High-heat-resistance PFA / PTFE composite film and preparation method thereof

Abstract

The invention relates to the technical field of polymer composite films, and particularly discloses a high-heat-resistance PFA / PTFE composite film 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 torque rheometer for blending, extruding at the temperature of 350-380 DEG C and the 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, chain segment slippage is effectively inhibited, and split-phase crystallization is eliminated; and finally, carrying out hot pressing to prepare the PFA / PTFE composite film. The preparation method eliminates macroscopic phase separation, keeps the stability of mechanical properties while improving the heat resistance of the material, and is suitable for manufacturing high-reliability cable insulation and nuclear-grade sealing elements.

Description

Technical Field

[0001] The invention belongs to the technical field of composite films, and in particular relates to a highly heat-resistant PFA / PTFE composite film and a preparation method thereof. Background Art

[0002] As an important modified variety of polytetrafluoroethylene (PTFE), fusible polytetrafluoroethylene (PFA) breaks through the bottleneck of PTFE's difficulty in melt processing by introducing perfluoroalkoxy side chains, allowing it to be formed through processes such as extrusion and injection molding. However, despite its certain melt processability, PFA still faces the dual challenges of thermal stability and mechanical properties under extreme working conditions: its semi-crystalline structure is prone to problems such as disordered lamellar thickness gradient and uneven spherulite size distribution during repeated thermal cycles, resulting in a significant attenuation of the elastic modulus at high temperatures and a lower crack propagation threshold. Therefore, how to improve the thermally induced structural stability and strength-toughness matching of PFA has become a key scientific issue in promoting its replacement of traditional fluoroplastics in advanced manufacturing.

[0003] In the prior art, the performance of PFA is mainly improved by copolymerization modification or physical blending. For example, the Chinese patent document with application number CN201910561032.1 uses a method of fluorination treatment after blending PTFE emulsion with PFA emulsion, uses a surfactant to promote two-phase dispersion, forms a uniform powder after coagulation, washing and drying, and then improves crack resistance by melt blending and granulation. Although this method can suppress brittleness by introducing high molecular weight PTFE (number average molecular weight ≥ 1 million) and increase the flexural life by about 22%, the difference in crystallization behavior between PTFE and PFA leads to the existence of a phase separation structure in the blend, and the problem of insufficient interfacial bonding force is not completely solved; another Chinese patent document with application number CN201180038634.0 induces epitaxial co-crystallization of PFA and PTFE by adding 15-50wt% of melt-flowable PTFE (low molecular weight PTFE powder) and combining it with high temperature thermal aging, but the introduction of low molecular weight PTFE causes a significant decrease in melt flow rate.

[0004] In summary, although the existing technology has achieved performance improvement through component design and thermal history regulation, there are still bottlenecks in phase separation suppression, processability-mechanical property balance and multifunctional integration. It is urgently needed to further optimize through innovative means such as modification and forced shearing process to improve the heat resistance of the material while maintaining the stability of the mechanical properties. Summary of the Invention

[0005] The present invention aims to solve the problems of poor thermal stability and insufficient mechanical properties of existing PFA / PTFE composite films caused by PTFE / PFA phase separation crystallization. A fluorinated ether monomer solution is introduced by physical methods to construct a volume expander-nucleator bifunctional agent, and a forced shear process is used to achieve three breakthroughs: first, the perfluoroalkyl side chains in the monomer interact with the polytetrafluoroethylene lamellae through van der Waals interaction, combined with the physical entanglement of the vinyl ends with PFA, to form a topological entanglement network that inhibits phase separation; second, the heterogeneous nucleation density is increased by short-chain monomers to obtain a fine-grained structure, or the homogeneous nucleation barrier is reduced by long-chain monomers to induce perfect crystal growth; third, the high shear field drives the physical entanglement of polytetrafluoroethylene fibrillated fragments with the PFA melt.

[0006] To achieve the above object, the present invention adopts the following technical solution: a method for preparing a highly heat-resistant PFA / PTFE composite film, comprising the following steps:

[0007] S1, subjecting polytetrafluoroethylene, a modifier, and a wetting agent to ball milling at room temperature and then centrifuging to obtain modified polytetrafluoroethylene;

[0008] S2. Add modified polytetrafluoroethylene and PFA pellets into a torque rheometer for blending, and extrude into pellets at a temperature of 350-380° C. and a rotation speed of 100-150 rpm for 5-10 min to obtain a PFA / PTFE composite.

[0009] S3. Hot pressing the PFA / PTFE composite material at 350-380° C. and a pressure of 2-5 MPa to obtain a highly heat-resistant PFA / PTFE composite film.

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

[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, modifier and wetting agent mixed and ball-milled is 1:(0.02-0.05):(0.05-0.2).

[0015] Preferably, in step S1, the ball milling time is 3-8 hours.

