High-temperature-resistant intrinsic self-recovery polypropylene insulating material as well as preparation method and application thereof

Abstract

The invention belongs to an insulating material, relates to a polypropylene-based insulating material, and in particular relates to a high-temperature-resistant intrinsic self-recovery polypropylene insulating material as well as a preparation method and application thereof. The material is formed by blending a polypropylene grafting material and an ethylene-tetrafluoroethylene copolymer grafting material according to a mass ratio of 6.0: 4.0-9.5: 0.5, wherein the PP graft material comprises a PP graft polymer and an antioxidant, and the PP graft polymer is a graft polymer formed by grafting 4-propenyloxy-2-hydroxybenzophenone to polypropylene; the ETFE graft material comprises an ETFE graft polymer and an antioxidant, and the ETFE graft polymer is a graft polymer of glycerol grafted ethylene-tetrafluoroethylene copolymer. On the basis of keeping the original excellent performance of polypropylene, the polypropylene has higher heat resistance and self-recovery capability through a grafting modification technical means.

Description

Technical Field

[0001] The present invention belongs to insulating materials, relates to polypropylene-based insulating materials, and particularly relates to a high-temperature resistant intrinsic self-recovery polypropylene insulating material, a preparation method thereof, and an application thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and it is not necessarily regarded as an admission or an indication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Polypropylene insulating materials have attracted much attention due to their good insulation performance, high temperature resistance grade, recyclability, etc. As a non-polar polymer, polypropylene performs excellently in terms of insulation properties such as breakdown field strength and volume resistivity. At the same time, it has a high melting point and a high long-term allowable working temperature. When used as an insulating material, the long-term operating temperature of the cable can be increased to 90°C or even 105°C. Although polypropylene insulating materials have many advantages, they still have deficiencies in high-temperature self-recovery performance.

[0004] In the context of modern industrial applications, first of all, attention needs to be focused on the thermal stability of polypropylene insulating materials. At present, the vast majority of polypropylene insulating materials on the market have obvious deficiencies in thermal stability from the perspective of their essential material characteristics. When such materials are in a high-temperature environment for a long time, due to the inherent characteristics of their internal chemical structure, a series of chemical reactions will be triggered. For example, degradation, aging and other phenomena occur. The main reason is that their molecular composition makes their resistance to thermal oxidation poor. Thermal oxidation will cause the polypropylene molecular chains to break and crosslink frequently. These microscopic changes can be reflected in the macroscopic properties, resulting in a significant reduction in the overall performance of the material. Key indicators such as insulation performance and mechanical strength decline. Although polypropylene insulating materials can cope with some high-temperature environments, once today's insulating materials are applied to high-temperature environments with higher and more stringent temperature requirements, the materials simply cannot effectively maintain their high-temperature resistance performance and are difficult to meet the demanding working conditions.

[0005] Secondly, the self-recovery characteristics of current polypropylene insulation materials have obvious defects and deficiencies. Generally, when the external environmental temperature gradually rises, the physical state of the material will inevitably change. During the transition from the solid state to the softened state, the original stable shape and precise dimensions of the material are difficult to maintain, and softening deformation becomes an inevitable result. This morphological change is by no means insignificant. It is directly related to the insulation performance of the material. After softening deformation, the internal molecular arrangement of the material is disordered and cannot effectively block the current as in the normal state, resulting in a sharp decline in insulation performance. In severe cases, it may even induce electrical faults, posing a great safety hazard to the operation of the entire system. Not only is the service life of the material itself significantly shortened, but its reliability in various application scenarios also deteriorates, making it difficult to ensure the stable operation of the system.

[0006] To improve the above deficiencies of polypropylene insulation materials, researchers have conducted various modification studies, such as copolymerization modification, nanoparticle modification, blending modification, etc. Among them, copolymerization modification involves adding one or more other monomers (such as olefins like ethylene and butene) during the polymerization stage of propylene monomers, and using highly efficient catalysts to copolymerize them to form copolymers, thereby improving the high-temperature resistance of polypropylene. However, these composite materials can improve the high-temperature resistance of polypropylene, but the improvement effect is not obvious. Summary of the Invention

[0007] To solve the deficiencies of the prior art, the purpose of the present invention is to provide a high-temperature resistant intrinsic self-recovery polypropylene insulation material, its preparation method and application. Based on maintaining the original excellent properties of polypropylene, through graft modification techniques, it is made to have higher heat resistance and self-recovery ability, that is, when the material is subjected to high temperature, it can maintain stable physical and chemical properties, and has the ability to automatically recover to the original state after the temperature drops.

