PVA based on carboxyl modification and preparation method thereof
Through the four-kettle series continuous polymerization system and multi-step processing, the problems of reaction control and product quality in the production of carboxy modified PVA are solved, efficient and low-cost production is achieved, and the mechanical properties and application adaptability of the material are improved.
Patent Information
- Application Number
- CN202411720277.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-28
- Publication Date
- 2025-01-07
AI Technical Summary
There are problems such as difficulty in reaction control, unstable product quality and high production costs in the production process of existing carboxy modified PVA, especially how to effectively control the reaction conditions during continuous polymerization to ensure uniform introduction of carboxylic groups and achieve efficient crosslinking and growth. Plastic treatment is a technically urgent problem.
Using a continuous polymerization system in series with four kettles, the carboxylic functional groups are uniformly distributed in the polymer chain by stepping the addition of the third comonomer and initiator, and plasticization and alcoholylation are carried out in the subsequent steps, combined with multiple washing and drying to Improve product quality and production efficiency.
It significantly improves the polymerization reaction efficiency and product consistency, improves cross-linking density and mechanical properties, reduces production costs and energy consumption, and ensures the green sustainability of the product and high market competitiveness.
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Figure CN119264318A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of polymer materials, and in particular to a carboxyl-modified PVA and a preparation method thereof. Background Art
[0002] Polyvinyl alcohol (PVA) is a widely used water-soluble polymer in the textile, papermaking, adhesives, coatings and pharmaceutical industries. Despite its good film-forming and adhesive properties, unmodified PVA still has limitations in certain properties, such as insufficient cross-linking performance, foaming tendency and poor dispersion stability. In order to improve these properties, academia and industry have tried to modify PVA by introducing carboxyl functional groups. Although carboxyl-modified PVA has shown significant advantages in improving the hydrophilicity and mechanical properties of the material, the existing modification methods usually involve complex process steps, are inefficient, and are difficult to adapt to the needs of large-scale industrial production.
[0003] In the prior art, common problems in the production process of carboxyl-modified PVA include difficult reaction control, unstable product quality and high production cost. Especially in the continuous polymerization process, how to effectively control the reaction conditions to ensure the uniform introduction of carboxyl groups, and how to achieve efficient cross-linking and plasticization treatment are technical problems that need to be solved urgently. In addition, traditional methods are inefficient in the post-processing stage, such as removing impurities and unreacted monomers, which often leads to substandard product performance or limited production efficiency.
[0004] Therefore, developing a new preparation method can not only improve the production efficiency and product quality of carboxyl-modified PVA, but also reduce the production cost, which is of great significance for expanding the application of PVA in various industries. Summary of the invention
[0005] Based on the above objectives, the present invention provides a carboxyl-modified PVA and a preparation method thereof.
[0006] A carboxyl-modified PVA comprises a main monomer, a second comonomer, a third comonomer, a crosslinking agent, an initiator, a plasticizer and a solvent; the weight percentage of each component is as follows: Main monomer: 45-70%; Second comonomer: 5-20%; The third comonomer: 3-10%; Cross-linking agent: 0.1-2%; Initiator: 0.5-2%; Plasticizer: 2-8%; The balance is solvent.
[0007] Optionally, the main monomer is vinyl acetate; the second comonomer is maleic acid, glutaconic acid or itaconic acid; the third comonomer is methacrylic acid or acrylic acid; the crosslinking agent is diethylenetriamine or ethylenediamine; the initiator is ammonium persulfate or azobisisobutyronitrile; the plasticizer is glycerol, ethylene glycol or propylene glycol; and the solvent is water.
[0008] A method for preparing carboxyl-modified PVA comprises the following steps: S1: mixing vinyl acetate and a second comonomer, adding a solvent, and stirring evenly to obtain a raw material mixture; S2: adding the raw material mixture in S1 to a continuous polymerization system with four reactors in series, carrying out a preliminary polymerization reaction in the first polymerization reactor, and transferring the reaction solution to the second, third and fourth polymerization reactors in sequence; S3: gradually adding the third comonomer and the initiator into the second, third and fourth polymerization kettles, and continuing the polymerization reaction to introduce carboxyl functional groups into the polymer chains; S4: in the fourth polymerization reactor, adding a crosslinking agent and continuing the reaction to form a crosslinked polymer; S5: the cross-linked polymer in S4 is discharged from the fourth polymerization reactor, and a plasticizer is added to perform plasticization treatment; S6: introducing the plasticized polymer into an alcoholysis reactor, adding an alcoholysis agent, and performing an alcoholysis reaction to convert the polymer into polyvinyl alcohol containing a carboxyl group; S7: filtering and washing the polymer after alcoholysis to remove impurities and unreacted monomers, and then drying to obtain the final carboxyl-modified polyvinyl alcohol powder.
