A method for regulating the stereoisomer ratio of polyvinyl acetal

Abstract

The present invention discloses a method for regulating the stereoisomer ratio of polyvinyl acetal. This method achieves this by adding an aldehyde solution as a reactant in multiple steps under specific temperature conditions. The process is simple, cost-effective, and less variable than existing production processes. The adjustable range of the stereoisomer ratio of polyvinyl acetal is wide, and no modifications are required to existing production equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, in particular to a method for regulating the stereoisomer ratio of polyvinyl acetal and a polyvinyl acetal resin prepared by the method. Background Art

[0002] Polyvinyl acetal (PVA) is produced by the acetalization reaction of polyvinyl alcohol (PVA) and aldehyde in the presence of a catalyst. It is widely used as an interlayer adhesive in applications such as automotive, construction, and photovoltaics. Due to its specific characteristics, PVA often requires excellent bonding and mechanical strength. Furthermore, the demanding application conditions of these industries, such as automotive, construction, and photovoltaics, place extremely high demands on the durability and stability of PVA interlayer materials.

[0003] The molecular structure of polyvinyl acetal mainly consists of three structural units: vinyl acetal, vinyl alcohol and vinyl acetate. Among them, the bonding performance of polyvinyl acetal materials is mainly related to the hydroxyl content and distribution of the vinyl alcohol monomer, and the content and distribution of the vinyl acetal structure largely determine the mechanical properties of polyvinyl acetal materials. However, there is a certain contradiction between bonding performance and mechanical properties: when the bonding strength is too strong, the polyvinyl acetal bonding layer cannot effectively dissipate energy through deformation and reduce the impact resistance of polyvinyl acetal. When the bonding performance is too weak, it cannot effectively bond with adhesives such as glass. How to precisely control the bonding strength and mechanical strength of polyvinyl acetal is the key to improving the application performance of polyvinyl acetal.

[0004] Typically, the bonding strength of polyvinyl acetal can be improved by increasing the hydroxyl value, or the content of vinyl alcohol units. However, this control method can lead to a decrease in the mechanical properties of polyvinyl acetal at high temperatures. Similarly, while increasing the molecular weight and degree of acetalization can improve the mechanical strength of polyvinyl acetal, it also increases the processing difficulty of downstream polyvinyl acetal interlayer materials and reduces low-temperature performance. In fact, regulating the molecular chain structure of polyvinyl acetal materials has a better effect on improving its overall performance.

[0005] Patent EP0402213B1 reports that the modulus of polyvinyl acetal can be controlled by adjusting the stereoisomer ratio of the polyvinyl acetal molecular chain. By adjusting the proportion of meso-acetal structures, the modulus of the polyvinyl acetal interlayer can be doubled. Similarly, patent CN100384887C also reports that increasing the meso- / racemic stereoisomer ratio of polyvinyl acetal can improve its creep resistance. However, these methods of controlling the stereoisomer ratio of polyvinyl acetal are achieved by adding an aldehyde reactant or an acidic catalyst in a single step with the addition of an emulsifier exceeding 0.1 wt%. The control effect is primarily due to the action of the emulsifier. Due to their amphiphilic nature, emulsifiers are often difficult to effectively and completely remove from the polyvinyl acetal product. Emulsifier residues are detrimental to the downstream processing and use of the polyvinyl acetal interlayer. Therefore, in actual industrial production, repeated water washing is often required to reduce emulsifier residues. At the same time, emulsifier residues will also reduce the fluidity and heat resistance of polyvinyl acetal. Summary of the Invention

[0006] In view of the deficiencies in the above-mentioned prior art, the main purpose of the present invention is to provide a method for regulating the stereoisomer ratio of polyvinyl acetal, and to prepare polyvinyl acetal resins with different stereoisomer ratios by using the method.

[0007] To achieve the purpose, the present invention adopts the following technical solutions:

[0008] A method for regulating the stereoisomer ratio of polyvinyl acetal is characterized in that it comprises the following steps:

[0009] (1) adding a portion of the aldehyde solution and the emulsifier to the polyvinyl alcohol aqueous solution at a temperature range of 5 to 30°C, mixing them uniformly, and then adding an acidic catalyst to trigger the reaction;

[0010] (2) After adding the acidic catalyst, the reaction system is kept in a temperature range of 5 to 30° C. for 0 to 30 minutes, then the temperature is raised to 50 to 75° C. and kept in temperature for aging; the remaining aldehyde solution is added at any time from the start of adding the acidic catalyst to the end of the aging;

[0011] (3) After the heat preservation and aging is completed, alkali solution is added to the reaction system, stirring is maintained for 5 to 30 minutes, and filtering is performed to obtain a solid resin product;

[0012] (4) washing the solid resin product 1 to 10 times and filtering to obtain a washed product;

[0013] (5) Drying the washed product at 40-60° C. to obtain polyvinyl acetal resin.

