Polytetrafluoroethylene and soluble polytetrafluoroethylene composite pipe as well as processing method and application thereof

Abstract

The invention belongs to the technical field of composite pipes, and relates to a polytetrafluoroethylene and soluble polytetrafluoroethylene composite pipe as well as a processing method and application thereof. The preparation method comprises the following steps: firstly, carrying out ring opening polymerization on D3F and blocking by using an amino-containing silane coupling agent to prepare amino-terminated fluorosilicone oil, and taking the amino-terminated fluorosilicone oil as a lubricating agent for compounding and processing PTFE and PFA. The amino-terminated fluorosilicone oil contains a CF3 chain segment which has excellent compatibility with PTFE or PFA, and meanwhile, the cross-linking agent is added to form a chemical bond and a cross-linked structure with amino at the tail end of the lubricant, so that the wear resistance, tensile strength, permeability resistance and high-temperature creep resistance of the PTFE and PFA composite pipe can be improved, and the PTFE and PFA composite pipe can adapt to a long-term high-temperature working environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite pipes, and particularly relates to a composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene, a processing method thereof, and an application thereof. Background Art

[0002] At present, fluorine-containing high-molecular materials are developing rapidly. Among them, polytetrafluoroethylene (PTFE), commonly known as the "king of plastics", has extremely excellent chemical stability, excellent thermal stability and anti-sticking property, and is often used for transporting strongly corrosive media at high temperatures. Also, because PTFE pipes can be used for a long time at extremely high or low temperatures and have excellent oil resistance, heat resistance and weather resistance, they are widely used in industries such as national defense, aerospace, electronics, electrical, chemical, machinery, instruments, meters, medical treatment, and food.

[0003] Among them, PTFE hoses have excellent acid and corrosion resistance, and can be used in media such as extremely strong acids and alkalis, oxidants or solvents within the temperature range of -195 to 260 °C, and are not prone to scaling during use, and are very suitable for use in the pipelines of heat exchange equipment. Although PTFE hoses have excellent strong acid, strong alkali and corrosion resistance, the flexibility of the pipe itself is not good, it is not resistant to bending and vibration, and the wear resistance is average. During the use of heat exchangers, it is easy to have problems such as the PTFE hose being cracked due to bending, vibration or friction with other metal pipe walls or other hoses, and local cracking or overall fracture due to creep deformation during long-term operation under high-temperature conditions. Therefore, it is necessary to improve the wear resistance, tensile strength, anti-permeability and high-temperature anti-creep property of PTFE hoses through modification, and at the same time, it is necessary to ensure that the flexibility of the composite pipe does not decrease too much, and to ensure the bend radius of the composite pipe, which is beneficial to improving the overall structural compactness and reliability.

[0004] To solve the above problems, Chinese Patent CN118109008A proposes to mix two raw materials of PTFE and soluble polytetrafluoroethylene (PFA) to produce pipes with better wear resistance. When the mass ratio of PFA powder increases from 0% to 20 - 30%, the wear resistance gradually becomes stronger; when the mass ratio of PFA powder exceeds 30%, the wear resistance cannot be further improved. Thus, it is found that mixing PTFE and PFA alone to prepare PTFE hoses has limited improvement in wear resistance, and there is no improvement in the high-temperature anti-creep property of the composite pipe, and it is difficult to expect that the composite pipe can be used as a heat exchanger pipe in a high-temperature environment above 100 °C for a long time. Summary of the Invention

[0005] Aiming at the defects of the prior art, the technical problem to be solved by the present invention is to add amino-terminated fluorosilicone oil and a crosslinking agent on the basis of mixing two raw materials of PTFE and PFA, wherein the amino-terminated fluorosilicone oil plays a lubricating role to assist the extrusion molding of the raw materials, and the crosslinking agent crosslinks with the amino group of the amino-terminated fluorosilicone oil, thereby further improving the wear resistance, tensile strength, impermeability and high-temperature creep resistance of the polytetrafluoroethylene hose.

[0006] To achieve the above technical purpose, the technical solution adopted by the present invention is as follows: In a first aspect, a composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene includes: Polytetrafluoroethylene (PTFE), soluble polytetrafluoroethylene (PFA), amino-terminated fluorosilicone oil and a crosslinking agent; Among them, the polytetrafluoroethylene is selected from polytetrafluoroethylene powder, and the average particle size of the powder does not exceed 100 μm; The soluble polytetrafluoroethylene is selected from soluble polytetrafluoroethylene powder, and the average particle size of the powder does not exceed 100 μm; The amino-terminated fluorosilicone oil is obtained by anionic or cationic ring-opening polymerization of 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)cyclotrisiloxane (D3F), and then terminated with an amino-containing silane coupling agent.

