High-crystallinity PVDF (Polyvinylidene Fluoride) and preparation method thereof
By using a dispersion system of polyvinyl alcohol with a degree of hydrolysis of 72-80% and hydroxypropyl methylcellulose, and a segmented temperature-controlled constant pressure polymerization process, the problems of low crystallinity and poor thermal stability of PVDF were solved, and the preparation of high crystallinity PVDF was achieved, which improved its strength and toughness and ensured the stability and performance optimization of the product.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HENAN FEITE MEMBRANE NEW MATERIALS CO LTD
- Filing Date
- 2026-03-26
- Publication Date
- 2026-05-19
AI Technical Summary
Traditional PVDF has low crystallinity, imperfect crystal form, low melting point, poor thermal stability, and it is difficult to balance strength and toughness in terms of mechanical properties. In addition, the polymerization process has weak controllability and is prone to burst polymerization and particle agglomeration, resulting in poor batch stability of products.
A dispersion system of polyvinyl alcohol with a degree of hydrolysis of 72-80% and hydroxypropyl methylcellulose was used. Combined with deep vacuum pretreatment and nitrogen replacement in the reactor, the oxygen content was controlled at 10-20 ppm. A segmented temperature-controlled constant pressure polymerization process was adopted, which included low-temperature initiation, medium-temperature polymerization and high-temperature curing. The initiator was added in stages and the stirring speed was controlled to avoid the instability of the polymerization reaction and improve the crystallinity and crystal structure regularity of PVDF.
It significantly improves the crystallinity and melting point of PVDF, achieving a synergistic improvement in high rigidity and good toughness, solving the problem that traditional PVDF cannot achieve both strength and toughness, and improving the overall performance stability of the product.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of PVDF processing technology, specifically relating to a highly crystalline PVDF and its preparation method. Background Technology
[0002] PVDF, also known as fluoropolymer, possesses properties such as high temperature resistance, chemical corrosion resistance, and hydrolysis resistance. As a pure polymer, it is widely used in pure water systems and the semiconductor industry for the transport of chemical reagents, and is also used in the welding of tanks, pipes, and other equipment components. This material combines high strength, low flammability, and excellent electrical insulation properties, making it suitable for applications in the electronics industry, chemical plants, and food processing machinery.
[0003] Traditional PVDF generally suffers from low crystallinity, imperfect crystal form, low melting point, and poor thermal stability. At the same time, its mechanical properties are prone to the dilemma of "strength and toughness cannot be achieved at the same time." Increasing crystallinity often leads to a decrease in toughness, making it difficult to meet the comprehensive requirements of applications. In addition, traditional polymerization processes are poorly controllable and prone to burst polymerization, local overheating, and particle agglomeration, resulting in poor batch stability of products. Summary of the Invention
[0004] The purpose of this invention is to provide a highly crystallinity PVDF and its preparation method in order to solve the above-mentioned problems.
[0005] The present invention achieves the above objectives through the following technical solutions: This invention provides a highly crystalline PVDF, comprising the following raw materials in parts by weight: 30-40 parts VDF monomer, 45-55 parts deionized water, 20-35 parts dispersion solution, 0.1-0.3 parts initiator and 0.1-1 parts chain transfer agent.
[0006] As a further optimization of the present invention, the dispersion solution comprises, by weight, 15-20 parts of dispersant A, 10-15 parts of dispersant B and 55-65 parts of hot water at 60-80°C, wherein dispersant A is polyvinyl alcohol with a degree of alcoholysis of 72-80% and dispersant B is hydroxypropyl methylcellulose.
[0007] As a further optimization of the present invention, the initiator is selected from one or more of diisopropyl peroxide dicarbonate, diethyl peroxide dicarbonate, and tert-butyl peroxypentanoate.
[0008] As a further optimization of the present invention, the chain transfer agent is selected from one or more of isopropanol, ethyl acetate, and dimethyl carbonate.
[0009] This invention also provides a method for preparing highly crystallinity PVDF, comprising the following steps: Pretreatment of the reactor: Evacuate the reactor to -0.095MPa and maintain the pressure for 30 minutes. Purge with nitrogen 2-3 times to ensure that the oxygen content in the reactor is 10-20ppm. Add deionized water to the reactor and stir at 120-200rpm for 30-45 minutes. Heat to 40-50℃ for later use. Feeding and preparation: Dissolve dispersant A and dispersant B in hot water at 60-80℃ to obtain a dispersion solution; slowly add the dispersion solution to the pretreated reactor and stir for 30 minutes until completely dissolved; add chain transfer agent and stir at 360 r / min for 15-20 minutes; slowly pump in VDF monomer at 40-50℃ and 0.5-1.0 MPa; after the VDF monomer is pumped in, close the feed valve, pressurize with nitrogen to raise the pressure inside the reactor to 2.0-2.5 MPa, and stir at 300-400 rpm for 30-45 minutes to obtain the preform. Segmented temperature-controlled constant pressure polymerization: The preform is subjected to segmented temperature-controlled constant pressure polymerization to obtain crude PVDF product; Post-processing: Centrifuge at 3000-4000 rpm for 15-30 min to separate PVDF particles from the aqueous phase in the crude PVDF product; collect the PVDF particles, wash them 2-3 times with hot water at 60-80℃, and then wash them 3-5 times with deionized water until the conductivity of the washing liquid is 5-10 μS / cm at room temperature of 25℃ to obtain primary PVDF particles; pre-dry the primary PVDF particles at 60℃ and vacuum degree -0.09MPa for 6-8 h to remove surface water, and then dry them at 80-90℃ and vacuum degree -0.095MPa for 12-24 h to make the moisture content of the PVDF particles 0.03-0.06% to obtain highly crystalline PVDF.
