Paper ball-like graphene microsphere, composite material thereof, and preparation method therefor

Abstract

The present invention provides a paper ball-like graphene microsphere, a composite material thereof, and a preparation method therefor. Such paper ball-like graphene microspheres are obtained by chemically reducing graphene oxide microspheres to slowly remove oxygen-containing functional groups on the surface of the graphene oxide to avoid the volume expansion caused by rapid removal of the groups, thereby maintaining a tight bond between graphene sheets without separation; and removing the remaining small number of oxygen-containing functional groups and repairing defect structures in the graphene oxide sheets by means of high temperature treatment, such that the graphene structure becomes perfect at an ultrahigh temperature (2500 to 3000° C.), thereby further improving the bonding ability between the graphene sheets in the microspheres and achieving a dense structure.

Claims

1. A paper ball-like graphene microsphere, characterized in that the graphene microsphere is formed by pleated single-layer graphene sheets and has a diameter of 500 nm-5 μm, a density of 0.2-0.4 g/cm3, a carbon/oxygen ratio of 20-60, and a specific surface area of less than 200 m2/g, wherein the method for preparing the paper ball-like graphene microsphere comprising the following steps: (1) drying a single-layer graphene oxide dispersion by atomization drying to obtain graphene oxide microspheres; (2) reducing the graphene oxide microspheres obtained in Step (1) under a reducing gas atmosphere to obtain reduced graphene oxide microspheres; and (3) subjecting the reduced graphene oxide microspheres obtained in Step (2) to high-temperature treatment at a temperature that is higher than 1000° C., to obtain ball-like graphene microspheres.

2. A graphene-based lubricating oil, comprising the following components in parts by weight: 100 parts of a base oil, 0.05-1 part of paper ball-like graphene microspheres, and 2-14 parts of additional auxiliary agents, wherein the paper ball-like graphene microsphere comprises pleated single-layer graphene sheets and has a diameter of 500 nm-5 μm, a density of 0.2-0.4 g/cm3, a carbon/oxygen ratio of 20-60, and a specific surface area of less than 200 m2/g.

3. The lubricating oil according to claim 2, wherein the additional auxiliary agents comprises 0.5-1 part of a dispersing agent, 0.5-1.5 parts of a compatilizer, 0.3 to 1 part of a viscosity modifier, 0.2 to 0.5 part of an antifoaming agent, and 0.5 to 10 parts of a preservative.

4. A lithium complex-based grease having paper ball-like graphene microspheres, comprising the following components in parts by weight: 70-90 parts of a base oil, 5-20 parts of a lithium complex-based thickener, 0.05-5 parts of paper ball-like graphene microspheres, and 1-5 parts of additional auxiliary agents, wherein the paper ball-like graphene microsphere comprises pleated single-layer graphene sheets and has a diameter of 500 nm-5 μm, a density of 0.2-0.4 g/cm3, a carbon/oxygen ratio of 20-60, and a specific surface area of less than 200 m2/g, wherein the method for preparing the paper ball-like graphene microsphere comprising the following steps: (1) drying a single-layer graphene oxide dispersion by atomization drying to obtain graphene oxide microspheres; (2) reducing the graphene oxide microspheres obtained in Step (1) under a reducing gas atmosphere to obtain reduced graphene oxide microspheres; and (3) subjecting the reduced graphene oxide microspheres obtained in Step (2) to high-temperature treatment at a temperature that is higher than 1000° C., to obtain ball-like graphene microspheres.

5. The grease according to claim 4, wherein the additional auxiliary agents comprise 0.5-2 parts of an antioxidant, 0-2 parts of a surfactant, and 0.5-1 part of a rust inhibitor.

6. The grease according to claim 4, wherein the lithium complex-based thickener is a complex of a large molecular acid and a small molecular acid reacted with lithium hydroxide, wherein the large molecular acid is a C12-C24 fatty acid, the small molecular acid is one of a C1-C24 fatty acid or boric acid, and the molar ratio of the large molecular acid to the small molecular acid is 1:0.1-2.

7. A compounded rubber modified with paper ball-like graphene microspheres, comprising the following components in parts by weight: 100 parts of a rubber, 0.1-10 parts of paper ball-like graphene microspheres, 0.5-5 parts of a vulcanizing agent, 3-10 parts of a vulcanization accelerator, and 5-20 parts of additional auxiliary agents, wherein the paper ball-like graphene microsphere comprises pleated single-layer graphene sheets and has a diameter of 500 nm-5 μm, a density of 0.2-0.4 g/cm3, a carbon/oxygen ratio of 20-60, and a specific surface area of less than 200 m2/g, wherein the method for preparing the paper ball-like graphene microsphere comprising the following steps: (1) drying a single-layer graphene oxide dispersion by atomization drying to obtain graphene oxide microspheres; (2) reducing the graphene oxide microspheres obtained in Step (1) under a reducing gas atmosphere to obtain reduced graphene oxide microspheres; and (3) subjecting the reduced graphene oxide microspheres obtained in Step (2) to high-temperature treatment at a temperature that is higher than 1000° C., to obtain ball-like graphene microspheres.

8. The compounded rubber according to claim 7, wherein the additional auxiliary agents comprise 2-5 parts of stearic acid, 0.5-2 parts of an anti-aging agent, 0.5-3 parts of liquid paraffin, and 2-10 parts of zinc oxide.

9. A graphene-based waterborne acrylic coating, comprising the following components in parts by weight: 100 parts of an acrylic resin emulsion, 0.1-5 parts of paper ball-like graphene microspheres, 30-60 parts of an inorganic filler, 0.9-12 parts of additional auxiliary agents, and 10-20 parts of water, wherein the paper ball-like graphene microsphere comprises pleated single-layer graphene sheets and has a diameter of 500 nm-5 μm, a density of 0.2-0.4 g/cm3, a carbon/oxygen ratio of 20-60, and a specific surface area of less than 200 m2/g, wherein the method for preparing the paper ball-like graphene microsphere comprising the following steps: (1) drying a single-layer graphene oxide dispersion by atomization drying to obtain graphene oxide microspheres; (2) reducing the graphene oxide microspheres obtained in Step (1) under a reducing gas atmosphere to obtain reduced graphene oxide microspheres; and (3) subjecting the reduced graphene oxide microspheres obtained in Step (2) to high-temperature treatment at a temperature that is higher than 1000° C., to obtain ball-like graphene microspheres.

10. The coating according to claim 9, wherein the acrylic resin emulsion is one or more of a pure acrylic emulsion, a styrene-acrylic emulsion, and a vinyl acetate-acrylic emulsion; and the inorganic filler is one or more of titania, silica, alumina, calcium carbonate, and potassium carbonate.

11. The coating according to claim 9, wherein the auxiliary agents comprise 0.1-0.5 part of a dispersing agent, 0.1-0.3 part of a preservative, 0.1-0.5 part of a film-forming agent, 0.05-0.2 part of a leveling agent, 0.5-10 parts of a thickener, and 0.05-0.5 part of a defoaming agent.

12. A method for improving the impact strength of nylon 6 with paper ball-like graphene, comprising toughening the nylon material by paper ball-like graphene microspheres, wherein the paper ball-like graphene microsphere comprises pleated single-layer graphene sheets and has a diameter of 500 nm-5 μm, a density of 0.2-0.4 g/cm3, a carbon/oxygen ratio of 20-60, and a specific surface area of less than 200 m2/g, wherein the method for preparing the paper ball-like graphene microsphere comprising the following steps: (1) drying a single-layer graphene oxide dispersion by atomization drying to obtain graphene oxide microspheres; (2) reducing the graphene oxide microspheres obtained in Step (1) under a reducing gas atmosphere to obtain reduced graphene oxide microspheres; and (3) subjecting the reduced graphene oxide microspheres obtained in Step (2) to high-temperature treatment at a temperature that is higher than 1000° C., to obtain ball-like graphene microspheres.

13. The method according to claim 12, comprising specifically the following steps: (1) pre-mixing nylon 6 with graphene microspheres at a weight ratio of 100:0.05-1 in a mixer, to obtain a uniformly mixed nylon 6/graphene premix, wherein nylon 6 and the graphene microspheres are dried in a vacuum oven at 80-105° C. for 8-12 hrs before pre-mixing; and (2) melt blending and extruding the premix obtained in Step (1) through a twin-screw extruder at a processing temperature of 230-250° C. and a rotation speed of 150-250 rpm, cooling, and granulating to obtain a nylon 6/graphene composite material.

14. A method for preparing a paper ball-like graphene microsphere, comprising the following steps: (1) drying a single-layer graphene oxide dispersion by atomization drying to obtain graphene oxide microspheres, wherein the single-layer graphene oxide dispersion comprises a reducing agent, where the reducing agent is hydrogen iodide, hydrogen bromide, hydrazine hydrate, vitamin C, or sodium borohydride, and a weight ratio of the reducing agent to the single-layer graphene oxide is 0.1 to 10; (2) reducing the graphene oxide microspheres obtained in Step (1) under a reducing gas atmosphere to obtain reduced graphene oxide microspheres; and (3) subjecting the reduced graphene oxide microspheres obtained in Step (2) to high-temperature treatment at a temperature that is higher than 1000° C., to obtain ball-like graphene microspheres.

15. The method according to claim 14, wherein the atomization drying in Step (1) is 100-200° C.

16. The method according to claim 14, wherein the reducing gas atmosphere in Step (2) is one or more of hydrazine hydrate vapor, hydroiodic acid vapor, and hydrobromic acid vapor; and the reducing condition is reducing at 60-200° C. for 30 min to 48 hrs.

17. The method according to claim 14, wherein the temperature for high-temperature treatment in Step (3) is 2500 to 3000° C., and the atmosphere for high-temperature treatment is one of nitrogen, helium, a mixture of hydrogen and argon, and argon, and the treatment time is 30 min to 48 hrs.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a photo of paper ball-like graphene microspheres produced in Example 1-1 of the present invention.

(2) FIG. 2 shows microscopic morphology of the paper ball-like graphene microspheres produced in Example 1-1 of the present invention.

(3) FIG. 3 shows microscopic morphology of expanded graphene microspheres produced in Comparative Example 1-1 of the present invention.

(4) FIG. 4 shows nanoindentation load-displacement curves of graphene microspheres produced in Example 1-8 and Comparative Example 1-1 of the present invention.

(5) FIG. 5 shows a microscopic photo of a graphene-based lubricating oil produced in Example 2-1 of the present invention.

DESCRIPTION OF THE EMBODIMENTS

(6) The present invention will be specifically described by the following examples, which are only used to further illustrate the present invention, and are not to be construed as limiting the scope of the present invention. Some non-essential changes and adjustments made by those skilled in the art according to the disclosure the present invention are contemplated in the scope of protection of the present invention.

Example 1-1

(7) (1) A single-layer graphene oxide dispersion was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres.

(8) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 1 hr at 60° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(9) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 1000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(10) The paper ball-like graphene microsphere obtained through the above steps appears as a black powder as shown in FIG. 1. The paper ball-like graphene microsphere is microscopically a pleated microsphere having a diameter of 3-5 μm, as shown in FIG. 2. The paper ball-like graphene microsphere has a density of 0.2 g/cm.sup.3, a carbon/oxygen ratio of 22.7, and a specific surface area of 190 m.sup.2/g.

Example 1-2

(11) (1) A single-layer graphene oxide dispersion was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres.

(12) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 1 hr at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(13) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 1000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(14) The paper ball-like graphene microsphere obtained through the above steps appears as a black powder, and is microscopically a pleated microsphere having a diameter of 3-5 μm. The paper ball-like graphene microsphere has a density of 0.23 g/cm.sup.3, a carbon/oxygen ratio of 23.1, and a specific surface area of 181 m.sup.2/g.

Example 1-3

(15) (1) A single-layer graphene oxide dispersion was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres.

(16) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(17) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 1000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(18) The paper ball-like graphene microsphere obtained through the above steps appears as a black powder, and is microscopically a pleated microsphere having a diameter of 3-5 μm. The paper ball-like graphene microsphere has a density of 0.25 g/cm.sup.3, a carbon/oxygen ratio of 22.9, and a specific surface area of 166 m.sup.2/g.

