Polyvinyl alcohol fiber coating and preparation method thereof

Abstract

The present invention relates to the technical field of coating compositions, and in particular to a polyvinyl alcohol fiber coating and a preparation method thereof. The present invention overcomes the shortcomings of poor mechanical properties and poor water resistance of existing polyvinyl alcohol coatings. The present invention uses hydrophobically modified nano-silica, short polyvinyl alcohol fibers with an average length of 3 mm, and glycidyl methacrylate as raw materials to prepare modified short polyvinyl alcohol fibers; plasma long polyvinyl alcohol fibers are obtained by first subjecting long polyvinyl alcohol fibers with an average length of 6 mm to plasma treatment, and then plasma long polyvinyl alcohol fibers and epichlorohydrin are used as raw materials to prepare modified long polyvinyl alcohol fibers; polyurethane resin, modified short polyvinyl alcohol fibers and modified long polyvinyl alcohol fibers, compounded plasticizers, waterproofing agents, defoaming agents, etc. are used as raw materials, and the polyvinyl alcohol fiber coating finally prepared has the advantages of good mechanical properties and strong water resistance.

Description

Technical Field

[0001] The invention relates to the technical field of coating compositions, in particular to a polyvinyl alcohol fiber coating and a preparation method thereof. Background Art

[0002] Paint plays an important role in the construction field. It not only provides decorative effects, but also protects building structures from external erosion and prolongs service life. In order to improve the performance of paint, a variety of materials are used in the preparation of paint, such as inorganic fillers, organic fillers and fiber materials. Fiber materials, with their unique properties, are outstanding in enhancing the performance of paints. They have high tensile strength and good flexibility, can effectively prevent cracking and peeling of the coating, and enhance the wear resistance and impact resistance of the coating.

[0003] However, not all fiber materials are suitable for coating reinforcement. For example, glass fiber production consumes a lot of energy, has poor dispersion in coatings, and is easy to agglomerate; carbon fiber is expensive and has poor compatibility with the matrix material. In contrast, polyvinyl alcohol fiber has significant advantages, such as good chemical corrosion resistance, ability to maintain stable performance in acidic and alkaline environments, good compatibility with the coating matrix, and can be evenly dispersed in the coating to form a stable network structure, thus improving the mechanical properties and durability of the coating.

[0004] The environment of underground structures is complex, with characteristics such as high humidity, microbial erosion, and chemical corrosion, which require higher performance of coatings. However, existing coatings containing polyvinyl alcohol fibers have many problems in underground structures. Its mechanical properties are poor, and it cannot effectively resist underground pressure and vibration, and it is easy to crack and peel off; poor mechanical properties cause the protective layer of the coating to be opened, resulting in other properties of the material being affected, such as unsatisfactory waterproof performance, which cannot effectively prevent groundwater infiltration, causing moisture inside the underground structure; poor corrosion resistance, the coating is easily corroded by microorganisms and chemicals in the long-term underground environment, which leads to a decline in coating performance over time.

[0005] In summary, the existing polyvinyl alcohol fiber coatings have poor mechanical properties and poor water resistance, and there is an urgent need to develop a new polyvinyl alcohol fiber coating to meet the high performance requirements of underground structures for coatings.

[0006] Therefore, a polyvinyl alcohol fiber coating and a preparation method thereof are proposed. Summary of the invention

[0007] The purpose of the present invention is to provide a polyvinyl alcohol fiber coating and a preparation method thereof. The present invention uses hydrophobically modified nano-silica, short polyvinyl alcohol fibers with an average length of 3 mm, and glycidyl methacrylate as raw materials to prepare modified short polyvinyl alcohol fibers; plasma long polyvinyl alcohol fibers are obtained by first subjecting long polyvinyl alcohol fibers with an average length of 6 mm to plasma treatment, and then plasma long polyvinyl alcohol fibers and epichlorohydrin are used as raw materials to prepare modified long polyvinyl alcohol fibers; polyurethane resin, modified short polyvinyl alcohol fibers and modified long polyvinyl alcohol fibers, compounded plasticizers, waterproofing agents, defoaming agents, etc. are used as raw materials, and the polyvinyl alcohol fiber coating finally prepared has the advantages of good mechanical properties and strong water resistance.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] In one aspect, the present invention provides a method for preparing a polyvinyl alcohol fiber coating, which specifically comprises the following steps:

[0010] The hydrophobically modified nano-silica was prepared by using nano-silica and methyltrimethoxysilane as raw materials;

[0011] Modified short polyvinyl alcohol fibers were prepared using hydrophobically modified nano-silica, short polyvinyl alcohol fibers, and glycidyl methacrylate as raw materials.

[0012] The long polyvinyl alcohol fiber is firstly subjected to plasma treatment to obtain plasma long polyvinyl alcohol fiber, and then the plasma long polyvinyl alcohol fiber and epichlorohydrin are used as raw materials to prepare modified long polyvinyl alcohol fiber;

[0013] Add a mixed solvent, a co-solvent and a polyurethane resin into a reaction kettle, then add modified short polyvinyl alcohol fiber, modified long polyvinyl alcohol fiber and a composite dispersant into the reaction kettle, stir and mix, then add a compound plasticizer, a waterproofing agent and a defoaming agent in sequence, stir for 20 minutes after each addition, finally add a color filler paste and stir to obtain a coating mixture system, add a curing agent into the coating mixture system, stir and perform vacuum degassing and filtration to finally obtain a polyvinyl alcohol fiber coating.