[0008] To achieve the above purpose, the present invention provides the following technical solutions:

[0009] First aspect, a high-temperature resistant intrinsic self-recovery polypropylene insulation material is formed by blending a polypropylene (PP) grafting material and an ethylene-tetrafluoroethylene copolymer (ETFE) grafting material in a mass ratio of 6.0:4.0 to 9.5:0.5;

[0010] Among them, the PP grafting material includes a PP grafting polymer and an antioxidant, and the PP grafting polymer is a grafting polymer of 4-propenyloxy-2-hydroxybenzophenone (AHB) grafted onto polypropylene (PP-g-AHB);

[0011] The ETFE graft material comprises an ETFE graft polymer and an antioxidant. The ETFE graft polymer is a graft polymer (ETFE-g-GL) of glycerol (GL) grafted onto ethylene-tetrafluoroethylene copolymer.

[0012] ETFE is a high-performance fluoropolymer with excellent chemical corrosion resistance, high temperature resistance, low surface energy and anti-aging properties. However, these characteristics also lead to high surface inertness and a melting point close to 280°C, so the difficulty of grafting modification agents is significantly increased. The present invention has tried many common modification agents (such as maleic anhydride, methyl methyl propionate, styrene, etc.), but it is difficult to graft and modify ETFE. Since GL has a polyhydroxy structure, contains three hydroxyl groups (-OH), has strong polarity and hydrophilicity, and can participate in esterification, etherification or condensation reactions, the present invention uses GL to graft and modify ETFE.

[0013] The present invention simultaneously grafts PP with AHB and ETFE with GL, wherein after PP is grafted with AHB polar groups, the compatibility between ETFE-g-GL and PP-g-AHB is improved, the composite material is more evenly distributed, the number of heterogeneous interfaces is increased, and the high temperature resistance of the material is improved; after ETFE is grafted with GL, it can form hydrogen bonds with the AHB polar groups in PP-g-AHB, which not only improves the crystallinity and stability, but also provides a more reliable protective barrier by virtue of the tight molecular chain arrangement, and the interaction of the grafted groups can make the composite material have higher intrinsic self-healing performance.

[0014] In some embodiments, the ETFE grafted material is composed of the following raw materials by weight: 89.0-98.5 parts of ethylene-tetrafluoroethylene copolymer, 1.0-10.0 parts of glycerol, 0.3-0.5 parts of initiator, and 0.2-0.4 parts of antioxidant. Studies have shown that the ETFE grafted material formed under such conditions has better performance when blended with the PP grafted polymer to make a polypropylene insulation material.

[0015] Specifically, the initiator is dicumyl peroxide (DCP), which has a better grafting effect in the blending grafting of ETFE and GL.

[0016] In some embodiments, the PP graft material comprises, by weight, 89.0 to 98.5 parts of polypropylene, 1.0 to 10.0 parts of 4-propyleneoxy-2-hydroxybenzophenone, 0.3 to 0.5 parts of initiator, and 0.2 to 0.4 parts of antioxidant. Studies have shown that the PP graft material formed under such conditions has better performance when blended with the ETFE graft polymer to make a polypropylene insulation material.

[0017] Specifically, the initiator is dicumyl peroxide (DCP). Using this initiator has a better grafting effect in the blending and grafting of PP and AHB.

[0018] In a second aspect, a method for preparing the above-mentioned high-temperature resistant intrinsically self-recovering polypropylene insulating material includes the following steps:

[0019] Provide a PP grafting material;

[0020] Melt-blend ethylene-tetrafluoroethylene copolymer, glycerol, an initiator, and an antioxidant at 250 - 300 °C. During the melt-blending process, under the action of the initiator, the ethylene-tetrafluoroethylene copolymer is grafted with glycerol to obtain ETFE-g-GL, and ETFE-g-GL is mixed evenly with the antioxidant to obtain an ETFE grafting material;

[0021] Melt-blend the PP grafting material and the ETFE grafting material according to a ratio to obtain the product.

[0022] In some embodiments, the temperature for melt-blending the PP grafting material and the ETFE grafting material is 250 - 300 °C.

[0023] In a third aspect, an application of the above-mentioned high-temperature resistant intrinsically self-recovering polypropylene insulating material in a cable.

[0024] The beneficial effects of the present invention are as follows:

[0025] Based on PP-g-AHB, the present invention further grafts ETFE with GL. The GL-grafted modified ethylene-tetrafluoroethylene undertakes part of the role of crystal nuclei, enabling the polypropylene molecular chains to be regularly arranged into spherulites starting from its surface at the crystallization temperature. Therefore, the polypropylene grafting material and the ethylene-tetrafluoroethylene grafting material can form a eutectic structure, thereby reducing the crystallization temperature and co-growing spherulites. This structure can better cope with high-temperature environments and improve the high-temperature resistance of the polypropylene insulating material; at the same time, research also shows that the polypropylene insulating material provided by the present invention has a certain intrinsic thermal self-recovery ability.

