or solidification of the gypsum slurry. Gas generation, escape, and gypsum crystal growth result in a rough surface in the foamed gypsum. Especially in decorative and artistic applications requiring high surface finish, current foamed gypsum technologies cannot simultaneously achieve the multiple requirements of lightweight, smooth surface, and environmental friendliness, and it is even more difficult to improve surface roughness using conventional fillers. Therefore, developing an environmentally friendly and simple preparation method for lightweight foamed gypsum with a highly smooth surface has significant practical importance and application value. Summary of the Invention

[0006] To address the common problems of surface roughness, exposed pores, and loose structure in the lightweighting process of existing foamed gypsum, this invention proposes an environmentally friendly and simple method for preparing a high-smoothness, lightweight foamed gypsum. This invention separates the foaming process from the gypsum hydration process and introduces fillers, thereby achieving significant weight reduction while maintaining a smooth surface. The expanded foamed microspheres are thoroughly mixed with gypsum powder and fillers, and then water is added for curing, resulting in a foamed gypsum with a smooth surface and environmentally friendly lightweight characteristics. The foamed gypsum prepared by this invention not only has a smooth surface suitable for decorative applications, but the entire preparation process is simple, requiring no complex machinery, and the raw materials are environmentally friendly, helping to reduce production costs.

[0007] The specific technical solution of the present invention includes: In a first aspect, the present invention provides a lightweight foamed gypsum with a highly smooth surface, comprising a mixed powder and water. The mixed powder comprises 70-90 wt% gypsum powder, 5-15 wt% (more preferably 3-7 wt%) expanded foamed microspheres, and 5-15% filler. The gypsum powder is α-type hemihydrate gypsum, and the powder-to-water mass ratio is (2-4):1.

[0008] Incorporating expanded foamed microspheres into a gypsum curing system allows the shell of the microspheres to provide support, thereby increasing the volume of the gypsum. However, after adding expanded foamed microspheres to the gypsum curing system, scanning electron microscopy revealed that the cured foamed gypsum exhibited a loose morphology of randomly stacked needle-like crystals with large pores around them, and poor interfacial bonding between the needle-like crystals and the expanded microspheres. This change in microstructure is mainly attributed to the fact that when the powder-to-water mass ratio of α-type hemihydrate gypsum is (2-4):1, the team found that after adding foamed microspheres to the gypsum powder, some water was used to wet the surface of the foamed microspheres, resulting in a significant reduction in the effective water available for gypsum curing. If the original powder-to-water mass ratio is maintained, the mixed powder cannot form a slurry; therefore, additional water must be added to obtain a uniform slurry. However, water plays a crucial role in gypsum crystal formation. With increasing water content, sufficient moisture provides conditions for the free growth of gypsum crystals along the one-dimensional direction, thus promoting the transformation of the crystal morphology from dense flakes to needles. However, the loose and irregular needle-like crystal structure, with its distinct crystal outline and reduced entanglement, will decrease the strength of foamed gypsum and increase its surface roughness.

[0009] This invention, through research, has discovered that adding appropriate amounts and specific types of fillers to a gypsum curing system can result in a precise structure and smooth surface in the cured foamed gypsum. In particular, heavy calcium carbonate particles can fill the tiny pores or gaps between microspheres within the cured gypsum body, making the structure denser and more uniform. Simultaneously, their strong chemical inertness prevents them from participating in the hydration reaction of gypsum, inhibiting volume shrinkage during the hardening process, filling gaps in the foamed gypsum structure, and reducing the surface roughness of the cured foamed gypsum.

[0010] Furthermore, this invention also reveals that the content of foamed microspheres in the system is particularly crucial. Foamed microspheres are used to increase the volume of gypsum, thereby forming a lightweight foamed material. This invention limits the content of foamed microspheres within the aforementioned range, resulting in better foaming effects. Similarly, the content of filler is also critical. This invention limits the amount of filler within the aforementioned range, enabling effective filling of the gaps between the foamed microspheres and the gypsum, achieving a smooth surface finish on the gypsum product.

[0011] The filler comprises one or more of heavy calcium carbonate, light calcium carbonate, and microcrystalline cellulose; more preferably, the filler is heavy calcium carbonate.