[0014] Preferably, the preparation method of hydrophobically modified nano-silica is: ultrasonically disperse nano-silica with a particle size of 30 nm in anhydrous ethanol, add methyltrimethoxysilane under stirring, and after the addition is completed, stir and react at 50°C for 2.5 hours. After the reaction is completed, centrifuge, wash, and dry to obtain hydrophobically modified nano-silica.

[0015] Preferably, the modified short polyvinyl alcohol fiber preparation method is as follows: short polyvinyl alcohol fiber is added to a solvent, and high-speed shear dispersion is performed for 45 minutes to obtain a pre-dispersed slurry of short polyvinyl alcohol fiber; glycidyl methacrylate is added to the pre-dispersed slurry of short polyvinyl alcohol fiber, and the reaction time is constant at 75°C for 2-3 hours. After the reaction is completed, the modified short polyvinyl alcohol fiber intermediate is obtained by washing and drying. The modified short polyvinyl alcohol fiber intermediate is added to anhydrous ethanol for dispersion, and then hydrophobically modified nano-silica is added, and ultrasonic dispersion is performed for 15 minutes. The reaction temperature is 30-40°C, and the reaction time is 1 hour. After the reaction is completed, the reaction product is washed and dried to obtain the modified short polyvinyl alcohol fiber.

[0016] Preferably, the modified long polyvinyl alcohol fiber preparation method is: first subjecting the long polyvinyl alcohol fiber to plasma treatment to obtain plasma long polyvinyl alcohol fiber; placing the plasma long polyvinyl alcohol fiber into a reactor, adding toluene, stirring evenly and then adding epichlorohydrin, at a reaction temperature of 60-70°C, the reaction time is 1.5 hours, after the reaction is completed, washing and drying the reaction product to obtain modified long polyvinyl alcohol fiber.

[0017] Preferably, the plasma treatment conditions are: using argon plasma for treatment, the treatment power is 70-80W, the treatment time is 5 minutes, and the gas flow rate is 20sccm.

[0018] Preferably, the preparation method of the polyvinyl alcohol fiber coating is as follows: adding a mixed solvent, a cosolvent and a polyurethane resin into a reaction kettle, stirring for 45 minutes, then adding modified short polyvinyl alcohol fibers, modified long polyvinyl alcohol fibers and a composite dispersant, continuing to stir for 75 minutes, then adding a compounded plasticizer, a waterproofing agent and a defoaming agent in sequence, stirring for 20 minutes after each addition, and finally adding the prepared color filler paste, stirring for 90 minutes to obtain a coating mixed system; adding a curing agent to the coating mixed system, stirring for 30 minutes, performing vacuum degassing for 20 minutes and then filtering to finally obtain the polyvinyl alcohol fiber coating.

[0019] Preferably, the mixed solvent is xylene and butyl acetate in a weight ratio of 1:1.8; the co-solvent is butanol.

[0020] Preferably, the preparation method of the color filler paste is:

[0021] Add titanium dioxide pigment, inorganic filler, compound dispersant and solvent into the ball mill, control the grinding temperature not to exceed 60°C, and grind and disperse at high speed for 75 minutes until the color paste fineness is less than 15 microns.

[0022] On the other hand, the present invention provides a polyvinyl alcohol fiber coating, which specifically includes the following components by weight: 60 parts of polyurethane resin, 4-8 parts of modified short polyvinyl alcohol fibers, 2-4 parts of modified long polyvinyl alcohol fibers, 4 parts of compound dispersant, 2-3 parts of compound plasticizer, 3-4 parts of waterproofing agent, 0.5-1 part of defoaming agent, 7 parts of inorganic filler, and 1 part of pigment.

[0023] Preferably, the weight ratio of the modified short polyvinyl alcohol fibers to the modified long polyvinyl alcohol fibers is 2:1.

[0024] Preferably, the compound plasticizer is prepared by mixing dioctyl sebacate and polyester plasticizer in a weight ratio of 1:3.

[0025] Preferably, the waterproofing agent is a silicone waterproofing agent emulsion.

[0026] Preferably, the defoamer is a silicone defoamer.

[0027] Preferably, the compound dispersant is prepared by mixing an anionic dispersant and a polymer dispersant in a weight ratio of 1:1; the anionic dispersant is a phosphate dispersant; and the polymer dispersant is BYK-190.

[0028] Preferably, the inorganic filler is light calcium carbonate.

[0029] Preferably, the raw materials for preparing the modified short polyvinyl alcohol fibers include: short polyvinyl alcohol fibers, glycidyl methacrylate, and hydrophobically modified nano-silica; the average length of the short polyvinyl alcohol fibers is 3 mm.

[0030] Preferably, the raw materials for preparing hydrophobically modified nano-silica include: nano-silica and a hydrophobic modifier; the amount of the hydrophobic modifier is 15-20% of the mass of the nano-silica; and the hydrophobic modifier is methyltrimethoxysilane.

[0031] Preferably, the raw materials for preparing the modified long polyvinyl alcohol fiber include: long polyvinyl alcohol fiber and epichlorohydrin.

