DESC:FIELD
The present disclosure relates to a process for the preparation of fluoropolymers. Particularly, the present disclosure relates to a process of polymerization of at least one fluoromonomer by using a non-fluorinated surfactant. More particularly, the present disclosure relates to a process for the preparation of fluoropolymers by using an alkali metal salt C8-C15 alkyl benzene sulfonic acid as a non-fluorinated hydrocarbon containing surfactant.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicates otherwise.
Standard specific gravity (SSG) is the property usually used to measure the relative molecular mass of the polymers used in the fluoropolymer industry. SSG is determined in accordance with the ASTM D4895 method. To perform the test, sample is allowed to go through sintering and cooling cycle with the appropriate sintering schedule as described in ASTM D4895.
Extended specific gravity (ESG) gives the indication of thermal stability. It may be measured by ASTM D4895. To determine the ESG, the fluoropolymer specimen is first moulded according to ASTM D4895. For ESG, sample is kept for extended period at sintering temperature as compared to sintering time measurement of SSG.
Thermal instability index (TII) refers to a measure of the decrease in the molecular weight of fluoropolymer material which has been heated for a prolonged period of time. The thermal instability index (TII) gives an indication of how a resin resists degradation during extended period of heating at sintering temperatures. It is measured by ASTM D4895. This test method compares the SSG of a resin to its extended specific gravity.
Stretching void index (SVI) refers to a measure of the change in specific gravity of fluoropolymer material which has been subjected to tensile strain.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Fluoropolymers are generally made by an aqueous dispersion polymerization process. The aqueous dispersion polymerization of fluorine containing monomers typically requires a surfactant capable of emulsifying both the reactants and the reaction products for the duration of the polymerization reaction. The surfactant of choice in the synthesis of fluoropolymers is generally a perfluorinated surfactant or a partially fluorinated surfactant. Although, the perfluorinated surfactants (perfluoroalkyl surfactants) are better in lowering the surface tension of water as compared to hydrocarbon surfactants, the fluorinated surfactants persist in the environment for a longer duration and have been detected in humans and wildlife. Moreover, the fluorosurfactants are expensive specialized materials.
Because of the high stability of the fluorinated surfactants and their resistance to chemical degradation, fluorosurfactants have the potential to accumulate in the environment and in organisms. Also, the high degree of fluorination of the surfactant avoids atom transfer between a growing polymer chain and the surfactant during polymerization that results in lowered molecular weights in the product and likely inhibition of the reaction. In order to address this issue, several different approaches have been attempted to reduce or eliminate the use of perfluoroalkyl surfactants in the polymerization of halogen-containing monomers.
Conventionally, an attempt to reduce the amount of perfluoroalkyl surfactant in heterogeneous polymerization involved a protocol wherein a conventional fluorinated surfactant was added in combination with a non-fluorinated hydrocarbon surfactant. However, this modification served to substantially lower the rate of the reaction.
The conventionally prepared fluoropolymer has several drawbacks and limitations such as increased or higher thermal instability and degradation during extended periods of heating at elevated temperatures. Further, the significant limitation of the conventionally prepared fluoropolymer is the tendency of polymer materials to generate higher pores when subjected to tensile strain.
Therefore, there is felt a need for a process for the preparation of fluoropolymers that mitigates the drawbacks mentioned hereinabove or at least provides a useful alternative.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to ameliorate one or more problems of the background or to at least provide a useful alternative.
Another object of the present disclosure is to provide a process for the preparation of fluoropolymers by using a surfactant.
Still another object of the present disclosure is to provide an efficient process for the preparation of fluoropolymers that yields a stable emulsion.
Yet another object of the present disclosure is to provide a simplified process for the preparation of fluoropolymers by using an alkali metal salt of C8-C15 alkyl benzene sulfonic acid as a non-fluorinated surfactant.
Still another object of the present disclosure is to provide a fluoropolymer resin obtained by aqueous polymerization by using a non-fluorinated surfactant.
Yet another object of the present disclosure is to provide a simple, efficient and economical process for the preparation of fluoropolymers.
Still another object of the present disclosure is to provide a process for the preparation of fluoropolymers that is environmental friendly.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to a process for the preparation of fluoropolymers. The process comprises heating a mixture of a stabilizing agent and water in a polymerization reactor to a predetermined temperature to obtain an aqueous slurry. The polymerization reactor is pressurized with a predetermined amount of at least one fluoromonomer to the aqueous slurry at a predetermined pressure under agitation to form an aqueous dispersion. At least one initiator is added to the aqueous dispersion to initiate a polymerization reaction. A predetermined amount of a surfactant is added to the aqueous dispersion to obtain a slurry. The agitation is continued to propagate the polymerization reaction. The polymerization reaction is terminated to obtain the fluoropolymers.