[0009] Optionally, the S1 specifically includes: S11: Weighing vinyl acetate and a second comonomer according to a predetermined ratio, and adding the mixture into a stirring tank; S12: adding solvent to the stirring tank, starting stirring, and controlling the stirring speed at 300-500 rpm; S13: During the stirring process, the temperature is raised to 50-70° C. and stirring is continued for 30-60 minutes until the vinyl acetate and the second comonomer are evenly dispersed to form a raw material mixture.
[0010] Optionally, the S2 specifically includes: S21: The raw material mixture obtained in S1 is conveyed to the first polymerization reactor of the continuous polymerization system of four reactors in series through a metering pump, and the raw material flow rate is controlled to be 10-30 liters per hour; S22: In the first polymerization reactor, the temperature is controlled at 50-70° C. to start a preliminary polymerization reaction, and the reaction time is controlled at 1-2 hours; S23: After the reaction is completed, the reaction liquid is transferred from the first polymerization kettle to the second, third and fourth polymerization kettles in sequence by using a transfer pump between the reactors. During each transfer process, the temperature is maintained at 50-70°C, and the reaction liquid in each kettle is ensured to be uniformly stirred. The stirring speed is controlled at 200-400rpm; and the residence time in each polymerization kettle is controlled at 60-180 minutes.
[0011] Optionally, the S3 specifically includes: S31: In the second polymerization kettle, gradually add the third comonomer through the dropping device at a predetermined time interval, control the addition rate to be 0.5-2 ml per minute, maintain the temperature in the kettle at 50-70° C., control the stirring speed at 200-400 rpm, and continue the polymerization reaction; S32: In the third polymerization reactor, repeat the operation of step S31, and gradually add the initiator solution through the dropping device, control the initiator addition rate to 0.2-1 ml per minute, and maintain the same temperature and stirring speed; S33: In the fourth polymerization kettle, continue to drop the third comonomer and the initiator in the manner described in steps S31 and S32 to ensure that the carboxyl functional groups are evenly distributed in the polymer chain, and finally form a polymer with a target structure.
[0012] Optionally, the S4 specifically includes: S41: In the fourth polymerization kettle, the temperature is maintained at 50-70° C., and a cross-linking agent is gradually added through a drop adding device, and the addition rate is controlled to be 0.1-0.5 ml per minute; S42: After the cross-linking agent is added, continue to stir the reaction, maintain the stirring speed at 200-400 rpm, and continue the reaction for 1-2 hours; S43: After the reaction is completed, the heating is stopped, stirring is continued for 5-10 minutes, and then the cross-linked polymer is discharged.
[0013] Optionally, the S5 specifically includes: S51: The cross-linked polymer that has completed the reaction in S4 is discharged from the fourth polymerization kettle through a discharge pipe, and transferred to a plasticizing treatment kettle; S52: In the plasticizing treatment kettle, the temperature is raised to 80-100°C, and the plasticizer is gradually added through a drop adding device, and the adding speed is controlled to be 0.5-1 ml per minute, while the stirring speed in the kettle is maintained at 150-300 rpm; S53: After all the plasticizers are added, continue stirring the reaction for 30-60 minutes, maintaining the temperature and stirring speed until the plasticization process is completed; S54: After the reaction is completed, the heating is stopped, stirring is continued for 5-10 minutes, and then the plasticized polymer is discharged.
[0014] Optionally, the S6 specifically includes: S61: introducing the plasticized polymer into the alcoholysis reactor through a delivery pipeline, and ensuring that the temperature in the reactor is pre-controlled at 30-60°C; S62: in the alcoholysis reactor, gradually adding an alcoholysis agent through a dropping device, wherein the alcoholysis agent is methanol or ethanol, and controlling the adding speed to be 0.5-2 ml per minute, and simultaneously starting stirring, and controlling the stirring speed to be 100-300 rpm; S63: After all the alcoholysis agent is added, the temperature is continued to be maintained at 30-60° C. and the reaction is stirred for 1-3 hours to complete the alcoholysis reaction and convert the polymer into polyvinyl alcohol containing a carboxyl group; S64: After the reaction is completed, stop heating and continue stirring for 5-10 minutes to ensure that the alcoholysis reaction is completed evenly, and then extract the polymer after alcoholysis.
