A carboxymethylcellulose encapsulated and adsorbed silica aramid fiber reinforced polymer matrix composite material and its method of preparation and use

Abstract

The application belongs to the field of composite materials, and particularly relates to a kind of aramid fiber reinforced polymer matrix composite material with carboxymethyl cellulose encapsulating and adsorbing silicon dioxide and a preparation method and use thereof. 2， Thus the surface modification of aramid fiber is realized; wherein the carboxymethyl cellulose is tightly coated on the surface of aramid fiber through hydrogen bond interaction between the polar groups on the surface of fiber, and the SiO2 adsorbed on the surface of CMC further improves the roughness of the surface of aramid fiber. The modification method of carboxymethyl cellulose encapsulating and adsorbing silicon dioxide in the application can effectively improve the interfacial bonding between aramid fiber and polymer matrix, so that the prepared aramid fiber composite material exhibits excellent mechanical properties, and has good application prospect in the fields of aerospace, transportation tools, energy equipment and the like.

Description

Technical Field

[0001] This invention belongs to the field of composite materials, specifically relating to an aramid fiber reinforced polymer-based composite material encapsulated with carboxymethyl cellulose and adsorbing silica, its preparation method, and its uses. Background Technology

[0002] Aramid fiber is a novel high-performance fiber material with excellent fatigue resistance, good high-temperature resistance, high modulus, corrosion resistance, high strength, low hysteresis loss, and low shrinkage, and is often used to prepare high-performance engineering composite materials. However, aramid molecular chains are highly regular, and the fiber surface has few active groups, making it difficult to react chemically with other atoms or groups. Furthermore, the fiber's high crystallinity and smooth surface result in weak interfacial bonding, affecting its adhesion to the matrix. Therefore, to fully utilize the excellent properties of aramid fiber and improve the interfacial bonding between the fiber and the matrix, surface modification of the aramid fiber is necessary.

[0003] Ethylene propylene diene monomer (EPDM) rubber has a low relative density and possesses properties such as ozone resistance, weather resistance, heat resistance, and chemical stability, and has been widely used in insulation materials. However, due to its low polarity, EPDM exhibits poor interfacial bonding strength with fibers, making it difficult to fully utilize the reinforcing effect of the fibers. Sa et al. (ACS Applied Materials & Interfaces. 2014; 6(23): 21730-21738) utilized the self-polymerization properties of polydopamine (PDA) to construct a PDA coating on the fiber surface and grafted KH560 to obtain epoxy resin functionalized modified fibers, thereby significantly improving interfacial bonding. To further improve the environmental friendliness, cost-effectiveness, and efficiency of the modification process, researchers have explored other methods. For example, by complexing Fe3+ ions with tannic acid, a polyphenol-metal ion composite coating was constructed on the surface of aramid fibers (The Journal of Adhesion. 2021; 97(4): 346-360). This method not only significantly improves the interfacial bonding of modified rubber composites but also demonstrates a simple, economical, and scalable surface modification approach, highlighting its potential for industrial applications. However, such surface modification methods require multi-step processing, and these chemical treatments may damage the fiber surface, causing greater defects and thus reducing the fiber's mechanical properties. Therefore, developing convenient and green sustainable surface modification methods for aramid fibers while improving the mechanical properties of aramid fiber-reinforced polymer matrix composites has become a research hotspot. Summary of the Invention

[0004] To address the problems of existing technologies, this invention provides an aramid fiber-reinforced polymer-based composite material encapsulated with carboxymethyl cellulose and adsorbing silica, as well as its preparation method and applications.

[0005] A surface-modified aramid fiber reinforced polymer matrix composite material is composed of surface-modified aramid fibers and a polymer matrix; the weight ratio of the surface-modified aramid fibers to the polymer matrix is ​​(1-30):100; the surface-modified aramid fibers are prepared by dispersing aramid fibers without sizing agent in a carboxymethyl cellulose aqueous solution, and then impregnating them in a silica solution, so that the carboxymethyl cellulose and silica coat the aramid fibers; the mass ratio of the carboxymethyl cellulose to silica is (1-10):(1-10).

