Sizing agent for recycling carbon fibers and composite material of sizing agent

Abstract

The invention relates to a sizing agent for recycling carbon fibers and a composite material of the sizing agent. The sizing agent comprises the following components in percentage by mass: 30-40% of a polyurethane emulsion, 5-10% of an epoxy resin emulsion, 1-2% of a wetting agent, 0.1-0.2% of a defoaming agent and the balance of deionized water. Wherein the epoxy resin emulsion is prepared from epoxy resin through a self-emulsifying method, and the solid content of the epoxy resin emulsion is 3-5%. When the epoxy resin emulsion in the sizing agent emulsion prepared by the invention is prepared, proper raw material ratio, reaction time and temperature are adopted, so that the sizing agent emulsion has good standing stability and mechanical stability and is convenient to store and transport; the prepared sizing agent can make recycled carbon fibers and a matrix PA prepared into a composite material, and the mechanical property, especially the tensile strength, is obviously improved. Therefore, the method is particularly suitable for the recycled carbon fibers, and resources can be reused and recycled.

Description

Technical Field

[0001] The invention relates to the technical field of sizing agents for carbon fibers, in particular to a sizing agent for recycled carbon fibers and a composite material thereof. Background Art

[0002] Carbon fiber (CF), a high-performance new fiber with a carbon content exceeding 90%, is typically produced from polyacrylonitrile precursor fibers through oxidation and carbonization. It boasts low density, high strength, high-temperature resistance, corrosion resistance, abrasion resistance, and high modulus, along with the flexibility and weavability of fibers. It is currently one of the primary reinforcement materials for advanced composite materials and is widely used in aerospace, sports equipment, and industrial applications. Composite materials such as carbon fiber-reinforced polyamide (PA, such as PA6 and PA66), carbon fiber-reinforced polycarbonate, carbon fiber-reinforced polypropylene, and carbon fiber-reinforced epoxy resin combine the high strength and modulus of carbon fiber with the toughness, chemical resistance, thermal stability, and corrosion resistance of polymers, and are therefore widely used.

[0003] Since the hydrophilicity of the carbon fiber surface itself is poor, the interfacial adhesion between it and the resin matrix is ​​not strong. Through the sizing agent process, the interfacial bonding force and overall performance of the composite material are improved. This is because: the sizing agent is evenly coated on the carbon fiber surface, which can change the fiber surface morphology, that is, the surface roughness changes, which helps to strengthen the adhesion anchoring effect between the fiber and the matrix; the sizing agent can form a functional organic polymer layer on the carbon fiber surface, thereby changing the originally inert surface of the carbon fiber, increasing the surface energy, and easily achieving full wetting of the matrix on its surface; the polarity and other active group content of the carbon fiber surface after sizing coating increases, and the polymer molecules in the sizing agent are easy to react with the matrix under temperature control, forming a chemical bond that makes the fiber and the matrix more firmly bonded. In order to improve the performance of recycled carbon fiber, in addition to improving the recycling carbon fiber process, the sizing process can also be improved.

[0004] Due to the extensive use of the above-mentioned composite materials, a large amount of waste carbon fiber composite materials are produced. If these materials are buried underground, they will not only have a serious impact on the environment, but also be a waste of resources. In recent years, the recycling and reuse of composite materials has become an important research topic. At present, there are mainly mechanical crushing recovery methods, thermochemical recovery methods, and solvent chemical recovery methods to recycle carbon fibers. However, the performance and monofilament length of the recycled carbon fibers are significantly reduced, which seriously limits their reuse. In the existing technology, there is a lack of sizing agents specifically for recycled carbon fibers to improve the performance of recycled carbon fibers in making composite materials. Summary of the Invention

[0005] The object of the present invention is to provide a sizing agent suitable for recycled carbon fibers, which can make the composite material have good and stable performance.

[0006] To achieve the purpose of the present invention, the technology of the solution is:

[0007] A sizing agent for recycled carbon fiber comprises the following components in percentage by mass: 30-40% polyurethane emulsion, 5-10% epoxy resin emulsion, 1-2% wetting agent, 0.1-0.2% defoaming agent, and the remainder is deionized water.

