Surface modification method of recycled carbon fibers for cement-based material

Abstract

The invention provides a surface modification method of recycled carbon fibers for a cement-based material. The preparation method comprises the following steps: 1, mixing deionized water, chitosan hydrochloride and sodium dodecyl sulfate to obtain a modified solution; 2, weighing the recycled carbon fibers, and soaking the carbon fibers in a modified solution; step 3, washing the soaked recycled carbon fibers with deionized water until the recycled carbon fibers are washed clean; and 4, putting the washed recycled carbon fibers into a drying oven, and drying to constant weight. According to the modification method disclosed by the invention, the surface roughness of the recycled carbon fibers can be improved, the contact angle with water is greatly reduced by 44.7%, the hydrophilicity is improved, the performance of active groups on molecular chains is improved, the surface energy is increased, and the bonding between the carbon fibers and a matrix is firmer, so that the breaking strength and the tensile strength of a test piece are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of civil engineering materials, and in particular relates to a surface modification method of recycled carbon fibers for cement-based materials. Background Art

[0002] Concrete has the characteristics of abundant raw materials, low price, simple production process and good durability, and has long become the main civil engineering material in modern times. However, ordinary concrete has high brittleness and low toughness, poor crack resistance, large shrinkage deformation and other problems, which limit its further application in engineering. Recycled carbon fiber comes from waste silk generated in the production process of carbon fiber prepreg and carbon fiber extracted from carbon fiber composite material waste. It retains the advantages of original carbon fiber such as high temperature resistance, acid and alkali resistance, and good electrical and thermal conductivity. Therefore, adding recycled carbon fiber to cement-based materials can not only effectively prevent and inhibit the shrinkage and cracks of cement concrete, but also give concrete excellent electrical conductivity. However, in the actual application process, there are problems such as the smooth surface of recycled carbon fiber, poor hydrophilicity and few active groups, the fiber is not easy to disperse in cement concrete, and the fiber is not firmly adhered to the matrix.

[0003] At present, carbon fiber surface modification methods can be mainly divided into three categories: coating modification, oxidation modification and polymer modification. However, these modifications all have shortcomings. For example, the adhesion between the coating and the fiber of the coated carbon fiber is low, and solvents need to be used in the manufacturing process, which has low preparation efficiency and is difficult to produce continuously. Polymerization modification mainly improves the surface activity of carbon fiber, but lacks the benefits of changing the physical morphology and increasing the specific surface area. Oxidation modification uses strong oxidants to oxidize and etch the fiber surface, which leads to a decrease in fiber strength after treatment. Therefore, developing a new carbon fiber surface modification method is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0004] In view of this, the present invention aims to overcome the defects in the prior art and proposes a surface modification method for recycled carbon fibers for cement-based materials.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] In a first aspect, the present invention provides a method for surface modification of recycled carbon fibers for cement-based materials, comprising the following steps:

[0007] Step 1, mixing deionized water, chitosan hydrochloride and sodium dodecyl sulfate to obtain a modified solution;

[0008] Step 2, weighing the recycled carbon fiber and soaking it in the modified solution;

[0009] Step 3, rinsing the soaked recycled carbon fiber with deionized water until it is clean;

[0010] Step 4: Place the rinsed recycled carbon fiber into an oven and dry to constant weight.

[0011] In some embodiments of the present invention, the mass fraction of the modified solution in step 1 is 0.1%-0.15%.

[0012] In some embodiments of the present invention, the mass ratio of chitosan hydrochloride to sodium dodecyl sulfate in step 1 is (15-25): 1. The modifier is placed in deionized water and stirred thoroughly until there is no obvious lumps.

[0013] In some embodiments of the present invention, in step 1, the mass fraction of the modified solution is 0.1%, and the mass ratio of the two modifying agents, chitosan hydrochloride and sodium dodecyl sulfate, is 20:1.

[0014] In some embodiments of the present invention, the deacetylation degree of chitosan hydrochloride in step 1 is 70%-90%; the sodium dodecyl sulfate is analytically pure and has a molecular formula of C 12 H 25 SO 3 Nah.

[0015] In some embodiments of the present invention, in the step 1, the deacetylation degree of the chitosan hydrochloride is 90%.

[0016] In some embodiments of the present invention, the solid-liquid ratio of the recovered carbon fiber to the modified solution in step 2 is (0.008-0.012) g: 1 mL.

[0017] In some embodiments of the present invention, the surface of the recycled carbon fiber in step 2 has no sizing agent. If the surface of the fiber is covered with a sizing agent, the sizing agent on the surface of the fiber is removed by soaking in an acetone solution, and then the pretreated fiber is placed in an oven and dried to a constant weight. Alternatively, the sizing agent on the surface of the recycled carbon fiber is removed by other existing methods.

