Preparation method of heat-resistant aging silicone rubber containing modified multi-walled carbon nanotubes

Abstract

The present invention belongs to the technical field of silicon material preparation, and particularly relates to a preparation method of a heat-resistant aging silicone rubber containing modified multi-walled carbon nanotubes. The present invention introduces surface-modified multi-walled carbon nanotubes into the silicone rubber structure by means of covalent bonds, greatly solving problems such as carbon nanotube agglomeration and compatibility with silicone rubber, and easily enabling the composite blending of a heat-conducting filler and a polymer matrix through a blending method. The prepared silicone rubber has excellent mechanical properties, heat-resistant aging properties and heat-conducting properties. The chemical structure designed by the present invention is novel, has excellent properties and broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon material preparation, and particularly relates to a preparation method of a heat-resistant aging silicone rubber containing modified multi-walled carbon nanotubes. Background Technique

[0002] Silicone rubber (SR) is a type of linear polymer. It is a polymer with a main chain formed by structural units of Si-O-Si bonds (where at least one organic group is connected to the silicon atom). The Si-O-Si bonds in the main chain structure are equivalent to the inorganic structure of silicate, and the side chains connected to the Si atoms are organic group structures, possessing some properties of organic substances. It is a polymer between organic and inorganic substances. Silicone has advantages such as resistance to high and low temperatures, radiation resistance, oxidation resistance, and weather resistance, and is widely used in fields such as electronics and electrical appliances, construction, chemical engineering, and transportation. With the development of science and technology, especially in the fields of national defense and cutting-edge technologies, the demand for the heat resistance and aging resistance of materials has further increased. Heat-resistant aging silicone rubber has a wide range of applications in fields such as machinery, electronics and electrical appliances, chemical engineering, and aerospace. The market demand for silicone rubber with heat resistance, aging resistance, and low price will also be getting higher and higher. However, traditional polysiloxane polymers have disadvantages such as low thermal conductivity and poor mechanical properties, which limit their applications as thermal interface materials and other aspects.

[0003] In recent years, silicone rubber with heat aging resistance has been widely used in the market. For example, Xiao Jianbin studied the effect of the content of cerium dioxide in the silicone rubber formula on the heat resistance of oil-resistant silicone rubber. The results showed that adding cerium dioxide as a heat-resistant additive could effectively increase the thermal degradation temperature of silicone rubber; with the increase of the content of cerium dioxide, the mechanical properties of silicone rubber changed little, but the heat resistance and high-temperature oil resistance of silicone rubber were greatly improved, indicating that cerium dioxide played a protective role in the thermal stability of silicone rubber. Zhang Jikai, Luo Hongjian et al. added a new plasticizer SAG1 to silicone rubber sealant; used 1,09-dimethyl diphenyl room temperature vulcanized silicone rubber to replace the commonly used dimethyl room temperature vulcanized silicone rubber as the main material of the sealant; and added 801CT silicone heat-resistant additive to room temperature vulcanized silicone rubber, low-temperature vulcanized silicone rubber and high-temperature vulcanized silicone rubber respectively. These methods could improve the heat resistance and antioxidant properties of silicone rubber and had been widely used. Li Chen, Sun Da et al. studied the effects of the dosages of iron(III) oxide and cerium dioxide and their synergistic effects on the heat resistance of silicone rubber. The results showed that iron(III) oxide and cerium dioxide could significantly improve the heat resistance of silicone rubber, and the improvement effect of cerium dioxide on the heat resistance of vulcanized silicone rubber was better than that of iron(III) oxide. It can be seen from the above inventions that most of the prepared heat aging-resistant silicone rubbers only changed the structural proportion of the fillers and used additives to improve the compatibility. Although they had good high-temperature resistance, they could not significantly change the interfacial fusion between the fillers and the polymer matrix. The contradiction between the large dosage of cerium dioxide and the polymer matrix was increasing, and the mechanical properties were not outstanding enough. It was still difficult to meet the usage requirements in most environments. There was no report on the application of heat aging-resistant silicone rubber that simultaneously had a simple manufacturing process, good mechanical properties, good thermal stability, and excellent thermal conductivity.