[0016] Preferably, in step S2, the diameter of the PFA pellets is ≤10 mm and the comonomer content thereof is greater than 2 wt%.

[0017] Preferably, in step S2, the blending mass ratio of the modified polytetrafluoroethylene to the PFA pellets is 1:1 to 7:3.

[0018] Preferably, the manufacturer of the torque rheometer is Shanghai Kechuang Rubber and Plastic Machinery Equipment Co., Ltd., and the model is XSS-300.

[0019] A second object of the present invention is to provide a highly heat-resistant PFA / PTFE composite film prepared by the method for preparing the highly heat-resistant PFA / PTFE composite film described in any one of the above.

[0020] The beneficial effects of the present invention compared to the prior art are:

[0021] (1) The present invention addresses the problems of interface defects and unstable mechanical properties caused by phase separation of PTFE and PFA blends in the prior art, and provides a method for preparing a highly heat-resistant PFA / PTFE composite film:

[0022] First, polytetrafluoroethylene (PTFE), a modifier, and a wetting agent are subjected to room temperature ball milling to achieve PTFE modification. Fluorinated ether monomers are then used to topologically modify the PTFE surface. Perfluoroalkyl side chains anchor the PTFE platelets, physically entangle the vinyl-terminated PFA, and construct a molecular bridge entanglement network.

[0023] Subsequently, the modified polytetrafluoroethylene and PFA pellets are added to the torque rheometer for blending, and extruded at high temperature and high speed. The high shear field drives the polytetrafluoroethylene fibrillated fragments to semi-molten entanglement with the PFA melt, so that the polytetrafluoroethylene and PFA form a mutually encapsulated structure, forming a fine-grained-physical entangled composite structure, which effectively inhibits segment slip and eliminates phase crystallization. Through physical methods, the molecular bridging mediated by fluorinated ether monomers and forced shearing work synergistically to fundamentally solve the phase crystallization problem of PTFE / PFA composite films: the formation of a topological entanglement network enables the PTFE lamellae and the PFA matrix to achieve nano-level interpenetration, significantly eliminating the macroscopic phase separation phenomenon of traditional blending and obtaining a homogeneous crystal structure; the fine-grained-entangled composite interface constructed simultaneously effectively blocks the crack propagation path and maintains the stability of mechanical properties. The PFA / PTFE composite film prepared by the present invention has high heat resistance and is suitable for the manufacture of high-reliability cable insulation and nuclear-grade seals. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 1 is the DSC curve of the PFA / PTFE composite film of the present invention and the single PFA film;

[0025] Figure 2Schematic diagram of the crystal structure of the PFA / PTFE composite film of the present invention;

[0026] Figure 3 These are the tensile curves of the PFA / PTFE composite film of the present invention and a single PFA film. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] Example 1

[0029] This embodiment provides a method for preparing a highly heat-resistant PFA / PTFE composite film, which specifically includes the following steps:

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

[0031] S2. Modified polytetrafluoroethylene and PFA pellets were added to a torque rheometer (manufactured by Shanghai Kechuang Rubber & Plastic Machinery Equipment Co., Ltd., model XSS-300) in a mass ratio of 1:1, and blended. The mixture was extruded and pelletized at 350° C. and 100 rpm for 10 min to obtain a PFA / PTFE composite. The PFA pellets had a diameter of ≤10 mm and a comonomer content of 2.9 wt % (greater than 2 wt %).

[0032] S3. Hot pressing the PFA / PTFE composite material on a hot press at 350° C. and a pressure of 2 MPa to obtain a highly heat-resistant PFA / PTFE composite film 1 with a thickness of 0.2 mm.

[0033] Example 2

[0034] This embodiment provides a method for preparing a highly heat-resistant PFA / PTFE composite film, which specifically includes the following steps:

[0035] S1, 60 parts by mass of PTFE powder (particle size 50-500 nm), 2 parts by mass of a modifier (perfluoroethyl vinyl ether) and 5 parts by mass of a wetting agent (perfluoropolyether oil) were ball milled at room temperature for 3 hours, and centrifuged to obtain modified polytetrafluoroethylene;

[0036] S2. Modified polytetrafluoroethylene and PFA pellets were added to a torque rheometer (manufactured by Shanghai Kechuang Rubber & Plastic Machinery Equipment Co., Ltd., model XSS-300) in a mass ratio of 3:2 for blending, and extruded at 350° C. and 120 rpm for 10 min to obtain a PFA / PTFE composite; the PFA pellets had a diameter of ≤10 mm and a comonomer content of 3.4 wt % (greater than 2 wt %);

[0037] S3. Hot pressing the PFA / PTFE composite material on a hot press at 350° C. and a pressure of 3 MPa to obtain a highly heat-resistant PFA / PTFE composite film 2 with a thickness of 0.2 mm.

