A method for modifying reinforcing fibers, reinforcing fibers and composite materials

Abstract

This invention discloses a method for modifying reinforcing fibers, comprising the following steps: S1: cleaning the surface of the fiber; S2: using plasma to activate a coupling agent vaporized under vacuum conditions, causing the coupling agent to be vapor-deposited onto the fiber surface to obtain a fiber with a coupling agent layer; S3: applying a wetting agent containing a film-forming agent to the surface of the coupling agent layer of the fiber obtained in S2, and drying to obtain a finished reinforcing fiber with a resin-modified layer. This invention's method for modifying reinforcing fibers involves plasma vapor-depositing a coupling agent onto the fiber surface, forming a dense and uniform coupling agent layer on the fiber surface. This increases the reaction sites between the fiber surface and the subsequent wetting agent, promoting the full reaction of the film-forming agent and other wetting agent components on the fiber surface to form a tightly adhered resin-modified layer. This invention also discloses a reinforcing fiber and a composite material containing the reinforcing fiber.

Description

Technical Field

[0001] This invention relates to the field of fiber-reinforced composite materials technology, specifically to a method for modifying reinforcing fibers, reinforcing fibers, and composite materials. Background Technology

[0002] Commonly used fibers in fiber-reinforced resins are classified into two categories based on their chemical composition: organic fibers and inorganic fibers. Inorganic fibers include glass fibers, carbon fibers, asbestos fibers, and basalt fibers. In the production of inorganic fiber-reinforced composites, the inorganic fibers must first undergo surface modification.

[0003] Conventional fiber reinforcement modification methods, such as those disclosed in CN106220003A, involve mixing coupling agents, film-forming agents, emulsifiers, etc., to formulate a fiber sizing agent. An improved technical solution involves first cleaning or pre-treating the fibers with water or chemical detergents to remove organic contaminants from the fiber surface or increase the surface roughness, and then coating the fiber surface with a resin solution.

[0004] The shortcomings of existing fiber modification methods are as follows: First, water and chemical detergents are used for cleaning and rinsing, which generates a large amount of wastewater. Second, air exists in the micro-cracks on the fiber surface, which prevents the sizing agent from adhering densely and evenly to the fiber surface. The fiber sizing agent system has a complex composition. The coupling agent and the hydrophilic groups of other components work together on the fiber surface. Although the resin compatibility of the fiber is improved after impregnation treatment, the amount of coupling agent used in the sizing agent is relatively large in order to achieve the desired compatibility improvement effect by adhering to the fiber surface through impregnation. Summary of the Invention

[0005] One of the objectives of this invention is to overcome the deficiencies in the prior art and provide a method for modifying reinforcing fibers, thereby improving the adhesion strength of the modified layer on the fiber surface and the strength of the fiber itself by optimizing the modification steps.

[0006] To achieve the above-mentioned technical effects, the technical solution of the present invention is: a method for modifying reinforcing fibers, comprising the following steps:

[0007] S1: Clean the surface of the fibers;

[0008] S2: The coupling agent is vaporized under plasma-activated vacuum conditions and deposited in the plasma reaction chamber onto the fiber surface to obtain a fiber with a coupling agent layer.

[0009] S3: Apply a wetting agent containing a film-forming agent to the surface of the coupling agent layer of the fiber obtained in S2, and dry it to obtain a finished reinforced fiber with a resin-modified layer.

[0010] A preferred technical solution is that S1 includes plasma etching of fibers. Further, the plasma etching of the fibers in S1 uses oxygen and / or argon as the processing gas;

[0011] A preferred technical solution is that the coupling agent is a silane coupling agent; further, the coupling agent is one or a combination of several selected from γ-(methacryloyloxy)propyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-glycidylpropanetrimethoxysilane, vinyltri-(2-methoxyethoxy)silane, and vinyltriacetoxysilane.

[0012] The preferred technical solution is a discharge power of 280–320 W, a working air pressure of 25–35 Pa, and a fiber winding speed of 0.4–3 m / min; further, a discharge power of 290–310 W, a working air pressure of 28–32 Pa, and a fiber winding speed of 0.7–1.5 m / min. Further, the discharge treatment time is 15–30 min.

[0013] A preferred technical solution is that the vaporization temperature of the coupling agent in S2 is not greater than 100°C, and / or the temperature of the plasma reaction chamber in S2 is less than 65°C; further, the vaporization temperature of the coupling agent in S2 is 80–100°C. Further, the temperature of the plasma reaction chamber in S2 is 40–60°C.

[0014] A preferred technical solution is that the main components of the wetting agent further include at least one selected from antistatic agents and lubricants; furthermore, the wetting agent does not contain coupling agents.