[0032] Preferably, the average length of the long polyvinyl alcohol fibers is 6 mm.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. In the present invention, the short fibers are first modified with glycidyl methacrylate to enhance the reactivity and compatibility with the polyurethane resin matrix, improve its dispersibility in the coating, and enable the short fibers to be evenly dispersed inside the coating, laying the foundation for enhancing the mechanical properties. Subsequently, the short fibers are compositely modified with hydrophobic nano-silica to give the short fiber surface hydrophobicity, and cooperate with the organosilicon waterproofing agent to improve the overall hydrophobicity and water resistance of the coating, thereby constructing an efficient waterproofing system.

[0035] 2. In the present invention, the long fibers are first treated with plasma to activate the fiber surface, introduce a large number of active groups, improve the surface reactivity and surface energy, prepare for subsequent modification and enhance the bonding strength with the resin matrix, and then modified with epichlorohydrin to further introduce epoxy groups to enhance the chemical bonding with the polyurethane resin matrix, form a firm interface, effectively transfer stress, and improve the tensile strength, elongation at break and other mechanical properties of the coating. At the same time, the weather resistance can be improved, and the modification with the short fibers can be coordinated to optimize the comprehensive performance of the coating. At the same time, the combination of the modification method of the long fibers and the short fibers and the amount of the two fibers is best compatible with the coating system of the present invention.

[0036] 3. In the present invention, the plasticizer is first added to pre-optimize the flexibility of the polyurethane resin matrix, reduce the cohesive force of the molecular chain, lay the foundation for the uniform dispersion of the fiber components, and preliminarily improve the macro flexibility of the coating. Then, the silicone waterproofing agent emulsion is introduced, relying on the anchoring effect of the pre-hydrophobic modified short fibers, to synergistically construct multiple hydrophobic protective layers inside and on the surface of the coating to achieve effective enhancement of water resistance. This step is based on a flexible substrate and avoids the risk of cracking that may be caused by the rigid waterproof layer. Finally, the silicone defoamer is added to eliminate microscopic bubbles, improve the density of the coating, further optimize the microstructure of the coating, and eliminate potential defects.

[0037] 4. In the present invention, the calcium carbonate particles used as inorganic fillers fill the gaps in the fiber network, improving the density, hardness and wear resistance of the coating. The two complement each other and significantly improve the comprehensive mechanical strength and durability of the coating. In terms of water resistance, calcium carbonate and silicone waterproofing agents construct a double internal and external protective barrier: the dense filling of calcium carbonate reduces the porosity of the coating and slows down the water penetration rate; the silicone waterproofing agent forms a hydrophobic layer on the surface of the coating to effectively prevent water from invading. The presence of calcium carbonate provides a better film-forming base for the silicone waterproofing agent, enhances the durability and effectiveness of its hydrophobic effect, and works together internally and externally to greatly improve the overall waterproof ability and long-term protective performance of the coating. In addition, calcium carbonate also plays an auxiliary dispersing role in the preparation of color paste, which helps to evenly disperse the pigment and indirectly improve the appearance quality and long-term stability of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a bar graph of tensile strength and elongation at break of Example 9, Examples 11-13 and Comparative Examples 9-13 of the present invention. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] See also Figure 1 The present invention provides a polyvinyl alcohol fiber coating and a preparation method thereof, and the technical scheme is as follows: Example 1

[0041] Preparation of hydrophobically modified nano-silica: Disperse 10 parts of nano-silica in 100 parts of anhydrous ethanol by weight, ultrasonically disperse for 30 minutes, add methyltrimethoxysilane at 15% of the weight of nano-silica under stirring, and control the drop rate. After the dropwise addition is completed, continue stirring and reacting at 50°C for 2.5 hours. After the reaction is completed, centrifuge, wash with anhydrous ethanol 3 times, place in a vacuum oven, and vacuum dry at 65°C for 2.5 hours to obtain hydrophobically modified nano-silica, which is sealed and dried for later use.

[0042] Preparation of pre-dispersed slurry of short polyvinyl alcohol fibers: Add 80 parts of short polyvinyl alcohol fibers with an average length of 3 mm into a high-speed disperser containing 2000 parts of anhydrous ethanol and 1 part of a composite dispersant, control the speed to 2000 rpm, high shear dispersion for 45 minutes, control the slurry temperature not to exceed 40°C, and finally obtain pre-dispersed slurry of short polyvinyl alcohol fibers.

[0043] The preparation method of the modified short polyvinyl alcohol fiber is as follows: the prepared short polyvinyl alcohol fiber pre-dispersed slurry is poured into a flask equipped with a magnetic stirrer, heated to 75°C in a water bath, stirred at a constant temperature, and 8 parts of glycidyl methacrylate are added and continued to stir at a constant temperature for 2 hours. After the reaction is completed, it is cooled to room temperature, and the fiber is washed with sufficient deionized water for multiple times until the pH value of the washing liquid is close to neutral, and dried in a 65°C blast oven for 2.5 hours to obtain a modified short polyvinyl alcohol fiber intermediate. It is placed in a flask equipped with a magnetic stirrer again, anhydrous ethanol is added for dispersion, and then 12 parts of hydrophobically modified nano-silica are added, ultrasonically dispersed for 15 minutes, stirred at 30°C for 1 hour, and the reaction product is washed with ethanol twice after the reaction is completed, and dried at 65°C for 2.5 hours to obtain a modified short polyvinyl alcohol fiber, which is sealed and dried for standby use.