[0012] Compared to light calcium carbonate and microcrystalline cellulose, heavy calcium carbonate is more suitable as a preferred filler for foamed gypsum. Microcrystalline cellulose can enhance the connection between gypsum crystals and expanded microspheres to some extent, reducing gaps between them. However, the organic material microcrystalline cellulose tends to agglomerate in gypsum, resulting in a loose crystalline structure and high surface roughness in the foamed gypsum. Light calcium carbonate has a lower bulk density, leading to uneven dispersion in gypsum powder and inducing uneven crystal size, resulting in relatively high surface roughness, reduced density, and significantly increased surface roughness in the foamed gypsum. Heavy calcium carbonate, on the other hand, shows the best effect, producing a smooth surface and short curing time in the prepared foamed gypsum. This is because the bulk density of heavy calcium carbonate is similar to that of α-type hemihydrate gypsum, resulting in more uniform dispersion after mixing. This makes the gypsum slurry easier to flow and spread, reducing surface porosity and roughness. Furthermore, heavy calcium carbonate itself can fill the gaps between gypsum and foamed microspheres, making the structure denser and the surface smoother.

[0013] Preferably, the mass ratio of water to gypsum powder is (0.8-1.2):1; more preferably (0.9-1):1.

[0014] This invention limits the amount of water used to the above-mentioned range. The amount of water affects the curing time of gypsum and the uniform dispersion of foamed microspheres in the gypsum. When there is too much water, the gypsum slurry becomes too thin, prolonging the curing time. When there is too little water, it cannot meet the crystallization water required for gypsum curing, making it difficult to mix the powder evenly, reducing the fluidity of the slurry, and affecting the molding of the gypsum and the surface roughness after molding.

[0015] Preferably, the α-type hemihydrate gypsum has a particle size of 6-10 μm and a whiteness of 90-95 degrees.

[0016] The gypsum powder of this invention preferably conforms to the above parameters and is α-type hemihydrate gypsum (α-CaSO4·0.5H2O). This gypsum exhibits excellent compressive strength. While the compressive strength decreases after adding an appropriate amount of foamed microspheres, it still meets product requirements. α-type hemihydrate gypsum has low surface roughness. By adding foamed microspheres to α-type hemihydrate gypsum powder, followed by fillers and water, the resulting foamed gypsum after curing still maintains a low surface roughness.

[0017] Preferably, the particle size of the filler is in the range of 1-10 μm.

[0018] The particle size of fillers has a significant impact on the structure and properties of foamed gypsum. Finer particle sizes result in more effective filling of gaps in the foamed gypsum structure, thus optimizing structural density. However, excessively fine particle sizes lead to a sharp increase in the total surface area of ​​the filler per unit volume. When the powder is mixed with water, a large amount of water is adsorbed and adheres to the filler surface, significantly reducing the free water content available for the hydration reaction of the gypsum powder. This directly causes a decrease in the fluidity of the gypsum slurry, hindering molding. Conversely, if the filler particle size is too coarse, it weakens its suspension stability in the slurry, easily causing problems such as particle sedimentation and component segregation, disrupting the overall uniformity of the slurry. This not only makes it difficult for the filler to effectively fill the gaps between the foamed microspheres and the gypsum, resulting in a loose internal structure in the finished product, but also increases the surface roughness of the foamed gypsum, severely affecting the mechanical properties and appearance quality of the product. In this invention, the gypsum powder has a particle size of 6-10 μm. In order to make the gypsum surface smooth after the slurry produced by the uniform mixing of filler with gypsum powder, foamed microspheres and water is cured, the particle size range of filler is limited to 1-10 μm.

[0019] Preferably, the shell material of the foamed microspheres is a thermoplastic polymer containing at least one functional group selected from hydroxyl, nitrile and carbonyl groups on its surface, and the core material is an alkane.

[0020] Foamed microspheres are a special type of microsphere material, consisting of a thermoplastic polymer shell encapsulating low-boiling-point alkanes, with hydroxyl, nitrile, and carbonyl groups on the surface. Their expansion principle is as follows: Figure 1As shown, when the foamed microspheres are heated, the low-boiling-point alkanes inside boil, increasing the gas pressure. Simultaneously, the thermoplastic polymer shell softens and deforms, causing the microspheres to expand in volume. When the temperature decreases, the microsphere shell cools and solidifies. The surface of the foamed microspheres contains hydroxyl groups, which are water-absorbing groups and have strong polarity. Therefore, after adding water in step 3), the foamed microspheres are more easily wetted by the slurry formed by the model plaster powder and water, resulting in a larger contact area. The plaster slurry can better encapsulate the foamed microspheres, increasing their bonding strength. In the plaster slurry, calcium sulfate hydrate undergoes a hydration reaction, producing calcium ions (Ca). 2+ The hydroxyl groups on the surface of the foamed microspheres undergo a complexation reaction, making the foamed microspheres more tightly bound to the slurry.

[0021] Secondly, the present invention provides an environmentally friendly and simple method for preparing lightweight foamed gypsum with a high-smoothness surface, which includes the following steps: 1) The foamed microspheres are heated and expanded to complete the volume expansion and enter a volume stable state, thus obtaining the expanded foamed microspheres.