[0010] As a further optimization of the present invention, the specific process of segmented temperature-controlled constant pressure polymerization includes: a low-temperature initiation stage, a medium-temperature polymerization stage, and a maturation stage; The specific process of the low-temperature initiation section is as follows: the reactor is heated to 45-55℃, nitrogen is continuously added to maintain the pressure inside the reactor at 2.5-3.0MPa, 2 / 5 of the total amount of initiator is added, and the reactor is stirred at 120rpm for 10min, with a reaction time of 1-3h. The specific process of the intermediate temperature polymerization section is as follows: slowly raise the temperature to 55-65℃ at a rate of 0.5℃ / h, continuously supplement nitrogen to maintain the pressure inside the reactor at 3.0-3.5MPa, add 2 / 5 of the total amount of initiator in 3-5 equal parts, with each part added at 10min intervals, and continuously stir at 120rpm during the addition. After that, stir at 300-400rpm for 10-15min every 2-3h, and the reaction time is 8-15h. Curing stage: Heat the reactor to 65-70℃, continuously add nitrogen to maintain the pressure inside the reactor at 2.5-3.0MPa, add the remaining initiator, stir at 120rpm for 10min, and cure at a constant temperature for 2-4h.
[0011] The beneficial effects of this invention are as follows: This invention uses a dispersion system of polyvinyl alcohol with a degree of hydrolysis of 72-80% and hydroxypropyl methylcellulose, combined with deep vacuum pretreatment of the reactor and nitrogen replacement to control the oxygen content at 10-20ppm, effectively reducing oxidation side reactions and molecular chain defects. Combined with a segmented temperature-controlled constant pressure polymerization process of low-temperature initiation, medium-temperature polymerization, and high-temperature ripening, as well as the addition of initiators and control of stirring speed, the polymerization reaction is stable and controllable, avoiding crystal defects caused by explosive polymerization and local overheating, significantly improving the degree of PVDF crystallization. The resulting product has high crystallinity and melting point, and regular crystal structure. At the same time, it breaks the performance contradiction of high strength and poor toughness of conventional high-crystallinity polymers, achieving a synergistic improvement in tensile strength and elongation at break, and possessing both high rigidity and good toughness. Detailed Implementation
[0012] The present application will now be described in further detail. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.
[0013] Unless otherwise specified, all methods used in this invention are conventional methods known to those skilled in the art, and all reagents and materials used are commercially available products.
[0014] Example 1 Pretreatment of the reactor: Evacuate the reactor to -0.095MPa and maintain the pressure for 30 minutes. Purge with nitrogen twice to ensure that the oxygen content in the reactor is 10ppm. Add 45 parts of deionized water to the reactor and stir at 120rpm for 30 minutes. Heat to 40℃ for later use. Feeding and preparation: Dissolve 15 parts of polyvinyl alcohol with a degree of hydrolysis of 72% and 10 parts of hydroxypropyl methylcellulose in 55 parts of hot water at 60℃ to obtain a dispersion solution; slowly add 20 parts of the dispersion solution into the pretreated reactor and stir for 30 minutes until completely dissolved; add 0.1 parts of isopropanol and stir at 360 r / min for 15 minutes; under conditions of 40℃ and 0.5 MPa pressure, slowly pump in 30 parts of VDF monomer. After the VDF monomer is pumped in, close the feed valve, pressurize the reactor with nitrogen to raise the pressure to 2.0 MPa, and stir at 300 rpm for 30 minutes to obtain the preform. Segmented temperature-controlled constant pressure polymerization: The preform is subjected to segmented temperature-controlled constant pressure polymerization to obtain crude PVDF product; The specific process of segmented temperature-controlled constant-pressure polymerization includes: a low-temperature initiation stage, a medium-temperature polymerization stage, and a maturation stage; The specific process of the low-temperature initiation section is as follows: the reactor is heated to 45°C, nitrogen is continuously added to maintain the pressure inside the reactor at 2.5 MPa, 2 parts of diisopropyl peroxide dicarbonate are added, and the mixture is stirred at 120 rpm for 10 min, with a reaction time of 1 h. The specific process of the intermediate temperature polymerization section is as follows: the temperature is slowly increased to 55℃ at a rate of 0.5℃ / h, nitrogen is continuously added to maintain the pressure inside the reactor at 3.0MPa, 2 parts of diisopropyl peroxide are added in 3 equal parts, with each part added at 10min intervals. During the addition, the mixture is continuously stirred at 120rpm. After that, every 2h, the mixture is stirred at 300rpm for 10min. The reaction time is 8h. Curing section: Heat the reactor to 65°C, continuously add nitrogen to maintain the pressure inside the reactor at 2.5 MPa, add 1 part of diisopropyl peroxide, stir at 120 rpm for 10 min, and cure at a constant temperature for 2 h. Post-processing: The PVDF particles in the crude PVDF product were separated from the aqueous phase by centrifugation at 3000 rpm for 15 min. The PVDF particles were collected and washed twice with hot water at 60℃ and then three times with deionized water until the conductivity of the washing solution was 5 μS / cm at room temperature of 25℃, thus obtaining primary PVDF particles. The primary PVDF particles were pre-dried at 60℃ and vacuum degree -0.09MPa for 6 h to remove surface water, and then dried at 80℃ and vacuum degree -0.095MPa for 12 h to reduce the moisture content of the PVDF particles to 0.03%, thus obtaining highly crystalline PVDF.