[0015] Optionally, the S7 specifically includes: S71: filtering the polymer after alcoholysis through a vacuum filtration device, and controlling the filtration pressure at 0.05-0.1 MPa to remove unreacted monomers and impurities; S72: washing the filtered polymer five times with deionized water, with the temperature of the washing solution controlled at 20-40° C., and each washing lasting 10-20 minutes, until the impurity content in the washing solution is less than 100 ppm; S73: After washing, the polymer is transferred to a drying oven and dried by hot air at a temperature of 60-80°C for 4-8 hours until the water content of the polymer drops below 5%, thereby obtaining the final carboxyl-modified polyvinyl alcohol powder.
[0016] Beneficial effects of the present invention: The present invention significantly improves the efficiency of the polymerization reaction and the consistency of the product by adopting four-reactor continuous polymerization in series. The method enables the carboxyl groups to be more evenly distributed on the PVA chain, thereby improving the crosslinking density and mechanical properties of the final product. In addition, by optimizing the plasticization and alcoholysis steps, the processing performance and final application performance of the material are enhanced, such as improving its flexibility and water resistance, so that the product is more suitable for use in high-demand application environments.
[0017] The present invention reduces energy consumption and waste of raw materials in the production process by precisely controlling reaction conditions and optimizing post-treatment processes, thereby improving the environmental friendliness of the production. In particular, in the process of removing impurities and unreacted monomers, effective filtering and multiple washing steps are adopted to ensure the green sustainability of the production process. The finally obtained carboxyl-modified PVA not only has stable quality, but also has better market competitiveness, thus meeting the strict requirements of modern industry for high-performance materials. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0019] Figure 1 Schematic diagram of each component of the modified PVA of an embodiment of the present invention; Figure 2 The figure is a schematic diagram of the preparation process of the modified PVA according to an embodiment of the present invention. DETAILED DESCRIPTION
[0020] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. At the same time, it is explained here that in order to make the embodiments more detailed, the following embodiments are the best and preferred embodiments, and those skilled in the art may also adopt other alternatives to implement some known technologies; and the accompanying drawings are only for more specific description of the embodiments, and are not intended to specifically limit the present invention.
[0021] It should be noted that the references to "one embodiment", "embodiment", "exemplary embodiments", "some embodiments" and the like in the specification indicate that the embodiments described may include specific features, structures or characteristics, but not every embodiment may include the specific features, structures or characteristics. In addition, when a specific feature, structure or characteristic is described in conjunction with an embodiment, it should be within the knowledge of a person skilled in the art to implement such feature, structure or characteristic in conjunction with other embodiments (whether or not explicitly described).
[0022] In general, a term can be understood, at least in part, from its use in context. For example, depending, at least in part, on the context, the term "one or more" as used herein can be used to describe any feature, structure, or characteristic in the singular sense, or can be used to describe a combination of features, structures, or characteristics in the plural sense. Additionally, the term "based on" can be understood as not necessarily intended to convey an exclusive set of factors, but can instead, depending, at least in part, on the context, allow for the presence of other factors that are not necessarily explicitly described.
[0023] Example 1 like Figure 1 As shown, a carboxyl-modified PVA includes a main monomer, a second comonomer, a third comonomer, a crosslinking agent, an initiator, a plasticizer and a solvent; the weight percentage of each component is: Main monomer: 60%; Second comonomer: 10%; The third comonomer: 5%; Cross-linking agent: 0.5%; Initiator: 1.5%; Plasticizer: 5%; The balance is solvent.
[0024] The main monomer is vinyl acetate (VAc); the second comonomer is maleic acid; the third comonomer is methacrylic acid, which is used to introduce additional functional groups to improve the flexibility and adhesion of the polymer; the crosslinking agent is diethylenetriamine, which is used to increase the crosslinking density and thermal stability of the polymer; the initiator is ammonium persulfate, which is used to start the polymerization reaction; the plasticizer is glycerol, which is used to improve the flexibility and processability of PVA; the solvent is water.