[0014] The polyvinyl acetal resin has the characteristics of an endo / racemic stereoisomer ratio m / r ratio of ≥3.5 under the condition of an acetalization degree of ≥78wt%.

[0015] Particularly, the reactant aldehyde solution is added in multiple steps at different temperatures, the content of the partial aldehyde solution in step (1) is 0 to 80 wt % of the total aldehyde solution, and the content of the remaining aldehyde solution in step (2) is 20 to 100 wt % of the total aldehyde solution.

[0016] More preferably, the content of the partial aldehyde solution in step (1) is 10-60 wt % of the total aldehyde solution, and the content of the remaining aldehyde solution in step (2) is 40-90 wt % of the total aldehyde solution.

[0017] Particularly, the remaining aldehyde solution in step (2) is added dropwise at a uniform speed.

[0018] More preferably, the time range for adding the remaining aldehyde solution in step (2) is any period from the start of adding the acidic catalyst to the end of heating.

[0019] Particularly, the heating to 50-75° C. in step (2) is a rapid heating within the range of 10-60 minutes.

[0020] The industrial production of polyvinyl acetal is typically a precipitation process. During the reaction, as the degree of acetalization increases, the product's solubility decreases and it gradually precipitates. This causes a transition from a homogeneous to a heterogeneous phase, reducing the degree of contact between the materials and further slowing the reaction rate. Based on the kinetics of the acetalization reaction, the meso-acetal structure is thermodynamically more stable than the racemic acetal structure, resulting in a predominantly meso-type reaction in the early stages. However, as the reaction proceeds, the concentration of isotactic hydroxyl groups that form the meso-acetal gradually decreases. After the product precipitates and transitions to a heterogeneous phase, particularly during the heat-maintaining aging process, the racemic acetalization reaction becomes the primary reaction.

[0021] From the perspective of regulating the kinetics of the acetalization reaction, the stepwise addition of aldehyde first involves thoroughly mixing the polyvinyl alcohol solution and a portion of the aldehyde solution with a small amount of emulsifier to ensure a homogeneous and complete homogeneous reaction, thereby increasing the proportion of the meso reaction. This also prevents excessive aldehyde solution from being difficult to disperse after addition to the system, leading to uneven local reactions and excessive precipitation that hinders the meso acetalization reaction. Furthermore, after the homogeneous reaction has fully proceeded, with a large amount of acid catalyst present in the system, the remaining aldehyde solution can be added dropwise to improve the contact efficiency of the materials. Subsequently, the system is rapidly heated to 50-75°C, further accelerating the meso reaction rate through increased temperature. At this point, as the reaction proceeds, the incompletely reacted aldehyde solution can continue to undergo the acetalization reaction at higher temperatures, thereby compensating for the reduced meso acetalization reaction rate caused by the concentration of isotactic hydroxyl groups and ultimately increasing the meso and meso ratios of the product.

[0022] Particularly, the emulsifier in step (1) is added after being dissolved in the aldehyde, and the amount added is 0 to 0.05% of the mass fraction of the polyvinyl alcohol.

[0023] In particular, the type of the emulsifier in step (1) includes at least one of anionic surfactants and nonionic surfactants, thereby achieving the control of the particle size of the polyvinyl acetal product.

[0024] Particularly, the solid content of polyvinyl alcohol in the polyvinyl alcohol aqueous solution in step (1) is 8% to 10%.

[0025] Particularly, the aldehyde solution in step (1) comprises at least one of formaldehyde, acetaldehyde, butyraldehyde, valeraldehyde, isovaleraldehyde, hexanal, heptanal, octanal, nonanal, decanal, benzaldehyde and phenylacetaldehyde.

[0026] Particularly, the mass of the aldehyde in step (1) is 50-60% of the mass of the polyvinyl alcohol.

[0027] Particularly, the acidic catalyst in step (1) comprises at least one of hydrochloric acid, sulfuric acid, nitric acid and p-toluenesulfonic acid;

[0028] Particularly, the heat preservation and aging time in step (2) is 0.5 to 2 hours.

