CN112679647B - Method for preparing meltable polytetrafluoroethylene emulsion with high solid content by miniemulsion polymerization - Google Patents
Method for preparing meltable polytetrafluoroethylene emulsion with high solid content by miniemulsion polymerization Download PDFInfo
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Abstract
The invention relates to the technical field of fluorine-containing polymers, in particular to a method for preparing meltable polytetrafluoroethylene emulsion with high solid content by a miniemulsion polymerization method. The method for preparing the meltable polytetrafluoroethylene emulsion with high solid content by the miniemulsion polymerization comprises the following steps: (1) Dissolving a dispersing agent in deionized water, and uniformly stirring to form a water phase; (2) Mixing and stirring a perfluoroalkyl vinyl ether monomer, an auxiliary emulsifier, a chain transfer agent and an organic auxiliary agent to form an oil phase; (3) Mixing the water phase and the oil phase, pre-emulsifying, and further emulsifying and dispersing to obtain a miniemulsion; (4) Continuously introducing a tetrafluoroethylene monomer into the miniemulsion, adding an initiator to carry out polymerization reaction, and stopping the reaction after the theoretical solid content of the target product is reached to obtain the meltable polytetrafluoroethylene emulsion of the target product. The invention improves the solid content of the emulsion and prepares the emulsion with high solid content in one step on the premise of ensuring the stability of the emulsion.
Description
Technical Field
The invention relates to the technical field of fluorine-containing polymers, in particular to a method for preparing meltable polytetrafluoroethylene emulsion with high solid content by a miniemulsion polymerization method.
Background
The emulsion with high solid content has the advantages of high production efficiency, short film forming time, low storage and transportation cost and the like. In most cases, the solid content of industrial emulsions is less than 55%, and above this limit, the viscosity of the emulsion increases dramatically, the self-acceleration during the reaction is more severe and shear-resistant, and stable polymer emulsions are not easily prepared. Increasing the particle size of the emulsion and widening the particle size distribution are effective ways to obtain the emulsion with high solid content.
For the polymer emulsion, if the small emulsion particles with proper particle size and quantity can be filled in the gaps of the large emulsion particles or the emulsion particles are deformed, the emulsion is in multi-element particle size distribution, the viscosity of the emulsion is reduced, and the solid content of the polymer can be further improved.
The miniemulsion is an emulsion polymerization method which is carried out by a monomer droplet dispersion system formed by a homogenization mode such as ultrasonic or high shearing force and the like under the combined action of an emulsifier, a co-emulsifier and the like in a droplet nucleation mode, and the diameter of the formed droplets is 50-1000nm. Miniemulsion polymerization differs from the micellar nucleation or homogeneous nucleation mechanisms of conventional emulsion polymerization, primarily monomer droplet nucleation.
Miniemulsion polymerization not only has high emulsion stability, but also the final polymer system exhibits polydispersity based on the stable polydisperse monomer droplet system formed before polymerization and the unique droplet nucleation site. Thus, miniemulsion polymerization has natural advantages in the preparation of high solids emulsions.
The PFA concentrated dispersion solution on the market at present has a solid content of 30-50% generally, and most of the PFA concentrated dispersion solution is obtained by a cloud point sedimentation method and a vacuum concentration method. At present, no report about the preparation of high-solid-content meltable polytetrafluoroethylene emulsion by adopting a miniemulsion polymerization method is found.
Disclosure of Invention
The invention aims to provide a method for preparing meltable polytetrafluoroethylene emulsion with high solid content by miniemulsion polymerization, which can improve the solid content of the emulsion and further improve the efficiency of product production equipment on the premise of ensuring the stability of the emulsion, not only can prepare the emulsion with high solid content in one step, but also can save the environmental protection problem of treating high COD supernatant fluid by using a large amount of emulsifying agent in the later period and solve the problems of high energy consumption, long time and high production cost compared with the traditional method for preparing concentrated dispersion by using a sedimentation method and a vacuum concentration process.
The method for preparing the meltable polytetrafluoroethylene emulsion with high solid content by the miniemulsion polymerization method comprises the following steps:
(1) Dissolving a dispersing agent in deionized water, and uniformly stirring to form a water phase;
(2) Mixing and stirring a perfluoroalkyl vinyl ether monomer, an auxiliary emulsifier, a chain transfer agent and an organic auxiliary agent to form an oil phase;
(3) Mixing the water phase and the oil phase, pre-emulsifying, and further emulsifying and dispersing to obtain a miniemulsion;
(4) Continuously introducing a tetrafluoroethylene monomer into the miniemulsion, adding an initiator to carry out polymerization reaction, and stopping the reaction after the theoretical solid content of the target product is reached to obtain the meltable polytetrafluoroethylene emulsion of the target product.