[0007] Preferably, the amino-containing silane coupling agent includes any one or more of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, N-aminoethyl-3-aminopropyltrimethoxysilane or N-aminoethyl-3-aminopropylmethyldimethoxysilane; The crosslinking agent is selected from: inorganic zinc salts, or any one or more of them, wherein Ar represents an aromatic ring composed of at least 3 carbon atoms or an aromatic heterocycle containing other heteroatoms; Preferably, the inorganic zinc salt is selected from any one or more of zinc chloride, zinc sulfate or zinc nitrate; Preferably, is selected from any one or more of 2-formylbenzeneboronic acid, 3-formylbenzeneboronic acid or 4-formylbenzeneboronic acid; Preferably, is selected from any one or more of terephthalaldehyde, o-phthalaldehyde or m-phthalaldehyde; More preferably, the crosslinking agent is selected from any one or more of zinc chloride, 2-formylbenzeneboronic acid or terephthalaldehyde.

[0008] Further, the composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene consists of the following components by weight percentage: polytetrafluoroethylene (PTFE) 50 - 75%, soluble polytetrafluoroethylene (PFA) 20 - 40%, amino-terminated fluorosilicone oil 10 - 20%, and crosslinking agent 1 - 5%.

[0009] Preferably, the composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene consists of the following components by mass parts: polytetrafluoroethylene (PTFE) 50 - 70%, soluble polytetrafluoroethylene (PFA) 20 - 35%, amino-terminated fluorosilicone oil 10 - 20%, and crosslinking agent 1 - 5%.

[0010] More preferably, the composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene consists of the following components by mass parts: polytetrafluoroethylene (PTFE) 50 - 65%, soluble polytetrafluoroethylene (PFA) 20 - 30%, amino-terminated fluorosilicone oil 10 - 20%, and crosslinking agent 1 - 5%.

[0011] In a second aspect, a processing method of the composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene includes: mixing polytetrafluoroethylene (PTFE), soluble polytetrafluoroethylene (PFA) and amino-terminated fluorosilicone oil in proportion, and then adding the crosslinking agent according to the formula ratio after aging.

[0012] Among them, the aging is to place the mixture in an oven at no less than 40 °C for 12 - 48 hours.

[0013] Further, the specific steps of the processing method of the composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene include: S1. Mix polytetrafluoroethylene (PTFE), soluble polytetrafluoroethylene (PFA) and amino-terminated fluorosilicone oil respectively according to the formula ratio, and use mechanical stirring to mix each component evenly; S2. Place the mixture of the above components in an oven at no less than 40 °C for 24 hours and then take it out, and then add the crosslinking agent according to the formula ratio, and use mechanical stirring to mix each component evenly; S3. Use a preforming device to process and shape it into a ring-shaped pipe; S4. Transfer it into an extruder device and extrude the raw material into a fibrous shape; S5. Sinter and form at high temperature to obtain a composite pipe.

[0014] In a third aspect, an application of the above-mentioned composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene in a heat exchanger tube.

[0015] The beneficial effects of the present invention are as follows: Amino-terminated fluorosilicone oil is selected as the lubricant for the compound processing of polytetrafluoroethylene and soluble polytetrafluoroethylene. The amino-terminated fluorosilicone oil is prepared by ring-opening polymerization of raw material D3F and end-capping with an amino-functional silane coupling agent. The amino-terminated fluorosilicone oil contains CF3 segments and has excellent compatibility with polytetrafluoroethylene or soluble polytetrafluoroethylene. Adding a crosslinking agent can form chemical bonds and crosslinked structures with the terminal amino groups of the lubricant amino-terminated fluorosilicone oil, which is beneficial to improving the wear resistance, tensile strength, anti-permeability and high-temperature creep resistance of the PTFE and PFA composite pipes, can adapt to the long-term high-temperature working environment, and at the same time avoids crosslinking of the PTFE and PFA polymer matrices and affects the processing performance. Specific Embodiments

[0016] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0017] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0018] If the specific experimental conditions are not specified in the embodiments, they are usually in accordance with the conventional conditions in the art or the conditions recommended by the reagent company; the materials, reagents, etc. used in the embodiments, unless otherwise specified, can be obtained through commercial channels.

