Polypropylene composite material and preparation method thereof

Abstract

The invention relates to an environment-friendly polypropylene composite material applied to a direct-current cable and a preparation method of the environment-friendly polypropylene composite material. The material comprises atactic polypropylene, a styrene-ethylene-butylene-styrene block copolymer (SEBS), a grafted nano inorganic oxide and an antioxidant. The preparation method comprises the following steps: grafting an elastomer styrene-butadiene-styrene copolymer (SBS) to a nano inorganic oxide through a ball-milling mechanochemical method, and blending the nano inorganic oxide with a polypropylene random copolymer and SEBS to prepare the PP composite material applied to the direct-current cable material. The PP composite material is characterized in that the PP composite material with better low-temperature toughness, higher direct-current breakdown strength and higher flashover voltage is prepared by using an environment-friendly and efficient modification method, and the requirements of direct-current cable application scenes are better met.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material modification, and in particular to an environmentally friendly polypropylene composite material applied to a DC cable and a preparation method thereof. Background Art

[0002] Although high-voltage direct current (HVDC) requires complex converter stations, it also has the advantages of no AC losses (no inductive and capacitive reactance), high stability, and large power capacity. Therefore, it is more suitable for ultra-long-distance power transmission, submarine cables, grid interconnection, and new energy grid connection.

[0003] Thermoplastic polypropylene has excellent insulation properties, high temperature resistance, is recyclable, and greatly saves energy and space during the production process, with obvious economic and environmental advantages. However, DC cable applications also place higher demands on the low-temperature toughness, DC flashover voltage, and DC breakdown strength of polypropylene insulated cable materials.

[0004] In response to the above problems, domestic and foreign experts have proposed methods such as blending modification, grafting modification and copolymerization modification to solve them, among which blending modification is the easiest to implement and the most studied method. CN115947895A uses an extrusion reaction to graft a double-bond polymer with a polar group onto a polypropylene molecular chain, thereby improving the DC breakdown strength and thermal decomposition temperature of the material. However, its reaction process is uncontrollable, the product quality is unstable, and an initiator is introduced, which is not environmentally friendly. CN118271748A mixes rare earth oxides and transition metal oxides into polypropylene to obtain a material with a higher threshold field strength, a larger nonlinear coefficient of conductivity, and a higher breakdown field strength. However, it does not consider the dispersion problem of inorganic oxides in polypropylene, and the effect achieved is limited. Summary of the Invention

[0005] In view of the problems existing in the above-mentioned prior art, one object of the present invention is to provide a PP composite material with high flashover / breakdown strength and high toughness at low temperature, which can be used in the production of DC cables.

[0006] Another object of the present invention is to provide a method for preparing the environmentally friendly polypropylene composite material.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0008] In one aspect, the present invention provides a polypropylene composite material, comprising polypropylene, SEBS, grafted nano-inorganic oxide, and an antioxidant;

[0009] In a preferred embodiment, the polypropylene composite material includes the following components in parts by weight: 65-80 parts by weight of polypropylene, for example, including but not limited to 65 parts by weight, 70 parts by weight, 75 parts by weight, 80 parts by weight, etc., 20-30 parts by weight of SEBS, for example, including but not limited to 20 parts by weight, 25 parts by weight, 30 parts by weight, etc., 0.1-2 parts of grafted nano-inorganic oxide, for example, including but not limited to 0.1 parts by weight, 1 part by weight, 2 parts by weight, etc., 0.2-0.4 parts by weight of antioxidant, for example, including but not limited to 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, etc.

[0010] In a specific embodiment, the polypropylene is selected from random copolymer polypropylene; preferably, the melt flow rate of the random copolymer polypropylene is 0.1-20 g / 10 min (230° C., 2.16 kg), for example including but not limited to 0.1 g / 10 min, 0.5 g / 10 min, 1 g / 10 min, 5 g / 10 min, 10 g / 10 min, 15 g / 10 min, 20 g / 10 min or a range consisting of any two thereof; preferably, the melt flow rate of the random copolymer polypropylene is 0.1-3 g / 10 min (230° C., 2.16 kg).