[0029] Particularly, the alkali solution in step (3) comprises at least one of sodium hydroxide, potassium hydroxide and magnesium hydroxide.

[0030] Polyvinyl acetal resin can be analyzed using nuclear magnetic resonance spectroscopy ( 1 H NMR) or carbon nuclear magnetic resonance spectroscopy ( 13The degree of acetalization and the ratio of meso- to racemic acetal isomers (m / r) can be measured using either or both of the following techniques: C NMR (C NMR) and 1H NMR. Taking the characterization of polyvinyl butyral (PVB) as an example, 5-10 mg of PVB can be fully dissolved in 0.6 mL of DMSO-d6 and scanned on a 400 MHz NMR spectrometer for at least 16 scans. The resulting NMR spectrum is integrated using MestReNova software, and the ratio of the molar fractions of hydrogen at 4.5 ppm (meso, m) and 4.75 ppm (racemic, r) is calculated. This ratio is referred to as the meso- to racemic acetal isomer ratio (m / r).

[0031] It should be noted that the acetalization degree is the mass percentage of the monomer containing the acetal group in the entire polyvinyl acetal molecular chain. Similarly, the acetalization degree can also be calculated by nuclear magnetic resonance spectroscopy. The specific method is:

[0032] Acetal degree (mole fraction): VB m =2 / ((3*A CH2 / A CH3 )-6).

[0033] Among them A CH2 and A CH3 The integrated areas are the methylene -CH2 at 1.0-1.9 ppm and the methyl -CH3 at 0.9 ppm, respectively.

[0034] The acetal degree VB m is the relative mole fraction. To be closer to the description in actual industrial processing, it is also necessary to convert this relative mole fraction into a relative mass fraction VB w , the specific method is:

[0035] Acetal degree (mass fraction): VB w =142*VB m / (142*VB m +(1-VB m )*44).

[0036] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0037] The present invention provides a simple process with low cost, minimal variability compared to existing production processes, a wide adjustable range for the stereoisomer ratio of polyvinyl acetal, and no modification of existing production equipment. Furthermore, the reaction process of the present invention significantly reduces the number of water washing steps, as it does not require the addition of large amounts of emulsifiers, resulting in energy conservation and environmental protection. Furthermore, the present invention offers advantages such as simple operation and the absence of additional process equipment and expensive raw materials, resulting in strong market competitiveness. DETAILED DESCRIPTION

[0038] The following is a clear and complete description of the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] Example 1

[0040] (1) Dissolve 100 g of polyvinyl alcohol (PVA) with an average degree of polymerization of 1700 in 900 mL of pure water and stir at 90°C for 1 h to fully dissolve the mixture. Then cool the mixture to 15°C. Add a mixed solution of 0.02 g of sodium dodecyl sulfate and 17.4 g of butyraldehyde and mix thoroughly. Then, add 20 g of hydrochloric acid (36% to 38% by mass) dropwise at a constant rate over 15 min.

[0041] (2) After the addition of hydrochloric acid, maintain the temperature for 15 minutes. Immediately, place the reaction system directly in a 70°C water bath and heat the reaction system to 70°C over 10-15 minutes. Stir and react at this temperature for 2 hours. Simultaneously, add 40.6 g of butyraldehyde dropwise to the system at a uniform rate from the time the hydrochloric acid is added until the temperature reaches 70°C.

[0042] (3) After the reaction is completed, 40 mL of 15 wt% sodium hydroxide is added to the reaction solution, and the mixture is stirred for 15 min and centrifuged for dehydration to obtain a solid resin product.

[0043] (4) The solid resin product was washed and filtered at 50°C for 5 times, and then filtered with suction.

[0044] (5) The solid product was placed in a forced air drying oven and dried at 50° C. for 4 h to obtain a polyvinyl acetal resin product.

[0045] Example 2

[0046] Except that the mass of butyraldehyde added in step (1) is 0 g and the mass of butyraldehyde added in step (2) is 58 g, the remaining steps and conditions are the same as those in Example 1.

[0047] Example 3

[0048] Except that the mass of butyraldehyde added in step (1) is 5.8 g and the mass of butyraldehyde added in step (2) is 52.2 g, the remaining steps and conditions are the same as those in Example 1.

[0049] Example 4

[0050] Except that the mass of butyraldehyde added in step (1) is 34.8 g and the mass of butyraldehyde added in step (2) is 23.2 g, the remaining steps and conditions are the same as those in Example 1.