In an embodiment of the present disclosure, the surfactant is a non-fluorinated surfactant.
The non-fluorinated surfactant is an alkali metal salt of C8-C15 alkyl benzene sulfonic acid.
The alkali metal salt of C8-C15 alkyl benzene sulfonic acid is selected from the group consisting of sodium salt of C8-C15 alkyl benzene sulfonic acid and potassium salt of C8-C15 alkyl benzene sulfonic acid.
The alkali metal salt of C8-C15 alkyl benzene sulfonic acid is alkali metal salt of C10-C13 alkyl benzene sulfonic acid.
In an embodiment of the present disclosure, the non-fluorinated surfactant is sodium salt of C10-C13 alkyl benzene sulfonic acid having the following structure:

The fluoromonomer is at least one selected from the group consisting of Perfluorobutylene ether (PFBE), trifluoroethylene, tetrafluoroethylene (TFE), Hexafluoropropylene (HFP), Perfluoro (propyl vinyl Ether) (PPVE), Perfluoro (methyl Vinyl Ether) (PMVE), chlorotrifluoroethylene (CTFE), vinylidene fluoride (VDF), vinylfluoride (VF), and a combination thereof.
In an embodiment of the present disclosure, the fluoromonomer is tetrafluoroethylene (TFE).
In an embodiment of the present disclosure, at least one comonomer is used along with the fluoromonomer.
The co-monomer is selected from the group consisting of Perfluorobutylene ether (PFBE), Perfluoro (propyl vinyl Ether) (PPVE), Hexa Fluopropylene (HFP), Perfluoro (methyl Vinyl Ether) (PMVE), chlorotrifluoroethylene (CTFE), vinylidene fluoride (VDF) and a combination thereof.
In accordance with an embodiment of the present disclosure, the co-monomer is selected from the group consisting of Perfluorobutylene ether (PFBE), Perfluoro (propyl vinyl Ether) (PPVE) and a combination thereof.
In one embodiment of the present disclosure, the co-monomer is Perfluorobutylene ether (PFBE).
In another embodiment of the present disclosure, the co-monomer is a mixture of Perfluorobutylene ether (PFBE) and Perfluoro (propyl vinyl Ether) (PPVE).
The initiator is selected from the group consisting of sodium persulfate, potassium persulfate, disuccinic acid peroxide (DSAP), ammonium persulphate (APS) and combinations thereof.
In accordance with an embodiment of the present disclosure, the initiator is selected from the group consisting of disuccinic acid peroxide (DSAP), ammonium persulphate (APS) and a combination thereof.
In an embodiment of the present disclosure, the initiator is disuccinic acid peroxide (DSAP).
In another embodiment of the present disclosure, the initiator is a combination of disuccinic acid peroxide (DSAP) and ammonium persulphate (APS).
The stabilizing agent is paraffin wax.
The predetermined temperature is in the range of 20 °C to 120 °C.
In an embodiment of the present disclosure, the predetermined temperature is in the range of 60 °C to 110 °C.
In a preferred embodiment of the present disclosure, the predetermined temperature is in the range of 70 °C to 90 °C.
The predetermined pressure is in the range of 200 kPa to 20000 kPa.
In an embodiment of the present disclosure, the predetermined pressure is in the range of 1000 kPa to 6000 kPa (10 bar to 60 bar).
In a preferred embodiment of the present disclosure, the predetermined pressure is in the range of 2000 kPa to 3000 kPa.
In an embodiment of the present disclosure, a weight ratio of the surfactant to the fluoromonomer is in the range of 1:300 to 1:1000.
In a preferred embodiment of the present disclosure, the weight ratio of the surfactant to the fluoromonomer is in the range of 1:600 to 1:900.
In another preferred embodiment of the present disclosure, the weight ratio of the surfactant to the fluoromonomer is in the range of 1:750 to 1:850.
In an embodiment of the present disclosure, the surfactant is added to the aqueous dispersion in a continuous manner at a predetermined rate.
In another embodiment of the present disclosure, the surfactant is added to the aqueous dispersion in one-shot.
In accordance with the embodiment of the present disclosure, the predetermined rate of adding the surfactant to the aqueous dispersion is in the range of 20 g/minute to 200 g/minute.