[0022] 2) Without introducing gas, the expanded foamed microspheres are mixed with gypsum powder and fillers to uniformly disperse the expanded foamed microspheres and fillers in the gypsum system, thus obtaining a mixed powder.

[0023] 3) Mix the powder with water evenly, pour it into the mold, let it solidify, and demold to obtain a high-smoothness, lightweight foamed plaster.

[0024] As a preferred option, step 2) specifically includes: first adding 40-60% of the expanded foamed microspheres to the gypsum powder and filler and stirring evenly, then adding the remaining expanded foamed microspheres and stirring evenly.

[0025] Further preferred, in step 2), the stirring speed is 500-700 rpm, the first stirring time is 2-3 min, and the second stirring time is 2-3 min.

[0026] Preferably, in step 3), the mold is made of plastic; more preferably, it is made of polypropylene.

[0027] When the mold is made of polypropylene, its surface porosity is extremely low, exhibiting a dense and smooth overall characteristic. During the curing process of foamed gypsum, the addition of foamed microspheres reduces the direct contact area between the gypsum and the plastic surface, facilitating demolding. Moreover, the foamed microspheres are added in a stable state after expansion, their role being only to fill and reduce weight, without participating in the volume changes of curing and hydration reactions. It is worth noting that when gypsum is cured from hemihydrate gypsum (CaSO4·0.5H2O) to dihydrate gypsum (CaSO4·2H2O), there is a certain volume expansion, with a theoretical expansion rate of approximately 0.5~1%. However, in the lightweight foamed gypsum system, most of the gypsum matrix is ​​replaced by foamed microspheres for the same volume. This replaced volume no longer undergoes the hydration expansion process, resulting in a lower overall volume expansion rate of the foamed gypsum. Ultimately, the cured foamed gypsum does not adhere tightly to the mold surface, further optimizing the demolding effect. Therefore, the preparation process of this invention does not require the addition of a release agent, further reducing the emission of chemical substances.

[0028] Preferably, in steps 2) and / or 3), the materials are mixed using a co-mixing method; this ensures that the expanded foamed microspheres are better dispersed in the gypsum curing system.

[0029] This invention uses a co-doping method to add expanded foamed microspheres or fillers to the curing system, which can fully ensure the uniform mixing of materials.

[0030] Preferably, in step 3), the mixing speed is 600-1000 rpm.

[0031] Preferably, in step 1), the conditions for heating and expansion are: heating temperature 90-110℃, heating time 40-60min, and stirring speed 100-500rpm.

[0032] Thirdly, the present invention provides the application of the above-mentioned high-smoothness surface lightweight foamed gypsum as a decorative material.

[0033] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention suppresses the formation of high roughness on the gypsum surface by the volume stabilizing support of the foamed microspheres and the filling of the filler.

[0034] (2) The present invention prepares foamed gypsum by mixing and solidifying foamed microspheres with gypsum powder, avoiding secondary foaming, gas leakage and surface bubbling, which can effectively reduce the weight of gypsum and achieve cost reduction and efficiency improvement.

[0035] (3) The foamed gypsum of the present invention does not require the use of a release agent during the demolding process and has no chemical residue. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the expansion of foamed microspheres.

[0037] Figure 2 The image shows the FTIR spectrum of the Dongjin MS140WS expandable microspheres.

[0038] Figure 3 This is a SEM image of the blank plaster in Comparative Example 1.

[0039] Figure 4 This is a SEM image of gypsum-doped foamed microspheres (without filler) in Comparative Example 2.

[0040] Figure 5 This is a SEM image of foamed gypsum doped with light calcium carbonate in Example 1.

[0041] Figure 6 This is a SEM image of foamed gypsum doped with microcrystalline cellulose in Example 2.

[0042] Figure 7 This is a SEM image of foamed gypsum doped with heavy calcium carbonate in Example 3.

[0043] Figure 8 The surface finish of the foamed gypsum in Examples 1-7 (ag) and Comparative Example 1 (h) is shown. Detailed Implementation

[0044] The present invention will be further described below with reference to embodiments.

[0045] General Implementation Examples Firstly, a method for producing lightweight foamed gypsum with a high-smoothness surface, comprising the following raw materials: Mixed powder: comprising 70-90 wt% gypsum powder, 5-15 wt% expanded foamed microspheres (more preferably 3-7 wt%), and 5-15% filler.

[0046] Water: The mass ratio of water to gypsum powder is (0.8-1.2):1; more preferably (0.9-1):1.

[0047] The filler comprises one or more of heavy calcium carbonate, light calcium carbonate, and microcrystalline cellulose; more preferably, the filler is heavy calcium carbonate.

[0048] Preferably, the particle size of the filler is in the range of 1-10 μm.

