Silicone graft modified poly(vinyl butyral) and method of making and use thereof

Abstract

This invention relates to the field of polymer material modification and preparation technology, and particularly to a siloxane-grafted modified polyvinyl butyral (PVA) and its preparation method and application. Using PVA with a specific degree of polymerization as raw material, which exhibits balanced reactivity, solubility, and mechanical properties, this invention achieves stable bonding between siloxane segments and PVA molecules through covalent grafting modification with siloxane and strict control of core parameters. This yields siloxane-grafted modified PVA, which is further prepared into a highly moisture-resistant siloxane-grafted modified PVB film. This process ensures a significant improvement in the moisture resistance of the siloxane-grafted modified PVB film while retaining excellent mechanical properties, optical transparency, and film-forming properties, achieving a balanced improvement in both moisture resistance and overall performance. It is suitable as an interlayer film for high-moisture-resistant safety glass, a special packaging film, or a substrate for outdoor water-resistant coatings, meeting the application requirements of high-moisture-resistant scenarios.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification and preparation technology, and in particular to a siloxane-grafted modified polyvinyl butyral, its preparation method and application. Background Technology

[0002] Polyvinyl butyral (PVB) is typically synthesized from polyvinyl alcohol (PVA) and n-butyral via an acetalization reaction. It possesses excellent toughness, adhesion, and optical transparency, making it widely used in safety glass, packaging, and electronic encapsulation. However, the residual hydrophilic hydroxyl groups in the PVA molecular chain lead to poor moisture resistance in PVB. In high-humidity environments, it easily absorbs water, swells, and its mechanical properties degrade, limiting its application in high-humidity environments. Therefore, modifying its moisture resistance is of significant practical importance.

[0003] Siloxanes are commonly used for moisture-resistant modification of PVB due to their excellent hydrophobicity. Current modification methods mainly involve physical blending and chemical grafting. While physical blending is simple, the lack of chemical bonds between siloxanes and PVB leads to easy migration and precipitation, resulting in decreased moisture resistance and affecting the overall performance of the PVB film, making it difficult to simultaneously improve both moisture resistance and overall performance. Covalent grafting of siloxanes with PVA before synthesizing PVB can fundamentally solve the siloxane migration problem, achieving a sustained improvement in moisture resistance, and is currently a research hotspot.

[0004] Different degrees of polymerization of PVA have their own suitable applications and are not inherently superior or inferior. Existing research mainly focuses on the grafting modification of PVA with low degree of polymerization (≤1500) or high degree of polymerization (≥2500). There is a lack of specific modification methods for PVA with a degree of polymerization of 1700~2400, and the existing grafting parameters are unreasonable, making it impossible to prepare PVB products with excellent moisture resistance and overall performance.

[0005] Therefore, for PVA with a degree of polymerization of 1700~2400, a siloxane covalent grafting modification method is developed to prepare PVB products with significant moisture resistance and excellent comprehensive performance. This fills the gap in existing technology, expands the application range of PVB, and has important practical significance and engineering value. Summary of the Invention

[0006] In view of this, the present invention provides a siloxane-grafted modified polyvinyl butyral, its preparation method and application. The preparation method provided by the present invention uses PVA with a degree of polymerization of 1700~2400 as raw material, and the obtained siloxane-grafted modified polyvinyl butyral has significant moisture resistance and excellent comprehensive performance.

[0007] This invention provides a method for preparing siloxane-grafted modified polyvinyl butyral, comprising the following steps: (1) A pre-hydrolysis reaction was carried out by mixing siloxane compound, anhydrous ethanol and glacial acetic acid to obtain a pre-hydrolysis solution; (2) The pre-hydrolyzed solution is mixed with PVA and water to carry out a dehydration condensation grafting reaction to obtain siloxane-modified PVA; the degree of polymerization of the PVA is 1700~2400; (3) The siloxane-modified PVA was mixed with water, pH adjuster and n-butyraldehyde to carry out acetalization reaction to obtain siloxane-grafted modified polyvinyl butyraldehyde.

[0008] Preferably, the siloxane compound includes one or more of hydroxyl-terminated polydimethylsiloxane (PDMS-OH), dimethoxy-terminated dimethylsiloxane, and epoxy-modified siloxane; the number average molecular weight of the siloxane compound is 1000-3000.

[0009] Preferably, the temperature of the dehydration condensation grafting reaction is 60~65℃, and the holding time is 3.5~4h; the dehydration condensation grafting reaction is carried out under stirring conditions.

[0010] Preferably, the acetalization reaction is carried out at a temperature of 12-15°C and a holding time of 4-6 hours; the acetalization reaction is carried out under stirring conditions.

[0011] The present invention also provides siloxane-grafted modified polyvinyl butyral obtained by the preparation method of siloxane-grafted modified polyvinyl butyral described in the above scheme.

[0012] Preferably, the siloxane-grafted modified polyvinyl butyral has a particle size of 80-120 mesh, a moisture content of ≤0.5%, and a degree of acetalization of 78-82%.