[0015] Example 2 Pretreatment of the reactor: Evacuate the reactor to -0.095MPa and maintain the pressure for 30 minutes. Purge with nitrogen three times to ensure that the oxygen content in the reactor is 10ppm. Add 50 parts of deionized water to the reactor and stir at 180rpm for 35 minutes. Heat to 45℃ for later use. Feeding and preparation: Dissolve 18 parts of polyvinyl alcohol with a degree of hydrolysis of 75% and 12 parts of hydroxypropyl methylcellulose in 60 parts of hot water at 70℃ to obtain a dispersion solution; slowly add 25 parts of the dispersion solution into the pretreated reactor and stir for 30 minutes until completely dissolved; add 0.5 parts of isopropanol and stir at 360 r / min for 18 minutes; under conditions of 45℃ and 0.8 MPa pressure, slowly pump in 35 parts of VDF monomer. After the VDF monomer is pumped in, close the feed valve, pressurize the reactor with nitrogen to raise the pressure to 2.2 MPa, and stir at 350 rpm for 40 minutes to obtain the preform. Segmented temperature-controlled constant pressure polymerization: The preform is subjected to segmented temperature-controlled constant pressure polymerization to obtain crude PVDF product; The specific process of segmented temperature-controlled constant-pressure polymerization includes: a low-temperature initiation stage, a medium-temperature polymerization stage, and a maturation stage; The specific process of the low-temperature initiation section is as follows: the reactor is heated to 50°C, nitrogen is continuously added to maintain the pressure inside the reactor at 2.8 MPa, 2 parts of diisopropyl peroxide dicarbonate are added, and the mixture is stirred at 120 rpm for 10 min, with a reaction time of 2 h. The specific process of the intermediate temperature polymerization section is as follows: the temperature is slowly increased to 60℃ at a rate of 0.5℃ / h, nitrogen is continuously added to maintain the pressure inside the reactor at 3.2MPa, 2 parts of diisopropyl peroxide are added in 4 equal parts, with each part added at 10min intervals. During the addition, the mixture is continuously stirred at 120rpm. After that, every 2.5h, the mixture is stirred at 350rpm for 12min. The reaction time is 12h. Curing section: Heat the reactor to 68°C, continuously add nitrogen to maintain the pressure inside the reactor at 2.5 MPa, add 1 part of diisopropyl peroxide, stir at 120 rpm for 10 min, and cure at a constant temperature for 3 h. Post-processing: The PVDF particles in the crude PVDF product were separated from the aqueous phase by centrifugation at 3500 rpm for 25 min. The PVDF particles were collected and washed three times with hot water at 70℃, and then washed five times with deionized water until the conductivity of the washing solution was 8 μS / cm at room temperature of 25℃, thus obtaining primary PVDF particles. The primary PVDF particles were pre-dried at 60℃ and vacuum degree -0.09MPa for 7 h to remove surface water, and then dried at 85℃ and vacuum degree -0.095MPa for 18 h to reduce the moisture content of the PVDF particles to 0.05%, thus obtaining highly crystalline PVDF.
