CN114874470A

CN114874470A - Modified carbon fiber/phenolic resin composite material and preparation method thereof

Info

Publication number: CN114874470A
Application number: CN202210322184.8A
Authority: CN
Inventors: 苏志强; 赵鑫; 张晓媛; 王敏; 全皓月
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2022-03-30
Filing date: 2022-03-30
Publication date: 2022-08-09
Anticipated expiration: 2042-03-30
Also published as: CN114874470B

Abstract

The invention relates to a modified carbon fiber/phenolic resin composite material, which is obtained by coating phenolic resin on the surface of surface modified carbon fiber and then performing hot-pressing compounding. The invention uses a plurality of methods to modify the surface of the carbon fiber, designs a multi-scale surface appearance, enhances the contact area of the carbon fiber and the resin substrate, effectively improves the interface bonding force between bonding surfaces, and finally achieves the purpose of improving the comprehensive performance of the carbon fiber/phenolic resin composite material.

Description

Modified carbon fiber/phenolic resin composite material and preparation method thereof

Technical Field

The invention belongs to the technical field of composite materials, and particularly relates to a modified carbon fiber/phenolic resin composite material and a preparation method thereof.

Background

The carbon fiber has a series of excellent performances such as high specific strength, high specific modulus, high temperature resistance, fatigue resistance, corrosion resistance, good heat transfer performance and the like, can be used as a structural material for bearing load and can also play a role as a functional material, the carbon fiber composite material is widely applied in daily life by virtue of the characteristics of excellent specific strength and specific elasticity, and the product relates to the fields of transportation, building engineering and the like, wherein the carbon fiber/phenolic resin composite material is widely applied to the fields of aerospace, transportation and the like due to the advantages of low cost, high temperature resistance, high specific strength specific modulus, corrosion resistance and the like. However, the carbon fiber surface is inert in chemical activity, lacks of functional groups with chemical activity, and has poor adhesion with a composite matrix, so that the performance of the carbon fiber composite material is limited. The interfacial bonding of the carbon fiber and phenolic resin matrix members determines the key to the overall performance of the composite, and the selection of an entirely new fiber material requires a great deal of capital and time. Therefore, the research at home and abroad mainly aims at carrying out surface modification on carbon fibers, and the surface activity of the carbon fibers is improved by a surface modification technology, so that the interface performance between the carbon fibers and a phenolic resin matrix material is enhanced, the bonding effect between the carbon fibers and the matrix is improved, and the value of the fiber material in industrial application is improved. The surface modification of carbon fiber mainly includes surface self-assembly, chemical vapor deposition, physical coating, etc.

The prior art has many studies on the method of modified carbon fiber/phenolic resin.

CN110938281A discloses a modified carbon fiber reinforced phenolic resin matrix composite material, which is prepared by coating an organic-inorganic hybrid zirconium silicate sol coating on carbon fiber cloth to uniformly and compactly coat the carbon fiber cloth, and further has good combination with phenolic resin. However, in industry, the preparation of the inorganic and inorganic hybrid zirconium silicate sol coating is not economical, the work is complex, strict process condition control is required, or a coating with uniform coverage cannot be obtained, which easily causes weak points of the composite material.

CN109897337A discloses a carbon fiber reinforced phenolic resin composite material and a preparation method thereof, wherein the carbon fiber reinforced phenolic resin composite material is obtained by mixing graphene dispersion liquid with a phenolic resin matrix, then mixing the mixture with carbon fibers to obtain a casting material, and performing casting, curing and curing. But the resulting composite surface lacks gloss; and the graphene dispersion liquid can lead to more micromolecular solvents to be introduced into the resin matrix, so that the mechanical property of the composite material is reduced.

CN105754056A discloses a carbon fiber modified phenolic resin, which is prepared by soaking carbon fibers in acetone, washing and drying; soaking the carbon fiber in a liquid oxidant, washing and drying to obtain oxidized carbon fiber; finally, soaking the oxidized carbon fiber in a coupling agent solution, and drying to obtain modified carbon fiber; adding phenol, aldehyde and an acid catalyst into a reaction kettle, reacting at 90-120 ℃ for 1-5h, adding the modified carbon fiber, continuing to react at 90-150 ℃ for 1-6h, and dehydrating to obtain the carbon fiber modified phenolic resin. However, the composite material obtained by the patent method is only modified by functional groups on a molecular level, and the improvement of the performance of the composite material is limited.

CN114032669A discloses a method for synchronously modifying a carbon fiber surface interface by electrophoretic deposition-electropolymerization, which is obtained by taking a carbon fiber as an anode and carrying out electrophoretic deposition and electropolymerization. The modification mode is single, and the effect is general.