[0006] Preferably, the polymer matrix is ​​made from raw materials comprising the following parts by weight:

[0007] 80-150 parts of polyolefin rubber

[0008] Activator 0.1-20 parts

[0009] 0.1-20 parts of softener

[0010] Vulcanizing agent 0.1-20 parts,

[0011] Reinforcing agent 0.1-20 parts.

[0012] Preferably, the polyolefin rubber is selected from at least one of ethylene propylene diene monomer (EPDM) rubber, polyethylene rubber, and polybutene rubber;

[0013] And / or, the activator is selected from at least one of zinc oxide, magnesium oxide, and lead oxide;

[0014] And / or, the softener is selected from at least one of phthalates, phosphates, and stearic acid;

[0015] And / or, the vulcanizing agent is selected from at least one of benzophenone peroxide, dicumyl peroxide, and sulfur;

[0016] And / or, the reinforcing agent is selected from silica.

[0017] Preferably, the mass ratio of carboxymethyl cellulose to silicon dioxide is 1:1-1.5.

[0018] Preferably, the mass fraction of the carboxymethyl cellulose aqueous solution is 0.1-2%, and the mass fraction of the silica solution is 0.1-2%.

[0019] Preferably, the method for preparing the surface-modified aramid fiber includes the following steps:

[0020] Step 1: Impregnate unsizing aramid fibers or desizing aramid fibers with a carboxymethyl cellulose aqueous solution, then dry to obtain aramid fibers encapsulated with carboxymethyl cellulose.

[0021] Step 2: Immerse the aramid fibers encapsulated with carboxymethyl cellulose in a silica ethanol solution and dry them to obtain the final product.

[0022] Preferably, in step 1, the stirring time is 1-10 minutes; the drying temperature is 80-150°C, and the drying time is 1-5 hours.

[0023] And / or, in step 2, the stirring time is 1-10 min; the drying temperature is 80-150℃, and the drying time is 1-5 h.

[0024] Preferably, the desizing step includes: immersing aramid fibers in a volatile organic solvent and then sonicating them to obtain desizing aramid fibers.

[0025] Preferably, the volatile organic solvent is selected from acetone; the ultrasound time is 1-5 hours.

[0026] The present invention also provides a method for preparing the above-mentioned surface-modified aramid fiber reinforced polymer matrix composite material, comprising the following steps:

[0027] a. React polyolefin rubber with activator, softener, vulcanizing agent, reinforcing agent, and surface-modified aramid fiber, adjust the roller gap, and pass through a thin stream to obtain a compound rubber;

[0028] b. The compounded rubber is obtained by vulcanization.

[0029] Preferably, in step a, the roller gap is adjusted to 0.1-1mm; the thin pass is performed 1-10 times;

[0030] Alternatively, in step b, the vulcanization temperature is 100-200℃ and the vulcanization time is 10-60 min.

[0031] The present invention also provides the application of the above-mentioned surface-modified aramid fiber reinforced polymer matrix composites in the fields of aerospace, electronic information, sporting goods, automotive industry, and transportation.

[0032] This invention involves coating the surface of aramid fibers with SiO2 nanoparticles and carboxymethyl cellulose (CMC) to modify the surface of the aramid fibers, resulting in aramid fibers encapsulated with CMC and adsorbing silica. The surface-modified aramid fibers exhibit significantly increased roughness and improved interfacial bonding performance. The resulting surface-modified aramid fiber-reinforced polymer matrix composite material effectively enhances the interfacial bonding ability and mechanical properties between aramid fibers and EPDM rubber, and possesses excellent tensile properties, making it widely applicable in aerospace, defense, and transportation industries.

[0033] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions, or alterations can be made without departing from the basic technical concept of the present invention.

[0034] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0035] Figure 1 A surface modification method for encapsulating carboxymethyl cellulose with adsorbed silica aramid fibers.

[0036] Figure 2 The surface morphology of aramid fibers before and after surface modification is shown. (a) The microstructure of RAF samples was observed using scanning electron microscopy; (b) The microstructure of AF / CMC samples was observed using scanning electron microscopy; (c) The microstructure of AF / Si samples was observed using scanning electron microscopy; (d) The microstructure of AF / CMC / Si samples was observed using scanning electron microscopy.

