Modified polypropylene fiber for gypsum mortar as well as preparation method and application of modified polypropylene fiber

Abstract

The invention relates to the technical field of gypsum mortar, in particular to a modified polypropylene fiber for gypsum mortar and a preparation method and application thereof. Comprising the following steps: performing swelling treatment on polypropylene fibers in a non-polar solvent system to prepare a precursor; the precursor and a silane coupling agent are subjected to a polymerization reaction in a first solvent system, the silane coupling agent is grafted to the surface of the precursor, and an intermediate is prepared; and performing hydrolysis and condensation reaction on the intermediate and nano silicon dioxide in a second solvent system to form chemical bonding, thereby obtaining the modified polypropylene fiber. The mechanical interlocking effect between the fibers and a matrix material can be enhanced, the dispersity of the fibers in mortar is improved, the binding force between the fibers and the matrix is improved, and the technical problem that the dispersity and interface bonding property of the polypropylene fibers in the gypsum mortar are poor is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of gypsum mortar, and particularly relates to a modified polypropylene fiber for gypsum mortar, a preparation method thereof, and an application thereof. Background Art

[0002] Gypsum mortar is a new type of wall plastering material and is widely used in the construction field. Limited by the material properties of gypsum itself, compared with traditional cement mortar, gypsum mortar has problems in performance such as lower flexural strength and compressive strength after hardening, which restricts the application range of gypsum mortar. To alleviate the above problems, the prior art improves the performance of gypsum mortar by adding additives to gypsum mortar.

[0003] Polypropylene fiber is a common additive, but the effect of polypropylene fiber on improving the performance of gypsum mortar is not ideal enough, mainly because the dispersibility and interfacial bonding property of polypropylene fiber in gypsum mortar are poor. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art, and provide a modified polypropylene fiber for gypsum mortar, a preparation method thereof, and an application thereof, and solve the technical problems of poor dispersibility and interfacial bonding property of polypropylene fiber in gypsum mortar.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] The present invention provides a preparation method of a modified polypropylene fiber for gypsum mortar, comprising the following steps:

[0007] The polypropylene fiber is subjected to a swelling treatment in a non-polar solvent system to obtain a precursor; the precursor and a silane coupling agent are subjected to a polymerization reaction in a first solvent system, and the silane coupling agent is grafted onto the surface of the precursor to obtain an intermediate; the intermediate and nano-silica are subjected to a hydrolysis and condensation reaction in a second solvent system to form a chemical bond, and a modified polypropylene fiber is obtained.

[0008] Optionally, the mass-volume ratio of the polypropylene fiber to the non-polar solvent is 0.1 kg / L to 0.3 kg / L.

[0009] Optionally, the non-polar solvent is xylene.

[0010] Optionally, the first solvent is an ethanol solution, and the volume ratio of ethanol to water in the ethanol solution is 9:1.

[0011] Optionally, the silane coupling agent and the first solvent form a mixed solution, and the mass percentage of the silane coupling agent in the mixed solution is 20% to 50%.

[0012] Optionally, the second solvent is ethanol.

[0013] Optionally, the nano-silica forms a dispersion in the second solvent, and the mass ratio of the nano-silica in the dispersion is 0.5% - 1.5%.

[0014] The present invention provides a modified polypropylene fiber, which is prepared by the above-mentioned preparation method of the modified polypropylene fiber for gypsum mortar.

[0015] The present invention provides an application of the above-mentioned modified polypropylene fiber in the preparation of gypsum mortar.

[0016] The beneficial effect of the present invention is that, compared with the prior art, after the polypropylene fiber is subjected to swelling treatment, the roughness of the fiber surface is improved, so that the matrix and the modified material can better fill and embed the concave and convex structures on the fiber surface, and the mechanical interlocking effect between the fiber and the matrix material can be enhanced. And by grafting a silane coupling agent on the surface of the precursor, the hydrophilicity of the fiber is improved, thereby improving the dispersibility of the fiber in the mortar, and the polymerization reaction, hydrolysis and condensation reaction between the modified material and the precursor improve the bonding force between the fiber and the substrate, thus solving the technical problems of poor dispersibility and interfacial bonding of polypropylene fibers in gypsum mortar. Description of the Drawings

[0017] Figure 1 It is a comparison diagram of the infrared spectra of the polypropylene fiber and the intermediate in Example 1.