CN113046864A discloses a lignin carbon fiber modified by phenolic resin and a preparation method thereof, which adopts lignin carbon fiber. But the cost of the lignin carbon fiber is far higher than that of carbon fiber derived from polyacrylonitrile at present. The patented process is not economical.

Disclosure of Invention

In order to overcome the interface bonding force of the carbon fiber/phenolic resin composite material in the prior art and further enhance the comprehensive performance of the composite material, the invention provides a carbon fiber surface active technology which improves the bonding tightness of the carbon fiber/phenolic resin composite material and the comprehensive performance of the composite material.

In order to realize the technical purpose of the invention, the technical scheme adopted by the invention is as follows:

the modified carbon fiber/phenolic resin composite material is obtained by coating phenolic resin on the surface of surface-modified carbon fiber and performing hot-pressing compounding, wherein the surface-modified carbon fiber is obtained by sequentially performing high-temperature treatment, electrochemical oxidation, polyisocyanate grafting modification and electrochemical deposition of carbon nanotubes.

Further, the Raman spectrum of the surface modified carbon fiber has 1400-1500 cm ^-1 D belt sum of position 1900-2000 cm ^-1 And the intensity ratio R of G/D is more than 2.

Further, the infrared spectrum of the surface modified carbon fiber is 1735 +/-50 cm ^-1 ，1261±50cm ^-1 And 1091 + -50 cm ^-1 Has characteristic peaks.

The modified carbon fiber/phenolic resin composite material is prepared by the preparation method comprising the following steps:

(1) carrying out high-temperature treatment on the carbon fiber cloth;

(2) putting the carbon fiber treated at high temperature in the step (1) into an electrolytic reaction tank as an electrolytic anode material, wherein the electrolyte is a dilute inorganic acid solution;

(3) washing and filtering the carbon fiber after electrochemical treatment in the step (2), and drying for later use;

(4) putting the carbon fiber obtained in the step (3) into a polyisocyanate solution for dipping and drying;

(5) putting the carbon fiber obtained in the step (4) as an anode material into an electro-deposition reaction tank for electrochemical deposition, wherein the electrolyte is a carbon nano tube dispersion liquid;

(6) washing, filtering and drying the carbon fiber subjected to electrochemical deposition obtained in the step (5) to obtain surface-modified carbon fiber;

(7) adding p-phenylphenol, ammonia water, phenol and formaldehyde into a reaction container, and reacting to prepare liquid phenolic resin;

(8) and (4) uniformly coating the surface of the carbon fiber subjected to surface modification in the step (6) with the liquid phenolic resin obtained in the step (7) to obtain the carbon fiber with the surface coated, putting the carbon fiber into a die, and carrying out hot pressing to obtain the modified carbon fiber/phenolic resin composite material.

Preferably, the liquid phenolic resin is uniformly coated on the surface of the carbon fiber subjected to surface modification in the step (8) to obtain a plurality of layers of phenolic resin-coated carbon fibers, and then the carbon fibers are placed into a mold for hot pressing.

Further, the raw material carbon fiber used in step (1) is not particularly limited, and may be any carbon fiber material that is conventional in the art, and in one embodiment of the present invention, the carbon fiber is PAN-based T300 carbon fiber cloth.

Preferably, the high temperature in the step (1) is 400-500 ℃, and the high temperature treatment time is 2-3 h.

Preferably, the electrolytic voltage in the step (2) is 4-5V, and the electrochemical treatment time is 15-20 min; the electrolyte solution is 30-50% dilute sulfuric acid solution.

Washing, suction filtering and drying in the step (3) and the step (7) are well known in the art, for example, at least one of ultrapure water, deionized water and distilled water is used for washing, suction filtering is carried out for 30-50 times, and the suction degree is-0.1 to-0.5 Mpa for suction filtering; the drying is oven drying, the temperature is 60-80 ℃, and the drying time is 3-6 h.

Further, in the step (4), the polyisocyanate is at least one selected from diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate and triphenylmethane triisocyanate. Triphenylmethane triisocyanate is preferred. Preferably, the concentration of the polyisocyanate solution is 10-20 wt%, and the carbon fiber is soaked in the polyisocyanate reagent for 30-60 min.

Preferably, the carbon nanotube dispersion liquid in step (5) is prepared by adding carbon nanotubes into an alcohol-water solution, and mechanically stirring and then ultrasonically dispersing. The carbon nanotube is multi-walled carbon nanotube, the outer diameter is 5-50nm, preferably 10-20nm, and the concentration of the carbon nanotube dispersion liquid is 5-10 wt%. The rotation speed of the mechanical stirring is 400-1000rpm, the ultrasonic dispersion condition is that the ultrasonic frequency is set to be 70-100KHZ, and the ultrasonic time is 1-3 h.