[0051] Example 5

[0052] Except that in step (2), the remaining 40.6 g of butyraldehyde was uniformly added dropwise to the system from the beginning of the heating until the heating reached 70°C, the other steps and conditions were the same as those in Example 1.

[0053] Example 6

[0054] Except that in step (2), the remaining 40.6 g of butyraldehyde was uniformly added dropwise to the system from the beginning of the 70° C. insulation to the end of the insulation aging, the other steps and conditions were the same as those in Example 1.

[0055] Example 7

[0056] The remaining steps and conditions were the same as those in Example A, except that in step (2), the reaction system was directly placed in a 50° C. water bath and the temperature of the reaction system was raised to 50° C. over 10 to 15 minutes.

[0057] Example 8

[0058] The remaining steps and conditions were the same as those in Example 1, except that in step (2), the reaction system was directly placed in a 60° C. water bath and the temperature of the reaction system was raised to 60° C. over 10 to 15 minutes.

[0059] Comparative Example 1

[0060] Except that the mass of butyraldehyde added in step (1) is 58 g and the mass of butyraldehyde added in step (2) is 0 g, the remaining steps and conditions are the same as those in Example 1.

[0061] Comparative Example 2

[0062] Except that the reaction system was heated to 70° C. in 200 min in step (2), the remaining steps and conditions were the same as those in Example 1.

[0063] Comparative Example 3

[0064] Except that the reaction system was heated to 70° C. in 200 min in step (2), the remaining steps and conditions were the same as those in Comparative Example 1.

[0065] Comparative Example 4

[0066] Except for heating the reaction system to 80° C. in step (2), the remaining steps and conditions were the same as those in Example 1.

[0067] Comparative Example 5

[0068] Except that in step (2), the remaining 40.6 g of butyraldehyde was rapidly added dropwise to the system all at once within 1 minute after the addition of hydrochloric acid was completed, the remaining steps and conditions were the same as those in Example 1.

[0069] Table 1 Test results of acetal degree, hydroxyl value and hydroxyl block degree of polyvinyl acetal resin

[0070]

[0071]

[0072] The above description is merely an exemplary embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for regulating the stereoisomer ratio of polyvinyl acetal, characterized in that: The steps include: (1) adding a portion of an aldehyde solution and an emulsifier to a polyvinyl alcohol aqueous solution at a temperature range of 5 to 30°C, mixing them uniformly, and then adding an acidic catalyst to trigger the reaction; the content of the portion of the aldehyde solution is 10 to 60 wt% of the total amount of the aldehyde solution; (2) After adding the acidic catalyst, the reaction system is kept in a temperature range of 5-30°C for 0-30 minutes, and then the temperature is rapidly raised to 50-75°C within a range of 10-60 minutes, and kept in temperature for aging; the remaining aldehyde solution is added at any time from the beginning of the addition of the acidic catalyst to the end of the aging; the content of the remaining aldehyde solution is 40-90wt% of the total amount of the aldehyde solution, (3) After the heat preservation and aging is completed, add alkali solution to the reaction system, stir for 5-30 minutes, and filter to obtain a solid resin product; (4) washing the solid resin product 1 to 10 times and filtering to obtain a washed product; (5) Drying the cleaned product at 40-60° C. to obtain a polyvinyl acetal resin, wherein the polyvinyl acetal resin has an acetalization degree of ≥78 wt % and an endo / racemic stereoisomer ratio m / r of ≥3.

5.

2. The method for controlling the stereoisomer ratio of polyvinyl acetal according to claim 1, wherein: The remaining aldehyde solution in step (2) is added dropwise at a uniform rate.

3. The method for controlling the stereoisomer ratio of polyvinyl acetal according to claim 1, wherein: The time range for adding the remaining aldehyde solution in step (2) is any period from the start of adding the acidic catalyst to the end of heating.

4. The method for controlling the stereoisomer ratio of polyvinyl acetal according to claim 1, wherein: The emulsifier in step (1) is added after being dissolved in aldehyde, and the amount added is 0-0.05% of the mass fraction of polyvinyl alcohol.

5. The method for controlling the stereoisomer ratio of polyvinyl acetal according to claim 1, wherein: The mass of the aldehyde solution is 50-60% of the mass of the polyvinyl alcohol.

6. The method for controlling the stereoisomer ratio of polyvinyl acetal according to claim 1, wherein: The heat preservation and aging time is 0.5 to 2 hours.

Images