[0026] In summary, after being modified by the present invention, the polypropylene insulating material has the characteristics of strong high-temperature resistance, can maintain high thermal stability for a long time, can automatically detect early defects and then repair and fill them. This polypropylene insulating material can inhibit the development of damage, effectively restore the material performance, extend the service life of the material, and thus reduce the economic losses caused by cable replacement. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings forming a part of this specification are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0028] Figure 1 It is the flow chart for preparing the composite material in the embodiments of the present invention;

[0029] Figure 2 It is the comparison chart of X-ray diffraction patterns of pure PP (A) of the present invention and three-component copolymers (B) prepared in Examples 1 to 3;

[0030] Figure 3 It is the DSC curve chart of three-component copolymers prepared in Examples 1 to 3 of the present invention. A is the heating curve from 25°C to 270°C, and B is the cooling curve from 270°C to 25°C;

[0031] Figure 4 It is the crystallization process chart of three-component polymers prepared in Examples 1 to 3 of the present invention, and the scale is 100μm for all;

[0032] Figure 5 It is the comparison chart of TG curves of pure PP of the present invention and three-component copolymers prepared in Examples 1 to 3;

[0033] Figure 6 It is the comparison chart of DGA curves of pure PP of the present invention and three-component copolymers prepared in Examples 1 to 3;

[0034] Figure 7 It is the comparison chart of thermal decomposition temperatures of polypropylene of the present invention and three-component copolymers prepared in Examples 1 to 3;

[0035] Figure 8 It is the thermally recovered polarized light image of pure PP. A is 30°C, B is 90°C, C is 110°C, D is 130°C, E is 150°C, F is 170°C, and the scale is 500μm for all;

[0036] Figure 9 It is the thermally recovered polarized light image of the three-component copolymer prepared in Example 1 of the present invention. A is 30°C, B is 90°C, C is 110°C, D is 130°C, E is 150°C, F is 170°C, and the scale is 500μm for all;

[0037] Figure 10 It is the thermally recovered polarized light image of the three-component copolymer prepared in Example 2 of the present invention. A is 30°C, B is 90°C, C is 110°C, D is 130°C, E is 150°C, F is 170°C, and the scale is 500μm for all;

[0038] Figure 11 It is the thermally recovered polarized light image of the three-component copolymer prepared in Example 3 of the present invention. A is 30°C, B is 90°C, C is 110°C, D is 130°C, E is 150°C, F is 170°C, and the scale is 500μm for all;

[0039] Figure 12This is a comparison chart of the set elongation heat recovery of pure PP of the present invention and three-component copolymers prepared in Examples 1 to 3. Detailed implementation mode

[0040] It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanations of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0041] It should be noted that the terms used herein are only for describing specific implementation modes and are not intended to limit the exemplary implementation modes 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.

[0042] In view of the problem that the existing composite materials have an insignificant improvement effect on the high-temperature resistance performance of polypropylene, the present invention proposes a high-temperature resistant intrinsically self-recovering polypropylene insulating material, its preparation method and application.

[0043] A typical implementation mode of the present invention provides a high-temperature resistant intrinsically self-recovering polypropylene insulating material, which is formed by blending a PP grafting material and an ETFE grafting material in a mass ratio of 6.0:4.0 to 9.5:0.5;

[0044] Among them, the PP grafting material includes a PP grafting polymer and an antioxidant, and the PP grafting polymer is a grafting polymer of 4-propenyloxy-2-hydroxybenzophenone grafted polypropylene;

[0045] The ETFE grafting material includes an ETFE grafting polymer and an antioxidant, and the ETFE grafting polymer is a grafting polymer of glycerol grafted ethylene-tetrafluoroethylene copolymer.

[0046] In some embodiments, the mass ratio of the PP grafting material to the ETFE grafting material is 6.9:3.1 to 9.1:0.9. Research shows that when the mass ratio of the PP grafting material to the ETFE grafting material is 8.9:1.1 to 9.1:0.9, the heat recovery effect of the polypropylene insulating material is better; when the mass ratio of the PP grafting material to the ETFE grafting material is 6.9:3.1 to 7.1:2.9, the recovery amount of the set elongation heat recovery of the polypropylene insulating material is better.

[0047] In some embodiments, the ETFE grafting material is composed of the following raw materials in terms of mass parts: 89.0 to 98.5 parts of ethylene-tetrafluoroethylene copolymer, 1.0 to 10.0 parts of glycerol, 0.3 to 0.5 parts of initiator, and 0.2 to 0.4 parts of antioxidant.

[0048] Specifically, the ETFE grafting material is composed of the following raw materials in parts by mass: 95.0 - 97.5 parts of ethylene-tetrafluoroethylene copolymer, 2.0 - 4.0 parts of glycerol, 0.3 - 0.5 parts of initiator, and 0.2 - 0.4 parts of antioxidant. Research shows that the effect is better under these conditions.

[0049] Specifically, the initiator is dicumyl peroxide.

[0050] Specifically, the antioxidant is antioxidant 168. The antioxidant 168 is a phosphite antioxidant.

[0051] In some embodiments, the PP grafting material, in parts by mass, is composed of 89.0 - 98.5 parts of polypropylene, 1.0 - 10.0 parts of 4 - allyloxy - 2 - hydroxybenzophenone, 0.3 - 0.5 parts of initiator, and 0.2 - 0.4 parts of antioxidant.