[0018] Figure 2 It is a comparison diagram of the surface morphologies of the polypropylene fiber and the modified polypropylene fiber in Example 1. Among them, a is the surface morphology diagram of the polypropylene fiber in Example 1, and b is the surface morphology diagram of the modified polypropylene fiber prepared in Example 1.

[0019] Figure 3 It is a comparison diagram of the microscopic observation results of the fiber distribution in the gypsum mortar doped with polypropylene fiber and the gypsum mortar doped with modified polypropylene fiber. Among them, a is the microscopic observation result diagram of the fiber distribution in the gypsum mortar doped with polypropylene fiber, and b is the microscopic observation result diagram of the fiber distribution in the gypsum mortar doped with the modified polypropylene fiber prepared in Example 1.

[0020] Figure 4 It is a comparison diagram of the test results of the flexural strength and compressive strength of different gypsum mortars at each age.

[0021] Among them, a is the comparison diagram of the test results of the flexural strength of different gypsum mortars at each age, and b is the comparison diagram of the test results of the compressive strength of different gypsum mortars at each age. Detailed Embodiments

[0022] To solve the above technical problems, the present invention provides a modified polypropylene fiber for gypsum mortar, its preparation method and application. Now, the technical solutions and embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0023] The technical solutions adopted by the present invention are as follows:

[0024] The idea of optimizing the interface of polypropylene fibers is mainly to improve the hydrophilicity of the fibers and the interfacial bonding between the fibers and the matrix material (mainly gypsum mortar in the present invention), thereby improving the performance of the composite material. There are mainly two purposes for modifying polypropylene fibers:

[0025] One is to improve the surface roughness of the fibers through modification, so that the matrix material can better fill and embed the concave and convex structures on the fiber surface, enhancing the mechanical interlocking effect between the fibers and the matrix material, and thus improving the adhesion. The other is to improve the hydrophilicity of the fibers through modification, thereby improving the dispersibility of the fibers in the mortar.

[0026] The modification treatment of polypropylene fibers mainly includes the following steps:

[0027] 1. Pretreatment with xylene

[0028] The molecular structure of PP fibers is regular and the surface shows chemical inertness, which is not conducive to directly carrying out hydrophilic modification treatment on its surface. Xylene is a non-polar solvent. When PP fibers are immersed in xylene, it will swell the surface of the fibers. This swelling makes the surface structure of the fibers become more relaxed and open, thus increasing the contact area between the fiber surface and the modifier and the surface roughness of the fibers, enabling the modifier to better diffuse and cover the fiber surface. At the same time, xylene can also oxidize the fiber surface, increasing the content of active groups on the fiber surface, and then better chemically combining with the modifier. Therefore, the surface of the fibers after swelling treatment becomes more affinity, which helps the modified material to form better chemical bonding and physical coupling with the fiber surface.

[0029] 2. Modification with silane coupling agent

[0030] Modifying PP fibers with coupling agents is a commonly used method to improve the interfacial bonding force between the fibers and the matrix material (such as cement, mortar or concrete), thereby improving the performance of the overall material. Coupling agents are usually amphiphilic molecules, with one end being fiber-philic and the other end being matrix-philic, and can form a bridge between the fibers and the matrix, enhancing the chemical or physical bonding between the two.

[0031] 3. Modification with nano-silica

[0032] Due to their extremely small size and high specific surface area, nano-silica particles can fill the microscopic pores and gaps in PP fibers, forming more sufficient physical contact with the polypropylene matrix. This provides physical support and reinforcement for the fibers, making the fiber structure more stable. Moreover, the surface of nano-silica contains hydroxyl groups, which can undergo chemical reactions with certain functional groups in the oxidized PP fibers. These chemical and physical bonds make the combination of nano-silica and fibers more stable.

[0033] There are a large number of hydroxyl groups on the surface of nano-silica. The presence of surface hydroxyl groups enables nano-silica to adsorb water molecules and form hydrogen bonds with water molecules, thereby making the modified fibers hydrophilic; in addition, the added silica particles can provide a high surface energy, which also helps to improve the hydrophilicity of the fibers, making the fibers have a high surface energy, resulting in a high adsorption capacity on the fiber surface, which can reduce the surface tension of the liquid, making the liquid easy to spread and wet the surface, thus showing good hydrophilicity.