[0015] A preferred technical solution is that the film-forming agent is selected from one or more of polyvinyl acetate, polyurethane, polyolefin, aliphatic polyether polyurethane, and epoxy resin.

[0016] The preferred technical solution is that the fiber in S1 is basalt fiber.

[0017] A second objective of this invention is to provide a reinforcing fiber, comprising a fiber body, wherein the surface of the fiber body comprises, from the inside out, a coupling agent chemical deposition modified layer and a resin modified layer.

[0018] A third objective of this invention is to provide a composite material comprising a substrate and reinforcing fibers, wherein the reinforcing fibers are obtained by the aforementioned method for modifying reinforcing fibers.

[0019] The advantages and beneficial effects of this invention are as follows:

[0020] The invention enhances the fiber modification method by depositing coupling agent plasma vapor phase onto the fiber surface, forming a dense and uniform coupling agent layer on the fiber surface, increasing the reaction sites between the fiber surface and subsequent wetting agent, and promoting the full reaction of film-forming agent and other wetting agent components on the fiber surface to form a tightly adhered resin modification layer.

[0021] The surface of the reinforcing fiber is coated with a coupling agent layer and a resin modification layer from the inside out, which improves the application of siloxane, enhances the mechanical strength of the fiber and its compatibility with the base resin, and thus improves the mechanical properties of the composite material.

[0022] The amount of coupling agent used in vapor deposition is significantly less than that used in fiber wetting agents, reduced to about one-tenth to one-fifth of the amount used in wetting methods. Detailed Implementation

[0023] The specific embodiments of the present invention will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0024] fiber

[0025] The fiber can be any type of fiber used in the production of composite materials, including organic fibers, inorganic fibers, and combinations of organic and inorganic fibers. Organic fibers include, but are not limited to, aramid fibers, and inorganic fibers include, but are not limited to, glass fibers, carbon fibers, boron fibers, basalt fibers, and metal fibers; preferably, the fiber is an inorganic fiber with a non-metallic surface, such as glass fibers, carbon fibers, boron fibers, or basalt fibers, and more preferably, an inorganic compound fiber such as basalt fiber.

[0026] Cleaning of fiber surface

[0027] Fiber surface cleaning refers to the removal of organic contaminants from the fiber surface. Compared with conventional cleaning solutions, plasma treatment of fibers can effectively remove organic contaminants and form micro- and nano-scale etching on the basalt fiber surface, increasing the fiber's specific surface area and improving its surface roughness. At the same time, it activates surface groups such as hydroxyl groups, providing a larger surface area for the adhesion of coupling agents and contact with the resin of the composite material substrate. It also eliminates the safety risks associated with etching fibers using hydrofluoric acid and other methods.

[0028] wetting agent

[0029] In addition to the main components of film-forming agents, antistatic agents, and lubricants, sizing agents may also include auxiliary components such as pH adjusters, wetting agents, plasticizers, crosslinking agents, bactericides, defoamers, and pigments. The composition of the sizing agent is specifically determined according to the type of fiber, the base resin, and the properties of the composite material.

[0030] The film-forming agent in the sizing agent is a known film-forming agent, such as unsaturated polyester resin, phenolic resin, epoxy resin, resorcinol resin, vinyl resin, amino resin, or a modified product of the resins listed above.

[0031] Process temperature of plasma chemical deposition

[0032] The plasma reaction chamber operates at a lower process temperature, which broadens the range of fiber types for chemically deposited coupling agents, making it suitable for organic fibers with low softening points. This method is gentler and more energy-efficient compared to other methods that use high temperatures (≥200°C).

[0033] If the vaporization temperature of the coupling agent is too high within the preferred temperature range, it will cause chemical reactions in the storage container before the coupling agent vaporizes or in the transmission pipeline after vaporization, leading to premature cross-linking, "explosive polymerization" and other reactions, resulting in coupling agent failure and pipeline blockage.

[0034] Furthermore, excessively high temperatures in the plasma reaction chamber are detrimental to controlling deposition uniformity. Even within the preferred temperature range, excessively high chamber temperatures, in the presence of plasma, can trigger a rapid chemical reaction in the coupling agent. Some of the coupling agent polymerizes within the chamber, forming tiny particles. These particles cannot effectively deposit with the active groups on the fiber surface through chemical bonding, ultimately leading to increased coupling agent consumption. However, the fiber treated by vapor deposition exhibits a decreased reinforcing effect on the composite material.

[0035] Composite materials

[0036] The main component of the composite material can be selected from known polymers such as nylon and polyolefins. Furthermore, the composite material also includes one or more of the known commonly used additives or functional additives such as antioxidants, antibacterial agents, plasticizers, and flame retardants.