Preferably, in the step (5), during the electrochemical deposition, the electrolytic voltage is 5-6V, and the electrodeposition time is 10-12 min.

Preferably, in the step (7), the mass ratio of phenol to formaldehyde is 1.33-1.67: 1, most preferably 1.5: 1. P-phenylphenol is 15-30%, preferably 20-25% by mass of formaldehyde; the reaction is carried out in the presence of a basic catalyst, such as barium hydroxide, sodium hydroxide, ammonia water, in an amount of 0.1 to 1% by mass based on the total mass of p-phenylphenol, ammonia water, phenol and formaldehyde, the mass of ammonia water being 15 to 30% by mass based on the mass of formaldehyde, preferably 20 to 25% by mass based on the mass of formaldehyde. The reaction comprises the steps of firstly adding p-phenylphenol, ammonia water, phenol and 40-60% of formaldehyde, heating to 90-98 ℃, preserving heat for 1-2 hours, adding an alkaline catalyst, preserving heat, slowly dropwise adding the residual formaldehyde, adjusting the pH value to be neutral after the mixed solution becomes turbid, and performing vacuum dehydration until the mixed solution is clear and stops dehydration to obtain the liquid phenolic resin.

Preferably, in step (8), the mass ratio of the surface-modified carbon fibers to the phenolic resin is 1-2:1-2, preferably 1-1.5: 1. And (3) repeating the coating process in the step (8) to obtain a plurality of phenolic resin coated carbon fibers, wherein the number of the plurality of phenolic resin coated carbon fibers is determined according to actual needs, and 2-15 layers can be selected, such as 3-10 layers, and further such as 3 layers, 4 layers, 5 layers, 6 layers, 7 layers, 8 layers, 9 layers and 10 layers. And the hot pressing is to align and stack the obtained multiple layers of carbon fibers into a mold, cover a layer of molding paper on the upper surface and the lower surface respectively, and then place the mold into a vulcanizing press. Setting the hot pressing temperature and the hot pressing time. And after hot pressing is finished, successfully preparing the carbon fiber/phenolic resin composite material with excellent performance. The hot pressing process is well known in the art, and in one embodiment of the invention, a temperature gradient is set in a flat vulcanizing machine, hot pressing is carried out for 1-1.5h at 90-110 ℃, then the temperature is raised to 130-.

FIG. 1 is a schematic view of the preparation process of the surface modified carbon fiber/phenolic resin composite material of the present invention. As can be seen from the schematic diagram, the surface modification technology of the carbon fiber in the present invention mainly includes high temperature treatment, electrochemical oxidation, surface grafting modification, electrochemical deposition and other treatment methods.

FIG. 2 is a schematic diagram of the interface reinforcing mechanism of the surface modified carbon fiber/phenolic resin composite material. The main reasons for improving the interfacial properties of the composite material by the surface modified carbon fiber are attributed to the following aspects: firstly, removing a sizing agent through high-temperature treatment, so that the surface of the carbon fiber can be directly contacted with phenolic resin, and the intermolecular interaction force is favorable for the contact of the carbon fiber and the phenolic resin; secondly, oxygen-containing functional groups such as C ═ O, C-O-C and the like generated on the surface of the carbon fiber after electrochemical treatment can form hydrogen bonds with resin molecules, so that the molecular level contact of the carbon fiber and the phenolic resin at the interface is improved; thirdly, grafting more active groups on the surface of the carbon fiber through polyisocyanate grafting modification, so that more covalent chemical reaction sites are generated between the carbon fiber and the phenolic resin; fourthly, the carbon nano tube effectively improves the specific surface area, the roughness and the wettability of the carbon fiber, and generates stronger mechanical meshing action between the fiber and the resin, thereby being beneficial to enhancing the interface bonding strength and the mechanical property of the composite material.

FIG. 3 is a diagram of an electrochemical oxidation treatment device and an electrodeposition treatment device for carbon fiber in the process of the surface modification technique of the present invention. In the diagram of the carbon fiber electrochemical oxidation device, the carbon fiber treated at high temperature is taken as an anode, a platinum electrode is taken as a cathode, and H in dilute sulfuric acid electrolyte solution is generated in the electrochemical oxidation process ⁺ Moving from the anode to the cathode, H is generated at the cathode ₂ While generating O at the anode ₂ Generation of O ₂ And the carbon fiber is oxidized with the anode carbon fiber, so that more oxygen-containing functional groups are generated on the surface of the carbon fiber. In a carbon fiber electro-deposition device diagram, carbon fibers subjected to electrochemical oxidation treatment are taken as an anode, and a platinum electrode is taken as a cathode; in the electrochemical deposition process, the carbon nanotubes with negative charge in the carbon nanotube dispersion liquid can move to the carbon fiber end; finally, under the drive of current, the carbon nanotubes are deposited on the surface of the carbon fiber.