[0008] Furthermore, the polyurethane emulsion is prepared from a diol, an isocyanate, and a catalyst, wherein the diol comprises 110-120 parts by weight, the isocyanate comprises 30-40 parts by weight, and the catalyst comprises 0-0.01 parts by weight. Preferably, the diol comprises 110 parts by weight, the isocyanate comprises 40 parts by weight, and the catalyst comprises 0.01 parts by weight. The diol is selected from polyethylene glycol; the isocyanate is selected from isophorone diisocyanate, hexamethylene diisocyanate, and hydrogenated diphenylmethane diisocyanate; and the catalyst is selected from dibutyltin dilaurate.

[0009] Furthermore, the epoxy resin emulsion is prepared from epoxy resin via a self-emulsification method, with a solid content of 3-5%. The epoxy resin is selected from a novolac epoxy resin, a bisphenol A epoxy resin, or a bisphenol F epoxy resin. The self-emulsification method utilizes a cationic method. The cationic method utilizes diisopropanolamine or diethanolamine as the cation. The cationic method comprises: adding ethanol as a solvent to the epoxy resin and stirring and dissolving it at 55-65°C; dissolving the diisopropanolamine in ethanol and then adding it dropwise to the epoxy resin solution, with a molar ratio of epoxy resin to diisopropanolamine of 1:2-1:3; then raising the temperature to 78-83°C, reacting for 1.8-2.2 hours, and then cooling to 55-65°C and adjusting the pH; placing the product in a vacuum oven at 55-65°C to remove the ethanol solvent, thereby obtaining the modified epoxy resin; and adding the modified epoxy resin to deionized water to form an epoxy emulsion with a solid content of 3-5%. Preferably, in the cationic method, the molar ratio of epoxy resin to diisopropanolamine is 1:3, the reaction temperature is 80° C., and the reaction time is 2 h.

[0010] Furthermore, the wetting agent is selected from polyethylene glycol laurate and polyethylene glycol stearate; and the defoaming agent is selected from silicone water-based defoaming agent.

[0011] Furthermore, the sizing agent also includes 0-0.2% of a preservative; the preservative is selected from benzoic acids and isothiazolinones.

[0012] Correspondingly, the present invention also provides a composite material, wherein the composite material contains carbon fibers, and the carbon fibers are sizing-treated using the aforementioned sizing agent for recycled carbon fibers.

[0013] Compared with the prior art, the present invention has the following significant advantages:

[0014] 1. The epoxy resin emulsion in the sizing agent emulsion prepared by the present invention is prepared by using appropriate raw material ratios and reaction time and temperature, so it has good static stability and mechanical stability, and is easy to store and transport;

[0015] 2. The sizing agent prepared by the present invention can be used to make composite materials from recycled carbon fibers and the matrix PA, significantly improving mechanical properties, especially tensile strength. Therefore, it is particularly suitable for recycled carbon fibers, allowing for resource reuse and recycling. DETAILED DESCRIPTION

[0016] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0017] Example 1

[0018] Preparation of polyurethane emulsion:

[0019] S1. Preparation of waterborne polyurethane prepolymer: Add 110 g of polyethylene glycol into a flask, vacuum dehydrate at 120°C for 30 min, cool to 70°C, add 40 g of isophorone diisocyanate and 0.005 g of catalyst dibutyltin dilaurate, control the reaction temperature to 70°C, react for 3 h, cool to 50°C, and obtain a waterborne polyurethane prepolymer with hydroxyl end groups.

[0020] S2. Aqueous polyurethane emulsion: Pour 350 g of deionized water into the mixture prepared in step S1, and perform high shear dispersion at 1200 rpm to obtain an aqueous polyurethane emulsion.

[0021] Epoxy emulsion preparation:

[0022] First, weigh 40g of epoxy resin MF-4101H and place it in a three-necked flask. Add ethanol as the solvent and stir at 60°C to dissolve it. Weigh 81.5g of diisopropanolamine and dissolve it in ethanol. Slowly add it dropwise to the three-necked flask containing the epoxy resin and complete the addition within 30 minutes (the molar ratio of epoxy resin to diisopropanolamine is 1:3). Then raise the temperature to 80°C and react for 2 hours, and appropriately increase the speed of the magnetic stirrer. After the reaction is completed, cool to 60°C and add glacial acetic acid to the three-necked flask to adjust the pH to neutral. After the addition is complete, react for 30 minutes. Place the product in a vacuum oven at 60°C to remove the solvent ethanol to obtain the modified cyclic resin MF-4101H.