[0004] Carbon nanotubes have a unique structure and excellent electrical and thermal conductivity. Therefore, carbon nanotubes are an ideal filler for polymer-based nanocomposites. However, there is a strong van der Waals force between carbon nanotubes, which makes carbon nanotubes prone to agglomeration in solvents or polymers, greatly limiting the application of carbon nanotubes. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a preparation method of a heat aging-resistant organosilicon rubber containing a modified multi-walled carbon nanotube structure, which has good heat aging resistance, thermal stability, and thermal conductivity.

[0006] The technical solution provided by the present invention is as follows:

[0007] A preparation method of a heat aging-resistant organosilicon rubber containing a modified multi-walled carbon nanotube, comprising the following steps:

[0008] (1) Place an appropriate amount of carbon nanotubes in a quartz tube furnace, sinter them at 1200 °C for 4 h under a N2 atmosphere, then add the surface modifier and the carbon nanotubes after the above high-temperature sintering to absolute ethanol, stir at high speed for 1 h, then ultrasonically disperse for 0.5 h. Subsequently, transfer the uniformly dispersed mixture to a three-necked flask, stir and reflux at 70 °C for 12 h, remove the solvent, wash with absolute ethanol to remove the excess surface modifier, and then dry at 80 °C for 24 h to obtain a surface-modified multi-walled carbon nanotube composite material;

[0009] (2) Weigh an appropriate amount of multi-walled carbon nanotubes and the surface-modified multi-walled carbon nanotube composite material and add them to methyl vinyl silicone rubber, ultrasonically treat for 1 h, then stir for 1 h, and then place them in a vacuum drying oven to remove air bubbles, and cure at 60 °C for 3 h, and then cool to room temperature to obtain a modified matrix raw rubber;

[0010] (3) Mix the modified matrix raw rubber on a two-roll mill, and then sequentially add glass powder, cerium dioxide, metal oxide filler, methyl silicone resin and vulcanizing agent and mix well to obtain a composite silicone rubber; the rotation speed of the roll is controlled at 20 - 30 r / min;

[0011] (4) Heat the upper and lower heating plates of the flat vulcanizer to 170 °C, perform tablet pressing on the composite silicone rubber obtained in step (3), heat in the flat vulcanizer for 8 min and then take out, and place it on the water-cooled plate of the flat vulcanizer to cool for 3 min to obtain a silicone rubber after the first-stage vulcanization; then place the silicone rubber after the first-stage vulcanization in a muffle furnace, heat it to 140 - 230 °C, and keep it warm for 1 h, and then take it out and cool to obtain a silicone rubber after the second-stage vulcanization.

[0012] Preferably, in step (1), the mass ratio of the surface modifier to the carbon nanotubes after high-temperature calcination is 1:4 - 12.

[0013] Preferably, in step (1), the surface modifier is any one of 2,6-diaminopyridine, polypyrrole, diphenylacetic acid, 4,4'-diaminodiphenyl disulfide, a mixture of phthalic anhydride and pyrrole, or bis(4-hydroxyphenyl) disulfide.

[0014] Preferably, in step (2), the mass ratio of the multi-walled carbon nanotubes, the surface-modified multi-walled carbon nanotube composite material and methyl vinyl silicone rubber is 1:30 - 50:550 - 650.

[0015] Preferably, in step (3), the mass ratio of the modified matrix raw rubber: glass powder: cerium dioxide: metal oxide filler: methyl silicone resin: vulcanizing agent is 100:4 - 8:15 - 30:15 - 25:4 - 8:1 - 2.

[0016] Preferably, in step (3), the metal oxide filler is iron(III) oxide or aluminum(III) oxide.