[0018] In some embodiments of the present invention, the carbon fiber recovered in step 2 is chopped fiber, the diameter of the recovered carbon fiber is 7 μm±1 μm, and the single fiber tensile strength is ≥2500 MPa.

[0019] In some embodiments of the present invention, in step 4, the oven temperature is 50-60° C., and the product is dried to a constant weight.

[0020] In a second aspect, the present invention also provides a carbon fiber obtained by the above-mentioned modification method.

[0021] In a third aspect, the present invention also provides the use of the above-mentioned carbon fiber in the preparation of cement-based materials.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) The raw material used in the present invention is recycled carbon fiber, which is obtained by high-temperature treatment and has a grooved surface. This irregular surface can provide more adsorption sites for physical adsorption, thereby enhancing the modification effect.

[0024] (2) The modification method of the present invention can improve the surface roughness of recycled carbon fiber and significantly reduce the contact angle with water by 44.7%, thereby improving the hydrophilicity, increasing the performance of active groups on the molecular chain, increasing the surface energy, and making the bonding between the carbon fiber and the matrix stronger, thereby improving the flexural strength and tensile strength of the specimen.

[0025] (3) The modification method of the present invention has the characteristics of simple modification technology operation and easy implementation and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The SEM images of the recycled carbon fibers before and after modification; (a) is a schematic diagram of the recycled carbon fibers before modification at a magnification of 2000 times; (b) is a schematic diagram of the recycled carbon fibers after modification at a magnification of 2000 times;

[0027] Figure 2 The test diagram of the contact angle of the recycled carbon fiber before and after modification; (a) is the contact angle of the recycled carbon fiber before modification; (b) is the contact angle of the recycled carbon fiber after modification;

[0028] Figure 3 The graph shows the tensile strength of the single fiber of recycled carbon fiber before and after modification; (a) is the tensile strength of the single fiber of recycled carbon fiber before modification; (b) is the tensile strength of the single fiber of recycled carbon fiber after modification. DETAILED DESCRIPTION

[0029] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0030] Unless defined otherwise herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0031] Where values ​​are described herein as a range, it should be understood that such disclosure includes disclosure of all possible sub-ranges within that range, as well as specific values ​​falling within that range, regardless of whether a specific value or a specific sub-range is explicitly stated.

[0032] In this document, "multiple" and the like, unless otherwise specified, refer to a number greater than 2 or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0033] In this document, the terms “preferred” and “more preferred” are only used to describe implementation methods or examples with better effects, and it should be understood that they do not constitute limitations on the scope of protection of the present invention.

[0034] In this document, the words "further" and the like are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of the present invention.

[0035] In this article, the term "and / or" is a description of the association relationship of objects, indicating that three relationships may exist. For example, A and / or B means: A or B, or A and B.

[0036] As used herein, the term "about" means + / - 10%, preferably + / - 5%, more preferably + / - 1% of the specified value.

[0037] The terms “include,” “including,” “have,” “contain,” etc. used in this article are open-ended terms, meaning including but not limited to.

[0038] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention pertains. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention.

[0039] The present invention will be described in detail below with reference to the embodiments.

[0040] Embodiment 1:

[0041] Prepare 500ml of chitosan hydrochloride-sodium dodecyl sulfate mixed solution, the solution mass fraction is 0.1%, and the mass ratio of the two modifiers chitosan hydrochloride and sodium dodecyl sulfate is 20:1; weigh 5g of recycled carbon fiber (without sizing agent on the surface), and soak it in the modified solution for 30min; rinse the soaked fiber repeatedly with deionized water until it is rinsed clean; put the rinsed recycled carbon fiber into an oven and dry it to constant weight at an oven temperature of 60°C. Among them, the chitosan hydrochloride used has a deacetylation degree of 90%, and the sodium dodecyl sulfate is analytically pure.

[0042] The modified effects of the tested embodiment 1 on the recycled carbon fiber are as follows:

[0043] Scanning electron microscope:

[0044] Figure 1The SEM images of the recycled carbon fibers before and after modification show that after modification with a mixed solution of chitosan hydrochloride and sodium dodecyl sulfate, some solid substances adhered to the fiber surface, increasing the roughness of the fiber surface. Chitosan hydrochloride, as a cationic polysaccharide polymer, can combine with anionic surfactants in the solution to form a polyelectrolyte / surfactant type complex. These substances increase the specific surface area of ​​the fiber, making the fiber and the matrix bond more firmly.

