A toughened polypropylene insulating material, its preparation method and application

Abstract

The application provides a toughened polypropylene insulating material and a preparation method and application thereof, and comprises the following steps: (1) grafting a polar monomer on an elastomer to obtain a grafted elastomer; and (2) melt blending the grafted elastomer with beta-crystal polypropylene to obtain the toughened polypropylene insulating material. The toughened polypropylene insulating material not only retains the toughening effect of the elastomer, but also has good high-temperature mechanical and electrical properties.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of insulating materials, and relates to a toughened polypropylene insulating material for power cables and a preparation method and application thereof. BACKGROUND

[0002] Cross-linked polyethylene has excellent electrical properties and high-temperature thermal mechanical properties, and is the most widely used cable insulating material. However, as a thermosetting material, cross-linked polyethylene is difficult to recycle after retirement, and the by-products in the cross-linking process also pollute the environment, and it does not have the characteristics of green environmental protection. Therefore, it is an urgent problem to be solved in the power industry to develop environmentally friendly cable insulating materials to replace cross-linked polyethylene. Polypropylene has excellent electrical properties, high temperature resistance, simple processing technology, and can be recycled after retirement, and is an important development direction of environmentally friendly cable insulation. However, polypropylene itself is rigid and has poor low-temperature toughness, and cannot meet the mechanical property requirements of cable insulation. Therefore, it is necessary to improve the mechanical properties of polypropylene to meet the use requirements of cables.

[0003] At present, the modification methods for polypropylene mainly include blending modification, copolymerization modification, addition of nucleating agents and nano addition, etc. Some scholars improve the direct current breakdown field strength, volume resistivity and other properties of polypropylene by nano doping and chemical grafting, and the space charge accumulation effect is also significantly inhibited. However, the research and improvement are limited to the electrical properties of polypropylene, and the mechanical properties are not significantly improved. The addition of elastomers can effectively improve the mechanical properties of polypropylene, but when the addition amount is small, the improvement effect on the mechanical properties of polypropylene is not obvious, and there is still a certain gap with XLPE. When the addition amount is too large, due to the low melting point and high content of the elastomer, the crystallinity of the blend decreases, the binding ability of the polypropylene crystallization to the chain segment decreases at high temperature, the chain segment relaxation is intensified, and the heat deformation resistance of the material is weakened, and the electrical properties are significantly deteriorated. Therefore, it is a key problem to simultaneously improve the high-temperature mechanical and electrical properties of the polypropylene / elastomer composite system for the use of polypropylene in cable insulation materials. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a toughened polypropylene insulating material and a preparation method and application thereof. The toughened polypropylene insulating material not only retains the toughening effect of the elastomer, but also has good high-temperature mechanical and electrical properties.

[0005] The present application is realized by the following technical solutions:

[0006] A preparation method of a toughened polypropylene insulating material, comprising the following steps:

[0007] (1) grafting a polar monomer on an elastomer to obtain a grafted elastomer;

[0008] (2) melt blending the beta-crystal polypropylene with the grafted elastomer to obtain the toughened polypropylene insulating material.

[0009] Preferably, the step (1) is specifically: grafting reaction and granulation of the elastomer, the polar monomer and the initiator at 160-180℃ to obtain the grafted elastomer.

[0010] Further, the initiator is dicumyl peroxide.

[0011] Further, the mass ratio of the elastomer, the polar monomer and the initiator is 100:(1-5):(0.1-0.5).

[0012] Preferably, in the step (1), the polar monomer is glycidyl methacrylate or maleic anhydride.

[0013] Preferably, in the step (1), the elastomer is one or more of polyolefin elastomer, ethylene-propylene-diene rubber and ethylene-vinyl acetate copolymer.

[0014] Preferably, in the step (2), the preparation method of the beta-crystal polypropylene is:

[0015] Preparation of polypropylene master batch containing beta nucleating agent; granulation after mixing the polypropylene master batch with polypropylene uniformly to obtain the beta-crystal polypropylene; the beta nucleating agent is one or more of acetal nucleating agent, rosin type nucleating agent, amide nucleating agent and rare earth nucleating agent.

[0016] Preferably, in the step (2), the mass ratio of the beta-crystal polypropylene and the grafted elastomer is (80-60):(20-40).

[0017] The toughened polypropylene insulating material obtained by the preparation method.

[0018] The application of the toughened polypropylene insulating material in power cable.