[0044] Modification of long polyvinyl alcohol fiber: First, the long polyvinyl alcohol fiber with an average length of 6 mm was treated with argon plasma, the treatment power was 70W, the treatment time was 3 minutes, and the gas flow rate was 20sccm. Then, the treated plasma long polyvinyl alcohol fiber was placed in a reactor, 50 parts of toluene were added, 0.4 parts of epichlorohydrin were added after stirring, and the mixture was heated to 70°C, stirred, and reacted for 1.5 hours. After the reaction was completed, the reaction product was rinsed with clean water and dried in an oven at 70°C for 2.5 hours to obtain the modified long polyvinyl alcohol fiber.

[0045] Preparation of color paste: Add 1 part of titanium dioxide pigment, 7 parts of calcium carbonate filler, 2 parts of composite dispersant and 10 parts of mixed solvent into a ball mill, control the grinding temperature not exceeding 60°C, and grind and disperse at high speed for 75 minutes until the color paste fineness is less than 15 microns.

[0046] Preparation of polyvinyl alcohol fiber coating: 15 parts of mixed solvent and 1 part of butanol cosolvent were added to the reactor, the stirring speed was set to 250 rpm, and 40 parts of polyurethane resin with a hydroxyl value of 155 mg KOH / g were slowly added, and stirring was continued for 45 minutes. Then 6 parts of composite modified short polyvinyl alcohol fibers, 3 parts of plasma modified long polyvinyl alcohol fibers and 2 parts of composite dispersants were added, and stirring was continued for 75 minutes. Subsequently, 2.5 parts of compound plasticizer, 3.5 parts of waterproofing agent and 0.75 parts of defoaming agent were added in sequence, and stirring was continued for 20 minutes after each addition. Finally, the prepared color filler paste was added and stirred for 90 minutes. The HDI trimer curing agent was added to the coating mixture according to NCO: OH = 1.1: 1 and stirred for 30 minutes. After the stirring, the coating mixture in the reactor was transferred to a vacuum degassing tank, and the vacuum degree was controlled at -0.06 MPa, and the degassing time was 20 minutes. Finally, the vacuum degassed coating was filtered through a 200-mesh filter to obtain a polyvinyl alcohol fiber coating.

[0047] The difference between Example 2-5 and Example 1 is that the amount of methyltrimethoxysilane added is different, the time of continuing the constant temperature reaction after adding glycidyl methacrylate is different, the reaction temperature of the modified short polyvinyl alcohol fiber intermediate and the hydrophobically modified nano-silica is different, the processing power when the long polyvinyl alcohol fiber is treated, and the reaction temperature when preparing the modified long polyvinyl alcohol fiber are different, and the other parameters and conditions are the same. The specific parameters are shown in Table 1.

[0048] Table 1 Parameters of Examples 1-9

[0049]

[0050] The difference between Comparative Example 1 and Example 1 is that unmodified short polyvinyl alcohol fibers are directly used when the polyvinyl alcohol fiber coating is finally prepared, and the other parameters and conditions are the same.

[0051] Comparative Example 2 is different from Example 1 in that the nano-silica is not hydrophobically modified, and the other parameters and conditions are the same.

[0052] Comparative Example 3 is different from Example 1 in that the nano-silicon dioxide is modified with n-propyltriethoxysilane, and the other parameters and conditions are the same.

[0053] Comparative Example 4 is different from Example 1 in that unmodified long polyvinyl alcohol fibers are directly used when finally preparing the polyvinyl alcohol fiber coating, and other parameters and conditions are the same.

[0054] Comparative Example 5 is different from Example 1 in that the long polyvinyl alcohol fiber is not subjected to plasma treatment and is only modified by using epichlorohydrin, and the other parameters and conditions are the same.

[0055] Comparative Example 6 is different from Example 1 in that the weight ratio of modified short polyvinyl alcohol fiber to modified long polyvinyl alcohol fiber is 3:1, 3 parts of modified long polyvinyl alcohol fiber and 9 parts of modified short polyvinyl alcohol fiber are added, and other parameters and conditions are the same.

[0056] The difference between Comparative Example 7 and Example 1 is that the short polyvinyl alcohol fibers are first subjected to plasma treatment and then reacted with epichlorohydrin to obtain modified short polyvinyl alcohol fibers A, and the long polyvinyl alcohol fibers are composite-modified with hydrophobically modified silica and glycidyl methacrylate to obtain modified long polyvinyl alcohol fibers B; the modified short polyvinyl alcohol fibers A replace the modified short polyvinyl alcohol fibers in the original scheme, and the modified long polyvinyl alcohol fibers B replace the modified long polyvinyl alcohol fibers in the original scheme, and the other parameters and conditions are the same.

[0057] Comparative Example 8 is different from Example 1 in that the average length of the short polyvinyl alcohol fibers is 6 mm, the average length of the long polyvinyl alcohol fibers is 9 mm, and the other parameters and conditions are the same.

[0058] Test Example 1

[0059] Test object: The coatings in Examples 1-9 and Comparative Examples 1-8 were used. The final test results are shown in Table 2.

