High-heat-resistance PFA / PTFE composite material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of polymer composite materials, and particularly discloses a high-heat-resistance PFA / PTFE composite material and a preparation method thereof. The preparation method comprises the following steps: carrying out ball milling on polytetrafluoroethylene (PTFE), a modifier and a wetting agent at room temperature to obtain modified PTFE; then adding the modified PTFE and fusible polytetrafluoroethylene (PFA) granules into a twin-screw extruder or a torque rheometer for blending, extruding at 350-380 DEG C and a rotating speed of 100-150rpm, and driving polytetrafluoroethylene fibrillated fragments and a PFA melt to generate semi-molten entanglement in a high shear field, so that the polytetrafluoroethylene and the PFA form a mutual coating structure, thereby obtaining the PTFE / PFA composite material. And chain segment slippage is effectively inhibited, split-phase crystallization is eliminated, and the PFA / PTFE composite material is prepared. According to the preparation method, macroscopic phase separation is eliminated, the heat resistance of the material is improved, meanwhile, the stability of the mechanical property is kept, and the preparation method is suitable for manufacturing high-reliability cable insulation, connectors and nuclear-grade sealing elements.

Description

[0001] The present application claims priority to the application with the application number 2025109734121, entitled "A high-heat-resistant PFA / PTFE composite film and a preparation method thereof", filed on July 15, 2025, and originally received by the China Intellectual Property Office. TECHNICAL FIELD

[0002] The present application belongs to the technical field of composite materials, and specifically relates to a high-heat-resistant PFA / PTFE composite material, a preparation method thereof and an application thereof. BACKGROUND

[0003] As an important modified variety of polytetrafluoroethylene (PTFE), the fusible polytetrafluoroethylene (PFA) breaks through the bottleneck of PTFE difficult to melt processing by introducing a perfluoroalkoxy side chain, so that it can be formed by processes such as extrusion and injection molding. However, although PFA has certain melt processability, it still faces the dual challenges of thermal stability and mechanical properties under extreme working conditions: the semi-crystalline structure of PFA is prone to problems such as disorder of lamellar thickness gradient and uneven distribution of spherulite size in repeated thermal cycling, resulting in significant attenuation of elastic modulus at high temperatures and reduction of crack propagation threshold. Therefore, how to improve the thermal structure stability and strength-toughness matching of PFA has become a key scientific problem for promoting its replacement of traditional fluoroplastics in the field of advanced manufacturing.

[0004] In the prior art, the performance of PFA is mainly improved by copolymerization modification or physical blending. For example, a Chinese patent document with the application number CN201910561032.1 uses a method of blending PTFE emulsion with PFA emulsion and then fluorinating, uses a surfactant to promote the dispersion of the two phases, forms a uniform powder after coagulation, washing and drying, and then improves the crack resistance by melt blending and granulation. Although this method can inhibit brittleness by introducing high molecular weight PTFE (number average molecular weight ≥ 1 million) and improve the flex life by about 22%, the difference in crystallization behavior between PTFE and PFA leads to a phase-separated structure in the blend, and the problem of insufficient interfacial bonding force is not completely solved. Another Chinese patent document with the application number CN201180038634.0 adds 15-50wt% of fusible flow PTFE (low molecular weight PTFE powder) and combines high-temperature thermal aging to induce PFA and PTFE to occur epitaxial co-crystallization, but the introduction of low molecular weight PTFE significantly reduces the melt flow rate.

[0005] In summary, although the prior art has achieved performance improvement through component design and thermal history control, there are still bottlenecks in phase separation suppression, processing-mechanical property balance and multi-functional integration, and it is necessary to further optimize the material through innovative means such as modification and forced shear process to improve the heat resistance while maintaining the stability of the mechanical properties. SUMMARY

[0006] The present application aims to solve the problems of poor thermal stability and insufficient mechanical properties caused by PTFE / PFA phase separation crystallization in the existing PFA / PTFE composite material, and introduces a fluorine-containing ether monomer solution by physical method to construct a compatibilization-nucleation dual functional agent, and cooperates with forced shear process to realize triple breakthrough: first, the perfluoroalkyl side chain in the monomer combines with the polytetrafluoroethylene lamella van der Waals interaction and the vinyl end physically entangles with PFA to form a topological entanglement network to inhibit phase separation; second, the short-chain monomer improves the heterogeneous nucleation density to obtain fine crystal structure or the long-chain monomer reduces the homogeneous nucleation barrier to induce perfect crystal growth; and third, the high shear field drives the polytetrafluoroethylene fibrillation fragments to physically entangle with PFA melt.