[0045] Fiber wettability test:

[0046] Figure 2 This is a test diagram of the contact angle of a single fiber before and after the modification of recycled carbon fiber. The surface wetting effect of liquid on solid depends on the interface contact angle. The smaller the contact angle, the better the wettability. The contact angle test results of the recycled carbon fiber before and after modification showed that the contact angle of the untreated recycled carbon fiber was 103.43°, and the contact angle of the recycled carbon fiber modified with the chitosan hydrochloride-sodium dodecyl sulfate composite solution was 57.16°. Compared with the unmodified fiber, the contact angle of the modified fiber decreased by 44.73%, indicating that the wettability of the recycled carbon fiber after modification has been greatly improved. This is because a large amount of -OH in the chitosan hydrochloride-sodium dodecyl sulfate modification solution combines with the surface of the recycled carbon fiber, which improves the wettability of the recycled carbon fiber in water.

[0047] Fiber performance test:

[0048] Test plan: The diameter of recycled carbon fiber is in accordance with GB / T 29762 "Determination of diameter and cross-sectional area of ​​carbon fiber". The strength of recycled carbon fiber monofilament is tested using a fiber strength and elongation tester (accuracy is level 1; the test force value should be within the range of 20% to 80% of the instrument range; the measurement resolution is 0.001N), and the test steps are carried out in accordance with Appendix B of the national standard "Chopped basalt fiber for cement concrete and mortar".

[0049] Table 1 shows the properties of recycled carbon fiber monofilaments before and after modification. There is no significant change in the diameter, strength and strength of the monofilaments before and after the modification of the recycled carbon fiber, indicating that the modification method does not damage the fiber and can improve the surface properties of the fiber without sacrificing mechanical properties. Figure 3 .

[0050] Table 1 Properties of recycled carbon fiber monofilament

[0051]

[0052] Effect of recycled carbon fiber modification on the performance of cement-based materials:

[0053] Test plan: Table 2 shows the test mix ratio of cement mortar. The recycled carbon fibers before and after modification were added to cement mortar to prepare flexural strength and tensile strength specimens to test the effect of recycled carbon fibers modified by chitosan hydrochloride-sodium dodecyl sulfate solution on the performance of cement mortar.

[0054] Table 2 Cement mortar test mix ratio

[0055]

[0056] Table 3 shows the mechanical properties of recycled carbon fiber cement mortar before and after modification. The modified recycled carbon fiber has a greater improvement effect on the mechanical properties of cement mortar specimens than before modification, with the flexural strength increased by 33.26% and the tensile strength increased by 14.49%.

[0057] Table 3 Mechanical properties of recycled carbon fiber cement mortar

[0058]

[0059] Embodiment 2:

[0060] Prepare 500ml of chitosan hydrochloride-sodium dodecyl sulfate mixed solution, the mass fraction of the solution is 0.15%, and the mass ratio of the two modifiers chitosan hydrochloride and sodium dodecyl sulfate is 15:1; weigh 4g of recycled carbon fiber (without sizing agent on the surface), and soak it in the modified solution for 30min; rinse the soaked fiber repeatedly with deionized water until it is rinsed clean; put the rinsed recycled carbon fiber into an oven and dry it to constant weight at an oven temperature of 50°C. Among them, the chitosan hydrochloride used has a deacetylation degree of 70%, and the purity of sodium dodecyl sulfate is analytical grade.

[0061] Embodiment 3:

[0062] Prepare 500ml of chitosan hydrochloride-sodium dodecyl sulfate mixed solution, the mass fraction of the solution is 0.15%, and the mass ratio of the two modifiers chitosan hydrochloride and sodium dodecyl sulfate is 25:1; weigh 7g of recycled carbon fiber (without sizing agent on the surface), and soak it in the modified solution for 30min; rinse the soaked fiber repeatedly with deionized water until it is rinsed clean; put the rinsed recycled carbon fiber into an oven and dry it to constant weight at an oven temperature of 60°C. Among them, the chitosan hydrochloride used has a deacetylation degree of 80%, and the purity of sodium dodecyl sulfate is analytical grade.

[0063] Comparative Example 1:

[0064] Prepare 500 ml of chitosan hydrochloride-sodium dodecyl sulfate mixed solution with a solution mass fraction of 0.1% and a mass ratio of two modifiers, chitosan hydrochloride and sodium dodecyl sulfate, of 10:1; weigh 5 g of recycled carbon fiber (without sizing agent on the surface) and soak it in the modified solution for 30 minutes; repeatedly rinse the soaked fiber with deionized water until it is rinsed clean; put the rinsed recycled carbon fiber into an oven and dry it to constant weight at a temperature of 50-60°C.