In a preferred embodiment of the present disclosure, the predetermined rate of adding the surfactant to said aqueous dispersion is in the range of 40 g/minute to 100 g/minute. The fluoropolymer prepared in accordance with the process of the present disclosure is characterized by having
• a particle size in the range of 150 nm to 250 nm;
• a standard specific gravity (SSG) in the range of 2.14 to 2.2;
• an extended specific gravity (ESG) in the range of 2.155 to 2.3;
• a thermal instability index (TII) in the range of 8 to 20; and
• a stretching void index (SVI) in the range of 35 to 50.
DETAILED DESCRIPTION
The present disclosure relates to a process for the preparation of fluoropolymers. Particularly, the present disclosure relates to a process of polymerization of at least one fluoromonomer by using a non-fluorinated surfactant. More particularly, the present disclosure relates to a process for the preparation of fluoropolymers by using an alkali metal salt C8-C15 alkyl benzene sulfonic acid as a non-fluorinated hydrocarbon containing surfactant.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, known processes or well-known apparatus or structures, and well known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure are not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
The surfactant of choice in the synthesis of fluoropolymers is generally a perfluorinated surfactant or a partially fluorinated surfactant. Although, the perfluorinated surfactants (perfluoroalkyl surfactants) are better in lowering the surface tension of water as compared to hydrocarbon surfactants, the fluorinated surfactants persist in the environment for a longer duration and have been detected in humans and wildlife. Moreover, the fluorosurfactants are expensive specialized materials.
Because of the high stability of the fluorinated surfactants and their resistance to chemical degradation, fluorosurfactants have the potential to accumulate in the environment and in organisms. Also, the high degree of fluorination of the surfactant avoids atom transfer between a growing polymer chain and the surfactant during polymerization that results in lowered molecular weights in the product and likely inhibition of the reaction. In order to address this issue, several different approaches have been attempted to reduce or eliminate the use of perfluoroalkyl surfactants in the polymerization of halogen-containing monomers.
Conventionally, an attempt to reduce the amount of perfluoroalkyl surfactant in heterogeneous polymerization involved a protocol wherein a conventional fluorinated surfactant was added in combination with a non-fluorinated hydrocarbon surfactant. However, this modification served to substantially lower the rate of the reaction.
The present disclosure provides a simple, economic and environment friendly process for the preparation of fluoropolymers.
Particularly, the present disclosure provides a process for the preparation of fluoropolymers by using an alkali metal salt of C8-C15 alkyl benzene sulfonic acid as a non-fluorinated hydrocarbon containing surfactant.
The process for the preparation of fluoropolymers comprises the following steps:
(a) heating a mixture of a stabilizing agent and water in a polymerization reactor to a predetermined temperature to obtain an aqueous slurry;
(b) pressurizing the polymerization reactor with a predetermined amount of at least one fluoromonomer to the aqueous slurry at a predetermined pressure under agitation to form an aqueous dispersion;
(c) adding at least one initiator to the aqueous dispersion to initiate a polymerization reaction;
(d) adding a predetermined amount of a surfactant to the aqueous dispersion to obtain a slurry;
(e) continuing the agitation to propagate the polymerization reaction; and
(f) terminating the polymerization reaction to obtain the fluoropolymers.
In an embodiment of the present disclosure, oxygen is removed from the polymerization reactor by applying vacuum and nitrogen cycle. The oxygen content is then checked and ensured that the oxygen content is less than 30 ppm.
In an embodiment of the present disclosure, the surfactant is a non-fluorinated surfactant.
In an embodiment of the present disclosure, the non-fluorinated surfactant is an alkali metal salt of C8-C15 alkyl benzene sulfonic acid.
The alkali metal salt of C8-C15 alkyl benzene sulfonic acid is selected from the group consisting of sodium salt of C8-C15 alkyl benzene sulfonic acid and potassium salt of C8-C15 alkyl benzene sulfonic acid.
The alkali metal salt of C8-C15 alkyl benzene sulfonic acid is alkali metal salt of C10-C13 alkyl benzene sulfonic acid.
In an exemplary embodiment of the present disclosure, the non-fluorinated surfactant is sodium salt of C10-C13 alkyl benzene sulfonic acid having the following structure:

In accordance with an embodiment, the non-fluorinated hydrocarbon containing surfactant used in the process of the present disclosure is not passivated.
The fluoromonomer is at least one selected from the group consisting of Perfluorobutylene ether (PFBE), trifluoroethylene, tetrafluoroethylene (TFE), Hexafluoropropylene (HFP), Perfluoro (propyl vinyl Ether) (PPVE), Perfluoro (methyl Vinyl Ether) (PMVE), chlorotrifluoroethylene (CTFE), vinylidene fluoride (VDF), vinylfluoride (VF), and a combination thereof. In an exemplary embodiment of the present disclosure, the fluoromonomer is tetrafluoroethylene (TFE).