The invention has the following excellent effects: 1. the surface of the carbon fiber is modified by adopting various methods such as high-temperature treatment, electrochemical oxidation, polyisocyanate grafting modification and electrochemical deposition. The high-temperature treatment aims at removing the sizing agent on the surface of the original carbon fiber, and simultaneously, the high temperature is beneficial to increasing the carbon-oxygen bond on the surface of the carbon fiber; the electrochemical oxidation aims at introducing more active functional groups, such as-OH, -COOH, -C ═ O, -C-O-C, and the like, on the surface of the carbon fiber; the purpose of polyisocyanate grafting modification is to graft more active groups on the surface of the carbon fiber, so that more covalent chemical reaction sites are generated between the carbon fiber and the phenolic resin; the electrochemical deposition aims at increasing the surface roughness of the fiber, increasing the contact area between the fiber and the resin, strengthening the mechanical meshing action of the interface of the fiber and the resin, and simultaneously playing a synergistic action of the carbon nanotube and the carbon fiber to improve the performance of the carbon fiber composite material. According to the invention, by various means, the molecular structure, the functional group structure and the distribution of the nano material on the surface of the carbon fiber are changed, the multi-scale surface morphology is designed, the contact area of the carbon fiber and the resin substrate is enhanced, the interface binding force between the binding surfaces is effectively improved, and finally the comprehensive performance of the carbon fiber/phenolic resin composite material is improved.

2. By improving the preparation process of the RTM liquid phenolic resin, the formula proportion of the phenolic resin which is optimally combined with the modified carbon fiber interface is prepared, the interface bonding force of the composite material is effectively enhanced, and the tensile strength and the impact resistance of the composite material are increased.

Drawings

FIG. 1 is a schematic view of a process for preparing a surface-modified carbon fiber/phenolic resin composite material;

FIG. 2 is a schematic diagram of the interface enhancement mechanism of the surface modified carbon fiber/phenolic resin composite material;

FIG. 3 is a diagram of a carbon fiber electrochemical oxidation treatment device and a carbon fiber electrodeposition treatment device in the process of a surface modification technology;

FIG. 4 is a Scanning Electron Microscope (SEM) image of carbon fibers after being treated at different temperatures during high-temperature treatment at different temperatures;

FIG. 5 is a graph of the composite shear plane topography obtained under different electrochemical oxidations, electrochemical depositions and different raw material ratios;

FIG. 6 is a surface topography of the carbon fiber at various stages in example 1;

FIG. 7 is a Raman spectrum and an infrared spectrum of the carbon fiber at different stages of surface modification;

FIG. 8 is C after surface treatment of carbon fiber _1s XPS spectrogram after peak separation fitting;

FIG. 9 is a schematic representation of the surface modified carbon fiber/phenolic resin composite material prepared.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. The following examples are intended to facilitate a better understanding of the invention, but are not intended to limit the invention thereto. The experimental procedures in the following examples are conventional unless otherwise specified.

Example 1

A carbon fiber surface modification technology is characterized by comprising the following operation steps:

(1) removing sizing agent on the surface of the raw carbon fiber at high temperature: putting the T300 carbon fiber cloth with the size of 10 x 10cm into a muffle furnace for high-temperature treatment, wherein the treatment temperature is set to 400 ℃, and the working time is 120 min;

(2) electrochemical oxidation: putting the carbon fiber treated at the high temperature in the step (1) into an electrolytic reaction tank as an electrolytic anode material, wherein the electrolyte is a dilute sulfuric acid solution with the volume fraction of 40%, the cathode material is a platinum electrode, the electrolytic voltage is 5V, and the electrochemical treatment time is 20 min;

(3) washing: washing and suction-filtering the carbon fiber subjected to electrochemical treatment in the step (2) by using a washing liquid at room temperature, wherein the used washing liquid is ultrapure water with the mass of 2kg, the suction-filtering frequency is 50 times, and the suction vacuum degree is-0.1 Mpa; the drying temperature was set to 60 ℃ and the drying time period was set to 180 min.

(4) Grafting TTI: and (4) putting the carbon fiber obtained in the step (3) into 20% Triphenylmethane Triisocyanate (TTI) chlorobenzene solution for dipping treatment for 60min, and then drying treatment.