[0037] Figure 3 The images show atomic force microscopy (AFM) images of aramid fibers before and after surface modification. (a) Microstructure scanning observation of RAF samples using AFM; (b) Microstructure scanning observation of AF / CMC samples using AFM; (c) Microstructure scanning observation of AF / Si samples using AFM; (d) Microstructure scanning observation of AF / CMC / Si samples using AFM.

[0038] Figure 4 The thermogravimetric curves of aramid fibers before and after modification in a nitrogen atmosphere are shown.

[0039] Figure 5 Elemental analysis of aramid fibers before and after modification.

[0040] Figure 6 The C1s fitting curves are for aramid fibers before and after modification.

[0041] Figure 7 The curves are the Si2p fitting curves of aramid fibers before and after modification.

[0042] Figure 8 The H-pull-out experiment of aramid fibers before and after modification.

[0043] Figure 9The images show the fiber morphology of aramid fibers after H-pull-out tests before and after modification. (a) SEM image of RAF sample; (b) SEM image of AF / CMC sample; (c) SEM image of AF / Si sample; (d) SEM image of AF / CMC / Si sample.

[0044] Figure 10 The tensile properties of modified aramid fiber reinforced polymer matrix composites. Detailed Implementation

[0045] In the following examples and experimental cases, reagents and raw materials not specifically described are all commercially available products.

[0046] Example 1: Preparation of aramid fibers encapsulated with carboxymethyl cellulose and adsorbed with silica

[0047] Step 1: Weigh 15g of aramid fiber (Inner Mongolia Synthetic Chemical Research Institute, F1414) and put it into a 500ml beaker. Add 500ml of acetone, sonicate for 3 hours, and then take it out. Wash it repeatedly in deionized water to obtain desizing aramid fiber, which is denoted as RAF.

[0048] Step 2: Disperse 15g of RAF in 500mL of a prepared 0.75wt% carboxymethyl cellulose aqueous solution (CMC / H2O) (carboxymethyl cellulose was purchased from Aladdin, molecular weight 25000). After the RAF has fully swollen, stir for 3min, filter, place on a tray, and treat in an oven at 110℃ for 3h to remove excess solvent, thus obtaining aramid fiber (AF / CMC) after CMC encapsulation treatment.

[0049] Step 3: Impregnate the CMC-encapsulated aramid fibers from the previous step into a prepared 500 mL solution of 1 wt% silica-ethanol (SiO2 / HtOH). After the AF / CMC has fully swelled, stir for 3 minutes, filter, remove, place on a tray, and treat in an oven at 110℃ for 3 hours to remove excess solvent, obtaining CMC-encapsulated and SiO2-adsorbed aramid fibers AF / CMC / Si, as shown in the schematic diagram. Figure 1 As shown.

[0050] Example 2: Preparation of aramid fiber-reinforced polymer matrix composite material encapsulated with carboxymethyl cellulose and adsorbed with silica

[0051] 100g of ethylene propylene diene monomer (EPDM) (Jilin Petrochemical, grade 4050) was placed on a two-roll mill for mixing. After the rubber compound wrapped around the rollers, 5g of zinc oxide, 0.5g of stearic acid, 1.5g of DCP, 10g of SiO2, 10g of modified aramid fiber (AF / CMC / Si) and 0.5g of sulfur were added in sequence. After mixing evenly, the roller gap was adjusted to 0.4mm, and the compound was prepared by two rollers. The compound was cut into 20*10cm sheets, laid in a 2mm thick mold, and vulcanized at 160℃ for 30min to obtain EPDM / AF / CMC / Si.

[0052] The comparative example provides the control samples used in the experiment:

[0053] Comparative Example 1: Desizing treated aramid fibers (RAF)

[0054] Prepared according to step 1 of Example 1, the product is obtained.

[0055] Comparative Example 2: Aramid fibers encapsulated with carboxymethyl cellulose (AF / CMC)

[0056] Prepared according to the method of Example 1, except that it does not adsorb SiO2.

[0057] Comparative Example 3: Aramid fibers (AF / SiO2) adsorbing silica

[0058] Prepared according to the method of Example 1, except that carboxymethyl cellulose is not encapsulated.

[0059] Comparative Example 4: Aramid fiber reinforced polymer matrix composite (EPDM / RAF) without carboxymethyl cellulose encapsulation and without adsorbed silica.