Although, the embodiments of the present disclosure are described in terms of polymerization of TFE, the process described herein can be applied to the polymerization of any fluoromonomer.
In an embodiment of the present disclosure, preferably, the fluoromonomer is tetrafluoroethylene (TFE) and its copolymer and the fluoropolymer is polytetrafluoroethylene (PTFE).
The term “fluoromonomer” or the expression “fluorinated monomer” means a polymerizable alkene which contains at least one fluorine atom, fluoroalkyl group, or fluoroalkoxy group attached to the double bond of the alkene that undergoes polymerization.
The term “fluoropolymer” means a polymer formed by the polymerization of at least one fluoromonomer, and it is inclusive of homopolymers, copolymers, terpolymers and higher polymers.
In an embodiment of the present disclosure, at least one comonomer is used along with the fluoromonomer in the process for the preparation of fluoropolymers.
The co-monomer is selected from the group consisting of Perfluorobutylene ether (PFBE), Perfluoro (propyl vinyl Ether) (PPVE), Hexa Fluopropylene (HFP), Perfluoro (methyl Vinyl Ether) (PMVE), chlorotrifluoroethylene (CTFE), vinylidene fluoride (VDF) and a combination thereof. In an exemplary embodiment of the present disclosure, the co-monomer is Perfluorobutylene ether (PFBE). In another exemplary embodiment of the present disclosure, the co-monomer is a mixture of Perfluorobutylene ether (PFBE), Perfluoro (propyl vinyl Ether) (PPVE).
The term “initiator” and the expressions “radical initiator” and “free radical initiator” refer to a chemical that is capable of providing a source of free radicals, either induced spontaneously, or by exposure to heat or light. Examples of suitable initiators can include, but is not limited to, peroxides, peroxy dicarbonates and azo compounds. Initiators may also include reduction-oxidation systems which provide a source of free radicals. The term “radical” and the expression “free radical” refer to a chemical species that contains at least one unpaired electron. The radical initiator is added to the reaction mixture in an amount sufficient to initiate and maintain the polymerization reaction rate.
In an embodiment of the present disclosure, the radical initiator comprises a reduction-oxidation system which provide a source of free-radicals.
In another embodiment of the present disclosure, the radical initiator comprises a redox system. “Redox system” is understood by a person skilled in the art to mean a system comprising an oxidizing agent, a reducing agent and optionally, a promoter as an electron transfer medium.
The initiator is selected from the group consisting of sodium persulfate, potassium persulfate, disuccinic acid peroxide (DSAP), ammonium persulphate (APS) and combinations thereof. In an exemplary embodiment of the present disclosure, the initiator is disuccinic acid peroxide (DSAP). In another exemplary embodiment of the present disclosure, the initiator is a combination of disuccinic acid peroxide (DSAP) and ammonium persulphate (APS).
In an embodiment, the stabilizing agent is paraffin wax.
In an embodiment of the present disclosure, the aqueous dispersion further comprises chain transfer agents, nucleation agents and reducing agents.
In accordance with the embodiment of the present disclosure, the chain transfer agents is selected from the group consisting of halogen compounds, aliphatic hydrocarbons, aromatic hydrocarbons, thiols (mercaptans), alcohols, esters and a combination thereof. Preferably, the chain transfer agent is ethyl acetate.
Chain transfer agents, also referred to as modifiers or regulators, comprise at least one chemically weak bond. A chain transfer agent reacts with the free radical site of a growing polymer chain and halts an increase in chain length. The chain transfer agents are often added during emulsion polymerization to regulate chain length of the polymer to achieve the desired properties in the polymer.
The nucleation agent as used in the present disclosure refers to a combination of the non-fluorinated anionic/non-ionic surfactant and a redox system comprising oxidizing agents such as ammonium persulfate, potassium persulfate, and Potassium permanganate; and reducing agents such as alkali metal sulfite, alkali metal bisulfite, and aliphatic acid.
A nucleation agents represents yet another important component used in emulsion polymerization of fluoromonomers. The use of nucleation agent generates a large number of free radical sites, which are dispersed in polymerization reactor. These numerous free radical sites counter the telogenic or inhibition effect of the non- fluorinated surfactant on polymerization. Generally, non-fluorinated surfactants inherently inhibit the free radical site to react further or participate in polymerization reaction due to telogenicity. Addition of the nucleation agent promotes the polymerization process even at low concentrations of the initiator. In a nutshell, the nucleation agent reduces the inhibition effect of the non-fluorinated surfactants on polymerization rates, leads to lower consumption of initiators and higher molecular weights of the fluoropolymers.