[0023] The modified cyclic resin MF-4101H was added to deionized water to prepare an epoxy emulsion with a solid content of 3%.

[0024] Sizing agent configuration:

[0025] Take 150g of the above-mentioned aqueous polyurethane emulsion and add it into a stirring tank. Under continuous stirring, add 25g of epoxy emulsion, 5g of wetting agent polyethylene glycol laurate, 0.05g of silicone water-based defoamer BYK-022, and 319.95g of deionized water in sequence. After stirring evenly, discharge the material to obtain a sizing agent.

[0026] Example 2

[0027] The preparation method of polyurethane emulsion is the same as that in Example 1.

[0028] Epoxy emulsion preparation:

[0029] First, weigh 40g of epoxy resin MF-4101H into a three-necked flask, add ethanol as the solvent, and stir at 60°C to dissolve it. Weigh 54.3g of diisopropanolamine, dissolve it in ethanol, and slowly add it dropwise to the three-necked flask containing the epoxy resin. The addition should be completed within 30 minutes (the molar ratio of epoxy resin to diisopropanolamine is 1:2). Then, raise the temperature to 80°C and react for 2 hours, while increasing the speed of the magnetic stirrer appropriately. After the reaction is completed, cool to 60°C and add glacial acetic acid to the three-necked flask to adjust the pH to neutral. After the addition is complete, react for 30 minutes. Place the product in a vacuum oven at 60°C to remove the solvent ethanol, and the modified cyclic resin MF-4101H is obtained.

[0030] The modified cyclic resin MF-4101H was added to deionized water to prepare an epoxy emulsion with a solid content of 3%.

[0031] Sizing agent configuration:

[0032] Take 150g of the above-mentioned aqueous polyurethane emulsion and add it into a stirring tank. Under continuous stirring, add 25g of epoxy emulsion, 5g of wetting agent polyethylene glycol laurate, 0.05g of silicone water-based defoamer BYK-022, and 319.95g of deionized water in sequence. After stirring evenly, discharge the material to obtain a sizing agent.

[0033] Example 3

[0034] The preparation method of polyurethane emulsion is the same as that in Example 1.

[0035] Epoxy emulsion preparation:

[0036] First, weigh 40g of epoxy resin MF-4101H and place it in a three-necked flask. Add ethanol as the solvent and stir at 60°C to dissolve it. Weigh 27.2g of diisopropanolamine and dissolve it in ethanol. Slowly add it dropwise to the three-necked flask containing the epoxy resin and complete the addition within 30 minutes (the molar ratio of epoxy resin to diisopropanolamine is 1:1). Then raise the temperature to 80°C and react for 2 hours, and appropriately increase the speed of the magnetic stirrer. After the reaction is completed, cool to 60°C and add glacial acetic acid to the three-necked flask to adjust the pH to neutral. After the addition is complete, react for 30 minutes. Place the product in a vacuum oven at 60°C to remove the solvent ethanol to obtain the modified cyclic resin MF-4101H.

[0037] The modified cyclic resin MF-4101H was added to deionized water to prepare an epoxy emulsion with a solid content of 3%.

[0038] Sizing agent configuration:

[0039] Take 150g of the above-mentioned aqueous polyurethane emulsion and add it into a stirring tank. Under continuous stirring, add 25g of epoxy emulsion, 5g of wetting agent polyethylene glycol laurate, 0.05g of silicone water-based defoamer BYK-022, and 319.95g of deionized water in sequence. After stirring evenly, discharge the material to obtain a sizing agent.

[0040] Example 4

[0041] The preparation method of polyurethane emulsion is the same as that in Example 1.

[0042] The preparation method of epoxy emulsion is the same as that in Example 1.

[0043] Sizing agent configuration:

[0044] Take 150g of the above-mentioned aqueous polyurethane emulsion and add it into a stirring tank. Under continuous stirring, add 50g of epoxy emulsion, 5g of wetting agent polyethylene glycol laurate, 0.05g of silicone water-based defoamer BYK-022, and 294.95g of deionized water in sequence. After stirring evenly, discharge the material to obtain a sizing agent.