(19) By comparing Examples 1-1 to 1-3, it can be seen that by increasing the reduction temperature and time in Step (2), the specific surface area of the final graphene microspheres can be significantly reduced, and the density is increased, but the carbon/oxygen ratio is not greatly affected. This is because the reduction in Step (2) is mainly to slowly remove the groups on the surface of the graphene oxide. The low reduction temperature or short reduction time may result in insufficient reduction, and the residual groups will continue to be removed during high-temperature thermal treatment in Step (3), during which a gas is generated to cause the graphene sheets to expand outward. The carbon/oxygen ratio is mainly affected by the reduction in Step (3), and has little to do with Step (3). Therefore, in view of the above, the reducing conditions in Step (2) are preferably high reduction temperature and long reduction time.

Example 1-4

(20) (1) A single-layer graphene oxide dispersion containing vitamin C was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres, where the weight ratio of vitamin C to graphene oxide is 0.1.

(21) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(22) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 1000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(23) The paper ball-like graphene microsphere obtained through the above steps appears as a black powder, and is microscopically a pleated microsphere having a diameter of 3-5 μm. The traits are shown in Table 1-1.

Example 1-5

(24) (1) A single-layer graphene oxide dispersion containing vitamin C was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres, where the weight ratio of vitamin C to graphene oxide is 1.

(25) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(26) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 1000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(27) The paper ball-like graphene microsphere obtained through the above steps appears as a black powder, and is microscopically a pleated microsphere having a diameter of 3-5 μm. The traits are shown in Table 1-1.

Example 1-6

(28) (1) A single-layer graphene oxide dispersion containing vitamin C was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres, where the weight ratio of vitamin C to graphene oxide is 5.

(29) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(30) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 1000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(31) The paper ball-like graphene microsphere obtained through the above steps appears as a black powder, and is microscopically a pleated microsphere having a diameter of 3-5 μm. The traits are shown in Table 1-1.

Example 1-7

(32) (1) A single-layer graphene oxide dispersion containing vitamin C was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres, where the weight ratio of vitamin C to graphene oxide is 1.

(33) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(34) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 2000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(35) The paper ball-like graphene microsphere obtained through the above steps appears as a black powder, and is microscopically a pleated microsphere having a diameter of 2-4 μm. The traits are shown in Table 1-1.

Example 1-8

(36) (1) A single-layer graphene oxide dispersion containing vitamin C was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres, where the weight ratio of vitamin C to graphene oxide is 1.

(37) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(38) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 3000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(39) The paper ball-like graphene microsphere obtained through the above steps appears as a black powder, and is microscopically a pleated microsphere having a diameter of 500 nm-3 μm. The traits are shown in Table 1-1.

Example 1-9

(40) (1) A single-layer graphene oxide dispersion was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres.

(41) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(42) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 3000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(43) The paper ball-like graphene microsphere obtained through the above steps appears as a black powder, and is microscopically a pleated microsphere having a diameter of 1-4 μm. The traits are shown in Table 1-1.

(44) Comparative Example 1-1: Direct thermal reduction without chemical reduction

(45) (1) A single-layer graphene oxide dispersion prepared by Hummers method was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres.

(46) (2) The reduced graphene oxide microspheres obtained in Step (1) were transferred to a tubular furnace, and heated to 2500° C. at a ramping rate of 5° C./min and maintained for 1 hr, while a mixed gas of hydrogen and argon was continuously introduced.

(47) The graphene obtained through the above steps appears as a black loose powder, and is microscopically a hollow sphere having a diameter of 1-10 μm, as shown in FIG. 3. The traits are shown in Table 1-1.

(48) TABLE-US-00001 TABLE 1-1 Physical properties of products obtained in various examples Weight Temperature for Before treatment of step After treatment of step 3 ratio of high-temperature Carbon/ Specific Carbon/ Specific Density reducing treatment in step oxygen ratio surface oxygen ratio surface (g/cm.sup.3) Example 1-3 0 1000 3.7 124 22.9 166 0.25 Example 1-4 0.1 1000 4.6 105 23.2 152 0.26 Example 1-5 1 1000 7.1 83 23.9 133 0.31 Example 1-6 5 1000 12.4 66 23.6 98 0.34 Example 1-7 1 2000 7.1 123 35.2 184 0.27 Example 1-8 1 3000 7.1 123 57.3 28 0.39 Example 1-9 0 3000 3.7 189 51.6 87 0.39 Comparative 0 3000 2 230 50.4 876 0.07 Example 1-1

(49) By comparing Examples 1-3 to 1-6, it can be found that the degree of reduction of the graphene oxide microspheres before the treatment in Step (3) can be effectively improved by increasing the amount of the reducing agent added before the atomization drying, because the reducing agent is uniformly dispersed on the surface of graphene oxide in a molecular form, and gradually reacts with the oxygen-containing functional groups in Steps (1) and (2) to slowly reduce the graphene, so that the carbon/oxygen ratio is increased and the specific surface area is lowered. Through comparison of the situations before and after the reduction in Step (3), it can be seen that the high-temperature thermal treatment removes the unremoved groups in the reduced graphene oxide microspheres (causing the carbon/oxygen ratio to increase), and the generated gas expands the intersheet structure of graphene, resulting in an increase in the specific surface area. However, after the reductivity is improved by the addition of the reducing agent, the graphene microspheres release less gas during high-temperature heat treatment in Step (3), which reduces the volume expansion and makes the structure more compact. Therefore, in order to obtain graphene microspheres with a high density and a low specific surface area, it is important to add a reducing agent.

(50) By comparing Examples 1-5 and 1-7, it can be found that while reducing conditions in the first two steps are identical, the increase of the reduction temperature in Step (3) increases the specific surface area and decreases the density, because the further release of the gas causes the sheet structure to be further expanded. However, unexpectedly, when the temperature rises to 3000° C. (Example 1-8), the specific surface area is greatly reduced, possibly because after the temperature is higher than the graphitization temperature, the large π-conjugated structure of graphene is repaired, the bonding force between the sheets is greatly improved, and the distance between the sheets is lowered, so that the graphene microspheres are “concentrated” toward the center and thus become more compact.

(51) By comparing Examples 1-3 and 1-9, it can be seen that the specific surface area of the graphene microspheres can be significantly reduced by thermal treatment at 3000° C. without the addition of a reducing agent. However, by comparing Example 8, it can be seen that the addition of a reducing agent to remove most of the functional groups before thermal treatment can give more compact graphene microspheres.

(52) By comparing Example 1-8 with Comparative Example 1-1, it can be seen that the graphene oxide microspheres are directly subjected to high-temperature thermal treatment in the comparative example, and a large amount of gas is released during the reduction to give rise to rapid volume expansion, high specific surface area, and low density. From the nanoindentation load-displacement curves, it is found that the maximum compressive stress, modulus and elastic resilience of the paper ball-like graphene microsphere are significantly higher than those of the expanded graphene sphere, as shown in FIG. 4.

Example 1-10

(53) In this example, the microspheres obtained in Examples 1-3, 1-5, and 1-8 and Comparative Example 1-1 were compounded with rubber. After the mechanical property test, the performances are shown in Table 1-2. It can be found that the use of paper ball-like graphene microspheres having a high density and a low specific surface area can significantly increase the tensile strength and tear strength of the rubber.

(54) TABLE-US-00002 TABLE 1-2 Tensile properties of rubber compounded with various examples Tensile strength Tearing strength (MPa) (kN m.sup.1) Example 1-3 23.8 25.6 Example 1-5 26.9 28.7 Example 1-8 28.4 31.2 Comparative Example 1-1 20.1 19.7

Example 2-1

(55) Steps 1-3 are the same as those in Example 1-1.

(56) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 0.5 part of a dispersing agent, 0.6 part of a compatilizer, 0.5 part of a viscosity modifier, 0.3 part of an antifoaming agent, and 1 part of a preservative were sequentially added to 100 parts a base oil, and stirred until uniform.

(57) Step 5: The mixture obtained in Step (4) was ultrasonically dispersed and defoamed.

(58) A graphene-based lubricating oil is obtained through the above steps, which is a black viscous liquid as shown in FIG. 5. The obtained lubricating oil has a friction coefficient of 0.094.

Example 2-2

(59) Steps 1-3 are the same as those in Example 1-2.

(60) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 0.5 part of a dispersing agent, 0.6 part of a compatilizer, 0.5 part of a viscosity modifier, 0.3 part of an antifoaming agent, and 1 part of a preservative were sequentially added to 100 parts of a base oil, and stirred until uniform.

(61) Step 5: The mixture obtained in Step (4) was ultrasonically dispersed and defoamed.

(62) A graphene-based lubricating oil is obtained through the above steps, which has a friction coefficient of 0.092.

Example 2-3

(63) Steps 1-3 are the same as those in Example 1-3.

(64) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 0.5 part of a dispersing agent, 0.6 part of a compatilizer, 0.5 part of a viscosity modifier, 0.3 part of an antifoaming agent, and 1 part of a preservative were sequentially added to 100 parts of a base oil, and stirred until uniform.

(65) Step 5: The mixture obtained in Step (4) was ultrasonically dispersed and defoamed.

(66) A graphene-based lubricating oil is obtained through the above steps, which has a friction coefficient of 0.089.

(67) The specific surface area of the paper ball-like graphene microspheres has a great influence on the anti-friction performance of the composite lubricating oil. The friction coefficient of Example 2-3 is the lowest. Therefore, in view of the above, the reducing conditions in Step (2) are preferably high reduction temperature and long reduction time.

Example 2-4

(68) Steps 1-3 are the same as those in Example 1-4.

(69) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 0.5 part of a dispersing agent, 0.6 part of a compatilizer, 0.5 part of a viscosity modifier, 0.3 part of an antifoaming agent, and 1 part of a preservative were sequentially added to 100 parts of a base oil, and stirred until uniform.

(70) Step 5: The mixture obtained in Step (4) was ultrasonically dispersed and defoamed.

(71) A graphene-based lubricating oil is obtained through the above steps. Specific properties are shown in Table 2.

Example 2-5

(72) Steps 1-3 are the same as those in Example 1-5.

(73) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 1 part of a dispersing agent, 0.6 part of a compatilizer, 0.3 part of a viscosity modifier, 0.3 part of an antifoaming agent, and 1 part of a preservative were sequentially added to 100 parts of a base oil, and stirred until uniform.

(74) Step 5: The mixture obtained in Step (4) was ultrasonically dispersed and defoamed.

(75) A graphene-based lubricating oil is obtained through the above steps. Specific properties are shown in Table 2.

Example 2-6

(76) Steps 1-3 are the same as those in Example 1-6.

(77) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 0.5 part of a dispersing agent, 1 part of a compatilizer, 0.5 part of a viscosity modifier, 0.5 part of an antifoaming agent, and 5 part of a preservative were sequentially added to 100 parts of a base oil, and stirred until uniform.

(78) Step 5: The mixture obtained in Step (4) was ultrasonically dispersed and defoamed.

(79) A graphene-based lubricating oil is obtained through the above steps. Specific properties are shown in Table 2.

Example 2-7

(80) Steps 1-3 are the same as those in Example 1-7.

(81) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 1 part of a dispersing agent, 1.5 parts of a compatilizer, 0.5 part of a viscosity modifier, 0.3 part of an antifoaming agent, and 5 parts of a preservative were sequentially added to 100 parts of a base oil, and stirred until uniform.

(82) Step 5: The mixture obtained in Step (4) was ultrasonically dispersed and defoamed.

(83) A graphene-based lubricating oil is obtained through the above steps. Specific properties are shown in Table 2.

Example 2-8

(84) Steps 1-3 are the same as those in Example 1-8.

(85) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 0.8 part of a dispersing agent, 0.6 part of a compatilizer, 1 part of a viscosity modifier, 0.5 part of an antifoaming agent, and 5 part of a preservative were sequentially added to 100 parts of a base oil, and stirred until uniform.

(86) Step 5: The mixture obtained in Step (4) was ultrasonically dispersed and defoamed.

(87) A graphene-based lubricating oil is obtained through the above steps. Specific properties are shown in Table 2.

Example 2-9

(88) Steps 1-3 are the same as those in Example 1-9.

(89) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 1 part of a dispersing agent, 0.7 part of a compatilizer, 0.5 part of a viscosity modifier, 0.3 part of an antifoaming agent, and 10 part of a preservative were sequentially added to 100 parts of a base oil, and stirred until uniform.

(90) Step 5: The mixture obtained in Step (4) was ultrasonically dispersed and defoamed.

(91) A graphene-based lubricating oil is obtained through the above steps. Specific properties are shown in Table 2.