[0019] Example 1 Synthesis of amino-terminated fluorosilicone oil: 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)cyclotrisiloxane (abbreviation D3F) is used as the initial raw material, ethylenediamine and water are used as catalysts, and 3-aminopropyltriethoxysilane is used as the end-capping agent.

[0020] 103.07 g (0.22 mol) of D3F was added to a three-necked flask, and then 2 g of ethylenediamine and 0.4 g of water were further added as catalysts. Nitrogen was introduced into the flask for protection and stirring was started. The temperature was raised to 60 °C and the reaction was carried out at a constant temperature for 10 hours. After the reaction, the temperature was lowered to 50 °C, and 146.10 g (0.66 mol) of 3-aminopropyltriethoxysilane (KH550) was added and the reaction was carried out at 50 °C for 4 hours. At the same time, nitrogen was continuously introduced to carry out the small-molecule alcohol products formed in the reaction. After the reaction, the temperature was raised to 120 °C and the ethylenediamine, water and excessive KH550 in the reaction system were removed by vacuum distillation to obtain amino-terminated silicone oil. The slightly yellow liquid remaining in the reaction flask was amino-terminated fluorosilicone oil.

[0021] Example 2 Synthesis of amino-terminated fluorosilicone oil: Using D3F as the initial raw material, ethylenediamine and water as catalysts, and 3-aminopropylmethyldiethoxysilane as the end-capping agent.

[0022] 103.07 g (0.22 mol) of D3F was added to a three-necked flask, and then 2 g of ethylenediamine and 0.4 g of water were further added as catalysts. Nitrogen was introduced into the flask for protection and stirring was started. The temperature was raised to 60 °C and the reaction was carried out at a constant temperature for 10 hours. After the reaction, the temperature was lowered to 50 °C, and 126.30 g (0.66 mol) of 3-aminopropylmethyldiethoxysilane was added and the reaction was carried out at 50 °C for 4 hours. At the same time, nitrogen was continuously introduced to carry out the small-molecule alcohol products formed in the reaction. After the reaction, the temperature was raised to 120 °C and the ethylenediamine, water and excessive 3-aminopropylmethyldiethoxysilane in the reaction system were removed by vacuum distillation to obtain amino-terminated silicone oil.

[0023] Example 3 Synthesis of amino-terminated fluorosilicone oil: Using D3F as the initial raw material, ethylenediamine and water as catalysts, and N-aminoethyl-3-aminopropylmethyldimethoxysilane as the end-capping agent.

[0024] 103.07 g (0.22 mol) of D3F was added to a three-necked flask, and then 2 g of ethylenediamine and 0.4 g of water were further added as catalysts. Nitrogen was introduced into the flask for protection and stirring was started. The temperature was raised to 60 °C and the reaction was carried out at a constant temperature for 10 hours. After the reaction, the temperature was lowered to 50 °C, and 136.20 g (0.66 mol) of N-aminoethyl-3-aminopropylmethyldimethoxysilane was added and the reaction was carried out at 50 °C for 4 hours. At the same time, nitrogen was continuously introduced to carry out the small-molecule alcohol products formed in the reaction. After the reaction, the temperature was raised to 120 °C and the ethylenediamine, water and excessive N-aminoethyl-3-aminopropylmethyldimethoxysilane in the reaction system were removed by vacuum distillation to obtain amino-terminated silicone oil.

[0025] Example 4 Composite pipe formula of polytetrafluoroethylene and soluble polytetrafluoroethylene: PTFE powder Dyneon TFM (3M), weight ratio 60%; amino-terminated fluorosilicone oil prepared in Example 1, weight ratio 15%; 340X PFA powder (Chemours), weight ratio 22.5%; crosslinking agent 2-formylbenzeneboronic acid, weight ratio 2.5%.

[0026] Example 5 Composite pipe formula of polytetrafluoroethylene and soluble polytetrafluoroethylene: PTFE powder Dyneon TFM (3M), weight ratio 55%; amino-terminated fluorosilicone oil prepared in Example 1, weight ratio 15%; 340X PFA powder (Chemours), weight ratio 27.5%; crosslinking agent terephthalaldehyde, weight ratio 2.5%.

[0027] Example 6 Composite pipe formula of polytetrafluoroethylene and soluble polytetrafluoroethylene: PTFE powder (Chemours), weight ratio 50%; amino-terminated fluorosilicone oil prepared in Example 1, weight ratio 18%; 340X PFA powder (Chemours), weight ratio 29%; crosslinking agent zinc chloride, weight ratio 3%.