[0025] like Figure 2 As shown, a method for preparing carboxyl-modified PVA comprises the following steps: S1: mixing vinyl acetate and a second comonomer, adding a solvent, and stirring evenly to obtain a raw material mixture; S2: adding the raw material mixture in S1 to a continuous polymerization system with four reactors in series, carrying out a preliminary polymerization reaction in the first polymerization reactor, and transferring the reaction solution to the second, third and fourth polymerization reactors in sequence; S3: gradually adding the third comonomer and the initiator into the second, third and fourth polymerization kettles, and continuing the polymerization reaction to introduce carboxyl functional groups into the polymer chains; S4: in the fourth polymerization reactor, adding a crosslinking agent and continuing the reaction to form a crosslinked polymer; S5: the cross-linked polymer in S4 is discharged from the fourth polymerization reactor, and a plasticizer is added to perform plasticization treatment; S6: introducing the plasticized polymer into an alcoholysis reactor, adding an alcoholysis agent, and performing an alcoholysis reaction to convert the polymer into polyvinyl alcohol containing a carboxyl group; S7: filtering and washing the polymer after alcoholysis to remove impurities and unreacted monomers, and then drying to obtain the final carboxyl-modified polyvinyl alcohol powder.
[0026] S1 specifically includes: S11: Weighing vinyl acetate and a second comonomer according to a predetermined ratio, and adding the mixture into a stirring tank; S12: adding solvent to the stirring tank, starting stirring, and controlling the stirring speed at 400 rpm; S13: During the stirring process, the temperature is raised to 60° C. and stirring is maintained for 40 minutes until the vinyl acetate and the second comonomer are evenly dispersed to form a stable raw material mixture.
[0027] S2 specifically includes: S21: The raw material mixture obtained in S1 is conveyed to the first polymerization reactor of the continuous polymerization system of four reactors in series through a metering pump, and the raw material flow rate is controlled to be 20 liters per hour; S22: In the first polymerization reactor, the temperature is controlled at 60° C. to start a preliminary polymerization reaction, and the reaction time is controlled at 1.5 hours; S23: After the reaction is completed, the reaction liquid is transferred from the first polymerization kettle to the second, third and fourth polymerization kettles in turn by using a transfer pump between the reactors. During each transfer process, the temperature is maintained at 60°C, and the reaction liquid in each kettle is ensured to be uniformly stirred. The stirring speed is controlled at 300rpm; and the residence time in each polymerization kettle is controlled at 120 minutes to ensure the gradual completion of the polymerization reaction and the introduction of carboxyl groups.
[0028] S3 specifically includes: S31: In the second polymerization kettle, gradually add the third comonomer through the dropping device at a predetermined time interval, control the addition rate to be 1 ml per minute, maintain the temperature in the kettle at 60° C., control the stirring speed at 300 rpm, and continue the polymerization reaction; S32: in the third polymerization reactor, repeat the operation of step S31, and gradually add the initiator solution through the dropping device, control the initiator addition rate to 0.5 ml per minute, maintain the same temperature and stirring rate, so as to promote the introduction of carboxyl functional groups in the polymer chain; S33: In the fourth polymerization kettle, continue to drop the third comonomer and the initiator according to steps S31 and S32 to ensure that the carboxyl functional groups are evenly distributed in the polymer chain, and finally form a polymer with a target structure.
[0029] S4 specifically includes: S41: In the fourth polymerization kettle, the temperature is maintained at 60° C., and a cross-linking agent is gradually added through a drop adding device, and the addition rate is controlled to be 0.3 ml per minute to ensure that the cross-linking agent and the polymer are evenly mixed; S42: After the cross-linking agent is added, the reaction is continued to be stirred at a stirring speed of 300 rpm, and the reaction is continued for 1.5 hours to ensure that the cross-linking reaction is fully carried out; S43: After the reaction is completed, the heating is stopped and stirring is continued for 7 minutes to ensure the uniformity of the polymer, and then the cross-linked polymer is extracted for subsequent processing.
[0030] S5 specifically includes: S51: The cross-linked polymer that has completed the reaction in S4 is discharged from the fourth polymerization kettle through a discharge pipe, and transferred to a plasticizing treatment kettle; S52: In the plasticizing treatment kettle, the temperature is raised to 90° C., and the plasticizer is gradually added through a dripping device, and the addition rate is controlled to be 0.8 ml per minute, while the stirring speed in the kettle is maintained at 200 rpm to ensure that the plasticizer and the cross-linked polymer are fully mixed; S53: After all the plasticizers are added, continue stirring the reaction for 45 minutes, maintaining the temperature and stirring speed until the plasticization process is completed; S54: After the reaction is completed, stop heating and continue stirring for 8 minutes to ensure mixing uniformity, then extract the plasticized polymer and prepare for the next step of processing.