[0060] Test method: (1) Tensile properties and elongation at break test: Test in accordance with GB / T19250-2013 "Polyurethane waterproof coating".

[0061] (2) Water resistance test: Test water resistance according to Method A in GB / T1733-1993 "Determination of water resistance of paint films".

[0062] (3) Salt spray resistance test: Conduct the experiment in accordance with GB / T10125-2021 "Artificial atmosphere corrosion test salt spray test", observe the surface of the sample after 48 hours and record the surface phenomena.

[0063] Table 2 Test results of Examples 1-9 and Comparative Examples 1-8

[0064]

[0065] By optimizing various parameters, the amount of methyltrimethoxysilane added affects the hydrophobicity of the nano-silica surface; the subsequent constant-temperature reaction time of glycidyl methacrylate needs to match the amount of silane coupling agent used to ensure that the epoxy groups are fully and efficiently grafted with the hydroxyl groups on the silica surface; the final reaction temperature and reaction time with the modified nano-silica need to be coordinated with the previous parameters in order to accurately control the degree of esterification reaction and ensure that the groups are successfully and appropriately grafted on the fiber surface; it can be seen that when the two parameters for preparing the modified long polyvinyl alcohol fiber remain unchanged, the coating finally prepared under the parameter conditions of Example 4 has the best performance.

[0066] To prepare high-performance modified long polyvinyl alcohol fibers, it is necessary to balance the plasma treatment power and the subsequent reaction temperature; the treatment power regulates the degree of fiber surface activation; the subsequent reaction temperature needs to be compatible with the plasma activation effect to ensure efficient grafting of epoxy groups while avoiding fiber degradation; various parameters work synergistically to prepare long fibers with uniform and controllable surface modification and excellent mechanical properties, giving full play to their skeleton reinforcement effect, and ultimately achieving optimal coating performance under the conditions of Example 9.

[0067] In Comparative Example 1, unmodified short polyvinyl alcohol fibers are directly used. Since the fiber surface is rich in hydrophilic hydroxyl groups, there is a lack of effective chemical bonding or strong physical interaction with the hydrophobic polyurethane resin matrix at the interface, and it mainly relies on weak interactions such as van der Waals forces, resulting in weakened interfacial bonding force; microscopically, stress is difficult to be effectively transmitted at the interface, and the fiber reinforcement phase cannot fully play its role, resulting in a decrease in the ability of the coating to resist deformation by external forces, which is manifested macroscopically as a decrease in tensile strength and elongation at break; at the same time, the hydroxyl groups on the surface of the unmodified fibers are exposed, which increases the hydrophilic center of the coating, and water molecules are more easily adsorbed and penetrated into the interior of the coating through hydrogen bonding, forming water vapor channels, resulting in a decrease in water resistance. In the salt spray resistance test, salt spray is more likely to erode the substrate interface and accelerate corrosion changes.

[0068] As for the improvement of the water resistance of the coating, it can be seen from Example 1 combined with Comparative Examples 2-3 that the water resistance after modification with methyltrimethoxysilane is better than that with n-propyltriethoxysilane, and is better than that without hydrophobic modification. Both n-propyltriethoxysilane and methyltrimethoxysilane belong to silane coupling agents of the alkyltriethoxysilane type, and have similar reactivity and modification mechanism. The alkyl group of n-propyltriethoxysilane is n-propyl, while the alkyl group of methyltrimethoxysilane is methyl, both of which are short-chain alkyl groups, but the alkyl chain length of methyl is less than that of n-propyl. After the surface modification of nano-silica, the shorter methyl group can achieve a closer arrangement and form a denser hydrophobic layer, thereby minimizing the surface free energy of the modified nano-silica and making its hydrophobicity better.

[0069] In Comparative Example 4, unmodified long polyvinyl alcohol fibers are directly used. Similar to unmodified short fibers, the hydroxyl groups on the fiber surface have poor compatibility with the hydrophobic matrix, and the interface bonding mainly relies on weak interactions. The stress transfer efficiency is reduced, resulting in a decrease in the tensile strength and elongation at break of the coating. Although the long fibers mainly contribute to the skeleton reinforcement of the coating, the poor interface bonding will still limit the full realization of its reinforcement effect. At the same time, the hydrophilicity of the fibers themselves increases the water absorption of the coating, and water molecules can enter through the fiber-matrix interface and the micropores inside the fibers, resulting in a decrease in water resistance and a reduction in the coating's ability to protect against salt spray corrosion. At the same time, in Comparative Example 5, only epichlorohydrin was used to modify the long polyvinyl alcohol fiber, and plasma pretreatment was lacking. The activation degree of active functional groups such as hydroxyl groups on the fiber surface was insufficient, which reduced the efficiency of the ring-opening grafting reaction between the epoxy group and the hydroxyl group on the fiber surface, resulting in a decrease in the amount of epoxy group grafted on the fiber surface and a decrease in the hydrophobic modification effect; microscopically, the covalent bonding sites between the modified fiber and the polyurethane matrix were reduced, the interfacial bonding strength was reduced, and the stress transfer efficiency was reduced, resulting in a slight decrease in the tensile strength and elongation at break of the coating; the fiber surface was not sufficiently hydrophobic, which increased the overall hydrophilicity of the coating, resulting in a slight deterioration in water resistance, and the salt spray protection capability was reduced due to the easy intrusion of water vapor.