[0045] Example 5

[0046] The preparation method of polyurethane emulsion is the same as that in Example 1.

[0047] The preparation method of epoxy emulsion is the same as that in Example 1.

[0048] Sizing agent configuration:

[0049] Take 200g of the above-mentioned aqueous polyurethane emulsion and add it into a stirring tank. Under continuous stirring, add 25g of epoxy emulsion, 5g of wetting agent polyethylene glycol laurate, 0.05g of silicone water-based defoamer BYK-022, and 269.95g of deionized water in sequence. After stirring evenly, discharge the material to obtain a sizing agent.

[0050] Example 6

[0051] The preparation method of polyurethane emulsion is the same as that in Example 1.

[0052] The preparation method of epoxy emulsion is the same as that in Example 1.

[0053] Sizing agent configuration:

[0054] Take 150g of the above-mentioned aqueous polyurethane emulsion and add it into a stirring tank. Under continuous stirring, add 5g of wetting agent polyethylene glycol laurate, 0.05g of silicone water-based defoamer BYK-022, and 344.95g of deionized water in sequence. After stirring evenly, discharge the material to obtain a sizing agent.

[0055] Example 7 Sizing agent stability test

[0056] 1. Room temperature static stability test

[0057] The sizing agents of Examples 1 to 5 were allowed to stand at room temperature for a period of time to observe whether the sizing agent emulsions produced stratification, precipitation, demulsification, and the like.

[0058] 2. Mechanical stability test

[0059] The sizing agent emulsions of Examples 1 to 5 were placed in centrifuge tubes, and the centrifuge tubes were then placed symmetrically in a centrifuge under the following test conditions: a rotation speed of 3000 r / min and a centrifugation time of 30 min. Observe whether precipitation or stratification occurs in the centrifuge tubes containing the sizing agent emulsions after centrifugation.

[0060] The results of the above two tests are shown in Table 1:

[0061] Table 1

[0062]

[0063] As can be seen from Table 1, Examples 1 and 2 exhibit better static and mechanical stability than 3. This is due to the different ratios of epoxy resin to diisopropanolamine in the epoxy emulsion preparation. When the molar ratio of epoxy resin MF-4101H to diisopropanolamine is 1:1, the low amount of diisopropanolamine results in a low ring-opening rate of the epoxy groups, resulting in poor hydrophilicity. During the addition of water to form the sizing emulsion, the unreacted epoxy resin aggregates to form larger emulsion particles. Consequently, the sizing emulsion prepared with the 1:1 ratio exhibits a milky white appearance. As the amount of diisopropanolamine increases, the resulting sizing emulsion becomes clearer and more transparent.

[0064] After standing for 7 days, the three sizing agents were relatively stable, without stratification or sedimentation. After standing for 30 days, only the sizing agent emulsion of Example 3 had precipitation at the bottom, because the sizing agent emulsion particles were large, and gravity and Brownian motion caused them to break and settle. The sizing agent emulsions of Examples 1 and 2 had good static stability, because as the amount of diisopropanolamine increased, the epoxy group ring opening rate of the epoxy resin MF-4101H increased, the hydrophilicity of the resin after modification was excellent, the emulsion particle size formed by self-emulsification was small, and the stability was good.

[0065] After centrifugation, only the sizing agent of Example 3 precipitated, indicating poor mechanical stability. The sizing agent emulsions of Examples 1 and 2 exhibited excellent mechanical stability. After centrifugation, the sizing agent emulsions remained clear and transparent, with no precipitation at the bottom. Combined with the static stability results, it is clear that as the amount of diisopropanolamine increases, the more hydrophilic groups introduced into the MF-4101H epoxy resin chains, the better the hydrophilicity, resulting in excellent mechanical stability of the sizing agent emulsions.

[0066] However, Examples 4 and 5 show that after the aqueous polyurethane emulsion is mixed in, the increase in the amount of the aqueous polyurethane emulsion has little effect on the stability of the sizing agent.

[0067] Before use, the sizing agent emulsion needs to be stored for a period of time. During storage, Brownian motion and gravity can cause demulsification, sedimentation, and stratification of the emulsion particles. Therefore, the sizing agent emulsion must have good static stability. Furthermore, collisions are inevitable during transportation. Epoxy resin emulsion particles with poor mechanical stability may demulsify and aggregate due to mechanical collisions, leading to emulsion sedimentation. Therefore, the stability of the sizing agent is a key factor in determining its performance.