[0060] Prepared according to the method of Example 2, the difference being that the prepared compound is vulcanized with aramid fibers that have not been encapsulated with carboxymethyl cellulose and have not adsorbed silica.

[0061] Comparative Example 5: Aramid fiber reinforced polymer matrix composite (EPDM / AF / Si) without carboxymethyl cellulose encapsulation and adsorbed silica.

[0062] Prepared according to the method of Example 2, the difference being that the prepared compound is vulcanized with aramid fibers that have not been encapsulated with carboxymethyl cellulose and adsorbed silica.

[0063] Comparative Example 6: Carboxymethyl cellulose encapsulated aramid fiber reinforced polymer matrix composite (EPDM / AF / CMC) without adsorbed silica

[0064] Prepared according to the method of Example 2, the difference being that the prepared compound is vulcanized with carboxymethyl cellulose-encapsulated aramid fibers that have not adsorbed silica.

[0065] The technical solution of the present invention will be further explained through experiments below.

[0066] Experimental Example 1: Microstructure of the interface of aramid fibers encapsulated with carboxymethyl cellulose and adsorbed with silica

[0067] The AF / CMC / Si, AF / Si, AF / CMC and RAF samples used in this experiment were prepared according to the methods of Example 1 and Comparative Examples 1-3.

[0068] I. Experimental Methods

[0069] Scanning electron microscopy (SEM): The surface structure morphology of aramid fibers was observed using a field emission scanning electron microscope (Apreo S, Thermo Scientific, USA). Operating voltage: 15 kV.

[0070] Atomic force microscopy (AFM): The surface morphology of the fiber was measured using an atomic force microscope (Smart SPM, AIST-NT, USA) in tapping test mode, with a test size of 2μm × 2μm.

[0071] II. Experimental Results

[0072] like Figure 2 As shown, the untreated RAF surface is very smooth, containing only a small amount of attached particles, which are likely residual sizing agent or contaminants on the fiber surface. A significant difference is observed in the significantly increased surface roughness of AF / CMC. Because CMC is rich in polar hydroxyl and carboxyl functional groups, it possesses excellent film-forming properties. Furthermore, it can form strong hydrogen bonds with the active carbonyl groups on the aramid fiber (AF) surface. Therefore, after impregnation with CMC aqueous solution, a coating with numerous wrinkles was successfully constructed on the AF surface. CMC has high strength and modulus, effectively forming a transition between rubber and fiber. SiO2 nanoparticles contain abundant hydroxyl groups and can form hydrogen bonds with some active groups on the AF surface, thus exhibiting a certain degree of adsorption. A small amount of SiO2 can be seen adsorbed on the AF surface. However, due to the large number of benzene rings and amide bonds in the molecular chain segments of aramid fibers, the molecular chain segments are planar, rigid, and straight. The fiber surface is smooth and highly inert, limiting the direct adsorption of SiO2, and the interfacial bonding ability is also poor. Aramid fibers encapsulated with CMC have a higher specific surface area and a higher adsorption capacity for SiO2. Furthermore, CMC is more polar and contains a large number of polar functional groups that "reinforce" the deposition of SiO2. Therefore, after CMC encapsulation, a large number of tightly adsorbed SiO2 are observed on the surface of AF / CMC / Si. These strongly adsorbed SiO2 further improve the surface roughness of the fiber.

[0073] As can be seen using an atomic force microscope (AFM), such as Figure 3 As shown, the surface of RAF is relatively smooth and flat with extremely low roughness. After CMC packaging modification, the surface roughness of AF / CMC is significantly improved, and the surface structure is accompanied by a large number of protrusions and wrinkles, which are tightly attached to the AF surface. In contrast, the surface of AF / Si only has a small amount of SiO2 adsorption, and the roughness is improved compared to AF, but the modification effect is limited. Figure 3 As shown in (d), a distinctly different phenomenon occurred on the surface (AF / CMC / Si) after CMC encapsulation and SiO2 adsorption. SiO2 nanoparticles were coated onto the AF surface by CMC, further increasing the surface roughness. These results indicate that the aramid fibers encapsulated with carboxymethyl cellulose and adsorbing SiO2 exhibited a significant increase in surface roughness, providing a structural basis for improved interfacial bonding performance.

