A modified basalt fiber, a modification method, a composite material and a preparation method thereof

Abstract

The present invention relates to the technical field of composite materials, and discloses a modified basalt fiber, a modification method, a composite material and a preparation method, including the following steps: Step 1: Break the chopped basalt fiber to an average length of 1 mm, wash and dry it to obtain chopped basalt fiber powder; Step 2: Uniformly lay the chopped basalt fiber powder obtained in Step 1 on a water-based filter membrane, and vacuum filter the cellulose nanofiber dispersion; Step 3: The chopped basalt fiber powder obtained in Step 2 can be obtained as modified basalt fiber after drying; in the present invention, cellulose nanofibers are grafted onto the surface of the chopped basalt fiber through chemical bonds, and the surface of the chopped basalt fiber is modified by vacuum filtration, providing rich oxygen-containing functional groups on the surface of the basalt fiber; the epoxy resin composite material prepared by using the modified chopped basalt fiber improves the bonding force at the resin-fiber interface and improves the mechanical properties of the composite material.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and specifically relates to a modified basalt fiber, a modification method, a composite material and a preparation method thereof. Background Art

[0002] Basalt fiber is prepared by melting basalt raw materials at a high temperature of 1300 - 1500 °C. Due to a series of advantages such as the material itself being harmless to the environment and the preparation process not requiring the addition of any chemical reagents, it has become a green and environmentally friendly material with a high research popularity in recent years. As a new type of environmentally friendly and high-performance inorganic fiber, basalt fiber has high strength and modulus, resistance to high and low temperatures, and excellent wave absorption properties, and has received great attention in the fields of the automotive industry, aerospace, and construction industry. Compared with long fiber reinforced resin composites, short fiber reinforced resin composites have better ductility and are characterized by easy processing and high production efficiency.

[0003] However, the surface of basalt fiber is smooth and chemically inert, which is very unfavorable for the wetting between the fiber and the resin, resulting in a very poor interfacial bonding force between the basalt fiber and the resin. Furthermore, when the basalt fiber reinforced resin composite is subjected to an external load, the stress cannot be better transmitted to the reinforcing phase of the basalt fiber, and the performance advantages of the basalt fiber cannot be fully exerted. Therefore, the surface modification of basalt fiber is a key research point and a difficulty in basalt fiber reinforced resin composites.

[0004] In the research on the surface modification of basalt fiber, common methods include silane coupling agent modification, acid-base etching modification, plasma modification, etc. However, in the above modification methods, there are problems such as low grafting rate and long reaction time in silane coupling agent modification; the modifiers for acid-base etching cause certain pollution to the environment, and plasma modification will damage the fiber itself and thus reduce the single filament tensile strength of the fiber. Summary of the Invention

[0005] The present invention provides a modified basalt fiber, a modification method, a composite material and a preparation method thereof for the problems existing in the prior art.

[0006] The technical solution adopted by the present invention is: a modification method for basalt fiber, comprising the following steps:

[0007] Step 1: Break the chopped basalt fiber into an average length of 1 mm, wash and dry it to obtain chopped basalt fiber powder;

[0008] Step 2: Uniformly lay the chopped basalt fiber powder obtained in Step 1 on a water-based filter membrane, and use reduced pressure filtration to filter the cellulose nanofiber dispersion; the mass ratio of the chopped basalt fiber to the cellulose nanofiber is 1:0.06 - 0.18;

[0009] Step 3: The chopped basalt fiber powder obtained in Step 2 can be dried to obtain modified basalt fiber.

[0010] Further, before cleaning and drying in Step 1, the chopped basalt fiber is dispersed in acetone, placed in a Soxhlet extractor, and heated under reflux in a water bath at 80 °C for 24 h.

[0011] Further, the cellulose nanofiber is an amino-terminated modified cellulose nanofiber.

[0012] Further, the modification method of the cellulose nanofiber is as follows:

[0013] NaIO is added to the cellulose nanofiber dispersion 4 , and the reaction is fully carried out in the dark; the mass ratio of the cellulose nanofiber to NaIO 4 is 1:2;

[0014] Diethylenetriamine is added, and after reflux reaction, amino-terminated modified cellulose nanofiber can be obtained.