[0013] This invention also provides a method for preparing a siloxane-grafted modified PVB film, comprising the following steps: The siloxane-grafted modified polyvinyl butyral, plasticizer, and alcohol solvent are mixed (referred to as the eighth mixture) and then subjected to degassing, casting, solvent removal, peeling, and annealing in sequence to obtain the siloxane-grafted modified PVB film; the siloxane-grafted modified polyvinyl butyral is the siloxane-grafted modified polyvinyl butyral described in the above scheme.

[0014] Preferably, the degassing is vacuum degassing; the vacuum degassing includes a first degassing and a second degassing performed sequentially; the vacuum degree of the first degassing is -0.055 to -0.045 MPa, and the time is more than 5 minutes; the vacuum degree of the second degassing is -0.095 to -0.085 MPa, the temperature is room temperature, and the time is more than 30 minutes.

[0015] Preferably, the solvent removal is performed by step-temperature drying; the step-temperature drying is carried out under ventilation conditions; the step-temperature drying includes pre-drying, first drying, second drying, and third drying performed sequentially; the pre-drying temperature is room temperature, and the drying time is 4-6 hours; the first drying temperature is 40°C, and the holding time is more than 2 hours; the second drying temperature is 60°C, and the holding time is more than 2 hours; the third drying temperature is 80°C, and the holding time is more than 1 hour.

[0016] The present invention also provides a siloxane-grafted modified PVB film obtained by the preparation method of the siloxane-grafted modified PVB film described in the above scheme.

[0017] To address the shortcomings of existing PVB technology, such as poor moisture resistance and deficiencies in existing modification methods, this invention provides a siloxane-grafted modified polyvinyl butyral, its preparation method, and its applications. Compared with existing technologies, this invention achieves the following beneficial effects: (1) This invention uses PVA with a specific degree of polymerization (degree of polymerization 1700~2400) as raw material. Its reactivity, solubility and mechanical properties are balanced. Through covalent grafting modification with siloxane and strict control of core parameters, the stable combination of siloxane segments and PVA molecules is achieved to obtain PVB powder. It is further prepared into a PVB film with high moisture resistance. While ensuring that the moisture resistance of the PVB film is significantly improved, it retains excellent mechanical properties, optical transparency and film-forming properties, and achieves a balanced improvement in moisture resistance and comprehensive performance. It is suitable as a high moisture-resistant safety glass interlayer film, special packaging film or outdoor water-resistant coating substrate and other products, which can meet the use requirements of high moisture resistance scenarios.

[0018] (2) The siloxane-grafted modified polyvinyl butyral provided by the present invention has significantly improved and sustained moisture resistance. The covalent grafting modification of siloxane and PVA stably grafts hydrophobic siloxane segments onto PVA molecules through Si-OC covalent bonds. Compared with physical blending, this avoids the problems of modifier migration and loss, resulting in sustained moisture resistance. The water contact angle of the obtained PVB film is ≥105°, and the water absorption rate after soaking in deionized water at 25°C for 24 hours is ≤3%, which is more than 70% higher than that of ordinary PVB film (water absorption rate 8~12%). At the same time, its comprehensive performance is balanced. By using PVA with a specific degree of polymerization and controlling the amount of siloxane added and various process parameters, the PVB film has excellent moisture resistance while retaining the original mechanical properties and optical transparency of PVB. The tensile strength is ≥14MPa, the elongation at break is ≥240%, and the light transmittance is ≥89%, which is superior in comprehensive performance and meets the actual use requirements.

[0019] (3) The preparation method provided by the present invention has simple steps, high process feasibility, easy industrialization, compatibility with traditional PVB synthesis and film-making processes, no need to significantly modify existing equipment, low difficulty in industrial scale-up, controllable parameters of each step, good repeatability, and moderate production cost.

[0020] (4) The siloxane-grafted modified polyvinyl butyral provided by this invention has excellent moisture resistance, mechanical properties, optical transparency and film-forming properties, which can effectively expand the application range of PVB materials, solve the defects of existing PVB materials in high moisture resistance scenarios, and has broad market application prospects and economic value. The siloxane-grafted modified polyvinyl butyral provided by this invention has a wide range of applications. It can be used to prepare thin films, coatings and other products. It is suitable for various scenarios such as high moisture resistance safety glass, outdoor special packaging, biomedical materials and electronic device packaging, and has important practical significance and economic value. For example, as an interlayer film for high moisture resistance safety glass, it is suitable for outdoor buildings, car windshields and other scenarios, which can avoid glass bonding failure and film swelling in high humidity environments; as a special packaging film, it is used in scenarios such as food and electronic devices that require moisture-proof packaging, which can extend the shelf life of products; as an outdoor water-resistant coating substrate, it is used for coatings on building exterior walls and outdoor equipment to improve the water resistance and weather resistance of coatings; as a biomedical material, it is used for surface coatings of medical packaging and implantable devices to improve water resistance and protein adsorption resistance. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of this invention, the accompanying drawings used in the embodiments of this invention or in the prior art are briefly described below. For those skilled in the art, other drawings can be derived from the following drawings without creative effort, and all such drawings are within the protection scope of this invention.