[0049] Preferably, the gypsum powder is α-type hemihydrate gypsum with a particle size of 6-10 μm, a whiteness of 90-95 degrees, and a powder-to-water mass ratio of (2-4):1.

[0050] Preferably, the shell material of the foamed microspheres is a thermoplastic polymer containing at least one functional group selected from hydroxyl, nitrile and carbonyl groups on its surface, and the core material is an alkane.

[0051] Secondly, an environmentally friendly and simple method for preparing lightweight foamed gypsum with a high-smoothness surface includes the following steps: 1) Heat the foamed microspheres to expand them, so that they complete the volume expansion and enter a volume stable state.

[0052] Preferably, in step 1), the conditions for heating and expansion are: heating temperature 90-110℃, heating time 40-60min, and stirring speed 100-500rpm.

[0053] 2) Without introducing gas, the expanded foamed microspheres obtained in step 1) are mixed with gypsum powder and filler to uniformly disperse the expanded foamed microspheres and filler in the gypsum system.

[0054] As a preferred option, step 2) specifically includes: first adding 40-60% of the expanded foamed microspheres to the gypsum powder and filler and stirring evenly, then adding the remaining expanded foamed microspheres and stirring evenly.

[0055] Further preferred, in step 2), the stirring speed is 500-700 rpm, the first stirring time is 2-3 min, and the second stirring time is 2-3 min.

[0056] 3) Mix the powder with water evenly, pour it into the mold, let it solidify, and demold to obtain a high-smoothness, lightweight foamed plaster.

[0057] Preferably, in step 3), the mold is made of plastic; more preferably, it is made of PP.

[0058] Preferably, in steps 2) and / or 3), the materials are mixed using a co-mixing method; this ensures that the expanded foamed microspheres are better dispersed in the gypsum curing system.

[0059] Preferably, in step 3), the mixing speed is 600-1000 rpm.

[0060] Thirdly, the aforementioned high-smoothness, lightweight foamed gypsum can be used as a decorative material in the field of art painting.

[0061] Specific embodiments and comparative examples Example 1 (using light calcium carbonate as filler) (1) Take 2g of foamed microspheres and add them to a beaker. Heat and stir at 100℃ for 60min at a stirring speed of 300rpm until the foamed microspheres are fully foamed.

[0062] (2) Mix the fully expanded foamed microspheres from step (1) with the model gypsum powder and light calcium carbonate at a stirring speed of 500 rpm. First, take 30g of gypsum powder (α-type hemihydrate gypsum, particle size 6-10μm, whiteness 90 degrees, standard powder-to-water mass ratio 3:1) and 2g of light calcium carbonate (particle size 1-10μm) and mix them evenly. Then, add half of the fully expanded foamed microspheres to the gypsum powder and light calcium carbonate and stir. After 2 minutes, add the other half and continue stirring for 2 minutes to ensure that the fully expanded foamed microspheres, gypsum powder and light calcium carbonate are mixed evenly to obtain a mixed powder.

[0063] (3) Add 30g of water (the mass ratio of gypsum powder to water is 1:1) to the mixed powder in step (2), stir at 800rpm for 30s, pour the resulting mixture into a mold and let it stand at room temperature to solidify to obtain foamed gypsum.

[0064] (4) Based on the volume of the foamed gypsum prepared in step (3), prepare blank gypsum samples (excluding foamed microspheres and fillers) with the same volume at a powder-to-water mass ratio of 3:1.

[0065] Example 2 (Using microcrystalline cellulose as filler) (1) Take 2g of foamed microspheres and add them to a beaker. Heat and stir at 100℃ for 60min at a stirring speed of 300rpm until the foamed microspheres are fully foamed.

[0066] (2) Mix the fully expanded foamed microspheres from step (1) with the model gypsum powder and microcrystalline cellulose at a stirring speed of 500 rpm. First, take 30g of gypsum powder (α-type hemihydrate gypsum, particle size 6-10μm, whiteness 90 degrees, standard powder-to-water mass ratio 3:1) and 2g of microcrystalline cellulose (particle size 1-10μm) and mix them evenly. Add half of the fully expanded foamed microspheres to the gypsum powder and microcrystalline cellulose and stir. After 2 minutes, add the other half and continue stirring for 2 minutes to ensure that the fully expanded foamed microspheres, gypsum powder and microcrystalline cellulose are mixed evenly to obtain a mixed powder.

[0067] (3) Add 30g of water (the mass ratio of gypsum powder to water is 1:1) to the mixed powder in step (2), stir at 800rpm for 30s, pour the resulting mixture into a mold and let it stand at room temperature to solidify to obtain foamed gypsum.

[0068] (4) Based on the volume of the foamed gypsum prepared in step (3), prepare blank gypsum samples (excluding foamed microspheres and fillers) with the same volume at a powder-to-water mass ratio of 3:1.