[0074] Experimental Example 2: Microstructure of the interface between aramid fibers encapsulated with carboxymethyl cellulose and adsorbed silica

[0075] The AF / CMC / Si, AF / Si, AF / CMC and RAF samples used in this experiment were prepared according to the methods of Example 1 and Comparative Examples 1-3.

[0076] I. Experimental Methods

[0077] Thermogravimetric analysis (TGA): Temperature range of 50-800℃, heating rate of 10℃ / min, conducted under nitrogen atmosphere.

[0078] II. Experimental Results

[0079] like Figure 4 As shown, this further confirms the adsorption of substances on the surface. CMC, due to its large number of polar groups, exhibits strong water absorption, leading to significant thermal degradation, specifically the breakage and pyrolysis of CMC molecular chains at 268℃. Comparing AF / CMC and CMC, thermal degradation of CMC was observed around 268℃, demonstrating successful introduction of CMC onto the AF surface. Meanwhile, the AF / Si curve consistently outperformed AF, achieving a residual weight of 38.4%, higher than RAF, with a residual weight increase of 0.8%, indicating successful adsorption of the difficult-to-degrade SiO2 on the surface. Furthermore, SiO2 possesses excellent antioxidant capabilities, and the dense silicon-containing coating constructed on the fiber surface effectively blocks the oxidation of aramid fibers. AF / CMC / Si further exhibited the highest thermal residual weight, reaching 38.9%, significantly higher than AF / CMC, with an increase of 1.5%, also higher than the increased residual weight of AF / Si (Table 1). The results show that after CMC and SiO2 are successfully introduced into the surface of aramid fibers, the resulting AF / CMC / Si exhibits excellent thermal stability and high-temperature resistance.

[0080] Table 1. Thermogravimetric parameters of modified aramid fibers in nitrogen atmosphere

[0081]

[0082] Experimental Example 3: Chemical Structure of Aramid Fiber Interface Encapsulated with Carboxymethyl Cellulose and Adsorbed Silica

[0083] The AF / CMC / Si, AF / Si, AF / CMC and RAF samples used in this experiment were prepared according to the methods of Example 1 and Comparative Examples 1-3.

[0084] I. Experimental Methods

[0085] X-ray photoelectron spectroscopy (XPS): X-ray photoelectron spectroscopy is used to detect elemental changes and molecular structure on the fiber surface. The test uses a 1keV Al Kα X-ray source with an emission current of 0.6μA.

[0086] II. Experimental Results

[0087] XPS spectra and elemental contents, such as Figure 5 As shown in Table 2, the C1s peak is at 284.8 eV, the N1s peak at 400.5 eV, and the O1s peak at 532.1 eV, which are the main components of the fiber. After CMC encapsulation modification, the O content of AF / CMC increased while the N content decreased, because CMC mainly consists of long-chain C and O structures. The O / C ratio increased from 0.206 in RAF to 0.223. After direct adsorption of SiO2, the O element ratio of AF / Si also increased significantly to 18.36%, while 1.71% Si appeared, which is twice the Si element content of RAF, indicating that the nano SiO2 is only electrostatically adsorbed on the fiber surface, and the adsorbed SiO2 content is limited. However, after CMC encapsulation treatment, the silicon content of the AF / CMC / Si surface with adsorbed SiO2 reached 10.71%, the O ratio increased to 30.2%, and the O / C ratio reached 0.557, which is significantly higher than that of AF / Si and AF / CMC. The results show that the increased silicon and oxygen content and the increased O / C ratio on the AF / CMC / Si surface improve the surface chemical activity and interfacial compatibility of aramid fibers. At the same time, it can be seen that CMC can promote the adsorption effect of SiO2 on the AF surface.

[0088] Table 2 Element content of modified aramid fibers before and after modification

[0089]

[0090] C1s peak fitting and percentage of C functional groups of different fibers, as shown in the figure. Figure 6As shown, the partial spectra of C and Si elements in the XPS spectra can effectively reflect the chemical structure of the fiber surface. The C1s peak can be fitted with three sub-peaks: amorphous C–C bonds (284.8 eV), C–O bonds (286.3 eV), CN bonds, and O–C=O bonds (288.7 eV). Compared with RAF, the C–N ratio on the fiber surface of AF / CMC and AF / CMC / Si is reduced, while the C=O ratio is doubled compared with 3.36% in RAF, indicating that CMC is successfully adsorbed on the AF surface.