(92) Comparative Example 2-1: Lubricating oil without graphene

(93) Comparative Example 2-2: Direct thermal reduction without chemical reduction

(94) (1) A single-layer graphene oxide dispersion was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres.

(95) (2) The graphene oxide microspheres obtained in Step (1) were transferred to a tubular furnace, and heated to 3000° C. at a ramping rate of 5° C./min and maintained for 1 hr, while a mixed gas of hydrogen and argon was continuously introduced.

(96) (3) 0.1 part of the graphene obtained in Step (2), 0.5 part of a dispersing agent, 0.6 part of a compatilizer, 0.5 part of a viscosity modifier, 0.3 part of an antifoaming agent, and 1 part of a preservative were sequentially added to 100 parts of a base oil, and stirred until uniform.

(97) (4) The mixture obtained in Step (3) was ultrasonically dispersed and defoamed.

(98) The graphene obtained through the above steps appears as a black loose powder, and is microscopically a hollow sphere having a diameter of 1-10 μm. Specific properties of the resulting lubricating oil are shown in Table 2.

(99) TABLE-US-00003 TABLE 2 Specific parameters and properties of the example Weight Temperature Before treatment of step After treatment of step 3 ratio of for high- Specific Specific reducing temperature Carbon/ surface Carbon/ surface agent to treatment in oxygen area oxygen area Density Friction graphene Step (3) ratio (m.sup.2/g) ratio (m.sup.2/g) (g/cm.sup.3) coefficient Example 2-3 0 1000 3.7 124 23 166 0.25 0.089 Example 2-4 0.1 1000 4.6 105 23.2 152 0.26 0.086 Example 2-5 1 1000 7.1 83 23.9 133 0.31 0.085 Example 2-6 5 1000 12.4 66 23.6 98 0.34 0.081 Example 2-7 1 2000 7.1 123 35.2 184 0.27 0.079 Example 2-8 1 3000 7.1 123 52.3 28 0.39 0.071 Example 2-9 0 3000 3.7 189 51.6 87 0.39 0.073 Comparative — — — — — — — 0.13 Example 2-1 Comparative 0 3000 2.3 230 50.4 876 0.07 0.112 Example 2-2

(100) When combined with a lubricating oil, the more compact spheres have better wear resistance and can provide more effective protection between the friction surfaces, thus reducing the friction and abrasive wear. In contrast, graphene microspheres with a large specific surface area and a large void ratio are prone to deformation under pressure, and the friction reducing ability declines.

Example 2-10

(101) (1) A single-layer graphene oxide dispersion containing vitamin C was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres, where the weight ratio of vitamin C to graphene oxide is 1.

(102) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(103) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 3000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(104) (4) 0.05 part of the paper ball-like graphene microspheres obtained in Step (3), 0.8 part of a dispersing agent, 0.6 part of a compatilizer, 1 part of a viscosity modifier, 0.5 part of an antifoaming agent, and 5 parts of a preservative were sequentially added to 100 parts of a base oil, and stirred until uniform.

(105) (5) The mixture obtained in Step (4) was ultrasonically dispersed and defoamed.

(106) Through the above steps, a graphene-based lubricating oil is obtained, where the paper ball-like graphene microsphere is microscopically a pleated microsphere having a diameter of 500 nm to 3 μm. Since Steps (1)-(3) are the same as those in Example 2-8, the graphene microsphere has the same carbon/oxygen ratio, density, and specific surface area as in Example 2-8, and has a friction coefficient of 0.75.

Example 2-11

(107) (1) A single-layer graphene oxide dispersion containing vitamin C was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres, where the weight ratio of vitamin C to graphene oxide is 1.

(108) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(109) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 3000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(110) (4) 1 part of the paper ball-like graphene microspheres obtained in Step (3), 0.8 part of a dispersing agent, 0.6 part of a compatilizer, 1 part of a viscosity modifier, 0.5 part of an antifoaming agent, and 5 parts of a preservative were sequentially added to 100 parts of a base oil, and stirred until uniform.

(111) (5) The mixture obtained in Step (4) was ultrasonically dispersed and defoamed.

(112) Through the above steps, a graphene-based lubricating oil is obtained, where the paper ball-like graphene microsphere is microscopically a pleated microsphere having a diameter of 500 nm to 3 μm. Since Steps (1)-(3) are the same as those in Example 2-8, the graphene microsphere has the same carbon/oxygen ratio, density, and specific surface area as in Example 2-8, and has a friction coefficient of 0.67.

(113) By comparing Examples 2-8, 2-10, and 2-11, it can be seen that the friction coefficient of the composite lubricating oil decreases with increasing amount of the paper ball-like graphene microspheres added, indicating the good lubricity of the graphene microspheres.

Example 3-1

(114) Steps 1-3 are the same as those in Example 1-1.

(115) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 51 parts of a base oil, 8.1 parts of 12-hydroxystearic acid and 3.8 parts of benzoic acid were mixed, and heated to 70° C. Lithium hydroxide was added for saponification.

(116) Step 5: The mixture obtained in Step (4) was heated to 160° C., dehydrated, and further heated to 190° C. for refining. After cooling, 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor and 35 parts of a base oil were added, mixed and ground to obtain a lithium complex-based grease comprising paper ball-like graphene microspheres.

(117) Through the above steps, a lithium complex-based grease comprising paper ball-like graphene microspheres is obtained. The performances of the resulting grease are shown in Table 3.

Example 3-2

(118) Steps 1-3 are the same as those in Example 1-2.

(119) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 51 parts of a base oil, 8.1 parts of 12-hydroxystearic acid and 3.8 parts of benzoic acid were mixed, and heated to 70° C. Lithium hydroxide was added for saponification.

(120) Step 5: The mixture obtained in Step (4) was heated to 160° C., dehydrated, and further heated to 190° C. for refining. After cooling, 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor and 35 parts of a base oil were added, mixed and ground to obtain a lithium complex-based grease comprising paper ball-like graphene microspheres.

(121) Through the above steps, a lithium complex-based grease comprising paper ball-like graphene microspheres is obtained. The performances of the resulting lithium complex-based grease are shown in Table 3.

Example 3-3

(122) Steps 1-3 are the same as those in Example 1-3.

(123) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 51 parts of a base oil, 8.1 parts of 12-hydroxystearic acid and 3.8 parts of benzoic acid were mixed, and heated to 70° C. Lithium hydroxide was added for saponification.

(124) Step 5: The mixture obtained in Step (4) was heated to 160° C., dehydrated, and further heated to 190° C. for refining. After cooling, 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor and 35 parts of a base oil were added, mixed and ground to obtain a lithium complex-based grease comprising paper ball-like graphene microspheres.

(125) Through the above steps, a lithium complex-based grease comprising paper ball-like graphene microspheres is obtained. The performances of the resulting lithium complex-based grease are shown in Table 3.

(126) A lower specific surface area and a higher density of the paper ball-like graphene microsphere means a more compact structure, and a better pressure resistance and elasticity, whereby the overall performance of the composite lubricating oil are much better, as shown in Table 3. Therefore, in view of the above, the reducing conditions in Step (2) are preferably high reduction temperature and long reduction time.

Example 3-4

(127) Steps 1-3 are the same as those in Example 1-4.

(128) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 47 parts of a base oil, 7.4 parts of 12-hydroxystearic acid and 4.5 parts of benzoic acid were mixed, and heated to 90° C. Lithium hydroxide was added for saponification.

(129) Step 5: The mixture obtained in Step (4) was heated to 170° C., dehydrated, and further heated to 200° C. for refining. After cooling, 0.5 part of an antioxidant, 1.5 parts of a rust inhibitor and 39 parts of a base oil were added, mixed and ground to obtain a lithium complex-based grease comprising paper ball-like graphene microspheres.

(130) A lithium complex-based grease comprising paper ball-like graphene microspheres is obtained through the above steps. Specific properties are shown in Table 3.

Example 3-5

(131) Steps 1-3 are the same as those in Example 1-5.

(132) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 63 parts of a base oil, 5.3 parts of 12-hydroxystearic acid and 6.6 parts of benzoic acid were mixed, and heated to 80° C. Lithium hydroxide was added for saponification.

(133) Step 5: The mixture obtained in Step (4) was heated to 165° C., dehydrated, and further heated to 200° C. for refining. After cooling, 0.5 part of an antioxidant, 1.5 parts of a rust inhibitor and 23 parts of a base oil were added, mixed and ground to obtain a lithium complex-based grease comprising paper ball-like graphene microspheres.

(134) A lithium complex-based grease comprising paper ball-like graphene microspheres is obtained through the above steps. Specific properties are shown in Table 3.

Example 3-6

(135) Steps 1-3 are the same as those in Example 1-6.

(136) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 63 parts of a base oil, 5.6 parts of 12-hydroxystearic acid and 5.3 parts of benzoic acid were mixed, and heated to 90° C. Lithium hydroxide was added for saponification.

(137) Step 5: The mixture obtained in Step (4) was heated to 180° C., dehydrated, and further heated to 220° C. for refining. After cooling, 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor and 24 parts of a base oil were added, mixed and ground to obtain a lithium complex-based grease comprising paper ball-like graphene microspheres.

(138) A lithium complex-based grease comprising paper ball-like graphene microspheres is obtained through the above steps. Specific properties are shown in Table 3.

Example 3-7

(139) Steps 1-3 are the same as those in Example 1-7.

(140) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 63 parts of a base oil, 5.6 parts of 12-hydroxystearic acid and 5.3 parts of benzoic acid were mixed, and heated to 90° C. Lithium hydroxide was added for saponification.

(141) Step 5: The mixture obtained in Step (4) was heated to 180° C., dehydrated, and further heated to 220° C. for refining. After cooling, 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor and 24 parts of a base oil were added, mixed and ground to obtain a lithium complex-based grease comprising paper ball-like graphene microspheres.

(142) A lithium complex-based grease comprising paper ball-like graphene microspheres is obtained through the above steps. Specific properties are shown in Table 3.

Example 3-8

(143) Steps 1-3 are the same as those in Example 1-8.

(144) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 63 parts of a base oil, 5.9 parts of 12-hydroxystearic acid and 5 parts of p-methylbenzoic acid were mixed, and heated to 90° C. Lithium hydroxide was added for saponification.

(145) Step 5: The mixture obtained in Step (4) was heated to 170° C., dehydrated, and further heated to 220° C. for refining. After cooling, 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor and 24 parts of a base oil were added, mixed and ground to obtain a lithium complex-based grease comprising paper ball-like graphene microspheres.

(146) A lithium complex-based grease comprising paper ball-like graphene microspheres is obtained through the above steps. Specific properties are shown in Table 3.

Example 3-9

(147) Steps 1-3 are the same as those in Example 1-9.

(148) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 61 parts of a base oil, 5.9 parts of 12-hydroxystearic acid and 4 parts of p-methylbenzoic acid were mixed, and heated to 90° C. Lithium hydroxide was added for saponification.

(149) Step 5: The mixture obtained in Step (4) was heated to 170° C., dehydrated, and further heated to 220° C. for refining. After cooling, 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor and 27 parts of a base oil were added, mixed and ground to obtain a lithium complex-based grease comprising paper ball-like graphene microspheres.

(150) A lithium complex-based grease comprising paper ball-like graphene microspheres is obtained through the above steps. Specific properties are shown in Table 3.

(151) Comparative Example 3-1: The lithium complex-based grease was prepared following the method as described in Example 3-1 except that no paper ball-like graphene microspheres were added during the preparation. The performances are shown in Table 3.

(152) Comparative Example 3-2: Direct thermal reduction of graphene oxide microspheres without chemical reduction

(153) (1) A single-layer graphene oxide dispersion was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres.

(154) (2) The graphene oxide microspheres obtained in Step) were transferred to a tubular furnace, and heated to 3000° C. for 1 hr, while a mixed gas of hydrogen and argon was continuously introduced.

(155) (3) 0.1 part of the graphene obtained in Step (2), 61 parts of a base oil, 5.9 parts of 12-hydroxystearic acid and 4 parts of p-methylbenzoic acid were mixed, and heated to 90° C. Lithium hydroxide was added for saponification.

(156) (4) The mixture obtained in Step (3) was heated to 170° C., dehydrated, and further heated to 220° C. for refining. After cooling, 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor and 27 parts of a base oil were added, mixed and ground to obtain a lithium complex-based grease.

(157) The graphene obtained through the above steps appears as a black loose powder, and is microscopically a hollow sphere having a diameter of 1-10 μm. The performances of the resulting lithium complex-based grease are shown in Table 3.