[0017] The beneficial effects of the present invention are as follows:

[0018] 1. By introducing covalently modified multi-walled carbon nanotubes into the silicone rubber structure, the present invention greatly solves the problems of carbon nanotube agglomeration and its compatibility with silicone rubber, and it is very easy to compound and blend the heat-conducting filler with the polymer matrix by blending.

[0019] 2. The heat-resistant aging performance of the silicone rubber is better than that of the silicone rubber filled with a single filler when the heat-conducting filler is selected as a compound of cerium dioxide, iron(III) oxide and glass powder.

[0020] 3. The chemical structure designed by the present invention is novel, with excellent performance and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the infrared spectrum diagram of the heat-resistant aging silicone rubber prepared in Example 1;

[0022] Figure 2 It is the comparison diagram of the thermal conductivity of the heat-resistant aging silicone rubbers prepared in Examples 1-7 and Comparative Examples 1-4;

[0023] Figure 3 It is the comparison diagram of the Shore hardness of the heat-resistant aging silicone rubbers prepared in Examples 1-7 and Comparative Examples 1-4;

[0024] Figure 4 It is the comparison diagram of the tensile strength of the heat-resistant aging silicone rubbers prepared in Examples 1-7 and Comparative Examples 1-4 at different aging times;

[0025] Figure 5 It is the comparison diagram of the elongation at break of the heat-resistant aging silicone rubbers prepared in Examples 1-7 and Comparative Examples 1-4 at different aging times;

[0026] Figure 6 It is the comparison diagram of the 5% thermal decomposition temperature and char residue rate of the heat-resistant aging silicone rubbers prepared in Examples 1-7 and Comparative Examples 1-4. DETAILED DESCRIPTION OF THE INVENTION

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0028] The thermal conductivity was tested using a TC3000E hot wire thermal conductivity meter; the test standards were an experimental voltage of 1.8 V, a normal acquisition mode, an acquisition time of 2 s, a time interval of 3 min, three repetitions, and taking the average value; the silicone rubber specimens were cut to appropriate sizes and placed above and below the coil for testing.

[0029] The tensile strength and elongation at break of the silicone rubber were tested using a WDT-10 microcomputer-controlled electronic universal testing machine, with GB / T 528-2009 as the test standard. The specimens were cut into dumbbell shapes (length 10.0 ± 0.5 cm, thickness 2.0 ± 0.2 mm), with no less than three specimens, and the pulling rate was 50 mm / min.

[0030] A TG 4000 thermogravimetric analyzer was used to test the effects of the thermal conductive filler and vulcanization temperature on the thermal stability of the thermally conductive silicone rubber. The test temperature range was from room temperature to 800 °C, the heating rate was 20 °C / min, and the air environment was used as the test gas atmosphere.

[0031] Heat aging test: The silicone rubber after secondary vulcanization was placed in a muffle furnace for hot air aging. The aging temperature was 400 °C, and the aging times were 24 h, 48 h, and 96 h respectively. The tensile strength of the specimens before and after aging was tested.

[0032] An XHS Shore A hardness tester was used to test the hardness of the silicone rubber.

[0033] Example 1

[0034] (1) 20 g of carbon nanotubes were placed in a quartz tube furnace and sintered at 1200 °C for 4 h in an N2 atmosphere. Then, 1.0 g of 2,6-diaminopyridine and 5.0 g of the carbon nanotubes after high-temperature calcination were added to 50 ml of absolute ethanol, and the mixture was stirred at high speed for 1 h and ultrasonically dispersed for 0.5 h. Subsequently, the above mixture was transferred to a three-necked flask, stirred and refluxed at 70 °C for 12 h, the solvent was removed, and the mixture was washed with absolute ethanol to remove the excess 2,6-diaminopyridine, and then dried at 80 °C for 24 h to obtain a 2,6-diaminopyridine-modified multi-walled carbon nanotube composite.