[0031] S6 specifically includes: S61: introducing the plasticized polymer into the alcoholysis reactor through a delivery pipeline, and ensuring that the temperature in the reactor is pre-controlled at 40° C.; S62: In the alcoholysis reactor, an alcoholysis agent is gradually added through a dropping device, wherein the alcoholysis agent is ethanol, and the adding speed is controlled to be 1.5 ml per minute, and stirring is started at the same time, and the stirring speed is controlled to be 150 rpm; S63: After all the alcoholysis agent is added, the temperature is maintained at 45° C. and the reaction is stirred for 2 hours to complete the alcoholysis reaction and convert the polymer into polyvinyl alcohol containing a carboxyl group; S64: After the reaction is completed, stop heating and continue stirring for 7 minutes to ensure that the alcoholysis reaction is evenly completed, and then extract the polymer after alcoholysis to prepare for subsequent filtration and washing.
[0032] S7 specifically includes: S71: filtering the polymer after alcoholysis through a vacuum filtration device, and controlling the filtration pressure at 0.08 MPa to remove unreacted monomers and impurities; S72: washing the filtered polymer five times with deionized water, with the temperature of the washing solution controlled at 30° C., and each washing lasting 15 minutes, until the impurity content in the washing solution is less than 100 ppm; S73: After washing, the polymer is transferred to a drying oven and dried by hot air at a temperature of 70°C for 6 hours until the water content of the polymer drops to 2%, thereby obtaining the final carboxyl-modified polyvinyl alcohol powder.
[0033] Example 2 1.1 Material ratio Main monomer (vinyl acetate): 45%; Second comonomer (glutaconic acid): 5%; The third comonomer (acrylic acid): 3%; Cross-linking agent (ethylenediamine): 0.1%; Initiator (azobisisobutyronitrile): 0.5%; Plasticizer (ethylene glycol): 2%; Solvent (water): balance.
[0034] 1.2 Preparation steps S1: After weighing vinyl acetate and glutaconic acid according to the proportion, add them into a stirring kettle, add solvent water and start stirring, control the stirring speed at 300 rpm, raise the temperature to 50° C., and keep stirring for 30 minutes until a uniform raw material mixture is formed; S2: The raw material mixture is delivered to a continuous polymerization system with four reactors in series through a metering pump, and the raw material flow rate is controlled to be 10 liters per hour. In the first polymerization reactor, the temperature is controlled at 50°C, and a preliminary polymerization reaction is started. The reaction time is 1 hour, and then the raw material mixture is transferred to the second, third and fourth polymerization reactors in sequence through a delivery pump. The temperature is maintained at 50°C, the stirring speed is controlled at 200 rpm, and the residence time in each polymerization reactor is 60 minutes; S3: In the second polymerization kettle, the third copolymer monomer acrylic acid is gradually added through a drop adding device, and the addition rate is controlled to be 0.5 ml per minute, the temperature is maintained at 50° C., and the stirring rate is 200 rpm; in the third polymerization kettle, the above operation is repeated, and the initiator azobisisobutyronitrile is gradually added at a rate of 0.2 ml per minute to continue the polymerization reaction; in the fourth polymerization kettle, acrylic acid and azobisisobutyronitrile are continued to be added dropwise in the above manner to ensure that the carboxyl functional groups are evenly distributed in the polymer chain; S4: In the fourth polymerization kettle, ethylenediamine was gradually added as a cross-linking agent through a drop adding device, the addition rate was controlled to be 0.1 ml per minute, the temperature was maintained at 50° C., the stirring rate was maintained at 200 rpm, and the stirring reaction was continued for 1 hour. After completion, the heating was stopped and the stirring was continued for 5 minutes to extract the cross-linked polymer; S5: The cross-linked polymer is transferred to a plasticizing treatment kettle, the temperature is raised to 80°C, and the plasticizer ethylene glycol is gradually added through a drop adding device at a rate of 0.5 ml per minute and a stirring rate of 150 rpm. The reaction is continued for 30 minutes. After the reaction is completed, the heating is stopped and the stirring is continued for 5 minutes to complete the plasticizing treatment; S6: introducing the plasticized polymer into an alcoholysis reactor, controlling the temperature at 30°C, gradually adding alcoholysis agent methanol through a dropping device, the adding speed is 0.5 ml per minute, the stirring speed is controlled at 100 rpm, the temperature is maintained at 30°C, and the alcoholysis reaction is carried out for 1 hour. After the reaction is completed, the heating is stopped, and the stirring is continued for 5 minutes to finally obtain carboxyl-containing polyvinyl alcohol; S7: The polymer after alcoholysis was filtered through a vacuum filtration device with a filtration pressure of 0.05 MPa, and washed with water 5 times, each washing lasting 10 minutes, and the temperature of the washing liquid was controlled at 20°C. Finally, the washed polymer was hot-air dried at a drying temperature of 60°C and a drying time of 4 hours to obtain a carboxyl-modified polyvinyl alcohol powder with a moisture content of less than 4%.