[0019] Compared with the prior art, the application has the following beneficial effects:

[0020] The application adopts two means of crystal form regulation and chemical grafting to modify the polypropylene / elastomer composite material. On one hand, the introduction of polar groups on the molecule by grafting modification can enhance the intermolecular interaction, improve the compatibility of two phases, weaken the interface polarization, thereby reducing the dielectric loss; the grafting modification can also effectively inhibit the charge accumulation in the polypropylene, limit the electrical conductivity, and improve the insulation performance; compared with the polypropylene, the side chain of the elastomer is relatively large, which is conducive to reducing the degree of gelation; and the branching degree is high, the grafting point is easy to obtain, and the grafting rate is high, so the elastomer is subjected to grafting treatment. On the other hand, the introduction of β crystals in the polypropylene can improve the stability of high temperature mechanics, and also has a positive effect on the improvement of electrical performance. The application further improves the high temperature mechanics and electrical performance of the composite system on the basis of maintaining the elastomer toughening effect, so as to obtain an electrical insulation material with more excellent performance. The results show that the composite material not only maintains good mechanical properties, but also has excellent high temperature mechanics and electrical performance.

[0021] Further, the preparation method of the β crystal polypropylene of the application adopts the method of adding a β nucleating agent, which is simple and stable in the reaction process; at the same time, the master batch method is used to prepare the β crystal polypropylene, so that the nucleating agent is uniformly dispersed. DETAILED DESCRIPTION

[0022] In order to further understand the application, the application will be described below in combination with examples, which are only used to further explain the features and advantages of the application, and are not used to limit the claims of the application.

[0023] A preparation method of a toughened polypropylene insulation material for power cables, comprising the following steps:

[0024] (1) a polypropylene master batch containing a β nucleating agent is prepared by using a double screw extruder:

[0025] (2) the polypropylene master batch prepared in step (1) is uniformly mixed with polypropylene according to a certain proportion, and then granulated by using a double screw extruder to obtain β crystal polypropylene;

[0026] (3) the elastomer is subjected to grafting treatment: the elastomer, a polar monomer and an initiator are put into a double screw extruder according to a certain proportion to obtain a grafted elastomer;

[0027] (4) the β crystal polypropylene obtained in step (2) and the grafted elastomer obtained in step (3) are melt blended in a double screw extruder according to a certain proportion to obtain a polypropylene cable insulation material.

[0028] As a preferred embodiment of the present application, the nucleating agent in step (1) comprises but is not limited to one or more of acetal nucleating agent, rosin type nucleating agent, amide nucleating agent and rare earth nucleating agent. The polypropylene in step (1) is isotactic polypropylene with isotacticity not less than 96%. The temperature of the twin-screw from the feeding port to the die port is set as 180℃, 190℃, 200℃, 200℃, 200℃, 190℃, 180℃ in sequence, and the rotating speed is set as 200 rpm. The length-diameter ratio of the twin-screw is preferably 40:1, and the polypropylene masterbatch preferably contains 5wt% of the beta nucleating agent.

[0029] As a preferred embodiment of the present application, the ratio of the beta nucleating agent to the polypropylene in the beta crystal polypropylene in step (2) is (0.01-5):100, and the ratio of the beta crystal to the total crystal is not less than 60%. The temperature and rotating speed parameters of the twin-screw are set as in step (1).

[0030] As a preferred embodiment of the present application, the elastomer in step (3) comprises but is not limited to one or more of polyolefin elastomer POE, ethylene propylene diene rubber EPDM and ethylene-vinyl acetate copolymer EVA, the polar monomer comprises but is not limited to glycidyl methacrylate (GMA) or maleic anhydride (MAH), and the initiator is dicumyl peroxide (DCP). The mass ratio of the elastomer: the polar monomer: the initiator in step (3) is 100:(1-5):(0.1-0.5). The temperature of the twin-screw from the feeding port to the die port is set as 160℃, 170℃, 180℃, 180℃, 180℃, 170℃, 160℃ in sequence, and the rotating speed is set as 200 rpm.

[0031] As a preferred embodiment of the present application, the mass ratio of the beta crystal polypropylene to the grafted elastomer in step (4) is (80-60):(20-40).

[0032] The present application solves the problem of the deterioration of the high-temperature mechanical and electrical properties of the polypropylene caused by the elastomer toughening through crystal type regulation and grafting modification. After the modification, the composite material not only maintains good mechanical properties, but also has excellent high-temperature mechanical and electrical properties.

[0033] Example 1

[0034] The preparation method of the toughened polypropylene insulating material for power cables of the present embodiment comprises the following steps:

[0035] (1) Put the polypropylene and the rare earth nucleating agent WBG-II into the twin-screw extruder according to the mass ratio of 95:5 for blending and granulation, and set the temperature of the twin-screw from the feeding port to the die port as 180℃, 190℃, 200℃, 200℃, 200℃, 190℃, 180℃ in sequence, and set the rotating speed as 200 rpm.