[0035] (2) 0.1 g of multi-walled carbon nanotubes and 3.0 g of the 2,6-diaminopyridine-modified multi-walled carbon nanotube composite were respectively added to 60 g of methyl vinyl silicone rubber, ultrasonically treated for 1 h, stirred for 1 h, placed in a vacuum drying oven to remove air bubbles, and then cured at 60 °C for 3 h, and then cooled to room temperature to obtain a modified matrix raw rubber.

[0036] (3) First, 100 g of the modified matrix raw rubber is mixed evenly on a two-roll mill. Subsequently, glass powder, cerium dioxide, iron(III) oxide, methyl silicone resin, and vulcanizing agent are sequentially added to the silicone rubber raw rubber and mixed thoroughly to obtain composite silicone rubber. The mass ratio of the modified matrix raw rubber: glass powder: cerium dioxide: iron(III) oxide: methyl silicone resin: vulcanizing agent is 100:5:20:20:5:2, and the rotational speed of the roll is controlled at 25 r / min.

[0037] (4) The upper and lower heating plates of the flat vulcanizer are heated to 170 °C, the composite silicone rubber is subjected to tablet pressing treatment and heated in the flat vulcanizer for 8 min and then taken out, and then placed on the water-cooled plate of the flat vulcanizer to cool for 3 min to obtain the silicone rubber after the first-stage vulcanization. Then, the silicone rubber after the first-stage vulcanization is placed in a muffle furnace, heated to 200 °C, and kept warm for 1 h, and then taken out and cooled to obtain the silicone rubber after the second-stage vulcanization.

[0038] Figure 1 This is the infrared spectrogram of the heat-resistant aging silicone rubber prepared in this example. It can be seen from the figure that infrared analysis shows that the characteristic peaks of -CH2 are around 1440 cm -1 and 2910 cm -1 The strong absorption band appearing at 1000 - 1130 cm -1 is the characteristic peak of Si-O-Si. The characteristic peaks at 890 cm -1 , 1060 cm -1 and 1210 cm -1 are the characteristic peaks of Si-R. The characteristic peak at 3450 cm -1 is the characteristic peak of the active hydrogen of the amino group. The appearance of the above characteristic peaks indicates the successful introduction of the multi-walled carbon nanotubes modified with 2,6-diaminopyridine and the successful synthesis of the heat-resistant aging silicone rubber containing the modified multi-walled carbon nanotubes.

[0039] Example 2

[0040] Compared with Example 1, the dosage of the multi-walled carbon nanotube composite modified with 2,6-diaminopyridine in step (2) is changed to 4.0 g, and the mass ratio of the modified matrix raw rubber: glass powder: cerium dioxide: iron(III) oxide: methyl silicone resin: vulcanizing agent in step (3) is changed to 100:5:30:20:5:2; the remaining steps are the same as those in Example 1.

[0041] Example 3

[0042] Compared with Example 1, the dosage of methyl vinyl silicone rubber in step (2) is changed to 55 g, and the mass ratio of the modified matrix raw rubber: glass powder: cerium dioxide: iron(III) oxide: methyl silicone resin: vulcanizing agent in step (3) is changed to 100:5:20:15:5:2; the remaining steps are the same as those in Example 1.

[0043] Example 4

[0044] Compared with Example 1, the dosage of carbon nanotubes after high-temperature calcination in step (1) was changed to 8.0 g, the dosage of the multi-walled carbon nanotube composite modified with 2,6-diaminopyridine in step (2) was changed to 5.0 g, and the dosage of methyl vinyl silicone rubber was changed to 65 g; the remaining steps were the same as those in Example 1.

[0045] Example 5

[0046] Compared with Example 1, in step (1), "1.0 g of 2,6-diaminopyridine" was changed to "1.0 g of 4,4'-diaminodiphenyl disulfide", and step (2) was changed to: Weigh 0.1 g of multi-walled carbon nanotubes and 3.0 g of the multi-walled carbon nanotube composite modified with 4,4'-diaminodiphenyl disulfide and add them to 60 g of methyl vinyl silicone rubber. The temperature of the second-stage vulcanization in the muffle furnace in step (4) was 180 °C; the remaining steps were the same as those in Example 1.