[0070] In Comparative Example 6, when the weight ratio of modified short polyvinyl alcohol fibers to modified long polyvinyl alcohol fibers is adjusted to 3:1, although the increase in the number of short fibers may improve the initial strength of the coating to a certain extent, the reduction in the content of long fibers as the coating skeleton weakens the overall load-bearing capacity and deformation resistance of the coating, resulting in a decrease in elongation at break; the total amount of fiber increases, and the hydroxyl groups on the fiber surface may slightly increase the hydrophilicity of the coating even after modification, resulting in poor water resistance, but the fine-tuning of the total amount of fiber has little effect on salt spray resistance.

[0071] When the modification process of the two fibers is interchanged and the coating is prepared, it can be seen from Comparative Example 7 that the overall waterproof effect of the coating is greatly reduced. Although the modified long polyvinyl alcohol fiber B has obtained waterproof properties, its number is far less than that of the short fibers, and it is distributed in a non-uniform fiber shape in the coating. This means that only a small amount of material in the coating is dispersed in a large area of ​​non-waterproof area. The effect of this non-uniform waterproofing is very limited, and water molecules can still easily penetrate into the coating from the non-waterproof area.

[0072] In Comparative Example 8, after increasing the fiber length, from the perspective of microscopic principles, the high aspect ratio characteristics of longer fibers in the coating system will intensify the entanglement between fibers. Even after modification, it is difficult to avoid the formation of microscopic fiber agglomerates; these agglomerates are like defects inside the coating, destroying the continuity and uniformity of the polymer matrix, and the stress is more concentrated in these parts, resulting in a decrease in the ability of the coating to resist deformation by external forces; at the same time, the increase in fiber length may also reduce the density of the coating to a certain extent, increase the microscopic porosity, and water molecules and corrosive ions are more likely to spread along the fiber-matrix interface or inside the fiber bundle, accelerating the diffusion of corrosive media into the coating, thereby weakening the protective performance of the coating at the microscopic level, and ultimately resulting in the macroscopic performance of tensile strength and elongation at break remaining basically unchanged, but the water resistance is deteriorated.

[0073] Example 10 differs from Example 9 in that the added amounts of the components are different, including 60 parts of polyurethane resin, 4 parts of modified short polyvinyl alcohol fibers, 2 parts of modified long polyvinyl alcohol fibers, 4 parts of compound dispersant, 2 parts of compound plasticizer, 3 parts of waterproofing agent, 0.5 parts of defoaming agent, 7 parts of inorganic filler, and 1 part of pigment, and the other parameters and conditions are the same.

[0074] Example 11 differs from Example 9 in that the added amounts of the components are different, including 60 parts of polyurethane resin, 8 parts of modified short polyvinyl alcohol fibers, 4 parts of modified long polyvinyl alcohol fibers, 4 parts of compound dispersant, 3 parts of compound plasticizer, 4 parts of waterproofing agent, 1 part of defoaming agent, 7 parts of inorganic filler, and 1 part of pigment, and the other parameters and conditions are the same.

[0075] Example 12 differs from Example 9 in that the added amounts of the components are different, including 60 parts of polyurethane resin, 8 parts of modified short polyvinyl alcohol fibers, 4 parts of modified long polyvinyl alcohol fibers, 4 parts of compound dispersant, 2.5 parts of compound plasticizer, 3.5 parts of waterproofing agent, 0.75 parts of defoaming agent, 7 parts of inorganic filler, and 1 part of pigment, and the other parameters and conditions are the same.

[0076] Comparative Example 9 is different from Example 9 in that, during the preparation of the coating mixture system, the compounded plasticizer, waterproofing agent and defoaming agent are added at one time, and the other parameters and conditions are the same.

[0077] The difference between Comparative Example 10 and Example 9 is that, in the process of preparing the coating mixture system, the waterproofing agent is added first, then the compound plasticizer is added, and finally the defoaming agent is added, and the other parameters and conditions are the same.

[0078] Comparative Example 11 is different from Example 9 in that, when preparing the compound plasticizer, dioctyl sebacate and the polyester plasticizer are prepared in a weight ratio of 1:1, and other parameters and conditions are the same.

[0079] Comparative Example 12 is different from Example 9 in that talc powder is used as the inorganic filler, and other parameters and conditions are the same.

[0080] The difference between Comparative Example 13 and Example 9 is that the fineness of the color paste during grinding is controlled at 60 microns, and the other parameters and conditions are the same.

[0081] Test Example 2

[0082] The coatings in Examples 10-12 and Comparative Examples 9-13 were tested in the same manner as in Test Example 1. The final test results are shown in Table 3.

[0083] Table 3 Test results of Examples 9-12 and Comparative Examples 9-13

[0084]

[0085] Through Table 3 and Figure 1 It can be seen that the synergistic effect of multiple components such as polyurethane resin matrix, modified long and short fibers, compounded dispersing plasticizer and waterproof defoamer, inorganic filler and pigment is adjusted in proportion, and the synergistic effect of multiple components is comprehensively reflected; the amount of polyurethane resin needs to ensure the continuity and integrity of the coating, which is the basis of performance; the amount of modified long and short fibers needs to balance the enhancement effect and dispersibility and workability; the amount of inorganic filler and pigment is adjusted to prevent excessive filling and damage to performance; it can be seen that the performance of the coating prepared under the conditions of Example 12 is in the best state.