[0015] Modified basalt fiber obtained by a modification method.

[0016] A preparation method of a composite material based on modified basalt fiber, wherein the modified basalt fiber is the above-mentioned modified basalt fiber, and the method includes the following steps:

[0017] The epoxy resin additive is fully mixed, and the modified basalt fiber is added, wherein the mass of the modified basalt fiber accounts for 2% of the mass of the epoxy resin;

[0018] Ultrasonic stirring is carried out at 50 °C, and after vacuum defoaming, curing is carried out to obtain the required composite material.

[0019] Further, the additive includes a curing agent, an accelerator, and an anti-settling agent.

[0020] Further, the curing agent is methyltetrahydrophthalic anhydride, the accelerator is 2, 4, 6-tris(dimethylaminomethyl)phenol, and the anti-settling agent is fumed silica.

[0021] Further, the curing process is as follows:

[0022] First, curing is carried out at 80 °C for 2 h, and then curing is carried out at 120 °C for 3 h.

[0023] A composite material based on modified basalt fiber.

[0024] The beneficial effects of the present invention are:

[0025] (1) In the present invention, cellulose nanofibers are grafted onto the surface of chopped basalt fibers through chemical bonds, and the surface of the chopped basalt fibers is modified by vacuum filtration, providing abundant oxygen-containing functional groups on the surface of the basalt fibers;

[0026] (2) The epoxy resin composite material prepared by using the modified chopped basalt fibers in the present invention improves the bonding force at the resin-fiber interface and enhances the mechanical properties of the composite material. Description of the Drawings

[0027] Figure 1 SEM images of the tensile fracture surfaces of the epoxy resin composite materials obtained in Example 2 and Comparative Example 1 of the present invention. a and b are the composite materials obtained in Comparative Example 1, and c and d are the composite materials obtained in Example 2.

[0028] Figure 2 Fourier transform infrared spectra of the chopped basalt fibers before and after modification in Example 2 of the present invention.

[0029] Figure 3 TGA curves of the modified basalt fibers and the unmodified basalt fibers in Examples 1-3 of the present invention.

[0030] Figure 4 Atomic force microscope images of the modified basalt fibers and the unmodified basalt fibers in Examples 1-3 of the present invention. a is the unmodified basalt fiber, b is the modified basalt fiber obtained in Example 1, c is the modified basalt fiber obtained in Example 2, and d is the modified basalt fiber obtained in Example 3.

[0031] Figure 5 Contact angles of the modified basalt fibers and the unmodified basalt fibers in Examples 1-3 of the present invention with water and diiodomethane.

[0032] Figure 6 Surface energies of the modified basalt fibers and the unmodified basalt fibers in Examples 1-3 of the present invention.

[0033] Figure 7 Tensile strength curves of the epoxy resin composite materials obtained in Examples 1-3 and Comparative Example 1 of the present invention.

[0034] Figure 8 Impact strength curves of the epoxy resin composite materials obtained in Examples 1-3 and Comparative Example 1 of the present invention. Detailed Embodiments

[0035] The present invention will be further described below with reference to the drawings and specific embodiments.

[0036] A method for modifying basalt fibers includes the following steps:

[0037] Step 1: Break the chopped basalt fibers into an average length of 1 mm, wash, dry, and obtain chopped basalt fiber powder; before washing and drying, disperse the chopped basalt fibers in acetone, place them in a Soxhlet extractor, and heat and reflux in an 80 °C water bath for 24 h.

[0038] Step 2: Uniformly lay the chopped basalt fiber powder obtained in Step 1 on a water-based filter membrane, and vacuum filter the cellulose nanofiber dispersion; the mass ratio of the chopped basalt fibers to the cellulose nanofibers is 1:0.06 - 0.18; the cellulose nanofibers are amino-terminated modified cellulose nanofibers. The modification method is as follows:

[0039] Add NaIO 4 to the cellulose nanofiber dispersion, and react fully in the dark; the mass ratio of the cellulose nanofibers to NaIO 4 is 1:2;

[0040] Add diethylenetriamine, and after reflux reaction, amino-terminated modified cellulose nanofibers can be obtained.