(158) TABLE-US-00004 TABLE 3 Wear resistance PB Oil value separation from by copper Worked Copper four- mesh at Dropping cone strip ball 100° C. point penetration corrosion method for 24 hrs (° C.) (0.1 mm) at 24 hr (kg) (%) Example 3-1 209 277 Acceptance 87 2.96 Example 3-2 213 275 Acceptance 89 2.91 Example 3-3 215 272 Acceptance 91 2.84 Example 3-4 219 269 Acceptance 95 2.72 Example 3-5 223 264 Acceptance 97 2.59 Example 3-6 228 261 Acceptance 102 2.51 Example 3-7 233 256 Acceptance 105 2.4 Example 3-8 241 252 Acceptance 112 2.22 Example 3-9 238 254 Acceptance 103 2.31 Example 3-10 245 246 Acceptance 124 2.1 Comparative 186 292 Acceptance 78 3.12 Example 3-1 Comparative 204 282 Acceptance 84 3.01 Example 3-2

(159) The density, size and specific surface area of the graphene microspheres have a great influence on the properties of the final composite grease. If the voids increase, the compressive strength, modulus, and elastic resilience of the microspheres decrease, and the effect of lubricating when acting on a friction surface is also reduced. Moreover, the dispersion is easier to become stable as the particle size decreases. Therefore, in view of the above, more compact graphene microspheres are needed. In the present invention, the densification of the graphene microspheres are achieved by controlling the reducing parameters in each step, thereby effectively improving the comprehensive performances of the grease.

Example 3-10

(160) (1) A single-layer graphene oxide dispersion containing vitamin C was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres, where the weight ratio of vitamin C to graphene oxide is 1.

(161) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(162) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 3000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(163) (4) 5 parts of the paper ball-like graphene microspheres obtained in Step (3), 63 parts of a base oil, 5.6 parts of 12-hydroxystearic acid and 5.3 parts of benzoic acid were mixed, and heated to 90° C. Lithium hydroxide was added for saponification.

(164) (5) The mixture obtained in Step (4) was heated to 180° C., dehydrated, and further heated to 220° C. for refining. After cooling, 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor and 24 parts of a base oil were added, mixed and ground to obtain a lithium complex-based grease comprising paper ball-like graphene microspheres.

(165) Through the above steps, a lithium complex-based grease comprising paper ball-like graphene microspheres is obtained, where the paper ball-like graphene microsphere is microscopically a pleated microsphere having a diameter of 500 nm to 3 μm. Since Steps (1)-(3) are the same as those in Example 3-8, the graphene microsphere has the same carbon/oxygen ratio, density, and specific surface area as in Example 3-8. Specific properties are shown in Table 3. It can be found that increasing the amount of graphene microspheres added can further enhance various performance of the grease.

Example 4-1

(166) Steps 1-3 are the same as those in Example 1-1.

(167) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 54 parts of a base oil, and 8.9 parts of stearic acid were mixed, and heated to 90° C. Barium hydroxide was added for saponification.

(168) Step 5: The mixture obtained in Step (4) was heated to 160° C., dehydrated, and further heated to 210° C. for refining. After cooling to 100° C., 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor and 35 parts of a base oil were added, mixed and ground to obtain a barium-based grease comprising paper ball-like graphene microspheres.

(169) Through the above steps, a barium-based grease comprising paper ball-like graphene microspheres is obtained. The performances of the resulting grease are shown in Table 4.

Example 4-2

(170) Steps 1-3 are the same as those in Example 1-2.

(171) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 54 parts of a base oil, and 8.9 parts of stearic acid were mixed, and heated to 90° C. Barium hydroxide was added for saponification.

(172) Step 5: The mixture obtained in Step (4) was heated to 160° C., dehydrated, and further heated to 210° C. for refining. After cooling to 100° C. 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor and 35 parts of a base oil were added, mixed and ground to obtain a barium-based grease comprising paper ball-like graphene microspheres.

(173) Through the above steps, a barium-based grease comprising paper ball-like graphene microspheres is obtained. The performances of the resulting grease are shown in Table 4.

Example 4-3

(174) Steps 1-3 are the same as those in Example 1-3.

(175) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 54 parts of a base oil, and 8.9 parts of stearic acid were mixed, and heated to 90° C. Barium hydroxide was added for saponification.

(176) Step 5: The mixture obtained in Step (4) was heated to 160° C., dehydrated, and further heated to 210° C. for refining. After cooling to 100° C., 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor and 35 parts of a base oil were added, mixed and ground to obtain a barium-based grease comprising paper ball-like graphene microspheres.

(177) Through the above steps, a barium-based grease comprising paper ball-like graphene microspheres is obtained. The performances of the resulting grease are shown in Table 4.

(178) A lower specific surface area and a higher density of the paper ball-like graphene microsphere means a more compact structure, and a better pressure resistance and elasticity, whereby the overall performance of the composite lubricating oil are much better, as shown in Table 4. Therefore, in view of the above, the reducing conditions in Step (2) are preferably high reduction temperature and long reduction time.

Example 4-4

(179) Steps 1-3 are the same as those in Example 1-4.

(180) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 51 parts of a base oil, and 9.8 parts of 12-hydroxystearic acid were mixed, and heated to 100° C. Barium hydroxide was added for saponification.

(181) Step 5: The mixture obtained in Step (4) was heated to 150° C., dehydrated, and further heated to 200° C. for refining. After cooling to 120° C., 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor, 1 part of a surfactant, and 36 parts of a base oil were added, mixed and ground to obtain a barium-based grease comprising paper ball-like graphene microspheres.

(182) Through the above steps, a barium-based grease comprising paper ball-like graphene microspheres is obtained. Specific properties are shown in Table 4.

Example 4-5

(183) Steps 1-3 are the same as those in Example 1-5.

(184) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 52 parts of a base oil, and 8.9 parts of stearic acid were mixed, and heated to 105° C. Barium hydroxide was added for saponification.

(185) Step 5: The mixture obtained in Step (4) was heated to 155° C., dehydrated, and further heated to 215° C. for refining. After cooling to 120° C., 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor and 37 parts of a base oil were added, mixed and ground to obtain a barium-based grease comprising paper ball-like graphene microspheres.

(186) Through the above steps, a barium-based grease comprising paper ball-like graphene microspheres is obtained. Specific properties are shown in Table 4.

Example 4-6

(187) Steps 1-3 are the same as those in Example 1-6.

(188) Step 4: 0.3 part of the paper ball-like graphene microspheres obtained in Step (3), 51 parts of a base oil, and 11.6 parts of 12-hydroxystearic acid were mixed, and heated to 100° C. Barium hydroxide was added for saponification.

(189) Step 5: The mixture obtained in Step (4) was heated to 150° C., dehydrated, and further heated to 200° C. for refining. After cooling to 120° C., 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor, 1 part of a surfactant, and 28 parts of a base oil were added, mixed and ground to obtain a barium-based grease comprising paper ball-like graphene microspheres.

(190) Through the above steps, a barium-based grease comprising paper ball-like graphene microspheres is obtained. Specific properties are shown in Table 4.

Example 4-7

(191) Steps 1-3 are the same as those in Example 1-7.

(192) Step 4: 0.05 part of the paper ball-like graphene microspheres obtained in Step (3), 48 parts of a base oil, and 13.1 parts of stearic acid were mixed, and heated to 100° C. Barium hydroxide was added for saponification.

(193) Step 5: The mixture obtained in Step (4) was heated to 150° C., dehydrated, and further heated to 200° C. for refining. After cooling to 120° C., 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor, 1 part of a surfactant, and 28 parts of a base oil were added, mixed and ground to obtain a barium-based grease comprising paper ball-like graphene microspheres.

(194) Through the above steps, a barium-based grease comprising paper ball-like graphene microspheres is obtained. Specific properties are shown in Table 4.

Example 4-8

(195) Steps 1-3 are the same as those in Example 1-8.

(196) Step 4: 0.2 part of the paper ball-like graphene microspheres obtained in Step (3), 58 parts of a base oil, and 17.8 parts of stearic acid were mixed, and heated to 100° C. Barium hydroxide was added for saponification.

(197) Step 5: The mixture obtained in Step (4) was heated to 155° C., dehydrated, and further heated to 200° C. for refining. After cooling to 120° C., 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor, 1 part of a surfactant, and 31 parts of a base oil were added, mixed and ground to obtain a barium-based grease comprising paper ball-like graphene microspheres.

(198) Through the above steps, a barium-based grease comprising paper ball-like graphene microspheres is obtained. Specific properties are shown in Table 4.

Example 4-9

(199) Steps 1-3 are the same as those in Example 1-9.

(200) Step 4: 0.1 part of the paper ball-like graphene microspheres obtained in Step (3), 41 parts of a base oil, and 9.4 parts of stearic acid were mixed, and heated to 100° C. Barium hydroxide was added for saponification.

(201) Step 5: The mixture obtained in Step (4) was heated to 155° C., dehydrated, and further heated to 210° C. for refining. After cooling to 110° C., 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor, 1 part of a surfactant, and 35 parts of a base oil were added, mixed and ground to obtain a barium-based grease comprising paper ball-like graphene microspheres.

(202) Through the above steps, a barium-based grease comprising paper ball-like graphene microspheres is obtained. Specific properties are shown in Table 4.

(203) Comparative Example 4-1: A barium-based grease was prepared following the method as described in Example 4-1, except that no paper ball-like graphene microspheres were added during preparation. The performances are shown in Table 4.

(204) Comparative Example 4-2: Direct thermal reduction of graphene oxide microspheres without chemical reduction

(205) (1) A single-layer graphene oxide dispersion was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres.

(206) (2) The graphene oxide microspheres obtained in Step (1) were transferred to a tubular furnace, and heated to 3000° C. for 1 hr, while a mixed gas of hydrogen and argon was continuously introduced.

(207) (3) 0.1 part of the graphene obtained in Step (2), 51 parts of a base oil, and 8.9 parts of 12-hydroxystearic acid were mixed, and heated to 100° C. Barium hydroxide was added for saponification.

(208) (4) The mixture obtained in Step (3) was heated to 160° C., dehydrated, and further heated to 210° C. for refining. After cooling, 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor and 38 parts of a base oil were added, mixed and ground to obtain a barium-based grease.

(209) The graphene obtained through the above steps appears as a black loose powder, and is microscopically a hollow sphere having a diameter of 1-10 μm. The performances of the resulting barium-based grease are shown in Table 4.

(210) TABLE-US-00005 TABLE 4 Friction performances Oil separation by copper Worked Copper mesh at Dropping cone strip Friction 100° C. point penetration corrosion Coef- for 24 hrs (° C.) (0.1 mm) at 24 hr ficient (%) Example 4-1 254 272 Acceptance 0.56 3.38 Example 4-2 255 768 Acceptance 0.53 3.31 Example 4-3 258 266 Acceptance 0.52 3.32 Example 4-4 259 264 Acceptance 0.49 3.3 Example 4-5 262 262 Acceptance 0.48 3.26 Example 4-6 263 259 Acceptance 0.42 3.24 Example 4-7 267 254 Acceptance 0.37 3.13 Example 4-8 274 249 Acceptance 0.33 3.04 Example 4-9 272 252 Acceptance 0.34 3.08 Example 4-10 279 241 Acceptance 0.28 2.87 Comparative 245 284 Acceptance 0.58 3.98 Example 4-1 Comparative 251 274 Acceptance 0.55 3.42 Example 4-2

(211) The density, size and specific surface area of the graphene microspheres have a great influence on the properties of the final composite grease. If the voids increase, the compressive strength, modulus, and elastic resilience of the microspheres decrease, and the effect of lubricating when acting on a friction surface is also reduced. Moreover, the dispersion is easier to become stable as the particle size decreases. Therefore, in view of the above, more compact graphene microspheres are needed. In the present invention, the densification of the graphene microspheres are achieved by controlling the reducing parameters in each step, thereby effectively improving the comprehensive performances of the grease.

Example 4-10

(212) (1) A single-layer graphene oxide dispersion containing vitamin C was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres, where the weight ratio of vitamin C to graphene oxide is 1.

(213) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(214) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 3000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(215) (4) 5 parts of the paper ball-like graphene microspheres obtained in Step (3), 58 parts of a base oil, and 17.8 parts of stearic acid were mixed, and heated to 100° C. Barium hydroxide was added for saponification.