[0091] The elemental spectra of Si2p are more effective in reflecting the bonding between SiO2 and the fiber surface. The elemental spectra of AF / Si and AF / CMC / Si are as follows: Figure 7 As shown in the figure, 102.1 eV, 102.5 eV, and 103.0 eV are attributed to Si(OH)3, SiO(OH)2, and SiO2(OH), respectively. The structure of Si(OH)3 originates from the hydrogen bonds between the O atoms on the fiber surface and CMC and the OH groups of nano-SiO2. SiO(OH)2 and SiO2(OH) are formed by the reaction of OH groups with OH groups on the AF surface (Si-OH+C-OH) → Si-O-C+H2O), while SiO2(OH) is formed by the self-condensation reaction of SiO2 (2Si-OH → Si-O-Si+H2O). Compared with AF / Si, the proportion of Si(OH)3 in AF / CMC / Si reaches 67.11%, which is significantly higher than that in AF / Si. The results indicate that the interfacial layer of CMC on the fiber surface effectively enhances the hydrogen bonding between nano-SiO2 and CMC, thereby increasing the adsorption amount of SiO2 on aramid fibers and thus enhancing the interfacial bonding force of aramid fibers.

[0092] Experimental Example 4: Interfacial bonding properties of rubber composite materials prepared by encapsulating aramid fibers with adsorbed silica using carboxymethyl cellulose

[0093] The AF / CMC / Si, AF / Si, AF / CMC and RAF samples used in this experiment were prepared according to the methods of Example 1 and Comparative Examples 1-3.

[0094] I. Experimental Methods

[0095] H-Pull-Out Test: Referring to GB / T 2942-2009, the prepared aramid fiber / rubber H-pull-out samples were tested for H-pull-out force on a universal tensile testing machine at a tensile rate of 100 mm / min. The preparation method for the pull-out sample was as follows: the compound rubber was cut into strips 11 mm wide and 220 mm long according to the H-pull-out mold. The cut strips were placed in the mold cavity, and the coated aramid fiber was placed between the mold grooves, embedded between the upper and lower mold rubber strips. The vulcanization conditions were 160℃ × 30 min, and the H-pull-out test samples were then obtained.

[0096] II. Experimental Results

[0097] Figure 8 The H-pull-out experiments of modified aramid fibers showed that the H-pull-out force was significantly improved after introducing CMC and SiO2 onto the AF and surface. The H-pull-out force of AF / CMC was 26.0% higher than that of RAF. This is because CMC also contains unsaturated active double bonds, which can participate in the vulcanization reaction of EPDM. At the same time, the abundant hydroxyl groups of CMC can form a large number of hydrogen bonds on the AF surface, thus forming a bridge between EPDM and AF and improving the interfacial bonding between them. After direct adsorption of nano-SiO2, the H-pull-out force was further improved, reaching 10.4 N. This is because the matrix itself contains a large amount of SiO2, which, together with the nanoparticles at the interface, improves the compatibility at the interface and thus improves the interfacial bonding ability. Compared with the two modification methods of CMC and SiO2, AF / CMC / Si showed the highest pull-out force, reaching 14.14 N, which is twice that of RAF. This is because AF encapsulated with CMC has a higher specific surface area and a higher adsorption capacity for SiO2. Furthermore, CMC has stronger polarity and contains a large number of polar functional groups that "reinforce" the deposition of SiO2. Therefore, after CMC encapsulation, a large amount of tightly adsorbed SiO2 was observed on the surface of AF / CMC / Si. This strongly adsorbed SiO2 further improved the surface roughness of the fiber, which created excellent conditions for the bonding between the fiber and the resin. Moreover, the improvement in AF / CMC / Si was greater than the sum of AF / CMC and AF / Si. The results indicate that CMC acts as an effective bridge between AF and Si, which enables CMC and SiO2 to have a synergistic effect on improving the interfacial properties of aramid fibers.