[0007] To achieve the above object, the present application adopts the following technical scheme: a preparation method of a high-heat-resistant PFA / PTFE composite material, comprising the following steps:

[0008] S1, mixing polytetrafluoroethylene, a modifier and a wetting agent, then room temperature ball milling reaction and centrifugal separation to obtain modified polytetrafluoroethylene;

[0009] S2, blending the modified polytetrafluoroethylene and PFA granules in a twin-screw extruder or a torque rheometer, extruding and granulating at a temperature of 350-380 DEG C and a speed of 100-150 rpm, with an extrusion time of 5-10 min, to obtain high-heat-resistant PFA / PTFE composite material.

[0010] Further improvement on the preparation method of the high-heat-resistant PFA / PTFE composite material:

[0011] Preferably, in step S1, the particle size of the polytetrafluoroethylene is 50-500 nanometers.

[0012] Preferably, in step S1, the modifier is one or a combination of two or more of perfluoromethyl vinyl ether, perfluoroethyl vinyl ether and perfluoropropyl vinyl ether.

[0013] Preferably, the wetting agent is one or a combination of two or more of ethanol, isopropyl alcohol, perfluoropolyether oil, hydrofluoroether, perfluorohexane and perfluoro(2-butyltetrahydrofuran).

[0014] Preferably, in step S1, the mass ratio of the polytetrafluoroethylene, the modifier and the wetting agent for ball milling is 1:(0.02-0.05):(0.05-0.2), and the ball milling time is 3-8 h.

[0015] Preferably, in step S2, the diameter of the PFA granules is ≤10 mm and the copolymer content is greater than 2wt%.

[0016] Preferably, in step S2, the blending mass ratio of the modified polytetrafluoroethylene and the PFA granules is 1:1-7:3.

[0017] Preferably, in step S2, the torque rheometer is produced by Shanghai Keyun Rubber and Plastic Machinery Equipment Co., Ltd., and the model is XSS-300; the double-screw extruder is produced by Kebeilong Keya Machinery Co., Ltd., and the model is CTE-35.

[0018] The second object of the present application is to provide a high-heat-resistant PFA / PTFE composite material prepared by the preparation method of any one of the above high-heat-resistant PFA / PTFE composite materials.

[0019] The third object of the present application is to provide an application of the above high-heat-resistant PFA / PTFE composite material in the manufacture of high-reliability cable insulation, connectors and nuclear-level sealing elements.

[0020] The beneficial effects of the present application compared with the prior art are:

[0021] (1) The present application provides a preparation method of a high-heat-resistant PFA / PTFE composite material aiming at the interface defects and unstable mechanical properties caused by the phase separation of PTFE and PFA in the prior art:

[0022] First, the polytetrafluoroethylene, the modifier and the wetting agent are subjected to room temperature ball milling reaction to realize the modification of the polytetrafluoroethylene. The fluorine-containing ether monomer is used to topologically modify the surface of PTFE, and the perfluoroalkyl side chain is used to anchor the PTFE lamella and physically entangle PFA at the vinyl end to construct a molecular bridge entanglement network.

[0023] Subsequently, the modified polytetrafluoroethylene and PFA granules are added to a double-screw extruder or a torque rheometer for blending, and are extruded at high temperature and high speed. The high shear field drives the polytetrafluoroethylene fibrillation fragments to occur semi-melt entanglement with the PFA melt, so that the polytetrafluoroethylene and PFA form a mutual coating structure, form a fine crystal-physical entanglement composite structure, effectively inhibit the chain segment slip and eliminate the phase separation crystallization. Through the physical method, the molecular bridging mediated by the fluorine-containing ether monomer and the forced shearing synergistic effect fundamentally solve the phase separation crystallization problem of the PTFE / PFA composite film: the formation of the topological entanglement network makes the PTFE lamella and the PFA matrix realize nanoscale interpenetration, significantly eliminates the macroscopic phase separation phenomenon of traditional blending, and obtains a homogeneous crystal structure; the fine crystal-entanglement composite interface constructed synchronously effectively blocks the crack propagation path, and keeps the stability of the mechanical properties. The PFA / PTFE composite material prepared by the present application has high heat resistance and is suitable for the manufacture of high-reliability cable insulation, connectors and nuclear-level sealing elements. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The DSC curves of the composite board 1 prepared from the high-heat-resistant PFA / PTFE composite material prepared in Example 1 and the single PFA material are shown in the figure.