[0052] Specifically, the PP grafting material is composed of the following raw materials in parts by mass: 95.0 - 97.5 parts of polypropylene, 2.0 - 4.0 parts of 4 - allyloxy - 2 - hydroxybenzophenone, 0.3 - 0.5 parts of initiator, and 0.2 - 0.4 parts of antioxidant. Research shows that the effect is better under these conditions.

[0053] Specifically, the initiator is dicumyl peroxide.

[0054] Specifically, the antioxidant is antioxidant 168.

[0055] Another embodiment of the present invention provides a preparation method of the above high - temperature - resistant intrinsically self - recovering polypropylene insulating material, including the following steps:

[0056] Provide the PP grafting material;

[0057] Melt - blend ethylene - tetrafluoroethylene copolymer, glycerol, initiator, and antioxidant at 250 - 300 °C. During the melt - blending process, under the action of the initiator, the ethylene - tetrafluoroethylene copolymer is grafted with glycerol to obtain ETFE - g - GL, and ETFE - g - GL is mixed uniformly with the antioxidant to obtain the ETFE grafting material;

[0058] Melt - blend the PP grafting material and the ETFE grafting material according to the ratio to obtain the product.

[0059] In some embodiments, polypropylene, 4 - allyloxy - 2 - hydroxybenzophenone, initiator, and antioxidant are melt - blended at 250 - 300 °C to obtain the PP grafting material. Specifically, the time of melt - blending is 10 - 15 min.

[0060] In some embodiments, in the preparation of the ETFE graft material, the melt blending time is 10 to 15 minutes.

[0061] In some embodiments, the ETFE graft material is first added for melt blending, and then the PP graft material is added for melt blending.

[0062] In some embodiments, the temperature for melt blending of the PP graft material and the ETFE graft material is 250 to 300 °C.

[0063] The third embodiment of the present invention provides an application of the above-mentioned high-temperature intrinsic self-healing polypropylene insulating material in a cable.

[0064] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in combination with specific examples and comparative examples.

[0065] Example 1

[0066] A preparation method of a high-temperature intrinsic self-healing polypropylene insulating material, as Figure 1 shown, includes the following steps:

[0067] Put polypropylene (PP), 4-propenyloxy-2-hydroxybenzophenone (AHB), antioxidant 168, ethylene-tetrafluoroethylene (ETFE), and GL (glycerol) into an oven and dry at a temperature of 50 °C for 12 hours to ensure that these raw materials are completely dry.

[0068] Put PP (96.3%, mass percentage), AHB (3%, mass percentage), antioxidant 168 (0.3%, mass percentage), and DCP (0.4%, mass percentage) into a torque rheometer, set the temperature to 190 °C, the rotation speed to 50 r / min, and blend for 10 minutes to obtain a PP graft material.

[0069] After cleaning the internal mixer, put ETFE (96.3%, mass percentage), GL (3%, mass percentage), DCP (0.4%, mass percentage), and antioxidant 168 (0.3%, mass percentage) into it, set the temperature to 260 °C, and the rotation speed is also 50 r / min, and blend for 10 minutes to obtain an ETFE graft material.

[0070] First, add the ETFE graft material and blend for 5 minutes, and then add the PP graft material and blend for 4 minutes. During the whole process, the temperature is maintained at 260 °C, the rotation speed is 50 r / min, the blending time is 10 minutes, and the mass ratio of the PP graft material to the ETFE graft material is 7:3. Finally, a PP-g-AHB / ETFE-g-GL composite material is obtained, and this composite material is represented by a 7:3 component copolymer (or 7:3, or 7 / 3).

[0071] The prepared PP-g-AHB / ETFE-g-GL composite material was subjected to tablet pressing for subsequent experiments. The tablet press used was the XLV25-D flat vulcanizing machine produced by Huzhou Shuangli Automation Co., Ltd. The composite material was placed into a mold, and both the upper and lower sides of the mold were covered with polyester film, and then placed between two thick steel plates. After aligning the upper and lower steel plates, they were placed into the flat vulcanizing machine. First, hot pressing was carried out at a pressure of 0 MPa for 2 minutes to fully melt the sample and eliminate air bubbles. Then, with a pressure increase of 4 MPa as one grade, the pressure was gradually increased to 8 MPa, and hot pressing was carried out for 2 minutes at each grade. After the pressure application was completed, cooling was carried out to complete the preparation of the sheet samples required for various experiments.

[0072] Example 2

[0073] A preparation method of a high-temperature resistant intrinsically self-healing polypropylene insulating material, as Figure 1 shown, includes the following steps:

[0074] Put PP, AHB, antioxidant 168, as well as ETFE and GL into an oven and dry them at a temperature of 50 °C for 12 hours to ensure that these raw materials are completely dry.