[0041] Step 3: After drying the chopped basalt fiber powder obtained in Step 2, modified basalt fibers can be obtained.

[0042] A preparation method of a composite material based on modified basalt fibers, the modified basalt fibers are used as the modified basalt fibers, and the method includes the following steps:

[0043] Fully mix the epoxy resin additives, and add the modified basalt fibers, where the mass of the modified basalt fibers accounts for 2% of the mass of the epoxy resin; the additives include a curing agent, an accelerator, and an anti-settling agent. The curing agent is methyltetrahydrophthalic anhydride, the accelerator is 2, 4, 6-tris(dimethylaminomethyl)phenol, and the anti-settling agent is fumed silica. The mass ratio of the curing agent, the accelerator, and the anti-settling agent to the epoxy resin is 85:1:0.5:100.

[0044] Under the condition of 50 °C, carry out ultrasonic stirring, remove bubbles under vacuum, and then cure to obtain the required composite material.

[0045] The curing process is as follows:

[0046] First, cure at 80 °C for 2 h, and then cure at 120 °C for 3 h.

[0047] The raw materials used in the following examples are as follows:

[0048] Short-cut basalt fiber BF, with a length of about 3 mm and a single-filament diameter of about 12 μm; cellulose nanofiber CNF, with a diameter of 50 nm and a length of 1 - 3 μm; bisphenol A epoxy resin, E-51; epoxy equivalent 180 - 200, methyltetrahydrophthalic anhydride (MeTHPA, curing agent) 98%, 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30, accelerator); fumed silica powder (anti-settling agent); acetone: 99.8%, sodium periodate (NaIO 4 ), 99%; ethylene glycol: 98%; triethylenetriamine DETA 99.8%.

[0049] Example 1

[0050] First, modify the short-cut basalt fiber according to the following steps:

[0051] Step 1: Break the short-cut basalt fiber into pieces with a length of about 1 mm using a blender, put it into a Soxhlet extractor filled with acetone, and heat and reflux in an 80 °C water bath for 24 h. Then take it out, wash it, and dry it for 24 h to obtain the surface-desized short-cut basalt fiber, BF.

[0052] Step 2: Uniformly spread 0.75 g of BF powder on a water-based filter membrane (with a pore size of 0.22 μm and a diameter of 50 mm), and use a water circulation vacuum pump to perform vacuum filtration on 5 mL of the cellulose nanofiber aqueous dispersion. The mass of cellulose nanofibers in the cellulose nanofiber aqueous dispersion is 0.06 g.

[0053] During the vacuum filtration process, due to the high specific surface energy, the CNF nanoparticles will gradually agglomerate as the CNF suspension is filtered with the solvent, resulting in uneven attachment of CNF to the BF surface. This will cause stress concentration at the interface between BF and the resin, thereby affecting the mechanical properties of the composite material. Therefore, during the vacuum filtration process, a 50 °C water bath heating is adopted, and an ultrasonic vibrating rod is inserted to keep the nanoparticles in a uniformly dispersed state. This is because the ultrasonic action acts on the CNF nanoparticles through the vibration and cavitation effects of sound waves, promoting the dispersion of CNF nanoparticles. The cavitation effect will generate tiny bubbles in the CNF suspension and then burst, generating strong shock waves, which helps the more uniform dispersion of CNF nanoparticles and keeps them in a uniformly dispersed state during the vacuum filtration process, enhancing the stability of the interface between BF and the resin.

[0054] During the vacuum filtration process, due to the short length of the chopped basalt fibers, they are evenly dispersed on the filter paper and their surfaces are not hydrophilic. The CNF suspension can come into full contact with the BF, and the droplets remain stable on the surface of the chopped basalt fibers, providing sufficient contact time for the functional groups such as hydroxyl groups and ether bonds on the CNF surface to fully contact the silanol groups on the BF surface, ensuring the formation of hydrogen bonds. When the pressure difference reaches a certain value, the solvent of the CNF suspension is filtered out through the pores of the filter paper, while the CNF is retained on the surface of the chopped basalt fibers.