In the step (1), the dispersing agent is a known fluorine-containing surfactant in the art, and may be a single surfactant or a mixed surfactant, such as perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorodecanoic acid, perfluorooctanesulfonic acid, perfluoroheptanesulfonic acid, perfluoro-2, 5-dimethyl-3, 6-dioxanonanoic acid, nonylphenol polyoxyethylene ether, and the like, and other commercially available fluorine-containing surfactants can be used as the dispersing agent used in the method of the present invention; the dosage of the dispersant is 2-5wt% of the dry material of the target product polytetrafluoroethylene emulsion.
In the step (1), the mass ratio of the deionized water to the tetrafluoroethylene monomer is 0.5-3.
In the step (2), the preferable perfluoroalkyl vinyl ether monomer is perfluoro-n-propyl vinyl ether, and the dosage of the perfluoroalkyl vinyl ether monomer is 1 to 15 percent of the mass of the tetrafluoroethylene monomer.
In the step (2), the coemulsifier has a structural formula of R f -CF 3 Of perfluorinated long-chain alkanes of (4), wherein R f Is a linear or branched perfluoroalkyl group having 6 to 10 carbon atoms, and the amount of the perfluoroalkyl group is 0.5 to 5 percent of the mass of the tetrafluoroethylene monomer.
In step (2), the chain transfer agent is a conventional chain transfer agent known in the art, such as hydrogen, methane, ethane, methanol, cyclohexane, difluoromethane, etc., and other hydrogen-containing substances can be used as the chain transfer agent in the polymerization reaction; the mass ratio of the chain transfer agent to the tetrafluoroethylene monomer is 1.
In the step (2), the organic assistant is perfluoroalkane or perfluorocycloalkane, preferably one or more of perfluorooctane, perfluoroheptane and perfluorocyclohexane, and the dosage ratio of the organic assistant to the perfluoroalkyl vinyl ether is 0.5-5.
In the step (3), pre-emulsification adopts a stirring mode, the stirring speed is 30-100r/min, and the stirring time is 10-100min; the emulsification and dispersion adopts an ultrasonic or high shear force action mode, the emulsification and dispersion temperature is 0-10 ℃, and the emulsification and dispersion time is 5-200min.
In the step (4), the initiator is one of perfluoroacyl peroxide, preferably perfluorobutyryl peroxide, perfluorohexanoyl peroxide, perfluoro (3-oxapentanoyl) peroxide, perfluoro (3, 6-dioxaoctanoyl) peroxide, perfluoro (3, 6, 9-trioxaundecanoyl) peroxide, perfluoro (2-methyl-3-oxahexanoyl) peroxide, perfluoro (2, 5-dimethyl-3, 6-dioxanonanoyl) peroxide or perfluoro (2, 5, 8-trimethyl-3, 6, 9-trioxaundecanoyl) peroxide; the amount used may depend on the desired melt index.
In the step (4), the polymerization reaction temperature is 40-65 ℃ and the pressure is 1-2MPa. The solid content of the target product is 30-60wt%. The polymerization is initiated at low temperature, so that the stability of the miniemulsion is good and the reaction is stable.
Specifically, the operation of the step (4) is as follows:
transferring the miniemulsion into a polymerization kettle, removing oxygen by replacement until the oxygen content is less than or equal to 20ppm, introducing a tetrafluoroethylene monomer into the polymerization kettle, maintaining the pressure of the polymerization kettle at 1-2MPa, heating the miniemulsion to 40-65 ℃, and adding an initiator to initiate polymerization; maintaining the polymerization temperature of 40-65 ℃, continuously introducing a tetrafluoroethylene monomer into the polymerization kettle to maintain the reaction pressure until the theoretical solid content of the target product is reached, stopping the reaction, slowly cooling to room temperature, and discharging to obtain the target product, namely the meltable polytetrafluoroethylene emulsion.
Compared with the prior art, the invention has the following beneficial effects:
(1) The invention adopts a miniemulsion polymerization method to ensure that the particle size of the emulsion presents polydispersibility, and the emulsion with high solid content is prepared in one step;
(2) The initiator perfluoroacyl peroxide used in the invention is a low-temperature initiator, and polymerization is initiated at low temperature, so that the miniemulsion has good stability and stable reaction;
(3) Compared with the traditional method for preparing the concentrated dispersion liquid by using a sedimentation method and a vacuum concentration process, the method disclosed by the invention has the advantages that the environmental protection problem of treating the supernatant liquid with high COD (chemical oxygen demand) by using a large amount of emulsifying agent in the later stage is saved, and the problems of high energy consumption, long time and high production cost are solved.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the practice of the invention.