[0037] The materials used in the examples are as follows:

[0038] Basalt fiber: 13μm in diameter;

[0039] The resin matrix of the composite material is PA6.

[0040] Coupling agent: Silane coupling agent KH-550;

[0041] Lubricant: PEG (polyethylene glycol)-MS, SG-10;

[0042] Film-forming agent: Epoxy resin E51;

[0043] Antistatic agent: hexadecyltrimethylammonium bromide (CTAB).

[0044] Example 1: The method for modifying reinforcing fibers includes the following steps:

[0045] S1: Oxygen or argon is used as the processing gas. Plasma treatment is used to clean the surface organic matter and simultaneously etch micro- and nano-scale grooves.

[0046] The plasma treatment process conditions are: discharge power 300W, working pressure 30Pa, fiber is wound in a roll-to-roll manner, winding speed 1m / min, and discharge treatment time 20min.

[0047] S2: The silane coupling agent KH-550, which is vaporized at 90°C in a vacuum environment, is sent into the plasma reaction chamber as the working gas. The coupling agent vaporized under vacuum conditions is activated by plasma, so that the coupling agent is deposited in the gas phase on the fiber surface in the plasma reaction chamber at 60°C. The other parameters are the same as those in S1, and a fiber with a coupling agent layer is obtained.

[0048] Ion bombardment generates heat, and the entire vapor deposition process is controlled within a temperature range of 40–60°C using a low-temperature circulating bath.

[0049] S3: Prepare wetting agent A according to the following proportions: epoxy resin E51 concentration of 6.0wt%, PEG-MS concentration of 0.5wt%, CTAB concentration of 0.1wt%, and the balance is water. Mix evenly to form an emulsion.

[0050] The sizing agent A is coated onto the surface of the coupling agent layer of the fiber obtained in S2, and then dried to obtain a finished reinforced fiber product with a resin-modified layer.

[0051] Production of basalt fiber reinforced composites: Continuous reinforcing fibers are fed into a twin-screw extruder, where they are cut and then blended with PA6, extruded, and granulated. The mass percentage of reinforcing fibers in the blend is 30%.

[0052] Example 2

[0053] Example 2 is based on Example 1, except that the winding speed of the plasma-treated basalt fiber in S1 is 5 m / min.

[0054] Example 3

[0055] Example 3 is based on Example 1, except that: in S1, the basalt fiber is cleaned with a surfactant sodium dodecyl sulfate (SDS) solution, then rinsed with pure water and dried.

[0056] Example 4

[0057] Example 4 is based on Example 3, except that: the basalt fiber, after being cleaned with surfactant solution and rinsed with pure water, is further etched with hydrofluoric acid at 25°C and 10% solute mass fraction for 1 hour, then rinsed with pure water and dried.

[0058] Example 5

[0059] Example 5 is based on Example 1, except that the temperature of the plasma reaction chamber in S2 is 80°C.

[0060] Comparative Example

[0061] Prepare wetting agent B according to the following proportions: epoxy resin E51 concentration of 6.0wt%, KH-550 concentration of 1.0wt%, PEG-MS concentration of 0.5wt%, CTAB concentration of 0.1wt%, and the balance being water. Mix thoroughly to form an emulsion.

[0062] Comparative Example 1

[0063] S1: Clean the organic contaminants on the surface of the basalt fiber using the same parameters and methods as in S1 of Example 1;

[0064] S2: Apply sizing agent B to basalt fiber and dry it to obtain modified basalt fiber.

[0065] The production process of the basalt fiber reinforced composite material in Comparative Example 1 is the same as that in Example 1.

[0066] I. Comparison of the mass of coupling agent consumed by two surface modification methods for basalt fibers

[0067] The table below compares the mass of coupling agent consumed in Example 1 with that consumed via the wetting agent in Comparative Example 1:

[0068]

[0069]

[0070] The table above shows that using vapor deposition coupling agents can effectively reduce the amount of coupling agent and wetting agent used in Example 1.