[0075] Put PP (96.3%, mass percentage), AHB (3%, mass percentage), antioxidant 168 (0.3%, mass percentage) and DCP (0.4%, mass percentage) into a torque rheometer, set the temperature to 190 °C, the rotation speed to 50 r / min, and blend for 10 min to obtain a PP grafted material.

[0076] After cleaning the internal mixer, put ETFE (96.3%, mass percentage), GL (3%, mass percentage), DCP (0.4%, mass percentage) and antioxidant 168 (0.3%, mass percentage) into it, set the temperature to 260 °C, and the rotation speed is also 50 r / min, and blend for 10 min to obtain an ETFE grafted material.

[0077] First, add the ETFE grafted material to the torque rheometer and blend for 5 min, then add the PP grafted material and blend for 4 min. Throughout the process, the temperature is maintained at 260 °C, the rotation speed is 50 r / min, the blending time is 10 min, and the mass ratio of the PP grafted material to the ETFE grafted material is 8:2. Finally, a PP-g-AHB / ETFE-g-GL composite material is obtained, and this composite material is represented by an 8:2 component copolymer (or 8:2, or 8 / 2).

[0078] Put the composite material into a mold, cover both the upper and lower sides of the mold with polyester film, and then place it between two thick steel plates. After aligning the upper and lower steel plates, put them into a flat vulcanizing machine. First, hot press at a pressure of 0 MPa for 2 minutes to fully melt the sample and eliminate air bubbles. Then, increase the pressure step by step to 8 MPa in increments of 4 MPa, and hot press for 2 minutes at each level. After the pressure application is completed, cool it to complete the preparation of sheet specimens required for various experiments.

[0079] Example 3

[0080] A preparation method of a high-temperature resistant intrinsically self-healing polypropylene insulating material, as Figure 1 shown, includes the following steps:

[0081] Put polypropylene (PP), 4-propenyloxy-2-hydroxybenzophenone (AHB), antioxidant (168), ethylene-tetrafluoroethylene (ETFE), and GL (glycerol) into an oven and dry at a temperature of 50 °C for 12 hours to ensure that these raw materials are completely dry.

[0082] Put PP (96.3%, mass percentage), AHB (3%, mass percentage), antioxidant 168 (0.3%, mass percentage), and DCP (0.4%, mass percentage) into a torque rheometer, set the temperature at 190 °C, the rotation speed at 50 r / min, and blend for 10 min to obtain a PP grafted material.

[0083] After cleaning the internal mixer, put ETFE (96.3%, mass percentage), GL (3%, mass percentage), DCP (0.4%, mass percentage), and antioxidant 168 (0.3%, mass percentage) into it, set the temperature at 260 °C, and the rotation speed at 50 r / min as well, and blend for 10 min to obtain an ETFE grafted material.

[0084] First, add the ETFE grafted material to the torque rheometer and blend for 5 min, then add the PP grafted material and blend for 4 min. During the whole process, the temperature is maintained at 260 °C, the rotation speed is 50 r / min, the blending time is 10 min, and the mass ratio of the PP grafted material to the ETFE grafted material is 9:1. Finally, a PP-g-AHB / ETFE-g-GL composite material is obtained, and this composite material is represented by a 9:1 component copolymer (or 9:1, or 9 / 1).

[0085] Put the composite material into a mold, cover both the upper and lower sides of the mold with polyester film, and then place it between two thick steel plates. After aligning the upper and lower steel plates, put them into a flat vulcanizing machine. First, hot press at a pressure of 0 MPa for 2 minutes to fully melt the sample and eliminate air bubbles. Then, increase the pressure step by step to 8 MPa in increments of 4 MPa, and hot press for 2 minutes at each level. After the pressure application is completed, cool it to complete the preparation of sheet specimens required for various experiments.

[0086] Comparative Example 1

[0087] A method for preparing a polypropylene composite material includes the following steps:

[0088] Put PP, AHB, antioxidant 168, and ETFE into an oven and dry them at 50 °C for 12 hours to ensure that these raw materials are completely dry.

[0089] Put PP (96.3%, mass percentage), AHB (3%, mass percentage), antioxidant 168 (0.3%, mass percentage), and DCP (0.4%, mass percentage) into a torque rheometer, set the temperature at 190 °C, the rotation speed at 50 r / min, and blend for 10 min to obtain a PP grafted material.

[0090] After cleaning the internal mixer, put ETFE (99.7%, mass percentage) and antioxidant 168 (0.3%, mass percentage) into it, set the temperature at 260 °C, the rotation speed at 50 r / min, and blend for 10 min to obtain an ETFE base material.

[0091] First, blend the ETFE base material for 5 min, and then add the PP grafted material and blend for 4 min. During the whole process, the temperature is maintained at 260 °C, the rotation speed is 50 r / min, the blending time is 10 min, and the mass ratio of the PP grafted material to the ETFE grafted material is 7:3. Finally, a PP-g-AHB / ETFE composite material is obtained.