[0069] Example 3 (using heavy calcium carbonate as filler) (1) Take 2g of foamed microspheres and add them to a beaker. Heat and stir at 100℃ for 60min at a stirring speed of 300rpm until the foamed microspheres are fully foamed.

[0070] (2) Mix the fully expanded foamed microspheres from step (1) with the model gypsum powder and heavy calcium carbonate at a stirring speed of 500 rpm. First, take 30g of gypsum powder (α-type hemihydrate gypsum, particle size 6-10μm, whiteness 90 degrees, standard powder-to-water mass ratio 3:1) and 2g of heavy calcium carbonate (particle size 1-10μm) and mix them evenly. Add half of the fully expanded foamed microspheres to the gypsum powder and heavy calcium carbonate and stir. After 2 minutes, add the other half and continue stirring for 2 minutes to ensure that the fully expanded foamed microspheres, gypsum powder and heavy calcium carbonate are mixed evenly to obtain a mixed powder.

[0071] (3) Add 30g of water (the mass ratio of gypsum powder to water is 1:1) to the mixed powder in step (2), stir at 800rpm for 30s, pour the resulting mixture into a mold and let it stand at room temperature to solidify to obtain foamed gypsum.

[0072] (4) Based on the volume of the foamed gypsum prepared in step (3), prepare blank gypsum samples (excluding foamed microspheres and fillers) with the same volume at a powder-to-water mass ratio of 3:1.

[0073] Example 4 (Compared to Example 3, the mass ratio of gypsum powder to water is 1:0.8 (in Example 3 it is 1:1)) (1) Take 2g of foamed microspheres and add them to a beaker. Heat and stir at 100℃ for 60min at a stirring speed of 300rpm until the foamed microspheres are fully foamed.

[0074] (2) Mix the fully expanded foamed microspheres from step (1) with the model gypsum powder and heavy calcium carbonate at a stirring speed of 500 rpm. First, take 30g of gypsum powder (α-type hemihydrate gypsum, particle size 6-10μm, whiteness 90 degrees, standard powder-to-water mass ratio 3:1) and 2g of heavy calcium carbonate (particle size 1-10μm) and mix them evenly. Add half of the fully expanded foamed microspheres to the gypsum powder and heavy calcium carbonate and stir. After 2 minutes, add the other half and continue stirring for 2 minutes to ensure that the fully expanded foamed microspheres, gypsum powder and heavy calcium carbonate are mixed evenly to obtain a mixed powder.

[0075] (3) Add 24g of water (the mass ratio of gypsum powder to water is 1:0.8) to the mixed powder in step (2), stir at 800rpm for 30s, pour the resulting mixture into a mold and let it stand at room temperature to solidify to obtain foamed gypsum.

[0076] (4) Based on the volume of the foamed gypsum prepared in step (3), prepare blank gypsum samples (excluding foamed microspheres and fillers) with the same volume at a powder-to-water mass ratio of 3:1.

[0077] Example 5 (Compared to Example 3, the mass ratio of gypsum powder to water is 1:1.2 (compared to 1:1 in Example 3)) (1) Take 2g of foamed microspheres and add them to a beaker. Heat and stir at 100℃ for 60min at a stirring speed of 300rpm until the foamed microspheres are fully foamed.

[0078] (2) Mix the fully expanded foamed microspheres from step (1) with the model gypsum powder and heavy calcium carbonate at a stirring speed of 500 rpm. First, take 30g of gypsum powder (α-type hemihydrate gypsum, particle size 6-10μm, whiteness 90 degrees, standard powder-to-water mass ratio 3:1) and 2g of heavy calcium carbonate (particle size 1-10μm) and mix them evenly. Add half of the fully expanded foamed microspheres to the gypsum powder and heavy calcium carbonate and stir. After 2 minutes, add the other half and continue stirring for 2 minutes to ensure that the fully expanded foamed microspheres, gypsum powder and heavy calcium carbonate are mixed evenly to obtain a mixed powder.

[0079] (3) Add 36g of water (the mass ratio of gypsum powder to water is 1:1.2) to the mixed powder in step (2), stir at 800rpm for 30s, pour the resulting mixture into a mold and let it stand at room temperature to solidify to obtain foamed gypsum.

[0080] (4) Based on the volume of the foamed gypsum prepared in step (3), prepare blank gypsum samples (excluding foamed microspheres and fillers) with the same volume at a powder-to-water mass ratio of 3:1.

[0081] Example 6 (Compared to Example 3, the content of foamed microspheres in the mixed powder is 4g, while in Example 3 it is 2g) (1) Add 4g of foamed microspheres to a beaker and heat and stir at 100℃ for 60min at a stirring speed of 300rpm until the foamed microspheres are fully foamed.