[0034] The present invention will be described in detail below through specific examples. The examples are exemplary and are intended to explain the present invention, but should not be construed as a limitation of the present invention.

[0035] Example 1

[0036] This example provides a method for preparing modified polypropylene, including the following steps:

[0037] Step 1, swelling modification.

[0038] Place 20 g of PP fibers in 200 ml of xylene and swell at room temperature for 80 min and then take out. After taking out the swollen fibers, first wash them with ethanol three times, and then place them in an oven at 60 °C and dry for 8 h and then take out to obtain a precursor, named swollen PP fibers.

[0039] Step 2, hydrophilic modification.

[0040] Use the silane coupling agent KH570 to prepare modified PP fibers. Add the silane coupling agent KH570 to 100 ml of an anhydrous ethanol-aqueous solution with a volume ratio of 9:1 to obtain a modified solution with a silane concentration of 40%. Then soak the fibers swollen in xylene in this KH570 solution for 2 h, take out and wash three times with anhydrous ethanol, and then place them in an oven at 60 °C and dry for 8 h and then take out to obtain an intermediate, named KH570-PP fibers.

[0041] Step 3, composite modification.

[0042] The prepared KH570-PP fibers were immersed in an anhydrous ethanol suspension of nano-silica with a mass fraction of 0.5% for 3 h and then taken out. After being washed three times with anhydrous ethanol, they were placed in an oven at 60 °C and dried for 8 h before being taken out to obtain modified polypropylene fibers, named KH570-SiO2-PP fibers.

[0043] Example 2

[0044] The difference from Example 1 is that 40 g of PP fibers were placed in 200 ml of xylene and swollen at room temperature for 80 min and then taken out. After the swollen fibers were taken out, they were first washed 3 times with ethanol and then placed in an oven at 60 °C and dried for 8 h before being taken out to obtain a precursor. The remaining steps and preparation parameters were the same.

[0045] Example 3

[0046] The difference from Example 1 is that 60 g of PP fibers were placed in 200 ml of xylene and swollen at room temperature for 80 min and then taken out. After the swollen fibers were taken out, they were first washed 3 times with ethanol and then placed in an oven at 60 °C and dried for 8 h before being taken out to obtain a precursor. The remaining steps and preparation parameters were the same.

[0047] Example 4

[0048] The difference from Example 1 is that silane coupling agent KH570 was used to prepare modified PP fibers (KH570-PP). Silane coupling agent KH570 was added to 100 ml of an anhydrous ethanol-aqueous solution with a volume ratio of 9:1 to obtain a modified solution with a silane concentration of 20%. Then, the fibers swollen in xylene were immersed in this KH570 solution for 2 h, taken out, washed three times with anhydrous ethanol, and then placed in an oven at 60 °C and dried for 8 h before being taken out to obtain an intermediate. The remaining steps and preparation parameters were the same.

[0049] Example 5

[0050] The difference from Example 1 is that silane coupling agent KH570 was used to prepare modified PP fibers (KH570-PP). Silane coupling agent KH570 was added to 100 ml of an anhydrous ethanol-aqueous solution with a volume ratio of 9:1 to obtain a modified solution with a silane concentration of 50%. Then, the fibers swollen in xylene were immersed in this KH570 solution for 2 h, taken out, washed three times with anhydrous ethanol, and then placed in an oven at 60 °C and dried for 8 h before being taken out to obtain an intermediate. The remaining steps and preparation parameters were the same.

[0051] Example 6

[0052] The difference from Example 1 is that the prepared KH570-PP fibers are immersed in an anhydrous ethanol suspension of nano-silica with a mass fraction of 1.5% for 3 h and then taken out, washed three times with anhydrous ethanol, and then placed in an oven at 60 °C for 8 h and taken out to obtain modified polypropylene fibers. The remaining steps and preparation parameters are the same.

[0053] Example 7

[0054] The difference from Example 1 is that the prepared KH570-PP fibers are immersed in an anhydrous ethanol suspension of nano-silica with a mass fraction of 1.0% for 3 h and then taken out, washed three times with anhydrous ethanol, and then placed in an oven at 60 °C for 8 h and taken out to obtain modified polypropylene fibers. The remaining steps and preparation parameters are the same.