[0016] Example 3 Pretreatment of the reactor: Evacuate the reactor to -0.095MPa and maintain the pressure for 30min. Purge with nitrogen three times to ensure that the oxygen content in the reactor is 20ppm. Add 55 parts of deionized water to the reactor and stir at 200rpm for 45min. Heat to 50℃ for later use. Feeding and preparation: Dissolve 20 parts of polyvinyl alcohol with a degree of alcoholysis of 80% and 15 parts of hydroxypropyl methylcellulose in 65 parts of hot water at 80℃ to obtain a dispersion solution; slowly add 35 parts of the dispersion solution into the pretreated reactor and stir for 30 minutes until completely dissolved; add 1 part of isopropanol and stir at 360 r / min for 20 minutes; under conditions of 50℃ and 1.0 MPa pressure, slowly pump in 40 parts of VDF monomer. After the VDF monomer is pumped in, close the feed valve, pressurize the reactor with nitrogen to raise the pressure to 2.5 MPa, and stir at 400 rpm for 45 minutes to obtain the preform. Segmented temperature-controlled constant pressure polymerization: The preform is subjected to segmented temperature-controlled constant pressure polymerization to obtain crude PVDF product; The specific process of segmented temperature-controlled constant-pressure polymerization includes: a low-temperature initiation stage, a medium-temperature polymerization stage, and a maturation stage; The specific process of the low-temperature initiation section is as follows: the reactor is heated to 55°C, nitrogen is continuously added to maintain the pressure inside the reactor at 3.0 MPa, 2 parts of diisopropyl peroxide dicarbonate are added, and the mixture is stirred at 120 rpm for 10 min, with a reaction time of 3 h. The specific process of the intermediate temperature polymerization section is as follows: the temperature is slowly increased to 65℃ at a rate of 0.5℃ / h, nitrogen is continuously added to maintain the pressure inside the reactor at 3.5MPa, 2 parts of diisopropyl peroxide are added in 5 equal parts, with each part added at 10min intervals. During the addition, the mixture is continuously stirred at 120rpm. After that, every 3h, the mixture is stirred at 400rpm for 15min. The reaction time is 15h. Curing section: Heat the reactor to 70°C, continuously add nitrogen to maintain the pressure inside the reactor at 3.0 MPa, add 1 part of diisopropyl peroxide, stir at 120 rpm for 10 min, and cure at a constant temperature for 4 h. Post-processing: The PVDF particles in the crude PVDF product were separated from the aqueous phase by centrifugation at 4000 rpm for 30 min. The PVDF particles were collected and washed three times with hot water at 80℃, and then washed five times with deionized water until the conductivity of the washing solution was 10 μS / cm at room temperature of 25℃, thus obtaining primary PVDF particles. The primary PVDF particles were pre-dried at 60℃ and vacuum degree -0.09MPa for 8 h to remove surface water, and then dried at 90℃ and vacuum degree -0.095MPa for 24 h to reduce the moisture content of the PVDF particles to 0.06%, thus obtaining highly crystalline PVDF.
[0017] Example 4 Pretreatment of the reactor: Evacuate the reactor to -0.095MPa and maintain the pressure for 30 minutes. Purge with nitrogen three times to ensure that the oxygen content in the reactor is 10ppm. Add 50 parts of deionized water to the reactor and stir at 180rpm for 35 minutes. Heat to 45℃ for later use. Feeding and preparation: Dissolve 18 parts of polyvinyl alcohol with a degree of hydrolysis of 75% and 12 parts of hydroxypropyl methylcellulose in 60 parts of hot water at 70℃ to obtain a dispersion solution; slowly add 25 parts of the dispersion solution into the pretreated reactor and stir for 30 min until completely dissolved; add 0.5 parts of ethyl acetate and stir at 360 r / min for 18 min; under conditions of 45℃ and 0.8 MPa pressure, slowly pump in 35 parts of VDF monomer. After the VDF monomer is pumped in, close the feed valve, pressurize the reactor with nitrogen to raise the pressure to 2.2 MPa, and stir at 350 rpm for 40 min to obtain the preform. Segmented temperature-controlled constant pressure polymerization: The preform is subjected to segmented temperature-controlled constant pressure polymerization to obtain crude PVDF product; The specific process of segmented temperature-controlled constant-pressure polymerization includes: a low-temperature initiation stage, a medium-temperature polymerization stage, and a maturation stage; The specific process of the low-temperature initiation section is as follows: the reactor is heated to 50°C, nitrogen is continuously added to maintain the pressure inside the reactor at 2.8 MPa, 2 parts of diisopropyl peroxide dicarbonate are added, and the mixture is stirred at 120 rpm for 10 min, with a reaction time of 2 h. The specific process of the intermediate temperature polymerization section is as follows: the temperature is slowly increased to 60℃ at a rate of 0.5℃ / h, nitrogen is continuously added to maintain the pressure inside the reactor at 3.2MPa, 2 parts of diisopropyl peroxide are added in 4 equal parts, with each part added at 10min intervals. During the addition, the mixture is continuously stirred at 120rpm. After that, every 2.5h, the mixture is stirred at 350rpm for 12min. The reaction time is 12h. Curing section: Heat the reactor to 68°C, continuously add nitrogen to maintain the pressure inside the reactor at 2.5 MPa, add 1 part of diisopropyl peroxide, stir at 120 rpm for 10 min, and cure at a constant temperature for 3 h. Post-processing: The PVDF particles in the crude PVDF product were separated from the aqueous phase by centrifugation at 3500 rpm for 25 min. The PVDF particles were collected and washed three times with hot water at 70℃, and then washed five times with deionized water until the conductivity of the washing solution was 8 μS / cm at room temperature of 25℃, thus obtaining primary PVDF particles. The primary PVDF particles were pre-dried at 60℃ and vacuum degree -0.09MPa for 7 h to remove surface water, and then dried at 85℃ and vacuum degree -0.095MPa for 18 h to reduce the moisture content of the PVDF particles to 0.05%, thus obtaining highly crystalline PVDF.