[0082] (2) Mix the fully expanded foamed microspheres from step (1) with the model gypsum powder and heavy calcium carbonate at a stirring speed of 500 rpm. First, take 30g of gypsum powder (α-type hemihydrate gypsum, particle size 6-10μm, whiteness 90 degrees, standard powder-to-water mass ratio 3:1) and 2g of heavy calcium carbonate (particle size 1-10μm) and mix them evenly. Add half of the fully expanded foamed microspheres to the gypsum powder and heavy calcium carbonate and stir. After 2 minutes, add the other half and continue stirring for 2 minutes to ensure that the fully expanded foamed microspheres, gypsum powder and heavy calcium carbonate are mixed evenly to obtain a mixed powder.

[0083] (3) Add 30g of water (the mass ratio of gypsum powder to water is 1:1) to the mixed powder in step (2), stir at 800rpm for 30s, pour the resulting mixture into a mold and let it stand at room temperature to solidify to obtain foamed gypsum.

[0084] (4) Based on the volume of the foamed gypsum prepared in step (3), prepare blank gypsum samples (excluding foamed microspheres and fillers) with the same volume at a powder-to-water mass ratio of 3:1.

[0085] Example 7 (Compared to Example 3, the content of foamed microspheres in the mixed powder is 6g, while in Example 3 it is 2g) (1) Take 6g of foamed microspheres and add them to a beaker. Heat and stir at 100℃ for 60min at a stirring speed of 300rpm until the foamed microspheres are fully foamed.

[0086] (2) Mix the fully expanded foamed microspheres from step (1) with the model gypsum powder and heavy calcium carbonate at a stirring speed of 500 rpm. First, take 30g of gypsum powder (α-type hemihydrate gypsum, particle size 6-10μm, whiteness 90 degrees, standard powder-to-water mass ratio 3:1) and 2g of heavy calcium carbonate (particle size 1-10μm) and mix them evenly. Add half of the fully expanded foamed microspheres to the gypsum powder and heavy calcium carbonate and stir. After 2 minutes, add the other half and continue stirring for 2 minutes to ensure that the fully expanded foamed microspheres, gypsum powder and heavy calcium carbonate are mixed evenly to obtain a mixed powder.

[0087] (3) Add 30g of water (the mass ratio of gypsum powder to water is 1:1) to the mixed powder in step (2), stir at 800rpm for 30s, pour the resulting mixture into a mold and let it stand at room temperature to solidify to obtain foamed gypsum.

[0088] (4) Based on the volume of the foamed gypsum prepared in step (3), prepare blank gypsum samples (excluding foamed microspheres and fillers) with the same volume at a powder-to-water mass ratio of 3:1.

[0089] Comparative Example 1 (non-foamed microspheres) (1) Take 90g of model plaster powder (α-type hemihydrate plaster, particle size 6-10μm, whiteness 90 degrees, standard powder-to-water mass ratio 3:1) and add it to a beaker. Add 30g of water (plaster powder to water mass ratio 3:1) to the beaker and stir at 1000rpm for 1min. Pour the resulting mixture into a mold and let it stand at room temperature to solidify to obtain blank plaster.

[0090] Comparative Example 2 (No filler) (1) Take 2g of foamed microspheres and add them to a beaker. Heat and stir at 100℃ for 60min at a stirring speed of 300rpm until the foamed microspheres are fully foamed.

[0091] (2) Mix the fully expanded foamed microspheres and model gypsum powder from step (1) at a stirring speed of 500 rpm. Take 30g of gypsum powder (α-type hemihydrate gypsum, particle size 6-10μm, whiteness 90 degrees, standard powder-to-water mass ratio 3:1), add half of the fully expanded foamed microspheres to the gypsum powder and stir. After 2 minutes, add the other half and continue stirring for 2 minutes to ensure that the fully expanded foamed microspheres and gypsum powder are mixed evenly to obtain a mixed powder.

[0092] (3) Add 30g of water (the mass ratio of gypsum powder to water is 1:1) to the mixed powder in step (2), stir at 800rpm for 30s, pour the resulting mixture into a mold and let it stand at room temperature to solidify to obtain foamed gypsum.