(216) (5) The mixture obtained in Step (4) was heated to 155° C., dehydrated, and further heated to 200° C. for refining. After cooling to 120° C., 0.6 part of an antioxidant, 1.4 parts of a rust inhibitor, 1 part of a surfactant, and 31 parts of a base oil were added, mixed and ground to obtain a barium-based grease comprising paper ball-like graphene microspheres.

(217) Through the above steps, a barium-based grease comprising paper ball-like graphene microspheres is obtained. The paper ball-like graphene microsphere is microscopically a pleated microsphere having a diameter of 500 nm to 3 μm. Since Steps (1)-(3) are the same as those in Example 4-8, the graphene microsphere has the same carbon/oxygen ratio, density, and specific surface area as in Example 4-8. Specific properties are shown in Table 4. It can be found that increasing the amount of graphene microspheres added can further enhance various performance of the grease.

Example 5-1

(218) Steps 1-3 are the same as those in Example 1-1.

(219) Step 4: 0.2 part of the paper ball-like graphene microsphere obtained in Step (3), 100 parts of butadiene rubber, 5 parts of vulcanization accelerator TMTD, 2 parts of stearic acid, 1 part of an anti-aging agent, 2 parts of liquid paraffin, and 4 parts of zinc oxide were mixed in an internal mixer for 15 min at a mixing temperature of 70° C., and then stood for 6 hrs.

(220) Step 5: The mixture obtained in Step (4) and 4 parts of sulfur were mixed in an open mill at 60° C., and finally vulcanized on a plate vulcanizer at 160° C. for 30 min, to obtain a compounded rubber modified with paper ball-like graphene microspheres.

(221) Through the above steps, a compounded rubber modified with paper ball-like graphene microspheres is obtained. The performances of the resulting rubber are shown in Table 5.

Example 5-2

(222) Steps 1-3 are the same as those in Example 1-2.

(223) Step 4: 0.2 part of the paper ball-like graphene microsphere obtained in Step (3), 100 parts of butadiene rubber, 6 parts of vulcanization accelerator TMTD, 2 parts of stearic acid, 1 part of an anti-aging agent, 2 parts of liquid paraffin, and 4 parts of zinc oxide were mixed in an internal mixer for 15 min at a mixing temperature of 70° C., and then stood for 6 hrs.

(224) Step 5: The mixture obtained in Step (4) and 3.5 parts of sulfur were mixed in an open mill at 60° C., and finally vulcanized on a plate vulcanizer at 160° C. for 30 min, to obtain a compounded rubber modified with paper ball-like graphene microspheres.

(225) Through the above steps, a compounded rubber modified with paper ball-like graphene microspheres is obtained. The performances of the resulting rubber are shown in Table 5.

Example 5-3

(226) Steps 1-3 are the same as those in Example 1-3.

(227) Step 4: 0.2 part of the paper ball-like graphene microsphere obtained in Step (3), 100 parts of butadiene rubber, 8 parts of vulcanization accelerator TMTD, 1.5 parts of stearic acid, 1 part of an anti-aging agent, 2 parts of liquid paraffin, and 4 parts of zinc oxide were mixed in an internal mixer for 15 min at a mixing temperature of 70° C., and then stood for 6 hrs.

(228) Step 5: The mixture obtained in Step (4) and 4 parts of sulfur were mixed in an open mill at 60° C., and finally vulcanized on a plate vulcanizer at 160° C. for 30 min, to obtain a compounded rubber modified with paper ball-like graphene microspheres.

(229) Through the above steps, a compounded rubber modified with paper ball-like graphene microspheres is obtained. The performances of the resulting rubber are shown in Table 5.

(230) A lower specific surface area and a higher density of the paper ball-like graphene microsphere means a more compact structure, and a better pressure resistance and elasticity, whereby the overall performances are much better after compounding with rubber, as shown in Table 5. Therefore, in view of the above, the reducing conditions in Step (2) are preferably high reduction temperature and long reduction time.

Example 5-4

(231) Steps 1-3 are the same as those in Example 1-4.

(232) Step 4: 0.1 part of the paper ball-like graphene microsphere obtained in Step (3), 100 parts of butadiene rubber, 4 parts of vulcanization accelerator TMTD, 2 parts of stearic acid, 1 part of an anti-aging agent, 1.5 parts of liquid paraffin, and 4 parts of zinc oxide were mixed in an internal mixer for 30 min at a mixing temperature of 80° C., and then stood for 5 hrs.

(233) Step 5: The mixture obtained in Step (4) and 3 parts of a vulcanizing agent were mixed in an open mill at 80° C., and finally vulcanized on a plate vulcanizer at 170° C. for 20 min, to obtain a compounded rubber modified with paper ball-like graphene microspheres.

(234) Through the above steps, a compounded rubber modified with paper ball-like graphene microspheres is obtained. Specific properties are shown in Table 5.

Example 5-5

(235) Steps 1-3 are the same as those in Example 1-5.

(236) Step 4: 0.3 part of the paper ball-like graphene microsphere obtained in Step (3), 100 parts of butadiene rubber, 4 parts of vulcanization accelerator TMTD, 2 parts of stearic acid, 1 part of an anti-aging agent, 1.5 parts of liquid paraffin, and 4 parts of zinc oxide were mixed in an internal mixer for 30 min at a mixing temperature of 80° C., and then stood for 5 hrs.

(237) Step 5: The mixture obtained in Step (4) and 3 parts of a vulcanizing agent were mixed in an open mill at 80° C., and finally vulcanized on a plate vulcanizer at 170° C. for 20 min, to obtain a compounded rubber modified with paper ball-like graphene microspheres.

(238) Through the above steps, a compounded rubber modified with paper ball-like graphene microspheres is obtained. Specific properties are shown in Table 5.

Example 5-6

(239) Steps 1-3 are the same as those in Example 1-6.

(240) Step 4: 0.3 part of the paper ball-like graphene microsphere obtained in Step (3), 100 parts of butadiene rubber, 4 parts of vulcanization accelerator TMTD, 2 parts of stearic acid, 1 part of an anti-aging agent, 1.5 parts of liquid paraffin, and 4 parts of zinc oxide were mixed in an internal mixer for 30 min at a mixing temperature of 80° C., and then stood for 5 hrs.

(241) Step 5: The mixture obtained in Step (4) and 3 parts of a vulcanizing agent were mixed in an open mill at 80° C., and finally vulcanized on a plate vulcanizer at 180° C. for 30 min, to obtain a compounded rubber modified with paper ball-like graphene microspheres.

(242) Through the above steps, a compounded rubber modified with paper ball-like graphene microspheres is obtained. Specific properties are shown in Table 5.

Example 5-7

(243) Steps 1-3 are the same as those in Example 1-7.

(244) Step 4: 0.2 part of the paper ball-like graphene microsphere obtained in Step (3), 100 parts of butadiene rubber, 8 parts of vulcanization accelerator TMTD, 2 parts of stearic acid, 1 part of an anti-aging agent, 1.5 parts of liquid paraffin, and 4 parts of zinc oxide were mixed in an internal mixer for 30 min at a mixing temperature of 80° C., and then stood for 5 hrs.

(245) Step 5: The mixture obtained in Step (4) and 4 parts of a vulcanizing agent were mixed in an open mill at 80° C., and finally vulcanized on a plate vulcanizer at 180° C. for 30 min, to obtain a compounded rubber modified with paper ball-like graphene microspheres.

(246) Through the above steps, a compounded rubber modified with paper ball-like graphene microspheres is obtained. Specific properties are shown in Table 5.

Example 5-8

(247) Steps 1-3 are the same as those in Example 1-8.

(248) Step 4: 0.2 part of the paper ball-like graphene microsphere obtained in Step (3), 100 parts of butadiene rubber, 8 parts of vulcanization accelerator TMTD, 2 parts of stearic acid, 1 part of an anti-aging agent, 1.5 parts of liquid paraffin, and 4 parts of zinc oxide were mixed in an internal mixer for 30 min at a mixing temperature of 80° C., and then stood for 5 hrs.

(249) Step 5: The mixture obtained in Step (4) and 4 parts of a vulcanizing agent were mixed in an open mill at 80° C., and finally vulcanized on a plate vulcanizer at 180° C. for 30 min, to obtain a compounded rubber modified with paper ball-like graphene microspheres.

(250) Through the above steps, a compounded rubber modified with paper ball-like graphene microspheres is obtained. Specific properties are shown in Table 5.

Example 5-9

(251) Steps 1-3 are the same as those in Example 1-9.

(252) Step 4: 0.2 part of the paper ball-like graphene microsphere obtained in Step (3), 100 parts of butadiene rubber, 7 parts of vulcanization accelerator TMTD, 1 parts of stearic acid, 1 part of an anti-aging agent, 2.5 parts of liquid paraffin, and 4 parts of zinc oxide were mixed in an internal mixer for 30 min at a mixing temperature of 80° C., and then stood for 5 hrs.

(253) Step 5: The mixture obtained in Step (4) and 4 parts of a vulcanizing agent were mixed in an open mill at 80° C., and finally vulcanized on a plate vulcanizer at 160° C. for 15 min, to obtain a compounded rubber modified with paper ball-like graphene microspheres.

(254) Through the above steps, a compounded rubber modified with paper ball-like graphene microspheres is obtained. Specific properties are shown in Table 5.

(255) Comparative Example 5-1: A compounded rubber was prepared following the method as described in Example 5-1, except that no paper ball-like graphene microspheres were added during preparation. The performances are shown in Table 5.

(256) Comparative Example 5-2: Direct thermal reduction of graphene oxide microspheres without chemical reduction

(257) (1) A Single-layer graphene oxide dispersion was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres.

(258) (2) The graphene oxide microspheres obtained in Step (1) were transferred to a tubular furnace, and heated to 3000° C. at a ramping rate of 5° C./min and maintained for 1 hr, while a mixed gas of hydrogen and argon was continuously introduced.

(259) (3) 0.2 part of the graphene obtained in Step (2), 100 parts of butadiene rubber, 8 parts of vulcanization accelerator TMTD, 2 parts of stearic acid, 1 part of an anti-aging agent, 1.5 parts of liquid paraffin, and 4 parts of zinc oxide were mixed in an internal mixer for 30 min at a mixing temperature of 80° C., and then stood for 5 hrs.

(260) (4) The mixture obtained in Step (3) and 4 parts of a vulcanizing agent were mixed in an open mill at 80° C., and finally vulcanized on a plate vulcanizer at 180° C. for 30 min, to obtain a compounded rubber modified with graphene.

(261) The graphene obtained through the above steps appears as a black loose powder, and is microscopically a hollow sphere having a diameter of 1-10 μm. The performances are shown in Table 5.

(262) TABLE-US-00006 TABLE 5 Friction performances Tensile Tearing Softening Wear strength strength temperature resistance (MPa) (kN m.sup.−1) (° C.) Example 5-1 Excellent 19.9 14.1 207 Example 5-2 Excellent 20.5 14.4 207 Example 5-3 Excellent 21 14.7 209 Example 5-4 Excellent 22.3 15.1 211 Example 5-5 Excellent 22.8 16.6 214 Example 5-6 Excellent 23.5 18.3 218 Example 5-7 Excellent 24.4 20.7 223 Example 5-8 Excellent 26.8 22.8 226 Example 5-9 Excellent 25.3 21.6 222 Example 5-10 Excellent 29.6 24.5 234 Comparative Good 18.5 9.6 193 Example 5-1 Comparative Good 19.6 13.6 205 Example 5-2

(263) The performance of graphene reinforced rubber is closely related to the performance of the filler. A higher density and a larger specific surface area of the filled paper ball-like graphene microsphere means a more compact structure, fewer voids, more stable structure, and better performance in impact absorption, elastic resilience and wear resistance Moreover, the dispersion is easier to become stable as the particle size decreases. Therefore, in view of the above, more compact graphene microspheres are needed. In the present invention, the densification, structural integrity and performance optimization of the graphene microspheres are achieved by controlling the reducing parameters in each step, thereby effectively improving the comprehensive performances of the compounded rubber.

Example 5-10

(264) (1) A single-layer graphene oxide dispersion containing vitamin C was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres, where the weight ratio of vitamin C to graphene oxide is 1.