[0025] Figure 2 is a schematic diagram of the crystal structure of the composite sheet 1 made of the high-heat-resistant PFA / PTFE composite material made in Example 1;

[0026] Figure 3 is a tensile curve of the composite sheet 1-3 made of the high-heat-resistant PFA / PTFE composite material made in Example 1 and a single PFA material. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application is further described in detail below in combination with examples, and all other examples obtained by those skilled in the art without creative labor on the basis of the examples in the present application belong to the scope of protection of the present application.

[0028] Example 1

[0029] The present embodiment provides a preparation method of a high-heat-resistant PFA / PTFE composite material, which specifically comprises the following steps:

[0030] S1, 50 parts by mass of PTFE powder (particle size 50-500 nanometers), 1 part by mass of a modifier (perfluoromethyl vinyl ether) and 10 parts by mass of a wetting agent (ethanol) are ball milled in a ball mill at room temperature for 3 hours, and centrifuged to obtain modified polytetrafluoroethylene;

[0031] S2, the modified polytetrafluoroethylene and PFA granules are added into a torque rheometer (manufacturer Shanghai Kechuang Rubber and Plastic Machinery Equipment Co., Ltd., model XSS-300) for blending at a mass ratio of 1:1, and extruded and granulated at 350℃ and a rotation speed of 100 rpm, with an extrusion time of 10 min, to obtain a PFA / PTFE composite material 1; the diameter of the PFA granules is ≤10 mm, and the copolymer monomer content thereof is 2.9wt% (greater than 2wt%).

[0032] Example 2

[0033] The present embodiment provides a preparation method of a high-heat-resistant PFA / PTFE composite material, which specifically comprises the following steps:

[0034] S1, 60 parts by mass of PTFE powder (particle size 50-500 nanometers), 2 parts by mass of a modifier (perfluoroethyl vinyl ether) and 5 parts by mass of a wetting agent (perfluoropolyether oil) are ball milled in a ball mill at room temperature for 3 hours, and centrifuged to obtain modified polytetrafluoroethylene;

[0035] S2, the modified polytetrafluoroethylene and PFA granules are added into a torque rheometer (manufacturer Shanghai Kexuehuangsu Rubber and Plastic Machinery Equipment Co., Ltd., model XSS-300) for blending in a mass ratio of 3:2, extruded at 350℃ and 120 rpm, and the extrusion time is 10 min, to obtain PFA / PTFE composite material 2; the diameter of the PFA granules is ≤10 mm and the copolymer monomer content thereof is 3.4wt% (greater than 2wt%).

[0036] Example 3

[0037] The embodiment provides a preparation method of a high-heat-resistant PFA / PTFE composite material, and specifically comprises the following steps:

[0038] S1, 70 parts by mass of PTFE powder (particle size 50-500 nanometers), 3 parts by mass of a modifier (perfluoropropyl vinyl ether) and 10 parts by mass of a wetting agent (hydrofluoroether) are ball milled in a ball mill for 3 hours at room temperature, centrifuged to obtain modified polytetrafluoroethylene;

[0039] S2, the modified polytetrafluoroethylene and PFA granules are added into a torque rheometer (manufacturer Shanghai Kexuehuangsu Rubber and Plastic Machinery Equipment Co., Ltd., model XSS-300) for blending in a mass ratio of 3:2, extruded at 350℃ and 120 rpm, and the extrusion time is 10 min, to obtain PFA / PTFE composite material 2; the diameter of the PFA granules is ≤10 mm and the copolymer monomer content thereof is 3.4wt% (greater than 2wt%).

[0040] Performance test:

[0041] The PFA / PTFE composite material 1 prepared in Example 1 is hot-pressed on a hot press at 350℃, and the pressure is 2MPa, to obtain a high-heat-resistant PFA / PTFE composite plate 1, and the thickness is 0.2mm.

[0042] The PFA / PTFE composite material 2 prepared in Example 1 is hot-pressed on a hot press at 350℃, and the pressure is 3MPa, to obtain a high-heat-resistant PFA / PTFE composite plate 2, and the thickness is 0.5mm.