[0065] The modified effects of the tested comparative example 1 on the recycled carbon fiber are as follows:

[0066] Fiber wettability:

[0067] Table 4 shows the contact angles of the recycled carbon fibers before and after modification. The contact angle of the untreated recycled carbon fibers is 103.43°. The contact angle of the recycled carbon fibers modified with a composite solution having a mass ratio of chitosan hydrochloride to sodium dodecyl sulfate of 10:1 is 65.60°. Compared with the unmodified fibers, the contact angle of the modified fibers decreases by 36.57%, indicating that the wettability of the modified recycled carbon fibers is improved to a certain extent. However, the contact angle is greater than that of Example 1, and the modification effect is better than that of the solution having a mass ratio of the two modifiers of 20:1.

[0068] Table 4 Contact angle of recycled carbon fiber before and after modification

[0069]

[0070] Effect of recycled carbon fiber modification on the performance of cement-based materials:

[0071] Table 5 shows the mechanical properties of recycled carbon fiber cement mortar before and after modification. Compared with the unmodified recycled carbon fiber, the modified cement mortar specimens have a certain improvement effect on mechanical properties, wherein the flexural strength is increased by 10.66% and the tensile strength is increased by 8.94%. However, the improvement is not as great as that in Example 1.

[0072] Table 5 Mechanical properties of recycled carbon fiber cement mortar

[0073]

[0074] Comparative Example 2:

[0075] Prepare 500 ml of chitosan hydrochloride-sodium dodecyl sulfate mixed solution with a solution mass fraction of 0.1% and a mass ratio of two modifiers, chitosan hydrochloride and sodium dodecyl sulfate, of 30:1; weigh 5 g of recycled carbon fiber (without sizing agent on the surface) and soak it in the modified solution for 30 minutes; repeatedly rinse the soaked fiber with deionized water until it is rinsed clean; put the rinsed recycled carbon fiber into an oven and dry it to constant weight at a temperature of 50-60°C.

[0076] The modified effects of the tested comparative example 2 on the recycled carbon fiber are as follows:

[0077] Fiber wettability test:

[0078] Table 6 shows the contact angles of the recycled carbon fibers before and after modification. The contact angle of the untreated recycled carbon fibers is 103.43°. The contact angle of the recycled carbon fibers modified with a composite solution having a mass ratio of chitosan hydrochloride to sodium dodecyl sulfate of 30:1 is 70.17°. Compared with the unmodified fibers, the contact angle of the modified fibers decreases by 32.16%, indicating that the wettability of the modified recycled carbon fibers is improved to a certain extent. However, the contact angle is greater than that of Example 1, and the modification effect is not as good as that of the solution having a mass ratio of the two modifiers of 20:1.

[0079] Table 6 Contact angle of recycled carbon fiber before and after modification

[0080]

[0081] Effect of recycled carbon fiber modification on the performance of cement-based materials:

[0082] Table 7 shows the mechanical properties of recycled carbon fiber cement mortar before and after modification. When the recycled carbon fiber modified by the modified solution with two modifiers in a mass ratio of 30:1 was added to the cement mortar, the flexural strength of the specimen increased by 12.39%, while the tensile strength decreased by 12.24%. This shows that the modified recycled carbon fiber has a negative effect on the mechanical properties of cement mortar compared with the fiber before modification.

[0083] Table 7 Mechanical properties of recycled carbon fiber cement mortar

[0084]

[0085] Comparative Example 3:

[0086] Prepare 500 ml of chitosan hydrochloride solution with a mass fraction of 0.1%; weigh 5 g of recycled carbon fiber (without sizing agent on the surface) and soak it in the modified solution for 30 minutes; repeatedly rinse the soaked fiber with deionized water until it is clean; put the rinsed recycled carbon fiber into an oven and dry it to constant weight at a temperature of 50-60°C.

[0087] The modified effects of the tested comparative example 3 on the recycled carbon fiber are as follows:

[0088] Fiber wettability:

[0089] Table 8 shows the contact angles of the recycled carbon fibers before and after modification. The contact angle of the untreated recycled carbon fibers is 103.43°, and the contact angle of the recycled carbon fibers modified with chitosan hydrochloride solution is 80.16°. Compared with the unmodified fibers, the contact angle of the modified fibers decreases by 22.50%, indicating that the wettability of the modified recycled carbon fibers is improved to a certain extent. However, the contact angle is greater than that of Example 1, and the modification effect is better than that of the solution with a mass ratio of the two modifiers of 20:1.