[0028] Example 7 Composite pipe formula of polytetrafluoroethylene and soluble polytetrafluoroethylene: PTFE powder Dyneon TFM (3M), weight ratio 60%; amino-terminated fluorosilicone oil prepared in Example 2, weight ratio 15%; 340X PFA powder (Chemours), weight ratio 22.5%; crosslinking agent 2-formylbenzeneboronic acid, weight ratio 2.5%.

[0029] Example 8 Composite pipe formula of polytetrafluoroethylene and soluble polytetrafluoroethylene: PTFE powder Dyneon TFM (3M), weight ratio 55%; amino-terminated fluorosilicone oil prepared in Example 2, weight ratio 15%; 340X PFA powder (Chemours), weight ratio 27.5%; crosslinking agent terephthalaldehyde, weight ratio 2.5%.

[0030] Example 9 Composite pipe formula of polytetrafluoroethylene and soluble polytetrafluoroethylene: PTFE powder Dyneon TFM (3M), weight ratio 60%; amino-terminated fluorosilicone oil prepared in Example 3, weight ratio 15%; 340X PFA powder (Chemours), weight ratio 22.5%; crosslinking agent 2-formylbenzeneboronic acid, weight ratio 2.5%.

[0031] Example 10 Formulation of PTFE and soluble PTFE composite pipe: Dyneon TFM (3M) PTFE powder, weight ratio 55%; amino-terminated fluorosilicone oil prepared in Example 3, weight ratio 15%; 340X PFA powder (Chemours), weight ratio 27.5%; crosslinking agent terephthalaldehyde, weight ratio 2.5%.

[0032] Comparative Example 1 Formulation of PTFE and soluble PTFE composite pipe: Dyneon TFM (3M) PTFE powder, weight ratio 55%; 300# paraffin oil 15%; 340X PFA powder (Chemours), weight ratio 30%.

[0033] Comparative Example 2 Formulation of PTFE and soluble PTFE composite pipe: Dyneon TFM (3M) PTFE powder, weight ratio 60%; amino-terminated fluorosilicone oil prepared in Example 1, weight ratio 15%; 340X PFA powder (Chemours), weight ratio 25%.

[0034] The preparation methods of the composite pipes in the above Examples 4 - 10 and Comparative Examples 1 and 2 include: S1. Mix the PFA powder, PTFE powder and amino-terminated fluorosilicone oil respectively according to the formulation ratio, and use mechanical stirring to mix the components evenly. S2. Place the mixture of the above components in an oven at no less than 40°C for 24 hours and then take it out, add the crosslinking agent according to the formulation ratio, and use mechanical stirring to mix the components evenly. S3. Process into a ring-shaped pipe and shape it with a pre-forming device. S4. Transfer it into an extruder device and extrude the raw materials into fibers. S5. Sinter at high temperature to form a PTFE and PFA composite pipe.

[0035] Testing part: Process the formulations in Examples 4 - 10 and Comparative Examples 1 and 2 into PTFE and PFA composite pipes according to the above steps, and conduct performance tests according to the following methods. The test results are recorded in Table 1 and Table 2.

[0036] Mechanical property test: The test of elongation at break and tensile strength refers to the test standard QB / T4877 - 2015, and test the longitudinal (MD) tensile strength and longitudinal (MD) elongation at break of different pipes.

[0037] Abrasion resistance test: Refer to the test standard QB / T 5101 - 2017, and test the mass wear rate and wall thickness wear rate of different specimens on a pipe abrasion resistance testing machine for 100,000 and 500,000 swing cycles.

[0038] Gas permeability test: Referring to the test standard GB / T 1038-2000 Test Method for Gas Permeability of Plastic Films and Sheets, the gas permeation rate of different pipes to air was tested.

[0039] High-temperature creep resistance test: The high-temperature creep resistance performance of PTFE and PFA composite pipes was evaluated by testing the compressive creep amount at room temperature and 150 °C. A plastic compressive creep tester equipped with a constant temperature box and an infrared displacement sensor was used for testing. The specimen size was a cylinder with dimensions of 20×20 mm. The test temperatures were room temperature and 150 °C, the compressive load was 15 MPa, and the test time was 60 h.