[0018] Example 5 Pretreatment of the reactor: Evacuate the reactor to -0.095MPa and maintain the pressure for 30 minutes. Purge with nitrogen three times to ensure that the oxygen content in the reactor is 10ppm. Add 50 parts of deionized water to the reactor and stir at 180rpm for 35 minutes. Heat to 45℃ for later use. Feeding and preparation: Dissolve 18 parts of polyvinyl alcohol with a degree of hydrolysis of 75% and 12 parts of hydroxypropyl methylcellulose in 60 parts of hot water at 70℃ to obtain a dispersion solution; slowly add 25 parts of the dispersion solution into the pretreated reactor and stir for 30 minutes until completely dissolved; add 0.5 parts of isopropanol and stir at 360 r / min for 18 minutes; under conditions of 45℃ and 0.8 MPa pressure, slowly pump in 35 parts of VDF monomer. After the VDF monomer is pumped in, close the feed valve, pressurize the reactor with nitrogen to raise the pressure to 2.2 MPa, and stir at 350 rpm for 40 minutes to obtain the preform. Segmented temperature-controlled constant pressure polymerization: The preform is subjected to segmented temperature-controlled constant pressure polymerization to obtain crude PVDF product; The specific process of segmented temperature-controlled constant-pressure polymerization includes: a low-temperature initiation stage, a medium-temperature polymerization stage, and a maturation stage; The specific process of the low-temperature initiation section is as follows: the reactor is heated to 50°C, nitrogen is continuously added to maintain the pressure inside the reactor at 2.8 MPa, 2 parts of diethyl peroxide dicarbonate are added, and the mixture is stirred at 120 rpm for 10 min, with a reaction time of 2 h. The specific process of the intermediate temperature polymerization section is as follows: the temperature is slowly increased to 60℃ at a rate of 0.5℃ / h, nitrogen is continuously added to maintain the pressure inside the reactor at 3.2MPa, 2 parts of diethyl peroxide are added in 4 equal parts, with each part added at 10min intervals. During the addition, the mixture is continuously stirred at 120rpm. After that, every 2.5h, the mixture is stirred at 350rpm for 12min. The reaction time is 12h. Curing section: Heat the reactor to 68°C, continuously add nitrogen to maintain the pressure inside the reactor at 2.5 MPa, add 1 part of diethyl peroxide, stir at 120 rpm for 10 min, and cure at a constant temperature for 3 h. Post-processing: The PVDF particles in the crude PVDF product were separated from the aqueous phase by centrifugation at 3500 rpm for 25 min. The PVDF particles were collected and washed three times with hot water at 70℃, and then washed five times with deionized water until the conductivity of the washing solution was 8 μS / cm at room temperature of 25℃, thus obtaining primary PVDF particles. The primary PVDF particles were pre-dried at 60℃ and vacuum degree -0.09MPa for 7 h to remove surface water, and then dried at 85℃ and vacuum degree -0.095MPa for 18 h to reduce the moisture content of the PVDF particles to 0.05%, thus obtaining highly crystalline PVDF.
[0019] Comparative Example 1 Pretreatment of the reactor: Evacuate the reactor to -0.095MPa and maintain the pressure for 30 minutes. Purge with nitrogen three times to ensure that the oxygen content in the reactor is 10ppm. Add 50 parts of deionized water to the reactor and stir at 180rpm for 35 minutes. Heat to 45℃ for later use. Feeding and preparation: 25 parts of polyvinyl alcohol with a degree of hydrolysis of 75% were added to the pretreated reactor and stirred for 30 minutes until completely dissolved; 0.5 parts of isopropanol were added and stirred at 360 r / min for 18 minutes; under the conditions of 45℃ and 0.8 MPa pressure, 35 parts of VDF monomer were slowly pumped in. After the VDF monomer pumping was completed, the feed valve was closed, and nitrogen was applied to raise the pressure in the reactor to 2.2 MPa. The mixture was stirred at 350 rpm for 40 minutes to obtain the preform. Segmented temperature-controlled constant pressure polymerization: The preform is subjected to segmented temperature-controlled constant pressure polymerization to obtain crude PVDF product; The specific process of segmented temperature-controlled constant-pressure polymerization includes: a low-temperature initiation stage, a medium-temperature polymerization stage, and a maturation stage; The specific process of the low-temperature initiation section is as follows: the reactor is heated to 50°C, nitrogen is continuously added to maintain the pressure inside the reactor at 2.8 MPa, 2 parts of diisopropyl peroxide dicarbonate are added, and the mixture is stirred at 120 rpm for 10 min, with a reaction time of 2 h. The specific process of the intermediate temperature polymerization section is as follows: the temperature is slowly increased to 60℃ at a rate of 0.5℃ / h, nitrogen is continuously added to maintain the pressure inside the reactor at 3.2MPa, 2 parts of diisopropyl peroxide are added in 4 equal parts, with each part added at 10min intervals. During the addition, the mixture is continuously stirred at 120rpm. After that, every 2.5h, the mixture is stirred at 350rpm for 12min. The reaction time is 12h. Curing section: Heat the reactor to 68°C, continuously add nitrogen to maintain the pressure inside the reactor at 2.5 MPa, add 1 part of diisopropyl peroxide, stir at 120 rpm for 10 min, and cure at a constant temperature for 3 h. Post-processing: The PVDF particles in the crude PVDF product were separated from the aqueous phase by centrifugation at 3500 rpm for 25 min. The PVDF particles were collected and washed three times with hot water at 70℃, and then washed five times with deionized water until the conductivity of the washing solution was 8 μS / cm at room temperature of 25℃, thus obtaining primary PVDF particles. The primary PVDF particles were pre-dried at 60℃ and vacuum degree -0.09MPa for 7 h to remove surface water, and then dried at 85℃ and vacuum degree -0.095MPa for 18 h to reduce the moisture content of the PVDF particles to 0.05%, thus obtaining highly crystalline PVDF.