[0022] Figure 1 This is a schematic diagram of the process flow for preparing siloxane-grafted modified polyvinyl butyral and siloxane-grafted modified PVB films according to the present invention. Detailed Implementation

[0023] This invention provides a method for preparing siloxane-grafted modified polyvinyl butyral, comprising the following steps: (1) A pre-hydrolysis reaction was carried out by mixing siloxane compound, anhydrous ethanol and glacial acetic acid to obtain a pre-hydrolysis solution; (2) The pre-hydrolyzed solution is mixed with PVA and water to carry out a dehydration condensation grafting reaction to obtain siloxane-modified PVA; (3) The siloxane-modified PVA was mixed with water, pH adjuster and n-butyraldehyde to carry out acetalization reaction to obtain siloxane-grafted modified polyvinyl butyraldehyde.

[0024] This invention involves mixing a siloxane compound, anhydrous ethanol, and glacial acetic acid to undergo a pre-hydrolysis reaction, yielding a pre-hydrolyzed solution. In this invention, the siloxane compound preferably includes one or more of hydroxyl-terminated polydimethylsiloxane (PDMS-OH), dimethoxy-terminated dimethylsiloxane, and epoxy-modified siloxanes.

[0025] In this invention, the number average molecular weight of the siloxane compound is preferably 1000-3000, more preferably 2000-3000.

[0026] In this invention, the mass ratio of the siloxane compound to anhydrous ethanol is preferably 1:2 to 3, more preferably 1:2.2 to 2.8, and even more preferably 1:2.4 to 2.7.

[0027] In this invention, the mass ratio of anhydrous ethanol to glacial acetic acid is preferably 2~3:0.05~0.1, more preferably 2.5:0.07~0.09, and even more preferably 2.5:0.08.

[0028] In this invention, the temperature of the pre-hydrolysis reaction is preferably room temperature, and the reaction time is preferably 30-40 min, more preferably 35 min; the pre-hydrolysis reaction is preferably carried out under stirring conditions. This invention, through the pre-hydrolysis reaction, enables the siloxane compound to be fully hydrolyzed, generating active silanol groups (Si-OH).

[0029] After obtaining the pre-hydrolyzed solution, the present invention mixes the pre-hydrolyzed solution with PVA and water (denoted as the first mixture) and performs a dehydration condensation grafting reaction to obtain siloxane-modified PVA. In the present invention, the PVA is preferably pretreated before use; the pretreatment is preferably drying; the drying temperature is preferably 55~65℃, more preferably 60℃, the vacuum degree is preferably -0.095~-0.085MPa, more preferably -0.09MPa, and the holding time is preferably 2~3h, more preferably 2h. The present invention removes adsorbed moisture from the PVA surface through pretreatment and cools it to room temperature for later use.

[0030] In this invention, the degree of polymerization of the PVA is preferably 1700-2400, more preferably 2000, and the degree of hydrolysis is preferably 98-99%. The PVA used in this invention balances reactivity and film-forming toughness, avoiding the insufficient mechanical properties caused by low degree of polymerization, and solving the problems of difficult dissolution and incomplete grafting of high degree of polymerization.

[0031] In this invention, the water is preferably deionized water; the mass ratio of PVA to water is preferably 1:8 to 10, more preferably 1:9.

[0032] In this invention, the preferred mass ratio of the siloxane compound to PVA is 4-7:100, more preferably 5-6:100. The amount of siloxane added is controlled at 4-7% of the mass of PVA. This amount ensures sufficient grafting rate and significantly improves moisture resistance, while also retaining sufficient PVA hydroxyl groups to ensure the smooth progress of the subsequent acetalization reaction.

[0033] In this invention, the first mixing preferably includes the following steps: mixing PVA and water (denoted as the second mixing) to obtain a PVA aqueous solution, and then mixing the PVA aqueous solution with a pre-hydrolyzed solution (denoted as the third mixing).

[0034] In this invention, the PVA is preferably added in batches; the batch addition is preferably done three or more times.

[0035] In this invention, the second mixing is preferably stirring; the stirring speed is preferably 150-180 rpm, more preferably 160-170 rpm; the temperature of the second mixing is preferably 90-95℃, more preferably 92℃; and the mixing time is preferably 2.5-3 h, more preferably 2.8 h. This invention, through the second mixing, ensures the complete dissolution of PVA, resulting in a transparent and homogeneous PVA aqueous solution.

[0036] In this invention, the third mixing is preferably dropwise mixing; the dropwise mixing preferably includes the following steps: adding a pre-hydrolyzed solution dropwise to a PVA aqueous solution.

[0037] In this invention, the temperature of the dehydration condensation grafting reaction is preferably 60-65°C, more preferably 62°C, and the holding time is preferably 3.5-4 h, more preferably 3.7 h; the dehydration condensation grafting reaction is preferably carried out under stirring conditions; the stirring speed is preferably 190-210 rpm, more preferably 200 rpm. This invention uses a dehydration condensation grafting reaction to cause Si-OH to undergo a dehydration condensation reaction with the hydroxyl groups on the PVA molecular chain, forming a stable Si-OC covalent bond. The conditions of the dehydration condensation grafting reaction, combined with the pre-hydrolysis reaction, can avoid the self-polymerization of siloxane compounds, ensuring that Si-OH and PVA hydroxyl groups react fully to form a stable covalent bond.