[0092] Put the composite material into a mold, cover the upper and lower sides of the mold with polyester film, and then place it between two thick steel plates. After aligning the upper and lower steel plates, put it into a flat vulcanizing machine. First, hot press at a pressure of 0 MPa for 2 minutes to fully melt the sample and eliminate bubbles. Then, increase the pressure step by step to 8 MPa in increments of 4 MPa, and hot press for 2 minutes at each level. After the pressure application is completed, cool it to complete the preparation of sheet samples required for various experiments.

[0093] High temperature resistance:

[0094] (1) XRD experiment:

[0095] After polypropylene is graft-modified with AHB, its crystal morphology also changes. First, characterize the crystal structures of polypropylene and AHB-grafted polypropylene through XRD patterns. The X-ray diffraction patterns of pure PP and the three samples prepared in Examples 1 to 3 are as Figure 2 shown.

[0096] From Figure 2It can be seen that polypropylene has diffraction peaks at around 14°, 16°, 17°, 19° and 22° respectively. Correspondingly, 14° is the (110) crystal plane, corresponding to the lattice constant of the polypropylene molecular chain. 17° is the (200) crystal plane, 19° is the (210) crystal plane, and 22° is the (220) crystal plane, all corresponding to the arrangement of the polypropylene molecular chain. After the graft modification of polypropylene with AHB, the diffraction peak at 16° disappears, and only the diffraction peak at 17° remains. Therefore, compared with polypropylene, the (200) crystal plane of polypropylene grafted with AHB decreases, and the (220) crystal plane increases. Moreover, the decrease of the (200) crystal plane indicates that a graft reaction has occurred between polypropylene and the blend, forming a new polymer structure, thereby changing the crystal structure of polypropylene.

[0097] Compared with conventional polypropylene (PP), the PP-g-AHB / ETFE-g-GL composite has achieved a significant improvement in crystallinity and molecular chain arrangement. Specifically, the disappearance and change of the diffraction peak reveal that a graft reaction has occurred in polypropylene, giving rise to a novel polymer structure. This graft structure improves the crystallinity of the polymer and reduces the presence of amorphous or low-crystalline regions. The presence of a high-crystalline state means that the molecular chains are arranged more closely and orderly, forming a solid lattice structure. This structure not only provides abundant cross-linking points, enhancing the stability and heat resistance of the polymer, but also due to the close arrangement of the molecular chains, the graft polymer is more resistant to damage at high temperatures, and the heat resistance is significantly improved. Therefore, compared with pure polypropylene, the PP-g-AHB / ETFE-g-GL composite shows obvious superiority in heat resistance. The improvement of this polymer structure not only increases the crystallinity and stability, but also provides a more reliable protective barrier due to the close arrangement of the molecular chains. This will make the PP-g-AHB / ETFE-g-GL composite an indispensable key material in high-temperature environments.

[0098] (2) DSC thermal experiment:

[0099] Use DSC to characterize the thermal properties and compare and analyze the melting and crystallization characteristics of the PP-g-AHB / ETFE-g-GL composite and PP.

[0100] From Figure 3 and Table 1, it can be seen that the melting peak temperatures of the PP-g-AHB / ETFE-g-GL composites with different ratios are relatively high, around 170 °C, and the peak intensities are relatively sharp. The crystallization peak temperature is around 110 °C, and the peak value of the 9:1 component copolymer is the highest. The crystallinities of different components are all around 44%, indicating that they have a relatively high crystallinity, further demonstrating that the composite has a more stable crystallization process.

[0101] Table 1 DSC data of the samples

[0102]

[0103] The reason for the high melting and crystallization temperatures of the composite material is mainly that after grafting polar groups of AHB, the compatibility between ETFE-g-GL and PP-g-AHB is improved, the composite material is more evenly distributed, the number of heterogeneous interfaces increases, and thus the high-temperature resistance of the material is improved. When the composite material is used as cable insulation, it should meet the operating requirements of power cables, and its melting temperature should be as high as possible so that when the cable is overloaded or fails, the insulation structure can be kept stable. After the PP of the present invention is graft-modified and blended with the ETFE grafting material, the melting temperature of the composite material is greatly increased, and thus it has high heat resistance and can be applied to different high-temperature scenarios.

[0104] (3) PLM polarized light crystallization experiment:

[0105] Use PLM and a variable-temperature hot stage to characterize the crystallization morphology of the three composite materials prepared in Examples 1 to 3, observe and compare and analyze the process of the material gradually cooling from the molten state to crystallization, and adopt isothermal crystallization. The crystallization temperature corresponding to the 7:3 component polymer is 126 °C, the crystallization temperature corresponding to the 8:2 component polymer is 123 °C, and the crystallization temperature corresponding to the 9:1 component polymer is 129 °C, and a photograph is taken every 15 minutes. The materials are all made into thin slices with a thickness of 20 μm, cut into squares with a side length of 1 cm and placed in the variable-temperature hot stage, and then the hot stage is placed on the stage of the polarized light microscope.