[0071] II. Composite Material Performance Testing in Examples and Comparative Cases

[0072] The tensile strength, elongation at break (ISO 527), and flexural strength (ISO 178) of the fiber-reinforced composite specimens in the test examples and comparative examples were determined by 20 parallel tests. The test results are as follows:

[0073] Sample Tensile strength (MPa) Bending strength (MPa) Elongation at break (%) Example 1 195 215 4 Example 2 170 188 8 Example 3 166 179 14 Example 4 180 200 6 Example 5 174 193 7 Comparative Example 1 170 180 11 PA6 blank sample 60 90 28

[0074] Example 1 and Comparative Example 1 were compared in terms of the method of applying the coupling agent to the fiber surface. The tensile strength, flexural strength, and elongation at break of the sample from Example 1 were superior to those of the sample from Comparative Example 1. The reason is:

[0075] In Example 1, plasma is used to activate the gas-phase coupling agent to form free radicals, which promotes the coupling agent to bond with activated hydroxyl groups and other groups on the fiber surface, forming a dense and uniform coupling agent layer. The coupling agent layer has more active sites to react with film-forming agents and other wetting agent components. The film-forming agent in the wetting agent reacts more effectively with the KH-550 amino groups on the surface of the coupling agent layer, improving fiber strength and surface coating adhesion strength, enhancing the compatibility between the fiber and nylon resin, and strengthening the uniform dispersion of the fiber in the nylon resin.

[0076] Examples 1, 2, 3, and 4 form a control group for the basalt fiber pretreatment method. The tensile strength of the fiber-reinforced composite material samples, arranged from highest to lowest, are Example 1, Example 4, Example 2, and Example 3. The trends in flexural strength and elongation at break are consistent with those in tensile strength. The reason is:

[0077] 1. The winding speed of Example 2 is significantly faster than that of Example 1, resulting in less cleaning, activation and etching of the basalt fiber surface, making the fiber surface roughness similar to that of the unetched fiber surface in Example 3; in addition, the less etching in Example 2 reduces the interface area on the fiber surface that can bond with the coupling agent, which in turn reduces the coating area on the fiber surface and affects the adhesion between the modified resin layer and the fiber surface.

[0078] 2. Compared with the basalt fiber surface cleaned with surfactant in Example 3, whether it is plasma etching in Example 1 or hydrofluoric acid etching in Example 4, the basalt fiber surface treated with coupling agent and wetting agent exhibits a surface with concave and convex textures corresponding to the etched structure. This enhances the increase in the interfacial area between the fiber and the resin, improves the interfacial bonding strength, and thus improves the mechanical properties of the composite material. In comparison, plasma pretreatment of basalt fiber can also activate the functional groups on the surface of basalt fiber, increasing the activity and probability of the reaction between the fiber surface functional groups and the coupling agent.

[0079] Example 1 and Example 5 form a comparison of plasma reaction chamber temperatures. Compared with Example 1, the mechanical properties of the composite material in Example 5 are significantly worse. The reason is that the coupling agent self-polymerizes in the plasma reaction chamber and fails to form a dense and uniform coupling agent layer on the surface of basalt fiber, which affects the continuity and uniformity of the sizing agent film formation, and thus affects the compatibility between basalt fiber and nylon resin.

[0080] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for modifying reinforcing fibers, characterized in that, Includes the following steps: S1: Clean the surface of the fibers; S2: Using a coupling agent vaporized under plasma-activated vacuum conditions, the coupling agent is deposited in gaseous phase on the fiber surface in the plasma reaction chamber to obtain a fiber with a coupling agent layer. S3: Apply a wetting agent containing a film-forming agent to the surface of the coupling agent layer of the fiber obtained in S2, and dry it to obtain a finished reinforced fiber with a resin-modified layer. The coupling agent is selected from one or more of γ-(methacryloyloxy)propyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-glycidylpropanetrimethoxysilane, vinyltri-(2-methoxyethoxy)silane, and vinyltriacetoxysilane; the vaporization temperature of the coupling agent in S2 is not greater than 100°C, and the temperature of the plasma reaction chamber in S2 is less than 65°C.

2. The method for modifying reinforcing fibers according to claim 1, characterized in that, The S1 includes fibers etched using plasma.

3. The method for modifying reinforcing fibers according to claim 1, characterized in that, The plasma treatment process conditions are: discharge power 280~320W, working gas pressure 25~35Pa, and fiber winding speed 0.4~3m / min.

4. The method for modifying reinforcing fibers according to claim 1, characterized in that, The main components of the wetting agent also include at least one selected from antistatic agents and lubricants.

5. The method for modifying reinforcing fibers according to claim 1, characterized in that, The fiber in S1 is basalt fiber.

6. A reinforcing fiber, comprising a fiber body, characterized in that, The reinforcing fiber is prepared by the modification method of the reinforcing fiber according to any one of claims 1 to 5, wherein the surface of the fiber body comprises, from the inside to the outside, a coupling agent chemical deposition modified layer and a resin modified layer.

7. A composite material comprising a matrix and reinforcing fibers, characterized in that, The reinforcing fiber is obtained by the modification method of the reinforcing fiber according to any one of claims 1 to 5.

Images