[0038] In this invention, the dehydration condensation grafting reaction preferably further includes post-processing of the obtained product; the post-processing preferably includes adjusting the pH value to 7, drying, pulverizing and sieving in sequence.

[0039] In this invention, the reagent used for pH adjustment is preferably a sodium hydroxide solution; the mass concentration of the sodium hydroxide solution is preferably 10-12 wt%, more preferably 10 wt%.

[0040] In this invention, the drying temperature is preferably 64~67℃, more preferably 65℃; the drying is preferably vacuum drying, and the vacuum degree of the vacuum drying is preferably -0.095~-0.085MPa, more preferably -0.09MPa; the drying is preferably carried out with a moisture content ≤0.5%.

[0041] In this invention, the aperture of the sieve used for sieving is preferably 100 mesh.

[0042] After obtaining siloxane-modified PVA, the present invention mixes the siloxane-modified PVA with water, a pH adjuster, and n-butyraldehyde (denoted as the fourth mixture) to undergo an acetalization reaction to obtain siloxane-grafted modified polyvinyl butyral. In the present invention, the water is preferably deionized water; the mass ratio of the siloxane-modified PVA to deionized water is preferably 1:8~12, more preferably 1:10.

[0043] In this invention, the fourth mixing preferably includes the following steps: mixing siloxane-modified PVA with water (referred to as the fifth mixing) to obtain a premix, then mixing the premix with a pH adjuster (referred to as the sixth mixing), adjusting the pH value to 1~1.5 to obtain a mixed solution, and then mixing the mixed solution with n-butyraldehyde (referred to as the seventh mixing).

[0044] In this invention, the temperature of the fifth mixing step is preferably 90~95℃, more preferably 93℃, and the mixing time is preferably 2~3h, more preferably 2h.

[0045] In this invention, the pH adjuster is preferably a hydrochloric acid solution; the hydrochloric acid solution is preferably an aqueous hydrochloric acid solution; and the mass concentration of the pH adjuster is preferably 35%.

[0046] In this invention, the sixth mixing is preferably dropwise mixing; the temperature of the sixth mixing is preferably 12~15℃; the dropwise mixing is preferably carried out under stirring conditions; the stirring speed is preferably 170~190 rpm.

[0047] In this invention, the mass ratio of the siloxane-modified PVA to n-butyraldehyde is preferably 1:0.4~0.6, more preferably 1:0.5.

[0048] In this invention, the seventh mixing is preferably a dropwise mixing.

[0049] In this invention, the preferred temperature for the acetalization reaction is 12-15°C, more preferably 14°C, and the preferred holding time is 4-6 hours, more preferably 5 hours. The acetalization reaction is preferably carried out under stirring conditions; the preferred stirring speed is 170-190 rpm. During the acetalization reaction, a white flocculent solid (siloxane-grafted modified polyvinyl butyral) precipitates from the reaction system. This invention controls the degree of acetalization to 78-82% by adjusting the temperature, pH value, and amount of n-butyral used in the acetalization reaction. This range ensures excellent film-forming properties of PVB while also considering moisture resistance and mechanical properties.

[0050] In this invention, the acetalization reaction preferably includes post-treatment of the obtained product; the post-treatment preferably includes neutralization to a system pH of 7-8, solid-liquid separation, water washing, drying, pulverization and sieving.

[0051] In this invention, the neutralization reagent is preferably a sodium hydroxide solution; the mass concentration of the sodium hydroxide solution is preferably 10 wt%. Neutralization terminates the acetalization reaction in this invention.

[0052] In this invention, the solid-liquid separation is preferably performed by vacuum filtration.

[0053] In this invention, the water used for washing is preferably deionized water; the temperature of the water used for washing is preferably 60-70°C; and the number of times the water is washed is preferably 3-4 times. This invention, through water washing, ensures that the filtrate has no butyraldehyde odor and that chloride ion detection is negative.

[0054] In this invention, the drying is preferably vacuum drying; the vacuum degree of the vacuum drying is preferably -0.095 to -0.085 MPa, more preferably -0.09 MPa; the drying temperature is preferably 70 to 80°C, and the holding time is preferably until constant weight (moisture content ≤ 0.5%).

[0055] In this invention, the aperture of the sieve used for sieving is preferably 120-80 mesh, and more preferably 100 mesh.

[0056] The present invention also provides siloxane-grafted modified polyvinyl butyral obtained by the preparation method of siloxane-grafted modified polyvinyl butyral described in the above scheme.

[0057] In this invention, the particle size of the siloxane-grafted modified polyvinyl butyral is preferably 80-120 mesh, the moisture content is preferably ≤0.5%, and the degree of acetalization is preferably 78-82%.

[0058] This invention also provides a method for preparing a siloxane-grafted modified PVB film, comprising the following steps: The siloxane-grafted modified polyvinyl butyral, plasticizer, and alcohol solvent are mixed (referred to as the eighth mixture) and then subjected to degassing, casting, solvent removal, peeling, and annealing in sequence to obtain the siloxane-grafted modified PVB film; the siloxane-grafted modified polyvinyl butyral is the siloxane-grafted modified polyvinyl butyral described in the above scheme.