[0106] It can be seen from Figure 4 that for the 7:3 component copolymer, the crystallization size gradually increases with the increase of crystallization time. The spherulite size at the 0th minute of isothermal crystallization is 30 ± 5 μm, and the size at the 15th minute is 100 ± 10 μm. From the 30th minute, the growth rate of the crystal region slows down, and the gap between each stage shrinks. The spherulite size of the 8:2 component copolymer at the 0th minute of isothermal crystallization is 35 ± 5 μm, the size at the 15th minute is 140 ± 5 μm, and the size at the 30th minute increases to 200 ± 10 μm. The spherulite size of the 9:1 component copolymer at the 0th minute of isothermal crystallization is 20 ± 5 μm, the size at the 15th minute is 95 ± 5 μm, and the size at the 30th minute is 190 ± 10 μm, and obvious grain boundaries are formed between the spherulites. Multiple irregularly shaped elliptical regions can also be seen in the crystal region, which are the crystal regions of the GL-grafted modified ethylene-tetrafluoroethylene material in the copolymer. It can be seen that part of the polypropylene spherulite structure grows attached to its surface. The GL-grafted modified ethylene-tetrafluoroethylene plays a part of the role of crystal nuclei, making the polypropylene molecular chains start to be regularly arranged into spherulites from its surface at the crystallization temperature.

[0107] In summary, the polypropylene grafted material and the ethylene-tetrafluoroethylene grafted material can form a eutectic structure, thereby reducing the crystallization temperature and co-growing spherulites. This structure can better cope with high-temperature environments and improve the high-temperature resistance of polypropylene materials.

[0108] (4) TGA (Thermogravimetric Analysis) experiment:

[0109] To reflect the influence of the material grafting process on the thermal stability of the material, a thermogravimetric (TG) analyzer was used to conduct a thermogravimetric analysis experiment.

[0110] From Figures 5 - 6 it can be seen that as the furnace temperature increases, the mass of composite materials with different ratios all shows a downward trend. This indicates that in a high-temperature environment, the mass of the material will decrease, that is, the thermal stability of the material will be affected. However, there are differences among different materials at the same furnace temperature, which reflects their different high-temperature resistance performances.

[0111] As can be seen from Table 2, whether it is the 7:3 component copolymer, the 8:2 component copolymer, or the 9:1 component copolymer, they all show a thermal decomposition temperature far exceeding that of polypropylene (PP). The thermal decomposition temperatures of 7:3, 8:2, and 9:1 are increased by 43 °C, 41 °C, and 40 °C respectively compared to polypropylene. This significant temperature increase fully proves that the PP-g-AHB / ETFE-g-GL composite material has superior heat resistance performance compared to polypropylene.

[0112] From Figure 5 and Figure 7 it can be seen that compared with pure PP, the complete decomposition temperatures of the copolymers of the three components of 7:3, 8:2, and 9:1 of the PP grafted material with different blending ratios are significantly higher than that of pure polypropylene, indicating that the grafted composite material has better high-temperature resistance performance. And it can also be seen from the figure that the decomposition rate process of pure PP is very fast, while the decomposition process of the composite material is relatively slow, indicating that the thermal stability of this composite material has been significantly improved compared to pure polypropylene.

[0113] In Figure 6 , the shape of the peak provides important information about the rate change of the mass loss process. A sharp peak usually indicates a faster mass loss rate, while a gentle peak means a slower mass loss rate. For high-temperature resistant materials, a gentle peak shape indicates that the decomposition process of the material at high temperature is relatively slow. The peak of pure PP is the sharpest and has the largest peak value, while the peak of the composite material is relatively gentle and has a lower peak value. This difference further shows that the polypropylene composite material has better high-temperature resistance ability compared to pure polypropylene.

[0114] Table 2 Thermal decomposition temperatures of samples

[0115]

[0116]

[0117] Self - recovery performance:

[0118] (1) Polarized light variable - temperature experiment:

[0119] Use a polarized light microscope (PLM) and a variable - temperature hot stage to characterize the heat - recovery performance of the material (intrinsic thermal self - recovery performance). Before placing on the hot stage, scratch the polypropylene composite material films with different components, and record the scratch recovery at different temperatures.

[0120] From Figures 8 - 11 it can be seen that during the process of the pure polypropylene material rising from 30 °C to 150 °C, the size of the scratch does not change much. When continuing to heat up to 170 °C, the scratch can still be seen. For the 7:3 copolymer, there are signs that the scratch gradually disappears at 150 °C, and most of the scratches have disappeared when reaching 170 °C. For the 8:2 copolymer, there is also a small amount of thermal recovery before 150 °C. When continuing to heat up to 170 °C, the scratch has disappeared by nearly 90%. For the 9:1 copolymer, the thermal recovery at 150 °C is generally the same as that of other components, but when the temperature rises to 170 °C, the scratch is hardly visible under the polarized light microscope.