(265) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(266) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 3000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(267) (4) 0.2 part of the paper ball-like graphene microsphere obtained in Step (3), 100 parts of butadiene rubber, 8 parts of vulcanization accelerator TMTD, 2 parts of stearic acid, 1 part of an anti-aging agent, 1.5 parts of liquid paraffin, and 4 parts of zinc oxide were mixed in an internal mixer for 30 min at a mixing temperature of 80° C., and then stood for 5 hrs.

(268) (5) The mixture obtained in Step (4) and 4 parts of a vulcanizing agent were mixed in an open mill at 80° C., and finally vulcanized on a plate vulcanizer at 180° C. for 30 min, to obtain a compounded rubber modified with paper ball-like graphene microspheres.

(269) Through the above steps, a compounded rubber modified with paper ball-like graphene microspheres is obtained. The paper ball-like graphene microsphere is microscopically a pleated microsphere having a diameter of 500 nm to 3 μm. Since Steps (1)-(3) are the same as those in Example 5-8, the graphene microsphere has the same carbon/oxygen ratio, density, and specific surface area as in Example 5-8. Specific properties are shown in Table 5. It can be found that increasing the amount of graphene microspheres added can further enhance the various properties of the rubber.

Example 6-1

(270) Steps 1-3 are the same as those in Example 1-1.

(271) Step 4: 0.3 part of the paper ball-like graphene microspheres obtained in Step (3) and 100 parts of pure acrylic emulsion were stirred until uniform and ultrasonically dispersed. Then, 15 parts of water, 0.3 part of a dispersing agent, 0.1 part of a preservative, 0.3 part of a film forming agent, 0.1 part of a leveling agent, 4 parts of a thickener, 0.3 part of a deforming agent, 10 parts of calcium carbonate, 10 parts of alumina, and 15 parts of titania were added in sequence, stirred at a high speed, and defoamed.

(272) Through the above steps, a graphene-based waterborne acrylic coating is obtained. The performances of the obtained coating are shown in Table 6.

Example 6-2

(273) Steps 1-3 are the same as those in Example 1-2.

(274) Step 4: 0.3 part of the paper ball-like graphene microspheres obtained in Step (3) and 100 parts of pure acrylic emulsion were stirred until uniform and ultrasonically dispersed. Then, 15 parts of water, 0.3 part of a dispersing agent, 0.1 part of a preservative, 0.3 part of a film forming agent, 0.1 part of a leveling agent, 4 parts of a thickener, 0.3 part of a deforming agent, 10 parts of calcium carbonate, 10 parts of alumina, and 15 parts of titania were added in sequence, stirred at a high speed, and defoamed.

(275) Through the above steps, a graphene-based waterborne acrylic coating is obtained. The performances of the obtained coating are shown in Table 6.

Example 6-3

(276) Steps 1-3 are the same as those in Example 1-3.

(277) Step 4: 0.3 part of the paper ball-like graphene microspheres obtained in Step (3) and 100 parts of pure acrylic emulsion were stirred until uniform and ultrasonically dispersed. Then, 15 parts of water, 0.3 part of a dispersing agent, 0.1 part of a preservative, 0.3 part of a film forming agent, 0.1 part of a leveling agent, 4 parts of a thickener, 0.3 part of a deforming agent, 10 parts of calcium carbonate, 10 parts of alumina, and 15 parts of titania were added in sequence, stirred at a high speed, and defoamed.

(278) Through the above steps, a graphene-based waterborne acrylic coating is obtained. The performances of the obtained coating are shown in Table 6.

(279) A lower specific surface area and a higher density of the paper ball-like graphene microsphere means a more compact structure, and a better pressure resistance and elasticity, whereby the overall performance after film formation with the coating is much better, as shown in Table 6. Therefore, in view of the above, the reducing conditions in Step (2) are preferably high reduction temperature and long reduction time.

Example 6-4

(280) Steps 1-3 are the same as those in Example 1-4.

(281) Step 4: 0.2 part of the paper ball-like graphene microspheres obtained in Step (3) and 100 parts of pure acrylic emulsion were stirred until uniform and ultrasonically dispersed. Then, 15 parts of water, 0.3 part of a dispersing agent, 0.1 part of a preservative, 0.3 part of a film forming agent, 0.1 part of a leveling agent, 4 parts of a thickener, 0.3 part of a deforming agent, 15 parts of calcium carbonate, and 20 parts of titania were added in sequence, stirred at a high speed, and defoamed.

(282) Through the above steps, a graphene-based waterborne acrylic coating is obtained. Specific properties are shown in Table 6.

Example 6-5

(283) Steps 1-3 are the same as those in Example 1-5.

(284) Step 4: 0.4 part of the paper ball-like graphene microspheres obtained in Step (3) and 100 parts of vinyl acetate-acrylic emulsion were stirred until uniform and ultrasonically dispersed. Then, 18 parts of water, 0.3 part of a dispersing agent, 0.1 part of a preservative, 0.3 part of a film forming agent, 0.1 part of a leveling agent, 5 parts of a thickener, 0.1 part of a deforming agent, 5 parts of calcium carbonate, 8 parts of alumina, and 18 parts of titania were added in sequence, stirred at a high speed, and defoamed.

(285) Through the above steps, a graphene-based waterborne acrylic coating is obtained. Specific properties are shown in Table 6.

Example 6-6

(286) Steps 1-3 are the same as those in Example 1-6.

(287) Step 4: 0.4 part of the paper ball-like graphene microspheres obtained in Step (3) and 100 parts of vinyl acetate-acrylic emulsion were stirred until uniform and ultrasonically dispersed. Then, 12 parts of water, 0.3 part of a dispersing agent, 0.1 part of a preservative, 0.3 part of a film forming agent, 0.1 part of a leveling agent, 5 parts of a thickener, 0.1 part of a deforming agent, 30 parts of calcium carbonate, and 18 parts of titania were added in sequence, stirred at a high speed, and defoamed.

(288) Through the above steps, a graphene-based waterborne acrylic coating is obtained. Specific properties are shown in Table 6.

Example 6-7

(289) Steps 1-3 are the same as those in Example 1-7.

(290) Step 4: 0.5 part of the paper ball-like graphene microspheres obtained in Step (3) and 100 parts of vinyl acetate-acrylic emulsion were stirred until uniform and ultrasonically dispersed. Then, 20 parts of water, 0.5 part of a dispersing agent, 0.1 part of a preservative, 0.3 part of a film forming agent, 0.2 part of a leveling agent, 10 parts of a thickener, 0.1 part of a deforming agent, 30 parts of calcium carbonate, 10 parts of alumina, and 18 parts of titania were added in sequence, stirred at a high speed, and defoamed.

(291) Through the above steps, a graphene-based waterborne acrylic coating is obtained. Specific properties are shown in Table 6.

Example 6-8

(292) Steps 1-3 are the same as those in Example 1-8.

(293) Step 4: 0.5 part of the paper ball-like graphene microspheres obtained in Step (3) and 100 parts of vinyl acetate-acrylic emulsion were stirred until uniform and ultrasonically dispersed. Then, 18 parts of water, 0.3 part of a dispersing agent, 0.1 part of a preservative, 0.3 part of a film forming agent, 0.1 part of a leveling agent, 5 parts of a thickener, 0.1 part of a deforming agent, 25 parts of calcium carbonate, 8 parts of alumina, and 16 parts of titania were added in sequence, stirred at a high speed, and defoamed.

(294) Through the above steps, a graphene-based waterborne acrylic coating is obtained. Specific properties are shown in Table 6.

Example 6-9

(295) Steps 1-3 are the same as those in Example 1-9.

(296) Step 4: 0.5 part of the paper ball-like graphene microspheres obtained in Step (3) and 100 parts of styrene-acrylic emulsion were stirred until uniform and ultrasonically dispersed. Then, 14 parts of water, 0.3 part of a dispersing agent, 0.1 part of a preservative, 0.3 part of a film forming agent, 0.1 part of a leveling agent, 5 parts of a thickener, 0.1 part of a deforming agent, 20 parts of calcium carbonate, 8 parts of alumina, and 14 parts of titania were added in sequence, stirred at a high speed, and defoamed.

(297) Comparative Example 6-1: A waterborne acrylic coating was prepared following the method as described in Example 6-1 except that no paper ball-like graphene microspheres were added during the preparation. The performances are shown in Table 6.

(298) Comparative Example 6-2: Direct thermal reduction of graphene oxide microspheres without chemical reduction

(299) (1) A single-layer graphene oxide dispersion was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres.

(300) (2) The graphene oxide microspheres obtained in Step (1) were transferred to a tubular furnace, and heated to 3000° C. at a ramping rate of 5° C./min and maintained for 1 hr, while a mixed gas of hydrogen and argon was continuously introduced.

(301) (3) 0.3 part of the graphene obtained in Step (2) and 100 parts of pure acrylic emulsion were stirred until uniform and ultrasonically dispersed. Then, 15 parts of water, 0.3 part of a dispersing agent, 0.1 part of a preservative, 0.3 part of a film forming agent, 0.1 part of a leveling agent, 4 parts of a thickener, 0.3 part of a deforming agent, 10 parts of calcium carbonate, 10 parts of alumina, and 15 parts of titania were added in sequence, stirred at a high speed, and defoamed.

(302) The graphene obtained through the above steps appears as a black loose powder, and is microscopically a hollow sphere having a diameter of 1-10 μm. The performances are shown in FIG. 6.

(303) TABLE-US-00007 TABLE 6 Friction performances Film Impact Rubbing forming strength number Hard- ability Adhesion (kg .Math. cm) (r) ness Example 6-1 Excellent 1 113 550 H Example 6-2 Excellent 1 116 610 H Example 6-3 Excellent 1 120 640 H Example 6-4 Excellent 1 122 710 H Example 6-5 Excellent 1 126 790 H Example 6-6 Excellent 1 129 820 H Example 6-7 Excellent 1 134 870 H Example 6-8 Excellent 1 137 890 H Example 6-9 Excellent 1 136 875 H Example 6-10 Excellent 1 148 940 H Comparative Excellent 1 90 450 2B Example 6-1 Comparative Excellent 2 104 530 H Example 6-2 Note: The wear resistance of the coating film is tested in accordance with GB/T18103-2013 “Engineered wood flooring”. The adhesion of the coating film is tested in accordance with GB/T9286-1998 “Paints and varnishes Cross cut test for films”.

(304) Although the mechanical properties of the coating can be improved to some extent after the addition of the coating, the adhesion is decreased due to the presence of expanded graphene sheet. From the viewpoint of coating properties, the hardness, impact strength and wear resistance of the coating are greatly improved after adding the paper ball-like graphene microsphere. Moreover, increasing the density and reducing the size and specific surface area of the graphene microspheres are more favorable for performances of the final graphene-based waterborne acrylic coating. This is because when the pores in the microspheres are excessive, the compressive strength, modulus, and elastic resilience of the microspheres are lowered, and the performance in the coating film is deteriorated. Moreover, the dispersion is easier to become stable as the particle size decreases. Therefore, in view of the above, more compact graphene microspheres are needed. In the present invention, the densification of the graphene microspheres are achieved by controlling the reducing parameters in each step, thereby effectively improving the comprehensive performances of the coating.

Example 6-10

(305) (1) A single-layer graphene oxide dispersion containing vitamin C was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres, where the weight ratio of vitamin C to graphene oxide is 1.

(306) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(307) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 3000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(308) (4) 5 parts of the paper ball-like graphene microspheres obtained in Step (3) and 100 parts of vinyl acetate-acrylic emulsion were stirred until uniform and ultrasonically dispersed. Then, 18 parts of water, 0.3 part of a dispersing agent, 0.1 part of a preservative, 0.3 part of a film forming agent, 0.1 part of a leveling agent, 5 parts of a thickener, 0.1 part of a deforming agent, 25 parts of calcium carbonate, 8 parts of alumina, and 16 parts of titania were added in sequence, stirred at a high speed, and defoamed.

(309) Through the above steps, a graphene-based waterborne acrylic coating is obtained. The paper ball-like graphene microsphere is microscopically a pleated microsphere having a diameter of 500 nm to 3 μm. Since Steps (1)-(3) are the same as those in Example 6-8, the graphene microsphere has the same carbon/oxygen ratio, density, and specific surface area as in Example 6-8. Specific properties are shown in Table 6. It can be found that increasing the amount of graphene microspheres added can further enhance the various properties of the coating.

Example 7-1

(310) Steps 1-3 are the same as those in Example 1-1.