[0055] When using cellulose nanofibers CNF, surface modification is first carried out:

[0056] Disperse the cellulose nanofibers in deionized water, and under the action of ultrasonic and stirring, make the CNF evenly dispersed, and configure it into an aqueous dispersion with a mass concentration of 1 wt.%.

[0057] Take an aqueous dispersion containing 0.15 g of CNF and 0.3 g of NaIO 4 In a flask, react under dark conditions at 50 °C for 12 h, and pour 30 mL of ethylene glycol to terminate the reaction.

[0058] Adjust the pH value to neutral, and then gradually add 20 mmol of DETA (after adding NaIO 4 After that, aldehyde groups will be generated at the ends of the CNF structural units. Adding DETA introduces amino groups into the system, which is conducive to the Schiff base reaction with the aldehyde groups to form terminal amino groups) solution. React under magnetic stirring and reflux in a water bath at 40 °C for 3 h, adjust the pH value to neutral, and freeze-dry to obtain end-amino modified cellulose nanofibers.

[0059] Step 3: Put it in a forced-air drying oven and dry it at 65 °C for 4 h to obtain powdery fibers. The fibers obtained in this example are denoted as BF-CNF5.

[0060] Use the fibers BF-CNF5 obtained in this example to prepare epoxy resin composites. The process is as follows:

[0061] Mix epoxy resin EP, curing agent, accelerator, and anti-settling agent in a mass ratio of 100:85:1:0.5, add 2 wt.% of the fibers BF-CNF5 based on the mass of the epoxy resin, and stir ultrasonically at 50 °C for 30 min.

[0062] Put the mixed solution into a vacuum oven for multiple vacuum degassing. After the solution is degassed cleanly, pour it into a mold, put it into the oven and cure it according to the stepwise temperature curing system of curing at 80 °C for 2 h and 120 °C for 3 h; finally, denote the obtained composite material as BF-CNF5 / EP.

[0063] Example 2

[0064] The method for modifying chopped basalt fibers and the method for preparing an epoxy resin composite material in this example are the same as those in Example 1, except that in step 2, the volume of the aqueous dispersion of cellulose nanofibers is 10 mL, and the mass of cellulose nanofibers is 0.12 g. The obtained modified chopped basalt fibers are BF-CNF10.

[0065] The epoxy resin composite material prepared using it is BF-CNF10 / EP.

[0066] Example 3

[0067] The method for modifying chopped basalt fibers and the method for preparing an epoxy resin composite material in this example are the same as those in Example 1, except that in step 2, the volume of the aqueous dispersion of cellulose nanofibers is 15 mL, and the mass of cellulose nanofibers is 0.18 g. The obtained modified chopped basalt fibers are BF-CNF10.

[0068] The epoxy resin composite material prepared using it is BF-CNF10 / EP.

[0069] Comparative Example 1

[0070] The method for modifying chopped basalt fibers and the method for preparing an epoxy resin composite material in this example are the same as those in Example 1, except that step 2 is not included, and the obtained epoxy resin is denoted as BF / EP.

[0071] Figure 1 FIG. 23 is a SEM image of the tensile fracture surface of the composite materials obtained in Example 2 and Comparative Example 1 of the present invention. a and b are SEM images of Comparative Example 1 at different magnifications, and c and d are SEM images of Example 2 at different magnifications. It can be seen from the figure that in the composite material obtained in Comparative Example 1, the surface of the BF after desizing but before modification is smooth, and almost no resin adheres to the fiber surface. There are obvious gaps between the exposed fibers and the resin matrix. From Figure 1 As can be seen from b, there are a large number of holes caused by fiber pull-out in the resin matrix of the tensile fracture surface, indicating poor bonding between the fibers and the resin. This shows that the main failure modes of the tensile fracture of BF / EP are fiber debonding and fiber pull-out.

[0072] For the tensile fracture surface of the composite material obtained in Example 2, Figure 1 as can be seen from c, the surface of the exposed basalt fibers becomes significantly rougher, the amount of residual resin increases significantly, and the fiber-resin gap is significantly smaller. From Figure 1 as can be seen from d, compared with b, the number of holes caused by fiber pull-out in the resin matrix of the tensile fracture surface is significantly reduced, indicating that the CNF-modified basalt fibers have achieved excellent modification effects.