[0035] Example 3 1.1 Material ratio Main monomer (vinyl acetate): 70%; Second comonomer (itaconic acid): 20%; The third comonomer (methacrylic acid): 10%; Crosslinking agent (diethylenetriamine): 2%; Initiator (ammonium persulfate): 2%; Plasticizer (propylene glycol): 8%; Solvent (water): balance.
[0036] 1.2 Preparation steps S1: After weighing vinyl acetate and itaconic acid according to the proportion, add them into a stirring kettle, add solvent water and start stirring, control the stirring speed at 500 rpm, raise the temperature to 70°C, and keep stirring for 60 minutes until a uniform raw material mixture is formed; S2: The raw material mixture is delivered to a continuous polymerization system with four reactors in series by a metering pump, and the raw material flow rate is controlled to be 30 liters per hour. In the first polymerization reactor, the temperature is controlled at 70°C, and a preliminary polymerization reaction is started for 2 hours. Then, the raw material mixture is transferred to the second, third and fourth polymerization reactors in sequence by a delivery pump, and the temperature is maintained at 70°C, the stirring speed is controlled at 400 rpm, and the residence time in each polymerization reactor is 180 minutes; S3: In the second polymerization kettle, the third comonomer methacrylic acid is gradually added through a drop adding device, the addition rate is controlled to be 2 ml per minute, the temperature is maintained at 70°C, and the stirring rate is 400 rpm; in the third polymerization kettle, the above operation is repeated, and the initiator ammonium persulfate is gradually added at a rate of 1 ml per minute to continue the polymerization reaction; in the fourth polymerization kettle, methacrylic acid and ammonium persulfate are continued to be added dropwise in the above manner to ensure that the carboxyl functional groups are evenly distributed in the polymer chain; S4: In the fourth polymerization kettle, diethylenetriamine was gradually added as a cross-linking agent through a drop adding device, the addition rate was controlled to be 0.5 ml per minute, the temperature was maintained at 70° C., the stirring rate was maintained at 400 rpm, and the stirring reaction was continued for 2 hours. After the reaction was completed, the heating was stopped and the stirring was continued for 10 minutes to extract the cross-linked polymer; S5: The cross-linked polymer is transferred to a plasticizing treatment kettle, the temperature is raised to 100°C, and the plasticizer propylene glycol is gradually added through a drop adding device at a rate of 1 ml per minute and a stirring rate of 300 rpm. The reaction is continued for 60 minutes. After the reaction is completed, the heating is stopped and the stirring is continued for 10 minutes to complete the plasticizing treatment; S6: introducing the plasticized polymer into an alcoholysis reactor, controlling the temperature at 60°C, gradually adding alcoholysis agent ethanol through a dropping device, the adding speed is 2 ml per minute, the stirring speed is controlled at 300 rpm, the temperature is maintained at 60°C, and the alcoholysis reaction is carried out for 3 hours. After the reaction is completed, the heating is stopped, and the stirring is continued for 10 minutes to finally obtain polyvinyl alcohol containing a carboxyl group; S7: The polymer after alcoholysis was filtered through a vacuum filtration device with a filtration pressure of 0.1 MPa, and washed with water 5 times, each washing lasting 20 minutes, and the temperature of the washing liquid was controlled at 40°C. Finally, the washed polymer was hot-air dried at a drying temperature of 80°C and a drying time of 8 hours to obtain a carboxyl-modified polyvinyl alcohol powder with a moisture content of less than 5%.
[0037] Table 1 Comparison of finished product experimental data As can be seen from Table 1 above, Example 1 performs best in all key performance indicators. Among them, the tensile strength of Example 1 is 55 MPa, and the elongation at break is 240%, showing the best toughness and strength, which is suitable for application scenarios requiring high mechanical properties; the thermal decomposition temperature of Example 1 is 240°C, showing the highest thermal stability, and can maintain the structural stability of the material at a higher temperature; the light transmittance of Example 1 is 95%, which performs best in optical properties and is suitable for products requiring high transparency; the water dissolution rate of Example 1 is 280 seconds, and the faster dissolution rate makes it have good dissolution performance in application; the hydrolysis resistance time of Example 1 is 80 hours, indicating that the material can still maintain good performance under long-term contact with water; the moisture content of Example 1 is only 2%, and the lowest moisture content means that the material has better drying effect and storage stability. In summary, Example 1 is superior to other examples in all performance indicators, showing the best comprehensive performance, and is the best implementation scheme based on carboxyl-modified PVA.