[0011] In a specific embodiment, the SEBS is a styrene-ethylene-butylene-styrene block copolymer with a melt index of 3-20 g / 10 min (230° C., 2.16 kg), including but not limited to 3 g / 10 min, 5 g / 10 min, 10 g / 10 min, 20 g / 10 min or a range consisting of any two thereof.

[0012] In a specific embodiment, the antioxidant includes one or more of hindered phenols, hindered amines, thioesters, and phosphites.

[0013] In a specific embodiment, the grafted nano-inorganic oxide is obtained by ball milling grafting reaction of nano-inorganic oxide and SBS;

[0014] Specifically, the nano inorganic oxide includes one or more of SiO2, Al2O3, and MgO, and commercially available products can be used;

[0015] Preferably, the particle size of the nano inorganic oxide is 10-50 nm, for example including but not limited to 10 nm, 20 nm, 30 nm, 40 nm, 50 nm or a range consisting of any two thereof;

[0016] More preferably, the surface hydroxyl content of the nano inorganic oxide is 2-8 OH / nm 2, for example including but not limited to 2OH / nm 2 、3OH / nm 2 、4OH / nm 2 、5OH / nm 2 、6OH / nm 2 、7OH / nm 2 、8OH / nm 2 Or a range between any two of them.

[0017] The surface hydroxyl content of the nano-inorganic oxide was tested using thermogravimetric analysis (TGA).

[0018] Specifically, the SBS is a styrene-butadiene-styrene block copolymer having a melt index of 5-20 g / 10 min (230° C., 2.16 kg), including but not limited to 5 g / 10 min, 10 g / 10 min, 20 g / 10 min, or a range consisting of any two thereof;

[0019] In a specific embodiment, a method for preparing a grafted nano-inorganic oxide is provided, comprising the following steps: mixing the nano-inorganic oxide with SBS and then ball milling the mixture.

[0020] Specifically, the mass ratio of the nano-inorganic oxide to SBS is 1:(1-4), the rotation speed of the ball milling process is 200-400 rpm, and the ball milling time is 3-6 hours.

[0021] Another aspect of the present invention provides a method for preparing an environmentally friendly polypropylene composite material for DC cables, which specifically comprises: adding each component according to a ratio into a mixing single-screw extruder, mixing each component uniformly at a processing temperature of 190-220°C, and extruding and granulating to obtain the environmentally friendly polypropylene composite material.

[0022] In another aspect, the present invention provides application of the PP composite material obtained by the aforementioned preparation method in the field of DC cables.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention adds SEBS and grafted nano-inorganic oxides to random copolymer polypropylene, wherein the nano-inorganic oxides are grafted and modified by a ball milling method, thereby enhancing their dispersibility in the matrix, so that a large number of shallow traps in the matrix replace deep traps, thereby enhancing the carrier migration ability and thus suppressing the accumulation of space charges, thereby enhancing the low-temperature toughness, flashover voltage and DC breakdown strength of the PP composite material, and better fitting the application scenario of DC cables.

[0025] (2) The present invention adopts a safe, efficient, green and environmentally friendly processing method. The entire processing process includes ball milling grafting and melt extrusion, without introducing chemical reagents such as solvents and initiators, to obtain a PP composite material with high DC flashover voltage and breakdown strength, high and low temperature toughness, thereby realizing the production and application of DC cable materials. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the embodiments. However, the protection scope of the present invention is not limited to the embodiments but also includes any other known changes within the scope of the claims of the present invention.

[0027] The sources of raw materials used in the Examples and Comparative Examples are as follows:

[0028] PP 5012XT: random polypropylene, melt index 1.5g / 10min (230℃, 2.16kg), Korea Petrochemical;

[0029] SEBS-6014: styrene-ethylene-butylene-styrene copolymer, melt index 5g / 10min (230°C, 2.16kg), TSRC;

[0030] SEBS-1657: styrene-ethylene-butylene-styrene copolymer, melt index 20 g / 10 min (230°C, 2.16 kg), Kraton;

[0031] SBS-3546: styrene-butadiene-styrene copolymer, melt index 6g / 10min (230°C, 2.16kg), Huizhou Li Changrong;

[0032] SBS-YH1401: styrene-butadiene-styrene copolymer, melt index 12g / 10min (230°C, 2.16kg), Sinopec;

[0033] AEROSIL: nano-SiO2, particle size 12nm, surface hydroxyl content 3.0OH / nm 2 , Evonik;

[0034] AA-03: nano-Al2O3, particle size 15nm, surface hydroxyl content 5.0OH / nm 2 , sumitomo (Sumitomo Chemical);

[0035] Macklin-MgO-30: nano-MgO, particle size 30nm, surface hydroxyl content 2.5OH / nm 2 , Shanghai MacLean Biochemical;

[0036] Antioxidant 300: MIANOX.