(5) Adding the carbon nano tube into 70% ethanol water solution, firstly carrying out magnetic stirring, and then carrying out ultrasonic dispersion in an ultrasonic cleaning machine, wherein the magnetic stirring speed is 800rpm, and the stirring time is 1 h; setting the ultrasonic frequency to be 70KHZ, and preparing to obtain 8% carbon nano tube dispersion liquid after the ultrasonic time is 1 h; putting the carbon fiber obtained in the step (4) as an anode material into an electro-deposition reaction tank for electrochemical deposition, wherein the electrolyte is the carbon nano tube dispersion liquid, a platinum electrode is selected as a cathode material, the electrolytic voltage is 6V, and the electro-deposition time is 10 min;

(6) and (5) washing and suction-filtering the carbon fiber subjected to electrochemical deposition in the step (5) by using a washing solution at room temperature. The washing liquid is ultrapure water with the mass of 2kg, the times of suction filtration are 50 times, and the suction vacuum degree is-0.1 Mpa; after washing, putting the carbon fiber into a forced air drying oven for drying, wherein the drying temperature is set to be 60 ℃, and the drying time is set to be 180min, and finally obtaining the surface modified carbon fiber;

(7) 400g of p-phenylphenol, 32g of ammonia water, 2000g of phenol and 564g of formaldehyde are added into a flask, the temperature is slowly increased to 96-98 ℃, and after 2 hours of heat preservation, 8g of Ba (OH) is added ₂ (ii) a 769g of formaldehyde (mass ratio of phenol to formaldehyde is 1.5:1) is slowly added dropwise in 1h while keeping the temperature at 96 ℃. Continuing to preserve heat after the dropwise addition is finished, and adding H after the mixed solution becomes turbid ₃ PO ₄ The pH was adjusted to neutral. Vacuum dehydration is started until the mixed solution becomes clear, dehydration is stopped, and the liquid phenolic resin is prepared when the reaction temperature is raised to 90 ℃;

(8) and (3) uniformly coating the RTM phenolic resin prepared in the step (7) on the surface of the surface modified carbon fiber obtained in the step (6), wherein the surface modified carbon fiber: the mass ratio of RTM phenolic resin is 1.5:1, repeating the steps to prepare 5 layers of carbon fiber coated with phenolic resin. And (3) aligning and stacking 5 layers of carbon fibers, placing the carbon fibers into a mold, covering a layer of molding paper on each of the upper surface and the lower surface of the carbon fibers, and then placing the mold into a flat vulcanizing machine. Setting temperature gradient in a vulcanizing press, hot pressing at 90 ℃ for 1.5h, then heating to 130 ℃ for 1h, and finally heating to 170 ℃ for 1 h. And after hot pressing is finished, preparing the modified carbon fiber/phenolic resin composite material.

FIG. 6 is a surface topography of the carbon fiber at various stages in example 1. FIG. 6(a) is a surface topography of a raw carbon fiber treated at a high temperature of 300 ℃ for 120 min; FIG. 6(b) is a surface topography of a carbon fiber after electrochemical oxidation treatment of the high-temperature treated carbon fiber at 5V for 20 min; FIG. 6(c) is a surface topography of electrochemically oxidized treated carbon fiber grafted TTI; FIG. 6(d) is a surface topography of the carbon fiber after electrochemical deposition treatment of the grafted TTI under the conditions of 6V and 10 min.

In the electrochemical oxidation and electrochemical deposition, the preferred embodiment 1 of the present invention selects a proper electrochemical working voltage and working time, and the higher the electrochemical oxidation working voltage is, the longer the working time is, the lower the tensile strength of the carbon fiber monofilament is, mainly because the carbon fiber surface structure will be changed in the electrochemical oxidation process, and the long treatment time or the too high working voltage will cause the carbon fiber surface to generate structural defects, the surface appearance is rough and uneven, and the carbon fiber structure is damaged. The working voltage during electrochemical deposition is larger than that of electrochemical oxidation, and the deposition of the carbon nanotubes on the surface of the carbon fibers in the electrochemical deposition process fills some grooves and micro defects on the surface of the carbon fibers, so that the monofilament tensile strength of the carbon fibers is improved.

Example 2

The other conditions were the same as in example 1 except that in the step (1), the temperature at the time of the high-temperature treatment was 300 ℃.

Example 3

The other conditions were the same as in example 1 except that in the step (1), the temperature at the time of the high-temperature treatment was 500 ℃.

Example 4

The other conditions were the same as in example 1 except that in the step (1), the temperature at the time of the high-temperature treatment was 600 ℃.