[0090] Table 8 Contact angle of recycled carbon fiber before and after modification

[0091]

[0092] Effect of recycled carbon fiber modification on the performance of cement-based materials:

[0093] Table 9 shows the mechanical properties of recycled carbon fiber cement mortar before and after modification. When the recycled carbon fiber modified by chitosan hydrochloride solution is added to the cement mortar, the flexural strength of the specimen is increased by 11.66%, while the tensile strength is reduced by 7.40%. This shows that the modified recycled carbon fiber has a negative effect on the mechanical properties of cement mortar compared with the fiber before modification.

[0094] Table 9 Mechanical properties of recycled carbon fiber cement mortar

[0095]

[0096] Comparative Example 4:

[0097] Prepare 500 ml of sodium dodecyl sulfate solution with a mass fraction of 0.1%; weigh 5 g of recycled carbon fiber (without sizing agent on the surface) and soak it in the modified solution for 30 minutes; rinse the soaked fiber repeatedly with deionized water until it is clean; put the rinsed recycled carbon fiber into an oven and dry it to constant weight at an oven temperature of 50-60°C.

[0098] The modified effects of the tested comparative example 4 on the recycled carbon fiber are as follows:

[0099] Fiber wettability:

[0100] Table 10 shows the contact angles of the recycled carbon fibers before and after modification. The contact angle of the untreated recycled carbon fibers is 103.43°, and the contact angle of the recycled carbon fibers modified with sodium dodecyl sulfate solution is 74.16°. Compared with the unmodified fibers, the contact angle of the modified fibers is reduced by 28.30%, indicating that the wettability of the modified recycled carbon fibers is improved to a certain extent. However, the contact angle is greater than that of Example 1, and the modification effect is not as good as that of the solution with a mass ratio of the two modifiers of 20:1.

[0101] Table 10 Contact angle of recycled carbon fiber before and after modification

[0102]

[0103] Effect of recycled carbon fiber modification on the performance of cement-based materials:

[0104] Table 11 shows the mechanical properties of recycled carbon fiber cement mortar before and after modification. When the recycled carbon fiber modified by sodium dodecyl sulfate solution is added to the cement mortar, the flexural strength of the specimen is reduced by 4.81%, while the tensile strength is increased by 7.30%. This shows that the modified recycled carbon fiber has a negative effect on the mechanical properties of cement mortar compared with the fiber before modification.

[0105] Table 11 Mechanical properties of recycled carbon fiber cement mortar

[0106]

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for surface modification of recycled carbon fiber for cement-based materials, characterized in that: The steps include: Step 1, mixing deionized water, chitosan hydrochloride and sodium dodecyl sulfate to obtain a modified solution; Step 2, weighing the recycled carbon fiber and soaking it in the modified solution; Step 3, rinsing the soaked recycled carbon fiber with deionized water until it is clean; Step 4: Place the rinsed recycled carbon fiber into an oven and dry to constant weight.

2. The surface modification method of recycled carbon fiber for cement-based materials according to claim 1, characterized in that: The mass fraction of the modified solution in step 1 is 0.1%-0.15%.

3. The surface modification method of recycled carbon fiber for cement-based materials according to claim 1, characterized in that: In the step 1, the mass ratio of chitosan hydrochloride to sodium dodecyl sulfate is (15-25):

1.

4. The surface modification method of recycled carbon fiber for cement-based materials according to claim 1, characterized in that: The mass fraction of the modified solution in step 1 is 0.1%, and the mass ratio of chitosan hydrochloride to sodium dodecyl sulfate is 20:

1.

5. The surface modification method of recycled carbon fiber for cement-based materials according to claim 1, characterized in that: The deacetylation degree of chitosan hydrochloride in step 1 is 70%-90%; the purity of sodium dodecyl sulfate is analytical grade.

6. The surface modification method of recycled carbon fiber for cement-based materials according to claim 1, characterized in that: The solid-liquid ratio of the recovered carbon fiber to the modified solution in the step 2 is (0.008-0.012) g: 1 mL.

7. The surface modification method of recycled carbon fiber for cement-based materials according to claim 1, characterized in that: The carbon fibers recovered in step 2 are chopped fibers, the diameter of the recovered carbon fibers is 7 μm±1 μm, and the single fiber tensile strength is ≥2500 MPa.

8. The surface modification method of recycled carbon fiber for cement-based materials according to claim 1, characterized in that: In the step 4, the oven temperature is 50-60° C., and the mixture is dried to a constant weight.

9. A carbon fiber obtained by the modification method according to any one of claims 1 to 8.

10. Use of the carbon fiber according to claim 9 in preparing cement-based materials.

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