[0037] Test methods and equipment:

[0038] (1) DC flashover voltage: The DC surface flashover test uses a high-voltage DC power supply of model TCM6000P as the discharge platform. The test electrode uses a stainless steel rod electrode with a diameter of 7mm. The voltage rise rate is 0.3kV / s and the distance between the two electrodes is 10mm. In order to avoid accidental experimental errors, this experiment tests multiple experimental samples of the same group of samples. Each sample undergoes 10 flashover characteristic tests and the average value is taken as the final flashover voltage. The interval between each test is 5 minutes. The different temperature conditions during the operation of the material are simulated by a constant temperature box and liquid nitrogen. The prepared samples are placed in a constant temperature box for preheating. The temperature is set to 40℃, 50℃, 60℃, 80℃ and 90℃ respectively. The sample temperature is monitored at all times using an infrared temperature gun. When the target temperature is reached, the flashover voltage test of each temperature step is performed using the high-voltage DC power supply of TCM6000P. The sample is then placed in a container filled with liquid nitrogen. When the target temperature reaches -20℃, the above operation is repeated to complete the experiment.

[0039] (2) DC breakdown field strength: The breakdown field strength of polypropylene composite materials was measured using a ball-ball electrode. The entire experimental system consists of a 50kV high-voltage DC power supply, a protective resistor, a stainless steel ball-ball electrode, an AC / DC resistor-capacitor divider (R2:R1=1:1000), etc. The thickness of the sample is 0.05mm, and the consistency of the thickness of different samples is ensured during the experiment. The diameter of the ball electrode is 20mm. In order to eliminate the influence of surface flashover along the edge of the sample, the ball-ball electrode and the sample are placed in transformer oil during the pressurization process. Before the test, the sample was wiped with alcohol to remove surface impurities, and then placed in a 60℃ oven for 24 hours to eliminate moisture interference. The DC breakdown field strength of the sample was measured using the continuous voltage step-up method, with a voltage step-up rate of 0.5kV / s.

[0040] (3) Izod notched impact strength: impact testing machine ZWICK HIT25P, tested according to ISO180:2023, test temperature -30°C;

[0041] (4) Planetary ball mill: QM2L, Nanjing Chishun Technology Development Co., Ltd.

[0042] (5) Surface hydroxyl content: Mettler Toledo TGA2 was tested according to ISO 11358-1:2014, with the test conditions being 30-800°C and a heating rate of 20°C / min.

[0043] 1) Preparation of grafted nano-inorganic oxides

[0044] The dried nano-inorganic oxide was weighed and added to a stainless steel ball mill containing stainless steel balls. The corresponding proportion of SBS was then added to the mill, and the mill was placed in a planetary ball mill for ball milling. The specific amounts of raw materials and milling conditions are shown in Table 1. After ball milling, the resulting grafted nano-inorganic oxide was stored in a vacuum drying oven at 50°C until use.

[0045] Table 1 Mass ratio of grafted nano inorganic oxide raw materials and ball milling conditions

[0046]

[0047] Note: The parts of each substance in Table 1 are parts by weight.

[0048] 2) Examples and Comparative Examples

[0049] Example 1: 30 parts by weight of SEBS-6014, 67.7 parts by weight of 5012XT, 2 parts by weight of SiO2-SBS and 0.3 parts by weight of antioxidant 300 were extruded and blended at a screw processing temperature of 190°C.

[0050] Example 2: 25 parts by weight of SEBS-6014, 73.7 parts by weight of 5012XT, 1 part by weight of Al2O3-SBS and 0.3 part by weight of antioxidant 300 were extruded and blended at a screw processing temperature of 200°C.