The% referred to in the present invention means mass% unless otherwise specified. Unless otherwise specified, the term "solid content" as used herein refers to the mass percentage of the emulsion or coating material remaining after drying under specified conditions.
Example 1
(1) 71g of ammonium perfluorooctanoate is dissolved in 5L of deionized water and uniformly stirred to form a water phase;
(2) Mixing 100g of perfluoro-n-propyl vinyl ether monomer, 50g of perfluorooctane, 0.5g of methanol and 100g of perfluoroheptane, and stirring to form an oil phase;
(3) Mixing the water phase and the oil phase, stirring at 50r/min, pre-emulsifying for 30min, and ultrasonically dispersing in ice water bath for 120min to obtain miniemulsion;
(4) Transferring the miniemulsion into a 10L polymerization kettle, removing oxygen by replacement until the oxygen content is less than or equal to 20ppm, introducing a tetrafluoroethylene monomer into the polymerization kettle, maintaining the pressure of the polymerization kettle at 1.5MPa, heating the miniemulsion to 50 ℃, and adding 28.5g of perfluorohexanoyl peroxide to initiate polymerization; maintaining the polymerization temperature at 50 ℃, continuously introducing tetrafluoroethylene monomer into the polymerization kettle to maintain the reaction pressure until the addition of the tetrafluoroethylene monomer is 2.85kg, and stopping the reaction after the theoretical solid content of the target product is 30wt%, slowly cooling to room temperature, and discharging to obtain the target product, namely the meltable polytetrafluoroethylene emulsion.
Example 2
(1) Dissolving 117g of ammonium perfluorooctanoate in 5L of deionized water, and uniformly stirring to form a water phase;
(2) Mixing 312g of perfluoro-n-propyl vinyl ether monomer, 80g of perfluorooctane, 1g of methanol and 200g of perfluoroheptane, and stirring to form an oil phase;
(3) Mixing the water phase and the oil phase, stirring at 50r/min, pre-emulsifying for 30min, and ultrasonically dispersing in ice water bath for 120min to obtain miniemulsion;
(4) Transferring the miniemulsion into a 10L polymerization kettle, removing oxygen by replacement until the oxygen content is less than or equal to 20ppm, introducing a tetrafluoroethylene monomer into the polymerization kettle, maintaining the pressure of the polymerization kettle at 1.5MPa, heating the miniemulsion to 50 ℃, and adding 46.87g of perfluorohexanoyl peroxide to initiate polymerization; maintaining the polymerization temperature at 50 ℃, continuously introducing a tetrafluoroethylene monomer into the polymerization kettle to maintain the reaction pressure until the addition of the tetrafluoroethylene monomer is 4.68kg, stopping the reaction after the theoretical solid content of the target product is 50wt%, slowly cooling to room temperature, and discharging to obtain the target product, namely the meltable polytetrafluoroethylene emulsion.
Example 3
(1) Dissolving 151g of ammonium perfluorooctanoate in 5L of deionized water, and uniformly stirring to form a water phase;
(2) 375g of perfluoro-n-propyl vinyl ether monomer, 108g of perfluorooctane, 1.2g of methanol and 240g of perfluoroheptane are mixed and stirred to form an oil phase;
(3) Mixing the water phase and the oil phase, stirring at 50r/min, pre-emulsifying for 30min, and ultrasonically dispersing in ice water bath for 120min to obtain miniemulsion;
(4) Transferring the miniemulsion into a 10L polymerization kettle, removing oxygen by replacement until the oxygen content is less than or equal to 20ppm, introducing a tetrafluoroethylene monomer into the polymerization kettle, maintaining the pressure of the polymerization kettle at 1.5MPa, heating the miniemulsion to 50 ℃, and adding 57g of perfluorohexanoyl peroxide to initiate polymerization; maintaining the polymerization temperature at 50 ℃, continuously introducing tetrafluoroethylene monomer into the polymerization kettle to maintain the reaction pressure until the addition of the tetrafluoroethylene monomer is 5.7kg, and stopping the reaction after the theoretical solid content of the target product is 60wt%, slowly cooling to room temperature, and discharging to obtain the target product, namely the meltable polytetrafluoroethylene emulsion.
Comparative example 1
Adding 71g of ammonium perfluorooctanoate, 100g of perfluoro-n-propyl vinyl ether, 0.5g of methanol, 100g of perfluoroheptane and 5L of deionized water into a 10L polymerization kettle, and uniformly stirring; after the oxygen content is reduced to less than or equal to 20ppm by displacement, introducing a tetrafluoroethylene monomer into a polymerization kettle, maintaining the pressure of the polymerization kettle at 1.5MPa, heating the emulsion to 50 ℃, and adding 28.5g of perfluorohexanoyl peroxide to initiate polymerization; maintaining the polymerization temperature at 50 ℃, continuously introducing tetrafluoroethylene monomer into the polymerization kettle to maintain the reaction pressure until the addition of the tetrafluoroethylene monomer is 2.85kg, and stopping the reaction after the theoretical solid content of the target product is 30wt%, slowly cooling to room temperature, and discharging to obtain the target product, namely the meltable polytetrafluoroethylene emulsion.