[0059] In this invention, the plasticizer is preferably triethylene glycol diisooctanoate (3GO).

[0060] In this invention, the mass ratio of the plasticizer to the siloxane-grafted modified polyvinyl butyral is preferably 25-35:100, more preferably 27-33:100, and even more preferably 29-31:100.

[0061] In this invention, the alcohol solvent is preferably ethanol; the ethanol is preferably anhydrous ethanol.

[0062] In this invention, the mass ratio of the siloxane-grafted modified polyvinyl butyral to the alcohol solvent is preferably 1:4~6, more preferably 1:4.5~5.5, and even more preferably 1:5.

[0063] In this invention, the eighth mixture preferably includes the following steps: premixing siloxane-grafted modified polyvinyl butyral and an alcohol solvent to obtain a mixture, and then mixing the mixture with a plasticizer (referred to as the ninth mixture).

[0064] In this invention, the premixing temperature is preferably room temperature, and the time is preferably 2 hours or more.

[0065] In this invention, the temperature of the ninth mixing is preferably room temperature, and the time is preferably 1 hour or more.

[0066] In this invention, the degassing is preferably vacuum degassing; the vacuum degassing preferably includes a first degassing and a second degassing performed sequentially; the vacuum degree of the first degassing is preferably -0.055~-0.045 MPa, more preferably -0.05 MPa, and the time is preferably 5 minutes or more; the vacuum degree of the second degassing is preferably -0.095~-0.085 MPa, more preferably -0.09 MPa, the temperature is preferably room temperature, more preferably 23°C, and the time is preferably 30 minutes or more. This invention removes large bubbles through the first degassing and further removes small bubbles through the second degassing.

[0067] In this invention, the wet film thickness of the cast film is preferably 0.3~0.8 mm, more preferably 0.4~0.5 mm.

[0068] In this invention, the solvent removal is preferably performed by step-heating drying; the step-heating drying preferably includes pre-drying, first drying, second drying and third drying performed sequentially.

[0069] In this invention, the pre-drying temperature is preferably room temperature, and the drying time is preferably 4 to 6 hours, more preferably 5 hours; the pre-drying is preferably carried out under ventilated conditions.

[0070] In this invention, the temperature of the first drying is preferably 40°C, and the heat preservation time is preferably 2 hours or more; the first drying is preferably carried out under ventilated conditions.

[0071] In this invention, the temperature of the second drying is preferably 60°C, and the heat preservation time is preferably 2 hours or more; the second drying is preferably carried out under ventilated conditions.

[0072] In this invention, the temperature of the third drying is preferably 80°C, and the heat preservation time is preferably more than 1 hour; the third drying is preferably carried out under ventilated conditions.

[0073] In this invention, the annealing temperature is preferably 58~62℃, more preferably 60℃, and the holding time is preferably 11~13h, more preferably 12h. This invention eliminates the internal stress of the siloxane-grafted modified PVB film through annealing.

[0074] The present invention also provides a siloxane-grafted modified PVB film obtained by the preparation method of the siloxane-grafted modified PVB film described in the above scheme.

[0075] In this invention, the water contact angle of the siloxane-grafted modified PVB film is ≥105°, the water absorption rate after soaking in deionized water at 25°C for 24 hours is ≤3%, the tensile strength is ≥14MPa, the elongation at break is ≥240%, and the light transmittance is ≥89%.

[0076] To further illustrate the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments and accompanying drawings.

[0077] Example 1: A method for preparing siloxane-grafted modified polyvinyl butyral and siloxane-grafted modified PVB films, the process flow is as follows: Figure 1 As shown, the specific preparation steps are as follows: (1) PVA pretreatment and siloxane grafting modification: PVA powder with a degree of polymerization of 2000 and a degree of hydrolysis of 98.5% was selected and dried in a vacuum (vacuum degree of -0.090±0.005MPa) drying oven at 60℃ for 2h, and then cooled to room temperature for later use. 90g of deionized water was added to a 1000mL three-necked flask, and stirring was started (speed 150rpm). The temperature was raised to 92℃, and 10g of pretreated PVA powder was added in 3 batches. The mixture was stirred at a constant temperature for 2.5h until the PVA was completely dissolved. The temperature was lowered to 62℃, and 0.5g of hydroxyl-terminated polydimethylsiloxane with a molecular weight of 2000 was selected. 1.25g of anhydrous ethanol and 0.04g of glacial acetic acid were added to prepare a pre-hydrolyzed solution. The solution was stirred at room temperature for 35min for later use. The above pre-hydrolyzed solution was slowly added dropwise to the PVA aqueous solution. After the addition was complete, the stirring speed was adjusted to 200 rpm, and the reaction was carried out at a constant temperature of 62℃ for 3.5 h. The pH value of the system was adjusted to 7 with 10 wt% sodium hydroxide solution. The solution with pH value 7 was poured into a petri dish and dried at 65℃ under vacuum (vacuum degree of -0.090±0.005MPa) until constant weight. After pulverization, it was passed through a 100-mesh sieve to obtain siloxane-modified PVA powder.