[0051] Example 3: 20 parts by weight of SEBS-1657, 79.2 parts by weight of 5012XT, 0.5 parts by weight of MgO-SBS and 0.3 parts by weight of antioxidant 300 were extruded and blended at a screw processing temperature of 220°C.

[0052] Comparative Example 1: 30 parts by weight of SEBS-6014, 69.8 parts by weight of 5012XT and 0.2 parts by weight of antioxidant 300 were extruded and blended at a screw processing temperature of 190°C.

[0053] Comparative Example 2: 25 parts by weight of SEBS-6014, 73.7 parts by weight of 5012XT, 1 part by weight of AA-03 and 0.3 parts by weight of antioxidant 300 were extruded and blended at a screw processing temperature of 200°C.

[0054] Comparative Example 3: 20 parts by weight of SEBS-1657, 79.2 parts by weight of 5012XT, 0.5 parts by weight of Macklin-MgO-30 and 0.3 parts by weight of Antioxidant 300 were extruded and blended at a screw processing temperature of 220°C.

[0055] The performance of the polypropylene composite materials obtained in Examples 1-3 and Comparative Examples 1-3 was tested, and the specific results are shown in Table 2.

[0056] Table 2 Performance test results of examples and comparative examples

[0057]

[0058] The results in Table 2 show that the addition of SEBS greatly improves the low-temperature toughness of the PP composite material. The synergistic effect of the grafted nano-inorganic oxide and SEBS also further improves the low-temperature toughness. The ordered structure obtained by introducing the grafted nano-inorganic oxide greatly improves the DC flashover voltage and DC breakdown strength of the PP composite material.

[0059] The above description of the embodiments is intended to facilitate understanding and application of the present invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the embodiments described herein. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A polypropylene composite material, characterized in that Including polypropylene, grafted nano inorganic oxide, SEBS, antioxidant; Preferably, the composite material comprises the following components in parts by weight: 65-80 parts by weight of polypropylene, 20-30 parts by weight of SEBS, 0.1-2 parts by weight of grafted nano inorganic oxide, and 0.2-0.4 parts by weight of antioxidant.

2. The composite material according to claim 1, characterized in that The polypropylene is selected from random copolymer polypropylene; Preferably, the melt flow rate of the random copolymer polypropylene is 0.1-20 g / 10 min, and the test conditions are 230° C. and 2.16 kg. More preferably, the melt flow rate of the random copolymer polypropylene is 0.1-3 g / 10 min, and the test conditions are 230° C. and 2.16 kg.

3. The composite material according to claim 1, characterized in that The grafted nano inorganic oxide is obtained by ball milling grafting reaction of nano inorganic oxide and SBS.

4. The composite material according to claim 3, characterized in that The nano inorganic oxide is one or more of SiO2, Al2O3, and MgO. Preferably, the particle size of the nano inorganic oxide is 10-50 nm. More preferably, the surface hydroxyl content of the nano inorganic oxide is 2-8 OH / nm. 2 .

5. The composite material according to claim 3, characterized in that SBS is a styrene-butadiene-styrene copolymer with a melt index of 5-20 g / 10 min. The test conditions are 230°C and 2.16 kg.

6. The composite material according to any one of claims 3 to 5, characterized in that: The ball milling speed is 200-400 rpm, and the ball milling time is 3-6 hours; and / or, the mass ratio of the nano-inorganic oxide to SBS is 1:(1-4).

7. The composite material according to claim 1, characterized in that The melt index of the SEBS is 3-20 g / 10 min, and the test conditions are 230° C. and 2.16 kg.

8. The composite material according to claim 1, characterized in that The antioxidant includes one or more of hindered phenols, hindered amines, thioesters, and phosphites.

9. A method for preparing the composite material according to any one of claims 1 to 8, characterized in that: The components are put into a mixing single-screw extruder according to the ratio, the components are mixed evenly, and granulated by extrusion to obtain the environmentally friendly polypropylene composite material; the preferred mixing processing temperature is 190-220°C.

10. Use of the environmentally friendly polypropylene composite material according to any one of claims 1 to 8 or the environmentally friendly polypropylene composite material prepared by the preparation method according to claim 9 in the field of DC cables.

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