(311) Step 4: 0.2 part of paper ball-like graphene microspheres was added to 100 parts of molten caprolactam monomer, and stirred and heated to 120° C. Water was removed by distillation under reduced pressure, and 0.15 part of sodium hydroxide was added, heated to 140° C. Water was removed by distillation under reduced pressure for 30 min, and the remainder was heated to 155° C.

(312) Step 5: 0.35 part of the cocatalyst tolyl 2,4-diisocyanate (TDI) was added to the mixture obtained in Step (4), stirred until uniform, casted into a mold preheated at 165° C., maintained at this temperature for 30 min, cooled, and released from the mold to obtain a graphene/cast nylon composite material.

(313) Through the above steps, a graphene/cast nylon composite material is obtained. The properties of the obtained composite material are shown in Table 7.

Example 7-2

(314) Steps 1-3 are the same as those in Example 1-2.

(315) Step 4: 0.2 part of paper ball-like graphene microspheres was added to 100 parts of molten caprolactam monomer, and stirred and heated to 120° C. Water was removed by distillation under reduced pressure, and 0.15 part of sodium hydroxide was added, heated to 140° C. Water was removed by distillation under reduced pressure for 30 min, and the remainder was heated to 155° C.

(316) Step 5: 0.35 part of the cocatalyst tolyl 2,4-diisocyanate (TDI) was added to the mixture obtained in Step (4), stirred until uniform, casted into a mold preheated at 165° C., maintained at this temperature for 30 min, cooled, and released from the mold to obtain a graphene/cast nylon composite material.

(317) Through the above steps, a graphene/cast nylon composite material is obtained. The properties of the obtained composite material are shown in Table 7.

Example 7-3

(318) Steps 1-3 are the same as those in Example 1-3.

(319) Step 4: 0.2 part of paper ball-like graphene microspheres was added to 100 parts of molten caprolactam monomer, and stirred and heated to 120° C. Water was removed by distillation under reduced pressure, and 0.15 part of sodium hydroxide was added, heated to 140° C. Water was removed by distillation under reduced pressure for 30 min, and the remainder was heated to 155° C.

(320) Step 5: 0.35 part of the cocatalyst tolyl 2,4-diisocyanate (TDI) was added to the mixture obtained in Step (4), stirred until uniform, casted into a mold preheated at 165° C., maintained at this temperature for 30 min, cooled, and released from the mold to obtain a graphene/cast nylon composite material.

(321) Through the above steps, a graphene/cast nylon composite material is obtained. The properties of the obtained composite material are shown in Table 7.

(322) A large specific surface area of the paper ball-like graphene microsphere is not conducive to the process of cast polymerization, and tends to cause phase separation, cracking, too high viscosity and even difficulty in polymerization. Moreover, the mechanical properties are weaker than the situation where more compact graphene microspheres are used. Therefore, in view of the above, the reducing conditions in Step (2) are preferably high reduction temperature and long reduction time.

Example 7-4

(323) Steps 1-3 are the same as those in Example 1-4.

(324) Step 4: 0.3 part of paper ball-like graphene microspheres was added to 100 parts of molten caprolactam monomer, and stirred and heated to 120° C. Water was removed by distillation under reduced pressure, and 0.15 part of sodium hydroxide was added, heated to 140° C. Water was removed by distillation under reduced pressure for 30 min, and the remainder was heated to 155° C.

(325) Step 5: 0.35 part of the cocatalyst tolyl 2,4-diisocyanate (TDI) was added to the mixture obtained in Step (4), stirred until uniform, casted into a mold preheated at 165° C., maintained at this temperature for 30 min, cooled, and released from the mold to obtain a graphene/cast nylon composite material.

(326) Through the above steps, a graphene/cast nylon composite material is obtained. Specific properties of the material are shown in Table 7.

Example 7-5

(327) Steps 1-3 are the same as those in Example 1-5.

(328) Step 4: 0.5 part of paper ball-like graphene microspheres was added to 100 parts of molten caprolactam monomer, and stirred and heated to 120° C., Water was removed by distillation under reduced pressure, and 0.15 part of sodium hydroxide was added, heated to 140° C. Water was removed by distillation under reduced pressure for 30 min, and the remainder was heated to 155° C.

(329) Step 5: 0.35 part of the cocatalyst tolyl 2,4-diisocyanate (TDI) was added to the mixture obtained in Step (4), stirred until uniform, casted into a mold preheated at 165° C., maintained at this temperature for 30 min, cooled, and released from the mold to obtain a graphene/cast nylon composite material.

(330) Through the above steps, a graphene/cast nylon composite material is obtained. Specific properties of the material are shown in Table 7.

Example 7-6

(331) Steps 1-3 are the same as those in Example 1-6.

(332) Step 4: 0.4 part of paper ball-like graphene microspheres was added to 100 parts of molten caprolactam monomer, and stirred and heated to 120° C. Water was removed by distillation under reduced pressure, and 0.15 part of sodium hydroxide was added, heated to 140° C. Water was removed by distillation under reduced pressure for 30 min, and the remainder was heated to 155° C.

(333) Step 5: 035 part of the cocatalyst tolyl 2,4-diisocyanate (TDI) was added to the mixture obtained in Step (4), stirred until uniform, casted into a mold preheated at 165° C., maintained at this temperature for 30 min, cooled, and released from the mold to obtain a graphene/cast nylon composite material.

(334) Through the above steps, a graphene/cast nylon composite material is obtained. Specific properties of the material are shown in Table 7.

Example 7-7

(335) Steps 1-3 are the same as those in Example 1-7.

(336) Step 4: 0.3 part of paper ball-like graphene microspheres was added to 100 parts of molten caprolactam monomer, and stirred and heated to 120° C. Water was removed by distillation under reduced pressure, and 0.15 part of sodium hydroxide was added, heated to 140° C. Water was removed by distillation under reduced pressure for 30 min, and the remainder was heated to 155° C.

(337) Step 5: 0.35 part of the cocatalyst tolyl 2,4-diisocyanate (TDI) was added to the mixture obtained in Step (4), stirred until uniform, casted into a mold preheated at 165° C., maintained at this temperature for 30 min, cooled, and released from the mold to obtain a graphene/cast nylon composite material.

(338) Through the above steps, a graphene/cast nylon composite material is obtained. Specific properties of the material are shown in Table 7.

Example 7-8

(339) Steps 1-3 are the same as those in Example 1-8.

(340) Step 4: 0.3 part of paper ball-like graphene microspheres was added to 100 parts of molten caprolactam monomer, and stirred and heated to 12.0° C. Water was removed by distillation under reduced pressure, and 0.15 part of sodium hydroxide was added, heated to 140° C. Water was removed by distillation under reduced pressure for 30 min, and the remainder was heated to 155° C.

(341) Step 5: 0.35 part of the cocatalyst tolyl 2,4-diisocyanate (TIM) was added to the mixture obtained in Step (4), stirred until uniform, casted into a mold preheated at 165° C., maintained at this temperature for 30 min, cooled, and released from the mold to obtain a graphene/cast nylon composite material.

(342) Through the above steps, a graphene/cast nylon composite material is obtained. Specific properties of the material are shown in Table 7.

Example 7-9

(343) Steps 1-3 are the same as those in Example 1-9.

(344) Step 4: 0.3 part of paper ball-like graphene microspheres was added to 100 parts of molten caprolactam monomer, and stirred and heated to 120° C. Water was removed by distillation under reduced pressure, and 0.15 part of sodium hydroxide was added, heated to 140° C. Water was removed by distillation under reduced pressure for 30 min, and the remainder was heated to 155° C.

(345) Step 5: 0.35 part of the cocatalyst tolyl 2,4-diisocyanate (TDI) was added to the mixture obtained in Step (4), stirred until uniform, casted into a mold preheated at 165° C., maintained at this temperature for 30 min, cooled, and released from the mold to obtain a graphene/cast nylon composite material.

(346) Through the above steps, a graphene/cast nylon composite material is obtained. Specific properties of the material are shown in Table 7.

(347) Comparative Example 7-1: A graphene/cast nylon composite material was prepared following the method as described in Example 7-1 except that no paper ball-like graphene microspheres were added during the preparation. The performances are shown in Table 7.

(348) Comparative Example 7-2: Direct thermal reduction of graphene oxide microspheres without chemical reduction

(349) (1) A single-layer graphene oxide dispersion was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres.

(350) (2) The graphene oxide microspheres obtained in Step (1) were transferred to a tubular furnace, and heated to 3000° C. at a ramping rate of 5° C./min and maintained for 1 hr, while a mixed gas of hydrogen and argon was continuously introduced.

(351) (3) 0.3 part of paper ball-like graphene microspheres were added to 100 parts of molten caprolactam monomer, stirred and heated to 120° C., Water was removed by distillation under reduced pressure, and 0.15 part of sodium hydroxide was added, and heated to 140° C. Water was removed by distillation under reduced pressure for 30 min, and the remainder was heated to 155° C.

(352) (4) 0.35 part of the cocatalyst tolyl 2, 4-diisocyanate (TDI) was added to the mixture obtained in Step (3), stirred until uniform, casted into a mold preheated at 165° C., maintained at this temperature for 30 min, cooled, and released from the mold to obtain a graphene/cast nylon composite material.

(353) The graphene obtained through the above steps appears as a black loose powder, and is microscopically a hollow sphere having a diameter of 1-10 μm. Specific properties of the obtained composite material are shown in Table 7.

(354) When compounded with nylon 6, the microspheres with lower specific surface area and higher density have better mechanical strength and shape stability, and have less impact on the process of cast polymerization. Therefore, the compact graphene microspheres obtained by addition of a reducing agent in the first step of spray drying, chemical reduction in the second step, and high-temperature thermal treatment in the third step have the best reinforcing effect on cast nylon, and improve the mechanical properties, tribological properties and heat distortion temperature of the material.

(355) TABLE-US-00008 TABLE 7 Comprehensive indices of composite materials Elongation Heat Tensile at Impact distortion strength break strength temperature Friction (MPa) (1%) (KJ/m.sup.2) (° C.) coefficient Example 7-1 60.1 103 5.2 127 0.37 Example 7-2 60.7 106 5.5 119 0.35 Example 7-3 60.9 104 5.6 124 0.32 Example 7-4 61.4 101 6.3 126 0.28 Example 7-5 62.1 108 7.8 129 0.27 Example 7-6 63.2 98 8.9 131 0.24 Example 7-7 65.8 95 9.2 136 0.22 Example 7-8 67.9 93 9.4 143 0.19 Example 7-9 66.2 99 9 135 0.23 Example 7-10 69.5 74 9.8 146 0.15 Example 7-11 72.7 46 10.3 151 0.12 Comparative 56.2 112 4.6 106 0.43 Example 7-1 Comparative 59.3 21 6.9 125 0.38 Example 7-2

Example 7-10

(356) (1) A single-layer graphene oxide dispersion containing vitamin C was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres, where the weight ratio of vitamin C to graphene oxide is 1.

(357) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(358) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 3000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(359) (4) 1.5 parts of paper ball-like graphene microspheres were added to 100 parts of molten caprolactam monomer, stirred and heated to 120° C. Water was removed by distillation under reduced pressure, and 0.15 part of sodium hydroxide was added, and heated to 140° C. Water was removed by distillation under reduced pressure for 30 min, and the remainder was heated to 155° C.

(360) (5) 0.35 part of the cocatalyst tolyl 2, 4-diisocyanate (TDI) was added to the mixture obtained in Step (4), stirred until uniform, casted into a mold preheated at 165° C., maintained at this temperature for 30 min, cooled, and released from the mold to obtain a graphene/cast nylon composite material.

(361) A graphene/cast nylon composite material is obtained through the above steps. The paper ball-like graphene microsphere is microscopically a pleated microsphere having a diameter of 500 nm to 3 μm. Since Steps (1)-(3) are the same as those in Example 7-8, the graphene microsphere has the same carbon/oxygen ratio, density, and specific surface area as in Example 7-8. Specific properties are shown in Table 7.

Example 7-11

(362) (1) A single-layer graphene oxide dispersion containing vitamin C was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres, where the weight ratio of vitamin C to graphene oxide is 1.

(363) (2) The graphene oxide microspheres obtained in Step (1) were reduced for 24 hrs at 90° C. under hydrazine hydrate vapor to obtain reduced graphene oxide microspheres.

(364) (3) The reduced graphene oxide microspheres obtained in Step (2) were transferred to a tubular furnace, and heated to 3000° C. for 1 hr while nitrogen was continuously introduced, to obtain paper ball-like graphene microspheres.