FIG. 4 is a Scanning Electron Microscope (SEM) image of carbon fiber after high temperature treatment at different temperatures, and FIG. 4(a) is a morphology image of raw carbon fiber;

FIG. 4(b) is a surface topography of carbon fiber treated at 300 ℃ for 120min in example 2, wherein it can be observed that some resin sizing agents are attached to the surface of the original carbon fiber, which greatly reduces the bonding force of the composite interface of the carbon fiber and the resin, so that the comprehensive performance of the composite material is reduced; FIG. 4(c) is a surface topography of the carbon fiber in example 1 after being treated at a high temperature of 400 ℃ for 120 min; FIG. 4(d) is a surface topography of carbon fiber treated at 600 ℃ for 120 min. As can be seen, the carbon fiber is at 300 ℃, because the treatment temperature is low and the time is short, part of the sizing agent is still adhered to the surface of the carbon fiber, and the presence of the sizing agent seriously influences the modification effect of the post-treatment process on the surface of the carbon fiber and the performance of the composite material; and the high temperature treatment at 600 ℃ can damage the carbon fiber structure and generate partial defects on the surface. Therefore, the high-temperature treatment temperature range of the invention is 400-500 ℃.

Example 5

The other conditions were the same as in example 1 except that in the step (2), the electrolytic voltage was 3V and the electrochemical treatment time was 20 min.

Example 6

The other conditions were the same as in example 1 except that the electrochemical treatment time in step (2) was 10 min.

Example 7

The other conditions were the same as in example 1 except that in step (2), the electrolytic voltage was 7V and the electrochemical treatment time was 20 min.

Example 8

The other conditions were the same as in example 1 except that in the step (5), the electrolysis voltage was 4V and the electrolysis time was 10 min.

Example 9

The other conditions were the same as in example 1 except that in step (5), the electrolysis voltage was 8V and the electrolysis time was 10 min.

Example 10

The other conditions were the same as in example 1 except that the concentration of carbon nanotubes in step (5) was 5%.

Example 11

The other conditions were the same as in example 1 except that in step (7), the amount of phenol was changed so that the mass ratio of phenol to formaldehyde was 1.33: 1.

Example 12

The other conditions were the same as in example 1 except that in step (7), the amount of phenol was changed so that the mass ratio of phenol to formaldehyde was 1.67: 1.

Example 13

The other conditions were the same as in example 1 except that in step (7), the amount of phenol was changed so that the mass ratio of phenol to formaldehyde was 1.8: 1.

Example 14

The other conditions were the same as in example 1 except that in step (7), the amount of phenol was changed so that the mass ratio of phenol to formaldehyde was 1.2: 1.

FIG. 5 is a surface topography and a composite shear plane topography after electrochemical oxidation and electrochemical deposition treatment of carbon fibers during surface modification. Wherein, fig. 5(a) is a surface topography of the carbon fiber after electrochemical oxidation treatment of the high-temperature treated carbon fiber at 3V for 20min in example 5, the carbon fiber surface after low-pressure treatment can not load more oxygen-containing functional groups, and the modification effect is not obvious; FIG. 5(b) is a surface topography of the carbon fiber after the electrochemical oxidation treatment of the high temperature treated carbon fiber in example 1 at 5V for 20 min; FIG. 5(c) is a surface topography of a carbon fiber after electrochemical oxidation treatment of the high-temperature treated carbon fiber at 7V for 20min in example 7, wherein the surface of the carbon fiber after high-pressure treatment has obvious structural defects, and the carbon fiber is damaged, rough and uneven in surface and poor in modification effect; FIG. 5(d) is a surface topography of the carbon fiber after electrochemical deposition treatment of the electrochemically oxidized carbon fiber in example 8 at 4V for 10min, wherein the surface of the fiber is only loaded with fewer carbon nanotubes, and the surface modification effect of the carbon fiber due to the deposition of fewer carbon nanotubes is not obvious; FIG. 5(e) is a surface topography of the carbon fiber after electrochemical deposition treatment of the electrochemically oxidized carbon fiber in example 1 at 6V for 10min, at this time, more carbon nanotubes are deposited on the surface of the carbon fiber, the deposition of the carbon nanotubes in the most appropriate proportion greatly increases the surface roughness of the carbon fiber, increases the contact area between the fiber and the resin, and enhances the mechanical engagement of the interface between the fiber and the resin; fig. 5(f) is a surface topography of the carbon fiber after electrochemical deposition treatment of the electrochemically oxidized carbon fiber in example 9 at 8V for 10min, in which carbon nanotubes are stacked on the surface of the carbon fiber, and at this time, the carbon nanotubes completely cover the surface of the carbon fiber, so that the contact area between the carbon fiber and the resin is reduced, and the composite effect is poor; FIG. 5(g) shows the surface-modified carbon fiber and phenol in example 13: formaldehyde 1.8: the shear surface topography of the phenolic resin composite material with the mass ratio of 1 can observe that certain cracks exist between the resin and the carbon fiber interface, because the mass ratio of phenol is large, the viscosity of a resin system is low, part of resin is still not cured in the later stage of thermal curing, and the bonding force between the resin and the carbon fiber is poor, so that the cracks are generated; FIG. 5(h) shows the surface-modified carbon fiber and phenol in example 1: formaldehyde 1.5: the shear surface topography of the phenolic resin composite material with the mass ratio of 1 can be seen, the carbon fiber is tightly attached to the phenolic resin, no pore exists between the carbon fiber and the phenolic resin, and the mass ratio of the ratio is favorable for improving the mechanical meshing degree between the resin and the carbon fiber; FIG. 5(i) shows the surface-modified carbon fiber and phenol in example 14: formaldehyde 1.2:1 mass ratio of the shear surface profile of the phenolic resin composite material, a resin area can be observed to have a plurality of holes, because the bubbles generated in the curing process can not be removed in time due to the high viscosity of the resin at the early stage, and the holes can seriously influence the mechanical property of the composite material.