[0078] (2) Synthesis of siloxane-grafted modified polyvinyl butyral: 10g of siloxane-modified PVA powder and 100g of deionized water were added to a three-necked flask, heated to 92℃, stirred for 2h to dissolve, cooled to 13℃, stirred (180r / min), and 35wt% hydrochloric acid solution was added dropwise to adjust the pH of the system to 1.2. 5g of n-butyral was slowly added dropwise, and the reaction was carried out at 13℃ for 5h. A white flocculent solid was precipitated. 10wt% sodium hydroxide solution was added dropwise to neutralize the pH to 7.5. The solid was separated by filtration and washed 4 times with 65℃ deionized water until the filtrate had no butyral odor and the chloride ion test was negative. The solid was dried at 75℃ under vacuum (vacuum degree of -0.090±0.005MPa) to constant weight, pulverized and passed through a 100-mesh sieve to obtain siloxane-grafted modified polyvinyl butyral powder.

[0079] (3) Preparation of siloxane-grafted modified PVB film: 10g of siloxane-grafted modified polyvinyl butyral powder was added to 50g of anhydrous ethanol and stirred at room temperature for 2h to dissolve. 3g of plasticizer 3GO was added and stirred for another 1h. The film was degassed under vacuum (vacuum degree of -0.090±0.005MPa) for 30min. The degassed casting solution was poured onto a clean glass plate. The wet film thickness was adjusted to 0.5mm using a casting film forming machine and leveled. The film was pre-dried at room temperature with ventilation for 5h, dried with hot air at 40℃ for 2h, dried with hot air at 60℃ for 2h, dried with hot air at 80℃ for 1h, and then annealed at 60℃ for 12h after peeling to obtain siloxane-grafted modified PVB film. The performance test results are shown in Table 1.

[0080] Example 2: A method for preparing siloxane-grafted modified polyvinyl butyral and siloxane-grafted modified PVB films, the specific preparation steps are as follows: (1) PVA pretreatment and siloxane grafting modification: PVA powder with a degree of polymerization of 1700 and a degree of alcoholysis of 99% was selected and dried in a vacuum (vacuum degree of -0.090±0.005MPa) drying oven at 60℃ for 2 hours and then cooled to room temperature for later use. Add 80g of deionized water to a three-necked flask, stir (160r / min) and heat to 90℃. Add 10g of pretreated PVA in three batches, stir at constant temperature for 3h to dissolve, cool to 60℃, take 0.4g of dimethoxy-terminated dimethylsiloxane (molecular weight 1000), add 0.8g of anhydrous ethanol and 0.03g of glacial acetic acid, stir at room temperature for 30min to prepare a pre-hydrolyzed solution, add the pre-hydrolyzed solution dropwise to the PVA aqueous solution, adjust the rotation speed to 190r / min, react at constant temperature of 60℃ for 4h, adjust the pH value to 7, dry at 65℃ under vacuum (vacuum degree is -0.090±0.005MPa) to constant weight, pulverize and pass through a 100-mesh sieve to obtain siloxane-modified PVA powder.

[0081] (2) Synthesis of siloxane-grafted modified polyvinyl butyral: 10g of siloxane-modified PVA powder was mixed with 80g of deionized water and stirred at 90℃ for 2h to dissolve. The temperature was lowered to 12℃, and stirring was started (170r / min). 35wt% hydrochloric acid solution was added dropwise to adjust the pH value to 1.0. 4g of n-butyral was added dropwise and reacted at a constant temperature of 12℃ for 6h. The pH value was neutralized to 7. The mixture was washed 3 times with hot deionized water at 60℃, filtered, and dried at 70℃ under vacuum (vacuum degree of -0.090±0.005MPa) to constant weight. The mixture was then pulverized and passed through a 100-mesh sieve to obtain siloxane-grafted modified polyvinyl butyral.

[0082] (3) Preparation of siloxane-grafted modified PVB film: The preparation method is the same as in Example 1, except that the amount of plasticizer added is adjusted to 2.5g and the wet film thickness is adjusted to 0.3mm to obtain siloxane-grafted modified PVB film. The performance test results are shown in Table 1.

[0083] Example 3: A method for preparing siloxane-grafted modified polyvinyl butyral and siloxane-grafted modified PVB films, the specific preparation steps are as follows: (1) PVA pretreatment and siloxane grafting modification: PVA powder with a degree of polymerization of 2400 and a degree of alcoholysis of 98% was selected and dried in a vacuum (vacuum degree of -0.090±0.005MPa) drying oven at 60℃ for 2 hours and then cooled to room temperature for later use. Add 100g of deionized water to a three-necked flask, stir (180r / min) and heat to 95℃. Add 10g of pretreated PVA in three batches, stir at constant temperature for 3h to dissolve, cool to 65℃, take 0.7g of epoxy-modified siloxane (molecular weight 3000), add 2.1g of anhydrous ethanol and 0.07g of glacial acetic acid, stir at room temperature for 40min to prepare a pre-hydrolyzed solution, add the pre-hydrolyzed solution dropwise to the PVA aqueous solution, adjust the rotation speed to 210r / min, react at constant temperature of 65℃ for 3.5h, adjust the pH value to 7, dry at 65℃ under vacuum (vacuum degree is -0.090±0.005MPa) to constant weight, pulverize and pass through a 100-mesh sieve to obtain siloxane-modified PVA powder.