(365) (4) 5 parts of paper ball-like graphene microspheres were added to 100 parts of molten caprolactam monomer, stirred and heated to 120° C. Water was removed by distillation under reduced pressure, and 0.15 part of sodium hydroxide was added, and heated to 140° C. Water was removed by distillation under reduced pressure for 30 min, and the remainder was heated to 155° C.;

(366) (5) 0.35 part of the cocatalyst tolyl 2, 4-diisocyanate (TDI) was added to the mixture obtained in Step (4), stirred until uniform, casted into a mold preheated at 165° C., maintained at this temperature for 30 min, cooled, and released from the mold to obtain a graphene/cast nylon composite material.

(367) A graphene/cast nylon composite material is obtained through the above steps. The paper ball-like graphene microsphere is microscopically a pleated microsphere having a diameter of 500 nm to 3 μm. Since Steps (1)-(3) are the same as those in Example 7-8, the graphene microsphere has the same carbon/oxygen ratio, density, and specific surface area as in Example 7-8. Specific properties are shown in Table 7.

(368) By comparing Examples 7-8, 7-10, and 7-11, it can be seen that most of the indices of the composite material are improved with the increase of the amount of the paper ball-like graphene microspheres, indicating that further increasing the amount can further optimize the performances, but the elongation at break is deteriorated, so an appropriate amount needs to be determined after in view of the above in practical applications.

Example 8-1

(369) Steps 1-3 are the same as those in Example 1-1.

(370) Step 4: Nylon 6 was mixed uniformly with the paper ball-like graphene microspheres obtained in Step (3) at a weight ratio of 100:0.2 in a mixer to obtain a nylon 6/graphene premix. Nylon 6 and the graphene microspheres were dried for 12 hrs under vacuum in a vacuum oven at 90° C. before premixing.

(371) Step 5: The premix obtained in Step (4) was melt-blended and extruded through a twin-screw extruder, where the melting temperature was 250° C., and the rotation speed of the screw was 200 rpm.

(372) The compounded material was injection molded by an injection molding machine into a standard test strip for mechanical property test. The graphene-toughened nylon 6 composite material was tested to have a notched Izod impact strength of 25.44 KJ/m.sup.2 at normal temperature.

Example 8-2

(373) Steps 1-3 are the same as those in Example 1-2.

(374) Step 4: Nylon 6 was mixed uniformly with the paper ball-like graphene microspheres obtained in Step (3) at a weight ratio of 100:0.2 in a mixer to obtain a nylon 6/graphene premix. Nylon 6 and the graphene microspheres were dried for 12 hrs under vacuum in a vacuum oven at 90° C. before premixing.

(375) Step 5: The premix obtained in Step (4) was melt-blended and extruded through a twin-screw extruder, where the melting temperature was 250° C., and the rotation speed of the screw was 200 rpm.

(376) The compounded material was injection molded by an injection molding machine into a standard test strip for mechanical property test. The graphene-toughened nylon 6 composite material was tested to have a notched Izod impact strength of 26.56 KJ/m.sup.2 at normal temperature.

Example 8-3

(377) Steps 1-3 are the same as those in Example 1-3.

(378) Step 4: Nylon 6 was mixed uniformly with the paper ball-like graphene microspheres obtained in Step (3) at a weight ratio of 100:0.2 in a mixer to obtain a nylon 6/graphene premix. Nylon 6 and the graphene microspheres were dried for 12 hrs under vacuum in a vacuum oven at 90° C. before premixing.

(379) Step 5: The premix obtained in Step (4) was melt-blended and extruded through a twin-screw extruder, where the melting temperature was 250° C., and the rotation speed of the screw was 200 rpm.

(380) The compounded material was injection molded by an injection molding machine into a standard test strip for mechanical property test. The graphene-toughened nylon 6 composite material was tested to have a notched Izod impact strength of 27.15 KJ/m.sup.2 at normal temperature.

(381) When the specific surface area of the paper ball-like graphene microsphere is large, the dispersion of the graphene powder becomes poor, and the toughening effect is affected. Therefore, in view of the above, the reduction conditions in the second step are preferably a high reduction temperature and a long reduction time.

Example 8-4

(382) Steps 1-3 are the same as those in Example 1-4.

(383) Step 4: Nylon 6 was mixed uniformly with the paper ball-like graphene microspheres obtained in Step (3) at a weight ratio of 100:0.2 in a mixer to obtain a nylon 6/graphene premix. Nylon 6 and the graphene microspheres were dried for 12 hrs under vacuum in a vacuum oven at 90° C. before premixing.

(384) Step 5: The premix obtained in Step (4) was melt-blended and extruded through a twin-screw extruder, where the melting temperature was 250° C., and the rotation speed of the screw was 200 rpm.

(385) A graphene-toughened nylon 6 composite material was obtained through the above steps. The compounded material was injection molded by an injection molding machine into a standard test strip for mechanical property test. The graphene-toughened nylon 6 composite material was tested to have a notched Izod impact strength of 29.80 KJ/m.sup.2 at normal temperature.

Example 8-5

(386) Steps 1-3 are the same as those in Example 1-5.

(387) Step 4: Nylon 6 was mixed uniformly with the paper ball-like graphene microspheres obtained in Step (3) at a weight ratio of 100:0.2 in a mixer to obtain a nylon 6/graphene premix. Nylon 6 and the graphene microspheres were dried for 12 hrs under vacuum in a vacuum oven at 90° C. before premixing.

(388) Step 5: The premix obtained in Step (4) was melt-blended and extruded through a twin-screw extruder, where the melting temperature was 250° C., and the rotation speed of the screw was 200 rpm.

(389) A graphene-toughened nylon 6 composite material was obtained through the above steps. The compounded material was injection molded by an injection molding machine into a standard test strip for mechanical property test. The graphene-toughened nylon 6 composite material was tested to have a notched Izod impact strength of 30.41 KJ/m.sup.2 at normal temperature.

Example 8-6

(390) Steps 1-3 are the same as those in Example 1-6.

(391) Step 4: Nylon 6 was mixed uniformly with the paper ball-like graphene microspheres obtained in Step (3) at a weight ratio of 100:0.2 in a mixer to obtain a nylon 6/graphene premix. Nylon 6 and the graphene microspheres were dried for 12 hrs under vacuum in a vacuum oven at 90° C. before premixing.

(392) Step 5: The premix obtained in Step (4) was melt-blended and extruded through a twin-screw extruder, where the melting temperature was 250° C., and the rotation speed of the screw was 200 rpm.

(393) A graphene-toughened nylon 6 composite material was obtained through the above steps. The compounded material was injection molded by an injection molding machine into a standard test strip for mechanical property test. The graphene-toughened nylon 6 composite material was tested to have a notched Izod impact strength of 30.87 KJ/m.sup.2 at normal temperature.

Example 8-7

(394) Steps 1-3 are the same as those in Example 1-7.

(395) Step 4: Nylon 6 was mixed uniformly with the paper ball-like graphene microspheres obtained in Step (3) at a weight ratio of 100:0.2 in a mixer to obtain a nylon 6/graphene premix. Nylon 6 and the graphene microspheres were dried for 12 hrs under vacuum in a vacuum oven at 90° C. before premixing.

(396) Step 5: The premix obtained in Step (4) was melt-blended and extruded through a twin-screw extruder, where the melting temperature was 250° C., and the rotation speed of the screw was 200 rpm.

(397) A graphene-toughened nylon 6 composite material was obtained through the above steps. The compounded material was injection molded by an injection molding machine into a standard test strip for mechanical property test.

(398) The graphene-toughened nylon 6 composite material was tested to have a notched Izod impact strength of 31.98 KJ/m.sup.2 at normal temperature.

Example 8-8

(399) Steps 1-3 are the same as those in Example 1-8.

(400) Step 4: Nylon 6 was mixed uniformly with the paper ball-like graphene microspheres obtained in Step (3) at a weight ratio of 100:0.2 in a mixer to obtain a nylon 6/graphene premix. Nylon 6 and the graphene microspheres were dried for 12 hrs under vacuum in a vacuum oven at 90° C. before premixing.

(401) Step 5: The premix obtained in Step (4) was melt-blended and extruded through a twin-screw extruder, where the melting temperature was 250° C., and the rotation speed of the screw was 200 rpm.

(402) A graphene-toughened nylon 6 composite material was obtained through the above steps. The compounded material was injection molded by an injection molding machine into a standard test strip for mechanical property test. The graphene-toughened nylon 6 composite material was tested to have a notched Izod impact strength of 32.40 KJ/m.sup.2 at normal temperature.

Example 8-9

(403) Steps 1-3 are the same as those in Example 1-9.

(404) Step 4: Nylon 6 was mixed uniformly with the paper ball-like graphene microspheres obtained in Step (3) at a weight ratio of 100:0.2 in a mixer to obtain a nylon 6/graphene premix. Nylon 6 and the graphene microspheres were dried for 12 hrs under vacuum in a vacuum oven at 90° C. before premixing.

(405) Step 5: The premix obtained in Step (4) was melt-blended and extruded through a twin-screw extruder, where the melting temperature was 250° C., and the rotation speed of the screw was 200 rpm.

(406) A graphene-toughened nylon 6 composite material was obtained through the above steps. The compounded material was injection molded by an injection molding machine into a standard test strip for mechanical property test. The graphene-toughened nylon 6 composite material was tested to have a notched Izod impact strength of 29.67 KJ/m.sup.2 at normal temperature.

(407) Comparative Example 8-1: Nylon 6 material without graphene. The obtained graphene-toughened nylon 6 composite material was tested to have a notched Izod impact strength of 11.69 KJ/m.sup.2 at normal temperature.

(408) Comparative Example 8-2: Direct thermal reduction without chemical reduction

(409) (1) A single-layer graphene oxide dispersion prepared by Hummers method was dried by atomization drying at a temperature of 130° C. to obtain graphene oxide microspheres.

(410) (2) The reduced graphene oxide microspheres obtained in Step (1) were transferred to a tubular furnace, and heated to 3000° C. at a ramping rate of 5° C./min and maintained for 1 hr, while a mixed gas of hydrogen and argon was continuously introduced.

(411) (3) Nylon 6 was mixed uniformly with the paper ball-like graphene microspheres obtained in Step (2) at a weight ratio of 100:0.2 in a mixer to obtain a nylon 6/graphene premix. Nylon 6 and the graphene microspheres were dried for 12 hrs under vacuum in a vacuum oven at 90° C. before premixing.

(412) (4) The premix obtained in Step (3) was melt-blended and extruded through a twin-screw extruder, where the melting temperature was 250° C., and the rotation speed of the screw was 200 rpm.

(413) A graphene-toughened nylon 6 composite material was obtained through the above steps, where the graphene appears as a black loose powder, and is microscopically a hollow sphere having a diameter of 1-10 μm. The compounded material was injection molded by an injection molding machine into a standard test strip for mechanical property test. The graphene-toughened nylon 6 composite material was tested to have a notched Izod impact strength of 9.55 KJ/m.sup.2 at normal temperature.

(414) The composite material prepared in the present invention was injection molded by an injection molding machine at 230-260° C. according to the ASTM standard. After molding, the sample was allowed to stand for 88 hrs in a standard environment with a temperature of 23±2° C. and a humidity of 50±5%, and then tested in a test environment with a temperature of 23±2° C. and a humidity of 50±5%.

(415) When the paper ball-like graphene microspheres are compounded with nylon 6 matrix, a large specific surface area can enhance the effect of interfacial adhesion between graphene and the matrix, so that the material absorbs more energy when impacted, and a better toughening effect is exerted. However, when the specific surface area is too large, the graphene powder tends to agglomerate and suffers from deteriorated dispersion in the matrix, causing the formation of a stress concentration point to reduce the material performance. In addition, because the pleated structure of the paper ball-like graphene microsphere makes it very flexible, and the more compact the structure of the microsphere is, the less likely it is that the toughness of the material will be damaged due to the large deformation of the microsphere after receiving pressure. Therefore, in practical applications, the method disclosed in the present invention can be used to balance the specific surface area and compactness of the paper ball-like graphene microsphere to prepare a graphene toughener with the optimum effect for improving the impact strength of nylon 6 material. Moreover, graphene also gives the material higher comprehensive properties such as heat resistance, aging resistance and antistatic property, and improves the water absorption, thus widening the scope of application of nylon 6 materials.