[0073] This is because a large number of hydroxyl groups on the surface of CNF form hydrogen bonds with the hydroxyl groups on the surface of BF, which not only increases the surface roughness of the fiber, but also provides a large number of active sites on the surface of BF. It not only enhances the mechanical interlock between the fiber and the resin, but also enhances the bonding force between the resin and the fiber during the curing process of the epoxy resin. The chemical structure of the chopped basalt fiber does not contain carbon elements and active functional groups, which cannot fully wet the surface of the basalt fiber during the curing process of the resin, resulting in voids at the interface. By vacuum filtration, cellulose nanofibers do not react with the solvent, and the chemical structures such as active functional groups are retained. At the interface between the resin and the fiber, cellulose nanofibers can fully provide active sites, enhance the wetting of the fiber during the resin curing process, and transfer stress when the composite material is stressed.

[0074] The short chopped basalt fiber is used in the present invention. Different from the long fiber reinforced composite material, the load in the short fiber reinforced composite material does not directly act on the fiber, but acts on the matrix material, and the load is transmitted to the fiber through the fiber end and the fiber surface near the end. CNF and BF are connected by hydrogen bonds and van der Waals forces, resulting in an increase in oxygen-containing active groups on the fiber surface, improving the infiltration of the fiber during the resin curing process, increasing the mechanical interlock between the resin and the fiber surface, and enhancing the interfacial bonding force between the resin and the fiber. When the composite material is subjected to an external load, when the stress is transmitted along the resin matrix to the resin-fiber interface, there are a large number of voids between the unmodified BF and the epoxy resin. These voids cause a large number of defects inside the composite material, and when the crack propagates to the interface, the stress cannot be transmitted to the reinforcing phase fiber, resulting in fiber pull-out and debonding at the interface, so the mechanical properties of the composite material are poor; while the good interfacial bonding force between the modified resin and the fiber will form a stable interfacial phase, transmit the stress to the reinforcing phase fiber through the interface, and the failure form changes from fiber pull-out and debonding to cohesive failure, thereby enhancing the mechanical properties of the composite material.

[0075] Figure 2 It is the FTIR spectrogram of the chopped basalt fiber before modification (obtained in step 1) and after modification (obtained in step 3) in Example 2 of the present invention. It can be seen from the figure that the changes in the functional groups on the basalt fiber before and after modification. The peaks at 1284 cm -1 and 857 cm -1 of the unmodified BF correspond to the Si-O-Si and Si-C vibrations of the basalt fiber respectively. The stretching vibration peak and bending vibration peak of the hydroxyl group are observed at 3398 cm -1 and 1622 cm -1 . The hydroxyl peak of the modified BF shows a significant enhancement, and blue-shifts to 3427 cm -1 and 1640 cm -1It is speculated that this is caused by the formation of hydrogen bonds between BF and CNF and the increase in polar groups on the BF surface.

[0076] The modified BF shows antisymmetric and symmetric stretching vibration peaks of -CH at 2931 cm -1 and 2858 cm -1 , and a stretching vibration peak of C-O-C is observed at 1012 cm 2 . After the CNF undergoes the processes of vacuum filtration and drying, it is successfully coated on the BF surface, which confirms that the modification method of CNF by vacuum filtration successfully modifies BF, and thus the corresponding functional groups of CNF can be observed on the BF surface. -1

[0077] Figure 3 Figure [ID] shows the TGA curves of BF before and after modification and the basalt fibers obtained in Examples 1-3 when heated from room temperature to 600 °C at a heating rate of 10 °C / min in an N 2 atmosphere. Figure 3 Figure [ID] is a curve showing the change in the weight loss ratio of BF-CNF with the CNF modification amount at 600 °C. As can be seen from Figure 3 Figure [ID], as the temperature rises to 600 °C, the weight loss of BF reaches 1.05%. It is analyzed that this may be because after the BF surface is extracted by Soxhlet extraction with acetone, there are still some sizing agents, some physically adsorbed water and impurities remaining; however, as the content of CNF on the BF surface increases with vacuum filtration, the content of CNF coated on the BF surface also increases accordingly, resulting in an increase in the weight loss of BF-CNFx at 600 °C, which also verifies the correctness of the speculation based on the previous Fourier transform infrared spectroscopy and SEM images of the tensile fracture surface. According to the weight loss of BF-CNFx at 600 °C, the CNF coating amounts on the surface of the modified BF are calculated to reach 1.79%, 2.15%, and 2.96% respectively.