[0020] Comparative Example 2 Pretreatment of the reactor: Evacuate the reactor to -0.095MPa and maintain the pressure for 30 minutes. Purge with nitrogen three times to ensure that the oxygen content in the reactor is 10ppm. Add 50 parts of deionized water to the reactor and stir at 180rpm for 35 minutes. Heat to 45℃ for later use. Feeding and preparation: 25 parts of hydroxypropyl methylcellulose were added to the pretreated reactor and stirred for 30 minutes until completely dissolved; 0.5 parts of isopropanol were added and stirred at 360 r / min for 18 minutes; under the conditions of 45℃ and 0.8 MPa pressure, 35 parts of VDF monomer were slowly pumped in. After the VDF monomer pumping was completed, the feed valve was closed, and nitrogen was applied to raise the pressure in the reactor to 2.2 MPa. The mixture was stirred at 350 rpm for 40 minutes to obtain the preform. Segmented temperature-controlled constant pressure polymerization: The preform is subjected to segmented temperature-controlled constant pressure polymerization to obtain crude PVDF product; The specific process of segmented temperature-controlled constant-pressure polymerization includes: a low-temperature initiation stage, a medium-temperature polymerization stage, and a maturation stage; The specific process of the low-temperature initiation section is as follows: the reactor is heated to 50°C, nitrogen is continuously added to maintain the pressure inside the reactor at 2.8 MPa, 2 parts of diisopropyl peroxide dicarbonate are added, and the mixture is stirred at 120 rpm for 10 min, with a reaction time of 2 h. The specific process of the intermediate temperature polymerization section is as follows: the temperature is slowly increased to 60℃ at a rate of 0.5℃ / h, nitrogen is continuously added to maintain the pressure inside the reactor at 3.2MPa, 2 parts of diisopropyl peroxide are added in 4 equal parts, with each part added at 10min intervals. During the addition, the mixture is continuously stirred at 120rpm. After that, every 2.5h, the mixture is stirred at 350rpm for 12min. The reaction time is 12h. Curing section: Heat the reactor to 68°C, continuously add nitrogen to maintain the pressure inside the reactor at 2.5 MPa, add 1 part of diisopropyl peroxide, stir at 120 rpm for 10 min, and cure at a constant temperature for 3 h. Post-processing: The PVDF particles in the crude PVDF product were separated from the aqueous phase by centrifugation at 3500 rpm for 25 min. The PVDF particles were collected and washed three times with hot water at 70℃, and then washed five times with deionized water until the conductivity of the washing solution was 8 μS / cm at room temperature of 25℃, thus obtaining primary PVDF particles. The primary PVDF particles were pre-dried at 60℃ and vacuum degree -0.09MPa for 7 h to remove surface water, and then dried at 85℃ and vacuum degree -0.095MPa for 18 h to reduce the moisture content of the PVDF particles to 0.05%, thus obtaining highly crystalline PVDF.
[0021] Comparative Example 3 Pretreatment of the reactor: Evacuate the reactor to -0.095MPa and maintain the pressure for 30 minutes. Purge with nitrogen three times to ensure that the oxygen content in the reactor is 10ppm. Add 50 parts of deionized water to the reactor and stir at 180rpm for 35 minutes. Heat to 45℃ for later use. Feeding and preparation: Dissolve 18 parts of polyvinyl alcohol with a degree of hydrolysis of 75% and 12 parts of hydroxypropyl methylcellulose in 60 parts of hot water at 70℃ to obtain a dispersion solution; slowly add 25 parts of the dispersion solution into the pretreated reactor and stir for 30 minutes until completely dissolved; add 0.5 parts of isopropanol and stir at 360 r / min for 18 minutes; under conditions of 45℃ and 0.8 MPa pressure, slowly pump in 35 parts of VDF monomer. After the VDF monomer is pumped in, close the feed valve, pressurize the reactor with nitrogen to raise the pressure to 2.2 MPa, and stir at 350 rpm for 40 minutes to obtain the preform. Temperature-controlled and constant-pressure polymerization: The preform is polymerized under controlled temperature and constant pressure to obtain crude PVDF product; The specific process of temperature-controlled and constant-pressure polymerization includes: heating the reactor to 50°C, continuously adding nitrogen to maintain the pressure inside the reactor at 2.8 MPa, adding 5 parts of diisopropyl peroxide, stirring at 120 rpm for 10 min, and reacting for 2 h. Post-processing: The PVDF particles in the crude PVDF product were separated from the aqueous phase by centrifugation at 3500 rpm for 25 min. The PVDF particles were collected and washed three times with hot water at 70℃, and then washed five times with deionized water until the conductivity of the washing solution was 8 μS / cm at room temperature of 25℃, thus obtaining primary PVDF particles. The primary PVDF particles were pre-dried at 60℃ and vacuum degree -0.09MPa for 7 h to remove surface water, and then dried at 85℃ and vacuum degree -0.095MPa for 18 h to reduce the moisture content of the PVDF particles to 0.05%, thus obtaining highly crystalline PVDF.