[0055] It should be noted that compared with Example 1, there is no obvious difference in the performance of the modified polypropylene fibers prepared in Examples 2-7.

[0056] Preparation of fiber gypsum mortar specimens

[0057] (1) Physical properties of polypropylene fibers

[0058] The length of the polypropylene fibers is 9 mm, and their physical properties are shown in Table 1.

[0059] Table 1 Other physical properties of polypropylene fibers

[0060]

[0061] (2) Mix proportion design of fiber gypsum mortar

[0062] The basic mix proportion of the gypsum mortar is shown in Table 2. The gypsum is desulfurized gypsum from a power plant, and its chemical composition is shown in Table 3. On the basis of the basic mix proportion, unmodified PP fibers and KH570-SiO2-PP fibers are respectively incorporated to prepare 3 kinds of gypsum mortars, and the fibers are added at a volume fraction of 0.05%.

[0063] Table 2 Basic mix proportion of gypsum mortar

[0064] Desulfurized gypsum Vitrified microspheres Ground calcium carbonate Lubricant Retarder Water 1125 105 270 1 2.7 750

[0065] Table 3 Main chemical components of desulfurized gypsum

[0066] Composition Type III anhydrous gypsum Hemihydrate Dihydrate Content / % 4.66 81.62 1.86

[0067] (3) Preparation of test specimens

[0068] Disperse the fibers in water first, then pour other materials into a blender and stir evenly. Finally, add water and stir. After completing the stirring process, pour the mixture into a mold to make specimens with dimensions of 40mm×40mm×160mm. For each type of fiber-reinforced gypsum mortar, make 1 group of specimens, with 3 specimens in each group, for determining the dispersibility of the fibers in the gypsum mortar. After curing the specimens for 3 days under natural conditions for the dispersibility test, cut them in the middle with a rock cutting machine and then conduct fiber dispersibility analysis. Additionally, make 3 groups of specimens for the gypsum mortar prepared according to the basic mix ratio, the gypsum mortar with unmodified PP fibers, and the gypsum mortar with KH570-SiO2-PP fibers, and measure the flexural strength and compressive strength at different ages (24h, 7d, 28d).

[0069] Infrared spectrum analysis:

[0070] Figure 1 Figure shows the infrared spectrum comparison of PP fibers before and after modification with silane coupling agent. It can be seen that new characteristic absorption peaks appear in the infrared absorption spectrum of KH570-PP50 fibers. The new characteristic peak at a wavelength of 1720 cm-1 represents the stretching vibration of the carbonyl group (C=O); the characteristic peaks at wavelengths of 1085 cm-1 and 815 cm-1 are the stretching vibration and bending vibration of (Si-O-Si). Since (C=O) and (Si-O-Si) are the unique structures of KH570, it indicates that the silane coupling agent has been grafted onto the surface of PP fibers, forming strong chemical bonding at the fiber interface.

[0071] Analysis of fiber surface characteristics:

[0072] Use a 3D laser confocal microscope to observe the surface morphology of unmodified and composite-modified PP fibers at different magnifications. Figure 2 Figure a shows the surface morphology of polypropylene fibers in Example 1, and Figure b shows the surface morphology of the modified polypropylene fibers prepared in Example 1. As Figure 2 can be seen, the untreated PP fibers have a relatively clean and smooth surface without longitudinal grooves, while obvious nanoparticles and silane coupling agent are distributed on the surface of the composite-modified PP fibers, and the surface roughness is significantly improved, which can enhance the bonding force between the fibers and the gypsum mortar matrix.

[0073] Dispersibility of fibers:

[0074] Cut the specimen into a cross-section of 40mm×40mm with a cutting machine, cover the cutting cross-section with a grid with a unit of 10mm, and divide the cross-section into 16 squares. Observe the distribution of fibers on the cross-section with a microscope and analyze the dispersion degree of the fibers using mathematical statistics methods. The average value of the number of fibers in a 10mm×10mm square on the cross-section of the mortar specimen Standard deviation S, coefficient of variation The fiber content γ and the fiber dispersion degree β are calculated according to formulas (1) to (4) respectively, and the calculation results are shown in Table 4.