[0078] Figure 4 ​Atomic force microscopy images of the modified basalt fibers and the unmodified basalt fibers in Examples 1-3 of the present invention. a is the unmodified basalt fiber, b is the modified basalt fiber obtained in Example 1, c is the modified basalt fiber obtained in Example 2, and d is the modified basalt fiber obtained in Example 3. It can be seen from the figure that the surface of the unmodified BF is relatively smooth, and the root mean square roughness Rq is 4.920 nm. For the BF surface modified by filtering 5 mL of CNF, it is observed that the surface of BF becomes rougher, and the Rq value increases to 19.747 nm. With the increase of the CNF filtration volume, when it reaches 15 mL, the Rq increases to 37.496 nm. Compared with the unmodified BF, the surface roughness is significantly improved, and irregular wrinkled morphologies are formed on the fiber surface. This is because as the content of CNF increases, more and more CNF adheres to the BF surface through hydrogen bonds, van der Waals forces, etc. Higher surface roughness can promote a stronger mechanical interlock between the resin and the fiber, achieving the effect of enhancing the interfacial bonding force.

[0079] Figure 5 Contact angles of the modified basalt fibers and the unmodified basalt fibers in Examples 1-3 of the present invention with water and diiodomethane. Figure 6 Surface energies of the modified basalt fibers and the unmodified basalt fibers in Examples 1-3 of the present invention. It can be seen from the figure that the contact angles of the unmodified BF with water are approximately 91.7°. With the increase of the CNF coating amount, a downward trend is presented. Therefore, this leads to an increase in the polar component of the surface energy of the modified BF from 6.82 mN / m to 14.83 mN / m. This phenomenon is caused because as the CNF coating amount on the BF surface increases, the number of oxygen-containing functional groups on the surface increases. Similarly, the contact angle of the fiber with diiodomethane decreases from 78.8° to 70.89°, resulting in a slight decrease in the dispersion component on the fiber surface from 31.41 mN / m to 29.52 mN / m. It is speculated that the uneven coating of CNF on the BF surface is caused by the agglomeration of nanoparticles, which also indicates that the coating of CNF slightly increases the surface roughness of the fiber. The surface energy of the fiber increases with the increase of the CNF coating amount. Due to the increase in the number of oxygen-containing functional groups on the fiber surface and the improvement of the fiber surface roughness, during the curing process of the epoxy resin, the resin matrix liquid can have a better wetting effect with the fiber, which is more conducive to the mechanical interlock and physical and chemical interactions between the resin and the fiber, thereby improving the bonding force at the resin-fiber interface and achieving the purpose of improving the mechanical properties of the composite material.

[0080] Figure 7 Tensile strength curves of the epoxy resin composites obtained in Examples 1-3 and Comparative Example 1 of the present invention. Figure 8The impact strength curves of the epoxy resin composites obtained in Examples 1-3 and Comparative Example 1 of the present invention. As can be seen from the figure, both the tensile strength and impact strength of the BF-CNFx / EP composites show a trend of first increasing and then decreasing, reaching the maximum tensile strength of 61.1 MPa at BF-CNF10 / EP, with a 22.4% increase; reaching the maximum impact strength of 12.4 kJ / m 2 , with a 55% increase. This is because as the CNF content increases, CNF is connected to BF through hydrogen bonds and van der Waals forces, resulting in an increase in oxygen-containing active groups on the fiber surface, improving the wetting of the fiber during the resin curing process, increasing the mechanical interlocking between the resin and the fiber surface, and enhancing the interfacial bonding force between the resin and the fiber. Combining the analysis in the introduction, when the composite material is subjected to an external load, when the stress is transmitted along the resin matrix to the resin-fiber interface, there are a large number of voids between the unmodified BF and the epoxy resin. These voids cause a large number of defects inside the composite material, and when the crack propagates to the interface, the stress cannot be transmitted to the reinforcing phase fiber, resulting in fiber pull-out and debonding at the interface, so the mechanical properties of the composite material are poor; while the good interfacial bonding force between the modified resin and the fiber will form a stable interfacial phase, transmitting the stress to the reinforcing phase fiber through the interface, and the failure form changes from fiber pull-out and debonding to cohesive failure, thereby enhancing the mechanical properties of the composite material; however, as the CNF content further increases, the tensile strength and impact strength of the composite material both show varying degrees of decline. This is because excessive coating will cause nanoparticle agglomeration of CNF at the resin-fiber interface. During the crack propagation process, stress concentration occurs at the interface, resulting in a decrease in the mechanical properties of the composite material.