[0022] Comparative Example 4 Pretreatment of the reactor: Evacuate the reactor to -0.095MPa and maintain the pressure for 30 minutes. Purge with nitrogen three times to ensure that the oxygen content in the reactor is 10ppm. Add 50 parts of deionized water to the reactor and stir at 180rpm for 35 minutes. Heat to 45℃ for later use. Feeding and preparation: Dissolve 18 parts of polyvinyl alcohol with a degree of hydrolysis of 75% and 12 parts of hydroxypropyl methylcellulose in 60 parts of hot water at 70℃ to obtain a dispersion solution; slowly add 25 parts of the dispersion solution into the pretreated reactor and stir for 30 minutes until completely dissolved; add 0.5 parts of isopropanol and stir at 360 r / min for 18 minutes; under conditions of 45℃ and 0.8 MPa pressure, slowly pump in 35 parts of VDF monomer. After the VDF monomer is pumped in, close the feed valve, pressurize the reactor with nitrogen to raise the pressure to 2.2 MPa, and stir at 350 rpm for 40 minutes to obtain the preform. Segmented temperature-controlled constant pressure polymerization: The preform is subjected to segmented temperature-controlled constant pressure polymerization to obtain crude PVDF product; The specific process of segmented temperature-controlled constant-pressure polymerization includes: a low-temperature initiation stage and a medium-temperature polymerization stage. The specific process of the low-temperature initiation section is as follows: the reactor is heated to 50°C, nitrogen is continuously added to maintain the pressure inside the reactor at 2.8 MPa, 2 parts of diisopropyl peroxide dicarbonate are added, and the mixture is stirred at 120 rpm for 10 min, with a reaction time of 2 h. The specific process of the intermediate temperature polymerization section is as follows: the temperature is slowly increased to 60℃ at a rate of 0.5℃ / h, nitrogen is continuously added to maintain the pressure inside the reactor at 3.2MPa, 3 parts of diisopropyl peroxide are added in 4 equal parts, with each part added at 10min intervals. During the addition, the mixture is continuously stirred at 120rpm. After that, every 2.5h, the mixture is stirred at 350rpm for 12min. The reaction time is 12h. Post-processing: The PVDF particles in the crude PVDF product were separated from the aqueous phase by centrifugation at 3500 rpm for 25 min. The PVDF particles were collected and washed three times with hot water at 70℃, and then washed five times with deionized water until the conductivity of the washing solution was 8 μS / cm at room temperature of 25℃, thus obtaining primary PVDF particles. The primary PVDF particles were pre-dried at 60℃ and vacuum degree -0.09MPa for 7 h to remove surface water, and then dried at 85℃ and vacuum degree -0.095MPa for 18 h to reduce the moisture content of the PVDF particles to 0.05%, thus obtaining highly crystalline PVDF.
[0023] Performance testing (a) In accordance with GB / T19466.3-2025 "Differential Scanning Calorimetry (DSC) for Plastics - Part 3: Determination of Melting and Crystallization Temperatures and Enthalpy", the crystallinity and melting point Tm of the high-crystallinity PVDF prepared by the methods of Examples 1-5 and Comparative Examples 1-4 were tested. The test results are shown in Table 1.
[0024] Table 1 As can be seen from Table 1, the crystallinity of the examples is 65%-75%, which is generally at a high level of crystallinity; the crystallinity of the comparative examples is 61%-64%, which is lower than that of the examples. The crystallinity of the examples is generally 3-14 percentage points higher than that of the comparative examples, which indicates that the preparation method in this invention can effectively improve the degree of PVDF crystallization. The melting point of the example is 165℃-175℃; the melting point of the comparative example is 161℃-164℃, which is significantly lower overall. The melting point increases with increasing crystallinity, proving that the PVDF crystals in the example are more regular, the lamellar crystals are more perfect, and the heat resistance is better.
[0025] (ii) In accordance with GB / T1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics", the tensile strength and elongation at break of the high crystallinity PVDF prepared by the methods of Example 2 and Comparative Examples 1-4 were tested. The test results are shown in Table 2.