[0047] Example 6

[0048] Compared with Example 1, in step (3), the mass ratio of the modified matrix raw rubber: glass powder: cerium dioxide: iron(III) oxide: methyl silicone resin: vulcanizing agent was changed to 100:5:15:15:5:1, and the temperature of the second-stage vulcanization in the muffle furnace in step (4) was 220 °C; the remaining steps were the same as those in Example 1.

[0049] Example 7

[0050] Compared with Example 1, in step (3), iron(III) oxide was changed to aluminum oxide, and the mass ratio of the modified matrix raw rubber: glass powder: cerium dioxide: aluminum oxide: methyl silicone resin: vulcanizing agent was changed to 100:6:30:25:5:2. The temperature of the second-stage vulcanization in the muffle furnace in step (4) was 230 °C; the remaining steps were the same as those in Example 1.

[0051] Control Example 1

[0052] Compared with Example 1, the order of adding raw materials in step (3) was different and was changed to: Methyl silicone resin, cerium dioxide, iron(III) oxide, glass powder, and vulcanizing agent were sequentially added to the silicone rubber raw rubber, and the remaining steps were the same as those in Example 1.

[0053] Compared with Example 1, the change in the filler order in step (3) of Comparative Example 1 affected the mixing uniformity of the material, thereby causing a decrease in the mechanical properties and heat aging properties of the material.

[0054] Control Example 2

[0055] (1) Place 20 g of carbon nanotubes in a quartz tube furnace and sinter them at 1200 °C for 4 h in an N2 atmosphere. Then add 5.0 g of the carbon nanotubes after high-temperature calcination to 50 ml of absolute ethanol, stir at high speed for 1 h, and ultrasonically disperse for 0.5 h. After that, transfer the above mixture to a three-necked flask, stir and reflux at 70 °C for 12 h, remove the solvent, and then dry at 80 °C for 24 h to obtain a multi-walled carbon nanotube composite material.

[0056] (2) Weigh 3.1 g of multi-walled carbon nanotubes and add them to 60 g of methyl vinyl silicone rubber. Ultrasonically treat for 1 h, then stir for 1 h, place in a vacuum drying oven to remove air bubbles, and then cure at 60 °C for 3 h. Subsequently, cool to room temperature to obtain a modified matrix raw rubber.

[0057] (3) It is the same as step (3) of Example 1.

[0058] (4) It is the same as step (4) of Example 1.

[0059] Compared with Example 1, it can be seen that when unmodified multi-walled carbon nanotubes and modified multi-walled carbon nanotubes are doped and used, a small amount of unmodified multi-walled carbon nanotubes acts as a diluent, which can significantly improve the phenomenon of carbon nanotube agglomeration, better enhance the dispersion compatibility between carbon nanotubes and silicone rubber, make their dispersion more uniform, and thus give full play to the enhancement effects of unmodified multi-walled carbon nanotubes and modified multi-walled carbon nanotubes in reinforcement and aging resistance performance.

[0060] Control Example 3

[0061] Compared with Example 1, in step (1), the amount of carbon nanotubes after high-temperature calcination is changed to 10.0 g, and in step (3), the heat-resistant filler cerium dioxide is not added; the remaining steps are the same as those of Example 1.

[0062] Compared with Example 1, the lack of cerium dioxide will cause a sharp drop in mechanical properties after thermal aging and poor heat-resistant aging performance. At the same time, cerium dioxide is also a metal filler, and when it is well dispersed, it has a good reinforcement effect on the overall material. Therefore, without adding cerium dioxide, the mechanical properties of the material will decrease significantly.