[0081] In the present invention, through the vacuum filtration technique, the solvent of the cellulose nanofiber suspension is filtered off through a filter paper, and the cellulose nanofibers are retained on the surface of the chopped basalt fibers, forming hydrogen bonds with the hydroxyl groups on the surface of the basalt fibers, providing a rich oxygen-containing functional group on the surface of the basalt fibers. The bonding force between the resin and the fiber is enhanced, and the mechanical properties of the composite material are improved. Compared with other modification methods, vacuum filtration also has the effects of energy saving and low cost, which can be achieved only by using a water circulation vacuum pump; in addition, during the vacuum filtration process, the cellulose nanofiber suspension does not react with the solvent, and no other reaction products will appear, so it has a stable modification effect.

Claims

1. A method for modifying basalt fiber, characterized in that: The following steps are involved: Step 1: Crush the chopped basalt fibers to an average length of 1 mm, wash and dry them to obtain chopped basalt fiber powder; Step 2: the chopped basalt fiber powder obtained in step 1 is evenly spread on a water filter membrane, and then the cellulose nanofiber dispersion is filtered under reduced pressure using the water filter membrane; wherein the mass ratio of the chopped basalt fiber to the cellulose nanofiber is 1:0.06-0.18; during the process of reduced pressure filtration, a 50°C water bath is used for heating, and an ultrasonic vibrator is inserted for ultrasonic treatment; Step 3: The chopped basalt fiber powder obtained in step 2 is dried to obtain modified basalt fiber.

2. The method for modifying basalt fiber according to claim 1, characterized in that: In the step 1, before washing and drying, the crushed chopped basalt fibers are dispersed in acetone, placed in a Soxhlet extractor, and heated under reflux in a water bath at 80° C. for 24 h.

3. The method for modifying basalt fiber according to claim 1, characterized in that: The cellulose nanofibers are amino-terminated cellulose nanofibers.

4. The method for modifying basalt fiber according to claim 3, characterized in that: The modification method of the cellulose nanofiber is as follows: Adding NaIO4 to the cellulose nanofiber dispersion and fully reacting in the dark; wherein the mass ratio of cellulose nanofiber to NaIO4 is 1:2; Add diethylenetriamine and reflux reaction to obtain amino-terminated modified cellulose nanofibers.

5. The modified basalt fiber obtained by any one of the modification methods of claims 1 to 4.

6. A method for preparing a composite material based on modified basalt fiber, characterized in that: The modified basalt fiber adopts the modified basalt fiber as claimed in claim 5, comprising the following steps: The epoxy resin additive is fully mixed, and the modified basalt fiber is added, wherein the mass of the modified basalt fiber accounts for 2% of the mass of the epoxy resin; The desired composite material can be obtained by ultrasonic stirring at 50 °C and curing after vacuum degassing.

7. The method for preparing a composite material based on modified basalt fiber according to claim 6, characterized in that: The additives include a curing agent, an accelerator and an anti-settling agent.

8. The method for preparing a composite material based on modified basalt fiber according to claim 7, characterized in that: The curing agent is methyltetrahydrophthalic anhydride, the accelerator is 2,4,6-tris(dimethylaminomethyl)phenol, and the anti-settling agent is fumed silica.

9. The method for preparing a composite material based on modified basalt fiber according to claim 7, characterized in that: The curing process is as follows: First, cure at 80 °C for 2 h and then at 120 °C for 3 h.

10. A composite material based on modified basalt fiber obtained by any one of the preparation methods of claims 6 to 9.

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