[0026] Table 2 As can be seen from Table 2, the tensile strength of Example 2 reached 58 MPa; the tensile strength of Comparative Examples 1-4 was only 51-53 MPa. The tensile strength of Example 2 was 5-7 MPa higher than that of the Comparative Examples, indicating that the highly crystalline structure makes the PVDF molecular chains more regularly arranged and the cohesive energy higher, which significantly enhances the ability to resist external damage. Example 2 showed an elongation at break of 45%; compared to Comparative Examples 1-4, the elongation at break was only 36%-41%. While the crystallinity and strength increased, the elongation at break remained at a higher level, indicating that the PVDF prepared by this invention has a better match between rigidity and toughness and does not show obvious embrittlement due to the increase in crystallinity.
[0027] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.
Claims
1. A highly crystallinity PVDF, characterized in that, It includes the following raw materials by weight: 30-40 parts VDF monomer, 45-55 parts deionized water, 20-35 parts dispersion solution, 1-5 parts initiator and 0.1-1 parts chain transfer agent.
2. The highly crystallinity PVDF according to claim 1, characterized in that, By weight, the dispersion solution comprises 15-20 parts of dispersant A, 10-15 parts of dispersant B, and 55-65 parts of hot water at 60-80°C. Dispersant A is polyvinyl alcohol with a degree of alcoholysis of 72-80%, and dispersant B is hydroxypropyl methylcellulose.
3. The highly crystallinity PVDF according to claim 1, characterized in that, The initiator is selected from one or more of diisopropyl peroxide dicarbonate, diethyl peroxide dicarbonate, and tert-butyl peroxypentanoate.
4. The highly crystallinity PVDF according to claim 1, characterized in that, The chain transfer agent is selected from one or more of isopropanol, ethyl acetate, and dimethyl carbonate.
5. A method for preparing highly crystallinity PVDF according to any one of claims 1-4, characterized in that, Includes the following steps: Pretreatment of the reactor: Evacuate the reactor to -0.095MPa and maintain the pressure for 30 minutes. Purge with nitrogen 2-3 times to ensure that the oxygen content in the reactor is 10-20ppm. Add deionized water to the reactor and stir at 120-200rpm for 30-45 minutes. Heat to 40-50℃ for later use. Preparation of materials: Dissolve dispersant A and dispersant B in hot water at 60-80℃ to obtain a dispersion solution; Slowly add the dispersion solution into the pretreated reaction vessel and stir for 30 minutes until completely dissolved. Add the chain transfer agent and stir at 360 rpm for 15-20 minutes. Under conditions of 40-50℃ and 0.5-1.0MPa pressure, VDF monomer is slowly pumped in. After the pumping of VDF monomer is completed, the feed valve is closed, and nitrogen is applied to raise the pressure inside the reactor to 2.0-2.5MPa. The mixture is stirred at 300-400rpm for 30-45min to obtain the preform. Segmented temperature-controlled constant pressure polymerization: The preform is subjected to segmented temperature-controlled constant pressure polymerization to obtain crude PVDF product; Post-processing: Centrifuge at 3000-4000 rpm for 15-30 min to separate PVDF particles from the aqueous phase in the crude PVDF product; collect the PVDF particles, wash them 2-3 times with hot water at 60-80℃, and then wash them 3-5 times with deionized water until the conductivity of the washing liquid is 5-10 μS / cm at room temperature of 25℃ to obtain primary PVDF particles; pre-dry the primary PVDF particles at 60℃ and vacuum degree -0.09MPa for 6-8 h to remove surface water, and then dry them at 80-90℃ and vacuum degree -0.095MPa for 12-24 h to make the moisture content of the PVDF particles 0.03-0.06% to obtain highly crystalline PVDF.
6. The method for preparing highly crystallinity PVDF according to claim 5, characterized in that, The specific process of segmented temperature-controlled constant-pressure polymerization includes: a low-temperature initiation stage, a medium-temperature polymerization stage, and a maturation stage; The specific process of the low-temperature initiation section is as follows: the reactor is heated to 45-55℃, nitrogen is continuously added to maintain the pressure inside the reactor at 2.5-3.0MPa, 2 / 5 of the total amount of initiator is added, and the reactor is stirred at 120rpm for 10min, with a reaction time of 1-3h. The specific process of the intermediate temperature polymerization section is as follows: slowly raise the temperature to 55-65℃ at a rate of 0.5℃ / h, continuously supplement nitrogen to maintain the pressure inside the reactor at 3.0-3.5MPa, add 2 / 5 of the total amount of initiator in 3-5 equal parts, with each part added at 10min intervals, and continuously stir at 120rpm during the addition. After that, stir at 300-400rpm for 10-15min every 2-3h, and the reaction time is 8-15h. Curing stage: Heat the reactor to 65-70℃, continuously add nitrogen to maintain the pressure inside the reactor at 2.5-3.0MPa, add the remaining initiator, stir at 120rpm for 10min, and cure at a constant temperature for 2-4h.