It can be seen that the composite material obtained by proper electrochemical oxidation, electrochemical deposition working voltage and working time and proper phenolic aldehyde proportion is optimal in appearance, so that the composite material also has more excellent properties.

Application example

The modified carbon fiber/phenolic resin material obtained in the above example was subjected to the following performance tests, and the results are shown in table 1 below:

surface O/C content: calculated according to the data value obtained after the peak fitting of C1s in the XPS result.

Tensile strength of monofilament: the method is carried out according to GB/T31290-.

Interfacial shear strength: according to a microdroplet debonding method, an FA620 type composite material interface evaluation device is adopted to represent the influence of carbon fiber on the interface shear strength of the composite material before and after modification.

TABLE 1

The O/C content and monofilament tensile strength of the carbon fibers at different stages in example 1, and the interfacial shear strength of the composite of carbon fibers and phenolic resin at different stages were also tested, and the results are shown in table 2 below:

TABLE 2

Wherein CF-0 is untreated virgin carbon fiber; CF-1 is carbon fiber of CF-0 after high-temperature treatment; CF-2 is carbon fiber of CF-1 after electrochemical oxidation treatment; CF-3 is carbon fiber of CF-2 after TTI grafting treatment; CF-4 is carbon fiber which is obtained by carrying out electrochemical deposition treatment on CF-3. The monofilament tensile strength is the strength of the carbon fiber filament itself. The original carbon fiber has surface sizing agent with high tensile strength, CF-2 is acid oxidized, the surface is oxidized, the structure is changed, and the tensile strength is lower than that of the original carbon fiber. Through the subsequent steps, the monofilament tensile strength is restored to the original level.

FIG. 7 is a Raman spectrum and an IR spectrum of the carbon fiber at each stage in the surface modification process in example 1; CF-0 is untreated raw carbon fiber; CF-1 is carbon fiber of CF-0 after high-temperature treatment; CF-2 is carbon fiber of CF-1 after electrochemical oxidation treatment; CF-3 is carbon fiber of CF-2 after TTI grafting treatment; CF-4 is carbon fiber of CF-3 after electrochemical deposition treatment. Wherein the Raman spectrum comprises 1400-1500 cm ^-1 The D band sum is 1900-2000 cm ^-1 G band of (c). The relative intensity of the D band reflects the degree of disorder of carbon, and the relative intensity of the G band reflects the integrity of the sp2 bond structure in the carbon structure. The degree of graphitization of the carbon fiber is generally evaluated by the strength ratio R value of the D band to the G band, and the larger R value indicates that the carbon fiber has more defects and higher disorder degree. By calculation, of raw carbon fibres, high-temperature treated carbon fibres, electrochemically oxidized carbon fibres, TTI grafted carbon fibres, electrochemically deposited carbon fibresR values are 1.975, 1.944, 1.992, 1.987 and 2.026 respectively. The carbon fiber after high temperature treatment has less disorder degree and increased disorder degree, which shows that the original carbon fiber surface sizing agent can be effectively removed at high temperature. The grafted TTI carbon fiber makes up the defects generated by the oxidation of the fiber surface after electrochemical oxidation treatment, and the R value is reduced from 1.992 to 1.987. The disorder degree of the carbon fiber surface of the deposited carbon nano tube is increased, the number of unsaturated carbon atoms is increased, and the graphitization degree is reduced, so that the improvement of the interface performance of the composite material is effectively promoted. As can be seen from the infrared spectrogram, the carbon fiber after electrochemical oxidation treatment, grafting TTI and electrochemical deposition is 1735, 1261 and 1091cm in comparison with the original carbon fiber ^-1 Three characteristic peaks exist, which respectively correspond to stretching vibration peaks of C ═ O, C-O and C-O-C functional groups, and the results show that the surface of the carbon fiber subjected to electrochemical oxidation treatment contains more oxygen-containing functional groups, and the oxygen-containing functional groups effectively increase the surface activity of the carbon fiber. Carbon fiber grafted TTI is 2320cm ^-1 And the formed-NCO stretching vibration peak indicates that the TTI is successfully grafted on the surface of the carbon fiber.