[0036] (2) The sample prepared in step (1) and polypropylene are put into a twin-screw extruder for blending and granulation at a mass ratio of 10:90 to obtain β-crystal polypropylene, and the parameters of the twin screw are set as in step (1);

[0037] (3) Polyolefin elastomer POE, maleic anhydride MAH and dicumyl peroxide DCP are put into a twin-screw extruder for blending and granulation at a mass ratio of 100:1:0.15 to obtain POE-g-MAH, and the temperature of the twin screw is set as 160℃, 170℃, 180℃, 180℃, 180℃, 170℃, 160℃ from the feeding port to the die port, and the rotating speed is set as 200 rpm;

[0038] (4) The β-crystal polypropylene obtained in step (2) and the POE-g-MAH obtained in step (3) are put into a twin-screw extruder for blending and granulation at a mass ratio of 60:40 to obtain polypropylene insulation material, and the parameters of the twin screw are set as in step (1).

[0039] Example 2

[0040] The method for preparing the toughened polypropylene insulation material for power cables in this embodiment comprises the following steps:

[0041] (1) Polypropylene and rare earth nucleating agent WBG-II are put into a twin-screw extruder for blending and granulation at a mass ratio of 95:5, and the temperature of the twin screw is set as 180℃, 190℃, 200℃, 200℃, 200℃, 190℃, 180℃ from the feeding port to the die port, and the rotating speed is set as 200 rpm;

[0042] (2) The sample prepared in step (1) and polypropylene are put into a twin-screw extruder for blending and granulation at a mass ratio of 6:94 to obtain β-crystal polypropylene, and the parameters of the twin screw are set as in step (1);

[0043] (3) Polyolefin elastomer POE, maleic anhydride MAH and dicumyl peroxide DCP are put into a twin-screw extruder for blending and granulation at a mass ratio of 100:1:0.15 to obtain POE-g-MAH, and the temperature of the twin screw is set as 160℃, 170℃, 180℃, 180℃, 180℃, 170℃, 160℃ from the feeding port to the die port, and the rotating speed is set as 200 rpm;

[0044] (4) The β-crystal polypropylene obtained in step (2) and the POE-g-MAH obtained in step (3) are put into a twin-screw extruder for blending and granulation at a mass ratio of 60:40 to obtain polypropylene insulation material, and the parameters of the twin screw are set as in step (1).

[0045] Comparative Example 1

[0046] The toughened polypropylene insulation material for power cable of the present comparative example is prepared by the following steps:

[0047] (1) Put the polypropylene and the polyolefin elastomer POE into the twin-screw extruder at a mass ratio of 60:40 to obtain the cable insulation polypropylene material, and the temperature of the twin-screw from the feeding port to the die port is set as 180℃, 190℃, 200℃, 200℃, 200℃, 190℃, 180℃, and the rotating speed is set as 200 rpm.

[0048] Comparative Example 2

[0049] The polypropylene insulation material for power cable of the present comparative example is prepared by the following steps:

[0050] (1) Put the polypropylene and the rare earth nucleating agent WBG-II into the twin-screw extruder at a mass ratio of 95:5 to obtain the β-crystal polypropylene, and the temperature of the twin-screw from the feeding port to the die port is set as 180℃, 190℃, 200℃, 200℃, 200℃, 190℃, 180℃, and the rotating speed is set as 200 rpm.

[0051] (2) Put the sample prepared in step (1) and the polypropylene into the twin-screw extruder at a mass ratio of 1:9 to obtain the β-crystal polypropylene, and the twin-screw parameters are set as in step (1);

[0052] (3) Put the β-crystal polypropylene obtained in step (2) and the polyolefin elastomer POE into the twin-screw extruder at a mass ratio of 60:40 to obtain the cable insulation polypropylene material, and the twin-screw parameters are set as in step (1).

[0053] Comparative Example 3

[0054] The toughened polypropylene insulation material for power cable of the present comparative example is prepared by the following steps:

[0055] (1) Put the polyolefin elastomer POE, maleic anhydride MAH and dicumyl peroxide DCP into the twin-screw extruder at a mass ratio of 100:1:0.15 to obtain POE-g-MAH, and the temperature of the twin-screw from the feeding port to the die port is set as 160℃, 170℃, 180℃, 180℃, 180℃, 170℃, 160℃, and the rotating speed is set as 200 rpm.

[0056] (2) Put the polypropylene and the POE-g-MAH obtained in step (1) into the twin-screw at a mass ratio of 60:40 to obtain the polypropylene insulation material, and the temperature of the twin-screw from the feeding port to the die port is set as 180℃, 190℃, 200℃, 200℃, 200℃, 190℃, 180℃, and the rotating speed is set as 200 rpm.