[0068] Example 8 Composite material performance test

[0069] Purchase recycled unsized carbon fibers and soak them in the sizing solutions of Examples 1, 2, 4, 5, and 6 to allow the sizing agent to fully infiltrate. After 20 minutes, place them in a constant-temperature oven at 80°C and dry them for 2 hours. Purchase unsized carbon fibers and soak them in the sizing solution of Example 1 to allow the sizing agent to fully infiltrate. After 20 minutes, place them in a constant-temperature oven at 80°C and dry them for 2 hours. All of the above-mentioned sized carbon fibers were mixed with a PA6 matrix at a content of 30wt% to prepare a composite material using a hot pressing process (260°C, 5MPa, 30min). The prepared composite sheets were cut into strips of equal specifications (12mm×80mm×2mm) for mechanical property testing. Five samples were prepared for each composite material group, and the values ​​were averaged. The results are shown in Table 2.

[0070] Table 2

[0071]

[0072] As shown in Table 2, the mechanical properties of the composites made from recycled carbon fibers and the PA matrix decrease slightly. However, the addition of epoxy emulsion to the sizing agent significantly improves these properties, particularly in tensile strength, as seen in Examples 1, 2, 4, and 5. Furthermore, the addition of a large amount of epoxy emulsion further enhances the tensile strength of the composite.

[0073] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A sizing agent for recycled carbon fiber, characterized in that: The invention comprises the following components in percentage by mass: 30-40% of polyurethane emulsion, 5-10% of epoxy resin emulsion, 1-2% of wetting agent, 0.1-0.2% of defoaming agent and the rest of deionized water.

2. The sizing agent for recycled carbon fiber according to claim 1, characterized in that: The polyurethane emulsion is prepared from diol, isocyanate and catalyst, wherein the diol is 110-120 parts by weight, the isocyanate is 30-40 parts by weight and the catalyst is 0-0.01 parts by weight.

3. The sizing agent for recycled carbon fiber according to claim 2, characterized in that: The diol is selected from polyethylene glycol; the isocyanate is selected from isophorone diisocyanate, hexamethylene diisocyanate, and hydrogenated diphenylmethane diisocyanate; and the catalyst is selected from dibutyltin dilaurate.

4. The sizing agent for recycled carbon fiber according to claim 1, wherein: The epoxy resin emulsion is prepared from epoxy resin through a self-emulsification method, and has a solid content of 3-5%.

5. The sizing agent for recycled carbon fiber according to claim 4, characterized in that: The epoxy resin is selected from phenolic epoxy resin, bisphenol A epoxy resin and bisphenol F epoxy resin.

6. The sizing agent for recycled carbon fiber according to claim 4, characterized in that: The self-emulsification method is a cationic method.

7. The sizing agent for recycled carbon fiber according to claim 6, characterized in that: The cationic method uses diisopropanolamine or diethanolamine as the cation.

8. The sizing agent for recycled carbon fiber according to claim 7, characterized in that: The cationic method includes: adding ethanol as a solvent to epoxy resin, stirring and dissolving at 55-65°C; dissolving diisopropanolamine in ethanol and dropwise adding it to the epoxy resin solution, with the molar ratio of epoxy resin to diisopropanolamine being 1:2-1:3; then raising the temperature to 78-83°C, reacting for 1.8-2.2 hours, and after the reaction is completed, cooling to 55-65°C and adjusting the pH; placing the product in a vacuum oven at 55-65°C to remove the solvent ethanol, thereby obtaining the modified epoxy resin; and adding the modified epoxy resin to deionized water to prepare an epoxy emulsion with a solid content of 3-5%.

9. The sizing agent for recycled carbon fiber according to claim 1, characterized in that: The wetting agent is selected from polyethylene glycol laurate and polyethylene glycol stearate; the defoaming agent is selected from silicone water-based defoaming agent; the sizing agent also includes 0-0.2% preservative; the preservative is selected from benzoic acid and isothiazolinone.

10. A composite material comprising carbon fibers, characterized in that: The carbon fiber is sizing treated using the sizing agent for recycled carbon fiber according to any one of claims 1 to 9.

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