FIG. 8 shows the carbon fibers in example 1 in the surface treatment process C _1s XPS spectrogram after peak separation fitting. Wherein 8(a) is C of raw carbon fiber _1s XPS spectrogram after peak separation fitting; FIG. 8(b) is C of carbon fiber after electrochemical oxidation treatment _1s XPS spectrogram after peak separation fitting; FIG. 8(C) is C after grafting of carbon fibers to TTI _1s XPS spectrogram after peak separation fitting. It can be seen that the carbon fiber surface subjected to electrochemical oxidation treatment has a reduced C — C content as compared with the untreated fiber; the content of O-C ═ O and C-O groups increases significantly. The electrochemical oxidation treatment has obvious effect on introducing polar groups on the surface of the carbon fiber, and is beneficial to improving the chemical activity of the surface of the fiber, thereby improving the interface bonding of the composite material. Compared with the carbon fiber subjected to electrochemical treatment, the carbon fiber with the surface grafted TTI has increased contents of O-C-O, C-O and C-N groups, and after the TTI grafting coating treatment, the number of oxygen-containing active groups on the surface of the fiber is increased, so that the chemical activity is enhanced.

Claims

1. The modified carbon fiber/phenolic resin composite material is obtained by coating phenolic resin on the surface of surface-modified carbon fiber and then performing hot-pressing compounding, and is characterized in that the surface-modified carbon fiber is obtained by sequentially performing high-temperature treatment, electrochemical oxidation, polyisocyanate grafting modification and electrochemical deposition on a carbon nano tube.

2. The modified carbon fiber/phenolic resin composite material as claimed in claim 1, wherein the surface modified carbon fiber has a Raman spectrum of 1400-1500 cm ^-1 The D band sum is 1900-2000 cm ^-1 And the intensity ratio R of G/D is more than 2.

3. The modified carbon fiber/phenolic resin composite material as claimed in claim 1, wherein the surface modified carbon fiber has an infrared spectrum of 1735 ± 50cm ^-1 ，1261±50cm ^-1 And 1091. + -. 50cm ^-1 Has characteristic peaks.

4. A method for preparing the modified carbon fiber/phenolic resin composite material as claimed in any one of claims 1 to 3, which comprises the steps of:

(1) carrying out high-temperature treatment on the carbon fiber cloth;

5. The production method according to claim 4, wherein the liquid phenolic resin is uniformly coated on the surface of the carbon fiber subjected to surface modification in the step (8) to obtain a plurality of layers of phenolic resin-coated carbon fibers, and the layers of phenolic resin-coated carbon fibers are placed in a mold and hot-pressed.

6. The method according to claim 4, wherein the high temperature in step (1) is 400-500 ℃, and the high temperature treatment time is 2-3 h; in the step (2), the electrolytic voltage is 4-5V, and the electrochemical treatment time is 15-20 min; and (5) during electrochemical deposition, the electrolytic voltage is 5-6V, and the electrodeposition time is 10-12 min.

7. The method according to claim 4, wherein the polyisocyanate in step (4) is at least one selected from the group consisting of diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and triphenylmethane triisocyanate. Triphenylmethane triisocyanate is preferred; preferably, the concentration of the polyisocyanate solution is 10-20 wt%, and the carbon fiber is soaked in the polyisocyanate reagent for 30-60 min.

8. The method according to claim 4, wherein the carbon nanotubes in step (5) are multi-walled carbon nanotubes having an outer diameter of 5 to 50nm, preferably 10 to 20nm, and the concentration of the carbon nanotube dispersion is 5 to 10 wt%.

9. The production method according to claim 4, wherein in the step (7), the mass ratio of phenol to formaldehyde is 1.33 to 1.67:1, preferably 1.5: 1.

10. The method of claim 4, wherein in step (8), the mass ratio of the surface-modified carbon fiber to the phenolic resin is 1-2:1-2, preferably 1-1.5: 1.