[0057] Performance test:

[0058] The Young's modulus at 25℃ and 90℃ was measured by DMA242E of Germany;

[0059] The heat distortion resistance of the sample at 150℃ was tested by heat extension experiment according to the standard GB / T 2951.21-2008, the cross-section stress of 0.2MPa was applied, and the elongation of the sample after 10min was recorded;

[0060] The AC breakdown strength of the sample at 25℃ and 90℃ was tested by using a ball electrode with a diameter of 25mm, the voltage rising rate was 3kV / s, and the thickness of the sample was 0.2mm;

[0061] The dielectric spectrum of the sample was tested by using the German Concept 43 broadband dielectric spectrum test system. The sample was a circular sheet with a diameter of 30mm and a thickness of about 1mm, the applied voltage was 1kV, the test frequency was 50Hz, and the test temperature was 25℃ and 90℃.

[0062] Table 1 Mechanical properties of toughened polypropylene insulation material for power cable

[0063]

[0064] From Table 1, compared with Comparative Example 1, the modulus of Comparative Example 2 at 25℃ and 90℃ was smaller, and the modulus difference was reduced by about 8.7%, and the stability of high temperature mechanics was improved, which was caused by the smaller modulus of β crystal. After the grafting treatment of the elastomer and the blending with polypropylene, the modulus of Comparative Example 3 increased, which was because the entanglement structure between the grafting chains in the sample inhibited the movement ability of the molecular chain, thereby leading to the increase of the modulus, and the modulus difference had no obvious change. The modulus of Example 1 and Example 2 was reduced at room temperature, the flexibility was improved, and the modulus difference was further reduced by using the two means of crystal type regulation and chemical grafting for synergistic modification. From the heat extension experiment, it can also be seen that only Example 1 and Example 2 had no deformation at 150℃, and had good heat distortion resistance.

[0065] Table 2 Electrical properties of toughened polypropylene insulation material for power cable

[0066]

[0067]

[0068] From Table 2, it can be seen that after the modification by means of crystal form regulation and chemical grafting, the breakdown field strength of Example 1 and Example 2 is greatly improved at 25℃ and 90℃. At 90℃, the breakdown field strength of Example 1 is 110.5 kV / mm, which is 26.3% higher than that of Comparative Example 1. Related researches show that energy is released in the processes of carrier trapping, detrapping and recombination, and part of the energy will act on the molecular chain to cause the chain to break. Grafting modification and the addition of β nucleating agent will produce deep traps in polypropylene, limiting the migration of carriers. In addition, the entanglement of the two phases is enhanced after grafting modification, and the β crystal is more likely to produce molecular chains across the interface due to its unique "bundle" structure, which improves the stability of the chain segment structure, so the breakdown field strength is greatly improved. Dielectric loss tanδ is an important parameter reflecting the insulation performance of polymers. The greater the loss under alternating voltage, the more heat is generated, which will accelerate the aging of the insulation and even cause thermal breakdown of the insulation. As can be seen from Comparative Example 1, the tanδ of the polypropylene / elastomer composite system increases significantly at high temperature. Although the polar groups introduced by grafting modification in Comparative Example 3 will increase the loss, the compatibility of the two phases is improved after grafting modification, which weakens the effect of interfacial polarization, resulting in a decrease in loss. The band gap of the β crystal introduced in Comparative Example 2 is wider, and the conduction current is reduced, resulting in a decrease in loss. When the two modifications work together, the loss is further reduced.

[0069] In summary, the composite material not only maintains good mechanical properties, but also has excellent high-temperature mechanical and electrical properties.

[0070] Although the embodiments of the present application are disclosed for the purpose of illustration, those skilled in the art can understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present application and the appended claims, therefore, the scope of the present application is not limited to the disclosed content.

Claims

1. A process for the production of a toughened polypropylene insulation material, characterised in that, The method comprises the following steps: (1) grafting reaction and granulation of the elastomer, polar monomer and initiator at 160-180℃ to obtain a grafted elastomer; the elastomer is one or more of polyolefin elastomer POE, ethylene-propylene-diene rubber and ethylene-vinyl acetate copolymer; the polar monomer is glycidyl methacrylate or maleic anhydride; the mass ratio of the elastomer, polar monomer and initiator is 100:(1-5):(0.1-0.5); (2) melt blending of the β-crystal polypropylene and the grafted elastomer to obtain a toughened polypropylene insulating material; the mass ratio of the β-crystal polypropylene and the grafted elastomer is (80-60):(20-40); The preparation method of the β-crystal polypropylene is: preparation of polypropylene masterbatch containing β nucleating agent; granulation after uniform mixing of the polypropylene masterbatch and polypropylene to obtain β-crystal polypropylene; the β nucleating agent is one or more of acetal nucleating agent, rosin type nucleating agent, amide nucleating agent and rare earth nucleating agent; the mass ratio of the β nucleating agent and polypropylene in the β-crystal polypropylene is (0.01-5):

100.

2. The method for preparing toughened polypropylene insulating material according to claim 1, characterized in that, The initiator is dicumyl peroxide.

3. The toughened polypropylene insulating material obtained by the preparation method of any one of claims 1-2.

4. Application of the toughened polypropylene insulating material of claim 3 in power cables.

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