[0093] Performance testing and characterization Figure 2 The FTIR spectra of the Dongjin MS140WS expandable microspheres (foamed microspheres) used in the examples and comparative examples are shown, with 3651 cm⁻¹ as the focal length. -1 The absorption peak at 2927 cm⁻¹ is the OH bond stretching vibration peak. -1 The absorption peak at 2248 cm⁻¹ is the stretching vibration peak of the CH bond. -1 The absorption peak for the stretching vibration of the C≡N bond is at 1737 cm⁻¹. -1 The absorption peak at 1456 cm⁻¹ is the stretching vibration peak of the C=O bond. -1 The absorption peak at 1232 cm⁻¹ is the bending vibration peak of the CH bond. -1 The absorption peak at 1122 cm⁻¹ represents the asymmetric stretching vibration of the COC bond. -1 The absorption peak at this point corresponds to the stretching vibration of the CN bond. This indicates that the surface of the Dongjin MS140WS expandable microspheres contains a large number of functional groups such as hydroxyl, nitrile, and carbonyl groups. The foamed microspheres are more easily wetted by the slurry formed from model gypsum powder and water, resulting in a larger contact area. The gypsum slurry can better encapsulate the foamed microspheres, increasing the bonding force between them. In the gypsum slurry, calcium sulfate hydrate undergoes a hydration reaction, producing calcium ions (Ca). 2+ The hydroxyl groups on the surface of the foamed microspheres undergo a complexation reaction, making the foamed microspheres more tightly bound to the slurry.

[0094] Figure 3 and Figure 4 SEM images of blank gypsum (Comparative Example 1) and foamed gypsum with only foamed microspheres but no filler (Comparative Example 2) are shown below. Figure 3 As shown, the internal crystals of blank plaster are layered and stacked in a plate-like manner, resulting in a dense and compact overall structure, which contributes to its high strength. Figure 4As shown, expanded microspheres were observed embedded in the cross-layered structure of gypsum crystals. With the addition of the expanded microspheres to the gypsum powder, some water was used to wet the surface of the microspheres, resulting in a significant reduction in the effective water available for gypsum curing. If the original 3:1 powder-to-water mass ratio was maintained, the mixed powder could not form a slurry; therefore, additional water had to be added to obtain a uniform slurry. However, the gypsum crystals in the SEM exhibited a loose, needle-like structure. This is because water plays a crucial role in gypsum crystal formation. Compared to Comparative Example 1, the increased water content in Comparative Example 2 (1:1 powder-to-water mass ratio) provided sufficient moisture for the free growth of gypsum crystals along one dimension, thus causing the crystal morphology to change from dense, plate-like to needle-like. However, the needle-like crystal structure is loose and irregular, with distinct crystal outlines and reduced entanglement, which reduces the strength of the foamed gypsum and increases its surface roughness. Therefore, fillers need to be added to improve the overall performance of the foamed gypsum.

[0095] Figure 5 , Figure 6 and Figure 7 SEM images of foamed gypsum doped with light calcium carbonate (Example 1), microcrystalline cellulose (Example 2), and heavy calcium carbonate (Example 3), respectively. Figure 4 Compared to SEM images of unfilled foamed gypsum, such as Figure 5 As shown, the surfaces of the foamed microspheres and the needle-like gypsum crystals are clearly defined, and the gaps between them are not completely filled by light calcium carbonate. This is because the bulk density of light calcium carbonate is relatively low, resulting in uneven dispersion of light calcium carbonate in the gypsum powder, leading to localized agglomeration and preventing effective filling of the gaps between the gypsum and the foamed microspheres. Figure 6 As shown, microcrystalline cellulose enhances the connection between expanded microspheres and gypsum within a certain range, reducing the gaps between them. However, the organic material microcrystalline cellulose can agglomerate in gypsum, and some gypsum crystal structures remain loose, resulting in a high surface roughness of the foamed gypsum. Figure 7 As shown, the gaps between the foamed microspheres and needle-like gypsum crystals are perfectly filled by heavy calcium carbonate, resulting in a dense structure. This is because the bulk density of heavy calcium carbonate is similar to that of α-type hemihydrate gypsum, allowing for more uniform dispersion in gypsum powder. This makes the gypsum slurry easier to flow and spread, reducing the surface roughness of the gypsum. Therefore, compared to the fillers added in Examples 1 and 2, the heavy calcium carbonate filler in Example 3 is more suitable for addition to foamed gypsum, resulting in a foamed gypsum with low surface roughness and a smooth, flat surface.

[0096] Depend on Figure 8 Digital photographs of samples from different Examples 1-7 (ag) and Comparative Example 1 (h) show that the sample surfaces of Examples 1 and 2 are very rough, the sample surface of Example 4 is powdery and rough, and the sample surfaces of Examples 3 and 5 are smooth. Figure 8The blank plaster in Comparative Example 1 had the same smoothness, and the samples in Examples 6 and 7 also had rough surfaces, but the sample in Example 7 was rougher and more powdery.

[0097] Table 1 records the time from pouring the slurry into the mold to complete curing and demolding in Examples 1-7 and Comparative Examples 1-2, with the results accurate to 1 minute. The blank plaster models prepared in Examples 1-7 (obtained in step (4)) were weighed and denoted as M1, and the foamed plaster models prepared in Examples 1-7 were weighed and denoted as M2. The weight loss rate of each example sample was calculated according to the following formula. The results are recorded in Table 1, with the test results accurate to 0.1%.