[0086] The order of adding compound plasticizer, waterproofing agent and defoaming agent also affects the performance of the final coating. In Comparative Example 9, compound plasticizer, waterproofing agent and defoaming agent are added at one time during the coating preparation process. There may be competitive adsorption or aggregation between the auxiliary agent molecules and between the auxiliary agent and the components such as resin, fiber and filler, resulting in uneven dispersion of the auxiliary agent in the coating system; microscopically, uneven dispersion of the auxiliary agent will reduce its effective concentration, and the decrease in the efficiency of the defoaming agent may lead to an increase in bubbles inside the coating, reducing the density of the coating. The uneven dispersion of the waterproofing agent will lead to insufficient hydrophobicity in the local area of ​​the coating, and water molecules are more easily permeable, resulting in a slight decrease in the tensile strength and elongation at break of the coating, and poor water resistance. At the same time, it can be seen from Example 13 combined with Comparative Example 10 that under the original order, the waterproofing agent is evenly dispersed and anchored in the soft matrix after plasticization, and cooperates with the hydrophobically modified short fibers to construct an internal and external waterproofing system to achieve a gradual increase in water resistance. In Comparative Example 10, there is a lack of plasticizer preparation, the waterproofing agent is unevenly dispersed in the rigid matrix, the waterproofing system is imperfectly constructed and has poor stability. The subsequent addition of plasticizer may further damage the waterproofing system, resulting in limited and uneven water resistance improvement effect, and ultimately a significant decrease in water resistance.

[0087] In Comparative Example 11, the ratio of dioctyl sebacate to polyester plasticizer in the compound plasticizer is adjusted to 1:1. As a small molecule plasticizer, the increase in the ratio of dioctyl sebacate will enhance the flexibility of the coating, but excessive small molecule plasticizer may cause the coating to be soft and sticky, reduce cohesion, and reduce the elongation at break, and may slightly reduce the hardness of the coating, resulting in a slight decrease in tensile strength. The adjustment of the plasticizer ratio has limited effect on the microstructure and hydrophobicity of the coating, and the water resistance and salt spray resistance do not change significantly.

[0088] As a filler, talcum powder has an inherent flaky structure, which limits the reinforcement effect and easily induces cracking. Its surface inertness makes it poorly dispersible and easy to agglomerate and introduce microscopic defects. Its loose accumulation and hydrophilic tendency lead to reduced coating density and deterioration of water and salt spray resistance. The flaky structure and dispersion problems will also lead to increased coating viscosity and poor construction leveling. It is difficult to achieve uniform three-dimensional filling and is not conducive to uniform dispersion of additives. It can be seen from Comparative Example 12 combined with Example 12 that the final effect is not as good as that of a spherical or cubic calcium carbonate system. At the same time, in the color paste where the inorganic filler is located, when the fineness of the color paste is within an appropriate range, the final coating performance is good. In Comparative Example 13, the color paste grinding fineness is controlled at 60 microns, the pigment particle size increases, the particle size distribution becomes wider, and the number of large-sized pigment particles in the color paste increases, resulting in a decrease in the uniformity of the dispersion of the color paste in the coating matrix; microscopically, coarse pigment particles form microscopic defects inside the coating, the stress of the resin matrix around the pigment agglomerates is concentrated, and the structural integrity of the coating is destroyed, resulting in a slight decrease in tensile strength, and the elongation at break is less affected by the slight decrease in pigment dispersion; slightly poor pigment dispersion may cause some hydrophilic additives or pigment components in the color paste to aggregate, which slightly increases the water resistance of the coating, and the salt spray resistance is slightly reduced due to the slight decrease in the protective performance of the coating.

[0089] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a polyvinyl alcohol fiber coating, characterized in that: The specific steps include: The hydrophobically modified nano-silica was prepared by using nano-silica and methyltrimethoxysilane as raw materials; The modified short polyvinyl alcohol fiber is prepared by using the hydrophobically modified nano-silica, short polyvinyl alcohol fiber and glycidyl methacrylate as raw materials; The long polyvinyl alcohol fiber is first subjected to plasma treatment to obtain plasma long polyvinyl alcohol fiber, and then the plasma long polyvinyl alcohol fiber and epichlorohydrin are used as raw materials to prepare modified long polyvinyl alcohol fiber; Adding a mixed solvent, a cosolvent and a polyurethane resin into a reaction kettle, then adding the modified short polyvinyl alcohol fiber, the modified long polyvinyl alcohol fiber and a composite dispersant into the reaction kettle, stirring and mixing, sequentially adding a compound plasticizer, a waterproofing agent and a defoaming agent, stirring for 20 minutes after each addition, finally adding a color filler paste and stirring to obtain a coating mixed system, adding a curing agent into the coating mixed system, performing vacuum degassing and filtering after stirring, and finally obtaining the polyvinyl alcohol fiber coating; The preparation method of the color paste is as follows: titanium dioxide pigment, inorganic filler, the composite dispersant and the mixed solvent are added into a ball mill, the grinding temperature is controlled not to exceed 60° C., and high-speed grinding and dispersion is performed for 75 minutes until the color paste fineness is less than 15 μm; the inorganic filler is light calcium carbonate.