[0040] Through the data analysis of Table 1 and Table 2, it can be seen that on the basis of mixing two raw materials, PTFE and PFA, adding amino-terminated fluorosilicone oil and the corresponding cross-linking agent can improve the wear resistance, tensile strength, gas permeability and high-temperature creep resistance of PTFE and PFA composite pipes. This is because chemical bonds can be formed between the amino groups of the amino-terminated fluorosilicone oil and the cross-linking agent. At the same time, the amino-terminated fluorosilicone oil has a CF3-containing fluorinated chain segment, which has good compatibility with the PTFE or PFA polymer matrix.

[0041] In Comparative Example 1, hydrocarbon-based solvent oil was used as the lubricant in the processing of PTFE and PFA pellets. The hydrocarbon-based solvent oil does not contain C-F bonds and has poor compatibility with the fluorine-based polymer materials PTFE and PFA. No cross-linking agent was added either, resulting in a significant decrease in its wear resistance, tensile strength, impermeability and high-temperature creep resistance compared with Examples 4-10.

[0042] In Comparative Example 2, the amino groups at the ends of the fluorosilicone oil were not cross-linked with a cross-linking agent. Although the elongation at break of the composite pipe was relatively higher, its wear resistance, tensile strength, impermeability and high-temperature creep resistance were not as good as those of Examples 4-10 after adding the cross-linking agent.

[0043] Table 1

[0044] Table 2

[0045] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of them. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention. Although the specific implementation manners of the present invention have been described above, it is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications or deformations that can be made without creative labor on the basis of the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene, characterized in that: The composite pipe includes: polytetrafluoroethylene, soluble polytetrafluoroethylene, amino-terminated fluorosilicone oil and cross-linking agent; Wherein, the polytetrafluoroethylene is selected from polytetrafluoroethylene powder, and its average particle size does not exceed 100 μm; The soluble polytetrafluoroethylene is selected from soluble polytetrafluoroethylene powder, and its average particle size does not exceed 100 μm; Amino-terminated fluorosilicone oil is obtained by anionic or cationic ring-opening polymerization of 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)cyclotrisiloxane and then end-capping with an amino-containing silane coupling agent. The crosslinking agent is selected from: inorganic zinc salts, or Any one or more of .

2. The polytetrafluoroethylene and soluble polytetrafluoroethylene composite pipe according to claim 1, characterized in that: The amino-containing silane coupling agent includes any one or more of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, N-aminoethyl-3-aminopropyltrimethoxysilane or N-aminoethyl-3-aminopropylmethyldimethoxysilane.

3. The composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene according to claim 1, characterized in that: The inorganic zinc salt is selected from any one or more of zinc chloride, zinc sulfate or zinc nitrate.

4. The composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene according to claim 1, characterized in that: Said Any one or more selected from 2-formylphenylboronic acid, 3-formylphenylboronic acid or 4-formylphenylboronic acid.

5. The composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene according to claim 1, characterized in that: Said Any one or more selected from terephthalaldehyde, o-phthalaldehyde or isophthalaldehyde.

6. The polytetrafluoroethylene and soluble polytetrafluoroethylene composite pipe according to claim 1, characterized in that: The polytetrafluoroethylene and soluble polytetrafluoroethylene composite pipe is composed of the following weight percentages: 50-75% polytetrafluoroethylene, 20-40% soluble polytetrafluoroethylene, 10-20% amino-terminated fluorosilicone oil, and 1-5% cross-linking agent.

7. The method for processing a composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene according to any one of claims 1 to 6, characterized in that: The polytetrafluoroethylene, soluble polytetrafluoroethylene and amino-terminated fluorosilicone oil are mixed in proportion, and after ripening, a cross-linking agent is added in accordance with the formula ratio; The aging is to place the mixture in an oven at a temperature not lower than 40° C. for 12-48 hours.

8. The method for processing a composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene according to claim 7, characterized in that: The specific steps of the processing method include: S1. Mix polytetrafluoroethylene, soluble polytetrafluoroethylene and amino-terminated fluorosilicone oil according to the formula ratio, and mix the components evenly by mechanical stirring; S2. Place the mixture of the above components in an oven at not less than 40° C. for aging for 24 hours, then take it out, add a cross-linking agent according to the formula ratio, and mix the components evenly by mechanical stirring; S3, using preforming equipment to process the tube into a ring shape and finalize the shape; S4, moving the raw material into an extruder device to extrude the raw material into a fiber shape; S5, high temperature sintering to obtain a composite pipe.

9. Use of the composite pipe of polytetrafluoroethylene and soluble polytetrafluoroethylene as claimed in any one of claims 1 to 6 in a heat exchanger tube.

Images