As discussed above, the reducing agents form a part of the nucleation agent, which counter the telogenic effect of non-fluorinated surfactants on the polymerization process. They act in conjunction with oxidizing agents such as ammonium persulfate and generate free radicals at very low to high reaction temperatures, thereby accelerating the polymerization reaction. Examples of the reducing agents useful in the present invention is selcted from sodium sulfite, sodium bisulfite, sodium acetate, oxalic acid and so forth, each of which can be used independently or in combination.
Polymerization conditions
The temperature used for polymerization is in the range of 20 °C to 120 °C, depending on the initiator system chosen and the reactivity of the fluoromonomer(s) selected. In an embodiment, the polymerization is carried out at a temperature in the range of 60 °C to 110 °C. In a preferred embodiment of the present disclosure, the predetermined temperature is in the range of 70 °C to 90 °C.
The pressure used for polymerization is in the range of 200 kPa to 20000 kPa (2 bar to 200 bar), depending on the reaction equipment, the initiator system, and the monomer selection. In an embodiment, the reaction is carried out at a pressure in the range of 1000 kPa to 6000 kPa (10 bar to 60 bar). In a preferred embodiment of the present disclosure, the predetermined pressure is in the range of 2000 kPa to 3000 kPa. In an exemplary embodiment, the polymerization reaction is carried out at 2400 kPa (24 bar).
In an embodiment of the present disclosure, a weight ratio of the surfactant to the fluoromonomer is in the range of 1:300 to 1:1000. In a preferred embodiment, the weight ratio of the surfactant to the fluoromonomer is in the range of 1:600 to 1:900. In another preferred embodiment of the present disclosure, the weight ratio of the surfactant to the fluoromonomer is in the range of 1:750 to 1:850. In an exemplary embodiment of the present disclosure, the weight ratio of the non-fluorinated surfactant to the fluoromonomers is 1: 800.
In an embodiment of the present disclosure, the surfactant is added to the aqueous dispersion in a continuous manner at a predetermined rate.
In another embodiment of the present disclosure, the surfactant is added to the aqueous dispersion in one-shot.
In accordance with the embodiment of the present disclosure, the predetermined rate of adding the surfactant to the aqueous dispersion is in the range of 20 g/minute to 200 g/minute. In a preferred embodiment, the predetermined rate of adding the non-fluorinated surfactant to the aqueous dispersion is in the range of 40 g/minute to 100 g/minute. In an exemplary embodiment, the predetermined rate of adding the non-fluorinated surfactant is 50 g/minute.
The polymerization occurs under stirring or agitation. The stirring may be constant, or may be varied to optimize process conditions during the course of the polymerization. In one embodiment, both multiple stirring speeds and multiple temperatures are used for controlling the reaction.
In accordance with an embodiment of the present disclosure, a pressurized polymerization reactor equipped with a stirrer and heat control means is charged with water, preferably deionized water, non-fluorinated hydrocarbon containing surfactant (alkali metal salt of C8-C15 alkyl benzene sulfonic acid), nucleation agent, reducing agent, chain transfer agents and at least one fluoromonomer. Preferably, the non-fluorinated hydrocarbon containing surfactant is added in an amount in the range from 40 ppm to 10000 ppm more preferably from 200 to 8000 ppm based on the weight of fluoropolymer dispersion. In a preferred embodiment, the dosing rate of the non-fluorinated hydrocarbon containing surfactant during the course of the polymerization reaction ranges from 0.008 g/(L*h) to 0.6 g/(L*h). Preferably, the reaction mixture comprises the chain transfer agents in an amount in the range from 50 to 4500 ppm. The mixture may optionally contain paraffin wax. The reactor is then heated up to the reaction temperature and pressurized. Thereafter, initiators are added into the reaction vessel to initiate the polymerization reaction. Preferably, the initiator is added in an amount in the range of 2 ppm to 2000 ppm, based on the weight of de-ionized water. Prior to introduction of the surfactant, and monomer or monomers into the reaction vessel and commencement of the reaction, air is preferably removed from the reactor in order to obtain an oxygen-free environment for the polymerization reaction. Preferably, the oxygen is removed from the reaction vessel until its concentration is less than 10 ppm. The reactor may also be purged with a neutral gas such as, nitrogen or argon.
Upon completion of the polymerization reaction, the reactor is brought to ambient temperature and the residual unreacted monomer is vented to atmospheric pressure. The aqueous reaction medium containing the fluoropolymer is then recovered from the reaction vessel. Preferably, the solid content ranges from 10% to 65%, more preferably from 15% to 35% and the particle size of the fluoropolymer particles preferably ranges from 50 nm to 300 nm.