2. The method for preparing a polyvinyl alcohol fiber coating according to claim 1, characterized in that: The preparation method of the hydrophobically modified nano-silica is as follows: ultrasonically disperse the nano-silica with a particle size of 30 nm in anhydrous ethanol, add the methyltrimethoxysilane under stirring, and after the dropwise addition is completed, stir and react at 50° C. for 2.5 hours. After the reaction is completed, centrifuge, wash, and dry to obtain the hydrophobically modified nano-silica.

3. The method for preparing a polyvinyl alcohol fiber coating according to claim 1, characterized in that: The preparation method of the modified short polyvinyl alcohol fiber is as follows: adding the short polyvinyl alcohol fiber to a solvent, dispersing it at high speed for 45 minutes, and obtaining a pre-dispersed slurry of the short polyvinyl alcohol fiber; adding glycidyl methacrylate to the pre-dispersed slurry of the short polyvinyl alcohol fiber, and reacting it at a constant temperature of 75° C. for 2-3 hours; after the reaction is completed, washing and drying the obtained product to obtain a modified short polyvinyl alcohol fiber intermediate; The modified short polyvinyl alcohol fiber intermediate is added to anhydrous ethanol for dispersion, and then hydrophobically modified nano-silica is added, and ultrasonic dispersion is performed for 15 minutes at a reaction temperature of 30-40° C. for 1 hour. After the reaction is completed, the reaction product is washed and dried to obtain the modified short polyvinyl alcohol fiber.

4. The method for preparing a polyvinyl alcohol fiber coating according to claim 1, characterized in that: The preparation method of the modified long polyvinyl alcohol fiber is as follows: the long polyvinyl alcohol fiber is first subjected to plasma treatment to obtain the plasma long polyvinyl alcohol fiber; The plasma long polyvinyl alcohol fiber is placed in a reaction kettle, toluene is added, and the epichlorohydrin is added after stirring evenly. The reaction temperature is 60-70° C. and the reaction time is 1.5 hours. After the reaction is completed, the reaction product is washed and dried to obtain the modified long polyvinyl alcohol fiber.

5. The method for preparing a polyvinyl alcohol fiber coating according to claim 4, characterized in that: The plasma treatment conditions are: using argon plasma for treatment, the treatment power is 70-80W, the treatment time is 5 minutes, and the gas flow rate is 20sccm.

6. The method for preparing a polyvinyl alcohol fiber coating according to claim 1, characterized in that: The preparation method of the polyvinyl alcohol fiber coating is as follows: adding the mixed solvent, the cosolvent and the polyurethane resin into the reaction kettle, stirring for 45 minutes, then adding the modified short polyvinyl alcohol fiber, the modified long polyvinyl alcohol fiber and the composite dispersant, continuing to stir for 75 minutes, then sequentially adding the compound plasticizer, the waterproofing agent and the defoaming agent, stirring for 20 minutes after each addition, and finally adding the prepared color filler paste, stirring for 90 minutes to obtain a coating mixed system; The curing agent is added to the coating mixture system, stirred for 30 minutes, vacuum degassed for 20 minutes and then filtered to finally obtain the polyvinyl alcohol fiber coating; the mixed solvent is xylene and butyl acetate prepared in a weight ratio of 1:1.8; the cosolvent is butanol.

7. A polyvinyl alcohol fiber coating prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The composition includes the following components by weight: 60 parts of polyurethane resin, 4-8 parts of modified short polyvinyl alcohol fiber, 2-4 parts of modified long polyvinyl alcohol fiber, 5 parts of composite dispersant, 2-3 parts of composite plasticizer, 3-4 parts of waterproofing agent, 0.5-1 parts of defoaming agent, 7 parts of inorganic filler and 1 part of titanium dioxide pigment; wherein, The weight ratio of the modified short polyvinyl alcohol fiber to the modified long polyvinyl alcohol fiber is 2:1; The compound plasticizer is prepared by mixing dioctyl sebacate and polyester plasticizer in a weight ratio of 1:3; The waterproofing agent is an organosilicon waterproofing agent emulsion; The defoamer is an organosilicon defoamer; The composite dispersant is prepared by mixing an anionic dispersant and a polymer dispersant in a weight ratio of 1:1; the anionic dispersant is a phosphate dispersant; and the polymer dispersant is BYK-190.

8. The polyvinyl alcohol fiber coating according to claim 7, characterized in that: The raw materials for preparing the modified short polyvinyl alcohol fiber include: short polyvinyl alcohol fiber, glycidyl methacrylate, and hydrophobically modified nano-silica; the average length of the short polyvinyl alcohol fiber is 3 mm; The raw materials for preparing the hydrophobically modified nano-silicon dioxide include: nano-silicon dioxide and a hydrophobic modifier; the amount of the hydrophobic modifier is 15-20% of the mass of the nano-silicon dioxide; and the hydrophobic modifier is methyltrimethoxysilane.

9. The polyvinyl alcohol fiber coating according to claim 7, characterized in that: The raw materials for preparing the modified long polyvinyl alcohol fiber include: long polyvinyl alcohol fiber and epichlorohydrin; The average length of the long polyvinyl alcohol fibers is 6 mm.

Images