[0098] Experimental Example 5: Interfacial Bonding Analysis of Rubber Composite Materials Prepared by Encapsulating Carboxymethyl Cellulose with Adsorbed Silica in Aramid Fibers

[0099] The EPDM / AF / CMC / Si, EPDM / AF / Si, EPDM / AF / CMC, and EPDM / RAF samples used in this experiment were prepared according to the methods of Example 2 and Comparative Examples 4-6.

[0100] I. Experimental Methods

[0101] Scanning electron microscopy (SEM): The surface structure morphology of aramid fibers was observed using a field emission scanning electron microscope (Apreo S, Thermo Scientific, USA). Operating voltage: 15 kV.

[0102] II. Experimental Results

[0103] Figure 9The image shows the fiber morphology of AF after H-pull-out testing following CMC encapsulation and SiO2 adsorption treatment. Due to the large number of benzene rings and amide bonds in the molecular chain segments of aramid fibers, the molecular chain segments are planar, rigid, and straight, resulting in a smooth fiber surface. This high surface inertness leads to poor interfacial bonding between AF and EPDM, thus maintaining a relatively smooth interfacial structure after the RAF pull-out test. Residual rubber was observed on the surfaces of AF / CMC and AF / Si. However, there is a difference: the residual rubber on the surface of AF / CMC appears as filaments and blocks, while the rubber remaining on the surface of AF / Si is scattered in small pieces, which corresponds to the modified fiber surface microstructure. Compared to the former, the surface of AF / CMC / Si has more residual rubber matrix, with a large number of blocky rubber tightly adhering to the AF surface, and localized fiber damage, indicating that the fiber bore a significant load during the damage process. On the one hand, the active carboxyl groups in CMC are distributed within and at the ends of the molecular chain, undergoing simultaneous repolymerization of the head-to-tail structure and crosslinking between molecular chains during vulcanization. This allows them to participate in the crosslinking of the matrix rubber, simultaneously improving the bonding performance of the aramid fiber / rubber interface through modulus transition and chemical bonding. Meanwhile, the SiO2 adsorbed on the CMC surface further increases the surface roughness, forming a stronger mechanical interlocking structure, thus more effectively transferring the load from the matrix to the fiber. The results show that after encapsulation and adsorption of CMC and SiO2, AF / CMC / Si exhibits excellent interfacial bonding performance with EPDM.

[0104] Experimental Example 6: Tensile Properties of Rubber Composite Materials Prepared by Encapsulating Carboxymethyl Cellulose-Adsorbed Silica Aramid Fibers

[0105] The EPDM / AF / CMC / Si, EPDM / AF / Si, EPDM / AF / CMC, and EPDM / RAF samples used in this experiment were prepared according to the methods of Example 2 and Comparative Examples 4-6.

[0106] I. Experimental Methods

[0107] Tensile test: According to standard GB / T 528–1998, the test is conducted on a mechanical testing machine at a speed of 200 mm / min. The preparation method of the tensile test specimen is as follows: the prepared rubber compound is cut into 20*10 cm sheets, stacked in a 2 mm thick mold, and vulcanized at 160℃ for 30 min to obtain the rubber composite material. Tensile test specimens are then cut on a stamping machine to the dimensions of type 3 of the GB / T 528–1998 standard.

[0108] II. Experimental Results

[0109] like Figure 10As shown in Table 3, the improved interface structure effectively enhanced the mechanical properties of the rubber composites. Tensile strength: EPDM / AF / CMC / Si > EPDM / AF / CMC > EPDM / AF / Si >

[0110] EPDM / RAF corresponds to the surface analysis of aramid fibers. The strength of EPDM / AF / CMC reached 7.16 MPa, which is 27.8% higher than that of EPDM / RAF, while the elongation at break did not change significantly. On the one hand, CMC is often used as a high-strength film or coating. Its high strength and modulus form a transition layer between the fiber and the rubber, avoiding stress concentration caused by the large difference in modulus. Furthermore, aramid fibers and CMC can form hydrogen bonds, allowing CMC to be tightly adsorbed on the surface of the aramid fibers and complete the load transfer. The wrinkles that accompany film formation also provide a large number of cavities for SiO2 adsorption and reinforce the accumulation of SiO2 on the surface of the aramid fibers. Under the dual action of nanoparticles and CMC, the mechanical interlocking effect between the nanoparticles and the rubber is improved. In addition, the carboxyl active functional groups in CMC can also participate in the vulcanization process, thereby further improving the interfacial bonding ability and mechanical properties of the rubber composite material under the action of chemical bonds.