[0038] Table 2 Comparison of other performance parameters Table 2 above shows the following conclusions by comparing the seven aspects of density, melting point, water absorption, chemical resistance, UV resistance, surface hardness and residual monomer content: the density of Example 1 is 1.26 g / cm³, which is higher than that of other examples, which means that the material is more compact and has better structural stability; the melting point of Example 1 is 180°C, which has better heat resistance at high temperatures; the water absorption of Example 1 is 1.8%, and the lowest water absorption indicates that the material performs better in a humid environment and is not easy to absorb water; the acid and alkali resistance of Example 1 is 98%, indicating that it has higher stability and corrosion resistance in various chemical environments; the UV resistance of Example 1 reaches 93%, which can more effectively block UV rays, thereby extending the service life of the material; the surface hardness of Example 1 is 70 (Shore D), showing stronger wear resistance and scratch resistance; the residual monomer content of Example 1 is only 15 ppm, and the lowest residual monomer content means that the material is safer in use and reduces the residual risk of harmful substances. On the whole, Example 1 performs best in multiple key performance indicators such as density, melting point, water absorption, chemical resistance, UV resistance, surface hardness and residual monomer content, and is the implementation scheme with the best comprehensive performance.
[0039] The present invention covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present invention. In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without the description of these details. In addition, in order to avoid unnecessary confusion about the essence of the present invention, well-known methods, processes, procedures, components and circuits are not described in detail.
[0040] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.
Claims
1. A carboxyl-modified PVA, characterized in that: It includes a main monomer, a second comonomer, a third comonomer, a crosslinking agent, an initiator, a plasticizer and a solvent; the weight percentage of each component is as follows: Main monomer: 45-70%; Second comonomer: 5-20%; The third comonomer: 3-10%; Cross-linking agent: 0.1-2%; Initiator: 0.5-2%; Plasticizer: 2-8%; The balance is solvent.
2. A carboxyl-modified PVA according to claim 1, characterized in that: The main monomer is vinyl acetate; the second comonomer is maleic acid, glutaconic acid or itaconic acid; the third comonomer is methacrylic acid or acrylic acid; the crosslinking agent is diethylenetriamine or ethylenediamine; the initiator is ammonium persulfate or azobisisobutyronitrile; the plasticizer is glycerol, ethylene glycol or propylene glycol; and the solvent is water.
3. A method for preparing a carboxyl-modified PVA according to any of claims 1-2, characterized in that: The following steps are involved: S1: mixing vinyl acetate and a second comonomer, adding a solvent, and stirring evenly to obtain a raw material mixture; S2: adding the raw material mixture in S1 to a continuous polymerization system with four reactors in series, carrying out a preliminary polymerization reaction in the first polymerization reactor, and transferring the reaction solution to the second, third and fourth polymerization reactors in sequence; S3: gradually adding the third comonomer and the initiator into the second, third and fourth polymerization kettles, and continuing the polymerization reaction to introduce carboxyl functional groups into the polymer chains; S4: in the fourth polymerization reactor, adding a crosslinking agent and continuing the reaction to form a crosslinked polymer; S5: the cross-linked polymer in S4 is discharged from the fourth polymerization reactor, and a plasticizer is added to perform plasticization treatment; S6: introducing the plasticized polymer into an alcoholysis reactor, adding an alcoholysis agent, and performing an alcoholysis reaction to convert the polymer into polyvinyl alcohol containing a carboxyl group; S7: filtering and washing the polymer after alcoholysis to remove impurities and unreacted monomers, and then drying to obtain the final carboxyl-modified polyvinyl alcohol powder.
4. The method for preparing a carboxyl-modified PVA according to claim 3, characterized in that: The S1 specifically includes: S11: Weighing vinyl acetate and a second comonomer according to a predetermined ratio, and adding the mixture into a stirring tank; S12: adding solvent to the stirring tank, starting stirring, and controlling the stirring speed at 300-500 rpm; S13: During the stirring process, the temperature is raised to 50-70° C. and stirring is continued for 30-60 minutes until the vinyl acetate and the second comonomer are evenly dispersed to form a raw material mixture.