[0063] Control Example 4

[0064] Compared with Example 1, step (2) is changed to: Weigh 3.1 g of 2,6-diaminopyridine-modified multi-walled carbon nanotube composite material and add it to 60 g of methyl vinyl silicone rubber; the remaining steps are the same as those of Example 1.

[0065] Compared with unmodified multi-walled carbon nanotubes, the modified multi-walled carbon nanotubes have stronger activity, so they are more likely to agglomerate, resulting in a significant increase in local mechanical properties and the formation of hard blocks. This structure will become the breakthrough point of the short board of the original stable system, causing a sharp decline in the overall uniformity of the material and making it extremely easy to appear the phenomenon of faults, thus causing a sudden drop in the overall mechanical properties and heat aging properties of the material.

Claims

1. A preparation method of a heat-resistant aging silicone rubber containing modified multi-walled carbon nanotubes, characterized in that, It includes the following steps: (1) Place the carbon nanotubes in a quartz tube furnace, sinter them at 1200 °C for 4 h in an N2 atmosphere, then add the surface modifier and the carbon nanotubes after high-temperature sintering to anhydrous ethanol, stir at high speed for 1 h, then ultrasonically disperse for 0.5 h. Subsequently, transfer the uniformly dispersed mixture to a three-necked flask, stir and reflux at 70 °C for 12 h, remove the solvent, wash with anhydrous ethanol, and then dry at 80 °C for 24 h to obtain a surface-modified multi-walled carbon nanotube composite material; the surface modifier is any one of 2,6-diaminopyridine, polypyrrole, diphenylacetic acid, 4,4'-diaminodiphenyl disulfide, a mixture of phthalic anhydride and pyrrole, or bis(4-hydroxyphenyl) disulfide; (2) Weigh the multi-walled carbon nanotubes and the surface-modified multi-walled carbon nanotube composite material and add them to methyl vinyl silicone rubber, ultrasonically treat for 1 h, then stir for 1 h, then put them into a vacuum drying oven to remove air bubbles, and cure at 60 °C for 3 h, and then cool to room temperature to obtain a modified matrix raw rubber; (3) Mix the modified matrix raw rubber on a two-roll mill, and then sequentially add glass powder, cerium dioxide, metal oxide filler, methyl silicone resin and vulcanizing agent and mix well to obtain a composite silicone rubber; the rotation speed of the roll is controlled at 20 - 30 r / min; the metal oxide filler is any one of iron(III) oxide or aluminum(III) oxide; (4) Heat the upper and lower heating plates of a flat vulcanizer to 170 °C, perform tablet pressing on the composite silicone rubber obtained in step (3), heat in the flat vulcanizer for 8 min and then take out, and place it on the water-cooled plate of the flat vulcanizer to cool for 3 min to obtain a silicone rubber after first-stage vulcanization; then place the silicone rubber after first-stage vulcanization in a muffle furnace, heat to 140 - 230 °C, and keep it warm for 1 h, and then take out and cool to obtain a silicone rubber after second-stage vulcanization.

2. The preparation method of the heat-resistant aging silicone rubber containing modified multi-walled carbon nanotubes according to claim 1, characterized in that In step (1), the mass ratio of the surface modifier to the carbon nanotubes after high-temperature calcination is 1:4 - 12.

3. The preparation method of the heat-resistant aging silicone rubber containing modified multi-walled carbon nanotubes according to claim 1, characterized in that, In step (2), the mass ratio of the multi-walled carbon nanotubes, the surface-modified multi-walled carbon nanotube composite material and the methyl vinyl silicone rubber is 1:30 - 50:550 - 650.

4. The preparation method of the heat-resistant aging silicone rubber containing modified multi-walled carbon nanotubes according to claim 1, characterized in that, In step (3), the mass ratio of the modified matrix raw rubber: glass powder: cerium dioxide: metal oxide filler: methyl silicone resin: vulcanizing agent is 100:4 - 8:15 - 30:15 - 25:4 - 8:1 - 2.

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