In an embodiment of the present disclosure, the polymerization reaction is terminated by stopping the fluoromonomers feeding after consumption of desired quantity of the fluoromonomers or the mixture of fluoromonomers to obtain the fluoropolymers.
In an embodiment of the present disclosure, the fluoropolymer is characterized by having
• a particle size in the range of 150 nm to 250 nm;
• a standard specific gravity (SSG) in the range of 2.140 to 2.2;
• an extended specific gravity (ESG) in the range of 2.155 to 2.3;
• a thermal instability index (TII) in the range of 8 to 20; and
• a stretching void index (SVI) in the range of 35 to 50.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to the industrial scale.
EXPERIMENTAL DETAILS
Experiment I: Preparation of fluoropolymer (Polytetrafluoroethylene) in accordance with the present disclosure
Polytetrafluoroethylene (PTFE) fine powder was manufactured in accordance with the process of the present disclosure (Examples 1 to 5) by using the alkali metal salt of C8-C15 alkyl benzene sulfonic acid (non-fluorinated hydrocarbon containing surfactant).
150 L (litres), horizontally disposed, jacketed, stainless steel polymerization reactor with a six-blade agitator was used. 80 litres of deionized, deaerated water and 0.5 kg of paraffin wax were added in the reactor to obtain a mixture. The reactor was sealed and placed under vacuum till the oxygen level reached to less than 30 ppm. The reactor pressure was raised to 24 bar (2400 kPa) with nitrogen and brought to vacuum 5 times. Reactor agitator was set at 40 RPM. The reactor was heated to a predetermined temperature to obtain an aqueous slurry.
After vacuum nitrogen cycles, a predetermined amount of tetrafluoroethylene (TFE) was pressurized at 24 bar (2400 kPa) into the reactor containing the aqueous slurry under agitation to form an aqueous dispersion. At least one initiator was added to the aqueous dispersion to initiate a polymerization reaction of the fluoromonomers. After 1.5 kg of TFE was fed, 30 g of sodium salt of C10-C13 alkyl benzene sulfonic acid (non-fluorinated surfactant) was pumped into the reactor at a rate of 50 g/min to obtain a slurry. The agitation is continued to propagate the polymerization reaction for growing of chain length of the fluoropolymer. After 24 kg of TFE had been added to the reactor, the batch time (Table A) was recorded, the agitator was stopped, the reactor was vented to atmospheric pressure and the dispersion was discharged. Upon cooling, wax was separated from the dispersion to obtain the fluoropolymer (Polytetrafluoroethylene).
The process details and the polymerization conditions for Examples 1 to 5 are summarized in Table 1.
Table 1: Process details and the polymerization conditions
Example 1 Example 2 Example 3 Example 4 Example 5
Sodium salt of C10-C13 alkyl benzene sulfonic acid
(non-fluorinated surfactant)
(g) 30 30 30 30 30
TFE consumption during propagation phase
(kg) 24 24 24 24 24
Co-monomer consumption
(g) 150 80 100 -- --
Co-monomer PFBE and PPVE mixture PFBE PFBE -- --
Total Initiator
(g) 36 (DSAP) and 24.53 (APS) 36 (DSAP) and 16.43 (APS) 37 (DSAP) and 18.5 (APS) 36 (DSAP) 36 (DSAP)
Reaction Pressure
(bar) 24 24 24 24 24
Reaction Temperature
(°C) 80.25 80.5 73.8 85.2 85.8
Total Reaction Time
(minutes) 229 152 180 135 142
pH 2.48 2.48 2.4 3.2 3.3
Solid Content
(%) 23.31 23.57 21.31 27.4 27.2
Primary Particle size
(nm) 176.8 168.5 196.3 190.8 200.5
The process details and the polymerization conditions for Comparative Examples 1 to 9 are summarized in Table 2.
Table 2: Process details and the polymerization conditions
Comparative Examples 1 2 3 4 5 6 7 8 9
Conventional Non-fluorinated
surfactant (alkyldiphenyloxide surfactant)
(g) 17.7 25.4 18.3 27.5 25.3 18.3 19.2 30 30
TFE consumption during propagation phase
(kg) 24 24 24 24 24 24 24 24 24
Co-monomer consumption
(g) 0 0 0 0 0 0 0 0 0
Co-monomer - - - - - - - - -
Total Initiator (DSAP + APS)
(g) 18.75+0.938 36+0 36+0 36+0 36+0 46.5+7 40+6 36+0.25 36+0.15
Reaction Pressure
(bar) 24 24 24 24 24 24 24 24 24
Reaction Temperature
(°C) 80 80.7 82.73 80 83.58 89.5 92.18 83.84 84.98
Total Reaction Time
(minutes) 146 180 172 146 152 187 160 115 113
pH 3.04 2.86 2.98 3.28 2.72 2.88 2.96 2.98 2.9
Solid Content
(%) 22.7 25.85 21.95 22.99 26.1 24.63 25.12 25.1 25.85
Primary Particle size
(nm) 228.3 223.3 232.1 249 234.1 174.6 182.1 221.3 247.5
Experiment II: Characteristic properties of the PTFE of Examples 1 to 5 and the PTFE of the comparative examples 1 to 9
The characteristic properties such as SSG, ESG, TII and SVI of the PTFE of Examples 1 to 5 were determined and compared with properties of the PTFE manufactured (comparative examples 1 to 9) by using the other non-fluorinated surfactant (alkyldiphenyloxide surfactant). The results are summarized in Table 3.