[0075]

[0076] In the formulas, x i —— the number of fibers in the i-th square in 16 square areas on the cross-section of the specimen;

[0077] n —— the number of square areas divided on the cross-section of the specimen, and in the present invention, n = 16 is taken.

[0078] Table 4 Statistical table of fiber dispersion data in gypsum mortar

[0079]

[0080] It can be seen from the results in Table 4 that the standard deviation and coefficient of variation of the distribution quantity of the modified fibers in the gypsum mortar are reduced to a large extent, and the fiber dispersion degree is improved, indicating that the fiber dispersion in the gypsum mortar can be improved after fiber modification. The uniform distribution of fibers in the gypsum mortar is beneficial to the improvement of the mechanical properties and crack resistance of the gypsum mortar.

[0081] Figure 3 Figure a is the microscopic observation result diagram of the fiber distribution in the gypsum mortar mixed with polypropylene fibers, and Figure b is the microscopic observation result diagram of the fiber distribution in the gypsum mortar mixed with the modified polypropylene fibers prepared in Example 1. It can be seen that after fiber modification, there is less aggregation and more uniform distribution in the gypsum mortar.

[0082] Strength of fiber gypsum mortar:

[0083] The flexural strength and compressive strength of the fiber-free gypsum mortar (Group M1), the gypsum mortar mixed with unmodified PP fibers (Group M2), and the gypsum mortar mixed with KH570-SiO2-PP fibers (Group M5) at each age are as Figure 4 shown. It can be seen that after adding fibers, both the flexural strength and the compressive strength of the mortar are improved. Compared with the mortar in Group M2, the flexural strengths of the mortar in Group M5 at 24 h, 3 d, and 28 d are increased by 42.9%, 24.4%, and 27.7% respectively, and the compressive strengths are increased by 14.5%, 8.0%, and 12.3% respectively. It shows that under the bridging and filling effects of the fibers, the flexural strength and compressive strength of the gypsum mortar are improved. After the fibers are compound-modified, the distribution of the fibers becomes uniform, the interfacial bonding force between the fibers and the matrix is further enhanced, and the strength is further improved.

[0084] The above-described are only the preferred embodiments of the present invention, and the above specific embodiments do not limit the present invention. Within the scope of the technical idea of the present invention, various deformations and modifications can occur. Any retouching, modification or equivalent replacement made by those of ordinary skill in the art according to the above description shall fall within the scope protected by the present invention.

Claims

1. A preparation method of modified polypropylene fibers for gypsum mortar, characterized in that, It includes the following steps: The polypropylene fiber is swelled in a non-polar solvent system to obtain a precursor; The precursor and the silane coupling agent are subjected to a polymerization reaction in a first solvent system, and the silane coupling agent is grafted onto the surface of the precursor to obtain an intermediate; The intermediate and the nano-silica are subjected to hydrolysis and condensation reactions in a second solvent system to form a chemical bond, and a modified polypropylene fiber is obtained.

2. The preparation method of the modified polypropylene fiber for gypsum mortar according to claim 1, characterized in that, The mass-volume ratio of the polypropylene fiber to the non-polar solvent is 0.1 kg / L to 0.3 kg / L.

3. The preparation method of the modified polypropylene fiber for gypsum mortar according to claim 2, characterized in that, The non-polar solvent is xylene.

4. The preparation method of the modified polypropylene fiber for gypsum mortar according to claim 1, characterized in that, The first solvent is an ethanol solution, and the volume ratio of ethanol to water in the ethanol solution is 9:

1.

5. The preparation method of the modified polypropylene fiber for gypsum mortar according to claim 4, characterized in that, The silane coupling agent and the first solvent form a mixed solution, and the mass percentage of the silane coupling agent in the mixed solution is 20% to 50%.

6. The preparation method of the modified polypropylene fiber for gypsum mortar according to claim 1, wherein, The second solvent is ethanol.

7. The preparation method of the modified polypropylene fiber for gypsum mortar according to claim 6, characterized in that, The nano-silica forms a dispersion in the second solvent, and the mass percentage of the nano-silica in the dispersion is 0.5% to 1.5%.

8. A modified polypropylene fiber, characterized in that, It is prepared by using the preparation method of the modified polypropylene fiber for gypsum mortar according to any one of claims 1 to 7.

9. Use of the modified polypropylene fiber according to claim 8 in the preparation of gypsum mortar.

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