Comparative example 2
Adding 117g of ammonium perfluorooctanoate, 312g of perfluoro-n-propyl vinyl ether, 1g of methanol, 200g of perfluoroheptane and 5L of deionized water into a 10L polymerization kettle, and uniformly stirring; after the oxygen content is reduced to less than or equal to 20ppm by displacement, introducing a tetrafluoroethylene monomer into a polymerization kettle, maintaining the pressure of the polymerization kettle at 1.5MPa, heating the emulsion to 50 ℃, and adding 46.87g of perfluorohexanoyl peroxide to initiate polymerization; maintaining the polymerization temperature at 50 ℃, continuously introducing a tetrafluoroethylene monomer into the polymerization kettle to maintain the reaction pressure until the addition of the tetrafluoroethylene monomer is 4.68kg, and stopping the reaction after the theoretical solid content of the target product is 50wt%, slowly cooling to room temperature, and discharging to obtain the target product, namely the meltable polytetrafluoroethylene emulsion.
The test results are shown in table 1.
TABLE 1 results of property test of polytetrafluoroethylene emulsions prepared in examples 1 to 3 and comparative examples 1 to 2
Claims (6)
1. A method for preparing meltable polytetrafluoroethylene emulsion with high solid content by miniemulsion polymerization is characterized by comprising the following steps: the method comprises the following steps:
(1) Dissolving a dispersing agent in deionized water, and uniformly stirring to form a water phase;
(2) Mixing and stirring a perfluoroalkyl vinyl ether monomer, an auxiliary emulsifier, a chain transfer agent and an organic auxiliary agent to form an oil phase;
(3) Mixing the water phase and the oil phase, pre-emulsifying, and further emulsifying and dispersing to obtain a miniemulsion;
(4) Continuously introducing a tetrafluoroethylene monomer into the miniemulsion, adding an initiator to carry out polymerization reaction, wherein the polymerization reaction temperature is 40-65 ℃, the pressure is 1-2MPa, and the reaction is stopped after the theoretical solid content of the target product is reached, so that the fusible polytetrafluoroethylene emulsion of the target product is obtained, wherein the solid content of the target product is 30-60wt%;
in the step (3), pre-emulsification is carried out in a stirring mode, the stirring speed is 30 to 100r/min, and the stirring time is 10-100min; the emulsification and dispersion adopt an ultrasonic or high shear force action mode, the emulsification and dispersion temperature is 0-10 ℃, and the emulsification and dispersion time is 5-200min;
in the step (4), the initiator is perfluoroacyl peroxide.
2. The process for preparing high solids meltable polytetrafluoroethylene emulsion by miniemulsion polymerization according to claim 1, wherein: in the step (1), the dispersant is fluorine-containing surfactant, and the dosage of the fluorine-containing surfactant is 2-5wt% of the dry material of the target product polytetrafluoroethylene emulsion; the mass ratio of the deionized water to the tetrafluoroethylene monomer is 0.5 to 3.
3. A process for preparing a high solids meltable polytetrafluoroethylene emulsion according to claim 1, said process comprising: in the step (2), the perfluoroalkyl vinyl ether monomer is perfluoro-n-propyl vinyl ether, and the dosage of the perfluoroalkyl vinyl ether monomer is 1 to 15 percent of the mass of the tetrafluoroethylene monomer.
4. The process for preparing high solids meltable polytetrafluoroethylene emulsion by miniemulsion polymerization according to claim 1, wherein: in the step (2), the coemulsifier has a structural formula of R f -CF 3 Of perfluorinated long-chain alkanes of (4), wherein R f Is a linear or branched perfluoroalkyl group with 6 to 10 carbon atoms, and the amount of the perfluoroalkyl group is 0.5 to 5 percent of the mass of the tetrafluoroethylene monomer.
5. The process for preparing high solids meltable polytetrafluoroethylene emulsion by miniemulsion polymerization according to claim 1, wherein: in the step (2), the mass ratio of the chain transfer agent to the tetrafluoroethylene monomer is 1 to 500-1.
6. A process for preparing a high solids meltable polytetrafluoroethylene emulsion according to claim 1, said process comprising: the organic auxiliary agent is perfluoroalkane or perfluorocycloalkane, and the dosage ratio of the organic auxiliary agent to the perfluoroalkyl vinyl ether is 0.5-5.
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