[0098] R = (M1 - M2) / M1 × 100% In the formula: M1 - is the mass of the blank plaster model in Examples 1-7, in g; M2 represents the mass of the foamed plaster molds from Examples 1-7, in g. Table 1 Table 1 shows the weight loss rate and curing / demolding time parameters of the foamed gypsum prepared in Examples 1-7 and Comparative Examples 1-2. The data in Table 1 show that the foamed gypsum in Examples 1-7, compared to the corresponding blank gypsum, had a weight loss rate ranging from 46% to 80% and a curing / demolding time of 30-60 minutes, indicating that the addition of foamed microspheres significantly reduced the weight of the gypsum. As shown in Examples 3, 4, and 5 of Table 1, the weight loss rate increased with the increase of the powder-to-water mass ratio (mass ratio of gypsum powder to water). However, an excessively high powder-to-water mass ratio leads to insufficient moisture during curing, incomplete curing, and high surface roughness of the gypsum (Example 4). An excessively low powder-to-water mass ratio results in a poorer weight loss effect and an increased curing time (Example 5). Therefore, a powder-to-water mass ratio of approximately 1:1 is preferred.

[0099] As shown in Examples 3, 6, and 7 of Table 1, the weight loss rate of foamed gypsum increases significantly with the increase of the content of foamed microspheres. However, in Examples 6 and 7, most of the water was used to wet the surface of the foamed microspheres, resulting in a significant reduction in the effective water available for gypsum curing. This leads to a noticeable roughness and powdering of the overall foamed gypsum surface, which does not meet decorative requirements. Therefore, the preferred content of foamed microspheres in the mixed powder is approximately 5%.

[0100] In summary, the data from Example 3 in Table 1 are more outstanding: the prepared foamed gypsum sample, while ensuring significant weight reduction (46% weight reduction rate), avoids problems such as large surface roughness and powdering and detachment of foamed gypsum; the preparation process has a small negative impact on curing efficiency and perfectly balances key performance indicators such as lightweight, structural density, and curing speed.

[0101] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A lightweight foamed gypsum with a highly smooth surface, characterized in that: Including the following raw materials: Mixed powder: including 70-90 wt% gypsum powder, 5-15 wt% expanded foamed microspheres, and 5-15 wt% filler; The mass ratio of water to gypsum powder is (0.8-1.2):1; The gypsum powder is α-type hemihydrate gypsum, and the powder-to-water mass ratio is (2-4):1; The filler includes one or more of heavy calcium carbonate, light calcium carbonate, and microcrystalline cellulose.

2. The high-smoothness, lightweight foamed gypsum according to claim 1, characterized in that: The filler is heavy calcium carbonate; The particle size of the filler is 1-10 μm.

3. The high-smoothness, lightweight foamed gypsum according to claim 1 or 2, characterized in that: The mass ratio of water to gypsum powder is (0.9-1):1; The content of expanded foamed microspheres in the mixed powder is 3-7 wt%.

4. The high-smoothness, lightweight foamed gypsum according to claim 1 or 2, characterized in that: The α-type hemihydrate gypsum has a particle size of 6-10 μm and a whiteness of 90-95 degrees.

5. The high-smoothness, lightweight foamed gypsum according to claim 1 or 2, characterized in that: The shell material of the foamed microspheres is a thermoplastic polymer containing at least one functional group selected from hydroxyl, nitrile and carbonyl groups on its surface, and the core material is an alkane.

6. An environmentally friendly and simple preparation method for high-smoothness surface lightweight foamed gypsum according to any one of claims 1-5, characterized in that... include: 1) Heating the foamed microspheres causes them to expand and reach a stable volume state; 2) Without introducing gas, the expanded foamed microspheres obtained in step 1) are mixed with gypsum powder and filler to make the expanded foamed microspheres and filler uniformly dispersed in the gypsum system. 3) Mix the obtained powder with water evenly, pour it into the mold, solidify, demold, and obtain a high-smoothness, lightweight foamed gypsum.

7. The preparation method according to claim 6, characterized in that: Step 2) Specifically includes: first, adding 40-60% of the expanded foamed microspheres to the gypsum powder and filler and stirring evenly, then adding the remaining expanded foamed microspheres and stirring evenly.

8. The preparation method according to claim 6, characterized in that: In step 3), the mold is made of plastic.

9. The use of the high-smoothness surface lightweight foamed gypsum according to any one of claims 1-5 or the high-smoothness surface lightweight foamed gypsum obtained by the preparation method according to any one of claims 6-8 as a decorative material.

10. Application of heavy calcium carbonate in reducing the surface roughness of foamed gypsum.

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