[0038] Example 3

[0039] This embodiment provides a method for preparing a highly heat-resistant PFA / PTFE composite film, which specifically includes the following steps:

[0040] S1, 70 parts by mass of PTFE powder (particle size 50-500 nm), 3 parts by mass of a modifier (perfluoropropyl vinyl ether) and 10 parts by mass of a wetting agent (hydrofluoroether) were ball milled at room temperature for 3 hours, and centrifuged to obtain modified polytetrafluoroethylene;

[0041] S2. Modified polytetrafluoroethylene and PFA pellets were added to a torque rheometer (manufactured by Shanghai Kechuang Rubber & Plastic Machinery Equipment Co., Ltd., model XSS-300) in a mass ratio of 7:3 for blending, and extruded at 350° C. and 150 rpm for 10 min to obtain a PFA / PTFE composite. The PFA pellets had a diameter of ≤10 mm and a comonomer content of 4.0 wt % (greater than 2 wt %).

[0042] S3. Hot pressing the PFA / PTFE composite material on a hot press at 350° C. and a pressure of 5 MPa to obtain a highly heat-resistant PFA / PTFE composite film 3 with a thickness of 0.2 mm.

[0043] The high heat-resistant PFA / PTFE composite film prepared in Example 1 was subjected to thermal performance testing, and the DSC curve of the test was as follows: Figure 1 As shown. Figure 1 The modified composite film's melting peak shifts toward higher temperatures and its peak width decreases, indicating a more homogenized crystalline structure. The material's DSC curve exhibits only a single melting peak. This improves heat resistance while maintaining stable mechanical properties.

[0044] The crystal structure of the highly heat-resistant PFA / PTFE composite film prepared by the present invention is as follows: Figure 2The focus is on demonstrating the spatial arrangement of PTFE platelets and PFA spherulites. PTFE platelets are dispersed in the PFA matrix in a parallel stacked or radially interlaced manner, and PFA spherulites grow epitaxially with the PTFE platelets as nucleation points to form radial spherulites.

[0045] The mechanical properties of the PFA / PTFE composite films 1-3 prepared in Examples 1-3 were tested. The test results are shown in FIG. Figure 3 As shown. Figure 3 It can be seen that the elongation at break of the prepared composite films 1-3 can still be maintained at more than 330% and the reduction rate of the elastic modulus compared with pure PFA is within 5%.

[0046] Those skilled in the art will appreciate that the foregoing descriptions are merely specific embodiments of the present invention, and not exhaustive. It should be noted that numerous variations and modifications are possible for those skilled in the art, and all such variations and modifications that do not exceed the scope of the claims should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a highly heat-resistant PFA / PTFE composite film, characterized in that: The steps include: S1, mixing polytetrafluoroethylene, a modifier and a wetting agent, ball milling the mixture at room temperature, and centrifuging to obtain modified polytetrafluoroethylene; S2. Add modified polytetrafluoroethylene and PFA pellets into a torque rheometer for blending, and extrude into pellets at a temperature of 350-380° C. and a rotation speed of 100-150 rpm for 5-10 min to obtain a PFA / PTFE composite. S3. Hot pressing the PFA / PTFE composite material at 350-380° C. and a pressure of 2-5 MPa to obtain a highly heat-resistant PFA / PTFE composite film.

2. The method for preparing a highly heat-resistant PFA / PTFE composite film according to claim 1, wherein: In step S1, the particle size of the polytetrafluoroethylene is 50-500 nanometers.

3. The method for preparing a highly heat-resistant PFA / PTFE composite film according to claim 1, wherein: 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 a highly heat-resistant PFA / PTFE composite film according to claim 1, wherein 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 a highly heat-resistant PFA / PTFE composite film according to claim 1, wherein: In step S1, the mass ratio of the polytetrafluoroethylene, the modifier and the wetting agent mixed and ball-milled is 1:(0.02-0.05):(0.05-0.2).

6. The method for preparing a highly heat-resistant PFA / PTFE composite film according to claim 1 or 5, wherein: In step S1, the ball milling time is 3-8 hours.

7. The method for preparing a highly heat-resistant PFA / PTFE composite film according to claim 1, wherein: In step S2, the diameter of the PFA pellets is ≤10 mm and the comonomer content thereof is greater than 2 wt%.

8. The method for preparing a highly heat-resistant PFA / PTFE composite film according to claim 1 or 7, wherein: In step S2, the blending mass ratio of the modified polytetrafluoroethylene and the PFA pellets is 1:1 to 7:

3.

9. The method for preparing a highly heat-resistant PFA / PTFE composite film according to claim 1, wherein: The torque rheometer is manufactured by Shanghai Kechuang Rubber & Plastic Machinery Equipment Co., Ltd., and the model is XSS-300.

10. A high-heat-resistant PFA / PTFE composite film prepared by the method for preparing a high-heat-resistant PFA / PTFE composite film according to any one of claims 1 to 9.

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