[0043] The PFA / PTFE composite material 3 prepared in Example 3 is hot-pressed on a hot press at 350℃, and the pressure is 5MPa, to obtain a high-heat-resistant PFA / PTFE composite plate 3, and the thickness is 0.8mm.

[0044] The high-heat-resistant PFA / PTFE composite plate 1 is subjected to thermal performance test, and the tested DSC curve is as shown in Figure 1 Figure 1 ​It can be seen that the melting peak of the modified composite board shifts to high temperature and the peak width decreases, indicating that the crystalline structure is uniform. The DSC curve of the material only has one melting peak. While improving the heat resistance, the mechanical properties remain stable.

[0045] The crystal structure of the high-heat-resistant PFA / PTFE composite board 1 is shown in Figure 2 , which focuses on showing the spatial arrangement relationship between PTFE lamellar crystals and PFA spherulites. PTFE lamellar crystals are dispersed in PFA matrix in parallel stacking or radial interpenetration mode, and PFA spherulites grow epitaxially with the PTFE lamellar crystals as nucleation points to form radial spherulites.

[0046] The high-heat-resistant PFA / PTFE composite board 1-3 was subjected to mechanical property test, and the test results are shown in Figure 3 . It can be seen from Figure 3 that the elongation at break of the prepared composite board 1-3 can still be maintained above 330%, and the elastic modulus is reduced by less than 5% compared with pure PFA.

[0047] Those skilled in the art should understand that the above description is only several specific embodiments of the present application, not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications and improvements that do not exceed the scope of the claims should be considered as the protection scope of the present application.

Claims

1. A method for producing a highly heat-resistant PFA / PTFE composite material, characterized by comprising the steps of: It comprises the following steps: ​ S1, mixing polytetrafluoroethylene, modifier and wetting agent, then ball milling at room temperature, centrifugal separation, to obtain modified polytetrafluoroethylene; S2, adding the modified polytetrafluoroethylene and PFA granules into a double screw extruder or torque rheometer for blending, extruding and granulating at a temperature of 350-380℃ and a speed of 100-150rpm, the extruding time being 5-10min, to obtain high heat-resistant PFA / PTFE composite material.

2. The method for producing a high heat-resistant PFA / PTFE composite material according to claim 1, characterized by, In step S1, the particle size of the polytetrafluoroethylene is 50-500nm.

3. The method for preparing the high heat-resistant PFA / PTFE composite material according to claim 1, characterized in that, In step S1, the modifier is one or a combination of two or more of perfluoromethyl vinyl ether, perfluoroethyl vinyl ether and perfluoropropyl vinyl ether.

4. The method for preparing the high heat-resistant PFA / PTFE composite material according to claim 1, characterized in that, In step S1, the wetting agent is one or a combination of two or more of ethanol, isopropyl alcohol, perfluoropolyether oil, hydrofluoroether, perfluorohexane and perfluoro(2-butyltetrahydrofuran).

5. The method for preparing the high heat-resistant PFA / PTFE composite material according to claim 1, characterized in that, In step S1, the mass ratio of the polytetrafluoroethylene, modifier and wetting agent for ball milling is 1:(0.02-0.05):(0.05-0.2), and the ball milling time is 3-8h.

6. The method for preparing the high heat-resistant PFA / PTFE composite material according to claim 1, characterized in that, In step S2, the diameter of the PFA granules is ≤10mm and the copolymer content is greater than 2wt%.

7. The method of producing a highly heat-resistant PFA / PTFE composite material according to claim 1 or 6, characterized by, In step S2, the blending mass ratio of the modified polytetrafluoroethylene and PFA granules is 1:1-7:

3.

8. The method for preparing the high heat-resistant PFA / PTFE composite material according to claim 1, characterized in that, In step S2, the torque rheometer is XSS-300 produced by Shanghai Kechuang Rubber and Plastic Machinery Equipment Co., Ltd., and the double screw extruder is CTE-35 produced by Kebailong Koyama Machinery Co., Ltd.

9. A high heat-resistant PFA / PTFE composite material prepared by the method of any one of claims 1-8.

10. Use of the high heat-resistant PFA / PTFE composite material of claim 9 in the manufacture of high-reliability cable insulation, connectors and nuclear-grade sealing elements.

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