Table 3: Characteristic properties of the PTFE of Examples 1 to 5 and comparative examples 1 to 9
PTFE fine powders SSG ESG TII SVI
Example-1 2.144 2.157 13 44
Example -2 2.149 2.169 20 41
Example -3 2.143 2.156 13 42
Example -4 2.154 2.165 9 45
Example -5 2.152 2.162 10 38
Comparative example-1 2.168 2.194 26 237
Comparative example -2 2.188 2.188 25 249
Comparative example -3 2.175 2.205 30 254
Comparative example -4 2.163 2.19 27 213
Comparative example -5 2.157 2.233 76 206
Comparative example -6 2.197 2.239 42 343
Comparative example -7 2.196 2.243 47 321
Comparative example -8 2.17 2.185 15 246
Comparative example -9 2.165 2.187 22 230
Lower TII value indicates higher thermal stability of a material. As key characteristic of PTFE material is high service temperature (up to 250 °C) with longer service life, so TII is one of critical requirement for acceptance of PTFE in various demanding end applications such as automotive, aerospace, defence, oil and gas, chemical process industries and the like.
PTFE manufactured in accordance with the present disclosure by using the alkali metal salt of C8-C15 alkyl benzene sulfonic acid (non-fluorinated surfactant) showed lower TII values as compared to the PTFE made by using the other non-fluorinated surfactant (alkyldiphenyloxide surfactant) and comparable to fluoropolymer made with the conventional fluoro-surfactant.
Higher SVI indicates tendency of material to generate higher pores when subjected to tensile strain. Higher induced porosity with material elongation under tensile strain restrict use of material in various critical application where low permeation is required such as gasket, tubing and lining for chemical process industries, fuel hoses for automotive application and the like.
PTFE manufactured in accordance with the present disclosure by using the alkali metal salt of C8-C15 alkyl benzene sulfonic acid (non-fluorinated surfactant) showed lower SVI in comparison to the PTFE made by using the other non-fluorinated surfactant (alkyldiphenyloxide surfactant) and comparable to PTFE made with the conventional fluoro-surfactant.
TECHNICAL ADVANCEMENTS AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for the preparation of fluoropolymers, that:
• is simple, efficient and environment friendly;
• is feasible on a large/commercial scale; and
• avoids using fluorinated surfactants.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation. ,CLAIMS:WE CLAIM:
1. A process for the preparation of fluoropolymers, said process comprising the following steps:
(a) heating a mixture of a stabilizing agent and water in a polymerization reactor to a predetermined temperature to obtain an aqueous slurry;
(b) pressurizing said polymerization reactor with a predetermined amount of at least one fluoromonomer to said aqueous slurry at a predetermined pressure under agitation to form an aqueous dispersion;
(c) adding at least one initiator to said aqueous dispersion to initiate a polymerization reaction;
(d) adding a predetermined amount of a surfactant to said aqueous dispersion to obtain a slurry;
(e) continuing said agitation to propagate said polymerization reaction; and
(f) terminating said polymerization reaction to obtain said fluoropolymers.
2. The process as claimed in claim 1, wherein said surfactant is a non-fluorinated surfactant.
3. The process as claimed in claim 2, wherein said non-fluorinated surfactant is an alkali metal salt of C8-C15 alkyl benzene sulfonic acid.
4. The process as claimed in claim 3, wherein said alkali metal salt of C8-C15 alkyl benzene sulfonic acid is selected from the group consisting of sodium salt of C8-C15 alkyl benzene sulfonic acid and potassium salt of C8-C15 alkyl benzene sulfonic acid.
5. The process as claimed in claim 3, wherein said alkali metal salt of C8-C15 alkyl benzene sulfonic acid is alkali metal salt of C10-C13 alkyl benzene sulfonic acid.