[0084] (2) Synthesis of siloxane-grafted modified polyvinyl butyral: 10g of siloxane-modified PVA powder was mixed with 120g of deionized water and stirred at 95℃ for 2h to dissolve. The temperature was lowered to 15℃, and stirring was started (190r / min). 35wt% hydrochloric acid solution was added dropwise to adjust the pH value to 1.5. 6g of n-butyral was added dropwise and reacted at a constant temperature of 15℃ for 4h. The pH value was neutralized to 8. The mixture was washed 4 times with hot deionized water at 70℃, filtered, and dried at 80℃ under vacuum (vacuum degree of -0.090±0.005MPa) to constant weight. The mixture was then pulverized and passed through a 100-mesh sieve to obtain siloxane-grafted modified polyvinyl butyral.

[0085] (3) Preparation of siloxane-grafted modified PVB film: The preparation method is the same as in Example 1, except that the amount of plasticizer added is adjusted to 3.5g and the wet film thickness is adjusted to 0.8mm to obtain siloxane-grafted modified PVB film. The performance test results are shown in Table 1.

[0086] Example 4: A method for preparing siloxane-grafted modified polyvinyl butyral and siloxane-grafted modified PVB films, the specific preparation steps are as follows: (1) PVA pretreatment and siloxane grafting modification: PVA powder with a degree of polymerization of 2200 and a degree of alcoholysis of 98.5% was selected, placed in a vacuum (vacuum degree of -0.090±0.005MPa) drying oven at 60℃ and dried for 2h, and then cooled to room temperature for use. Add 95g of deionized water to a three-necked flask, stir (170r / min) and heat to 93℃. Add 10g of pretreated PVA in three batches, stir at constant temperature for 2.8h to dissolve, cool to 63℃, mix 0.6g of hydroxyl-terminated polydimethylsiloxane (molecular weight 2000) and 0.1g of epoxy-modified siloxane (molecular weight 2500), add 1.75g ​​of anhydrous ethanol and 0.05g of glacial acetic acid, stir at room temperature for 35min to prepare a pre-hydrolyzed solution, add the pre-hydrolyzed solution dropwise to the PVA aqueous solution, adjust the rotation speed to 200r / min, react at constant temperature of 63℃ for 3.8h, adjust the pH value to 7, dry under vacuum (vacuum degree of -0.090±0.005MPa) at 65℃ to constant weight, pulverize and pass through a 100-mesh sieve to obtain siloxane-modified PVA powder.

[0087] (2) Synthesis of siloxane-grafted modified polyvinyl butyral: 10g of siloxane-modified PVA powder was mixed with 110g of deionized water and stirred at 93℃ for 2h to dissolve. The temperature was lowered to 14℃, and stirring was started (180r / min). 35wt% hydrochloric acid solution was added dropwise to adjust the pH value to 1.3. 5.5g of n-butyral was added dropwise and reacted at a constant temperature of 14℃ for 4.5h. The pH value was neutralized to 7.5. The mixture was washed 4 times with hot deionized water at 68℃, filtered, and dried at 78℃ under vacuum (vacuum degree of -0.090±0.005MPa) to constant weight. The mixture was then pulverized and passed through a 100-mesh sieve to obtain siloxane-grafted modified polyvinyl butyral.

[0088] (3) Preparation of siloxane-grafted modified PVB film: The preparation method is the same as in Example 1, except that the amount of plasticizer added is adjusted to 3.2g and the wet film thickness is adjusted to 0.6mm to obtain siloxane-grafted modified PVB film. The performance test results are shown in Table 1.

[0089] Comparative Example 1: A method for preparing a siloxane physically blended modified PVB film, the specific preparation steps are as follows: PVA powder with a degree of polymerization of 2000 and a degree of hydrolysis of 98.5% was selected. PVA aqueous solution was prepared according to steps (1) to (2) of Example 1. Without performing siloxane grafting reaction, 0.5g of hydroxyl-terminated polydimethylsiloxane (molecular weight 2000) was directly added to the PVA aqueous solution and stirred for 1h to achieve physical blending. Subsequently, PVB membrane was prepared according to steps (2) to (3) of Example 1. Without performing siloxane pre-hydrolysis and grafting reaction, siloxane physically blended modified PVB membrane was obtained. Its performance test results are shown in Table 1.

[0090] Comparative Example 2: A method for preparing a low-polymerization-degree PVA siloxane-grafted modified PVB film is provided. The preparation steps are the same as in Example 1, except that PVA powder with a polymerization degree of 1500 and a degree of alcoholysis of 98.5% is selected to obtain a siloxane-grafted modified PVB film. The performance test results are shown in Table 1.