5. The method for preparing a carboxyl-modified PVA according to claim 3, characterized in that: The S2 specifically includes: S21: The raw material mixture obtained in S1 is conveyed to the first polymerization reactor of the continuous polymerization system of four reactors in series through a metering pump, and the raw material flow rate is controlled to be 10-30 liters per hour; S22: In the first polymerization reactor, the temperature is controlled at 50-70° C. to start a preliminary polymerization reaction, and the reaction time is controlled at 1-2 hours; S23: After the reaction is completed, the reaction liquid is transferred from the first polymerization kettle to the second, third and fourth polymerization kettles in sequence by using a transfer pump between the reactors. During each transfer process, the temperature is maintained at 50-70°C, and the reaction liquid in each kettle is ensured to be uniformly stirred. The stirring speed is controlled at 200-400rpm; and the residence time in each polymerization kettle is controlled at 60-180 minutes.
6. The method for preparing a carboxyl-modified PVA according to claim 3, characterized in that: The S3 specifically includes: S31: In the second polymerization kettle, gradually add the third comonomer through the dropping device at a predetermined time interval, control the addition rate to be 0.5-2 ml per minute, maintain the temperature in the kettle at 50-70° C., control the stirring speed at 200-400 rpm, and continue the polymerization reaction; S32: In the third polymerization reactor, repeat the operation of step S31, and gradually add the initiator solution through the dropping device, control the initiator addition rate to 0.2-1 ml per minute, and maintain the same temperature and stirring speed; S33: In the fourth polymerization kettle, continue to drop the third comonomer and the initiator in the manner described in steps S31 and S32 to ensure that the carboxyl functional groups are evenly distributed in the polymer chain, and finally form a polymer with a target structure.
7. The method for preparing a carboxyl-modified PVA according to claim 3, characterized in that: The S4 specifically includes: S41: In the fourth polymerization kettle, the temperature is maintained at 50-70° C., and a cross-linking agent is gradually added through a drop adding device, and the addition rate is controlled to be 0.1-0.5 ml per minute; S42: After the cross-linking agent is added, continue to stir the reaction, maintain the stirring speed at 200-400 rpm, and continue the reaction for 1-2 hours; S43: After the reaction is completed, the heating is stopped, stirring is continued for 5-10 minutes, and then the cross-linked polymer is discharged.
8. The method for preparing a carboxyl-modified PVA according to claim 3, characterized in that: The S5 specifically includes: S51: The cross-linked polymer that has completed the reaction in S4 is discharged from the fourth polymerization kettle through a discharge pipe, and transferred to a plasticizing treatment kettle; S52: In the plasticizing treatment kettle, the temperature is raised to 80-100°C, and the plasticizer is gradually added through a drop adding device, and the adding speed is controlled to be 0.5-1 ml per minute, while the stirring speed in the kettle is maintained at 150-300 rpm; S53: After all the plasticizers are added, continue stirring the reaction for 30-60 minutes, maintaining the temperature and stirring speed until the plasticization process is completed; S54: After the reaction is completed, the heating is stopped, stirring is continued for 5-10 minutes, and then the plasticized polymer is discharged.
9. The method for preparing a carboxyl-modified PVA according to claim 3, characterized in that: The S6 specifically includes: S61: introducing the plasticized polymer into the alcoholysis reactor through a delivery pipeline, and ensuring that the temperature in the reactor is pre-controlled at 30-60°C; S62: in the alcoholysis reactor, gradually adding an alcoholysis agent through a dropping device, wherein the alcoholysis agent is methanol or ethanol, and controlling the adding speed to be 0.5-2 ml per minute, and simultaneously starting stirring, and controlling the stirring speed to be 100-300 rpm; S63: After all the alcoholysis agent is added, the temperature is continued to be maintained at 30-60° C. and the reaction is stirred for 1-3 hours to complete the alcoholysis reaction and convert the polymer into polyvinyl alcohol containing a carboxyl group; S64: After the reaction is completed, stop heating and continue stirring for 5-10 minutes to ensure that the alcoholysis reaction is completed evenly, and then extract the polymer after alcoholysis.
10. The method for preparing a carboxyl-modified PVA according to claim 3, characterized in that: The S7 specifically includes: S71: filtering the polymer after alcoholysis through a vacuum filtration device, and controlling the filtration pressure at 0.05-0.1 MPa to remove unreacted monomers and impurities; S72: washing the filtered polymer five times with deionized water, with the temperature of the washing solution controlled at 20-40° C., and each washing lasting 10-20 minutes, until the impurity content in the washing solution is less than 100 ppm; S73: After washing, the polymer is transferred to a drying oven and dried by hot air at a temperature of 60-80°C for 4-8 hours until the water content of the polymer drops below 5%, thereby obtaining the final carboxyl-modified polyvinyl alcohol powder.