[0121] In summary, polypropylene itself does not have high - temperature self - recovery ability. After grafting improvement by the present invention, each component copolymer has a certain degree of thermal self - recovery ability. Materials with different components will self - repair damage at the scratched part when heated. Through Figures 9 - 11 it can be observed that the scratch becomes significantly narrower, indicating that the polymer is self - filling the damaged part. Among them, the 9:1 copolymer has the best thermal recovery effect. In practical applications, high - temperature intrinsic self - recovery materials and technologies have broad application prospects in many fields. For example, in the aerospace field, the durability of cable materials in high - temperature environments is crucial.

[0122] (2) Constant - length tensile experiment:

[0123] All materials are subjected to a constant - length tensile experiment using dumbbell - shaped specimens with a length of 75 mm. Stretch all materials by 2 cm at a constant elongation, and the initial length after constant elongation is 77 cm. Calculate the length of the specimen after 24 - hour recovery at room temperature and the length of the specimen after 24 - hour recovery at 50 °C as follows Figure 12 and shown in Table 3:

[0124] Table 3 Constant - length tensile and heat - recovery data of specimens at room temperature and when heated

[0125]

[0126] FromFigure 12 It can be seen that there is no change in the PP-g-AHB / ETFE composite material prepared in Comparative Example 1. The polypropylene composite materials blended in different ratios have a certain recovery amount at room temperature. When the temperature rises to 50 °C, the recovery amount begins to change significantly. Pure PP has no change, while the copolymers of each component begin to change in length. Among them, the 7:3 component copolymer has the best recovery, being closest to the initial unstretched state of 75 mm. This proves that the polypropylene composite material of the present invention has a certain intrinsic thermal self-recovery ability, enabling it to be applied to insulating cable materials, effectively suppressing the development of damage, thereby extending the service life of the material and reducing economic losses.

[0127] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high temperature resistant intrinsic self-recovering polypropylene insulation material, characterized in that: The PP graft material and the ETFE graft material are blended in a mass ratio of 6.0:4.0 to 9.5:0.5; Wherein, the PP graft material comprises a PP graft polymer and an antioxidant, and the PP graft polymer is a graft polymer of 4-propyleneoxy-2-hydroxybenzophenone grafted polypropylene; The ETFE graft material comprises an ETFE graft polymer and an antioxidant, wherein the ETFE graft polymer is a graft polymer of a glycerol graft olefin-tetrafluoroethylene copolymer.

2. The high temperature resistant intrinsic self-healing polypropylene insulation material according to claim 1, characterized in that: The mass ratio of PP grafted material to ETFE grafted material is 6.9:3.1 to 9.1:0.

9.

3. The high temperature resistant intrinsic self-healing polypropylene insulation material according to claim 1, characterized in that: The ETFE grafted material is composed of the following raw materials, calculated by weight: 89.0-98.5 parts of ethylene-tetrafluoroethylene copolymer, 1.0-10.0 parts of glycerol, 0.3-0.5 parts of initiator, and 0.2-0.4 parts of antioxidant.

4. The high temperature resistant intrinsic self-recovering polypropylene insulation material according to claim 1, characterized in that: The ETFE grafted material is composed of the following raw materials, calculated by weight: 95.0-97.5 parts of ethylene-tetrafluoroethylene copolymer, 2.0-4.0 parts of glycerol, 0.3-0.5 parts of initiator, and 0.2-0.4 parts of antioxidant.

5. A method for preparing the high temperature resistant intrinsic self-recovering polypropylene insulation material according to claim 1, characterized in that: The steps include: Provide PP grafted materials; The ethylene-tetrafluoroethylene copolymer, glycerol, an initiator and an antioxidant are melt-blended at 250-300° C. During the melt-blending process, the ethylene-tetrafluoroethylene copolymer is grafted with glycerol under the action of the initiator to obtain ETFE-g-GL, and the ETFE-g-GL and the antioxidant are evenly mixed to obtain an ETFE grafted material; The PP grafted material and the ETFE grafted material are melt-blended according to a ratio to obtain the product.

6. The preparation method according to claim 5, characterized in that: Polypropylene, 4-propyleneoxy-2-hydroxybenzophenone, an initiator and an antioxidant are melt-blended at 250-300° C. to obtain a PP grafted material; preferably, the melt-blending time is 10-15 minutes.

7. The preparation method according to claim 5, characterized in that: In the preparation of ETFE grafted material, the melt blending time is 10 to 15 minutes.

8. The preparation method according to claim 5, characterized in that: First, the ETFE grafted material is added for melt blending, and then the PP grafted material is added for melt blending.

9. The preparation method according to claim 5, characterized in that: The temperature for melt blending the PP grafted material and the ETFE grafted material is 250-300°C.

10. Use of the high temperature resistant intrinsic self-healing polypropylene insulation material according to any one of claims 1 to 4 in cables.

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