[0091] Performance testing: Table 1. Performance test results of Examples 1-4 and Comparative Examples 1-2:

[0092] As shown in Table 1, Examples 1-4 (using PVA with a degree of polymerization of 1700-2400 and covalently grafted with siloxane) exhibited excellent and balanced properties: water contact angle ≥105°, water absorption rate ≤3% after immersion at 25℃ for 24 hours, significantly improving moisture resistance; tensile strength ≥16MPa, elongation at break ≥280%, demonstrating excellent mechanical properties; light transmittance ≥89%, acetal degree 78-82%, retaining the good optical properties and film-forming properties of PVB materials. Among them, Example 4, using mixed siloxane reagents, had the best overall performance, while Example 3 had the highest degree of polymerization and the best moisture resistance.

[0093] In comparison, Comparative Example 1, which uses physical blending modification, has the same degree of polymerization of PVA as Example 1, but its water contact angle is only 85°, its 24-hour water absorption rate is as high as 6.8%, and it exhibits problems such as unsustainable moisture resistance due to modifier migration. Its mechanical properties also decrease slightly, highlighting the significant advantages of covalent grafting modification over physical blending. Comparative Example 2 uses PVA with a low degree of polymerization of 1500. Although its moisture resistance basically meets the standard, its tensile strength is only 11 MPa, its elongation at break is 180%, and its mechanical properties are significantly reduced. This proves that PVA with a degree of polymerization of 1700~2400 can balance moisture resistance and mechanical properties, verifying the superiority of the present invention.

[0094] The embodiments of the present invention have been described above; however, these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the above embodiments of the present invention without inventive effort are within the protection scope of the present invention.

Claims

1. A method for preparing siloxane-grafted modified polyvinyl butyral, characterized in that, Includes the following steps: (1) A pre-hydrolysis reaction was carried out by mixing siloxane compound, anhydrous ethanol and glacial acetic acid to obtain a pre-hydrolysis solution; (2) The pre-hydrolyzed solution is mixed with PVA and water to carry out a dehydration condensation grafting reaction to obtain siloxane-modified PVA; the degree of polymerization of the PVA is 1700~2400; (3) The siloxane-modified PVA was mixed with water, pH adjuster and n-butyraldehyde to carry out acetalization reaction to obtain siloxane-grafted modified polyvinyl butyraldehyde.

2. The method for preparing siloxane-grafted modified polyvinyl butyral according to claim 1, characterized in that, The siloxane compound includes one or more of hydroxyl-terminated polydimethylsiloxane, dimethoxy-terminated dimethylsiloxane, and epoxy-modified siloxane; the number average molecular weight of the siloxane compound is 1000-3000.

3. The method for preparing siloxane-grafted modified polyvinyl butyral according to claim 1, characterized in that, The dehydration condensation grafting reaction is carried out at a temperature of 60~65℃ and a holding time of 3.5~4h. The dehydration condensation grafting reaction is carried out under stirring conditions.

4. The method for preparing siloxane-grafted modified polyvinyl butyral according to claim 1, characterized in that, The acetalization reaction is carried out at a temperature of 12-15°C for 4-6 hours; the acetalization reaction is carried out under stirring conditions.

5. A siloxane-grafted modified polyvinyl butyral, characterized in that, The siloxane-grafted modified polyvinyl butyral is the siloxane-grafted modified polyvinyl butyral obtained by the preparation method of the siloxane-grafted modified polyvinyl butyral according to any one of claims 1 to 4.

6. The siloxane-grafted modified polyvinyl butyral according to claim 5, characterized in that, The siloxane-grafted modified polyvinyl butyral has a particle size of 80-120 mesh, a moisture content of ≤0.5%, and an acetal degree of 78-82%.

7. A method for preparing a siloxane-grafted modified PVB film, characterized in that, Includes the following steps: The siloxane-grafted modified polyvinyl butyral, plasticizer, and alcohol solvent are mixed and then subjected to degassing, casting, solvent removal, peeling, and annealing to obtain the siloxane-grafted modified PVB film. The siloxane-grafted modified polyvinyl butyral is the siloxane-grafted modified polyvinyl butyral as described in any one of claims 5 to 6.

8. The method for preparing the siloxane-grafted modified PVB film according to claim 7, characterized in that, The degassing is vacuum degassing; the vacuum degassing includes a first degassing and a second degassing performed sequentially; the vacuum degree of the first degassing is -0.055 to -0.045 MPa, and the time is more than 5 minutes; the vacuum degree of the second degassing is -0.095 to -0.085 MPa, the temperature is room temperature, and the time is more than 30 minutes.

9. The method for preparing the siloxane-grafted modified PVB film according to claim 7, characterized in that, The solvent removal process involves step-temperature drying; the step-temperature drying is carried out under ventilated conditions; the step-temperature drying includes pre-drying, first drying, second drying, and third drying performed sequentially; the pre-drying temperature is room temperature, and the drying time is 4-6 hours; the first drying temperature is 40°C, and the holding time is at least 2 hours; the second drying temperature is 60°C, and the holding time is at least 2 hours; the third drying temperature is 80°C, and the holding time is at least 1 hour.

10. A siloxane-grafted modified PVB film, characterized in that, The siloxane-grafted modified PVB film is the siloxane-grafted modified PVB film obtained by the preparation method of the siloxane-grafted modified PVB film according to any one of claims 7 to 9.

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