[0111] This experimental example shows that EPDM / AF / CMC / Si has the highest tensile strength, and the improvement of the aramid fiber interface structure effectively improves the tensile properties of its rubber composite material.

[0112] Table 3 Tensile strength of modified aramid fiber / ethylene propylene diene monomer (EPDM) rubber composites

[0113]

[0114] In summary, the aramid fibers encapsulated with carboxymethyl cellulose and adsorbed with SiO2 prepared in this invention, with SiO2 nanoparticles and CMC coating the surface of the aramid fibers, can significantly improve the surface roughness of the aramid fibers. Under the dual action of nanoparticles and CMC, the improvement of interfacial properties exhibits a significant synergistic effect. The surface-modified aramid fiber reinforced polymer matrix composite material prepared in this invention can effectively improve the interfacial bonding ability and mechanical properties between aramid fibers and EPDM rubber, and has good tensile properties, showing great application prospects in aerospace, defense, and transportation fields.

Claims

1. A surface-modified aramid fiber-reinforced polymer matrix composite material, characterized in that, It is composed of surface-modified aramid fibers and a polymer matrix; the weight ratio of the surface-modified aramid fibers to the polymer matrix is ​​(1-30):100; the preparation method of the surface-modified aramid fibers includes the following steps: Step 1: Impregnate unsizing aramid fibers or desizing aramid fibers with a carboxymethyl cellulose aqueous solution and then dry to obtain aramid fibers encapsulated with carboxymethyl cellulose; Step 2: Impregnate the aramid fibers encapsulated with carboxymethyl cellulose in a silica ethanol solution and then dry to obtain the product; the mass ratio of carboxymethyl cellulose to silica is (1-10):(1-10).

2. The surface-modified aramid fiber reinforced polymer matrix composite material according to claim 1, characterized in that, The polymer matrix is ​​made from raw materials comprising the following parts by weight: 80-150 parts of polyolefin rubber Activator 0.1-20 parts 0.1-20 parts of softener Vulcanizing agent 0.1-20 parts, Reinforcing agent 0.1-20 parts.

3. The surface-modified aramid fiber-reinforced polymer matrix composite material according to claim 2, characterized in that, The polyolefin rubber is selected from at least one of ethylene propylene diene monomer (EPDM) rubber and polybutene rubber. And / or, the activator is selected from at least one of zinc oxide, magnesium oxide, and lead oxide; And / or, the softener is selected from at least one of phthalates, phosphates, and stearic acid; And / or, the vulcanizing agent is selected from at least one of benzophenone peroxide, dicumyl peroxide, and sulfur; And / or, the reinforcing agent is selected from silica.

4. The surface-modified aramid fiber reinforced polymer matrix composite material according to claim 1, characterized in that: The mass ratio of carboxymethyl cellulose to silicon dioxide is 1:1-1.

5.

5. The surface-modified aramid fiber reinforced polymer matrix composite material according to claim 1, characterized in that: The carboxymethyl cellulose aqueous solution has a mass fraction of 0.1-2%, and the silica solution has a mass fraction of 0.1-2%.

6. The surface-modified aramid fiber-reinforced polymer matrix composite material according to claim 1, characterized in that, The desizing process includes: immersing aramid fibers in a volatile organic solvent and then sonicating them to obtain desizing aramid fibers.

7. A method for preparing the surface-modified aramid fiber reinforced polymer matrix composite material according to any one of claims 1-6, characterized in that, Includes the following steps: a. React polyolefin rubber with activator, softener, vulcanizing agent, reinforcing agent, and surface-modified aramid fiber, adjust the roller gap, and pass through a thin stream to obtain a compound rubber; b. The compounded rubber is obtained by vulcanization.

8. The application of the surface-modified aramid fiber reinforced polymer matrix composite material according to any one of claims 1-6 in the fields of aerospace, electronic information, sporting goods, automotive industry, and transportation.

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