6. The process as claimed in claim 2, wherein said non-fluorinated surfactant is sodium salt of C10-C13 alkyl benzene sulfonic acid having the following structure:

7. The process as claimed in claim 1, wherein said fluoromonomer is at least one selected from the group consisting of Perfluorobutylene ether (PFBE), trifluoroethylene, tetrafluoroethylene (TFE), Hexafluoropropylene (HFP), Perfluoro (propyl vinyl Ether) (PPVE), Perfluoro (methyl Vinyl Ether) (PMVE), chlorotrifluoroethylene (CTFE), vinylidene fluoride (VDF), vinylfluoride (VF), and a combination thereof.
8. The process as claimed in claim 1, wherein said fluoromonomer is tetrafluoroethylene (TFE).
9. The process as claimed in claim 1, wherein at least one comonomer is used along with the fluoromonomer.
10. The process as claimed in claim 9, wherein said co-monomer is selected from the group consisting of Perfluorobutylene ether (PFBE), Perfluoro (propyl vinyl Ether) (PPVE), Hexa Fluopropylene (HFP), Perfluoro (methyl Vinyl Ether) (PMVE), chlorotrifluoroethylene (CTFE), vinylidene fluoride (VDF) and a combination thereof.
11. The process as claimed in claim 9, wherein said co-monomer is selected from the group consisting of Perfluorobutylene ether (PFBE), Perfluoro (propyl vinyl Ether) (PPVE) and a combination thereof.
12. The process as claimed in claim 9, wherein said co-monomer is Perfluorobutylene ether (PFBE).
13. The process as claimed in claim 9, wherein said co-monomer is a mixture of Perfluorobutylene ether (PFBE) and Perfluoro (propyl vinyl Ether) (PPVE).
14. The process as claimed in claim 1, wherein said initiator is selected from the group consisting of sodium persulfate, potassium persulfate, disuccinic acid peroxide (DSAP), ammonium persulphate (APS) and combinations thereof.
15. The process as claimed in claim 1, wherein said initiator is selected from the group consisting of disuccinic acid peroxide (DSAP), ammonium persulphate (APS) and a combination thereof.
16. The process as claimed in claim 1, wherein said initiator is disuccinic acid peroxide (DSAP).
17. The process as claimed in claim 1, wherein said initiator is a combination of disuccinic acid peroxide (DSAP) and ammonium persulphate (APS).
18. The process as claimed in claim 1, wherein said stabilizing agent is paraffin wax.
19. The process as claimed in claim 1, wherein said predetermined temperature is in the range of 20 °C to 120 °C.
20. The process as claimed in claim 1, wherein said predetermined temperature is in the range of 60 °C to 110 °C.
21. The process as claimed in claim 1, wherein said predetermined temperature is in the range of 70 °C to 90 °C.
22. The process as claimed in claim 1, wherein said predetermined pressure is in the range of 200 kPa to 20000 kPa.
23. The process as claimed in claim 1, wherein said predetermined pressure is in the range of 1000 kPa to 6000 kPa.
24. The process as claimed in claim 1, wherein said predetermined pressure is in the range of 2000 kPa to 3000 kPa.
25. The process as claimed in claim 1, wherein a weight ratio of said surfactant to said fluoromonomer is in the range of 1:300 to 1:1000.
26. The process as claimed in claim 1, wherein a weight ratio of said surfactant to said fluoromonomer is in the range of 1:600 to 1:900.
27. The process as claimed in claim 1, wherein a weight ratio of said surfactant to said fluoromonomer is in the range of 1:750 to 1:850.
28. The process as claimed in claim 1, wherein said surfactant is added to said aqueous dispersion in a continuous manner at a predetermined rate.
29. The process as claimed in claim 28, wherein said predetermined rate of adding said surfactant to said aqueous dispersion is in the range of 20 g/minute to 200 g/minute.
30. The process as claimed in claim 28, wherein said predetermined rate of adding said surfactant to said aqueous dispersion is in the range of 40 g/minute to 100 g/minute.
31. The process as claimed in claim 1, wherein said surfactant is added to said aqueous dispersion in one-shot.
32. The process as claimed in claim 1, wherein said fluoropolymer is characterized by having
• a particle size in the range of 150 nm to 250 nm;
• a standard specific gravity (SSG) in the range of 2.14 to 2.2;
• an extended specific gravity (ESG) in the range of 2.155 to 2.3;
• a thermal instability index (TII) in the range of 8 to 20; and
• a stretching void index (SVI) in the range of 35 to 50.
Dated this 31st day of January, 2024

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
of R.K.DEWAN & CO.
Authorized Agent of Applicant

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, AT NEW DELHI